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The spin kinetics of liquid 3He in contact with the microsized DyF3 powder at ferromagnetic ordering of Dy^{3+}

For the first time the magnetic phase transition in DyF3 at low temperatures was observed by 3He NMR. The spin kinetics of liquid 3He in contact with a mixture of microsized powders LaF3 (99.67%) and DyF3 (0.33%) at temperatures 1.5-3 K was studied by pulse NMR technique. The DyF3 is a dipole dielectric ferromagnet with a phase transition temperature Tc = 2.55 K, while as the diamagnetic fluoride LaF3 used as a diluent for optimal conditions for observation of 3He NMR. The phase transition in DyF3 is accompanied by a significant changes in the magnetic fluctuation spectrum of the dysprosium ions. The spin kinetics of 3He in contact with the substrate is sensitive to this fluctuations. An significant change in the rates of the longitudinal and transverse nuclear magnetization of 3He in the region of magnetic ordering of solid matrix was observed. A technique is proposed for studying the static and fluctuating magnetic fields of a solid matrix at the low temperatures using liquid 3He as a probe.

.. lakshin, .I. Kondratyeva, V.V. Kuzmin, .R. Safiullin, .. Stanislavovas, .V. Savinkov, .V. Klochkov,  .S. Tagirov

JETP Letters 107 issue 2, 2018

Microparticles at the surface of liquid helium. Quantum version of Archimedes' principle

Microspheres at the surface of liquid are widely used now for visualization of wave and vortex motion [1, 2]. The experiments of this kind had been performed recently to study of turbulence at the surface of liquid helium [3]. That’s why it is of interest to consider the corrections to a classic Archimedes' principle, because while the size of a particle floating at the surface decreases, the forces of surface tension and molecular interaction start to play a significant role. 

We study the deviations from Archimedes' principle for spherical particles made of molecule hydrogen near the surface of liquid He4. Classic Archimedes' principle takes place if particle radius $R_0$ is greater than capillary length of helium $L_{k} \approx $ 500 µm and the height $h_+$  of the part of the particle above He is proportional to  $R_0$ . Over the range of $30 <R_0 <500$ µm Archimedes' force is suppressed by the force of surface tension and  $h_{+}  \sim R^{3}_{0} / L^{2}_{k}$.  When $R_0<30$µm, the particle is situated under the surface of liquid helium. In this case Archimedes' force competes with Casimir force which repels the particle from the surface to the depth of liquid. The distance from the particle to the surface $h_{-} \sim R^{5/3}_c / R^{2/3}_0$ if  $R_0>R_c...R_c$  can be expressed as  $R_c \approx (\frac {\hbar c}{\rho g}) \approx $ 1µm, $\hbar $ is Planck's constant, c is speed of light, $\rho $ is helium density. For the very small particles ( $R_0<R_c)$  $h_{-}$does not depend on their size: $h_{-}$=$R_c$.

1. S. V. Filatov,  S. A. Aliev, A. A. Levchenko, and D. A. Khramov, JETP Letters, , 104(10), 702 (2016).

2.  S. V. Filatov,  D. A. Khramov,   A. A. Levchenko, JETP Letters, 106(5), 330 (2017).

3. A. A. Levchenko, L. P. Mezhov-Deglin, A. A. Pel’menev, JETP Letters, 106(4), 252 (2017).

4. E. V. Lebedeva, A. M. Dyugaev , and P. D. Grigoriev, JETP, 110(4), 693 (2010).

5. A. M. Dyugaev,  P. D. Grigoriev, and E. V. Lebedeva, JETP Letters, 89(3), 145 (2009).

Superconductor-insulator transition in disordered NbTiN films

One of the frontiers of quantum condensed matter physics seeks to analyze and classify scenarios of the superconductor-insulator quantum phase transition (SIT). Fermionic scenario [1] rules that disorder, when strong enough, breaks down Cooper pairs thus transforming a superconductor into a metal. The further cranking up disorder strength localizes quasiparticles turning the metal into an insulator. According to Bosonic scenario [2,3] disorder localizes Cooper pairs which survive on the insulating side of the SIT and provide an insulating gap. In the Fermionic scenario, the disorder-driven SIT is a two-stage transition through the intermediate state that exhibits finite resistance R and is ordinarily referred to as quantum metal. In Bosonic scenario, the SIT this intermediate state shrinks into a single point in which the resistance assumes the universal quantum resistance per square Rc = 6.45 kΩ/□ [3]. The disorder-driven SIT was reported in films of InOx [4, 5], Be [6], TiN [7]. However, the resistance Rc that separates superconducting and insulating states in these films is not universal. The access and detailed study of the phases in the critical vicinity of the SIT in different materials remains one of the major challenges.

            Here we observe the direct disorder-driven superconductor-insulator transition in NbTiN films with Rc = 2.7 kΩ/□ at room temperature. We show that the increasing the film's resistance suppresses the superconducting critical temperature Tc in accord with the Fermion model. We find that incrementally increasing R suppresses the Berezinskii-Kosterlitz-Thouless temperature down to zero, while the critical temperature Tc remains finite, which complies with the Bosonic model. Upon further increase of R, the ground state of system becomes insulating. Finally, we demonstrate that the temperature dependence of the resistance of insulating films follows the Arrhenius law.

[1] A. M. Finkel'stein, Superconducting transition temperature in amorphous films, JETP Lett. 45, 46 (1987).

[2] A. Gold, Dielectric properties of disordered Bose condensate, Phys. Rev. A 33, 652 (1986).

[3] M.P. A. Fisher, G. Grinstein, S. Grivin, Presence of quantum diffusion in two dimensions: Universal resistance at the superconductor-insulator transition, Phys. Rev. Lett. 64, 587 (1990).

[4] A. F. Hebard, M. A. Paalanen, Magnetic-field-tuned superconductor-insulator transition in two-dimensional films, Phys. Rev. Lett. 65, 927 (1990).

[5] D. Shahar, Z. Ovadyahu, Superconductivity near the mobility edge, Phys. Rev. B 46, 10917 (1992).

[6] E. Bielejec, J. Ruan, W. Wu, Anisotropic magnetoconductance in quench-condensed ultrathin beryllium films, Phys. Rev. B 63, 1005021 (2001).

[7] T. I. Baturina et al., Localized superconductivity in the quantum-critical region of the disorder-driven superconductor-insulator transition in TiN thin films, Phys. Rev. Lett. 99, 257003 (2007).


M. V. Burdastyh, S. V. Postolova, T. I. Baturina, T. Proslier, V. M. Vinokur,

A.Yu. Mironov

JETP Letters 106 (11) (2017)


Detection of spin excitation transfer in a 2D electron system by photoluminescence of multi-particle exciton complexes

We demonstrate that non-equilibrium spin excitations drift to macroscopically large distances in
a 2D electron gas (symmetrically doped GaAs/AlGaAs quantum well) in a quantizing magnetic
field at filling factor $\nu $ = 2. The effect is induced by low-temperature photoexcitation of a dense
ensemble of long-lived ($\sim 1 $ ms) spin excitations − cyclotron spin-flip magnetoexcitons. The spin
excitation is a bound state of an electron at the first Landau level and a Fermi-hole at the zeroth
Landau level with a total spin S = 1 [1-3]. Direct photoexcitation and radiative annihilation of
such excitations are forbidden (“dark” excitons), yet, their binding energy and spin structure are
reliably established by inelastic light scattering spectra [4, 5]. Recently, we were able to measure
the dark exciton density and relaxation rate by newly developed technique – photo-induced
resonant light reflection [6]. At the temperatures below 1 K, we discovered the condensate-like
behavior of the dense exciton ensemble [7]. Furthermore, these spin excitations modify
photoluminescence spectrum by binding to a photo-excited valence hole: an allowed radiative
recombination channel of three-particle complexes gets active [8]. Our paper presents
observation of spin exciton drift to the distance up to 200 μm. This unique phenomenon was
experimentally studied utilizing spatial separation of pump (photoexcitation) and probe
(photoluminescence detection) laser spots. Enhancement of the multi-particle complexes in
photoluminescence spectrum was observed far away from the pump area. Both pump intensity
and temperature dependencies correlate well with the phase diagram of dark exciton
condensation [7]. Time dependence of the spin drift rate in a 2D electron gas is the subject of our
near-future research.

1. Yu.A. Bychkov, S.V. Iordanskii, and G.M. Eliashberg, Two-dimensional electrons in a strong
magnetic field, JETP Letters 33, 143 (1981).
2. I.V. Lerner and Yu.E. Lozovik, Two-dimensional electron-hole system in a strong magnetic field as an
almost ideal exciton gas, Sov. Phys. JETP 53, 763 (1981).
3. C. Kallin and B.I. Halperin, Excitations from a filled Landau level in the two-dimensional electron gas,
Phys. Rev. B 30, 5655 (1984).
4. L.V. Kulik, I.V. Kukushkin, S. Dickmann, V.E. Kirpichev, A.B. Van'kov, A.L. Parakhonsky, J.H.
Smet, K. von Klitzing, and W. Wegscheider, Cyclotron spin-flip mode as the lowest-energy excitation of
unpolarized integer quantum Hall states, Phys. Rev. B 72, 073304 (2005).
5. L.V. Kulik, S. Dickmann, I.K. Drozdov, A.S. Zhuravlev, V.E. Kirpichev, I.V. Kukushkin, S. Schmult,
and W. Dietsche, Antiphased cyclotron-magnetoplasma mode in a quantum Hall system, Phys. Rev. B 79,
121310 (2009).
6. L.V. Kulik, A.V. Gorbunov, A.S. Zhuravlev, V.B. Timofeev, S.M. Dickmann, and I.V. Kukushkin,
Super-long life time for 2D cyclotron spin-flip excitons, Sci. Rep. 5, 10354 (2015).
7. L.V. Kulik, A.S. Zhuravlev, S. Dickmann, A.V. Gorbunov, V.B. Timofeev, I.V. Kukushkin, and S.
Schmult, Magnetofermionic condensate in two dimensions, Nature Commun. 7, 13499 (2016).
8. A.S. Zhuravlev, V.A. Kuznetsov, L.V. Kulik, V.E. Bisti, V.E. Kirpichev, and I.V. Kukushkin,
Artificially Constructed Plasmarons and Plasmon-Exciton Molecules in 2D Metals, Phys. Rev. Lett. 117,
196802 (2016).

                                                    Gorbunov A.V., Kulik L.V., Kuznetsov V.A., Zhuravlev .S.,
                                                             Larionov A.V., Timofeev V. B., Kukushkin I.V. 

                                                                                      JETP Letters 106, issue 10 (2017)

Helical edge transport in the presence of a magnetic impurity

Two-dimensional topological insulators are have attracted much recent interest since they feature helical edge states inside their band gap [1,2]. In the absence of time-reversal symmetry breaking, spin-momentum locking prohibits elastic backscattering of these helical states, i.e., the helical edge is a realization of an ideal transport channel with conductance equal to e2/h. However, this theoretical prediction was not confirmed by experiments on HgTe/CdTe [3-6] and InAs/GaSb [7,8] quantum wells. The time-symmetric interaction of the helical states with a "quantum magnetic impurity'' (an impurity which has its own quantum dynamics) is a leading candidate for explaining these experiments. In spite of recent theoretical studies of this problem [9-14], several key questions has not been addressed in details.

 We study theoretically the modification of the ideal current-voltage characteristics of the helical edge in a two-dimensional topological insulator by weak scattering off a single magnetic impurity. As a physical realization of such a system we have in mind the (001) CdTe/HgTe/CdTe quantum well (QW) with a Mn impurity that possesses spin S=5/2. Contrary to previous works, we allow for a general structure of the matrix describing exchange interaction between the edge states and the magnetic impurity. For S=1/2 we find an analytical expression for the backscattering current at arbitrary voltage. For larger spin, S>1/2, we derive analytical expressions for the backscattering current at low and high voltages. We demonstrate that the differential conductance may exhibit a non-monotonous dependence on the voltage with several extrema.

[1] X.-L. Qi, S.-C. Zhang, Topological insulators and superconductors, Rev. Mod. Phys. 83, 1057 (2011).

[2] M. Z. Hasan, C. L. Kane, Colloquium: Topological insulators, Rev. Mod. Phys. 82, 3045 (2010).

[3] M. Konig, S. Wiedmann, C. Brune, A. Roth, H. Buhmann, L. W. Molenkamp, X.-L. Qi, S.-C. Zhang,    Quantum spin Hall insulator state in HgTe quantum wells, Science 318, 766 (2007)

[4] K. C. Nowack, E. M. Spanton, M. Baenninger, M. Konig, J. R. Kirtley, B. Kalisky, C. Ames, P. Leubner, C. Brune, H. Buhmann, L. W. Molenkamp, D. Goldhaber-Gordon, K. A. Moler, Imaging currents in HgTe  quantum wells in the quantum spin Hall regime, Nat. Mater. 12, 787 (2013).

[5] G. Grabecki, J. Wrobel, M. Czapkiewicz, L. Cywinski, S. Gieratowska, E. Guziewicz, M. Zholudev, V. Gavrilenko, N. N. Mikhailov, S. A. Dvoretski, F. Teppe, W. Knap, T. Dietl, Nonlocal resistance and its fluctuations in microstructures of band-inverted HgTe/(Hg,Cd)Te quantum wells, Phys. Rev. B 88, 165309 (2013).

[6] G. M. Gusev, Z. D. Kvon, E. B. Olshanetsky, A. D. Levin, Y. Krupko, J. C. Portal, N. N. Mikhailov, S. A. Dvoretsky, Temperature dependence of the resistance of a two-dimensional topological insulator in a HgTe quantum well, Phys. Rev. B 89, 125305 (2014).

[7] E. M. Spanton, K. C. Nowack, L. Du, G. Sullivan, R.-R. Du, K. A. Moler, Images of edge current in InAs/GaSb quantum wells, Phys. Rev. Lett. 113, 026804 (2014).

[8] L. Du, I. Knez, G. Sullivan, R.-R. Du, Observation of quantum spin Hall states in InAs/GaSb bilayers under broken time-reversal symmetry, Phys. Rev. Lett. 114, 096802 (2015).

[9] J. Maciejko, Ch. Liu, Y. Oreg, X.-L. Qi, C. Wu, S.-C. Zhang, Kondo effect in the helical edge liquid of the quantum spin Hall state, Phys. Rev. Lett. 102, 256803 (2009).

[10] Y. Tanaka, A. Furusaki, K. A. Matveev, Conductance of a helical edge liquid coupled to a magnetic impurity, Phys. Rev. Lett. 106, 236402 (2011).

[11] J. I. Vayrynen, M. Goldstein, L. I. Glazman, Helical edge resistance introduced by charge puddles, Phys. Rev. Lett. 110, 216402 (2013).

[12] J. I. Vayrynen, M. Goldstein, Y. Gefen, L. I. Glazman, Resistance of helical edges formed in a semiconductor heterostructure, Phys. Rev. B 90, 115309 (2014).

[13] V. Cheianov, L. I. Glazman, Mesoscopic fluctuations of conductance of a helical edge contaminated by magnetic impurities, Phys. Rev. Lett. 110, 206803 (2013).

[14] L. Kimme, B. Rosenow, A. Brataas, Backscattering in helical edge states from a magnetic impurity and Rashba disorder, Phys. Rev. B 93, 081301 (2016).


  Kurilovich P.D. , Kurilovich V.D., Burmistrov I.S. , Goldstein M.                                                                               JETP Letters 106 (9) (2017)

Breather chimeras in the system of phase oscillators

Chimera is, according to Greek mythology, a monstrous creature combining the parts of different animals (a lion with a head of a goat and a tail of a snake). Physicists recently adopted this name for complex states in nonlinear dynamical systems, where instead of an expected symmetric synchronous state one observes coexistence of synchronous and asynchronous elements [1]. Since the discovery of chimeras by Kuramoto and Battogtokh in 2002 [2], these states have been reported in numerous theoretical studies and experiments.
In this paper, we study formation of chimeras in a one-dimensional medium of identical oscillators with nonlinear coupling. This coupling crucially depends on the local order parameter measuring the level of synchrony: the coupling promotes synchrony for asynchronous states and breaks synchrony if it is strong [3]. As a result, spatially homogenous state in this medium is that of partial synchrony. To study the evolution of this state we formulate the problem in terms of the local complex order parameter, which describes local level of synchrony, and formulate the system of partial differential equations for this quantity [4]. This allows us to formulate the problem of inhomogeneous states as the pattern formation one. First, we construct stationary chimeras and explore their linear stability properties. Next, based on numerical modeling, we show that within a certain range of parameters, such structures can evolve into periodically varying long-lived chimera states (breather-chimeras), or, for other values of the parameters, turn into more complex regimes with irregular behavior of the local order parameter (turbulent chimeras).

[1] M. J. Panaggio, D. M. Abrams, Chimera states: coexistence of coherence and incoherence in networks of coupled oscillators, Nonlinearity 28 , R67 (2015).

[2] Y. Kuramoto, D. Battogtokh, Coexistence of Coherence and Incoherence in Nonlocally Coupled Phase Oscillators, Nonlinear Phenom. Complex Syst. 5 , 380 (2002).

[3] M. Rosenblum, A. Pikovsky, Self-Organized Quasiperiodicity in Oscillator Ensembles with Global Nonlinear Coupling, Phys. Rev. Lett. 98 , 064101 (2007).

[4] L. A. Smirnov, G. V. Osipov, A. Pikovsky, Chimera patterns in the Kuramoto-Battogtokh model, J. Phys. A: Math. Theor. 50 , 08LT01 (2017).


                                                              Bolotov M.I., Smirnov L.A., Osipov G.V., Pikovsky A.

                                                                                           JETP Letters 106, issue 6 (2017)

Faraday Waves and Vortices on the Surface of Superfluid He-II.

Well-known Faraday waves can be parametrically generated on a free surface of ordinary (classical) fluids such as water or on superfluid helium He-II surface when a sample cell is vibrated vertically. Standing-wave patterns appear on the surface, and their frequencies are one-half the driving frequency. The acceleration threshold for the parametric excitation of Faraday waves on the surface of water is near an order of magnitude higher than on the surface of He-II at the same frequencies [1]. Generation of vorticity by interacting nonlinear surface waves has been predicted theoretically in a number of papers [2, 3] and generation of vortices by noncollinear gravity waves on a water surface has been observed experimentally [4].Our study has shown that classical 2-D vortices can be generated by Faraday waves on the surface of superfluid He-II also, more over one can observe formation of the vortex lattice in addition to the wave lattice on the surface of He-II in a rectangular cell. Combined with predictions [5] that the sharpest features (about nm sizes) in the cell walls can induce nucleation of quantum vortex filaments and coils on the interface and formation a dense turbulent layer of quantum vortices near the solid walls with a nonclassical average velocity profile which continually sheds small vortex rings into the bulk of vibrating He-II, this opens up new prospects for studying the properties of a quantum liquid and turbulent phenomena on the surface and in bulk of supefluid liquids.

[1] Haruka Abe, Tetsuto Ueda, Michihiro Morikawa, Yu Saitoh, Ryuji Nomura, Yuichi Okuda, Faraday instability of superfluid surface, Phys. Rev. E 76, 046305 (2007).
[2] S.V. Filatov, V.M. Parfenyev, S.S. Vergeles, M.Yu. Brazhnikov, A.A. Levchenko, V.V. Lebedev, Nonlinear Generation of Vorticity by Surface Waves, Phys. Rev. Lett. 116, 054501 (2016).
[3] V. M. Parfenyev, S.S. Vergeles, V.V. Lebedev, Effects of thin film and Stokes drift on the generation of vorticity by surface waves, Phys. Rev. E 94, 052801 (2016).
[4] S. V. Filatov, S. A. Aliev, A. A. Levchenko, D. A. Khramov, “Generation of vortices by gravity waves on a water surface”, JETP Letters, 104(10), 702–708 (2016).
[5] G.W. Stagg, N. G. Parker, and C. F. Barenghi, Superfluid Boundary Layer. PRL 118, 135301 (2017). DOI: 10.1103/PhysRevLett.118.135301


Levchenko A.A., Mezhov-Deglin L. P., Pel’menev A.A.

JETP Letters  106, issue 4 (2017)


Superradiance Properties of a Suspension of Composite

Nanoscale integration of organic and metallic particles is expected to open up new opportunities for the design high-performance nanoscale devices.  Optimization of heterostructures requires experimental and theoretical analysis of their specific physical properties.  Nanosystem consisting in gold
nanospheres  covered by silica shell impregnated with the organic dye molecules  comes into focus as a possible plasmonic based
nanolaser, i.e. "spaser" [1]. Depending on the distance between the emitters and metal there are possible various phenomena [2,3].
In this paper we experimentally studied the characteristics of a suspension of  spasers at the temperatures $T_N=77.4K,T_R=293K$. It was found  that the
system possesses characteristics of a laser medium. The S-shaped dependence of the radiation intensity and the compression of the lasing line with increase of the pumping power were observed. Ten-fold increase of the intensity of the radiation generated by the medium and line narrowing with  temperature change $T_R\to T_N$ was found. The experimental results were compared with a numerical simulation of a spaser model consisting of 20 two-level media and a metallic nanosphere. The temperature effects were modeled by the introduction of the Markov process.

It was found that observed effects can be explained by means of the feedback caused by the nonlinear interaction of polarizations with their total reflection in the metallic core. At low temperatures  Bloch vectors related with two-level systems form an analog of a ferromagnetic state. With increasing fluctuations, antiferromagnetic states are formed along with the desynchronization of ferromagnetic one. These properties allows us to explain the observed changes in the intensity of the and line form of laser generation with temperature.

Experimental and numerical results of the work demonstrate that the synchronization of the polarization of dye molecules caused by inverse nonlinear coupling yields an analog of plasmon-polariton superradiance.

1. D.J. Bergman  and  M.I. Stockman, Phys.Rev.Lett. 90, 027401 (2003).

2.  M. Haridas et al, J. Appl. Phys.114, 064305 (2013).

3. M. Praveena et al, Phys. Rev. B  92, 235403 (2015).

                                                               A. S. Kuchyanov, A.A. Zabolotskii, Plekhanov A.I.

                                                                                                JETP Letters 106 (2) (2017)

Energy Spectrum of the Spin States in $Sr_2FeSi_2O_7$ and Origin of the Magneto- Electric Coupling

Recently Sr2FeSi2O7 comes into focus as a possible compound with unusual magneto-electric coupling or, in other words, as a novel potential multiferroic [1,2]. Results of terahertz spectroscopy in the paramagnetic state show that the multiplet Fe+2(S=2) of the ground state splits due to the spin-orbit coupling. However the energy intervals between the low-lying singlet state and excited states are quite small so that all spin states are populated at the temperature of about 100 K. The Fe+2 ion occupies the center of a tetragonally distorted tetrahedron. In the present communication the origin of the magneto-electric coupling is described as follows. The odd crystal field from the tetrahedral environment induces the coupling of the orbital momentum of the Fe+2( 5D) state with the external electric field. On the other hand, the orbital momentum is coupled with spin via the spin –orbit interaction. Both angular momenta are coupled with the external magnetic field, which is enhanced due to the presence of the superexchange interaction between neighboring Fe+2 ions. Combining all these couplings, the author derived the affective spin Hamiltonian for the magneto-electric coupling, which made it possible to calculate relative intensities of the electric dipole transitions between spin states and estimate the magnetization caused by the external electric field as well as the electric polarization induced by the magnetic field.



  1. Thuc T. Mai, C. Svoboda, M. T. Warren, T.-H. Jang, J. Brangham, Y. H. Jeong, S.-W. Cheong, and R. Valdes Aguilar. Phys. Rev. B,  94, 224416 (2016)
  2. Yongping Pu, Zijing Dong, Panpan Zhang, Yurong Wu, Jiaojiao Zhao, Yanjie Luo. Journal of Alloys and Compounds, 672 , 64-71 (2016)



                                                                        M.V. Eremin

                                                                              JETP Letters 105 (11) (2017)

Electron-topological transition in copper-oxide high-TC superconductors before superconducting transition

It is well known the conductivity of high-temperature superconductors (HTSCs) with TC ~100 K (YBaCuO, BiSrCaCuO, etc.) is provided at T~300 K by hole (h) fermions [1]. It is also known the superconducting transition in such cuprates is accomplished by means of the Cooper pairing, while the fluctuating Cooper pairs with charge -2e exist even at T=TC+(~30 K) [2]. Hence it inevitably follows in the interval TC<T<300 K the hole Fermi surface (FS) of these HTSCs transforms into an electron one as a result of a topological transformation (the Lifshitz transition (LT) [3]. There is one of the central questions in the problem of the pseudogap state [1] of copper-oxide high-TC superconductors:  how and at what temperatures this transformation occurs.

To evidence the charge carrier conversion the Hall effect is used usually. As for the BiSrCaCuO and YBaCuO, their Hall coefficients (RH) have several features in the temperature range TC…300 K [4,5]. The most significant of them is observed before the TC in the region of fluctuation conductivity and can be interpreted as a manifestation of a scale hole-electron (h-e) conversion in a system of charge carriers, i.e. as the LT. However, this point of view is not universally accepted. As for the data on the transformation of the FS obtained by the ARPES (Angle Resolved Photoemission Spectroscopy) method [7], they, like [4,5], support several rearrangements of the FS, including those occurring near TC.

Meanwhile, it is the possibility to evidence the h-e conversion in a hole HTSC (the last condition is sure), which does not require either electric or magnetic fields to create the Hall potential difference. The technique developed by us [7,8] is based on the phenomenon of rearrangement of the spectrum of charge carriers in the near-surface layer of a hole HTSC being in contact with a normal metal (Me). This phenomenon is a consequence of the annihilation of "aboriginal" hole fermions in the HTSC/Me interface with electrons penetrated from Me. The essence of this technique is the registration of changes in the resistance of the HTSC/Me interface r, which is characterized by a small number of hole carriers. The appearance of the temperature singularities of rC and the sign of rC  variation (dr) make it possible to obtain an idea of the character of the changes in the system of charge carriers of the HTSC array.

The dependences rC(T) of the Bi(Pb)SrCaCuO/Pb and YBaCuO/In interfaces have been studied and anomalies near the temperature of the pseudogap opening and before the superconducting transition have been observed. We are shown that in Bi(Pb)SrCaCuO and YBaCuO, when the temperature T=TC+(~10 K) is reached, that do not concerns to fluctuating Cooper pairs condensation. So, there is due to changing the topology of the FS. As a result, significant piece of FS becomes electronic. The most probable reason for the topological transition is the achievement of the temperature of the 2D-3D crossover (the temperature of the three-dimensionality of HTSC), which is a consequence of a modification in the electronic subsystem that leads to a change in the interaction mechanisms of the fluctuation Cooper pairs [9, 10].

1. The Physics of Superconductors, Vol.1. Conventional and High-TC Superconductors. Ed. by K.H. Bennemann and J.B. Katterson, Berlin, Springer, (2003).

2. K. Kawabata, S. Tsukui, Y. Shono, O. Michikami, H. Sasakura, K. Yoshiara, Y. Kakehi, T. Yotsuya, Phys. Rev. B58, 2458 (1998).

3. I.M. Lifshits, JETP 38, 1569 (1960) (in Russian).

4. Q. Zhang, J. Xia, M. Fang, Z. He, S. Wang, Z. Chen, Physica C 162-164, 999 (1989).

5. A.L. Solovjov, FNT 24, 215 (1998) (in Russian).

6. T. Kondo, A.D. Palczewski, Y. Hamaya, T. Takeuchi, J.S. Wen, Z.J. Xu, G. Gu, A. Kaminski, arXive: 1208.3448v1 (2012).

7. V.I. Sokolenko, V.A. Frolov, FN 39, 134 (2013) (in Russian).

8. V.A. Frolov, VAN, Ser.: Vacuum, pure materials, superconductors, 1, 176 (2016) (in Russian).

9. Y.B. Xie, Phys. Rev., B46, 13997 (1992).

10. A.L. Solovjov, V.M. Dmitriev, FNT 35, 227 (2009) (in Russian).


Sokolenko V.I., Frolov V.A.

JETP Letters 105, issue 10 (2017)



Correct allowing for the interparticle interaction in many-body systems faces considerable mathematical difficulties. The most frequently used approximation in such problems is the mean field approximation (MFA) which neglects fluctuations and the particles are considered as a continuous medium of inhomogeneous density. If , moreover, the system is described by the classical distribution function ( the statistics can be a quantum one) we obtain the well known Thomas - Fermi approach .However there are situations when at least some of the degrees of freedom of the system have to be treated in accord with quantum mechanics. Such examples are electrons in quantum wells or dipolar excitons in an electrostatic trap. In such cases the density of particles appearing in MFA is to be expressed via wave functions of a particle in the effective potential. The latter, in its turn, depends on the wave functions and occupation numbers, so one has to solve a self-consistent problem. In case of a short-range interparticle pair potential (2D gas of dipolar excitons) a nonlinear wave equation arises while for the long-range ( Coulomb) pair interaction the corresponding equation becomes integro-differential (nonlocal effects).

            Two different systems are considered: bose - gas of dipolar excitons in a ring shape trap and fermi-gas of electrons in a quantum well of a MOS-structure. The trapped excitons are described by the Gross-Pitaevskyi nonlinear equation and for the very simple case of the rectangular potential of the “empty” trap the exact analytical solution is found. The most interesting result of this problem is criterion for existence of bound state in the effective potential ( in the one particle problem a 1D symmetric potential well always contains at least one bound state) . Methodologically instructive is the way of obtaining the eigenvalue of the Gross-Pitaevskyi equation: the ground state energy is found from the normalization condition.

            In case of electrons in a quantum well one deals with nonlinear integro-differential equation for which the exact solution is unknown. The direct variational method was used to find the frequency of the intersubband transition. This frequency turned out to be scaled with the electron concentration N as $N^{2/3}$.



Chaplik A.V. JETP Letters 105 (9) (2017)

Toward a self-consistent theory of Fermi systems with flat bands

 A model of fermion condensation, advanced more than 25 years ago, still remains the subject of hot debates,  due to the fact that  within its frameworks, non-Fermi-liquid (NFL) behavior, ubiquitously exhibited  by  strongly correlated Fermi systems, including electron   systems of solids, is properly elucidated.  The model  is   derived  with the aid of   the same  Landau postulate  that the ground state energy $E$ is  a functional of its quasiparticle momentum distribution $n$,  giving  rise to the conventional Landau state. However, the model discussed deals with completely different  solutions,  emergent beyond  a critical point, at which the topological stability of the Landau state breaks down, and therefore relevant solutions of the problem  are found from   the well-known   variational condition of mathematical physics  $\delta E(n)/\delta n({\bf p})=\mu$ where $\mu$ is the chemical potential. Since the left side of this condition   is nothing but the quasiparticle energy $\epsilon({\bf p})$, the variational condition    does  imply formation of the flat band or, in different words,  a fermion condensate (FC). In fact,  variational condition  furnishes an opportunity to find solely the FC quasiparticle momentum distribution $n_*({\bf p}\in \Omega)$.

    A missing point is  concerned with   the single-particle spectrum of  quasiparticles in the complementary  domain   ${\bf p}\notin\Omega$. Originally,  at variance with recent experimental data, the  model spectrum $\epsilon({\bf p}\notin\Omega )$ was assumed to be gapless. To clarify the situation with the true character of this spectrum  we employ a    microscopic  approach to theory of Bose liquid created by S.Belyaev, where the interaction between  the condensate and non-condensate particles, giving rise to the emergence of a singular part of the self-energy, is treated properly.
    Unfortunately, in systems having a FC, evaluation of any FC propagator in closed form is impossible, since in contrast to the BC, the FC occupies a finite domain of momentum space. As a result, methods appropriate to evaluation of the multi-particle BC  propagators, fail to deal with corresponding FC propagators.
    In this situation, the only practical approach to solution of the problem involves the implementation of  an iterative  procedure, appealing to the smallness of the ratio $\eta=\rho_c/\rho$ where the numerator is   the FC density  and the denominator, total density. In the article, leading,  in the limit $\eta\to 0$,  contributions  to the singular part $\Sigma_s$ of the self-energy are calculated along the  Belyaev's theory lines. By virtue of the finite range of the FC domain, the  structure  of $\Sigma_s$ turns out   to be different, compared with that in the  boson case, treated by Belyaev. As a result,  the evaluated spectrum     of single-particle excitations of Fermi  systems, hosting flat bands, acquires a gap, so that the FC itself becomes a midgap state.

 In obtaining  the gap solution  we assumed  the effective interaction between particles in the particle-particle channel to have   sign,  which  prevents Cooper pairing, implying that the  ground state constructed  is not superfluid. In this situation, the gap  in the  single-particle spectrum is a Mott-like gap.

 The  theory   constructed is applied to   the explanation of the metal-insulator transition in  low-density homogeneous  2D  electron systems, like  those, which reside in silicon field-effect  transistors. These systems are known to become insulators  at  $T\to 0$ provided electron density declines below  a critical value $n_c\simeq 0.8\times 10^{11}cm^{-2} $ [1-4], its value being substantially larger  than that dictated by a standard Wigner crystallization scenario. Importantly,  the electron effective mass $M^*(n)$,  extracted from  corresponding measurements of   the   thermopower  diverges at almost the same value $n_t=0.78\times 10^{11}cm^{-2} $ [5], in agreement with the proposed scenario for the metal-insulator  transition in MOSFETs, triggered by the onset of fermion condensation  and  subsequent   opening  the Mott-like gap in the electron single-particle spectrum.        

     This scenario is also applied to the elucidation of a challenging  phenomenon uncovered in the analysis of ARPES data on  two-dimensional anisotropic  electron systems of cuprates. It consists in  breaking down of the Fermi line   into several  disconnected segments located in the antinodal region, (the  Fermi arc structure),  and   usually attributed to superconducting fluctuations  [6]. In the context of this article, the existence or disappearance of   the Fermi line is related to the FC arrangement. In cuprates, the FC occupies four different spots, every of which  is   associated with its own saddle point. Such a    configuration of the FC spots promotes the occurrence of   a  well pronounced gap in the spectrum   of  single-particle states,  located in the antinodal region. However, for single-particle states, located in the nodal region, the situation with the gap is opposite and therefore  in this domain of momentum space,  the  spectrum $\epsilon({\bf p})$  remains  gapless, in agreement with the experiment.

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                                                                             Khodel V. A., JETP Lett. 105 (8) (2017).  

New allotropes of carbon based in the C60 and C20 fullerenes with outstanding mechanical properties

Materials harder than diamond are always attract great attention from the scientists all over the world. Many attempts were made towards the synthesis especially of carbon material harder than diamond, which is the hardest possible material nowadays. A special interest belongs to materials called as fullerites. There are several experimental and theoretical works, where the synthesis and investigation of superhard fullerite were carried out. [1]–[4] Such materials reveal outstanding mechanical properties with the bulk modulus of several times higher than that of diamond.

In this case the computational approaches and methods allow the theoretical investigations and prediction of a new materials with desired properties without using very expensive experimental equipment. Here we used the state-of-the-art theoretical methods of computational predictions to predict new carbon phases based on the fullerene molecules of different sizes (C60 and C20). Using the evolutionary algorithm, implemented in USPEX package, [5] we considered more than 3000 possible crystal structures to find the most stable ones. The important point, that predicted phases are based on the polymerized fullerites, displaying the superior mechanical properties. We defined the crystal structure of predicted 4 stable allotropes by simulating the XRD patterns. All predicted structures are highly symmetric. The mechanical properties were studied in details in terms of elastic tensor, bulk and shear moduli and velocities of acoustic waves. All predicted structures display elastic constants and bulk modulus very close to diamond, which allows to say that we indeed predict new superhard phases. The possible way of synthesis of such phases was proposed consisting in the cold compression of a mixture of graphite and C60 fullerenes. The important feature of predicted phases (besides the mechanical properties) is that they have relatively small band gap ~2.5 eV, while the cI24 phase has the direct gap of 0.53 eV.

All obtained data allows the conclusion that predicted superhard semiconducting phases based on the polymerized fullerenes reveal necessary properties for applications in the electronic as basic elements.


[1] V.D. Blank, S.G. Buga, G.A. Dubitsky, N. R Serebryanaya, M.Y. Popov, and B. Sundqvist, Carbon 36, 319 (1998).

[2] M. Popov, V. Mordkovich, S. Perfilov, A. Kirichenko, B. Kulnitskiy, I. Perezhogin, and V. Blank, Carbon 76, 250 (2014).

[3] Y.A. Kvashnina, A.G. Kvashnin, M.Y. Popov, B.A. Kulnitskiy, I.A. Perezhogin, E.V. Tyukalova, L.A. Chernozatonskii, P.B. Sorokin, and V.D. Blank, J. Phys. Chem. Lett. 6, 2147 (2015).

[4] Y.A. Kvashnina, A.G. Kvashnin, L.A. Chernozatonskii, and P.B. Sorokin, Carbon 115, 546 (2017).

[5] C.W. Glass, A.R. Oganov, and N. Hansen, Comput. Phys. Commun. 175, 713 (2006).





Kvashnina Yu.A., Kvashnin D.G., Kvashnin A.G., Sorokin P.B.

 JETP Letters  105 ( 7) (2017)


Stochastic clustering of materials by plasma - surface interaction

Recently  stochastic clustering  with statistical self-similarity (fractality) has been found on material surface exposed under extreme plasma thermal loads in fusion devices (see [1]). In such devices, multiple processes of erosion and redeposition of the eroded material, surface melting and motion of the surface layers lead to a stochastic surface growth on the scales from tens of nanometers to hundreds of micrometers. The moving of eroded material species during redeposition from plasma and agglomeration on the surface is governed by stochastic electric fields generated by the high-temperature plasma. The specific property of the near-wall plasma in fusion device is the non-Gaussian statistics of electric field fluctuations with long-range correlations [2]. It leads to the stochastic agglomerate growth with a self-similar structure (hierarchical granularity - fractality) of non-Gaussian statistics contrary to a trivial roughness observed in ordinary processes of stochastic agglomeration. The dominant factor in such process in fusion device is the collective effect during stochastic clustering rather than the chemical element composition and physical characteristics of the solid material. In support of this view it is reported in this Letter, that such similar stochastic fractal structure with hierarchical granularity and self-similarity is formed on various materials, such as  tungsten, carbon materials and stainless steel exposed to high-temperature plasma in fusion devices.  In the literature it is discussed hypotheses of universal scalings of stochastic objects and processes with multi-scale invariance property (statistical self-similarity), see e.g. [3]. The kinetic models propose the describing of the stochastic clustering with a self-similar structure and considering the power law solutions for the number N of agglomerating clusters with mass m (see e.g. [4]), N(m)=Cm-(3+h)/2,  where h is a self-similarity exponent of the agglomeration kinetic model, C is a constant factor.  It is surprisingly found in this Letter that such the power laws (with power exponents from -2.4 to -2.8) describing the roughness of the test specimens from fusion devices are strictly deviated from that of the reference samples formed in a trivial agglomeration process forming   Brownian-like rough surface (such as samples exposed to low-temperature glow discharge plasma  and rough steel casting with the power law exponent in  the range of -1.97 to -2.2).  Statistics of  stochastic clustering samples from fusion devices is typically non-Gaussian and has a "heavy" tails of probability distribution functions (PDF) of stochastic surface heights (of the Hurst exponent from 0.68 to 0.86). It is contrary to the Gaussian PDF of the reference samples with trivial stochastic surface.  Stochastic clustering of materials from fusion devices is characterised by multifractal statistics. Quantitative characteristics of statistical inhomogeneity of such material structure, including multifractal spectrum with broadening of  0.5 ¾ 1.2, are in the range observed for typical multifractal objects and processes in nature. This may indicate a universal mechanism of stochastic clustering of materials under the influence of high-temperature plasma.


1. V.P. Budaev et al., JETP Letters vol. 95,   2, 78 (2012).

2. V.P. Budaev, S.P. Savin, L.M.  Zelenyi,   Physics-Uspekhi 54 (9),   875   (2011)

 3. A. L. Barabasi and H. E. Stanley, Fractal Concepts in Surface Growth (Cambridge Univ. Press, Cambridge, 1995).

4. C. Connaughton, R. Rajesh, O. Zaboronski, PRL 94 (19), 194503 (2005).





V.P. Budaev, JETP Letters    vol. 105, issue 5 (2017)

Fluctuational shift of nematic - isotropic phase transition temperature

Modern physics of liquid crystals is much younger than its traditional condensed matter material counterparts. Therefore the field is not yet completely elaborated and exhausted, and one may  still expect discoveries of new mesogen materials exhibiting of new types of liquid-crystalline ordering. A few years ago such a discovery of so-called bent-core or dimer mesogens which can form short pitch heli-conical nematic state (also known as twist-bend nematics, $N_{TB}$) [1, 2], attracted a lot of interest to this new state of matter with nano-scale orientational modulation. First, to understand the nature of the phase, basically different from conventional uniform nematics and from modulated in mass density smectics (see e.g., Landau theory approach, [3,4]). Second, to exploit potentially very perspective applications of the $N_{TB}$ liquid crystals. Along this way, very recently S.M.Saliti, M.G.Tamba, S.N. Sprunt, C.Welch, G.H.Mehl, A.Jakli, J.T.Gleeson [5] observed of the unprecedentedly large magnetic field induced shift $\Delta T_c(H)$ of the nematic - isotropic transition temperature. What is even more surprising $\Delta T_c(H)$ does not follow the thermodynamics text-book wisdom prediction $H^2$ scaling. Our  interpretation of such a behavior is based on singular longitudinal fluctuations of the nematic order parameter. Since these fluctuations are governed by the Goldstone director fluctuations they exist only in the nematic state. External magnetic field suppresses the singular longitudinal fluctuations of the order parameter. The reduction of the fluctuations changes the equilibrium value of the modulus of the order parameter in the nematic state, and leads  to additional (with respect to the mean field contribution) fluctuational shift of the nematic - isotropic transition temperature. The mechanism works for any nematic liquid crystals, however the magnitude of the fluctuational shift increases with decrease of the Frank elastic moduli. Since some of these moduli supposed to be anomalously small for the  bent-core or dimer mesogen formed nematic liquid crystals, just these liquid crystals  are promising candidates for the observation of the predicted fluctuational shift of the phase transition temperature.
[1] V.P.Panov, M.Nagaraj, J.K.Vij, et al., Phys. Rev. Lett., 105, 167801 (2010).
[2] M.Cestari, S.Diez-Berart, D.A.Dunmur, et al., Phys. Rev. E, 84, 031704 (2011).
[3]  E.I.Kats, V.V.Lebedev, JETP Letters,  100, 118-121 (2014).
[4] L.Longa, G.Pajak, Phys. Rev. E,  93, 040701 (2016).
[5] S.M.Saliti, M.G.Tamba, S.N. Sprunt, C.Welch, G.H.Mehl, A.Jakli, J.T.Gleeson, Phys. Rev. Lett., 116, 217801 (2016).

                                                                      E.I. Kats JETP  Letters 105 (4)  (2017)

Paradox of photons disconnected trajectories being located by means of "weak measurements" in the nested Max-Zehnder interferometer

In a recent letter A. Danan et al. [A. Danan, D. Farfurnik, S. Bar-Ad et al., Phys. Rev. Lett. 111, 240402 (2013)] have experimentally demonstrated an intriguing behavior of photons in an interferometer. Simplified layout of the experimental setup represents a nested Mach-Zehnder interferometer (MZI) and is shown below.

The surprising result is obtained when the inner MZI is tuned to destructive interference of the light propagating toward mirror F. In that case the power spectrum shows not only peak at the frequency of mirror C but two more peaks at the frequencies of mirrors A and B, and no peaks at the frequencies of mirrors E and F. From these results authors conclude that the path of the photons is not represented by connected trajectories, because the photons are registered inside the inner MZI and not registered outside it.

These unusual results have raised an active discussion. Nevertheless, until now there was no comprehensive and clear analysis of the experiment within the framework of the classical electromagnetic waves approach.

In this letter, we calculate  the signal power spectrum at the output of the nested MZI, based on traditional concept of the classical electromagnetic waves (or quantum mechanics).  This concept imply the continuity of the wave (photon) trajectories. We give intuitive clear and  comprehensive explanation of paradoxical results. So,  there is no necessity for a new concept of disconnected trajectories.


Simplified experimental setup with two nested Mach-Zehnder interferometers. A, B, C, E, and F stands for mirrors; BS1 and BS2, and PBS1 and PBS2 stands for ordinary and polarized beam splitters respectively. The elements BS1, A, B, and BS2 form an inner MZI whereas the elements PBS1, C, E, F and PBS2 form an outer MZI. Various mirrors inside the MZI vibrate with different frequencies. The rotation of a mirror causes a vertical shift of the light beam reflected off that mirror. The shift is measured by a quad-cell photodetector QCD.  When the vibration frequency of a certain mirror appears in the power spectrum, authors conclude that photons have been near that particular mirror




                                                                 G.N.Nikolaev JETP Letters 105 (3)  (2017)

Dark matter from dark energy in q-theory

   The dynamics of the quantum vacuum is one of the major unsolved problems of relativistic quantum field theory and cosmology. The reason is that relativistic quantum field theory and general relativity describe processes well below the Planck energy scale, while the deep ultraviolet quantum vacuum at or above the Planck energy scale remains unknown. Following the condensed matter experience we develop a special macroscopic approach called q-theory, which incorporates the ultraviolet degrees of freedom of the quantum vacuum into an effective theory and allows us to study the dynamics of the quantum vacuum and its influence on the evolution of the Universe.

     The vacuum in our approach is considered as the Lorentz-invariant analog of a condensed-matter system (liquid or solid) which is stable in free space. The variable q is the Lorentz-invariant analog of the particle number density, whose conservation regulates the thermodynamics and dynamics of many-body systems. This approach is universal in the sense that the same results are obtained using different formulations of the q-field. In the paper, we choose the q-field in terms of a 4-form field strength, which has, in particular, been used by Hawking for discussion of the main cosmological constant problem -- why is the observed value of the cosmological constant many orders of magnitude smaller than follows from naive estimates of the vacuum energy as the energy of zero-point motion. In q-theory, the huge zero-point energy is naturally cancelled by the microscopic (trans-Planckian) degrees of freedom, as follows from the Gibbs-Duhem identity, which is applicable to any equilibrium ground state including the one of the physical


            In the paper, we consider a further extension of q-theory. We demonstrate that, in an expanding Universe, the variable  effectively splits into two components. The smooth part of the relaxing vacuum field is responsible for dark energy, while the rapidly oscillating component behaves as cold dark matter. In this way, q-theory provides a combined solution to the missing-mass problem and the cosmological constant problem. If this scenario is correct, the implication would be that direct searches for dark-matter particles remain unsuccessful in the foreseeable future.

F.R. Klinkhamer and G.E. Volovik,

JETP Letters  105, issue 1 (2017)


The ability to detect nonequilibrium spin accumulation (imbalance) by all electrical means is one of the key ingredients in spintronics . Transport detection typically relies on a nonlocal measurement of a contact potential difference induced by the spin imbalance by means of ferromagnetic contacts  or spin resolving detectors . A drawback of these approaches lies in a difficulty to extract the absolute value of the spin imbalance without an independent calibration. An alternative concept of a spin-to-charge conversion via nonequilibrium shot noise was introduced and  investigated in  experiment recently . Here, the basic idea is that a nonequilibrium spin imbalance generates spontaneous current fluctuations, even in the absence of a net electric current. Being a primary approach , the shot noise based detection is potentially suitable for the absolute measurement of the spin imbalance. In addition, the noise measurement can be used for a local non-invasive sensing.

In this letter, we calculate the impact of a spin relaxation on the spin imbalance generated shot noise in the absence of inelastic processes. We find that the spin relaxation increases the noise up to a factor of two, depending on the ratio of the conductor length and the spin relaxation length. The design of the system. A diffusive normal wire of the length L is attached to normal islands on both ends. Nonequilibrium energy distribution on the left hand side of the wire generates the shot noise at a zero net current. The spin imbalance on the left-hand side of the wire is due to the electric current flowing from one ferromagnetic lead (red) to another one with opposite magnetization (blue).



V.S. Khrapai and K.E. Nagaev JETP  Letters 105, №1 (2017)