Order parameter phase locking as a cause of a zero bias peak in the differential tunneling conductance of bilayers with electron-hole pairing

In n-p bilayer systems an exotic phase-coherent state emerges due to Coulomb pairing of n-layer electrons with p-layer holes. Unlike Josephson junctions, the order parameter phase may be locked by matrix elements of interlayer tunneling in n-p bilayers. Here we show how the phase locking phenomenon specifies the response of the electron-hole condensate to interlayer voltages. In the absence of an applied magnetic field, the phase is steady-state (locked) at low interlayer voltages, V<V_c, however the phase increases monotonically with time (is unlocked) at V>V_c. The change in the system dynamics at V=V_c gives rise to a peak in the differential tunneling conductance. The peak width V_c is proportional to the absolute value of the tunneling matrix element |T_{12}|, but its height does not depend on |T_{12}|; thus the peak is sharp for small |T_{12}|. A sufficiently strong in-plane magnetic field reduces considerably the peak height. The present results are in qualitative agreement with the zero bias peak behavior that has recently been observed in bilayer quantum Hall ferromagnets with spontaneous interlayer phase coherence.Comment: 6 pages, extended version, phenomenological derivation of the main equation is added, references are adde

Spin Seebeck effect and phonon energy transfer in heterostructures containing layers of a normal metal and a ferromagnetic insulator

This is the final version. Available from the American Physical Society via the DOI in this recordIn the framework of the kinetic approach based on the Boltzmann equation for the phonon distribution function, we analyze phonon heat transfer in a heterostructure containing a layer of a normal metal (N) and a layer of a ferromagnetic insulator (F). Two realistic methods for creating a temperature gradient in such a heterostructure are considered: by heating the N layer by an electric current and by placing the N/F bilayer between massive dielectrics with different temperatures. The electron temperature Te in the N layer and the magnon temperature Tm in the F layer are calculated. The difference in these temperatures determines the voltage VISHE on the N layer in the Seebeck spin effect regime. The dependence of VISHE on the bath temperature and on the thickness of the N and F layers is compared with the available experimental data.European Union Horizon 202

Order parameter phase locking as a cause of a zero bias peak in the differential tunneling conductance of bilayers with electron-hole pairing

In n—p bilayer systems an exotic phase-coherent state emerges due to Coulomb pairing of n-layer electrons with p-layer holes. Unlike Josephson junctions, the order parameter phase may be locked by matrix elements of interlayer tunneling in n—p bilayers. Here we show how the phase locking phenomenon specifies the response of the electron—hole condensate to interlayer voltages. In the absence of an applied magnetic field, the phase is steady-state (locked) at low interlayer voltages, V Vc. The change in the system dynamics at V = Vc gives rise to a peak in the differential tunneling conductance. The peak width Vc is proportional to the absolute value of the tunneling matrix element |T₁₂|, but its height does not depend on |T12|; thus the peak is sharp for small |T₁₂|. An in-plane magnetic field reduces the peak height considerably. The present results are in qualitative agreement with the zero-bias peak behavior that has recently been observed in bilayer quantum Hall pseudoferromagnets with spontaneous interlayer phase coherence

Strongly nonequilibrium flux flow in the presence of perforating submicron holes

We report on the effects of perforating submicron holes on the vortex dynamics of amorphous Nb0.7Ge0.3 microbridges in the strongly nonequilibrium mixed state, when vortex properties change substantially. In contrast to the weak nonequilibrium - when the presence of holes may result in either an increase (close to Tc) or a decrease (well below Tc) of the dissipation, in the strong nonequilibrium an enhanced dissipation is observed irrespectively of the bath temperature. Close to Tc this enhancement is similar to that in the weak nonequilibrium, but corresponds to vortices shrunk due to the Larkin-Ovchinnikov mechanism. At low temperatures the enhancement is a consequence of a weakening of the flux pinning by the holes in a regime where electron heating dominates the superconducting properties.Comment: 6 pages, 5 figure

Non linear flux flow in TiN superconducting thin film

We have studied the superconducting behavior of 100 nm Titanium Nitride (TiN) thin film in a perpendicular magnetic field. We found a zero field transition temperature of 4.6 K and a slope in the H-T plane of -0.745 T/K. At 4.2 K, we have performed careful transport measurements by measuring both the differential resistivity and voltage as a function of a DC current. Our results are analyzed in the framework of linear and non linear flux flow behavior. In particular, we have observed an electronic instability at high vortex velocities and from its dependence with respect to the applied magnetic field, we can exctract the inelastic scattering time and diffusion length of the quasiparticles

On the microscopic theory of the exciton ring fragmentation

The description is presented for the dependence of the indirect exciton condensate density at the ring as a function of the polar angle at zero temperature with the involvement of the processes of formation and recombination of the excitons. In particular, starting from the quasi one-dimensional Gross-Pitaevskii equation with a spatially uniform generating term, we derive an exact analytical solution yielding the fragmentation of an exciton ring which is probably observed in the experiments.Comment: 4 pages, 1 figure. The preprint has been brought into accord with the journal's varian

Temperature dependence of the magnon-phonon energy relaxation time in a ferromagnetic insulator

This is the final version. Available from the American Physical Society via the DOI in this recordWe have used the Boltzmann kinetic equation for the phonon distribution function to analyze the relaxation kinetics of the spin system of a ferromagnetic insulator (F) lying on a massive dielectric substrate with high thermal conductivity. Under periodic heating of the spin system, the relaxation depends on the thickness of the F layer and on the frequency of the thermal source ω. When the thickness of the F layer is much greater than the phonon-magnon scattering length, the magnon temperature dependence on the frequency has two features related to specific characteristic times of the system. One of them determines the dependence in the low-frequency regime and is related to the average phonon escape time from the F layer to the substrate τes. In turn, the high-frequency behavior is determined by the magnon-phonon collisions time τmp. From the latter, the time of phonon-magnon collisions τpm can be found. In contrast, the response of effectively thin F layers is characterized by just one feature, which is determined by the time τmp. Thus, based on the obtained theoretical results, the times τes,τmp, and τpm can be deduced from experiments on the parametric excitation of spin waves by electromagnetic radiation modulated at frequency ω.European Union Horizon 202

Transport properties of \nu=1 quantum Hall bilayers. Phenomenological description

We propose a phenomenological model that describes counterflow and drag experiments with quantum Hall bilayers in a \nu_T=1 state. We consider the system consisting of statistically distributed areas with local total filling factors \nu_{T1}>1 and \nu_{T2}<1. The excess or deficit of electrons in a given area results in an appearance of vortex excitations. The vortices in quantum Hall bilayers are charged. They are responsible for a decay of the exciton supercurrent, and, at the same time, contribute to the conductivity directly. The experimental temperature dependence of the counterflow and drive resistivities is described under accounting viscous forces applied to vortices that are the exponentially increase functions of the inverse temperature. The presence of defect areas where the interlayer phase coherence is destroyed completely can result in an essential negative longitudinal drag resistivity as well as in a counterflow Hall resistivity

Superfluidity of electron-hole pairs in randomly inhomogeneous bilayer systems

In bilayer systems electron-hole (e-h) pairs with spatially separated components (i.e., with electrons in one layer and holes in the other) can be condensed to a superfluid state when the temperature is lowered. This article deals with the influence of randomly distributed inhomogeneities on the superfluid properties of such bilayer systems in a strong perpendicular magnetic field. Ionized impurities and roughenings of the conducting layers are shown to decrease the superfluid current density of the e-h pairs. When the interlayer distance is smaller than or close to the magnetic length, the fluctuations of the interlayer distance considerably reduce the superfluid transition temperature.Comment: 13 pages, 3 figure