arXiv subjects
Publications and source records attributed to A. V. Shtyk.
We develop a theory of ultrasound decay rate $α$ in a model of a superconductor with a large pseudogap $Δ_P$, and show that at low temperatures ($T \ll T_c$) the magnitude of the decay rate $α$ is controlled by the ratio of $T/Δ$, where $Δ\ll Δ_P$ is a superconducting collective gap. Thus we propose new method to measure the collective gap $Δ$ in a situation when strong pseudogap is present.
Relaxation of soft modes (e.g. charge density in gated semiconductor heterostructures, spin density in the presence of magnetic field) slowed down by disorder may lead to giant enhancement of energy transfer (cooling power) between overheated electrons and phonons at low bath temperature. We show that in strongly disordered systems with time-reversal symmetry broken by external or intrinsic exchange magnetic field the cooling power can be greatly enhanced. The enhancement factor as large as $10^{2}$ at magnetic field $B \sim 10$ Tesla in 2D {\rm InSb} films is predicted. A similar enhancement is found for the ultrasound attenuation.
Plasmons in two-dimensional electron systems with nonparabolic bands, such as graphene, feature strong dependence on electron-electron interactions. We use a many-body approach to relate plasmon dispersion at long wavelengths to Landau Fermi-liquid interactions and quasiparticle velocity. An identical renormalization is shown to arise for the magnetoplasmon resonance. For a model with N>>1 fermion species, this approach predicts a power-law dependence for plasmon frequency vs. carrier concentration, valid in a wide range of doping densities, both high and low. Gate tunability of plasmons in graphene can be exploited to directly probe the effects of electron-electron interaction.
We consider spin ice magnets (primarily, $\mathrm{Dy_2Ti_2O_7}$) in the vicinity of their critical point on the $(H,T)$ plane. We find that the longitudinal susceptibility diverges at the critical point, leading to the behaviour qualitatively similar to the one which would result from non-zero conductance of magnetic charges. We show that dynamics of critical fluctuations belongs to the universality class of easy-axis ferroelectric and calculate logarithmic corrections (within two-loop approximation) to the mean-field critical behavior.