AQP Seminar: Transverse Magnetosonic Waves and Viscoelastic Resonance in Two-Dimensional Highly Viscous Electron Fluid

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Dr. Pavel Alekseev (Ioffe Institute, Russia)

In modern ultra-pure conductors, electrons can form a viscous fluid at low temperatures. The properties of viscous fluids at high frequencies become similar to those of amorphous solids. In particular, the propagation of not only longitudinal acoustic waves (plasmons in the case of an electron fluid), but also transverse acoustic waves, associated with shear deformations, becomes possible. We demonstrate that in a two-dimensional highly viscous electron fluid in a magnetic field the two types of excitations can coexist: those of the shear stress (previously unknown transverse magnetosound) and those associated with the charge density (conventional magnetoplasmons). Both the viscoelastic and the plasmonic components of the flow exhibit the recently proposed viscoelastic resonance which is related to the own dynamics of shear stress of charged fluids in a magnetic field. Consideration of the transverse magnetosound is performed within phenomenological Landau’s Fermi-liquid model. We show that the dynamics of Fermi-liquid excitations is described by hydrodynamic equations at a rather strong quasiparticle interaction. The dispersion law and the damping coefficient of transverse magnetosound are closely related to the time dispersion of viscosity of the magnetized fluid. We demonstrate that the cyclotron frequency entering the viscosity coefficients and the dispersion law of magnetosound is renormalized and typically becomes somewhat smaller than the ordinary cyclotron frequency determining the cyclotron resonance. We argue that the generation of transverse magnetosound, manifesting itself by the viscoelastic resonance with the renormalized cyclotron frequency, is apparently responsible for the peak in photoresistance and peculiarities in photovoltage observed in ultra-high-mobility GaAs quantum wells.

[1] P. S. Alekseev and A. P. Alekseeva, Phys. Rev. Lett. 123, 236801 (2019).
[2] P. S. Alekseev, Semiconductors 53, 1367 (2019).