Fundamental Acoustic Wave Generation in Crystalline Organic Conductors with Two Conducting Channels

Abstract

A linear thermoelectric generation of a fundamental acoustic wave in organic conductors with two conducting channels, quasi-one dimensional (q1D) and quasi-two dimensional (q2D), is analyzed theoretically. Specifically, the case when an acoustic wave with a fundamental frequency w is generated along the most conducting axis of the multi-band organic conductor a-(BEDT-TTF)2KHg(SCN)4 is considered. The magnetic field and angular dependences of the wave amplitude for two boundary conditions, isothermal and adiabatic are obtained. Findings show that the wave amplitude for the isothermal boundary is much larger than the one for the adiabatic boundary although there is a heat flux through the conductor's surface in the former. This is completely different compared to the case of a wave generated along the least conducting axis and the possible reasons behind this behavior are discussed. The angular oscillations of the fundamental wave amplitude are associated with the charge carriers motion on both the cylindrical part and quasi-planar sheets of the Fermi surface in a tilted magnetic field. The changes in the wave amplitude with the field orientation are correlated with the corresponding angular changes in the in-plane thermoelectric coefficient and thermal conductivity. Following the magnetic field behavior of both the in-plane electromagnetic and thermal skin depth we find that the wave generation and propagation in the plane of the layers are determined mainly by the thermal wave as its skin depth is thousand times larger than the one of the electromagnetic wave. It is shown that both the q1D and q2D charge carriers contribute to the observation of the effect but the group of charge carriers with a q1D energy spectrum is significantly dominant in the generation of the fundamental acoustic wave in the plane of the layers.