Near-surface thermal generation of longitudinal bulk acoustic waves in organic conductors

Abstract

The linear thermal generation of near-surface longitudinal bulk acoustic waves (NSLBAWs) in organic conductors with layered structure is considered. These are waves that are generated and propagate at a distance of order or less than the thermal source attenuation length, i.e., are confined to the thermal skin layer of the conductor. The Green’s functions approach is applied to obtain the integral form for the solutions of the thermal conduction equation and wave equation. Analytical expressions for the temperature distribution and the wave amplitude are obtained in case when a current is applied along the least conducting direction of the quasi-two-dimensional organic conductor $ \beta - ({\rm BEDT}-{\rm TTF})_{2}{\rm IBr}_{2}$ as a thermal source. The behavior of both thermal and acoustic field is investigated near the conductor’s surface. In addition, the angular and magnetic field dependencies of the NSLBAWs amplitude are obtained and analyzed in order to emphasize the specific features of these waves. Furthermore, a comparison of the properties of both NSLBAWs and the longitudinal bulk acoustic waves that are generated and attenuate in the depth of the conductor, i.e., deep longitudinal bulk acoustic waves (DLBAWs) reveals some similarities and important differences in the process of thermal generation of the waves. We discuss the possible application of the thermal generation of NSLBAWs in organic conductors and why these waves are more preferable than the DLBAWs for studying some of the properties and/or states in layered organic conductors as well as for determining the parameters that shape the Fermi surface that cannot be obtained through the DLBAWs or transport measurements.