Phonon quarters-wave loss

Abstract

There has been a growing interest in the phase of phonon, due to the theoretical prediction (Phys. Rev. Lett. 115.11 (2015)) and the experimental observation (Science 359.6379 (2018)) of chiral phonons, which have different phases in different components. While half-wave loss is a well-known concept in optics, in this work, a series of plateaus of quarters-wave loss are first found for the reflected phonon across an interface by using an atomic junction model. These plateaus can be understood by the Smatrix in the system with time-reversal symmetry. If a phonon wave propagates from a low acousticimpedance material (or a low cutoff frequency material) to a higher one in the long-wave limit (or in the high frequency limit), a half-wave loss takes place for the reflected phonon; however, the plateau of half-wave loss for reflected phonon occurs in the whole frequency domain if phonon transfers to a material with a larger spring constant. Besides the half-wave loss, we also observe plateaus of quarterwave (three-quarters-wave) loss in long wave limit when the two leads with identical acoustic impedance are coupled by a weak (strong) coupling in comparison with the optimum thermal coupling. The quarters-wave loss for phonons can be applied to chiral phonon manipulation and other phononics devices.

Dramatic enhancement of interfacial thermal transport by mass-graded and coupling-graded materials

“…Model and method. -To study the phonon transport across an interface, we use the 1D atomic junction model which is a general model [36][37][38][39], where two semi-infinite leads and a central region are coupled by harmonic springs with strength k 12 and k 23 , as depicted in fig. 1(a).…”