Circular Nonlinear Peltier Effect of Phonons as a Probe for Chiral Phonons

In semiconductors, steady electric currents induce temperature gradients, which is a phenomenon known as the Peltier effect. The Peltier effect is a thermoelectric effect that is related to the energy carried by the carriers in semiconductors. As other quasiparticles, such as magnons and phonons, also carry energy, a phenomenon similar to the Peltier effect may occur with the quasiparticles. In fact, a recent study proposed the Peltier effect of phonons induced by a nonlinear optical effect, which is called the nonlinear Peltier effect [1]. This phenomenon might be useful for probing the properties of phonons.

In this work, we show that the nonlinear Peltier effect induced by the circularly polarized light is related to one of the unique features of chiral phonons, the non-zero group velocity at k=0. Using the nonlinear response theory, we analyze the nonlinear Peltier effect in a chiral phonon model. We show that, in a material with chiral phonons, the energy current of phonons occurs through a mechanism similar to the injection current; this mechanism is distinct from the one proposed before. Moreover, for chiral phonon bands doubly degenerate at k=0, we show that the phonon current is related to the asymmetric excitation of phonons with opposite angular momentum.

[1] H. Ishizuka and M. Sato, Phys. Rev. B 110, L020303 (2024).