Chiral-phonon-induced current in helical crystals

TL;DR

This paper theoretically demonstrates that chiral phonons in helical crystals induce a current along the helical axis in the metallic phase, with the current's behavior governed by the system's symmetries and topological properties.

Contribution

It introduces a theoretical framework linking chiral phonons to induced currents in helical crystals, highlighting the role of symmetries and topological invariants.

Findings

Finite time-averaged current in metallic phase along helical axis.

Vanishing time-averaged current in insulating phase due to topological reasons.

Current behavior governed by space-time symmetries of the helical system.

Abstract

In this study, we theoretically show that in a helical crystal, a current is induced by chiral phonons representing the microscopic local rotation of atoms. By treating the rotational motion as a perturbation, we calculate the time-dependent current by using the adiabatic Berry phase method. The time average of the current along the helical axis becomes finite in the metallic phase but it vanishes in the insulating phase. On the other hand, the current in the hexagonal plane changes with time, but its time average vanishes due to the threefold rotation space-time symmetry. We show that the time evolutions of the current follow the space-time symmetries of the helical systems. Moreover, we explain the reason for the vanishing of the time average of the current in the insulating phase from the aspect of the Chern number in the parameter space.