Bulk angular momentum and Hall viscosity in chiral superconductors

TL;DR

This paper derives Berry-phase formulas for angular momentum and Hall viscosity in chiral superconductors, revealing their relationship at zero temperature and differences at finite temperatures.

Contribution

It introduces a unified Berry-phase framework to calculate angular momentum and Hall viscosity in chiral superconductors, including nodal cases.

Findings

Zero-temperature angular momentum is proportional to magnetic quantum number and electron count.

Hall viscosity equals half the angular momentum at zero temperature in full-gap and nodal chiral SCs.

Finite temperature behavior of Hall viscosity differs between full-gap and nodal chiral superconductors.

Abstract

We establish the Berry-phase formulas for the angular momentum (AM) and the Hall viscosity (HV) to investigate chiral superconductors (SCs) in two and three dimensions. The AM is defined by the temporal integral of the anti-symmetric momentum current induced by an adiabatic deformation, while the HV is defined by the symmetric momentum current induced by the symmetric torsional electric field. Without suffering from the system size or geometry, we obtain the macroscopic AM $L_z = \hbar m N_0/2$ at zero temperature in full-gap chiral SCs, where $m$ is the magnetic quantum number and $N_0$ is the total number of electrons. We also find that the HV is equal to half the AM at zero temperature not only in full-gap chiral SCs as is well-known but also in nodal ones, but its behavior at finite temperature is different in the two cases.