# Nuclear Spin Relaxation Time due to the Orbital Currents in Dirac Electron Systems

## TL;DR

This paper calculates the nuclear spin relaxation time in Dirac electron systems considering orbital currents, revealing a temperature dependence that aligns with recent experimental observations in topological insulators.

## Contribution

It introduces a model for nuclear spin relaxation due to orbital currents in Dirac electron systems and predicts a specific temperature dependence of relaxation time.

## Key findings

- $T_1$ shows a $T^3$ dependence at high temperatures.
- Results qualitatively match recent $eta$-NMR experiments.
- Provides insight into nuclear spin dynamics in topological insulators.

## Abstract

The nuclear spin relaxation time $T_1$ is calculated taking account of the contributions from orbital currents of Dirac electrons. We consider a simple model of non-interacting Dirac electron gas in the three-dimensional bulk system. The obtained result shows $T^3$ dependence of $1/T_1$ at temperatures $T$ above the energy gap. This temperature dependence agrees qualitatively with the recent $\beta$-NMR experiment on the bulk of the topological insulator $\mathrm{Bi}_{0.9}\mathrm{Sb}_{0.1}$.