Spontaneous time reversal symmetry breaking at individual grain boundaries in graphene

TL;DR

This study demonstrates spontaneous time reversal symmetry breaking at individual graphene grain boundaries, revealing magnetic phenomena that could enable new electronic and spintronic applications.

Contribution

It provides experimental evidence of TRS breaking at graphene grain boundaries using quantum transport and conductance fluctuation measurements, highlighting magnetic states at high doping and low temperature.

Findings

TRS is spontaneously broken at graphene grain boundaries.

Complete TRS lifting observed at high carrier densities and low temperatures.

Significant reduction in conductance fluctuations indicates emergent magnetic states.

Abstract

Graphene grain boundaries have attracted interest for their ability to host nearly dispersionless electronic bands and magnetic instabilities. Here, we employ quantum transport and universal conductance fluctuations (UCF) measurements to experimentally demonstrate a spontaneous breaking of time reversal symmetry (TRS) across individual GBs of chemical vapour deposited graphene. While quantum transport across the GBs indicate spin-scattering-induced dephasing, and hence formation of local magnetic moments, below $T\lesssim 4$ K, we observe complete lifting of TRS at high carrier densities ($n \gtrsim 5\times 10^{12}$cm$^{-2}$) and low temperature ($T\lesssim 2$ K). An unprecedented thirty times reduction in the UCF magnitude with increasing doping density further supports the possibility of an emergent frozen magnetic state at the GBs. Our experimental results suggest that realistic GBs of graphene can be a promising resource for new electronic phases and spin-based applications.