Electron Spin Relaxation in Graphene Nanoribbon Quantum Dots

TL;DR

This paper calculates electron spin relaxation times in graphene nanoribbon quantum dots, showing potential for long coherence times due to suppressed relaxation mechanisms, making them promising for spintronics.

Contribution

The study provides an analytical calculation of spin relaxation times in armchair graphene nanoribbons, revealing conditions for very long T_1 times and highlighting their suitability for quantum spin applications.

Findings

T_1 can reach seconds under certain conditions

Destructive interference reduces relaxation mechanisms

Van Vleck cancellation occurs at low magnetic fields

Abstract

Graphene is promising as a host material for electron spin qubits because of its predicted potential for long coherence times. In armchair graphene nanoribbons (aGNRs) a small bandgap is opened, allowing for electrically gated quantum dots, and furthermore the valley degeneracy is lifted. The spin lifetime T_1 is limited by spin relaxation, where the Zeeman energy is absorbed by lattice vibrations, mediated by spin-orbit and electron-phonon coupling. We have calculated T_1 by treating all couplings analytically and find that T_1 can be in the range of seconds for several reasons: (i) low phonon density of states away from Van Hove singularities; (ii) destructive interference between two relaxation mechanisms; (iii) Van Vleck cancellation at low magnetic fields; (iv) vanishing coupling to out-of-plane modes in lowest order due to the electronic structure of aGNRs. Owing to the vanishing nuclear spin of 12C, T_1 may be a good measure for overall coherence. These results and recent advances in the controlled production of graphene nanoribbons make this system interesting for spintronics applications.