Theory of Field-Angle-Resolved Magnetoacoustic Resonance in Spin-Triplet Systems for Application to Nitrogen-Vacancy Centers in Diamond

TL;DR

This paper develops a theoretical framework for understanding how oscillating strain fields interact with spin-triplet states in NV centers in diamond, revealing new ways to probe spin-strain couplings and tune resonance frequencies.

Contribution

It introduces a Floquet theory-based model for spin-strain interactions in NV centers, highlighting the control of phonon resonances via magnetic field orientation.

Findings

Two-phonon transition probabilities depend on magnetic field rotation.

Level splitting can be tuned by changing the magnetic field direction.

Magnetoacoustic resonance can probe unquantified spin-strain couplings.

Abstract

Motivated by the recent studies of acoustically driven electron spin resonance applied to diamond nitrogen-vacancy (NV) centers, we investigate the interaction of an electronic spin-triplet state with periodically time-dependent oscillating strain fields. On the basis of a lowest-lying two-level system, we show the importance of two-phonon transition probabilities controlled by rotating an applied magnetic field using the Floquet theory. In particular, we demonstrate how to evaluate coupling-strength parameters in the spin--strain interaction for the $C_{3v}$ point group considering the NV spin states. The level splitting of spin states can be adjusted by changing the field directions relative to the NV axis to obtain lower phonon resonance frequencies suitable for practical applications. Focusing on a field-rotation angle for the vanishment of a longitudinal phonon-mediated transition, we show that the magnetoacoustic resonance presented here provides useful information as a new probe of unquantified spin--strain couplings possessed by NV defects.