A planar defect spin sensor in a two-dimensional material susceptible to strain and electric fields 

Péter Udvarhelyi, Tristan Clua-Provost, Alrik Durand, Jiahan Li, James H. Edgar, Bernard Gil, Guillaume Cassabois, Vincent Jacques & Adam Gali

npj Computational Materials 9: 150 (2023).

doi.org/10.1038/s41524-023-01111-7

Published: 22 August, 2023

编辑概述

二维材料中的平面缺陷自旋传感器：应变和电场调谐

电场和应变场效应对于严密控制固态自旋缺陷至关重要，可应用于量子技术。准确理解与这些扰动相关的耦合可以被主动利用（如用于调整缺陷的磁光特性），或被动利用（如用于感知其近距离环境）。目前嵌入二维（2D）范德华材料中的自旋缺陷最受关注。2D主体的主要优点是量子缺陷接近表面，这提高了其光学效率和传感能力。六方氮化硼（hBN）就是这类二维材料之一，hBN上的缺陷更是被认为是单光子发射源，可提供窄而可调的发射线、高亮度和完美的光稳定性。此外，最近的研究表明，可以通过光学检测磁共振（ODMR）方法来推断出一些缺陷的电子自旋共振频率，这便为量子感应得应用提供了重要资源。迄今为止，带负电荷的硼空位中心（）是hBN中唯一具有ODMR响应的点缺陷，其微观结构已被明确确定。这种缺陷很容易通过辐照、离子注入和激光书写技术来产生，最近已被用于传感磁场、应变和温度。ODMR光谱观察到的中心合团的轴向零场分裂（ZFS）最初被归因于hBN晶体中的应变效应，导致缺陷对称性降低。但最近的研究表明，它实际上是由与局部电场的相互作用而引起的。因此，迫切需要了解应变和电场对缺陷自旋的磁共振的协同影响。在本工作中，来自匈牙利维格纳物理研究中心的Adam Gali教授团队，采用第一性原理计算方法，确定了外部电场和应变场对hBN中中心基态电子自旋结构的影响。结果表明，在大多数实验条件下，缺陷经历了波动电场，这导致了在零外部磁场下记录的ODMR光谱的正交分裂。作者分析了这种效应的微观起源，并确定了自旋应变和自旋电场耦合参数。该研究证明了正交ZFS是由波动电场引起的，并表明中心对应变和电场的耦合强度与金刚石中氮空位（NV⁻）中心的耦合强度相当。同时，工作也证明了在自旋-电场耦合参数中的压电效应很强，这可以推广到hBN中的其他空位型缺陷。这项工作对指导未来中心在hBN中的应用，如在高压下进行量子感应和电测量，铺平了康庄大道。

Editorial Summary

Planar defect spin sensor in 2D material: Strain and electric fields

Electric and strain field effects are highly important ingredients in the tight control of solid-state spin defects for quantum technology applications. The accurate knowledge of the couplings to these perturbations can be harnessed either actively, e.g., for tuning the magneto-optical properties of the defect, or passively, e.g., for sensing its close environment. The main advantage of a 2D host is the proximity of the quantum defect to the surface, which improves both its optical efficiency and sensing capabilities. One of these 2D materials is hexagonal boron nitride (hBN), and defects in hBN were first studied as single-photon emitters, providing narrow and tunable emission lines, high brightness, and perfect photostability. In addition, it was recently shown that the electron spin resonance frequencies of some defects can be inferred through optically detected magnetic resonance (ODMR) methods, providing a central resource for quantum sensing applications. To date, the negatively-charged boron-vacancy centre (V−BVB−) is the only point defect in hBN possessing an ODMR response whose microscopic structure has been unambiguously identified. This defect, which can be readily created by irradiation, ion-implantation and laser writing techniques, has been recently employed for sensing magnetic fields, strain, and temperature. The axial zero-field-splitting (ZFS) on ensembles of centres observed by ODMR spectra was originally attributed to strain effects in the hBN crystal leading to a reduced symmetry of the defect. But a recent study suggested that it results instead from the interaction with a local electric field. Therefore. there is of great significance to understand the effects of strain and electric fields on magnetic resonance ofdefect spins. In this work, a team led by Prof. Adam Gali from the Advanced Materials and Engineering, Hungary, employed first-principles simulations to determine the effect of external electric and strain fields on the ground state electronic spin structure of centres in hBN. The results showed that in most of the experimental conditions the defect experiences fluctuating electric fields that leads to an orthorhombic splitting in ODMR spectra recorded at zero external magnetic field. They analyzed the microscopic origin of this effect and determined the spin-strain and spin-electric field coupling parameters. The study proved that the orthorhombic ZFS is caused by fluctuating electric fields and suggested that the coupling strengths of the centres to strain and electric fields are comparable to those of the nitrogen-vacancy (NV⁻) centre in diamond. Meanwhile, the authors showed that the piezo effect is strong in the spin-electric field coupling parameters, which may be generalised for other vacancy-type defects in hBN. This work paves an avenue for the future applications of centres in hBN, such as quantum sensing under high pressure and electrometry.