Relaxation dynamics of spin- 32 silicon vacancies in 4H -SiC

Abstract

Room temperature optically detected magnetic resonance experiments on spin 3/2 V2 Silicon vacancies in 4H-SiC are reported. The ms = +1/2 ↔ −1/2 transition is accessed using a two microwave frequency excitation protocol. The ratio of the Rabi frequencies of the +3/2 ↔ +1/2 and +1/2 ↔ −1/2 transitions is measured to be (0.90 ± 0.02) √ 3/2. The deviation from √ 3/2 is attributed to small difference in g-factor for different magnetic dipole transitions. Whereas a spin-1/2 system is characterized by a single T1 time, we show that the spin 3/2 system has three distinct relaxation modes that can be preferentially excited and detected. Compared to model where relaxation is caused by fluctuating B-field, a relatively fast relaxation between ms = ±1/2 states is observed.The density matrix of a qubit is often decomposed into the identity and three Pauli spin-half matrices. The resulting Bloch-vector provides an intuitive picture of the spin-half dynamics, and the populations relax with a single spin-lifetime termed T 1 . A spin 3/2 system has four states, and is described by a 4x4 density-matrix. By extension, the relaxation of the four spin populations is described by three relaxation modes, characterized by three time constants. Furthermore, the 4x4 density matrix can be represented by a multipole expansion of the identity, x3 dipole (P), x5 quadrupole (D), and x7 octupole (F)modes providing a more intuitive representation of the spin-3/2 density-matrix.[1] This representation has advantages for understanding the spin-relaxation processes of S=3/2. For example, a dipole-like perturbation does not mix different order poles fixing the spin relaxation times such that T p = 3T d = 6T f , as recently discussed theoretically in the case of a fluctuating magnetic field acting on a silicon vacancy in SiC.[2] [3] An accessible spin 3/2 system for testing this prediction is the V2 silicon vacancy in 4H-SiC [2,4,5]. Recently, a number of groups have demonstrated that defects in SiC have optically accessible spins with coherence times on a par with diamond [5,6]. Unlike diamond, the manufacturing of SiC electronic devices is advanced. For example, n-and p-type doping can be routinely achieved and good quality SiO 2 films can be deposited or grown on the surface, enabling CMOS processing. Due to the large breakdown voltages of SiC diodes and transistors, SiC devices are increasingly used in power electronic applications relevant to electric trains, cars and power transmission. As such rapid improvement in materials and device quality is to be expected, and there is growing interest in SiC for quantum devices [7][8][9][10][11].In this letter, we report room temperature optically detected magnetic resonance (ODMR) experiments on an ensemble of V2 silicon vacancies in 4H-SiC. By using a two microwave frequency setup, the +1/2 ↔ −1/2 transition can be detected optically [2] [12]. Rabi oscillations of all three magnetic dipole allowed transitions are measured. The ratio of the Rabi frequencies is compared to the value of √ 3/2, expected f...

Exhaustive characterization of Si vacancy complex in 4H-SiC

“…Banks et al state that the strain and electric field perturbation are low, and these signals most likely correspond to other defects. This is echoed by Ramsey et al, who state that the most likely source of such signals is nearby defects perturbing the silicon vacancy [19]. Furthermore, in an array of silicon vacancies created with ion implantation, 30% of the measured spots showed even larger spectral drift, as large as 3 nm (5 meV), towards smaller energies [9].…”

Low-field microwave-free sensors using dipolar spin relaxation of quartet spin states in silicon carbide

“…For high spin defects, the dipolar spin relaxation depends on the initial spin state. 30 For the silicon vacancy, we calculate the spin relaxation effect starting from two different spin states. The initial population is either evenly distributed in the m S = {−1/2, +1/2} subspace or set completely in the m S = −1/2 state.…”

“…In recent years, considerable attention has been paid to experimental characterization of the relaxation dynamics of the quartet silicon vacancy spin states in a broad temperature range in various SiC samples. 21,29,30 The external field dependence of the relaxation processes have received little attention thus far, but must be understood in detail for various relaxometry applications. Recent theoretical developments have enabled parameter-free calculations of the two major contributions to the longitudinal spin relaxation, namely the temperature dependent spin-lattice relaxation [31][32][33] and the magnetic field dependent dipolar spin relaxation induced by local environmental spins 15,34,35 .…”