Study of Dipole Spin Relaxation of SiC Double Vacancy Quantum Dots

Study of Dipole Spin Relaxation of SiC Double Vacancy Quantum Dots

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Silicon carbide (SiC) is a semiconductor with mature related technologies, controllable p-type and n-type doping, and mature nanomanufacturing technology. However, at present, it is necessary to reveal the coherence characteristics, decay time T1, and longitudinal spin relaxation process of the double vacancy quantum dots for their dynamic decoupling and sensing processes.

A research team conducted a systematic study on the spin relaxation dynamics of double vacancy quantum dots in 4H-SiC. The research team first investigated the magnetic field dependence of spin mixing caused by different spins in the local environment of double vacancy quantum dots, and demonstrated that adjacent double vacancy centers and spin 3/2 silicon vacancy centers generate multiple relaxation modes with multiple relaxation peaks. The spin relaxation modes with different magnetic field dependencies can be identified and studied through optical means for the local environment of individual or a group of double vacancy quantum dots.

Subsequently, the author simulated the concentration correlation between the magnetic field and spin relaxation time T1 of the most relevant spin defects in SiC. In high-purity samples, the main non thermal contribution to spin relaxation comes from the 29Si nuclear spin slot, which maximizes the overall average T1 time at 100 ms at low temperatures far from GSLAC resonance. For adjacent nuclear spin configurations, the relaxation time can be reduced to 40 ms under zero magnetic field.

Fig. 1 Diagram of approximate values used in dipole spin relaxation calculations

Fig. 1 Diagram of approximate values used in dipole spin relaxation calculations

Fig. 2 a. Relaxation caused by 29Si (solid dark blue line) and 13C (solid light blue line) nuclear spins

Fig. 2 a. Relaxation caused by 29Si (solid dark blue line) and 13C (solid light blue line) nuclear spins; b. Magnetic field correlation of the longitudinal spin relaxation rate caused by spin-1/2 point defects of various concentrations.

It is worth noting that the limited spin relaxation time of the 29Si spin slot is equivalent to or even shorter than the coherence time of the double vacancy quantum dot subspace with decoherence protection (64ms). In this case, longitudinal spin relaxation may be the main factor limiting the lifetime of coherent protected subspaces. In addition, the author also demonstrated that the bipolar spin relaxation caused by paramagnetic point defects may have significant implications in ion implantation samples. The analytical formula provided by this study can be used to estimate the T1 of a given sample with known spin defect concentrations, as well as to analyze experimentally measured T1, in order to estimate the local spin defect concentration of double vacancy quantum dots. By using the latter method, the author found that in N2 ion implanted samples, the local concentration of paramagnetic point defects can reach up to 4×1018cm-3, and the maximum coherence time is about 0.5 ms, which is only half of the 1.3 ms of the natural isotope abundance of 4H-SiC.

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