Generation of spin-polarized currents via cross-relaxation with dynamically pumped paramagnetic impurities

Key to future spintronics and spin-based information processing technologies is the generation, manipulation, and detection of spin polarization in a solid state platform. Here, we theoretically explore an alternative route to spin injection via the use of dynamically polarized nitrogen-vacancy (NV) centers in diamond. We focus on the geometry where carriers and NV centers are confined to proximate, parallel layers and use a 'trap-and-release' model to calculate the spin cross-relaxation probabilities between the charge carriers and neighboring NV centers. We identify near-unity regimes of carrier polarization depending on the NV spin state, applied magnetic field, and carrier g-factor. In particular, we find that unlike holes, electron spins are distinctively robust against spin-lattice relaxation by other, unpolarized paramagnetic centers. Further, the polarization process is only weakly dependent on the carrier hopping dynamics, which makes this approach potentially applicable over a broad range of temperatures.C.A.M. acknowledges support from the National Science Foundation through Grant No. NSF-1314205. M.W.D. acknowledges support from the Australian Research Council through Grant No. DP120102232

The electron-phonon processes of the nitrogen-vacancy center in diamond

Applications of negatively charged nitrogen-vacancy center in diamond exploit the center's unique optical and spin properties, which at ambient temperature, are predominately governed by electron-phonon interactions. Here, we investigate these interactions at ambient and elevated temperatures by observing the motional narrowing of the center's excited state spin resonances. We determine that the center's Jahn-Teller dynamics are much slower than currently believed and identify the vital role of symmetric phonon modes. Our results have pronounced implications for center's diverse applications (including quantum technology) and for understanding its fundamental properties.Comment: 5 pages, 4 figure

Spin-Dependent Quantum Emission in Hexagonal Boron Nitride at Room Temperature

Optically addressable spins associated with defects in wide-bandgap semiconductors are versatile platforms for quantum information processing and nanoscale sensing, where spin-dependent inter-system crossing (ISC) transitions facilitate optical spin initialization and readout. Recently, the van der Waals material hexagonal boron nitride (h-BN) has emerged as a robust host for quantum emitters (QEs), but spin-related effects have yet to be observed. Here, we report room-temperature observations of strongly anisotropic photoluminescence (PL) patterns as a function of applied magnetic field for select QEs in h-BN. Field-dependent variations in the steady-state PL and photon emission statistics are consistent with an electronic model featuring a spin-dependent ISC between triplet and singlet manifolds, indicating that optically-addressable spin defects are present in h-BN $-$ a versatile two-dimensional material promising efficient photon extraction, atom-scale engineering, and the realization of spin-based quantum technologies using van der Waals heterostructures.Comment: 38 pages, 34 figure

Spin polarization through intersystem crossing in the silicon vacancy of silicon carbide

Silicon carbide (SiC)-based defects are promising for quantum communications, quantum information processing, and for the next generation of quantum sensors, as they feature long coherence times, frequencies near the telecom, and optical and microwave transitions. For such applications, the efficient initialization of the spin state is necessary. We develop a theoretical description of the spin-polarization process by using the intersystem crossing of the silicon vacancy defect, which is enabled by a combination of optical driving, spin-orbit coupling, and interaction with vibrational modes. By using distinct optical drives, we analyze two spin-polarization channels. Interestingly, we find that different spin projections of the ground state manifold can be polarized. This paper helps in understanding initialization and readout of the silicon vacancy and explains some existing experiments with the silicon vacancy center in SiC.S.E.E. acknowledges support from the NSF, Grant No. DMR1737921. M.W.D. acknowledges support from the ARC, Grant No. DE170100169

Singlet levels of the NV−^{-} centre in diamond

The characteristic transition of the NV- centre at 637 nm is between ${}^3\mathrm{A}_2$ and ${}^3\mathrm{E}$ triplet states. There are also intermediate ${}^1\mathrm{A}_1$ and ${}^1\mathrm{E}$ singlet states, and the infrared transition at 1042 nm between these singlets is studied here using uniaxial stress. The stress shift and splitting parameters are determined, and the physical interaction giving rise to the parameters is considered within the accepted electronic model of the centre. It is established that this interaction for the infrared transition is due to a modification of electron-electron Coulomb repulsion interaction. This is in contrast to the visible 637 nm transition where shifts and splittings arise from modification to the one-electron Coulomb interaction. It is also established that a dynamic Jahn-Teller interaction is associated with the singlet ${}^1\mathrm{E}$ state, which gives rise to a vibronic level 115 $\mathrm{cm}^{-1}$ above the ${}^1\mathrm{E}$ electronic state. Arguments associated with this level are used to provide experimental confirmation that the ${}^1\mathrm{A}_1$ is the upper singlet level and ${}^1\mathrm{E}$ is the lower singlet level.Comment: 19 pages, 6 figure

The fine structure of the neutral nitrogen-vacancy center in diamond

The nitrogen-vacancy (NV) center in diamond is a widely utilized system due to its useful quantum properties. Almost all research focuses on the negative charge state (NV−) and comparatively little is understood about the neutral charge state (NV0). This is surprising as the charge state often fluctuates between NV0 and NV− during measurements. There are potentially underutilized technical applications that could take advantage of NV0, either by improving the performance of NV0 or utilizing NV− directly. However, the fine structure of NV0 has not been observed. Here, we rectify this lack of knowledge by performing magnetic circular dichroism measurements that quantitatively determine the fine structure of NV0. The observed behavior is accurately described by spin-Hamiltonians in the ground and excited states with the ground state yielding a spin-orbit coupling of λ = 2.24 +- 0.05 GHz and a orbital g-factor of 0.0186 +- 0.0005. The reasons why this fine structure has not been previously measured are discussed and strainbroadening is concluded to be the likely reason.We would like to acknowledge various funding sources for support during this work. In particular, NM would like to acknowledge the Australian Research Council through grants DP170103098. MD would like to acknowledge the Australian Research Council through grants DP170103098 and DE170100169. EK would like to acknowledge the Australian Research Council through grants DP110104565 and DP150103137