Transition metal (TM) defects in silicon carbide have favorable spin coherence properties and are suitable as quantum memory for quantum communication. To characterize TM defects as quantum spin-photon interfaces, we model defects that have one active electron with spin 1/2 in the atomic $D$ shell. The spin structure, as well as the magnetic and optical resonance properties of the active electron emerge from the interplay of the crystal potential and spin-orbit coupling and are described by a general model derived using group theory. We find that the spin-orbit coupling leads to additional allowed transitions and a modification of the $g$-tensor. To describe the dependence of the Rabi frequency on the magnitude and direction of the static and driving fields, we derive an effective Hamiltonian. This theoretical description can also be instrumental to perform and optimize spin control in TM defects.
Transition metal (TM) defects in silicon carbide (SiC) are a promising platform in quantum technology, especially because some TM defects emit in the telecom band. We develop a theory for the interaction of an active electron in the $D$-shell of a TM defect in SiC with the TM nuclear spin and derive the effective hyperfine tensor within the Kramers doublets formed by the spin-orbit coupling. Based on our theory we discuss the possibility to exchange the nuclear and electron states with potential applications for nuclear spin manipulation and long-lived nunclear-spin based quantum memories.
Silicon carbide (SiC) has become a key player in realization of scalable quantum technologies due to its ability to host optically addressable spin qubits and wafer-size samples. Here, we have demonstrated optically detected magnetic resonance (ODMR) with resonant excitation, and clearly identified the ground state energy levels of the NV centers in 4H-SiC. Coherent manipulation of NV centers in SiC has been achieved with Rabi and Ramsey oscillations. Finally, we show the successful generation and characterization of single nitrogen vacancy (NV) center in SiC employing ion implantation. Our re…
Transition metal defects in SiC give rise to localized electronic states that can be optically addressed in the telecom range in an industrially mature semiconductor platform. This has led to intense scrutiny of the spin and optical properties of these defect centers. For spin-1/2 defects, a combination of the defect symmetry and the strong spin-orbit coupling may restrict the allowed spin transitions, giving rise to defect spins that are long lived, but hard to address via microwave spin manipulation. Here, we show via analytical and numerical results that the presence of a central nuclear sp…
Optically-active point defects in various host materials, such as diamond and silicon carbide (SiC), have shown significant promise as local sensors of magnetic fields, electric fields, strain and temperature. Current sensing techniques take advantage of the relaxation and coherence times of the spin state within these defects. Here we show that the defect charge state can also be used to sense the environment, in particular high frequency (MHz-GHz) electric fields, complementing established spin-based techniques. This is enabled by optical charge conversion of the defects between their photol…
Quantum technology relies on proper hardware, enabling coherent quantum state control as well as efficient quantum state readout. In this regard, wide-bandgap semiconductors are an emerging material platform with scalable wafer fabrication methods, hosting several promising spin-active point defects. Conventional readout protocols for such defect spins rely on fluorescence detection and are limited by a low photon collection efficiency. Here, we demonstrate a photo-electrical detection technique for electron spins of silicon vacancy ensembles in the 4H polytype of silicon carbide (SiC). Furthe…
The silicon monovacancy in 4H-SiC is a promising candidate for solid-state quantum information processing. We perform high-resolution optical spectroscopy on single V2 defects at cryogenic temperatures. We find favorable low temperature optical properties that are essential for optical readout and coherent control of its spin and for the development of a spin-photon interface. The common features among individual defects include two narrow, nearly lifetime-limited optical transitions that correspond to $m_s{=}\pm 3/2$ and $m_s{=}\pm 1/2$ spin states with no discernable zero-field splitting flu…
Defects in silicon carbide (SiC) have emerged as a favorable platform for optically-active spin-based quantum technologies. Spin qubits exist in specific charge states of these defects, where the ability to control these states can provide enhanced spin-dependent readout and long-term charge stability of the qubits. We investigate this charge state control for two major spin qubits in 4H-SiC, the divacancy (VV) and silicon vacancy (Vsi), obtaining bidirectional optical charge conversion between the bright and dark states of these defects. We measure increased photoluminescence from VV ensemble…
Point defects and their dynamic behaviors in silver monolayer intercalated between graphene and SiC
Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e. V.（柏林莱布尼茨固体电子学保罗·德鲁德研究所）；Department of Materials Science and Engineering, The Pennsylvania State University（宾夕法尼亚州立大学材料科学与工程系）；Dimensional Crystal Consortium, The Pennsylvania State University（宾夕法尼亚州立大学二维晶体联盟）；Center for 2-Dimensional and Layered Materials, The Pennsylvania State University（宾夕法尼亚州立大学二维与层状材料中心）；Center for Atomically Thin Multifunctional Coatings, The Pennsylvania State University（宾夕法尼亚州立大学原子级薄多功能涂层中心）
In this work, the implications of high field bias conditions in radiation-induced defect recovery in 3C-SiC crystals is studied. It is well known that transient heating effects (or thermal spikes) occur when energetic swift heavy ions (SHIs) deposit energy to the surrounding medium via ionization. Here, we explore the dynamics of this transient event under high background electric fields in 3C-SiC, which is what occurs when an ion strike coincides with field-sensitive volumes. In this study, we use the Ensemble Monte Carlo method to quantify how the energy deposition of the ionized regions cha…
The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a mechanism for high-fidelity spin-to-photon conversion, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here we demonstrate a high-fidelity spin-to-photon interface in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin-mixing, and that the…
Ongoing efforts in quantum engineering have recently focused on integrating magnonics into hybrid quantum architectures for novel functionalities. While hybrid magnon-quantum spin systems have been demonstrated with nitrogen-vacancy (NV) centers in diamond, they have remained elusive on the technologically promising silicon carbide (SiC) platform mainly due to difficulties in finding a resonance overlap between the magnonic system and the spin centers. Here we circumvent this challenge by harnessing nonlinear magnon scattering processes in a magnetic vortex to access magnon modes that overlap …
Single-photon emitting point defects in semiconductors have emerged as strong candidates for future quantum technology devices. In the present work, we exploit crystalline particles to investigate relevant defect localizations, emission shifting and waveguiding. Specifically, emission from 6H-SiC micro- and nanoparticles ranging from 100 nm to 5 $μ$m in size is collected using cathodoluminescence (CL), and we monitor signals attributed to the Si vacancy (V$_{\textrm{Si}}$) as a function of its location. Clear shifts in the emission wavelength are found for emitters localized in the particle ce…
Point defects in solids promise precise measurements of various quantities. Especially magnetic field sensing using the spin of point defects has been of great interest recently. When optical readout of spin states is used, point defects achieve optical magnetic imaging with high spatial resolution at ambient conditions. Here, we demonstrate that genuine optical vector magnetometry can be realized using the silicon vacancy in SiC, which has an uncommon S=3/2 spin. To this end, we develop and experimentally test sensing protocols based on a reference field approach combined with multi frequency…
Optically active spins in solid-state systems can be engineered to emit photons that are entangled with the spin in the solid. This allows for applications such as quantum communications, quantum key distribution, and distributed quantum computing. Recently, there has been a strong interest in silicon carbide defects, as they emit very close to the telecommunication wavelength, making them excellent candidates for long range quantum communications. In this work we develop explicit schemes for spin-photon entanglement in several SiC defects: the silicon monovacancy, the silicon divacancy, and t…
A theoretical approach is proposed to treat the spin dynamics in defect color centers. The method explicitly takes into account the spin dynamics in the ground state and excited state of the defect center as well as spin state dependent transitions involving the ground state and excited state, as well as an additional intermediate state. The proposed theory is applied to treat spin-dependent phenomena is silicon carbide, namely, in spin-3/2 silicon-vacancy centers, VSi or V2 centers. Theoretical predictions of magnetic field dependent photoluminescence intensity and optically detected magnetic…
Spins bound to point defects are increasingly viewed as an important resource for solid-state implementations of quantum information technologies. In particular, there is a growing interest in the identification of new classes of defect spin that can be controlled optically. Here we demonstrate ensemble optical spin polarization and optically detected magnetic resonance (ODMR) of the S = 1 electronic ground state of chromium (Cr4+) impurities in silicon carbide (SiC) and gallium nitride (GaN). Spin polarization is made possible by the narrow optical linewidths of these ensembles (< 8.5 GHz), w…
Silicon carbide is a very promising platform for quantum applications because of extraordinary spin and optical properties of point defects in this technologically-friendly material. These properties are strongly influenced by crystal vibrations, but the exact relationship between them and the behavior of spin qubits is not fully investigated. We uncover the local vibrational modes of the Si vacancy spin qubits in as-grown 4H-SiC. We apply the resonant microwave field to isolate the contribution from one particular type of defects, the so-called V2 center, and observe the zero-phonon line toge…
The effect of different surface defects on the atomic and electronic structures of cubic $β$-SiC(110) surface are studied by means of a first principles calculation based on Density Functional Theory using the SIESTA code. In the calculations, the possibility of different spin population at each atom is allowed. We find that while adsorption of oxygen or nitrogen and adsorption of hydrogen at the C surface carbon atoms do not induce magnetic moments on SiC(110); Si vacancies, substitutional C at the Si site and H or F adsorbed at the silicon surface sites induce localized magnetic moments as l…
Epitaxial graphene is grown on a non-polar n+ 6H-SiC m-plane substrate and studied using atomic scale scanning tunneling microscopy. Multilayer graphene is found throughout the surface and exhibits rotational disorder. Moiré patterns of different spatial periodicities are found, and we found that as the wavelength increases, so does the amplitude of the modulations. This relationship reveals information about the interplay between the energy required to bend graphene and the interaction energy, i.e. van der Waals energy, with the graphene layer below. Our experiments are supported by theoretic…
In this paper, we study the electron spin decoherence of single defects in silicon carbide (SiC) nuclear spin bath. We find that, although the natural abundance of $^{29}\rm{Si}$ ($p_{\rm{Si}}=4.7\%$) is about 4 times larger than that of $^{13}{\rm C}$ ($p_{\rm{C}}=1.1\%$), the electron spin coherence time of defect centers in SiC nuclear spin bath in strong magnetic field ($B>300~\rm{Gauss}$) is longer than that of nitrogen-vacancy (NV) centers in $^{13}{\rm C}$ nuclear spin bath in diamond. The reason for this counter-intuitive result is the suppression of heteronuclear-spin flip-flop proces…
Transition metal (TM) defects in silicon carbide (SiC) are a promising platform for applications in quantum technology. Some TM defects, e.g. vanadium, emit in one of the telecom bands, but the large ground state hyperfine manifold poses a problem for applications which require pure quantum states. We develop a driven, dissipative protocol to polarize the nuclear spin, based on a rigorous theoretical model of the defect. We further show that nuclear-spin polarization enables the use of well-known methods for initialization and long-time coherent storage of quantum states. The proposed nuclear-…
Defects in silicon carbide are of intense and increasing interest for quantum-based applications due to this material's properties and technological maturity. We calculate the multi-particle symmetry adapted wave functions of the negatively charged silicon vacancy defect in hexagonal silicon carbide via use of group theory and density functional theory and find the effects of spin-orbit and spin-spin interactions on these states. Although we focused on $\textrm{V}_{\textrm{Si}}^-$ in 4H-SiC, because of its unique fine structure due to odd number of active electrons, our methods can be easily a…
Principal structural defects in graphene layers, synthesized on a carbon-terminated face, i.e. the SiC(000) face of a 4H-SiC substrate, are investigated using microscopic methods. Results of high-resolution transmission electron microscopy (HRTEM) reveal their atomic arrangement. Mechanism of such defects creation, directly related to the underlying crystallographic structure of the SiC substrate, is elucidated. The connection between the 4H-SiC(000) surface morphology, including the presence of the single atomic steps, the sequences of atomic steps, and also the macrosteps, and the correspond…
Silicon carbide (SiC) hosts many interesting defects that can potentially serve as qubits for a range of advanced quantum technologies. Some of them have very interesting properties, making them potentially useful, e.g. as interfaces between stationary and flying qubits. Here we present a detailed overview of the relevant properties of the spins in silicon vacancies of the 6H-SiC polytype. This includes the temperature-dependent photoluminescence, optically detected magnetic resonance, and the relaxation times of the longitudinal and transverse components of the spins, during free precession a…
The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries. Nonetheless, because the electronic states of SiC defects can have sharp optical and spin transitions, they are increasingly recognized as a valuable resource for quantum-information and nanoscale-sensing applications. Here, we show that individual electron spin states in highly purified monocrystalline 4H-SiC can be isolated and coherently controlled. Bound to neutral divacancy defects, these states exhibit exceptionally long ensemble Hahn-echo spin coherence,…
Divacancy defects in silicon carbide have long-lived electronic spin states and sharp optical transitions, with properties that are similar to the nitrogen-vacancy defect in diamond. We report experiments on 4H-SiC that investigate all-optical addressing of spin states with the zero-phonon-line transitions. Our magneto-spectroscopy results identify the spin $S=1$ structure of the ground and excited state, and a role for decay via intersystem crossing. We use these results for demonstrating coherent population trapping of spin states with divacancy ensembles that have particular orientations in…
Quasi free standing monolayer graphene (QFMLG) grown on SiC by selective Si evaporation from the Si-rich SiC(0001) face and H intercalation displays irregularities in STM and AFM analysis, appearing as localized features, which we previously identified as vacancies in the H layer coverage [Y Murata, et al. Nano Res, in press, DOI: 10.1007/s12274-017-1697-x]. The size, shape, brightness, location, and concentration of these features, however, are variable, depending on the hydrogenation conditions. In order to shed light on the nature of these features, in this work we perform a systematic Dens…
Color-center defects in silicon carbide promise opto-electronic quantum applications in several fields, such as computing, sensing and communication. In order to scale down and combine these functionalities with the existing silicon device platforms, it is crucial to consider SiC integrated optics. In recent years many examples of SiC photonic platforms have been shown, like photonic crystal cavities, film-on-insulator waveguides and micro-ring resonators. However, all these examples rely on separating thin films of SiC from substrate wafers. This introduces significant surface roughness, stra…
Control of local lattice perturbations near optically-active defects in semiconductors is a key step to harnessing the potential of solid-state qubits for quantum information science and nanoscale sensing. We report the development of a stroboscopic scanning X-ray diffraction microscopy approach for real-space imaging of dynamic strain used in correlation with microscopic photoluminescence measurements. We demonstrate this technique in 4H-SiC, which hosts long-lifetime room temperature vacancy spin defects. Using nano-focused X-ray photon pulses synchronized to a surface acoustic wave launcher…
Defects in wide-bandgap semiconductors provide a pathway for applications in quantum information and sensing in solid state materials. The silicon vacancy in silicon carbide has recently emerged as a new candidate for optical control of single spin qubit with significant material benefits over nitrogen vacancies in diamond. In this work, we present a study of the coherence of silicon vacancies generated via proton irradiation as a function of implantation depth. We show clear evidence of dephasing interactions between the silicon vacancies and the spin environment of the bulk crystal. This res…
Spin defects in silicon carbide (SiC) with mature wafer-scale fabrication and micro/nano-processing technologies have recently drawn considerable attention. Although room temperature single-spin manipulation of colour centres in SiC has been demonstrated, the typically detected contrast is less than 2%, and the photon count rate is also low. Here, we present the coherent manipulation of single divacancy spins in 4H-SiC with a high readout contrast (-30%) and a high photon count rate (150 kilo counts per second) under ambient conditions, which are competitive with the nitrogen-vacancy (NV) cent…
Spin-active color centers in solids show good performance for quantum technologies. Several transition-metal defects in SiC offer compatibility with telecom and semiconductor industries. However, whether their strong spin-orbit coupling degrades their spin lifetimes is not clear. We show that a combination of a crystal-field with axial symmetry and spin-orbit coupling leads to a suppression of spin-lattice and spin-spin interactions, resulting in remarkably slow spin relaxation. Our optical measurements on an ensemble of Mo impurities in SiC show a spin lifetime $T_1$ of $2,4$ s at $2$ K.
It has been shown that the first C layer on the SiC(0001)(2{\times}2)C surface already exhibits graphene-like electronic structure, with linear pi bands near the Dirac point. Indeed, the (2{\times}2)C reconstruction, with a Si adatom and C restatom structure, efficiently passivates the SiC(0001) surface thanks to an adatom/restatom charge transfer mechanism. Here, we study the effects of interface modifications on the graphene layer using density functional theory calculations. The modifications we consider are inspired from native interface defects observed by scanning tunneling microscopy. O…
Resonantly-enhanced Raman response in graphene-capped bismuthene on SiC
Universität Würzburg（维尔茨堡大学）；Würzburg-Dresden Cluster of Excellence ctd.qmat, Universität Würzburg（维尔茨堡大学 würtzburg-dresden 卓越集群 ctd.qmat）；Sapienza University of Rome（罗马第一大学）；RWTH Aachen University（亚琛工业大学）；Forschungszentrum Jülich（于利希研究中心）；Institut für Theoretische Physik und Astrophysik, Universität Würzburg（维尔茨堡大学理论与天体物理研究所）；TUD Dresden University of Technology（德累斯顿工业大学）
Spins in solids are cornerstone elements of quantum spintronics. Leading contenders such as defects in diamond, or individual phosphorous dopants in silicon have shown spectacular progress but either miss established nanotechnology or an efficient spin-photon interface. Silicon carbide (SiC) combines the strength of both systems: It has a large bandgap with deep defects and benefits from mature fabrication techniques. Here we report the characterization of photoluminescence and optical spin polarization from single silicon vacancies in SiC, and demonstrate that single spins can be addressed at…
Nanoscale materials usually can trap light and strongly interact with it leading to many photonic device applications. The light-matter interactions are commonly probed by optical spectroscopy, which, however, have some limitations such as diffraction-limited spatial resolution, tiny momentum transfer and non-continuous excitation/detection. In this work, using scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) with ultra-wide energy and momentum match and sub-nanometer spatial resolution, we study the optical microcavity resonant spectroscopy in a single S…
The development of novel quantum bits is key to extend the scope of solid-state quantum information science and technology. Using first-principles calculations, we propose that large metal ion - vacancy complexes are promising qubit candidates in two binary crystals: 4H-SiC and w-AlN. In particular, we found that the formation of neutral Hf- and Zr-vacancy complexes is energetically favorable in both solids; these defects have spin-triplet ground states, with electronic structures similar to those of the diamond NV center and the SiC di-vacancy. Interestingly, they exhibit different spin-strai…
We numerically study the tuning of the radiative heat transfer between a spherical InSb nanoparticle in the vicinity of a flat SiC surface assisted by a static magnetic field. By changing the value of the applied magnetic field, the dielectric function of the nanosphere becomes anisotropic due to the excitation of magneto-plasmons. In the dipolar approximation, the plasmon resonance of the particle splits into two additional satellite resonances that shift to higher and lower frequencies as the field increases. When one of the particle resonances overlaps with the phonon-polariton frequency of…
We have theoretically studied how resonant spin wave modes in an elliptical nanomagnet are affected by fabrication defects, such as small local thickness variations. Our results indicate that defects of this nature, which can easily result from the fabrication process, or are sometimes deliberately introduced during the fabrication process, will significantly alter the frequencies, magnetic field dependence of the frequencies, and the power and phase profiles of the resonant spin wave modes. They can also spawn new resonant modes and quench existing ones. All this has important ramifications f…
Understanding the stability limitations and defect formation mechanisms in 2D magnets is essential for their utilization in spintronic and memory technologies. Here, we correlate defects in mono- to multilayer CrSBr with their structural, vibrational and magnetic properties. We use resonant Raman scattering to reveal distinct vibrational defect signatures. In pristine CrSBr, we show that bromine atoms mediate vibrational interlayer coupling, allowing for distinguishing between surface and bulk defect modes. We show that environmental exposure causes drastic degradation in monolayers, with the …
Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon car…
