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The chemical vapor deposition of diamond is known to introduce complexes of silicon, vacancy, and hydrogen. We theoretically examined several such complexes, some of which have already been observed, others which could potentially form. Using hybrid density functional theory for the treatment of highly correlated orbitals, many measurable quantities are calculated. The SiV2H(-) negatively charged defect is found to be a promising candidate for a long lived solid state quantum memory. The study is highlighted as Editor's suggestion in PRB.
Phys. Rev. B 92 165203 (2015). DOI:10.1103/PhysRevB.92.165203
In collaboration with German (Jörg Wrachtrup group at Stuttgart University) and Swedish (Erik Janzén group at Linköping University) researchers, 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 room temperature. We show coherent control of a single defect spin and find long spin coherence times under ambient conditions. Our study provides evidence that SiC is a promising system for atomic-scale spintronics and quantum technology. Our study is highlighted in a News and Views article from Nature Materials.
Nature Materials 14 164-168 (2015). DOI:10.1038/nmat4145
Working together with Professor Awshalom's group we demonstrate optically pumped dynamic nuclear polarization of 29Si nuclear spins that are strongly coupled to paramagnetic color centers in 4H- and 6H-SiC. The 99%1% degree of polarization that we observe at room temperature corresponds to an effective nuclear temperature of 5 μK. By combining ab initio theory with the experimental identification of the color centers’ optically excited states, we quantitatively model how the polarization derives from hyperfine-mediated level anticrossings. These results lay a foundation for SiC-based quantum memories, nuclear gyroscopes, and hyperpolarized probes for magnetic resonance imaging. The study is featured in Physics and highlighted as Editor's suggestion in PRL.
Physical Review Letters 114 247603 (2015). DOI:10.1103/PhysRevLett.114.247603
Together with colleagues in the United States, we have investigated and proposed a new kind of material for photovoltaics. In strongly correlated insulators, strong Coulomb interactions make highly photoexcited electron-hole pairs decay fast into multiple electron-hole pairs via impact ionization, thus preventing slower energy dissipation to heat by phonons. The prototypical M1-type vanadium-oxide insulator have been used for computational simulations, which may be a first example of a new class of photovoltaic materials.
Phys. Rev. B 90, 165142 (2014). DOI:10.1103/PhysRevB.90.165142
In collaboration with Bremen Center for Computational Materials Science we have identified such a diamond surface that would be ideal to host shallow implanted nitrogen-vacancy centers in diamond for sensing at the nanoscale.
Nano Letters 14 4772-4777 (2014). DOI:10.1021/nl501927y
In the field of methodology development, we have constructed a DFT scheme combining hybrid exchange and DFT+U strategies. This machinery seems to be an efficient tool in DFT calculations involving solid-state defects with highly localized electronic orbitals, as its tests on two typical systems show.
Physical Review B 90 035146 (2014) DOI:10.1103/PhysRevB.90.035146
Our group members at Wigner ADMIL laboratory have succeeded manufacturing carbon antisite–vacancy colour centres in silcon carbide nanoparticles. These colour centres behave as single-photon emitters, and therefore may be used in the future in nanometrology and quantum informatics. The biocompatibiliy of SiC makes these defects ideal candidates for biosensing at the molecular level.
ACS Nano 8 7938-7947 (2014). DOI:10.1021/nn502719y
The electron spins of semiconductor defects can have complex interactions with their host, particularly in polar materials like SiC where electrical and mechanical variables are intertwined. By combining pulsed spin resonance (David Awschalom group at Chicago University) with ab initio simulations, we show that spin-spin interactions in 4H−SiC neutral divacancies give rise to spin states with a strong Stark effect, sub-10−6 strain sensitivity, and highly spin-dependent photoluminescence with intensity contrasts of 15%–36%. These results establish SiC color centers as compelling systems for sensing nanoscale electric and strain fields.
Physical Review Letters 112 187601 (2014). DOI:10.1103/PhysRevLett.112.187601
In an international cooperation with Japanese and Australian colleagues, we supported the establishment and identification of the carbon antisite–vacancy pair as a new kind of single-photon emitter in silicon carbide with theoretical work and computational simulation. The results have been highlighted in Nature Physics and Nature Photonics.
Nature Materials 13 151-156 (2014) DOI:10.1038/nmat3806
In a cooperation with partners in Russia and Germany, we have taken part in the work of predicting and validating the properties of silicon-vacancy colour centres in nanosized diamond particles. We have contributed with time-dependent DFT calculations, not carried out on such large systems so far. Nanoparticles for validating experiments have been extracted from a meteorite sample, but production of similar artificial nanoparticles seems to be very prospective in e.g. biosensing. This article has been selected for review in Nature News and Views.
Nature Nanotechnology 9, 54–58 (2014) DOI:10.1038/NNANO.2013.255