Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userIdentification of nickel-vacancy defect in the photocurrent spectrum of diamond by means of emph{ab initio} calculations
134
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
There is a continuous search for solid-state spin qubits operating at room temperature with excitation in the IR communication bandwidth. Recently we have introduced the photoelectric detection of magnetic resonance (PDMR) to read the electron spin state of nitrogen-vacancy (NV) center in diamond, a technique which is promising for applications in quantum information technology. By measuring photoionization spectra on a diamond crystal we found two ionization thresholds that were not reported before. On the same sample we also observed absorption and photoluminescence signatures that were identified in literature as Ni associated defects. We performed emph{ab initio} calculation of the photo-ionization cross-section of the nickel split vacancy complex (NiV) and N-related defects in their relevant charge states and fitted the concentration of these defects to the measured photocurrent spectrum, which led to a surprising match between experimental and calculated spectra. This study enabled to identify the two unknown ionization thresholds with the two acceptor levels of NiV. Because the excitation of NiV is in infrared, the photocurrent detected from the paramagnetic NiV color centers is a promising way towards designing a novel type of electrically readout qubits.
rate research
Read More
Quantum-mechanical ab initio calculations are performed to elucidate the vibrational spectroscopic features of a common irradiation-induced defect in diamond, i.e. the neutral vacancy. Raman spectra are computed analytically through a Coupled-Perturbed-Hartree-Fock/Kohn-Sham approach as a function of both different defect spin states and defect concentration. The experimental Raman features of defective diamond located in the 400-1300 cm-1 spectral range, i.e. below the first-order line of pristine diamond at 1332 cm-1 , are well reproduced, thus corroborating the picture according to which, at low damage densities, this spectral region is mostly affected by non-graphitic sp3 defects. No peaks above 1332 cm-1 are found, thus ruling out previous tentative assignments of different spectral features (at 1450 and 1490 cm-1) to the neutral vacancy. The perturbation introduced by the vacancy to the thermal nuclear motion of carbon atoms in the defective lattice is discussed in terms of atomic anisotropic displacement parameters (ADPs), computed from converged lattice dynamics calculations.
We study coherent backscattering phenomena from single and multiple stacking faults (SFs) in 3C- and 4H-SiC within density functional theory quantum transport calculations. We show that SFs give rise to highly dispersive bands within both the valance and conduction bands that can be distinguished for their enhanced density of states at particular wave number subspaces. The consequent localized perturbation potential significantly scatters the propagating electron waves and strongly increases the resistance for $n$-doped systems. We argue that resonant scattering from SFs should be one of the principal degrading mechanisms for device operation in silicon carbide.
In a recent paper, Iba~nez-Azpiroz et al. [Phys. Rev. B 97, 245143 (2018)] derive a band-truncation-error-free formula for calculating the generalized derivative of the interband dipole matrix using Wannier interpolation. In practice, the denominators involving intermediate states are regularized by introducing a finite broadening parameter. In this Comment, I show that when a finite broadening parameter is used, a correction term must be added to the generalized derivative to obtain results that are independent of the phase convention for the Bloch sums.
Motivated by the discovery of multiferroicity in the geometrically frustrated triangular antiferromagnet CuCrO$_2$ below its Neel temperature $T_N$, we investigate its magnetic and ferroelectric properties using ab initio calculations and Monte Carlo simulations. Exchange interactions up to the third nearest neighbors in the $ab$ plane, inter-layer interaction and single ion anisotropy constants in CuCrO$_2$ are estimated by series of density functional theory calculations. In particular, our results evidence a hard axis along the [110] direction due to the lattice distortion that takes place along this direction below $T_N$. Our Monte Carlo simulations indicate that the system possesses a Neel temperature $T_Napprox27$ K very close to the ones reported experimentally ($T_N = 24-26$ K). Also we show that the ground state is a proper-screw magnetic configuration with an incommensurate propagation vector pointing along the [110] direction. Moreover, our work reports the emergence of spin helicity below $T_N$ which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model. We confirm the electric control of spin helicity by simulating $P$-$E$ hysteresis loops at various temperatures.
Photochromism in single nitrogen-vacancy optical centers in diamond is demonstrated. Time-resolved optical spectroscopy shows that intense irradiation at 514 nm switches the nitrogen-vacancy defects to the negative form. This defect state relaxes back to the neutral form under dark conditions. Temporal anticorrelation of photons emitted by the different charge states of the optical center unambiguously indicates that the nitrogen-vacancy defect accounts for both 575 nm and 638 nm emission bands. Possible mechanism of photochromism involving nitrogen donors is discussed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
