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Register a new userElectronic properties and metrology of the diamond NV- center under pressure
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The negatively charged nitrogen-vacancy (NV-) center in diamond has realized new frontiers in quantum technology. Here, the centers optical and spin resonances are observed under hydrostatic pressures up to 60 GPa. Our observations motivate powerful new techniques to measure pressure and image high pressure magnetic and electric phenomena. Our observations further reveal a fundamental inadequacy of the current model of the center and provide new insight into its electronic structure.
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Ab initio calculations show an antiferromagnetic-ferromagnetic phase transition around 9-10 GPa and a magnetic anomaly at 12 GPa in BiFeO3. The magnetic phase transition also involves a structural and insulator-metal transition. The G-type AFM configuration under pressure leads to an increase of the y component and decrease of the z component of the magnetization, which is caused by the splitting of the dz2 orbital from doubly degenerate eg states. Our results agree with recent experimental results.
Significant attention has been recently focused on the realization of high precision nano-thermometry using the spin-resonance temperature shift of the negatively charged nitrogen-vacancy (NV-) center in diamond. However, the precise physical origins of the temperature shift is yet to be understood. Here, the shifts of the centers optical and spin resonances are observed and a model is developed that identifies the origin of each shift to be a combination of thermal expansion and electron-phonon interactions. Our results provide new insight into the centers vibronic properties and reveal implications for NV- thermometry.
The electronic and local structural properties of CuO under pressure have been investigated by means of X-ray absorption spectroscopy (XAS) at Cu K edge and ab-initio calculations, up to 17 GPa. The crystal structure of CuO consists of Cu motifs within CuO$_4$ square planar units and two elongated apical Cu-O bonds. The CuO$_4$ square planar units are stable in the studied pressure range, with Cu-O distances that are approximately constant up to 5 GPa, and then decrease slightly up to 17 GPa. In contrast, the elongated Cu-O apical distances decrease continuously with pressure in the studied range. An anomalous increase of the mean square relative displacement (EXAFS Debye Waller, sigma$^2$) of the elongated Cu-O path is observed from 5 GPa up to 13 GPa, when a drastic reduction takes place in sigma$^2$. This is interpreted in terms of local dynamic disorder along the apical Cu-O path. At higher pressures (P>13 GPa), the local structure of Cu$^{2+}$ changes from a 4-fold square planar to a 4+2 Jahn-Teller distorted octahedral ion. We interpret these results in terms of the tendency of the Cu$^{2+}$ ion to form favorable interactions with the apical O atoms. Also, the decrease in Cu-O apical distance caused by compression softens the normal mode associated with the out-of-plane Cu movement. CuO is predicted to have an anomalous rise in permittivity with pressure as well as modest piezoelectricity in the 5-13 GPa pressure range. In addition, the near edge features in our XAS experiment show a discontinuity and a change of tendency at 5 GPa. For P < 5 GPa the evolution of the edge shoulder is ascribed to purely electronic effects which also affect the charge transfer integral. This is linked to a charge migration from the Cu to O, but also to an increase of the energy band gap, which show a change of tendency occurring also at 5 GPa.
The neutrally-charged silicon vacancy in diamond is a promising system for quantum technologies that combines high-efficiency, broadband optical spin polarization with long spin lifetimes (T2 ~ 1 ms at 4 K) and up to 90% of optical emission into its 946 nm zero-phonon line. However, the electronic structure of SiV0 is poorly understood, making further exploitation difficult. Performing photoluminescence spectroscopy of SiV0 under uniaxial stress, we find the previous excited electronic structure of a single 3A1u state is incorrect, and identify instead a coupled 3Eu - 3A2u system, the lower state of which has forbidden optical emission at zero stress and so efficiently decreases the total emission of the defect: we propose a solution employing finite strain to form the basis of a spin-photon interface. Isotopic enrichment definitively assigns the 976 nm transition associated with the defect to a local mode of the silicon atom.
The negatively-charged silicon-vacancy (SiV$^-$) center in diamond is a promising single photon source for quantum communications and information processing. However, the centers implementation in such quantum technologies is hindered by contention surrounding its fundamental properties. Here we present optical polarization measurements of single centers in bulk diamond that resolve this state of contention and establish that the center has a $langle111rangle$ aligned split-vacancy structure with $D_{3d}$ symmetry. Furthermore, we identify an additional electronic level and evidence for the presence of dynamic Jahn-Teller effects in the centers 738 nm optical resonance.
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