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Register a new userElectron paramagnetic resonance and photochromism of $mathrm{N}_{3}mathrm{V}^{0}$ in diamond
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The defect in diamond formed by a vacancy surrounded by three nearest-neighbor nitrogen atoms and one carbon atom, $mathrm{N}_{3}mathrm{V}$, is found in $approx98%$ of natural diamonds. Despite $mathrm{N}_{3}mathrm{V}^{0}$ being the earliest electron paramagnetic resonance spectrum observed in diamond, to date no satisfactory simulation of the spectrum for an arbitrary magnetic field direction has been produced due to its complexity. In this work, $mathrm{N}_{3}mathrm{V}^{0}$ is identified in $^{15}mathrm{N}$-doped synthetic diamond following irradiation and annealing. The $mathrm{^{15}N}_{3}mathrm{V}^{0}$ spin Hamiltonian parameters are revised and used to refine the parameters for $mathrm{^{14}N}_{3}mathrm{V}^{0}$, enabling the latter to be accurately simulated and fitted for an arbitrary magnetic field direction. Study of $mathrm{^{15}N}_{3}mathrm{V}^{0}$ under excitation with green light indicates charge transfer between $mathrm{N}_{3}mathrm{V}$ and $mathrm{N_s}$. It is argued that this charge transfer is facilitated by direct ionization of $mathrm{N}_{3}mathrm{V}^{-}$, an as-yet unobserved charge state of $mathrm{N}_{3}mathrm{V}$.
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A quite unusual diffuse scattering phenomenology was observed in the single-crystal X-ray diffraction pattern of cubic perovskite BMT ($mathrm{BaMg}_{1/3}mathrm{Ta}_{2/3}mathrm{O}_3$). The intensity of the scattering is parametrized as a set of cube-like objects located at the centers of reciprocal space unit cells, resembling very broad and cubic-shaped (1/2,1/2,1/2)-satellites. BMT belongs to perovskites of formula AB$_{1/3}$B$_{2/3}$O$_{3}$ (A=Mg, B$=$Ta, B$=$Mg). The cubes of the intensity can be attributed to the partial correlations of the occupancies of the B site. The pair correlation function is the Fourier transform of the diffuse scattering intensity and the latters idealized form yields the unusual property of a power-law correlation decay with distance. Up to now this is observed only in a few exotic instances of magnetic order or nematic crystals. Therefore it cannot be classified as a short-range order phenomenon, as in most situations originating diffuse scattering. A Monte-Carlo search in configuration space yielded solutions that reproduce faithfully the observed diffuse scattering. Analysis of the results in terms of the electrostatic energy and the entropy point to this phase of BMT as a metastable state, kinetically locked, which could be the equilibrium state just below the melting point.
Let $mathsf k$ be a local field. Let $I_ u$ and $I_{ u}$ be smooth principal series representations of $mathrm{GL}_n(mathsf k)$ and $mathrm{GL}_{n-1}(mathsf k)$ respectively. The Rankin-Selberg integrals yield a continuous bilinear map $I_ utimes I_{ u}rightarrow mathbb C$ with a certain invariance property. We study integrals over a certain open orbit that also yield a continuous bilinear map $I_ utimes I_{ u}rightarrow mathbb C$ with the same invariance property, and show that these integrals equal the Rankin-Selberg integrals up to an explicit constant. Similar results are also obtained for Rankin-Selberg integrals for $mathrm{GL}_n(mathsf k)times mathrm{GL}_n(mathsf k)$.
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.
We measure the electron spin resonance spectrum of the endohedral fullerene molecule $^{15}mathrm{N@C}_{60}$ at pressures ranging from atmospheric pressure to 0.25 GPa, and find that the hyperfine coupling increases linearly with pressure. We present a model based on van der Waals interactions, which accounts for this increase via compression of the fullerene cage and consequent admixture of orbitals with a larger hyperfine coupling. Combining this model with theoretical estimates of the bulk modulus, we predict the pressure shift and compare it to our experimental results, finding fair agreement given the spread in estimates of the bulk modulus. The spin resonance linewidth is also found to depend on pressure. This is explained by considering the pressure-dependent viscosity of the solvent, which modifies the effect of dipolar coupling between spins within fullerene clusters.
We report comprehensive temperature and doping-dependences of the Raman scattering spectra for $mathrm{BaFe_{2}}(mathrm{As}_{1-x}mathrm{P}_{x}mathrm{)_{2}}$ ($x =$ 0, 0.07, 0.24, 0.32, and 0.38), focusing on the nematic fluctuation and the superconducting responses. With increasing $x$, the bare nematic transition temperature estimated from the Raman spectra reaches $T =$ 0 K at the optimal doping, which indicates a quantum critical point (QCP) at this composition. In the superconducting compositions, in addition to the pair breaking peaks observed in the $A_{mathrm{1g}}$ and $B_{mathrm{1g}}$ spectra, another strong $B_{mathrm{1g}}$ peak appears below the superconducting transition temperature which is ascribed to the nematic resonance peak. The observation of this peak indicates significant nematic correlations in the superconducting state near the QCP in this compound.
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