Nuclear quadrupole resonance

About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.

Possible star-of-David pattern charge density wave with additional modulation in the kagome superconductor CsV3Sb5

Abstract: $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) is a novel kagome superconductor coexisting with the charge density wave (CDW) order. Identifying the structure of the CDW order is crucial for understanding the exotic normal state and superconductivity in this system. Here, we report $^{51}$V nuclear magnetic resonance (NMR) and $^{121/123}$Sb nuclear quadrupole resonance (NQR) studies on kagome-metal CsV$_3$Sb$_5$. Below the CDW transition temperature $T_\textrm{CDW} \sim$ 98 K, an abrupt change of spectra was observed, indicating that the transition is of the first order. By further analysing the spectra, we find that the CDW order is commensurate. And most remarkably, the obtained experimental results suggest that the charge modulation of the CDW order is of star-of-David pattern and accompanied by an additional charge modulation in bulk below $T^* \sim$ 40 K. Our results revealing the unconventional CDW order provide new insights into $A$V$_3$Sb$_5$.

Short-range magnetic order and temperature-dependent properties of cupric oxide

Abstract: The temperature dependence of the optical and magnetic properties of CuO were examined by means of hybrid density functional theory calculations Our work shows that the spin exchange interactions in CuO are neither fully one-dimensional nor fully three-dimensional The temperature dependence of the optical band gap and the 63Cu nuclear quadrupole resonance frequency of CuO originate from the combined effect of a strong coupling between the spin order and the electronic structure and the progressive appearance of short-range order with temperature

17O NMR study of La2−xSrxCuO4 in the lightly-and heavily-doped regions

Abstract: A 17 O NMR study has been carried out for La 2− x Sr x CuO 4 in the lightly- ( x =0.075) and heavily-doped ( x =0.24) regions in the normal state. Together with the data previously reported for x =0.15, it was found that the nuclear quadrupole frequency ν Q in the apical oxygen (O(1)) does not change with x , suggesting that the doped hole does not go into the LaO layer at all. On the contrary, ν Q in the planar oxygen (O(2)) increases appreciably with Sr doping. By analyzing ν Q of Cu and O(2), it was shown that the increase of holes on the planar O 2p σ orbit is more appreciable than that in the Cu 3d orbit. From the ratio of the hole density in Cu to that in oxygen, and the spin fluctuation probed by 63 ( T 1 T ), it is suggested that the depression of T c in the “heavily-doped” region is neither due to the over-doping nor to the collapse of the two-dimensionality, but to other causes. The temperature dependences of the Knight shift 17 K in two samples are in sharp contrast with each other. In the lightly-doped region, 17 K decreases with decreasing temperature. In the heavily-doped region, however, 17 K increases slightly with decreasing temperature, becoming almost T -independent below 100 K. An increase of the anisotropic part of spin Knight shift 17 K s,ani with x also indicates that the hole density at the O 2p σ orbit increases with Sr doping.

On the Electric Field Gradient at Copper Nuclei in Oxides

Abstract: A useful interpretation is presented of the material dependence of Cu electric field gradient (EFG) in a great variety of insulating and superconducting copper oxides. The present study is concerned only with copper sites in nearly tetragonal symmetry and in stoichiometric compositions. The experimental data of Cu EFGs have been analyzed in terms of ionic picture. The analysis has revealed for the first time a systematic correlation between the observed Cu EFG and the ionic contribution to the EFG. By using the correlation, we have extracted empirical values of the Sternheimer antishielding factor γ ∞ and the hyperfine constant for Cu 2+ and Cu 1+ ions. Those values are somewhat different from the traditional ones of the results of unrestricted Hartree-Fock (UHF) calculations for free ions.