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تسجيل مستخدم جديدElectronic spin susceptibilities and superconductivity in HgBa$_{2}$CuO$_{4+delta}$ from nuclear magnetic resonance
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Nuclear magnetic resonance (NMR) experiments on single crystals of HgBa$_{2}$CuO$_{4+delta}$ are presented that identify two distinct temperature-dependent spin susceptibilities: one is due to a spin component that is temperature-dependent above the critical temperature for superconductivity ($T_{rm c}$) and reflects pseudogap behavior; the other is Fermi-liquid-like in that it is temperature independent above $T_{rm c}$ and vanishes rapidly below $T_{rm c}$. In addition, we demonstrate the existence of a third, hitherto undetected spin susceptibility: it is temperature independent at higher temperatures, vanishes at lower temperatures (below $T_0 eq T_{rm c}$), and changes sign near optimal doping. This susceptibility either arises from the coupling between the two spin components, or it could be given by a distinct third spin component.
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The magnitude of the powder spin susceptibility of an optimally doped superconductor HgBa$_2$CuO$_{4+delta}$ (Hg1201) in the normal state is found to be nearly the same as that of La$_{2-x}$Sr$_{x}$CuO$_{4}$ near the optimally doped level. The Stoner
enhancement factor of Hg1201 is larger than that of La$_{2-x}$Sr$_{x}$CuO$_{4}$. The magnitude correlation of the Stoner enhancement factor is inconsistent with the effect of the recent theoretical Coulomb repulsion between 3$d$ electrons and that of the superexchange intereraction of a charge transfer type.
We present an inelastic neutron scattering study of the structurally simple single-layer compound HgBa$_2$CuO$_{4+delta}$ close to optimal doping ($T_c approx 96$ K). A well-defined antiferromagnetic resonance with energy $omega_r = 56$ meV ($approx
6.8 k_BT_c$) is observed below the superconducting transition temperature $T_c$. The resonance mode is energy-resolution limited and exhibits an intrinsic momentum width of about $0.2 mathrm{mathring{A}^{-1}}$, consistent with prior work on several other cuprates. However, the unusually large value of the mode energy implies a non-universal relationship between $omega_r$ and $T_c$ across different families of cuprates.
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ngle crystals were investigated with doping corresponding to superconducting transition temperatures from 74,K underdoped, to 78,K overdoped. The apical oxygen site was chosen since its NMR spectrum has narrow quadrupolar satellites that are well separated from any other resonance. Non-vortex contributions to the spectra can be deconvolved in the time domain to determine the local magnetic field distribution from the vortices. Numerical analysis using Brandts Ginzburg-Landau theory was used to find structural parameters of the vortex lattice, penetration depth, and coherence length as a function of magnetic field in the vortex solid phase. From this analysis we report a vortex structural transition near 15,T from an oblique lattice with an opening angle of $73^{circ}$ at low magnetic fields to a triangular lattice with $60^{circ}$ stabilized at high field. The temperature for onset of vortex dynamics has been identified with vortex lattice melting. This is independent of the magnetic field at sufficiently high magnetic field similar to that reported for YBa$_2$Cu$_3$O$_7$ and Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+delta}$ and is correlated with mass anisotropy of the material. This behavior is accounted for theoretically only in the limit of very high anisotropy.
Various forms of spin and charge ordering have been identified in a wide range of cuprate superconducting materials, but whether these behaviors are ubiquitous phenomena is not established. In this work we focus on one of the simplest compounds, HgBa
$_{2}$CuO$_{4+delta}$ (Hg1201), a superconductor with a high transition temperature, 97 K, having only a single layer and tetragonal structure, in contrast to one of the most extensively studied materials, YBa$_{2}$Cu$_{3}$O$_{6+y}$ (Y123). Using nuclear magnetic resonance we have discovered a coherent spatial modulation of both spin and charge that is temperature and magnetic field independent, in competition with superconductivity similar to other cuprates. However, there is no evidence for the magnetic field and temperature induced charge order observed in Y123. Electronic instabilities are a common feature of cuprates as in the present work on Hg1201, but their manifestations are not universal.
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