P. L. Kuhns

Magnetic Field Independence of the Spin Gap in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}

We report, for magnetic fields of 0, 8.8, and 14.8thinspthinspT, measurements of the temperature dependent {sup 63}Cu NMR spin lattice relaxation rate for near optimally doped YBa{sub 2}Cu {sub 3}O{sub 7{minus}{delta}} , near and above T{sub c} . In sharp contrast with previous work we find no magnetic field dependence. We discuss experimental issues arising in measurements of this required precision and implications of the experiment regarding issues including the spin gap or pseudogap. {copyright} {ital 1998} {ital The American Physical Society}

Critical point and the nature of the pseudogap of single-layered copper-oxide Bi2Sr2-xLaxCuO6+δ superconductors

We apply strong magnetic fields of H=28.5 to 43 T to suppress superconductivity (SC) in the cuprates Bi2Sr2-xLaxCuO6+delta (x=0.65, 0.40, 0.25, 0.15, and 0), and investigate the low temperature (T) normal state by 63Cu nuclear spin-lattice relaxation rate (1/T1) measurements. We find that the pseudogap (PG) phase persists deep inside the overdoped region but terminates at x approximately 0.05, which corresponds to the hole doping concentration of approximately 0.21. Beyond this critical point, the normal state is a Fermi liquid that persists as the ground state when superconductivity is removed by the magnetic field. A comparison of the superconducting state with the H-induced normal state in the x=0.40 (Tc=32 K) sample indicates that there remains substantial part of the Fermi surface even in the fully developed PG state, which suggests that the PG and SC are coexisting matters.

Ac susceptibility and 51V NMR study of MnV2O4

We report 51V zero-field NMR of the manganese vanadate spinel compound, MnV2O4, together with both ac and dc magnetization measurements. The field and temperature dependences of ac susceptibilities show a re-entrant-spin-glass-like behavior below the ferrimagnetic (FEM) ordering temperature. The zero-field NMR spectrum consists of multiple lines ranging from 240 to 320 MHz. Its temperature and field dependences are discussed in terms of the persistence of a small fraction of the cubic phase within the FEM ordered ground state. Due to strong spin–orbit couplings the disordered phase induces an anomalous structural and electronic state in an external field. This suggests a close correlation between magnetism and structure.

SUPERCONDUCTING FLUCTUATION EFFECTS ON THE SPIN-LATTICE RELAXATION RATE INYBA2CU3O6.95

We report 63Cu(2) spin-lattice relaxation rate measurements of YBa_2Cu_3O_{6.95} in magnetic fields from 2.1 T to 27.3 T obtained from 17O(2,3) nuclear magnetic resonance spin-spin relaxation. For T < 120 K, the spin-lattice rate increases with increasing magnetic field. We identify this magnetic field dependence with the change in the low-energy spectral weight originating from d-wave pairing fluctuation corrections to the density of states.

Absence of static loop-current magnetism at the apical oxygen site in HgBa2CuO4+δ from NMR

The simple structure of HgBa(2)CuO(4+δ) (Hg1201) is ideal among cuprates for study of the pseudogap phase as a broken symmetry state. We have performed (17)O nuclear magnetic resonance on an underdoped Hg1201 crystal with a transition temperature of 74 K to look for circulating loop currents proposed theoretically and inferred from neutron scattering. The narrow spectra preclude static local fields in the pseudogap phase at the apical site, suggesting that the moments observed with neutrons are fluctuating. The nuclear magnetic resonance frequency shifts are consistent with a dipolar field from the Cu(2+) site.

Absence of static orbital current magnetism at the apical oxygen site in HgBa

The simple structure of HgBa(2)CuO(4+δ) (Hg1201) is ideal among cuprates for study of the pseudogap phase as a broken symmetry state. We have performed (17)O nuclear magnetic resonance on an underdoped Hg1201 crystal with a transition temperature of 74 K to look for circulating loop currents proposed theoretically and inferred from neutron scattering. The narrow spectra preclude static local fields in the pseudogap phase at the apical site, suggesting that the moments observed with neutrons are fluctuating. The nuclear magnetic resonance frequency shifts are consistent with a dipolar field from the Cu(2+) site.

_2

Magnetometry measurements in high-quality LiFeAs single crystals reveal a change in the sign of the magnetic hysteresis in the vicinity of the upper critical field

CuO

{H}_{c2}

_{4+\delta}

, from a clear diamagnetic response dominated by the pinning of vortices to a considerably smaller net hysteretic response of opposite sign, which disappears at

from NMR

{H}_{c2}