Magnetic-field-induced vortex-lattice transition in HgBa2CuO4+δ

Jeongseop A. Lee, Yizhou Xin, I. Stolt, W. P. Halperin, A. P. Reyes, P. L. Kuhns, M. K. Chan
2017 Physical review B  
Measurements of the ^17O nuclear magnetic resonance (NMR) quadrupolar spectrum of apical oxygen in HgBa_2CuO_4+δ were performed over a range of magnetic fields from 6.4 to 30 T in the superconducting state. Oxygen isotope exchanged single 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
more » ... 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 Brandt's 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^∘ at low magnetic fields to a triangular lattice with 60^∘ 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_2Cu_3O_7 and Bi_2Sr_2CaCu_2O_8+δ and is correlated with mass anisotropy of the material. This behavior is accounted for theoretically only in the limit of very high anisotropy.
doi:10.1103/physrevb.95.024512 fatcat:fstjeygcpbb2bpe5zojiepv4vy