For La2-xSrxCuO4 single-crystals in the underdoped and overdoped regimes, we have measured the electrical resistivity along the c-axis, ρc, under constant magnetic fields, changing the field direction in the ab-plane. At x = 0.08, 0.12 and 0.16 in the underdoped and almost optimally-doped regimes, clear anisotropy of ρc with the fourfold symmetry in the ab-plane has been observed. This symmetry is regarded as the fourfold symmetry of the upper critical field, Hc2, and explained as being mainly due to the anisotropy of the superconducting energy gap owing to the dx2-y2 pairing. The magnitude of the fourfold component of Hc2, ΔHc2/Hc2, is largest in x = 0.08 among the three crystals. At x = 0.20 in the overdoped regime, no clear fourfold symmetry has been observed. It appears that the fourfold symmetry is easy to observe in the underdoped regime rather than in the overdoped regime.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Materials Science(all)
- Condensed Matter Physics