Electronic Raman Scattering of Overdoped Tl2Ba2CuO6+δ in High Magnetic Fields

The excitations across the superconducting gap (2Δ-peak in B1g-symmetry Raman spectra) in an overdoped Tl2Ba2CuO6+δ single crystal have been studied as a function of temperature and field. The 2Δ-peak intensity, which we interpret as the density of the superconducting condensate around the gap antinodes, is a linear function of temperature, but a nonlinear function of the field. The latter is attributed to renormalization of quasiparticle spectra in the vicinity of vortex lines in the mixed state. The 2Δ-peak is present above the irreversibility line and yields a conventional temperature dependence of the effective upper critical field. copyright 1997 The American Physical Society