Abstract
The excitations across the superconducting gap (2{Delta}-peak in B{sub 1g}-symmetry Raman spectra) in an overdoped Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} single crystal have been studied as a function of temperature and field. The 2{Delta}-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 2{Delta}-peak is present above the irreversibility line and yields a conventional temperature dependence of the effective upper critical field. {copyright} {ital 1997} {ital The American Physical Society}