Determination of the superconducting gap in near optimally doped Bi2Sr2-xLaxCuO6+δ (x ∼ 0.4) from low-temperature specific heat

Low-temperature specific heat of the monolayer high-T-c superconductor Bi2Sr2-xLaxCuO6+delta has been measured close to the optimal doping point (x similar to 0.4) in different magnetic fields. The identification of both a T-2 term in zero field and a root H dependence of the specific heat in fields is shown to follow the theoretical prediction for d-wave pairing, which enables us to extract the slope of the superconducting gap in the vicinity of the nodes (v(Delta), which is proportional to the superconducting gap Delta(0) at the antinodes according to the standard d(x2-y2) gap function). The v(Delta) or Delta(0) (similar to 12 meV) determined from this bulk measurement shows close agreement with that obtained from spectroscopy or tunneling measurements, which confirms the simple d-wave form of the superconducting gap.