T. W. Li | Searcharxiv

arXiv1999

Interlayer Conductivity in the Superconductor Tl-Ba-Cu-O: Energetics and Energy Scales

We report on infrared studies of the c-axis electrodynamics of Tl-Ba-Cu-O (Tl-2201) crystals. A sum rule analysis reveals spectral weight shifts that can be interpreted as a kinetic energy change at the superconducting transistion. In optimally doped crystals, showing an incoherent normal state response, the kinetic energy is lowered at T < Tc, but no significant change is found in the over-doped samples, which have more coherent conductivity at T > Tc.

cond-mat.supr-con↗

arXiv1998

Lower critical field H_c1 and barriers for vortex entry in Bi_2Sr_2CaCu_2O_{8+delta} crystals

The penetration field H_p of Bi_2Sr_2CaCu_2O_{8+delta} crystals is determined from magnetization curves for different field sweep rates dH/dt and temperatures. The obtained results are consistent with theoretical reports in the literature about vortex creep over surface and geometrical barriers. The frequently observed low-temperature upturn of H_p is shown to be related to metastable configurations due to barriers for vortex entry. Data of the true lower critical field H_c1 are presented. The low-temperature dependence of H_c1 is consistent with a superconducting state with nodes in the gap function. [PACS numbers: 74.25.Bt, 74.60.Ec, 74.60.Ge, 74.72.Hs]

cond-mat.supr-con↗