Lower critical fields in BKBO single crystals

摘要

We performed dc-magnetization measurements in low magnetic fields on single crystals of Ba_(1-x)K_xBiO_y (BKBO) with the different potassium content. The single crystals reveal the superconducting transition at 29 - 31 K. It is shown that the lower critical fields H_(C1) in crystals amount to 104 Oe (x = 0.34), 126 (x = 0.37) and 112 Oe (x = 0.4). The values of the penetration depth λ(0) are equal to 2530 A, 2430 A and 2670 A for x = 0.34, 0.37, and 0.4, respectively.