Temperature dependence of anisotropic lower critical fields in (La1-xSrx)2CuO4

The anisotropic lower critical fields Hc1 are determined from a novel procedure based on the Beans critical-state model to pick up the onset of flux penetration in broad zero-field-cooled magnetization curves in (La1-xSrx)2CuO4 (x0.07) single crystals. The values of Hc1 at T=0 K are estimated to be 70 G for H layer and 300 G for H layer. The temperature dependence of Hc1 is such that it tends to saturate towards the lowest temperature measured (2 K) in contrast to the other recent results which report the abnormal upturn of the Hc1-T curve at low temperatures. Instead the results indicate that the critical current density in plane has a strong temperature dependence even in the temperature range well below Tc and becomes 106 A/cm2 at 2 K.