d波Bi_2Sr_2CaCu_2O_8+ δ单晶表面势垒的形状和取向关系
Shape- and orientation-dependence of surface barriers in single crystalline d-wave Bi_2Sr_2CaCu_2O_8+delta
摘要：
本文用磁光成像和霍尔探针阵列磁强计测量了同一Bi_2Sr_2CaCu_2O_8+ δ单晶体切割成不同晶体厚宽比（d/w）时，当晶体边缘与面内主晶轴（a，b）成两个角度α时，第一磁通进入的磁场H_p。在所有温度下，H_p随纵横比的变化都可以用所谓几何势垒[E. H. Brandt，Phys.Rev.B60，11939（1999）]。但是，由于晶体的正方形形状，H_p的强度大大增强。在中温区（T < ~ 50 K），Bean-Livingston势垒限制了涡旋进入，当样品边缘与晶轴成45 ° \degree角而不是平行于晶轴时，有证据表明微小的晶体取向依赖性增强。
英文摘要：
Magneto-optical imaging and Hall-probe array magnetometry are used to measure the field of first flux entry, H_p, into the same Bi_2Sr_2CaCu_2O_8+delta single crystal cut to different crystal thickness-to-width ratios (d/w), and for two angles alpha between the edges and the principal in-plane crystalline (a,b) axes. At all temperatures, the variation with aspect ratio of H_p is qualitatively well described by calculations for the so-called geometric barrier [E.H. Brandt, Phys. Rev. B 60, 11939 (1999)]. However, the magnitude of H_p is strongly enhanced due to the square shape of the crystal. In the intermediate temperature regime (T < ~ 50 K) in which the Bean-Livingston barrier limits vortex entry, there is some evidence for a tiny crystal-orientation dependent enhancement when the sample edges are at an angle of 45\degree with respect to the crystalline axes, rather than parallel to them.
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