Finite-size effects on the vortex-glass transition in thin YBa2Cu3O7-d films

Nonlinear current-voltage characteristics have been measured at high magnetic fields in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films of a thickness {ital t} ranging from 3000 down to 16 A. Critical-scaling analyses of the data for the thinner films ({ital t}{le}400 A) reveal deviations from the vortex-glass critical scaling appropriate for three-dimensional (3D) systems. This is argued to be a finite-size effect. At large current densities {ital J}, the vortices are probed at length scales smaller than the film thickness, i.e., 3D vortex-glass behavior is observed. At low {ital J} by contrast, the vortex excitations involve typical length scales exceeding the film thickness, resulting in 2D behavior. Further evidence for this picture is found directly from the 3D vortex-glass correlation length, which, upon approach of the glass transition temperature, appears to level off at the film thickness. The results indicate that a vortex-glass phase transition does occur at finite temperature in 3D systems, but not in 2D systems. In the latter an onset of 2D correlations occurs towards zero temperature. This is demonstrated in our thinnest film (16 A), which, in a magnetic field, displays a 2D vortex-glass correlation length which critically diverges at zero temperature.

在厚度\(t\)从3000埃到16埃的\(YBa_{2}Cu_{3}O_{7 - \delta}\)薄膜中，在高磁场下测量了非线性电流 - 电压特性。对较薄薄膜（\(t\leq400\)埃）数据的临界标度分析表明，偏离了适用于三维（3D）系统的涡旋玻璃临界标度。这被认为是一种有限尺寸效应。在大电流密度\(J\)下，在小于薄膜厚度的长度尺度上探测涡旋，即观察到3D涡旋玻璃行为。相比之下，在低\(J\)下，涡旋激发涉及超过薄膜厚度的典型长度尺度，导致2D行为。从3D涡旋玻璃关联长度直接找到了这一图像的进一步证据，当接近玻璃转变温度时，该关联长度似乎在薄膜厚度处趋于平稳。结果表明，在3D系统中，涡旋玻璃相变确实在有限温度下发生，但在2D系统中不会发生。在后者中，二维关联在趋近于零温度时开始出现。这在我们最薄的薄膜（16埃）中得到了证明，该薄膜在磁场中显示出二维涡旋玻璃关联长度，该长度在零温度下临界发散。