A surprisingly strong variation of resistance with perpendicular magneticfield, and a peak in the resistance vs. field, R(B) has been found ininsulating films of a sequence of homogeneous, quench-condensed films ofamorphous Bi undergoing a thickness-tuned superconductor-insulator transition.Isotherms of magnetoresistance, rather than resistance, vs. field were found tocross at a well-defined magnetic field higher than the field corresponding tothe peak in R(B). For all values of B, R(T) was found to obey an Arrheniusform. At the crossover magnetic field the prefactor became equal to the quantumresistance of electron pairs, h/4e^2, and the activation energy returned to itszero field value. These observations suggest that the crossover is thesignature of a quantum phase transition between two distinct insulating groundstates, tuned by magnetic field.
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机译：在垂直磁场中，电阻具有令人惊讶的强大变化，并且在电阻与磁场之间存在一个峰值R（B），该绝缘膜包含一系列经过厚度调整的超导体-绝缘体转变的非晶态Bi均匀，淬火压缩膜序列发现在一个明确定义的磁场（比R（B）中的峰值对应的磁场）高的情况下，磁阻，而不是电阻与磁场的等温线交叉。对于所有的B值，发现R（T）服从阿伦尼乌斯形式。在交叉磁场下，预因子等于电子对的量子电阻h / 4e ^ 2，并且活化能返回到其零场值。这些观察结果表明，交叉是两个不同的绝缘基态之间的量子相变的特征，并通过磁场进行了调谐。
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