A growing number of two-dimensional superconductors are being discovered in the family of layered van der Waals (vdW) materials. Due to small sample volume, their characterization has been largely limited to electrical transport measurements. As a consequence, characterization of the diamagnetic response of the superfluid to an applied magnetic field, a defining property of any superconductor, has been lacking. Here, we use a local magnetic probe to directly measure the superfluid response of the tunable, gate-induced superconducting state in MoS$_2$. We find that the backgate changes the superconducting transition temperature non-monotonically whereas the superfluid stiffness at low temperature and the normal state conductivity monotonically increase with backgate voltage. In some devices, we find direct signatures in agreement with a Berezinskii-Kosterlitz-Thouless transition, whereas in others we find a broadened, shallow onset of the superfluid response. We show that the observed behavior is consistent with disorder playing an important role in determining the superconducting properties in superconducting MoS$_2$. Our work demonstrates that magnetic property measurements are within reach for vdW superconductors and reveals that the superfluid response significantly deviates from simple BCS-like behavior.

中文翻译：

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原子级薄门调谐范德华超导体的超流体响应

在层状范德华 (vdW) 材料家族中发现了越来越多的二维超导体。由于样本量小，它们的表征在很大程度上仅限于电传输测量。因此，一直缺乏超流体对施加磁场的抗磁响应的表征，这是任何超导体的定义特性。在这里，我们使用局部磁探针直接测量 MoS$_2$ 中可调谐门诱导超导态的超流体响应。我们发现背栅非单调地改变超导转变温度，而低温下的超流体刚度和常态电导率随着背栅电压单调增加。在某些设备中，我们发现与 Berezinskii-Kosterlitz-Thouless 转变一致的直接特征，而在其他情况下，我们发现超流体响应的扩大、浅开始。我们表明，观察到的行为与在确定超导 MoS$_2$ 中的超导特性中起重要作用的无序一致。我们的工作表明，磁特性测量对于 vdW 超导体是触手可及的，并揭示了超流体响应显着偏离了简单的 BCS 样行为。