Anomalous transport induced by inhomogeneity in layered superconductors probed by Van der Pauw geometry

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Abstract
Two-dimensional superconductors provide a versatile platform to explore fundamental physics and applications where the properties of the two-dimensional samples are characterized by the transport of multiple or single layers. However, spatial inhomogeneities introduced during sample preparation can critically alter transport properties, potentially masking intrinsic physics and producing extrinsic signatures that resemble unconventional phenomena. In this work, we systematically investigated the transport signatures arising from different origins of inhomogeneity in superconducting van der Waals NbSe 2 samples. Two distinct categories of spatial variation were examined: growth-induced inhomogeneity (introduced via non-stoichiometric crystal growth) and fabrication-induced inhomogeneity (achieved by modulating layer thickness and step morphology during mechanical exfoliation). Both types of inhomogeneities resulted in anomalous resistance peaks, with growth-induced inhomogeneity producing more pronounced and configuration-dependent transport signatures. The transport response showed strong geometrical dependence. The observed behavior was consistently described within a framework in which spatially separated regions of the device undergo superconducting transitions at different temperatures, reflecting a distribution of local T c values in the samples. The fitting results further reveal that an inhomogeneous superconducting landscape can generate even more complex anomalous transport signatures, including double-peak structures and sign reversals in resistance. In conclusion, our results demonstrate that transport anomalies should be carefully analyzed and inhomogeneity in sample and measurement geometry should be ruled out before attributing them to intrinsic physical mechanisms.
Funding Information
  • National Natural Science Foundation of China (11974158)
  • Key-Area Research and Development Program of Guangdong Province (2020B0303050001)

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