Effect of ferromagnet on superconductor in NbSe₂/Fe_5-xGeTe₂ heterostructures

Studies on exfoliated 2D superconductors began a decade ago, but little has been reported for heterostructures comprising superconductors with other materials. In this talk, we will present transport properties of exfoliated NbSe₂ when contacted with an exfoliated ferromagnet like Fe_5-xGeTe₂ in a heterostructure. The temperature dependent resistivity of the NbSe₂/Fe_5-xGeTe₂ stack clearly reveals the anomalies associated to Fe_5-xGeTe₂ and the superconducting transition of NbSe₂ although only NbSe₂ is in contact with the electrodes. This indicates their strong coupling. The superconducting transition temperature is observed to decrease slightly with respect to that of the pure NbSe₂ layer revealing a broader transition. For both, the exfoliated NbSe₂ layer and the NbSe₂/Fe_5-xGeTe₂ heterostructure, the planar upper critical fields are observed to far exceed the Pauli paramagnetic limit. Intriguingly, when the superconducting phase diagram under magnetic field is normalized by T_c, the heterostructure shows comparatively higher upper critical fields H_c2 with respect to the NbSe₂ layer. Remarkably, the I-V characteristics and also the differential resistivity, shows two features, as if this combined system was composed of two-distinct superconducting gaps.