Full superconducting gap and type-I to type-II superconductivity transition in single crystalline NbGe2

We report a mechanical point-contact spectroscopy study on the single crystalline NbGe\(_2\) with a superconducting transition temperature \(T\rm_c\) = 2.0 - 2.1 K. The differential conductance curves at 0.3 K can be well fitted by a single gap s-wave Blonder-Tinkham-Klapwijk model and the temperature dependent gap follows a standard Bardeen-Cooper-Schrieffer behavior, yielding \(\Delta_0 \sim\) 0.32 meV and 2\(\Delta_0\)/$k\rm_{B}$$T\rm_{c}\( = 3.62 in the weak coupling limit. In magnetic field, the superconducting gap at 0.3 K keeps constant up to \)H_{c1}\sim\(150 Oe and gradually decreases until \)H_{c2}\sim\(350 Oe, indicating NbGe\)_2$ going through a transition from type-I to type-II (possible type-II/1) superconductor at low temperature.