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 ${\mathrm{NbGe}}₂$ with a superconducting transition temperature ${T}_c=2.0$--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 ${\mathrm{\ensuremath{\Delta}}}₀\ensuremath{\sim}0.32$ meV and $2{\mathrm{\ensuremath{\Delta}}}₀/{k}_{\text{B}}{T}_c=3.62$ in the weak-coupling limit. In magnetic field, the superconducting gap at 0.3 K remains constant up to ${H}_c1\ensuremath{\sim}150$ Oe and gradually decreases until ${H}_c2\ensuremath{\sim}350$ Oe, indicating ${\mathrm{NbGe}}₂$ is going through a transition from a type-I to type-II (possible type-II/1) superconductor at low temperature.