$\mu$SR study on noncentrosymmetric superconductor NbGe$_{\mathbf{2}}$

We report a muon spin relaxation ($\mu$SR) study on polycrystalline noncentrosymmetric superconductor NbGe$_2$~with the superconducting transition temperature $T_c=2.0\sim2.1$~K. Zero-field $\mu$SR~experiment indicates the absence of spontaneous magnetic field in the superconducting state, showing the preservation of time-reversal symmetry in the superconducting state. Transverse-field $\mu$SR~experiment is performed to map the phase diagram of NbGe$_2$, from which clear evidence of both type-I and type-II superconductivity is obtained. More importantly, we clearly delineate the region in the phase diagram where type-I and type-II superconductivity coexist.