  We report the electronic structures and transport properties of a chiral
crystal NbGe$_2$, which is a candidate for a coupled electron-phonon liquid.
The electrical resistivity and thermoelectric power of NbGe$_2$ exhibit clear
differences compared to those of NbSi2 even though both niobium ditetrelides
are isostructural and isoelectronic. We discuss the intriguing transport
properties of NbGe$_2$ based on a van Hove-type singularity in the density of
states. The analysis of de Haas-van Alphen oscillations measured by the field
modulation and magnetic torque methods reveals the detailed shape of the Fermi
surface of NbGe$_2$ by comparison with the results of energy band structure
calculations using a local density approximation. The electron and hole Fermi
surfaces of NbGe$_2$ split into two because of the anti-symmetric spin-orbit
interaction. The temperature dependence of quantum oscillations indicates that
the effective mass is isotropically enhanced in NbGe$_2$ due to strong
electron-phonon interaction.
