  Temperature-dependent electronic and magnetic properties are reported for a
Z2 topological metal single-crystalline nickel-deficient NiV$_2$Se$_4$. It is
found to crystallize in the monoclinic Cr3S4 structure type with space group
I2=m. From single-crystal x-ray diffraction, we find that there are vacancies
on the Ni site, resulting in the composition Ni0:85V2Se4 in agreement with our
electron-probe microanalysis. The electrical resistivity shows metallic
behavior with a broad anomaly around 150{200 K that is also observed in the
heat capacity data. This anomaly indicates a change of state of the material
below 150 K. We believe that this anomaly could be due to spin fluctuations or
charge-density-wave (CDW) fluctuations, where the lack of long-range order is
caused by vacancies at the Ni site of Ni0:85V2Se4. Although we fail to observe
any structural distortion in this crystal down to 1.5 K, its electronic and
thermal properties are anomalous. The observation of non-linear temperature
dependence of resistivity as well as an enhanced value of the Sommerfeld
coefficient = 104.0(1) mJ/molK2 suggests strong electron-electron correlations
in this material. The first-principles calculations performed for
NiV$_2$Se$_4$, which are also applicable to Ni0:85V2Se4, classify this material
as a topological metal with Z2 = (1; 110) and coexisting electron and hole
pockets at the Fermi level. The phonon spectrum lacks any soft phonon mode,
consistent with the absence of periodic lattice distortion in the present
experiments.
