Coupled Electrical Transport Crossover and Phonon Anomalies in 1T-SnSe 2

We present temperature-dependent electrical transport and Raman spectroscopy measurements of 1T-SnSe2 single crystals. Room-temperature in-plane optical absorption spectra through spectroscopic ellipsometry analysis reveal indirect and direct band gaps of 1.19 and 1.52 eV, respectively. The transport data exhibit a broad conductivity maximum near 100 K and can be described by a thermally activated semimetallic conduction channel over 28-300 K, coexisting with a two-dimensional variable-range hopping conductivity. Temperature-dependent Raman spectra resolve the first-order Eg and A1g phonon modes at 109 and 183 cm-1. These phonon modes are fitted using Breit-Wigner-Fano (BWF) and Voigt line shapes, respectively. Notably, the Fano asymmetry parameter and the Voigt broadening exhibit anomalies near 100 K that quantitatively track the transport signature, whereas the peak positions and spectral widths evolve monotonically from 10 to 300 K. First-principles calculations of the electronic band structure and phonon dispersion corroborate the extracted band gap energies and spectral assignments. These findings establish a consistent picture for the electronic band structure, charge transport, and lattice dynamics in 1T-SnSe2.