Strontium disilicide SrSi2: Narrow band gap semiconductor or Weyl semimetal?

The physical properties of SrSi 2 were systematically investigated experimentally and computationally to clarify whether the material is a narrow band gap semiconductor or Weyl semimetal. Samples were prepared using the vertical Bridgeman method. Analysis of the electrical transport properties showed that the carrier density ( n ) was small (5.4 × 10 18 cm –3 ) and remained essentially constant below 100 K but increased above 100 K through thermal activation, and data fitting yielded a band gap of 62.8 meV. The small n at low temperatures is consistent with the small density of states at the Fermi energy ( E F ) determined by specific heat measurements. Density functional theory calculations using the projector augmented wave method with the HSE06 hybrid functional, along with an appropriate screening parameter ( ω = 0.11 bohr –1 ), revealed that SrSi 2 is a semiconductor with a band gap of 62 meV. Both the experimental and computational results indicate that SrSi 2 behaves as a narrow-gap semiconductor with its E F located slightly below the valence band maximum, resulting in a small number of carriers at low temperatures. Its thermoelectric properties were also examined. The power factor was 1.77 mW·K –2 m –1 at 220 K and the figure of merit was 0.13 at 300 K, confirming that SrSi 2 is a potential thermoelectric material at temperatures below 300 K. • Physical properties of SrSi 2 were investigated experimentally and computationally. • The DFT calculation with HSE06 hybrid functional shows that SrSi 2 has a band gap. • The carrier density of SrSi 2 increases through thermal activation above 100 K. • SrSi 2 is a narrow-gap semiconductor, not a Weyl semimetal. • The Fermi energy of synthesized SrSi 2 is slightly below the valence band maximum.