Phonon anomaly near a Fermi surface topological transition

Pressure-induced electronic topological transition in Sb2S3

We report the high-pressure vibrational properties and a pressure-induced electronic topological transition in the wide bandgap semiconductor Sb2S3 (E g  =  1.7-1.8 eV) using Raman spectroscopy, resistivity and x-ray diffraction (XRD) studies. In this report, high-pressure Raman spectroscopy and resistivity studies of Sb2S3 have been carried out to 22 GPa and 11 GPa, respectively. We observed the softening of phonon modes [Formula: see text], [Formula: see text] and B 2g and a sharp anomaly in their line widths at 4 GPa. The resistivity studies corroborate this anomaly around similar pressures. The changes in resistivity as well as Raman line widths can be ascribed to the strong phonon-phonon coupling, indicating clear evidence of isostructural electronic topological transition in Sb2S3. The previously reported pressure dependence of a/c ratio plot obtained also showed a minimum at ~5 GPa consistent with our high-pressure Raman and resistivity results.

Strain induced peculiarities in transport properties of Bi nanowires

We report results on the effect of strain on the thermopower and electrical resistance of glass-coated individual Bi nanowires. Here, we show that there is a critical diameter of wires below which the contribution of holes to the charge transport in pure Bi nanowires is more significant than that of electrons. The properties of Bi nanowires are examined in the light of a strain induced electronic topological transition. At low temperatures, the thermopower dependences on strain exhibit a non-monotonic behavior inherent in thinner wires, where the thermopower is dominated by the diffusion transport mechanism of holes. The hole-dominated transport can be transformed into electron-dominated transport through a smooth manipulation with the phonon spectrum and Fermi surface by applying a uniaxial strain. A fairly high value of the thermoelectric power factor (S(2)/ρ = 89 μW cm(-1) K(-2)) was found in the temperature range of 80-300 K, where the dominant mechanism contributing to the thermopower is diffusive thermoelectric generation with electrons as the majority carrier.

Electronic topological and structural transitions in AuGa(2) under pressure

Results of electronic band structure calculations, electrical resistance, thermoelectric power (TEP), and x-ray diffraction measurements, under pressure carried out on AuGa(2) to investigate its anomalous behaviour are reported. The first principles electronic band structure calculations confirm that a flat band close to the Fermi level along the Γ-X direction of the Brillouin zone is responsible for the unusual behaviour of AuGa(2). In synchrotron-based high-pressure x-ray diffraction measurements, it is observed to undergo a structural phase transition above 7 GPa. The TEP variation with pressure and the P-V data up to 7 GPa transformed to the universal equation of state (UEOS) indicate the existence of an electronic topological transition (ETT) near 3.2 GPa. Consistent with this, in electronic structure calculations carried out at reduced sample volume corresponding to 4 GPa, it is seen that the flat band crosses the Fermi level. The structure above 7 GPa is a distortion of the CaF(2) phase. This structure continuously evolves with increasing pressure. The continuous variation of electrical resistance across the transition is consistent with this.