Pressure-tuning structural and electronic transitions in semimetal CoSb

Abstract

Recently, theoretical work predicted that the cobalt mono-antimonide (CoSb) with a NiAs-type structure could be stabilized in the form of a monolayer PbO-type FeSe structure on a $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrate [Ding et al., Phys. Rev. Lett. 124, 027002 (2020)], which may host high-temperature superconductivity comparable with monolayer FeSe [Wang et al., Chin. Phys. Lett. 29, 037402 (2012)]. Motivated to explore the possible pressure-induced superconductivity in bulk CoSb associated with structural instability, utilizing the diamond anvil cell technique, we herein report a comprehensive study of the electrical transport, crystalline structure, and electronic band structure of the bulk CoSb with electrical conductivity, synchrotron x-ray diffraction, and first-principles calculations. No pressure-induced superconductivity is detected down to 2 K with pressure up to 42.0 GPa, but a structural phase transition occurs between 11.7 and 16.2 GPa. Instead, an electronic transition, featured by a carrier-type switch from an electron $<10\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ to a hole ($n\ensuremath{\rightarrow}p$) dominant one at higher pressure, is observed. The $n\text{\ensuremath{-}}p$ switch at room temperature is ascribed to a pressure-induced structural phase transition from hexagonal ($P{6}_{3}/mmc$, No. 194) to orthorhombic ($Pnma$, No. 62), which is confirmed by a combination of first-principles calculations and structural refinement. Interestingly, the temperature-driven $p\text{\ensuremath{-}}n$ switch also occurs in the orthorhombic phase at \ensuremath{\sim}90 K, emphasizing the tunable multiband structure (with charge neutrality point) of the semimetal CoSb by pressure or temperature. Moreover, the electronic transition is assigned as a semimetal-semimetal transition. The resistivity shows a robust ${T}^{3}$ dependence trend $<30\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for both semimetal phases. At high temperature, all the $\ensuremath{\rho}(T)$ curves become saturated, as described by the parallel-resistor model. The results support that the $s\text{\ensuremath{-}}d$ interband scattering dominates the conductivity of both the hexagonal and orthorhombic phases under pressure. The superconductivity absence implications are discussed, assuming the electron-phonon interaction in CoSb drives the superconductivity.