Competing Phases, Strong Electron-Phonon Interaction and Superconductivity in Elemental Calcium under High Pressure

Abstract

The observed "simple cubic" (sc) phase of elemental Ca at room temperature in the 32-109 GPa range is, from linear response calculations, dynamically unstable. By comparing first principle calculations of the enthalpy for five sc-related (non-close-packed) structures, we find that all five structures compete energetically at room temperature in the 40-90 GPa range, and three do so in the 100-130 GPa range. Some competing structures below 90 GPa are dynamically stable, i.e., no imaginary frequency, suggesting that these sc-derived short-range-order local structures exist locally and can account for the observed (average) "sc" diffraction pattern. In the dynamically stable phases below 90 GPa, some low frequency phonon modes are present, contributing to strong electron-phonon (EP) coupling as well as arising from the strong coupling. Linear response calculations for two of the structures over 120 GPa lead to critical temperatures in the 20-25 K range as is observed, and do so without unusually soft modes.

8 pages, 6 figures, 1 table, accepted for publication in Phys. Rev. B

References in corpus (2)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Origin of Strong Coupling in Lithium under Pressure

Cited by in corpus (10)

• Cubic H${}_3$S around 200 GPa: an atomic hydrogen superconductor stabilized by sulfur
• Correlation-enhanced electron-phonon coupling: Applications of GW and screened hybrid functional to bismuthates, chloronitrides, and other high Tc superconductors
• Elemental Phosphorus: structural and superconducting phase diagram under pressure
• A perspective on pnictide superconductors
• Rational material design of mixed-valent high T${}_c$ superconductors
• Characterization of the high-pressure superconductivity in the Pnma phase of calcium
• Superconductivity of calcium under the pressure at 120 GPa
• The superconducting phase of Calcium under the pressure at 200 GPa: the strong-coupling description
• Specifc Heat and Thermodynamic Critical Field for Calcium under the Pressure at 120 GPa
• High pressure Ca-VI phase between 158-180 GPa: Stability, electronic structure and superconductivity