Pressure effects on the superconducting transition innH-CaAlSi

2007/12/18 by Lilia Boeri, L. Boeri, J. S. Kim +7 · 11 citations
Chemistry · Materials Science · Physics and Astronomy · #Ab initio #Boron and Carbon Nanomaterials Research #Chemistry #Condensed matter physics #Crystallography #Iron-based superconductors research #Materials science #Nuclear magnetic resonance #Physics #Quantum mechanics #Softening #Stacking #Superconducting transition temperature #Superconductivity #Superconductivity in MgB2 and Alloys #Thermodynamics #cond-mat.mtrl-sci #cond-mat.supr-con

paper · pdf · doi:10.1103/physrevb.77.144502

published in Physical Review B 77(14) (American Physical Society) · 6 pages, 5 figures

arxiv created 2007/12/18 · openalex publication_date 2008/04/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05

Abstract

We present a combined experimental and theoretical study of the effects of pressure on T_c of the hexagonal layered superconductors nH-CaAlSi (n=1, 5, and 6), where nH denotes the different stacking variants that were recently discovered. Experimentally, the pressure dependence of T_c has been investigated by measuring the magnetic susceptibility of single crystals up to 10 kbars. In contrast to previous results on polycrystalline samples, single crystals with different stacking sequences display different pressure dependences of T_c. 1H-CaAlSi shows a decrease in T_c with pressure, whereas 5H- and 6H-CaAlSi exhibit an increase in T_c with pressure. Ab initio calculations for 1H-, 5H-, and 6H-CaAlSi reveal that an ultrasoft phonon branch associated with out-of-plane vibrations of the Al-Si layers softens with pressure, leading to a structural instability at high pressures. For 1H-CaAlSi, the softening is not sufficient to cause an increase in T_c, which is consistent with the present experiments but adverse to previous reports. For 5H and 6H, the softening provides the mechanism to understand the observed increase in T_c with pressure. Calculations for hypothetical 2H and 3H stacking variants reveal qualitative and quantitative differences.

Citations

• Phonons and related crystal properties from density-functional perturbation theory
• Anisotropics-wave superconductivity in CaAlSi single crystals from penetration depth measurements
• Generalized Gradient Approximation Made Simple
• Superconductivity of BulkCaC6
• Ab initio pseudopotentials for electronic structure calculations of poly-atomic systems using density-functional theory
• Electronic and structural properties of superconductingMgB2,CaSi2,and related compounds
• Special points for Brillouin-zone integrations
• Electrons and phonons in the ternary alloyCaAl2−xSixas a function of composition
• Electronic Structures of CaAlSi with Different Stacking AlSi Layers by First-Principles Calculations

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