Electron phonon coupling

The discovery of large superconducting transition temperature of Tc=190 K in metallic H2S under high pressures of 200 GPa, has renewed the interest in the superconducting properties of metal-hydrogen systems. These materials are expected to be electron-phonon superconductors and hydrogen with its low mass can contribute new optic phonons that may couple with the conduction electrons. Often, though not always, a large electron-phonon coupling parameter λ (and consequently high Tc) can result from a high electronic density of states at the Fermi level (N(EF)) and the presence of soft phonons. Our first-principles calculations of cubic TiH2 which has a large 3d N(EF)=2.8 states/eV/f.u. Our calculated phonon dispersions show that Ti modes active below frequencies of 10 THz whereas much lighter H modes are active between 32 and 40~THz. Electron-phonon coupling calculations reveal a λ=0.98 which corresponds to a Tc=6.1 K. However, the large N(EF) also leads to a tetragonal instability at low temperatures in TiH2, which may be overcome by a uniaxial strain, potentially making it a candidate for electron-phonon superconductor.

29. Electronic structure and electron-phonon coupling in TiH2
K. V. Shanavas, L. Lindsay, David S. Parker
Sci. Rep. 6, 28102 (2016) |
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