2012/10/09 by Maxime Leroux, Mathieu Le Tacon, Matteo Calandra +6 · 1 citation
Physics and Astronomy · #cond-mat.other #cond-mat.str-el #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.86.155125
6 pages, 5 figures, accepted for publication in Physical Review B
arxiv created 2012/10/09 · arxiv updated 2015/06/11
The temperature dependence of the phonon spectrum in the superconducting transition metal dichalcogenide 2H-NbS2 is measured by diffuse and inelastic x-ray scattering. A deep, wide and strongly temperature dependent softening, of the two lowest energy longitudinal phonons bands, appears along the ΓM symmetry line in reciprocal space. In sharp contrast to the iso-electronic compounds 2H-NbSe2, the soft phonons energies are finite, even at very low temperature, and no charge density wave instability occurs, in disagreement with harmonic ab-initio calculations. We show that 2H-NbS2 is at the verge of the charge density wave transition and its occurrence is only suppressed by the large anharmonic effects. Moreover, the anharmonicity and the electron phonon coupling both show a strong in-plane anisotropy.