Single-crystalline transition metal phosphide superconductor WP studied by Raman spectroscopy and first-principles calculations

We present a study of phonon modes and electron-phonon coupling in superconductor WP using angle-resolved polarized Raman spectroscopy. Seven out of twelve Raman-active modes are detected, with frequencies in good accordance by the first-principles calculations. We analyze parallel- and cross-polarized configurations of ${\mathrm{A}}_{\mathrm{g}}$ and ${\mathrm{B}}_{3\mathrm{g}}$ phonon modes with polarization- and angle-resolved Raman measurements. For the observed seven modes, the total electron-phonon coupling parameter $\ensuremath{\lambda}$ is only about 0.07, which is too small to achieve superconductivity. Our results elucidate that the low-frequency phonon modes play a key role in the superconductivity within the Bardeen-Cooper-Schrieffer theory framework.