First-principles calculations of the electronic and phonon properties of APt_3P (A = Ca, Sr, and La): Evidence for a charge-density-wave instability and a soft phonon

摘要

The electronic and phonon properties of the platinum pnictide superconductors APt_3 P (A = Ca, Sr, and La) were studied using first-principles calculations. The spin-orbit-coupling effect is significant in LaPt_3P but negligible in CaPt_3P and SrPt_3P. Moreover, SrPt_3P has been demonstrated to exhibit an unexpected weak charge-density-wave (CDW) instability, which is related neither directly to the Fermi-surface nesting nor to the momentum-dependent electron-phonon coupling alone. The instability is absent in CaPt_3P and can be quickly suppressed by the external pressure, accompanied with decreases in the phonon softening and BCS T_C. Our results suggest SrPt_3P as a rare example where superconductivity is enhanced by the CDW fluctuations.