The charge density wave (CDW) or nematicity has been found to coexist with superconductivity in many systems. It is thus interesting that the superconducting transition temperature Tc in the doped BaNi2As2 system can be enhanced up to six times as the CDW or nematicity in the undoped compound is suppressed. Here we show that the transverse acoustic phonons of Ba1−xSrxNi2As2 are strongly damped in a wide doping range and over the whole Q range, which excludes its origin from either CDW or nematicity. The damping of TA phonons can be understood as large electron-phonon coupling and possible strong hybridization between acoustic and optical phonons as shown by the first-principle calculations. The superconductivity can be quantitatively reproduced by the change of electron-phonon coupling constant calculated by the McMillan equation in the BCS framework, which suggests that no quantum fluctuations of any order is needed to promote the superconductivity. On the contrary, the change of Tc in this system should be understood as the six-fold suppression of superconductivity in undoped compounds.
@article{arxiv.2311.03649,
title = {Strong electron-phonon coupling in Ba$_{1-x}$Sr$_x$Ni$_2$As$_2$},
author = {Linxing Song and Jianguo Si and Tom Fennell and Uwe Stuhr and Guochu Deng and Jinchen Wang and Juanjuan Liu and Lijie Hao and Huiqian Luo and Miao Liu and Sheng Meng and Shiliang Li},
journal= {arXiv preprint arXiv:2311.03649},
year = {2024}
}