Among hundreds of spinel oxides, LiTi2O4 (LTO) is the only one that exhibits superconductivity (Tc ~13 K). Although the general electron-phonon coupling is still the main mechanism for electron pairing in LTO, unconventional behaviors such as the anomalous magnetoresistance, anisotropic orbital/spin susceptibilities, etc. reveal that both the spin and the orbital interactions should also be considered for understanding the superconductivity. Here, we investigate tunneling spectra of [111]-, [110]- and [001]-oriented high quality LTO thin films. Several bosonic modes in tunneling spectra are observed in the [111]- and [110]-oriented films but not in [001]-oriented ones, and these modes still exist at T = 2Tc and beyond the upper critical field, which are confirmed as stemming from electron-phonon interaction by DFT calculations. These modes only appear in special surface orientations, indicating that the electron-phonon coupling in LTO system is highly anisotropic and may be enhanced by orbital-related state. The anisotropic electron-phonon coupling should be taken seriously in understanding the nature of LTO superconductivity.
@article{arxiv.1606.06109,
title = {Anisotropic electron-phonon coupling in the spinel oxide superconductor},
author = {Ge He and Yanli Jia and Xingyuan Hou and Zhongxu Wei and Haidong Xie and Zhenzhong Yang and Jinan Shi and Jie Yuan and Lei Shan and Beiyi Zhu and Hong Li and Lin Gu and Kai Liu and Tao Xiang and Kui Jin},
journal= {arXiv preprint arXiv:1606.06109},
year = {2017}
}