Observation of Electronic Structure and Extraction of Anharmonic Phonon Mode on Cage Compound Using Focused Incident Light

Electron-phonon interaction is one of the most fundamental interactions. Anharmonic vibrational modes interact with the conductive electrons and provide fascinating phenomena such as unusual superconductivity or high thermoelectric properties. BaIr2Ge7, a cage-structured compound with encapsulated Ba atoms, shows superconductivity at Tc＝2.5 K. Although specific heat measurements suggest the presence of anharmonic phonon modes, the atomic displacement parameter (ADP) is unusually small. Thus, the existence of anharmonic phonon modes and their relationship with the electronic state has not been clarified. In this study, we performed micro-focused angle-resolved photoemission spectroscopy (ARPES) on BaIr2Ge7 to explore the existence of the anharmonic phonon mode through the temperature-dependent spectra. The presence of two domains was identified by scanning the electronic states of the cleavage surface. The anharmonic phonon modes, extracted from the temperature-dependent photoemission linewidth, provide insight into its relationship with electrical resistivity, specific heat, and ADP.