Soft x-ray spectroscopy of Ba24Ge100: Electronic phase transition and Ba-atom rattling

Abstract

The electronic states of Ba24Ge100 are studied by soft x-ray photoelectron spectroscopy (XPS) at a high-energy photon factory. A large reduction in the density of states (DOS) at the Fermi level is clearly shown before and after the electronic phase transition at 200 K. The changes in the spectrum widths and the fine structures of the core-level Ba 4d spectra give a very reasonable indication of the Ba-atom rattlings in the clathrate polyhedra. On-resonance experiments using the excitation from Ba 3d to 4f levels display that the wave functions of Ba 5d and 6s orbitals give only a small contribution to make a Fermi surface through the hybridization with the Ge20 cluster orbitals. Importantly, reliable values of the DOS at the Fermi level NEF are successfully deduced, using two data sets of DOS obtained from high-resolution XPS and the total magnetic susceptibilities by a superconducting quantum interference device, to be 0.149 and 0.0427 states eV(-1) (Ge atom)(-1) for a high-temperature and for a low-temperature phase.

Energetics of endohedral atoms in type-I clathrates observed by soft x-ray spectroscopy

“…11 Soft XPS measurements were performed under vacuum of 10 −8 Pa at the BL25SU beam port of SPring-8 as reported elsewhere. 12,13 Clean sample surfaces were prepared by cleaving the ingot samples directly in a chamber. The sample surfaces were irradiated with a 776 eV soft x-ray beam with a 10 meV bandwidth and the density of states at 20 K was recorded by measuring the kinetic energy of the ejected electrons using a Scienta high-resolution energy analyzer.…”

Electron-Phonon Interactions ofSi100andGe100Superconductors with Ba Atoms Inside

“…Preliminary data for Ba 24 Ge 100 were previously reported [12], where it is noted that the Fermi level consists of the hybridized IV 20 orbital with little contribution of Ba 5d and 6s ones. We have collected accurate data for both Ba 24 Ge 100 and Ba 24 Si 100 in the present experiments.…”

Specific heat capacity and magnetic susceptibility of superconducting Ba24Si100

“…Knowing that the ratio of N EF values in high-T phase to that in low-T phase of Ba 24 Ge 100 , which can be achieved from soft X ray photoelectron spectroscopy [11], is 3.5-1, the c Pauli values can be directly extracted in combination with the c const values experimentally determined described earlier. By tuning the value of c dia as an off-set, the c Pauli Zc const Kc dia can be evaluated from this ratio.…”