Anomalies in the core level spectroscopy of a noncentrosymmetric solid, BiPd

TL;DR

This study investigates the electronic structure of the noncentrosymmetric solid BiPd using high-resolution photoemission spectroscopy, revealing surface-bulk differences and deviations in core level features due to symmetry and spin-orbit effects.

Contribution

It demonstrates the limitations of hard x-ray spectroscopy for surface-bulk differentiation and uncovers novel deviations in core level branching ratios linked to noncentrosymmetry and spin-orbit interactions.

Findings

Hard x-ray spectroscopy alone cannot distinguish surface and bulk electronic structures.

Surface sensitivity of ARPES depends on photon energy, affecting measurements.

Deviation in Bi core level branching ratios suggests new physics beyond conventional theories.

Abstract

Understanding exotic solids is a difficult task as interactions are often hidden by the symmetry of the system. Here, we study the electronic properties of a noncentrosymmetric solid, BiPd, which is a rare material exhibiting both superconductivity and topological phase of matter. Employing high resolution photoemission spectroscopy with photon energies ranging from hard x-ray to extreme ultraviolet regime, we show that hard x-ray spectroscopy alone is not enough to reveal surface-bulk differences in the electronic structure. We derived the escape depths close to the extreme surface sensitivity and find that the photon energies used for high resolution measurements such as ARPES fall in the surface sensitive regime. In addition, we discover deviation of the branching ratio of Bi core level features derived from conventional quantum theories of the core hole final states. Such paradigm shift in core level spectroscopy can be attributed to the absence of center of symmetry and spin-orbit interactions.