Electronic Structure of Quantum Materials for Quantum Technology

Quantum materials exhibit distinctive electronic, magnetic, and optical properties, including topologically protected surface states, strong spin-orbit coupling, and quantum confinement effects. In this study, two experimental techniques, angleresolved photoemission spectroscopy (ARPES) and resonant inelastic X-ray scattering (RIXS), were employed to investigate the electronic structure of three quantum materials: Hafnium (0001), monolayer WSe2 on template stripped gold surface, and (Ge0.87Mn0.13)Te. For Hafnium (0001), theoretical predictions indicated the presence of Rashbasplit surface states with significant spin-momentum locking, characterized by a strong d-character. While our ARPES measurements are in close agreement with the theoretical band structures, minor deviations are observed due to surface contaminants and the absence of certain predicted surface states. Furthermore, linear and circular dichroism experiments highlight the sensitivity of electronic states to light polarization, elucidating the orbital character of surface bands. In the case of monolayer WSe2, large area monolayers were exfoliated using template-stripped gold method utilising two different templates: mica and silicon. Both experimental (μARPES) and theoretical spectra of WSe2/Au show a strong hybridization influencing the electronic states around the Brillouin zone centre at " and of charge transfer between Au and WSe2. This is further corroborated by corelevel spectra taken on di↵erent regions of WSe2 on Au, revealing a mixture of van der Waals and covalent interactions for the WSe2-Au interface, with an intermediate interaction strength. RIXS measurements were carried out on the multiferroic material (Ge0.87Mn0.13)Te to examine the e↵ect of external electric and magnetic fields on dd excitations. Under the application of an applied voltage, RIXS spectra show a clear change in dd excitations, indicating a response related to the ferroelectric order of the material. Theoretical simulations were performed using the single ion model (SIM) within the Quanty software framework. The theoretical spectra of XAS and RIXS align with the experimental spectra for Oh symmetry with a crystal field parameter (10Dq) of 0.4 eV, o↵ering critical insights into the behavior of this material under external perturbations. These findings not only enhance our understanding of the complex electronic and magnetic behaviors of quantum materials but also pave the way for their integration into next-generation technologies, such as spintronics and optoelectonics.