Electronic Structure of Quantum Materials for Quantum Technology

Structure électronique des matériaux quantiques pour la technologie quantique Quantum materials exhibit distinctive electronic, magnetic, and optical properties, including topologically protected surface states, strong spin-orbit coupling, and quantum confinement effects. These properties make them promising for next-generation technologies like quantum computing and spintronics.Two different experimental techniques, such as Angle-resolved photoemission spectroscopy (ARPES) and Resonant in-elastic X-ray scattering (RIXS), have been utilized to study the electronic structure of three quantum materials: Hafnium (0001), Monolayer WSe2 on Au, and (Ge(0.87)Mn(0.13)Te.For Hafnium (0001), Our theoretical predictions indicated the presence of Rashba-split surface states with significant spin-momentum locking, characterized by a strong d-character. Experimental ARPES measurements, conducted with both He lamp sources and synchrotron radiation, are in excellent agreement with the theoretical band structures. However, deviations such as additional flat bands due to surface contaminants and the absence of certain predicted surface states were observed. Furthermore, linear and circular dichroism experiments highlighted the sensitivity of electronic states to light polarization, elucidating the orbital character of surface bands.In the case of monolayer WSe2, large-area monolayers of WSe2 were exfoliated using a well-established template-stripped gold method using two different templates, Mica and Silicon. Both experimental (microARPES) and theoretical spectra of WSe2/Au showed a strong hybridization influencing the electronic states around the Brillouin zone centre at Gamma and of charge transfer between Au and WSe2, however unaffected at valence band maximum (VBM) K point. Further corroborated by core level spectra taken on different regions of the thickness of WSe2 on Au, a substrate interaction of the nature covalent like quasi bonding (CLQB) was revealed.RIXS measurements were carried out on multiferroicmaterial Ge(0.87)Mn(0.13)Te to fathom the effect of external electric and magnetic fields on dd excitations. By applying a 3.1 V electric field, RIXS measurements showed a clear change in dd excitations, indicating a response related to the ferroelectric order of the material. Theoretical simulations were performed using the Anderson Impurity Model (AIM) within the Quanty software framework. The theoretical spectra of XAS and RIXS are in good agreement with the experimental spectra for oh symmetry with a crystal field parameter (10Dq) of 0.4 eV.