2 research outputs found
Orbital Ordering of the Mobile and Localized Electrons at Oxygen-Deficient LaAlO<sub>3</sub>/SrTiO<sub>3</sub> Interfaces
Interfacing
different transition-metal oxides opens a route to functionalizing
their rich interplay of electron, spin, orbital, and lattice degrees
of freedom for electronic and spintronic devices. Electronic and magnetic
properties of SrTiO<sub>3</sub>-based interfaces hosting a mobile
two-dimensional electron system (2DES) are strongly influenced by
oxygen vacancies, which form an electronic dichotomy, where strongly
correlated localized electrons in the in-gap states (IGSs) coexist
with noncorrelated delocalized 2DES. Here, we use resonant soft-X-ray
photoelectron spectroscopy to prove the e<sub>g</sub> character of
the IGSs, as opposed to the t<sub>2g</sub> character of the 2DES in
the paradigmatic LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface. We
furthermore separate the d<sub><i>xy</i></sub> and d<sub><i>xz</i></sub>/d<sub><i>xz</i></sub> orbital
contributions based on deeper consideration of the resonant photoexcitation
process in terms of orbital and momentum selectivity. Supported by
a self-consistent combination of density functional theory and dynamical
mean field theory calculations, this experiment identifies local orbital
reconstruction that goes beyond the conventional e<sub>g</sub>-<i>vs</i>-t<sub>2g</sub> band ordering. A hallmark of oxygen-deficient
LaAlO<sub>3</sub>/SrTiO<sub>3</sub> is a significant hybridization
of the e<sub>g</sub> and t<sub>2g</sub> orbitals. Our findings provide
routes for tuning the electronic and magnetic properties of oxide
interfaces through “defect engineering” with oxygen
vacancies
First-Principles Assessment of CdTe as a Tunnel Barrier at the α‑Sn/InSb Interface
Majorana zero modes, with prospective applications in
topological
quantum computing, are expected to arise in superconductor/semiconductor
interfaces, such as β-Sn and InSb. However, proximity to the
superconductor may also adversely affect the semiconductor’s
local properties. A tunnel barrier inserted at the interface could
resolve this issue. We assess the wide band gap semiconductor, CdTe,
as a candidate material to mediate the coupling at the lattice-matched
interface between α-Sn and InSb. To this end, we use density
functional theory (DFT) with Hubbard U corrections, whose values are
machine-learned via Bayesian optimization (BO) [npj Computational Materials 2020, 6, 180]. The results of DFT+U(BO) are validated against angle resolved
photoemission spectroscopy (ARPES) experiments for α-Sn and
CdTe. For CdTe, the z-unfolding method [Advanced Quantum Technologies 2022, 5, 2100033] is used to resolve the contributions of different kz values to the ARPES. We then study
the band offsets and the penetration depth of metal-induced gap states
(MIGS) in bilayer interfaces of InSb/α-Sn, InSb/CdTe, and CdTe/α-Sn,
as well as in trilayer interfaces of InSb/CdTe/α-Sn with increasing
thickness of CdTe. We find that 16 atomic layers (3.5 nm) of CdTe
can serve as a tunnel barrier, effectively shielding the InSb from
MIGS from the α-Sn. This may guide the choice of dimensions
of the CdTe barrier to mediate the coupling in semiconductor–superconductor
devices in future Majorana zero modes experiments