The Bethe-Salpeter equation for the electron-hole correlation function is the state-of-the-art formalism for optical and core spectroscopy in condensed matter. Solutions of this equation yield the full dielectric response, including both the absorption and the inelastic scattering spectra. Here, we present an efficient implementation within the all-electron full-potential code exciting, which employs the linearized augmented plane-wave (L)APW+LO basis set. Being an all-electron code, exciting allows the calculation of optical and core excitations on the same footing. The implementation fully includes the effects of finite momentum transfer which may occur in inelastic x-ray spectroscopy and electron energy-loss spectroscopy. Our implementation does not require the application of the Tamm-Dancoff approximation that is commonly employed in the determination of absorption spectra in condensed matter. The interface with parallel linear-algebra libraries enables the calculation for complex systems. The capability of our implementation to compute, analyze, and interpret the results of different spectroscopic techniques is demonstrated by selected examples of prototypical inorganic and organic semiconductors and insulators. arXiv:1904.05575v1 [cond-mat.mtrl-sci]
We present an ab initio study of core excitations of solid-state materials focusing on the role of electron-hole correlation. In the framework of an all-electron implementation of many-body perturbation theory into the exciting code, we investigate three different absorption edges of three materials, spanning a broad energy window, with transition energies between a few hundred to thousands of eV. Specifically, we consider excitations from the Ti K edge in rutile and anatase TiO2, from the Pb M4 edge in PbI2, and from the Ca L2,3 edge in CaO. We show that the electronhole attraction rules x-ray absorption for deep core states, when local fields play a minor role. On the other hand, the local-field effects introduced by the exchange interaction between the excited electron and the hole dominate excitation processes from shallower core levels, separated by a spin-orbit splitting of a few eV. Our approach yields absorption spectra in good agreement with available experimental data, and allows for an in-depth analysis of the results, revealing the electronic contributions to the excitations, as well as their spatial distribution.
An outstanding hurdle for defect spin qubits in silicon carbide (SiC) is single-shot readout, a deterministic measurement of the quantum state. Here, we demonstrate single-shot readout of single defects in SiC via spin-to-charge conversion, whereby the defect’s spin state is mapped onto a long-lived charge state. With this technique, we achieve over 80% readout fidelity without pre- or postselection, resulting in a high signal-to-noise ratio that enables us to measure long spin coherence times. Combined with pulsed dynamical decoupling sequences in an isotopically purified host material, we report single-spin
T
2
> 5 seconds, over two orders of magnitude greater than previously reported in this system. The mapping of these coherent spin states onto single charges unlocks both single-shot readout for scalable quantum nodes and opportunities for electrical readout via integration with semiconductor devices.
The
search for new wide-band-gap materials is intensifying to satisfy
the need for more advanced and energy-efficient power electronic devices.
Ga2O3 has emerged as an alternative to SiC and
GaN, sparking a renewed interest in its fundamental properties beyond
the main β-phase. Here, three polymorphs of Ga2O3, α, β, and ε, are investigated using X-ray
diffraction, X-ray photoelectron and absorption spectroscopy, and ab initio theoretical approaches to gain insights into their
structure–electronic structure relationships. Valence and conduction
electronic structure as well as semicore and core states are probed,
providing a complete picture of the influence of local coordination
environments on the electronic structure. State-of-the-art electronic
structure theory, including all-electron density functional theory
and many-body perturbation theory, provides detailed understanding
of the spectroscopic results. The calculated spectra provide very
accurate descriptions of all experimental spectra and additionally
illuminate the origin of observed spectral features. This work provides
a strong basis for the exploration of the Ga2O3 polymorphs as materials at the heart of future electronic device
generations.
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