Hole States Research Articles

Self-interaction-correction and electron removal energies

The paper addresses the problem of the self-interaction correction (SIC) in static calculations of atoms and molecules. Key observable is the electron removal energy, the energy required to remove one electron from the given system and to leave it in a definite hole state whereby we discuss hole states not only in the Highest Occupied Molecular Orbital (HOMO), but also deeper lying holes. To that end, we employ a newly developed technique to compute a stationary state for a configuration with a definite hole in a chosen single-particle state. We also compare two different definitions of removal energies, first, the genuine one taking the difference of the total energy of the original system and the energy of final system sustaining the hole, and second, simply the single-particle energy in the original system. According to Koopman’s theorem, both should be close to each other. Four different systems are considered, one atom and three molecules with different bond types, covalent, metallic, and dipolar. The general result is that any SIC brings considerable improvement as compared to the initial Local-Density Approximation (LDA), the better the closer the hole stays to the HOMO. There are variations between different SIC approximations whereby systems with strong binding (atom and covalent molecule) show least variations. Here, the quality of Koopman’s theorem is very satisfying for the HOMO and degrades slightly toward deeper binding. Systems with metallic or dipolar binding are more reactive and show stronger changes with approximation and hole level.

Theoretical studies on the cascade decay processes of 1s-core-hole state of Ar ion

The cascade decay processes from the 1s-core-hole state of Ar ion have been studied theoretically via straightforward construction of de-excitation trees and high-accuracy level-to-level calculations using the flexible atomic code (FAC). The final charge state distribution (FCSD), contributions of different cascade routes to the FCSD, and the main production pathways of each Ari+ ion which are never discussed before are analyzed carefully. It is found that the de-excitation processes is very complex and Auger decay is the predominant channel, the most probable final charge state is 4, while Ar+ to Ar6+ ions can be produced in the 5-step Auger cascade decay processes for Ar+1s−1 hole state. Ar+ is mainly derived from KM23 channel, Ar2+ is associated mainly with KL23 channel, when Ar3+, Ar4+, Ar5+ and Ar6+ions are mainly coming from KL23M23, KL23L23, KL1L23 and KL1L1 channels, respectively. Present studies would be helpful for further researches on the cascade decay processes of deep inner-shell hole states, and for the interaction between x-ray free-electron lasers and matter.

Hawking radiation and page curves of the black holes in thermal environment

As realistic objects in the Universe, the black holes are surrounded by complex environment. By taking the effect of thermal environment into account, we investigate the evaporation process and the time evolutions (page curves) of the entanglement entropies of Hawking radiation of various types of black holes. It is found that the black holes with the thermal environments evaporate slower than those without the environments due to the environmental contribution of the energy flux in addition to Hawking radiation. For Schwarzschild black hole and Reissner-Nordström black hole in flat spaces, when the initial temperature of the black hole is higher than the environment temperature, the black holes evaporate completely and the Hawking radiation is eventually purified. For Schwarzschild-AdS black hole, it will evaporate completely and the Hawking radiation is purified when the environment temperature is lower than the critical temperature. Otherwise, it will reach an equilibrium state with the environment and the radiation is maximally entangled with the black hole. Our results indicate that the final state of the black hole is determined by the environmental temperature and the temporal evolution and the speed of the information purification process characterized by the page curve of the Hawking radiation is also influenced by the thermal environment significantly.

Tuning electronic structures and optical properties in CdSe/CdS Dot-in-rod colloidal nanostructures: Atomistic tight-binding theory

Using the atomistic tight-binding theory, in this study, the electronic structures and optical properties of CdSe/CdS dot-in-rod nanocrystals are modified by engineering the core and rod diameters. The ground electron states favor an s-like orbital, while the ground hole states are formed by light hole-like characteristics. The quantum confinement effect is attributed to the reduction in excitonic band gaps as the core and rod diameters increase. Changing the core and rod sizes produces excitonic band gaps across the visible light spectra. The highest oscillation strength, excitonic-binding energy, and dark-bright excitonic splitting are witnessed at a 3.0 nm CdSe core diameter. The oscillation strength, excitonic-binding energy, and dark-bright excitonic splitting decrease as the CdS rod diameters increase. This study highlights the importance of theoretically understanding and controlling the active materials’ structural parameters in optoelectronic technology.

Tuning Valleys and Wave Functions of van der Waals Heterostructures by Varying the Number of Layers: A First‐Principles Study

In van der Waals heterostructures of 2D transition-metal dichalcogenides (2D TMDCs) electron and hole states are spatially localized in different layers forming long-lived interlayer excitons. Here, the influence of additional electron or hole layers on the electronic properties of a MoS2 /WSe2 heterobilayer (HBL), which is a direct bandgap material, is investigated from first principles. Additional layers modify the interlayer hybridization, mostly affecting the quasiparticle energy and real-space extend of hole states at the Γ and electron states at the Q valleys. For a sufficient number of additional layers, the band edges move from K to Q or Γ, respectively. Adding electron layers to the HBL leads to more delocalized K and Q states, while Γ states do not extend much beyond the HBL, even when more hole layers are added. These results suggest a simple and yet powerful way to tune band edges and the real-space extent of the electron and hole wave functions in TMDC heterostructures, potentially affecting strongly the lifetime and dynamics of interlayer excitons.

Charged 4D Einstein-Gauss-Bonnet black hole: Vacuum solutions, Cauchy horizon, thermodynamics

In this paper, we investigate the four-dimensional Einstein-Gauss-Bonnet black hole. The thermodynamic variables and equations of state of black holes are obtained in terms of a new parameterization. We discuss a formulation of the van der Waals equation by studying the effects of the temperature on P-V isotherms. We show the influence of the Cauchy horizon on the thermodynamic parameters. We prove by different methods, that the black hole entropy obey area law (plus logarithmic term that depends on the Gauss-Bonnet coupling {\alpha}). We propose a physical meaning for the logarithmic correction to the area law. This work can be extended to the extremal EGB black hole, in that case, we study the relationship between compressibility factor, specific heat and the coupling {\alpha}.

Room temperature CNOT operation in a diluted magnetic semiconductor quantum dot

Population evolution in a magnetic impurity doped semiconductor quantum dot has been studied by applying a sequence of pulses of chosen pulse area. By optical excitation mechanism, the population in (J_z=+3/2), heavy hole state of valence band is carried over to (J_z=-3/2), valance band state, via the (J=+1/2) conduction band states. The injected microwaves entangle conduction band states. This arrangement is successfully employed to ascertain quantum CNOT operation, and the calculation predicts maximum fidelity of 80\% for the CNOT operation.

New effective precession spin for modeling multimodal gravitational waveforms in the strong-field regime

Accurately modeling the complete gravitational-wave signal from precessing binary black holes through the late inspiral, merger, and ringdown remains a challenging problem. The lack of analytic solutions for the precession dynamics of generic double-spin systems, and the high dimensionality of the problem, obfuscate the incorporation of strong-field spin-precession information into semianalytic waveform models used in gravitational-wave data analysis. Previously, an effective precession spin ${\ensuremath{\chi}}_{p}$ was introduced to reduce the number of spin degrees of freedom. Here, we show that ${\ensuremath{\chi}}_{p}$ alone does not accurately reproduce higher-order multipolar modes, in particular the ones that carry strong imprints due to precession such as the (2,1)-mode. To improve the higher-mode content, and in particular to facilitate an accurate incorporation of precession effects in the strong-field regime into waveform models, we introduce a new dimensional reduction through an effective precession spin vector, ${\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\chi}}}_{\ensuremath{\perp}}$, which takes into account precessing spin information from both black holes. We show that this adapted effective precession spin (i) mimics the precession dynamics of the fully precessing configuration remarkably well, (ii) captures the signature features of precession in higher-order modes, and (iii) reproduces the final state of the remnant black hole with high accuracy for the overwhelming majority of configurations. We demonstrate the efficacy of this two-dimensional precession spin in the strong-field regime, paving the path for meaningful calibration of the precessing sector of semianalytic waveform models with a faithful representation of higher-order modes through merger and the remnant black hole spin.

First-principles investigation of the electronic and thermoelectric properties of SiGe doped with Sn and one percent B

Silicon-Germanium (SiGe) has recently attracted much interest as a room temperature thermoelectric (TE) material for converting heat into electrical output power. With the advantage of silicon being non-toxic, cost-effective, and abundant on earth, a silicon base TE material has a promising future. A first-principle calculation based on the fully self-consistent Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA) to treat several forms of chemical disorders of SiGe by Sn-doping was carried out. In SiGe1-xSnx, as the Sn content increases the Fermi level shifts to the conduction band edge. Similarly, in Si1-xSnxGe, a high Sn content (x = 0.4 to 0.9) results in the Fermi level shifting to the conduction band edge. On the contrary, a low amount of Sn content (x = 0.1 to 0.3) causes the Fermi level to fluctuate between the conduction band and the valence band states. With the addition of 1% Boron impurity to the alloys Si1-xSnxGe and SiGe1-xSnx, the number of carriers (electron and hole) states was enhanced by 0.05 states/eV. This makes the alloys Si0.3Sn0.69B0.01Ge and SiGe0.4Sn0.59B0.01 promising for application as n-type electrodes in a thermoelectric generator (TEG).

Approach to achieving ap-type transparent conducting oxide: Doping of bismuth-alloyedGa2O3with a strongly correlated band edge state

$P$-type doping in oxides is usually difficult due to their low valence-band energy. In order to make them $p$ type, the electronic structure of the oxides should be fundamentally changed; that is, the occupied valence band should be raised significantly. Here, using first-principles calculations, we propose that by adding a small amount of ${\mathrm{Bi}}_{2}{\mathrm{O}}_{3}$ into ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ to form dilute ${({\mathrm{Bi}}_{x}{\mathrm{Ga}}_{1--x})}_{2}{\mathrm{O}}_{3}$ alloys and, more importantly, with properly chosen dopants, we can achieve efficient $p$-type doping in a transparent oxide. We show that adding a few percent of Bi to ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ leads to an intermediate valence band that is sufficiently high in energy to facilitate $p$-type doping; however, the commonly expected shallow acceptors, Mg and Zn substitution on the Ga site (${\mathrm{Mg}}_{\mathrm{Ga}}$ and ${\mathrm{Zn}}_{\mathrm{Ga}}$), are still deep acceptors, whereas the expected deep acceptor, ${\mathrm{Cu}}_{\mathrm{Ga}}$, actually creates a relatively shallow level in ${({\mathrm{Bi}}_{x}{\mathrm{Ga}}_{1--x})}_{2}{\mathrm{O}}_{3}$ alloys. This trend is opposite to what is found in pure ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$. The puzzling behavior of the acceptor levels in the ${({\mathrm{Bi}}_{x}{\mathrm{Ga}}_{1--x})}_{2}{\mathrm{O}}_{3}$ alloys is attributed to the polaronic character of the holes in the Zn- and Mg-doped cases, and the decoupling of the hole state and the valence-band edge in the Cu-doped case. This understanding provides insights into the realization of $p$-type doping in dilute ${({\mathrm{Bi}}_{x}{\mathrm{Ga}}_{1--x})}_{2}{\mathrm{O}}_{3}$ alloys and paves a way to dope semiconductor materials with a strongly correlated band edge state, i.e., materials with a tendency to form polaronic acceptor or donor states.

Temperature modeling for wellbore circulation and shut-in with application in vertical geothermal wells

This paper presents the development and application of a numerical model to predict the temperature distribution of the vertical borehole system during circulation and shut-in conditions. The presented model can simulate the transient temperature disturbances of the drilling fluids, the drill string, the casing strings, the cement behind the casing, and also the surrounding rock formation. The transient temperature profiles resulting from the presented model are compared with a CFD (Computational Fluid Dynamics) model using ANSYS-FLUENT. A good agreement between the results of both models is found. However, the developed model has a great advantage over the CFD model in terms of computation time and power. In addition, a comparison with field results showed a good agreement between the simulated temperature and the experimental data using the presented model. Moreover, a sensitivity analysis on the influence of the size and length of the bottom hole assembly (BHA) on the temperature of the borehole is performed. The analysis is performed for both static and dynamic conditions. The results showed a significant influence of the BHA size on the static and dynamic bottom hole temperature. However, the length of the BHA only affects the dynamic bottom hole temperature. • We present a transient numerical model for wellbore system temperature simulation. • Prediction of wellbore temperature during flowing and shut-in conditions. • Feasible for complex wellbore with multi-casing and drill-string sizes. • Application and comparison with field temperature log data. • Effect of the BHA design on the bottom hole temperature.

A level set approach to simulate grain growth with an evolving population of second phase particles

In numerous polycrystalline materials, grain size is controlled by second phase particles (SPPs) that hinder the grain boundaries (GBs) by pinning mechanisms. The Smith–Zener pinning (SZP) model describes the physical interaction between SPPs and GBs. Both of them can evolve when applying a heat treatment to the material. As industrial forging processes involve hot deformation steps near the solvus temperature, it is thus of prime importance to characterize the evolution of the SPPs due to their impact on the final microstructure, notably on the grain size. The level set (LS) method is classically used to describe the influence of SPPs on grain growth (GG) by considering the simulated particles as inert and represented by static holes in the used finite element (FE) mesh. A new formalism to model GG mechanism under the influence of the SZP phenomenon, able to take into account evolving particles is proposed. It involves the representation of SPPs by a LS function and a particular numerical treatment around the grain interfaces encountering SPP, making possible the modelling of SPPs evolution without altering the undergoing pinning pressure. Validation and comparison of the new method regarding previous FE-LS formulation in 2D and 3D simulations and an application on GG under the influence of dissolving particles are described.

Quantification of Ni L2,3 core-hole relaxation pathways utilizing Auger photoelectron coincidence spectroscopy

Ni $LVV$ Auger spectra, in coincidence with the corresponding $2{p}_{1/2}$, $2{p}_{3/2}$, and $6\phantom{\rule{0.28em}{0ex}}\text{eV}$ satellite photoelectrons, have been used to examine electron correlation and itinerance effects in Ni. In coincidence with the $2{p}_{3/2}$ core level, the Auger spectral shape is represented by localized $3{d}^{8}$ and itinerant valence final states with an additional $3{d}^{7}$ Auger shake-up contribution. The spectra in coincidence with the $6\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ satellite probe the decay of localized $2{p}^{5}3{d}^{9}$ double hole states, leading to $3{d}^{7}$ final states. It is found that a fraction of the double hole states delocalize before the Auger decay. A similar delocalization is observed for the double hole states produced by the ${L}_{2}{L}_{3}{M}_{45}$ Coster-Kronig process, and the delocalization rates have been determined.

Tailoring the Electronic Structures of the La2NiMnO6 Double Perovskite as Efficient Bifunctional Oxygen Electrocatalysis

Double perovskite oxides are one of the most promising bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) due to their adjustable electronic structures via doping with different metal cations or engineering of defects. Herein, we report a systematic study on the tuning of the electronic structure of La2-xSrxNiMnO6 with 0 ≤ x ≤ 1.0 to promote the bifunctional OER/ORR activity. The bifunctional index (ΔE) is substantially reduced with increasing of Sr contents and achieves an optimal value of 0.85 V for La1.4Sr0.6NiMnO6, exceeding that of widely studied LaNiO3. Our study on electronic structures reveals that the enhancement of the ORR and OER activities strongly correlates with the appearance of Ni3+ oxidation states and the upshift of the O 2p-band center promoted by Sr doping. Furthermore, an increase of hole states, derived from Ni3+ states, reduces the energy barrier for the electron transfer from 0.44 to 0.12 eV and hence improves the intrinsic OER activities. The tuning of the electronic structure that leads to higher OER and ORR activities in La2-xSrxNiMnO6 can be extended to other materials for the design of active bifunctional electrocatalysts.

Intrinsic and extrinsic spin-orbit coupling and spin relaxation in monolayer PtSe2

Monolayer PtSe$_2$ is a semiconducting transition metal dichalcogenide characterized by an indirect band gap, space inversion symmetry, and high carrier mobility. Strong intrinsic spin-orbit coupling and the possibility to induce extrinsic spin-orbit fields by gating make PtSe$_2$ attractive for fundamental spin transport studies as well as for potential spintronics applications. We perform a systematic theoretical study of the spin-orbit coupling and spin relaxation in this material. Specifically, we employ first principles methods to obtain the basic orbital and spin-orbital properties of PtSe$_2$, also in the presence of an external transverse electric field. We calculate the spin mixing parameters $b^2$ and the spin-orbit fields $\Omega$ for the Bloch states of electrons and holes. This information allows us to predict the spin lifetimes due to the Elliott-Yafet and D'yakonov-Perel mechanisms. We find that $b^2$ is rather large, on the order of $10^{-2}$ and $10^{-1}$, while $\Omega$ varies strongly with doping, being about $10^{3} - 10^{4}$\,ns$^{-1}$ for %typical Fermi levels in the interval $(10-100)$ meV, carrier density in the interval $10^{13}-10^{14}$\,cm$^{-2}$ at the electric field of 1 V/nm. We estimate the spin lifetimes to be on the picosecond level.

A dynamical mechanism for the Page curve from quantum chaos

If the evaporation of a black hole formed from a pure state is unitary, the entanglement entropy of the Hawking radiation should follow the Page curve, increasing from zero until near the halfway point of the evaporation, and then decreasing back to zero. The general argument for the Page curve is based on the assumption that the quantum state of the black hole plus radiation during the evaporation process is typical. In this paper, we show that the Page curve can result from a simple dynamical input in the evolution of the black hole, based on a recently proposed signature of quantum chaos, without resorting to typicality. Our argument is based on what we refer to as the “operator gas” approach, which allows one to understand the evolution of the microstate of the black hole from generic features of the Heisenberg evolution of operators. One key feature which leads to the Page curve is the possibility of dynamical processes where operators in the “gas” can “jump” outside the black hole, which we refer to as void formation processes. Such processes are initially exponentially suppressed, but dominate after a certain time scale, which can be used as a dynamical definition of the Page time. In the Hayden-Preskill protocol for young and old black holes, we show that void formation is also responsible for the transfer of information from the black hole to the radiation. We conjecture that void formation may provide a microscopic explanation for the recent semi-classical prescription of including islands in the calculation of the entanglement entropy of the radiation.

Theoretical Investigation on Structural and Magnetic Properties of Mn-doped and C co-doped Zn12Se12 Nanoclusters

Background: Mn doped ZnSe low dimensional materials are attractive for different biological labels, gene silencing and dilute-magnetic device. ZnSe clusters are one of the basic building blocks of quantum dots and even cluster-assembled nanodevices, stable structures of undoped ZnSe clusters were established by previous pioneering work, and the Mn doped ZnSe clusters had been investigated, but the stable clusters in the ferromagnetic state have not been found yet. Objective: Our work is mainly based on Mn doped clusters (Mn2Zn10Se12) and C codoped clusters (Mn2Zn10Se11) structure, magnetic properties through theoretical calculations. Methods: First principle density functional theory calculation with Dmol3 is used to execute all calculations. Results: Mn atoms prefer to substitute the nearest neighbor Zn atom sites in the rhombi part, and C atom prefers to occupy Se atom sites with shortest Mn-C bond length in Zn12Se12 nanocluster doping. Mn doped clusters (Mn2Zn10Se12) are in antiferromagnetic states and the most stable C codoped clusters (Mn2Zn10Se11) are in ferromagnetic states. Magnetic behavior localized at the 3d orbitals of transitional metal Mn, 4p orbital of atom Se and 2p orbital of C atom. Mn2Zn10Se12 clusters are in antiferromagnetic states as the p-d hybridization introduced Mn-Mn superexchange mechanism. For the ferromagnetism of Mn2Zn10Se12 nanocluster, hole mediated double exchange mechanism introduced by C atom p-d hole state hybridization has been suggested. Conclusion: The codoping of C atom can stabilize the ferromagnetism of clusters through hole mediated double exchange mechanism, which may be meaningful for the exploring materials for cluster- assembled spin-electronic devices.

Effects of dissipative electron tunneling manifested in the photocurrent of a GaAs p-i-n photodiode with a double InAs quantum dot layer

We report on the results of experimental studies of the photocurrent (PC) of photodiodes based on GaAs p-i-n structures with InAs/GaAs(001) double asymmetric quantum dot (DAQD) arrays obtained by self-assembling in the process of low-pressure metal-organic vapor phase epitaxy (LP-MOVPE). Three peaks were observed in the dependence of the PC on the reverse bias, measured under photoexcitation with a photon energy equal to the energy of the interband ground state transition in larger InAs QDs. These peaks were attributed to photoexcitation of electrons from the ground hole states in larger QDs into the ground electron states followed by resonant dissipative (with absorption or emission of optical phonons) and conservative tunneling into the GaAs conduction band via the ground electron states in smaller QDs. The PC dependence on the bias voltage agrees qualitatively with the theoretical field dependence of the probability of 1D dissipative tunneling between the QDs.

Quasibound states of charged dilatonic black holes

Investigation of quasibound states of black holes is significant for expected ultralight particles, as well as black holes through gravitational waves. We first investigate quasibound states of a massive scalar field for dilatonic charged black holes via numerical analysis. We study the complex eigenfrequencies of the massive scalar field in a wide range of gravitational fine structure constant $\ensuremath{\mu}M$ in detail, and show the effects of charge. Further, we study the eigenfrequencies of the massive field through an analytical approach by matching the near horizon solution and far field solution, and find its spectra for excited states by the iteration method. We demonstrate that the numerical solution and analytical solution perfectly agree with each other in the region where charge of the black hole is large, both for real and imaginary parts of the eigenfrequencies.

Near-threshold two-photon double ionization of Kr in the vacuum ultraviolet

We report angle-resolved measurements on photoelectrons emitted upon near-threshold two-photon double ionization (TPDI) of Kr irradiated by free-electron laser (FEL) pulses. These photoelectron angular distributions (PADs) are compared with the results of semirelativistic $R$-matrix calculations. As reported by Augustin et al. [Phys. Rev. A 98, 033408 (2018)], it is found that the presence of autoionizing resonances within the bandwidth of the exciting FEL pulse strongly influences the PADs. In contrast to measurements on lower-$Z$ targets such as Ne and Ar, the larger spin-orbit interaction, inherent in $4p$-subshell hole states of Kr, permits us to resolve and study PADs associated with some of the fine-structure components of the ${\mathrm{Kr}}^{+}$ and ${\mathrm{Kr}}^{2+}$ ions.