Motion Of Holes Research Articles

On a drift‐diffusion model for perovskite solar cells

AbstractWe introduce a vacancy‐assisted charge transport model for perovskite solar cells. This instationary drift‐diffusion system describes the motion of electrons, holes, and ionic vacancies and takes into account Fermi–Dirac statistics for electrons and holes and the Fermi–Dirac integral of order for the mobile ionic vacancies in the perovskite. The free energy functional we work with corresponds to that choice of the statistical relations. To verify the existence of weak solutions, we consider a problem with regularized state equations and reaction terms on any arbitrarily chosen finite time interval. We motivate its solvability by time discretization and passage to the time‐continuous limit. A priori estimates for the chemical potentials that are independent of the regularization level ensure the existence of solutions to the original problem. These types of estimates rely on Moser iteration techniques and can also be obtained for solutions to the original problem.

Surface thermomigration of 2D voids

In a thermal gradient, surface nanostructures have been experimentally observed to move due to thermomigration. However, analytical models that describe the thermomigration force acting on surfaces are still controversial. In this work, we start from a thermodynamic approach based on the Massieu function, which is used to describe thermomigration of single adatoms, to develop an expression for the velocity of thermomigrating 2D holes. The model can be simplified in two limiting cases: (i) When the hole motion is limited by adspecies diffusion, the velocity is independent from the hole size (as in our experiments). (ii) If the hole motion is limited by the attachment or detachment of species to or from steps, then the velocity is proportional to the hole width. We have studied the thermomigration of 2D monatomic deep holes on Si(100) using low energy electron microscopy. From the velocity measurements taken at different temperatures, we find, using our model, that the sum of the migration energy and the adatom creation energy is 1.95 ± 0.16 eV. This value is consistent with those found by other authors, reinforcing the validity of our thermomigration model.

Localized dopant motion across the 2D Ising phase transition

I investigate the motion of a single hole in 2D spin lattices with square and triangular geometries. While the spins have nearest neighbor Ising spin couplings JJ, the hole is allowed to move only in 1D along a single line in the 2D lattice with nearest neighbor hopping amplitude tt. The non-equilibrium hole dynamics is initialized by suddenly removing a single spin from the thermal Ising spin lattice. I find that for any nonzero spin coupling and temperature, the hole is localized. This is an extension of the thermally induced localization phenomenon [Phys. Rev. Res. 6, 023325 (2024)] to the case, where there is a phase transition to a long-range ordered ferromagnetic phase. The dynamics depends only on the ratio of the temperature to the spin coupling, k_BT / |J|kBT/|J|, and on the ratio of the spin coupling to the hopping J/tJ/t. I characterize these dependencies in great detail. In particular, I find universal behavior at high temperatures, common features for the square and triangular lattices across the Curie temperatures for ferromagnetic interactions, and highly distinct behaviors for the two geometries in the presence of antiferromagnetic interactions due geometric frustration in the triangular lattice.

Particle motion, shadows and thermodynamics of regular black hole in pure gravity

This paper investigates the thermodynamic behaviors and optical properties of regular black holes within pure gravity theories, notable for their absence of singularities. Using both analytical and numerical methods, we analyze the thermodynamics to identify stability and phase transitions, and explore the particle dynamics behavior of regular black holes. We analyze the particle dynamics properties by investigating the effective potential, energy density, angular momentum, ISCO, photon, and shadow radius. We analyze the thermal features by exploring the mass, temperature, specific heat, and Gibbs free energy. Our findings demonstrate that regular black holes exhibit distinct behaviors from traditional singular black holes, providing valuable insights into black hole physics and general relativity. This study suggests new directions for future research in fundamental gravitational theories.

Exciton migration in two-dimensional materials

Excitons play an essential role in the optical response of two-dimensional materials. These are bound states showing up in the band gaps of many-body systems and are conceived as quasiparticles formed by an electron and a hole. By performing real-time simulations in hBN, we show that an ultrashort (few-fs) UV pulse can produce a coherent superposition of excitonic states that induces an oscillatory motion of electrons and holes between different valleys in reciprocal space, leading to a sizeable exciton migration in real space. We also show that an ultrafast spectroscopy scheme based on the absorption of an attosecond pulse in combination with the UV pulse can be used to read out the laser-induced coherences, hence to extract the characteristic time for exciton migration. This work opens the door towards ultrafast electronics and valleytronics adding time as a control knob and exploiting electron coherence at the early times of excitation.

Performance of Density Functionals for Excited-State Properties of Isolated Chromophores and Exciplexes: Emission Spectra, Solvatochromic Shifts, and Charge-Transfer Character.

This study assesses the performance of various meta-generalized gradient approximation (meta-GGA), global hybrid, and range-separated hybrid (RSH) density functionals in capturing the excited-state properties of organic chromophores and their excited-state complexes (exciplexes). Motivated by their uses in solar energy harvesting and photoredox CO2 reduction, we use oligo-(p-phenylenes) and their excited-state complexes with triethylamine as model systems. We focus on the fluorescence properties of these systems, specifically emission energies. We also consider solvatochromic shifts and wave function characteristics. The latter is described by using reduced quantities such as natural transition orbitals (NTOs) and exciton descriptors. The functionals are benchmarked against the experimental fluorescence spectra and the equation-of-motion coupled-cluster method with single and double excitations. Both in isolated chromophores and in exciplexes, meta-GGA functionals drastically underestimate the emission energies and exhibit significant exciton delocalization and anticorrelation between electron and hole motion. The performance of global hybrid functionals is strongly dependent on the percentage of exact exchange. Our study identifies RSH GGAs as the best-performing functionals, with ωPBE demonstrating the best agreement with experimental results. RSH meta-GGAs often overestimate emission energies in exciplexes and yield larger hole NTOs. Their performance can be improved by optimally tuning the range-separation parameter.

Finite-Temperature Hole-Magnon Dynamics in an Antiferromagnet.

Employing the numerically accurate multiple Davydov Ansatz in combination with the thermo-field dynamics approach, we delve into the interplay of the finite-temperature dynamics of holes and magnons in an antiferromagnet, which allows for scrutinizing previous predictions from the self-consistent Born approximation while offering, for the first time, accurate finite-temperature computation of detailed magnon dynamics as a response and a facilitator to the hole motion. The study also uncovers a pronounced temperature dependence of the magnon and hole populations, pointing to the feasibility of potential thermal manipulation and control of hole dynamics. Our methodology can be applied not only to the calculation of steady-state angular-resolved photoemission spectra but also to the simulation of femtosecond terahertz pump-probe and other nonlinear signals for the characterization of antiferromagnetic materials.

The short-term stability and tilting motion of a well-observed low-latitude solar coronal hole

Context. Our understanding of the solar magnetic coronal structure is tightly linked to the shape of open field regions, specifically coronal holes. A dynamically evolving coronal hole coincides with the local restructuring of open to closed magnetic field, which leads to changes in the interplanetary solar wind structure. Aims. By investigating the dynamic evolution of a fast-tilting coronal hole, we strive to uncover clues about what processes may drive its morphological changes, which are clearly visible in extreme ultraviolet (EUV) filtergrams. Methods. Using combined 193 Å and 195 Å EUV observations by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and the Extreme UltraViolet Imager on board the Solar Terrestrial Relations Observatory-Ahead, in conjunction with line-of-sight magnetograms taken by the Helioseismic and Magnetic Imager, also on board the Solar Dynamics Observatory, we tracked and analyzed a coronal hole over 12 days to derive changes in morphology, area, and magnetic field. We complemented this analysis by potential field source surface modeling to compute the open field structure of the coronal hole. Results. We find that the coronal hole exhibits an apparent tilting motion over time that cannot solely be explained by solar differential rotation. It tilts at a mean rate of ∼3.2° day−1 that accelerates up to ∼5.4° day−1. At the beginning of May the area of the coronal hole decreased by more than a factor of three over four days (from ∼13 × 109 km2 to ∼4 × 109 km2), but its open flux remained constant (∼2 × 1020 Mx). Furthermore, the observed evolution is not reproduced by modeling that assumes the coronal magnetic field to be potential. Conclusions. In this study we present a solar coronal hole that tilts at a rate that has yet to be reported in literature. The rate exceeds the effect of the coronal hole being advected by either photospheric or coronal differential rotation. Based on the analysis we find it likely that this is due to morphological changes in the coronal hole boundary caused by ongoing interchange reconnection and the interaction with a newly emerging ephemeral region in its vicinity.

Study on Nonlinear Dynamic Responses of the p–n GaN/AlN Heterojunction in Piezoelectric Semiconductor Composite Fibers

Herein, a p–n GaN/AlN heterojunction in a piezoelectric semiconductor (PSC) composite fiber driven by dynamic magnetic loads is studied. The numerical results of nonlinear dynamic responses of a composite p–n heterojunction subjected to a time‐harmonic magnetic load and a pulse magnetic load are obtained by the finite‐element method, respectively. The effects of different magnetic loads on the I–V curve and piezoelectric behavior of a composite p–n heterojunction are investigated. Numerical results show that when driven by uniformly dynamic magnetic loads, the electromechanical fields show significant asymmetry due to electric nonlinearity. The time‐harmonic magnetic loads drive the round‐trip motion of electrons and holes, and the dynamic electric behaviors driven by pulsed magnetic loads are nonlinear pulse motions. Further analysis of the p–n heterojunction subjected to the bias voltage shows that positive magnetic loads increase the depletion layer's width but decrease the carrier concentration. The results presented in this study have a referential significance to contactless performance tuning of a PSC heterojunction structure and new‐generation piezotronic devices.

Efficiency Enhancement of Biophotovoltaic Solid‐State Solar Cells

Biophotovoltaic solid‐state solar cells are new environmentally friendly solar cells inspired by photosynthesis phenomena. Photosystem I, a complex protein located in the chloroplast of the plant leaves that has a principal role in light absorption, is the most common light absorber used in biophotovoltaic solid‐state solar cells. Low efficiency and low current density are the main challenges in this kind of solar cell. Herein, to vacillate the motion of electrons and holes, carbon nanotubes and tyrosine are used as transfer layers and to increase light absorbance, a solution of Photosystem I with silver nanoparticles as an absorber layer is used. It is shown that the short circuit current density and the efficiency can be enhanced to 6.61 mA cm−2 and 0.83%, respectively which are the highest values for current density and efficiency reported for this kind of solar cell. These enhancements are due to the high electrical conductivity of carbon nanotubes, proper porosity of tyrosine, and the localized surface plasmon resonance of silver nanoparticles induced under light irradiation. The results can illuminate hopes and dreams for biophotovoltaic solid‐state solar cells with higher current density and higher efficiency.

Quantifying hole-motion-induced frustration in doped antiferromagnets by Hamiltonian reconstruction

Unveiling the microscopic origins of quantum phases dominated by the interplay of spin and motional degrees of freedom constitutes one of the central challenges in strongly correlated many-body physics. When holes move through an antiferromagnetic spin background, they displace the positions of spins, which induces effective frustration in the magnetic environment. However, a concrete characterization of this effect in a quantum many-body system is still an unsolved problem. Here we present a Hamiltonian reconstruction scheme that allows for a precise quantification of hole-motion-induced frustration. We access non-local correlation functions through projective measurements of the many-body state, from which effective spin-Hamiltonians can be recovered after detaching the magnetic background from dominant charge fluctuations. The scheme is applied to systems of mixed dimensionality, where holes are restricted to move in one dimension, but SU(2) superexchange is two-dimensional. We demonstrate that hole motion drives the spin background into a highly frustrated regime, which can quantitatively be described by an effective J1–J2-type spin model. We exemplify the applicability of the reconstruction scheme to ultracold atom experiments by recovering effective spin-Hamiltonians of experimentally obtained 1D Fermi-Hubbard snapshots. Our method can be generalized to fully 2D systems, enabling promising microscopic perspectives on the doped Hubbard model.

Impact of System-F in Delivering Vascular Plugs for Aortic Side Branch Embolization During Endovascular Aneurysm Repair.

This study aimed to illustrate the utility of our original system to deliver vascular plugs into aortic side branches during endovascular aneurysm repair (EVAR). Our device, which we named "System-F," consists of a 14 Fr sheath, a 12 Fr long sheath with a side hole, a stiff guidewire as a shaft, and a parallelly-inserted delivery catheter navigated through the side hole into the aneurysm sac. Vertical motion and horizontal rotation of the side hole allow multidimensional movement of the delivery catheter within the aneurysm. This system was applied in 7 cases undergoing EVAR; 4 inferior mesenteric arteries and 14 lumbar arteries were embolized using vascular plugs. Type II endoleak (T2EL) was not observed in the follow-up survey of any case. Conclusion: The applicability of System-F for vascular plug placement in the side branches of abdominal aortic aneurysms has the potential to achieve high delivery capability and be widely applied for the prevention of T2EL. System-F has potential to change the strategies of pre-EVAR embolization.

Gas dynamical friction as a binary formation mechanism in AGN discs

ABSTRACT In this paper, we study how gaseous dynamical friction (DF) affects the motion of fly-by stellar-mass black holes (sBHs) embedded in active galactic nucleus (AGN) discs. We perform three-body integrations of the interaction of two co-planar sBHs in nearby, initially circular orbits around the supermassive black hole. We find that DF can facilitate the formation of gravitationally bound near-Keplerian binaries in AGN discs, and we delineate the discrete ranges of impact parameters and AGN disc parameters for which such captures occur. We also report trends in the bound binaries’ eccentricity and sense of rotation (prograde or retrograde with respect to the background AGN disc) as a function of the impact parameter of the initial encounter. While based on an approximate description of gaseous friction, our results suggest that binary formation in AGN discs should be common and may produce both prograde and retrograde, as well as both circular and eccentric binaries.

Exact hole-induced resonating-valence-bond ground state in certain U=∞ Hubbard models

We prove that the motion of a single hole induces the nearest-neighbor resonating-valence-bond ground state in the $U=\ensuremath{\infty}$ Hubbard model on a triangular cactus---a treelike variant of a kagome lattice. The result can be easily generalized to $t\ensuremath{-}J$ models with antiferromagnetic interactions $J\ensuremath{\ge}0$ on the same graphs. This is a weak converse of Nagaoka's theorem of ferromagnetism on a bipartite lattice.

Meet the Parents: The Progenitor Binary for the Supermassive Black Hole Candidate in E1821+643

The remnants of binary black hole mergers can be given recoil kick velocities up to 5000 km s−1 due to anisotropic emission of gravitational waves. E1821+643 is a recoiling supermassive black hole candidate with spectroscopically offset, broad emission lines, consistent with motion of the black hole at ∼2100 km s−1 along the line of sight relative to its host galaxy. This suggests a recoil kick of ∼2200 km s−1. Such a kick is powerful enough to eject E1821+643 from its M gal ∼ 2 × 1012 M ⊙ host galaxy. In this work, we address the question: assuming that E1821+643 is a recoiling black hole, what are the likely properties of the progenitor binary that formed E1821+643? Using astrophysically motivated priors, we infer that E1821+643 was likely formed from a binary black hole system with masses of , (90% credible intervals). Given our model, the black holes in this binary were likely to be spinning rapidly with dimensionless spin magnitudes of , . Such a high recoil velocity is impossible for spins aligned to the orbital angular momentum axis. This suggests that the progenitor for E1821+643 merged in hot gas, which is thought to provide an environment where spin alignment from accretion proceeds slowly relative to the merger timescale. We infer that E1821+643, if it is a recoiling black hole, is likely to be a rapidly rotating black hole with a dimensionless spin of χ = 0.92 ± 0.04. A 2.6 × 109 M ⊙ black hole, recoiling from a gas-rich environment at v ∼ 2200 km s−1, is likely to persist as an active galactic nucleus for ∼107 yr, in which time it traverses ∼25 kpc.

Morphology of Broad Emission Lines from Binary Supermassive Blackholes

Accretion onto a blackhole can indue extreme radiation stimulating emission lines in nearby gases. In the deep gravitational well, these clouds move at speeds up to 10,000 km/s, and so broadens the emission lines via the relativistic Doppler Effect. These broad emission lines on spectra are the most prominent feature of AGNs. The region around central black hole, where such broad emission lines are produced, is known as the broad-line region (BLR). We developed a self-consistent model to describe both the geometry of the BLR and the dynamics of the gas clouds in the BLR. The motion of clouds is described by a series of Keplerian orbits. The spectral shift of emission line can be derived by the radial velocity at each point in Keplerian orbits. Assuming that the BLR is stable, that is, the structure and distribution of gas in BLR doesn’t change over a considerable period of time, the accumulated emission line profile can be constructed by simple addition of all Keplerian orbits in the BLR. By comparing the calculated profiles to spectra observed in SDSS (Sloan Digital Sky Survey), we found that our model can satisfactorily match most observed profiles. We attempted to review and summarize potential binary AGNs. We applied the model to the study of binary AGNs and their profiles of emission lines. We considered the velocity offset due to mutual Keplerian motion of black holes in binary and added their respective profiles to produce the final, resulting emission line profile from binary AGNs. Three kinds of emission line profiles are featured in our simulations: twin-peak structures where two strong broad-lines are present; sub-peak structures where a smaller but still visible emission line accompanies the dominant line; single broad emission peak but with significant velocity offset from the systematic redshift that is derived from the narrow emission-lines on the same spectrum. We then analyzed 1,348 AGN spectra with high S/N ratio in SDSS database, and selected 26 as candidate binary supermassive blackhole systems. These candidates are valuable for following-up observation, their binary nature could be confirmed by detecting the profile variation due to orbital motions.

Aeroelastic analysis and active control of one-dimensional acoustic black hole structures in supersonic airflow

In this paper, the aeroelastic characteristic and active control of one-dimensional acoustic black hole structures in supersonic airflow are analyzed. Utilizing Hamilton's principle, the equation of motion of the one-dimensional acoustic black hole (ABH) structures in supersonic airflow with attached piezoelectric elements is established. The first-order piston theory is used to simulate the aerodynamic pressure of the composites, and the controller is designed based on speed feedback and proportional feedback algorithms. Through numerical simulations, the variation of the natural frequency concerning the aerodynamic pressure is carried out studies to determine the flutter point of the system. Besides, the influences of piezoelectric actuators and sensors on the aeroelastic flutters of one-dimensional ABH structures are analyzed. Results show that the velocity negative feedback can improve the critical pneumatic pressure of the system, thereby increasing the aerodynamic elastic stability of the composite structure. The kinetic and strain energies of the proposed system varied with the different feedback gains are also investigated. We found that the application of velocity negative feedback can effectively suppress the vibration of the proposed system, whereas, there are no apparent effects on the dynamics for varying the proportional feedback.

Моделирование процессов в полупроводниковых структурах при радиационном воздействии

The radiation impact of outer space has an impact on electronic equipment and their characteristics change. The paper considers the simulation of the process of motion of holes generated in the oxide, which cause local deformation of the potential field of the lattice. Jumps of polarons make the motion of holes dispersed and highly dependent on temperature and oxide thickness. The article presents the temperature dependences of the voltage shift after a single radiation pulse. When holes move to the Si/SiO2 interface, some of the holes are captured by traps. The effect of the influence of the capture cross section on the increase in holes in traps is noticeable in the electrical dependence of the increase in the number of oxide traps immediately after irradiation. The graphs of the dependence of the threshold voltage shift due to oxide traps on the electric field in the oxide are plotted in this work. Immediately after its appearance, the charge of oxide traps begins to be neutralized. To study this process, time, temperature, and electrical dependences are plotted, and the ratio of trapped electrons to the number of trapped holes is shown for dry and wet gate oxide technologies at different oxide thicknesses. Thus, the influence of temperature and radiation influences on the motions of holes and oxide traps in semiconductor structures is shown.

Dressing due to correlations strongly reduces the effect of electron-phonon coupling

We investigate the difference between the coupling of a bare carrier to phonons versus the coupling of a correlations-dressed quasiparticle to phonons, and show that latter may be weak even if the former is strong. Specifically, we analyze the effect of the hole-phonon coupling on the dispersion of the quasiparticle that forms when a single hole is doped into a cuprate layer. To model this, we start from the three-band Emery model supplemented by the Peierls modulation of the $p$-$d$ and $p$-$p$ hoppings due to the motion of O ions. We then project onto the strongly correlated $U_{dd}\rightarrow \infty$ limit where charge fluctuations are frozen on the Cu site. The resulting effective Hamiltonian describes the motion of a doped hole on the O sublattice, and its interactions with Cu spins and O phonons. We show that even though the hole-phonon coupling is moderate to strong, it leads to only a very minor increase of the quasiparticle's effective mass as compared to its mass in the absence of coupling to phonons, consistent with a weak coupling to phonons of the correlations-dressed quasiparticle. We explain the reasons for this suppression, revealing why it is expected to happen in any systems with strong correlations.

Piercing of a boson star by a black hole

New light fundamental fields are natural candidates for all or a fraction of dark matter. Self-gravitating structures of such fields might be common objects in the universe, and could comprise even galactic halos. These structures would interact gravitationally with black holes, a process of the utmost importance since it dictates their lifetime, the black hole motion, and possible gravitational radiation emission. Here, we study the dynamics of a black hole piercing through a much larger fully relativistic boson star, made of a complex minimally coupled massive scalar without self-interactions. As the black hole pierces through the bosonic structure, it is slowed down by accretion and dynamical friction, giving rise to gravitational-wave emission. Since we are interested in studying the interaction with large and heavy scalar structures, we consider mass ratios up to $q\ensuremath{\sim}10$ and length ratios $\mathcal{L}\ensuremath{\sim}62$. Somewhat surprisingly, for all our simulations, the black hole accretes more than 95% of the boson star material, even if an initially small black hole collides with large velocity. This is a consequence of an extreme ``tidal capture'' process, which binds the black hole and the boson star together, for these mass ratios. We find evidence of a ``gravitational atom'' left behind as a product of the process.