Electron irradiation is essential for materials characterization and modification, though the fundamental interactions between incident electrons and host materials remain under investigation. Here, we employ first-principles simulations to study electron dynamics under external electron irradiation. We quantify differences in key observables, including kinetic energy loss, secondary electron emission, and backscattered electrons, between classical and quantum mechanical descriptions of the incident electron. Around 400 eV incident energy, we identify significant differences in backscattered electron yields between classical point-charge and quantum wave-packet descriptions, whereas the quantum-mechanical effects diminish at incident energies above 600 eV. These differences highlight the critical importance of quantum effects in electron irradiation phenomena that occur in a specific energy range of the incident electron. Our results provide clear guidance for selecting appropriate incident, electron descriptions based on kinetic-energy regimes, identify a targeted experimental window for isolating quantum-only backscattering, and enable the rational design of 2D materials for nanofabrication and high-resolution electron-beam technologies.

Optical and magneto-optical properties of magnetic materials have been widely exploited to characterize magnetic structures and phenomena, however, their temperature dependence is not well understood. This study implements the supercell approach with thermal lattice and magnetic disorders to obtain optical and magneto-optical spectra at finite temperatures based on Williams-Lax theory. Our results show that large optical spectrum signals are generated at photon energies below 1 eV, originating from the phonon- and magnon-assisted intraband transitions as lattice and magnetic temperatures increase. In addition, the prominent peak near 2.7 eV is redshifted proportionally to magnetic temperature but depends much less on lattice temperature. By analyzing unfolded bands, we show that the reduction of exchange splitting due to the thermal demagnetization causes this redshift. Our unfolded electronic band structure with magnetic disorder shows band kinks, which are characteristic evidence of the coupling between electrons and magnetic excitations. First-order magneto-optical spectra at finite temperature are also predicted, but due to their small magnitude suffer more from sampling errors. We discuss the effect of zero-point vibrations and the connection of these simulations to the Drude model for intraband transitions.

Quantum computers, currently in the noisy intermediate-scale quantum (NISQ) era, have started to provide scientists with a novel tool to explore quantum physics and chemistry. While several electronic systems have been extensively studied, Frenkel excitons, as prototypical optical excitations, remain among the less-explored applications. Here, we first use variational quantum deflation to calculate the eigenstates of the Frenkel Hamiltonian and evaluate the observables based on the oscillator strength for each eigenstate. Furthermore, using NISQ quantum computers requires performing error mitigation techniques alongside simulations. To deal with noisy qubits, we developed a deep-learning-based framework combined with a post-selection technique to learn the noise pattern and mitigate the error. Our mitigation methods work well and outperform the conventional post-selection and remain valid on real hardware.

Reduced exciton mass (μ) was recently reported to correlate strongly with a framework distortion in a series of nine single-layer (2D) metal-halide perovskite (HOIP) compounds. Specifically, μ was observed to increase in tandem with an alternating PbI4 octahedral tilt about an in-plane axis. In this work, we use group representation theory to decompose the observed framework distortions into displacive symmetry modes of a common high-symmetry parent framework. We find that all nine distorted frameworks involve linear combinations of the same six symmetry modes, which have been reported to contribute to the framework distortions of a wide range of HOIP compounds. We show that these modes have highly correlated impacts on the band structure. To differentiate causation from correlation, we vary the amplitude of each mode independently and use density-functional theory to determine the resulting electronic band structures, from which μ is extracted. We find that bond-transverse displacements of the equatorial halide atoms increase μ, while bond-transverse displacements of the apical halide atoms decrease it. Bond-axis displacements appear to have little or no effect on μ. Our results demonstrate three new structure-property relationships, revealing a promising new avenue for exciton engineering in layered perovskite materials.

Alloyed mercury cadmium chalcogenide semiconductors are promising materials for photoemission and photodetector applications in the near- to far-infrared regions of the electromagnetic spectrum, with HgxCd1-xTe already used widely in focal plane arrays in the mid- to far-infrared. While HgxCd1-xS and HgxCd1-xSe alloys are also promising for these applications, especially in their nanocrystalline forms, characterization of their optical properties has been limited. Using density functional theory, we calculate the electronic structure, effective masses, Luttinger parameters, and optical response functions of zinc blende CdS, HgS, CdSe, and HgSe. We further predict the dielectric function of HgxCd1-xS and HgxCd1-xSe alloys in thermodynamic equilibrium at 300 K for compositions between x = 0 to x = 1 using a cluster expansion approach with the generalized quasichemical approximation. We find that spin-orbit coupling increases the band gap by up to 0.1 eV, and the use of a hybrid functional increases the alloy band gaps up to 1 eV. We map the E1 and E2 optical critical point peaks and derive the nonlinear relationship between peak energy and composition, resulting in bowing parameters that are distinct from those of the band edges. These findings can serve as a reference for identifying mercury cadmium chalcogenide alloy composition from optical spectroscopic measurements in the visible and ultraviolet spectra.

Here, we use atomic resolution scanning transmission electron microscopy (STEM) and first-principles calculations to study the atomic and electronic structure of strongly charged domain walls in α-In2Se3. STEM imaging and density functional theory (DFT) show that head-to-head (HH) domain walls contain a layer of β/β'-In2Se3, whereas tail-to-tail (TT) domain walls are atomically abrupt. We apply 4D STEM and multislice electron ptychography to map ferroelectric domains in 2D and 3D, showing that nearly 180° domain walls exhibit complex, curved 3D structures that differ from ideal 180° structures. First-principles simulations predict localized conducting states within an ∼1 nm thick layer at both HH and TT domain walls, such as a midgap state at the β layer of the HH domain wall. These properties make strongly charged domain walls in α-In2Se3 excellent candidates for realizing 2D electron or hole gases and domain wall engineering in van der Waals ferroelectrics.

Conductivity models for warm dense matter inform simulations of planetary structure and fusion experiments. State-of-the-art conductivity calculations based on density functional theory approximate many-body physics and neglect electron-electron scattering lifetimes. We introduce a many-body framework for electrical conductivity using the GW approximation of the electronic self-energy. For beryllium, improved transition energies yield a surprisingly large reduction in low-temperature DC conductivity, while electron-electron scattering primarily reduces high-temperature DC conductivity.

Semiconductor quantum dots (QDs) are a class of nanomaterials with tunable electronic structure that enables precise control of light-matter interactions for diverse optoelectronic applications. Mercury cadmium chalcogenides are an emerging QD composition for infrared photonic applications, and their heterostructures are expected to expand functionality. Here, we introduce core/shell HgCdTe/HgCdSe QDs with bandgap energies in the infrared and charge carrier wave functions controlled by domain dimensions and the radial distribution of mercury and cadmium. As prepared via mercury cation exchange of core/shell CdTe/CdSe QDs, mercury can be selectively concentrated in either the core or shell, and can fully deplete cadmium to generate HgTe/HgSe QDs. Different alloying regimes shift band offsets between type-I and type-II alignments, in which the electron and hole are colocalized or separated, respectively. Broad bandgap tunability across the infrared spectra with long-term stability in air addresses problems of the constituent QD homostructures of HgTe and HgCdTe with low chemical stability and HgSe and HgCdSe with n-type doping. The photophysical features and oscillator strengths are reported as figures of merit and compared with quantum mechanical calculations. An optical metrology method based on ultraviolet E1 critical-point features is also introduced for assaying cation distributions, which is otherwise difficult in small core/shell QDs. These small-bandgap QDs with controllable charge carrier wave functions offer new opportunities to investigate photoluminescence, excited-state photophysics, and light-matter interactions at infrared wavelengths.

Transport phenomena in quantum spin systems have long intrigued physicists due to their potential applications in spintronic devices and spin qubits. Quantum simulations of the spin-spin autocorrelation function (ACF) have been used to probe spin transport, but methods based on the spin-current ACF have yet to be demonstrated due to their high gate cost, despite offering more direct information relevant to transport properties. Here, using a superconducting-qubit-based transmon device, we show that pre-fault-tolerant digital quantum simulation is reliable for studying transport phenomena via spin-current ACF. Overcoming the resource constraints of indirect measurement schemes like the Hadamard test, we showcase a direct measurement scheme using nonunitary operations, particularly midcircuit measurements, to investigate spin transport for the 40-site 1D XXZ Heisenberg model in the near-ballistic, superdiffusive, and diffusive regimes. We observe the power-law behavior consistent with the Kardar-Parisi-Zhang scaling in the superdiffusive regime and vanishing of the Drude weight in the diffusive regime.

A central goal of quantum computation is the realistic simulation of quantum materials. Although quantum processors have advanced rapidly in scale and fidelity, it has remained unclear whether pre-fault-tolerant devices can perform quantitatively reliable material simulations within their limited gate budgets. Here, we demonstrate that a superconducting quantum processor operating on up to 50 qubits can already produce meaningful, quantitative comparisons with inelastic neutron-scattering measurements of KCuF_3, a canonical realization of a gapless Luttinger liquid system with a strongly correlated ground state and a spectrum of emergent spinons. The quantum simulation is enabled by a quantum-classical workflow for computing dynamical structure factors (DSFs). The resulting spectra are benchmarked against experimental measurements using multiple metrics, highlighting the impact of circuit depth and circuit fidelity on simulation accuracy. Finally, we extend our simulations to 1D XXZ Heisenberg model with next-nearest neighbor interactions and a strong anisotropy, producing a gapped excitation spectrum, which could be used to describe the CsCoX_3 compounds above the Néel temperature. Our results establish a framework for computing DSFs for quantum materials in classically challenging regimes of strong entanglement and long-range interactions, enabling quantum simulations that are directly testable against laboratory measurements.

A new type of superlattice has been found in blended metal-thiolate crystals, AgSCnH2n + 1 and AgSCmH2m + 1 (n, m = 6-18, n < m, n and m are even), with various chain length mismatches (η = (m - n)/n), precipitated from a mixture of hot solutions of individual thiolates. The superlattice consists of alternating sublayers of crystalline thiolate lamellae and chain-end regions with distinct properties. Diffraction patterns suggest that the superlattice stacks are highly periodic and well registered. Carbons from these two alternating sublayers are exposed to different chemical environments, as shown by nuclear magnetic resonance measurements. The chain-end region exhibits a new material state that is ordered but behaves like an amorphous state in calorimetric measurements, without a chain-melting transition. Its thickness, estimated from X-ray diffraction and calorimetric analysis, coincides with the chain length difference between -CnH2n + 1 and -CmH2m + 1 ligands, presumably indicating that the chain-end regions consist of surplus parts of the longer alkyl chains protruding from adjacent lamellar layers. Mixed thiolates exhibit a melting point depression of the crystalline lamellae in comparison with the individual components. Triggered by the existence of the unique nonmelting layer, this effect is described by the Gibbs-Thomson model. The synthetic procedure yields good-quality crystals with η up to 1 over a wide range of mixing ratios, which is employed as a control parameter to continuously tune the structure of the superlattice.

Charged domain walls (CDW) in ferroelectrics are emerging as functional interfaces with potential applications in nonvolatile memory, logic, and neuromorphic computing. However, CDWs in conventional ferroelectrics are vertical, buried, or electrically inaccessible interfaces that prevent their use in functional devices. Here, we overcome these challenges by stacking two opposite polar domains of van der Waals ferroelectric α-In_2Se_3 to generate artificial head-head (H-H) CDWs and use edge contact to fabricate charged domain wall-based field-effect transistors (CDW-FET). We relate the atomic structure to the temperature-dependent electrical and magneto-transport of the CDW-FET. CDW-FETs exhibit a metal-to-insulator transition with decreasing temperature and enhanced conductance and field-effect mobility compared to single domain α-In_2Se_3. We identify two regimes of transport: variable range hopping due to disorder in the band edge below 70 K and thermally activated interfacial trap-assisted transport above 70 K. The CDW-FETs show room-temperature resistance down to 3.1 kΩ which is 2-9 orders of magnitude smaller than the single CDW in thin-film ferroelectrics. These results resolve longstanding challenges with high CDW resistance and their device integration, opening opportunities for gigahertz memory and neuromorphic computing.

Anisotropic 2D materials are gaining interest recently as building blocks for angular-dependent optical/electrical devices. However, the fundamental understanding of their structure-property-relationship is limited, which hinders further modulation of their unique characteristics via structure tailoring. Here the in-plane structural anisotropy and the tunable optical/electrical properties of a series of radiation-sensitive (X-ray, e-beam) metal-organic chalcogenide (MOC) single crystals are comprehensively revealed with ligands of variable length/parity. Their monoclinic crystallography is determined at atomic resolution by a simple method that couples X-ray/electron diffraction with first-principles calculations. The in-plane inorganic backbone of the MOCs exhibits a strong lattice anisotropy with odd/even alternations, which originates from that of the out-of-plane organic motifs via organic/inorganic accommodation. Such structural anisotropy is implied mechanically by the preferred orientation of crystal cleavage. It triggers a maximum approximate to 8 x distinction of in-plane electrical conductivity of the semiconducting MOCs, plus a distinct birefringence (maximum Delta n approximate to 0.03) with a dispersive orientation of dielectric axes, which rotate up to 25.7 degrees from UV to visible-light regime, inspiring an emerging pathway for color filtering via single crystal rotation. Such in-plane optical characteristics also exhibit odd/even alternation and can be flexibly tuned by the designable out-of-plane ligands.

Solid-state electrolytes (SSEs) require ionic conductivities that are competitive with liquid electrolytes to realize applications in all-solid-state batteries. Although candidate SSEs have been discovered, the underlying mechanisms enabling superionic conduction (>1 mS cm-1) remain elusive. In particular, the role of ultrafast lattice dynamics in mediating ion migration, which involves couplings between ions, phonons, and electrons, is rarely explored experimentally at their corresponding time scales. To investigate the complex contributions of coupled lattice dynamics on ion migration, we modulate the charge density occupations within the crystal framework and then measure the time-resolved change in impedance on picosecond time scales for a candidate SSE, Li0.5La0.5TiO3 (LLTO). Upon perturbation, we observe enhanced ion migration at ultrafast time scales. The respective transients match the time scales of optical and acoustic phonon vibrations, suggesting their involvement in ion migration. We further computationally evaluate the effect of a charge transfer from the O 2p to the Ti 3d band on the electronic and physical structure of LLTO. We hypothesize that the charge-transfer excitation distorts the TiO6 polyhedra by altering the local charge density occupancy of the hopping site at the migration pathway saddle point, thereby causing a reduction in the migration barrier for the Li+ hop. We rule out the contribution of photogenerated electron carriers and laser heating. Overall, our investigation introduces a new spectroscopic tool to probe fundamental ion hopping mechanisms transiently at ultrafast time scales, which has previously only been achieved in a time-averaged manner or solely via computational methods.

Applications of colloidal nanocrystals in polar solvents often require nanocrystals synthesized in non-polar solvents. However, solvent transfer processes are problematic and deteriorate nanocrystal quality. Here we report syntheses of nanocrystals with nearly universal solvent dispersibility using ligands and solvents with alkoxy repeating units. Core syntheses, shell deposition and cation exchange proceed similarly to traditional methods while products are more stable in aqueous solution than those generated by solvent transfer. (CdSe)CdZnS nanocrystals retain photoluminescence in cells for single-particle tracking experiments and outperform other nanocrystal classes in diffusion metrics reflecting stability and resistance to non-specific binding. Distinct reaction classes yield nanocrystals with either methoxy or hydroxy ligand terminations, both of which can be purified by aqueous methods that are chemically greener than traditional methods. These reactions can further generate nanocrystals with diverse oxide, sulfide and selenide compositions, shapes and spectral bands with wide dispersibility that may make applications in polar solvents more widely accessible. Nanocrystals are synthesized with long-term colloidal stability in both polar and non-polar solvents without the need for ligand exchange. During synthesis, conventional coordinating ligands and solvents with long alkyl chains are replaced with those bearing alkoxy repeating units.

The quasi-one-dimensional charge density wave (CDW) material (TaSe4)2I has been recently predicted to host Kramers-Weyl (KW) fermions which should exist in the vicinity of high symmetry points in the Brillouin zone in chiral materials with strong spin-orbit coupling. However, direct spectroscopic evidence of KW fermions is limited. Here we use helicity-dependent laser-based angle-resolved photoemission spectroscopy (ARPES) in conjunction with tight-binding and first-principles calculations to identify KW fermions in (TaSe4)2I. We find that topological and symmetry considerations place distinct constraints on the (pseudo-) spin texture and the observed spectra around a KW node. Our findings highlight the unique topological nature of (TaSe4)2I and provide a pathway for identifying KW fermions in other chiral materials. It has been predicted that the quasi-one-dimensional charge density wave material (TaSe4)2I hosts Kramers-Weyl fermions, but direct spectroscopic evidence of this is limited. Here, ARPES and theoretical calculations reveal signatures that may indicate the presence of Kramers-Weyl fermions.