Various methods have been explored to enhance thermoelectric efficiency, including the use of magnetic interactions. This study examines the connections between magnetism and thermoelectricity by investigating the thermoelectric properties of PbSnTeSe high-entropy alloy doped with magnetic Cr and Fe impurities using first-principles calculations based on the density functional theory. For n-type materials, the results show that magnetic doping with Cr significantly enhances thermoelectric effects. Cr doping effectively improves the Seebeck coefficient, mainly because Cr atoms primarily contribute near the Fermi level and introduce isolated flat bands into the energy band structure, which increases the slope of the density of states. The enhanced Seebeck coefficient consequently boosts the power factor, leading to an increase in the figure of merit ($ZT$) value. At 300 K, the optimal $ZT$ value increases from 1.0 in pure PbSnTeSe to 1.6 in Cr-doped PbSnTeSe. However, the impact of magnetic doping with Fe on thermoelectric effects is less pronounced, as the difference in thermoelectric properties between magnetic and nonmagnetic Fe doping is minimal. Both types of doping contribute to the increase in the Seebeck coefficient, thereby enhancing the thermoelectric figure of merit.

Within a Hubbard model, we investigate the superconducting pairing behavior of infinite-layer nickelate ${\mathrm{NdNiO}}_2$ and cuprate superconductors by using the determinant quantum Monte Carlo method. Our focus is on comparing their dominant pairing symmetries. The results indicate that the $d_{x^2-y^2}$ pairing interaction is significantly enhanced at low temperatures in both doped nickelates and cuprates, whereas other typical pairing symmetries are effectively suppressed, highlighting the dominance of the $d_{x^2-y^2}$ pairing form. Additionally, we find that the effective pairing interaction for $d_{x^2-y^2}$ pairing in doped nickelates is slightly lower than that in doped cuprates, which may be attributed to the different degrees of Fermi surface warping caused by the third-nearest hopping $t^{\prime \prime }$. Further studies show that the hole doping and interaction strength have significant effects on the $d_{x^2-y^2}$ pairing interaction within the selected parameter range. The $d_{x^2-y^2}$ pairing interaction is notably weakened when the hole doping increases, whereas it is significantly enhanced with increasing Coulomb interaction strength $U$. This comparative analysis reveals the similarities and differences in the pairing behaviors of doped nickelates and cuprates, which may provide further insights into understanding the superconducting properties of these two classes of materials.

This study investigates the emission of cations from silica samples by single-cycle THz pulses, focusing on the influence of pulse polarity. Negative THz pulses were found to efficiently trigger the evaporation of cations from nanoneedles in amorphous silica samples compared to positive pulses. Conversely, this dependence on pulse polarity is strongly reduced and reversed in samples with metallic behavior such as ${\mathrm{LaB}}_6$ and could not be found when multicycle pulses in different frequency ranges such as ultraviolet (UV) are used. First-principles simulations focus on silica under THz laser irradiation and show critical fields for ion evaporation of hydroxyl groups from $\mathrm{Si}{\left(\mathrm{OH}\right)}_4$, which serves as a model precursor molecule for the amorphous solid matrix. To explain our experimental results, we propose a simplified theoretical model that determines the role of the polarity of the THz pulse by taking into account the differences in electron mobility between silica and semimetallic samples. The study explores the nonlinear microscopic mechanisms of atomic evaporation under external static and THz laser fields and clarifies the dynamics of THz-enhanced atom probe tomography and related applications.

We present a kinetic Monte Carlo (KMC) algorithm designed to study spin correlation phenomena in organic semiconductors including the effect of a magnetic field on electroluminescence and organic magnetoresistance. It allows for an arbitrary relation between hopping rates and spin-precession frequencies, and it incorporates an intermediate averaging procedure to model the spin relaxation within a single KMC simulation run. Our results demonstrate that even a small fraction of hops occurring faster than spin precession can significantly impact the width of the magnetic field dependence of the electroluminescence, which is typically associated with the strength of the hyperfine interaction between electron and nuclear spins.

Magnetic frustrations and degeneracies profoundly affect ground-state magnetic properties emerging from competing exchange interactions. Controlling such frustrations using orbital and phonon engineering via the Kugel-Khomskii-type (KK-type) interactions has recently enabled the orbital enhancement of magnetoelectric (ME) coupling. Using combined spectroscopic techniques and first-principle simulations, here we demonstrate that the magnetically frustrated Cairo lattice, ${\mathrm{Bi}}_2{\mathrm{Fe}}_4{\mathrm{O}}_9$, exhibits a strong KK-type interaction resulting in a coupled spin-orbital phase below 1.8 times the Néel temperature ($T_{\mathrm{N}}\sim 245\mathrm{K}$). We observe an order of magnitude change in phonon linewidths that is not explainable considering spin-phonon coupling channels alone. Instead, the observed change is reminiscent of orbitally active materials, which we explicitly confirm by measuring the $T$ dependence of low-energy orbital excitations. We further find that ${\mathrm{Bi}}_2{\mathrm{Fe}}_4{\mathrm{O}}_9$ harbors an unstable polar mode, driving the lattice to a symmetry-lowered ferroelectric (FE) phase below $T_{\mathrm{N}}$, in line with the previously reported hysteresis in polarization. Nonetheless, the FE phase leads to extremely small calculated superlattice Bragg peak intensities that are yet to be experimentally confirmed. Moreover, thermal conductivity measurements do not show any measurable effect of KK-type interactions on thermal transport across $T_{\mathrm{N}}$. However, we observe a repeatable anomaly at $\sim 57\mathrm{K}$ appearing only in the heating cycle, which co-occurs with the $\sim 400\mathrm{meV}$ broad continuum observed in Raman measurements. The observed KK-type interaction in ${\mathrm{Bi}}_2{\mathrm{Fe}}_4{\mathrm{O}}_9$ provides an opportunity for orbital enhancement of ME coupling by phonon control of superexchange interactions.

We study the ground-state phase diagram of an unfrustrated antiferromagnetic Ising chain with longitudinal and transverse fields in the full range of interactions: from all-to-all to nearest-neighbors. First, we solve the model analytically in the strong long-range regime, confirming in the process that a mean-field treatment is exact for this model. We compute the order parameter and the correlations and show that the model exhibits a tricritical point where the phase transition changes from first to second order. This is in contrast with the nearest-neighbor limit where the phase transition is known to be second order. To understand how the order of the phase transition changes from one limit to the other, we tackle the analytically intractable interaction ranges numerically, using a variational quantum Monte Carlo method with a neural-network-based ansatz, the visual transformer. We show how the first-order phase transition shrinks with decreasing interaction range and establish approximate boundaries in the interaction range for which the first-order phase transition is present. Finally, we establish that the key ingredient to stabilize a first-order phase transition and a tricritical point is the presence of ferromagnetic interactions between spins of the same sublattice on top of antiferromagnetic interactions between spins of different sublattices. Tunable-range unfrustrated antiferromagnetic interactions are just one way to implement such staggered interactions.

Performing ferromagnetic resonance (FMR) experiments on a polycrystalline FeRh (270 nm)/Ta (100 nm)/GaAs film, we evidence a low-field hysteretic signal, in addition to the usual nonhysteretic FMR absorption peaks. Its coercivity coincides with the static coercivity of the sample, which can be strongly tuned with temperature, thanks to the first-order nature of the antiferromagnetic to ferromagnetic transition of FeRh. The sample was made using a graded composition technique which allows us to obtain the Fe/Rh stoechiometry required for the presence of an antiferromagnetic-ferromagnetic transition. We show that the low-field microwave absorption (LFMA) signal can be well modeled by simply introducing the hysteresis of the static magnetization in the dynamic magnetic susceptibility. Finally, previous observations of LFMA on a cobalt thin film are also reproduced by this model.

We propose an in-plane magnon valve (MV), a sandwich structure composed of ferromagnetic insulator–heavy metal–ferromagnetic insulator (MI/HM/MI). When the magnetizations of the two MI layers are parallel, the longitudinal conductance of the HM layer is greater than that in the antiparallel state according to the magnetic proximity effect. We investigate the dependence of MV ratio (MVR), which is the relative change in longitudinal conductance between the parallel and antiparallel MV states, on the difference in electronic structure between magnetized and nonmagnetized HM atoms, revealing that MVR can reach 100%. Additionally, the dependence of MVR on the thickness of HM layer is analyzed, revealing an exponential decrease with increasing thickness. Then we investigate the dependence of HM layer conductance on the relative angle between the magnetizations of two MI layers, illustrating the potential of MV as a magnetic sensor. Due to the low coercive force ($\sim 1$ Oe) and wide intrinsic frequency range (GHz to THz) of YIG, a magnetic sensor based on a MV can theoretically detect weaker magnetic fields and exhibit improved high-frequency response. We also investigate the effect of Joule heating on the measurement signal based on the spin Seebeck effect and find that the transverse conductance of HM layer differs between the parallel and antiparallel MV states. Quantitative calculation shows that the transverse voltage difference between the two states can be detected experimentally. The difference of longitudinal and transverse conductance of HM layer between parallel and antiparallel MV state is called the in-plane magnon valve effect. Our work contributes valuable insights for the design, development, and integration of magnon devices.

We investigate the thermal properties of the $\frac{1}{3}$ plateau in the Shastry-Sutherland model with infinite projected entangled-pair states by performing the imaginary-time evolution of the infinite-temperature density matrix. We show that both the ${\mathbb{Z}}_2$ and ${\mathbb{Z}}_3$ broken symmetries of the ground state are restored at a unique temperature where the correlation length has a peak, and that the melting of the plateau occurs via a single weakly first-order transition. We focus on the experimentally relevant coupling constants deep into the $\frac{1}{3}$ plateau phase at $h=1$ and $J^{\prime }/J=0.63$, which was estimated to describe the ${\mathrm{SrCu}}_2{\left({\mathrm{BO}}_3\right)}_2$ compound. By computing the free energy we are able to locate the transition temperature around $T_c\simeq 4.8\mathrm{K}$, well above the temperature $T=2\mathrm{K}$ at which the $\frac{1}{3}$ plateau was observed in experiments. The investigation is supplemented by adding a bias term to the Hamiltonian and studying the induced crossover. We further map the transition line in the field-temperature phase diagram.

Motivated by the recent proposals for unconventional emergent physics in twisted bilayers of nodal superconductors, we study the peculiarities of the Josephson effect at the twisted interface between $d$-wave superconductors. We demonstrate that for clean interfaces with a twist angle ${\theta }_0$ in the range $0^{\circ }<{\theta }_0<{45}^{\circ }$, the critical current can exhibit nonmonotonic temperature dependence with a maximum at a nonzero temperature as well as a complex dependence on the twist angle at low temperatures. These effects are shown to reflect the destructive interference between the $d$-wave order parameters near the nodes at nonzero twist angle. Close to ${\theta }_0={45}^{\circ }$ we find that the critical current does not vanish due to Cooper pair cotunneling, which can lead to the transition to a time-reversal breaking superconducting $d+id$ phase, which can be suppressed by the interface roughness. We provide a comprehensive theoretical analysis of experiments that can reveal this cotunneling for twisted superconductors close to ${\theta }_0={45}^{\circ }$. In particular, we demonstrate that both the emergence of the Fraunhofer interference pattern near ${\theta }_0={45}^{\circ }$ and fractional Shapiro steps yield unambiguous evidence of Cooper pair cotunneling, necessary for topological superconductivity.

Motivated by the recent discovery of superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under high pressure, we explore its potential charge and spin instabilities through combined model analysis and first-principles calculations. Taking into account the small charge-transfer nature of high valence nickel, a fully correlated two-cluster model identifies a lattice-coupled charge instability characterized by substantial short-range fluctuations of oxygen holes. This periodicity-two instability is corroborated by density functional theory plus $U$ calculations that also reveal a strong tendency towards concurrent antiferromagnetic ordering. The charge, spin, and associated lattice instabilities are significantly suppressed with increasing external pressure, contributing to the emergence of superconductivity in pressurized ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. Carrier doping and chemical substitution at the La site is found to effectively suppress these instabilities, suggesting a viable strategy to stabilize a superconducting phase under ambient pressure.

High-pressure electride (HPE) superconductors are distinguished from other superconductors by non-nuclear attractors (NNAs), which enable a seemingly paradoxical combination of highly localized electride states and robust superconductivity. However, the superconducting mechanism of HPE superconductors remains poorly understood, particularly the role of NNAs in superconductivity. Here, we take metal-rich ${\mathrm{Sc}}_4\mathrm{H}$ as a model to study the relationship between NNAs and superconductivity in HPEs through using first-principles calculations. We first identify that satellite interstitial electrons (SIEs) of ions, which span bands across the Fermi level and are linked to ions, are active components of NNAs and significantly affect the HPE electron–phonon coupling. The SIE electron density and interaction with neighboring ions are key determinants for adjusting the high superconducting critical temperatures of HPE superconductors. This finding effectively harmonizes the previously perceived contradictory perspectives on the impact of NNAs on the superconductivity of HPEs and deepens the understanding of the superconducting properties of HPE superconductors.

Strontium titanate is a classic quantum paraelectric oxide material that has been widely studied in bulk and thin films. It exhibits a well-known cubic-to-tetragonal antiferrodistortive phase transition at 105 K, characterized by the rotation of oxygen octahedra. A possible second phase transition at lower temperature is suppressed by quantum fluctuations, preventing the onset of ferroelectric order. However, recent studies have shown that ferroelectric order can be established at low temperatures by inducing strain and other means. Here, we used in situ multireflection Bragg coherent x-ray diffraction imaging to measure the strain and rotation tensors for two strontium titanate microcrystals at low temperature. We observe strains induced by dislocations and inclusion-like impurities in the microcrystals. Based on radial magnitude plots, these strains increase in magnitude and spread as the temperature decreases. Pearson's correlation heat maps show a structural transition at 50 K, which could possibly be the formation of a low-temperature ferroelectric phase in the presence of strain. We do not observe any change in local strains associated with the tetragonal phase transition at 105 K.

The negatively charged boron-vacancy center (${\mathrm{V}}_{\mathrm{B}}^{-}$) in hexagonal boron nitride (hBN) has recently emerged as a highly promising quantum sensor. Compared to the nitrogen-vacancy (NV) center in diamond, the change with temperature of the spin transition energy of ${\mathrm{V}}_{\mathrm{B}}^{-}$ is more than an order of magnitude larger, making it a potential nanoscale thermometer with superior sensitivity. However, the underlying mechanism of the observed large temperature dependence remains an open question. In this work, using isotopically purified $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$, we systematically characterize the zero-field splitting, hyperfine interaction, and spin-relaxation time of ${\mathrm{V}}_{\mathrm{B}}^{-}$ from 10 to 350 K. We carry out first-principles calculations of the ${\mathrm{V}}_{\mathrm{B}}^{-}$ spin-phonon interaction and show that a second-order effect from finite-temperature phonon excitations is responsible for the observed changes in experiments. By fitting our experimental results to a physically motivated model, we extract the dominant phonon mode which agrees well with our simulations. Finally, we investigate the dynamic nuclear spin-polarization process at cryogenic temperatures. Our results provide key insights in ${\mathrm{V}}_{\mathrm{B}}^{-}$ centers and their utilization as nanoscale thermometers and phonon sensors.

Modeling charge and energy transport in energetically and spatially disordered materials has been an active research area, with various theoretical frameworks proposed and applied. In this study, we present a supervised machine learning algorithm that offers valuable insights into transport mechanisms within these systems. By employing a variational encoder-decoder architecture, we train a deep neural network that generates accurate statistics of transport properties. The network's effectiveness is demonstrated through its successful verification of the widely accepted transport energy concept. The network exhibits an effective dimensionality reduction, encoding raw input data of hopping transport into a minimal yet comprehensive representation necessary for describing the transport mechanism. This attribute offers a promising tool for future deep learning applications aimed at acquiring deeper physical insights into transport mechanisms in disordered materials.

We performed ab initio molecular dynamics simulations for $\mathrm{C}{\mathrm{H}}_4-{\mathrm{H}}_2\mathrm{S}$ mixtures at temperatures ranging from 3000 to 10 000 K and pressures up to 1500 GPa. We calculated pair distribution functions and bond-overlap populations to examine the structural and chemical bonding properties of this mixed system. The results indicate the breaking of C–H and S–H bonds, followed by the formation of strong covalent C–C and C–S bonds, suggesting phase separation between hydrogen and heavier atoms such as carbon and sulfur. Moreover, our findings reveal that hydrogen sulfide promotes the molecular dissociation of methane and facilitates carbon aggregation below ∼200 GPa at 4000 K. However, above this pressure, it potentially inhibits carbon aggregation because of the strong correlation between carbon and sulfur atoms. Our insights into the microscopic behavior of this mixture can potentially enhance the understanding of diamond formation processes within the icy giants Uranus and Neptune.

We consider how to target evolution conditioned on atypical measurement outcomes in monitored quantum circuits, i.e., the post-selection problem. We show that for a simple class of measurement schemes, post-selected light cone dynamical correlation functions can be obtained efficiently from the averaged correlations of a different unitary circuit. This connects rare measurement outcomes in one circuit to typical outcomes in another one. We derive conditions for the existence of this rare-to-typical mapping in brickwork quantum circuits made of XYZ gates. We illustrate these general results with a model system that exhibits a dynamical crossover (a smoothed dynamical transition) in event statistics, and discuss extensions to more general dynamical correlations.

The electronic structure of ferromagnetic half-metal ${\mathrm{CrO}}_2$ was studied by means of ${}^{53}\mathrm{Cr}$ nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT). The measured NMR spectrum consists of three distinct spectral lines and is interpreted as a triplet arising due to electric quadrupole interaction. The observed NMR parameters agree well with those obtained from electronic structure calculations, corresponding to the presence of ${\mathrm{Cr}}^{4+}$ with fully occupied localized $d_{xy}$ singlet and partially occupied degenerated $d_{xz}$ and $d_{yz}$ states, as required by the ferromagnetic double exchange mechanism. With high accuracy, the orbital occupations and valence states of all Cr atoms within the ${\mathrm{CrO}}_2$ structure are found to be uniform.