Despite the large number of papers devoted to the magnetoluminescence from CdTe/(Cd,Mg)Te quantum wells, there have been no attempts to analyze it on the basis of band-structure calculations. This has been proposed in the present paper. Samples containing one or ten CdTe quantum wells with ${\mathrm{Cd}}_{0.7}{\mathrm{Mg}}_{0.3}\mathrm{Te}$ barriers are grown by molecular beam epitaxy on a semi-insulating GaAs substrate. Each well is modulation-doped with iodine donors, which leads to the creation of a two-dimensional electron gas in the wells. Polarization-resolved (${\sigma }^{+}/{\sigma }^{-}$) photoluminescence spectra are measured at liquid helium temperatures and magnetic fields up to 9 T. The results are interpreted on the basis of calculations of the energy of Landau levels in conduction and valence bands. In the latter case, we use the Luttinger Hamiltonian while the conduction band is described within a three-level $\mathbf{k}·\mathbf{p}$ model. Both models, originally formulated for bulk materials, are adapted for two-dimensional structures. We have found that the majority of all observed transitions is well-reproduced by this theory. However, some strong transitions are not, which allows us to propose an enlarged scheme of selection rules of the photoluminescence transitions resulting from mixing of the conduction and valence bands. We observe transitions involving Landau levels in the valence band with the index up to 7. To understand the origin of occupation with photoexcited holes of these levels, lying deep in the valence band, we carry out time-resolved measurements, which show that the photoexcited barrier is a source of long-lived holes tunneling into quantum wells. Calculations of the conduction-band electron effective $g$-factor show its strong variation with the electron's energy and the external magnetic field.

Magnetization noise measurements on the spin ice ${\mathrm{Dy}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ have revealed a remarkable “pink noise” power spectrum $S(f,T)$ below 4 K, including evidence of magnetic monopole excitations diffusing in a fractal landscape. However, at higher temperatures, the reported values of the anomalous exponent $b\left(T\right)$ describing the high-frequency tail of $S(f,T)$ are not easy to reconcile with other results in the literature, which generally suggest significantly smaller deviations from the Brownian motion value of $b=2$, that become negligible above $T=20$ K. We accurately estimate $b\left(T\right)$ at temperatures between 2 and 20 K, using ac susceptibility measurements that, crucially, stretch up to the relatively high frequency of $f={10}^6$ Hz. We show that previous noise measurements underestimate $b\left(T\right)$ and we suggest reasons for this. Our results establish deviations in $b\left(T\right)$ from $b=2$ up to about 20 K. However, we confirm that $b\left(T\right)$ is sample dependent: The details of this dependence agree in part, though not completely, with previous studies of the effect of crystal defects on monopole population and diffusion. Our results establish the form of $b\left(T\right)$ which characterizes the subtle, and evolving, nature of monopole diffusion in the dense Coulomb fluid, a highly correlated state, where several dynamical processes combine.

Topology plays a cardinal role in explaining phases and quantum phase transitions beyond the Landau-Ginzburg-Wilson paradigm. In this Letter, we formulate a set of models of Dirac fermions in $2+1$ dimensions with $\mathrm{SU}\left(N\right)\times \mathrm{SU}\left(2\right)\times \mathrm{U}\left(1\right)$ symmetry that have the potential to host critical points described by field theories with topological terms. For $N=2$ it shows a rich phase diagram containing semimetallic, quantum spin Hall insulating, Kekulé valence bond solid, and $s$-wave superconducting phases, and features multiple Landau-Ginzburg-Wilson phase transitions driven by interaction strength. At $N=1$ a deconfined quantum critical point is observed. At $N=2$ one expects the critical theory to correspond to a level 2 Wess-Zumino-Witten theory in $2+1$ dimensions. Here, the numerical results however show a strong first-order transition. Another transition can be governed by a topological $\theta$ term which is rendered irrelevant for even values of $N$, thus leading to Landau-Ginzburg-Wilson behavior.

Quantum electrodynamics in $2+1$ dimensions (${\mathrm{QED}}_3$) with two Dirac fermions displays time reversal symmetry, nontrivial SPT phases, and anomalies. The fate of this theory in its strongly coupled regime has been debated extensively. Surprisingly, we find that gluing together the phase diagrams of two standard Wilson-Fisher $O\left(4\right)$ theories suffices to reproduce all the SPT phases, anomalies, and semiclassical limits. A central mechanism behind it is “SPT absorption.” The patching of the $O\left(4\right)$ transitions makes very concrete predictions for the behavior of the theory in its strongly coupled limits; for instance, the $\theta =\pi$ sigma model with $S^3$ topology appears due to monopole condensation.

We consider the entanglement dynamics of a subsystem initialized in a pure state at high energy density (corresponding to negative temperature) and coupled to a cold bath. The subsystem's Rényi entropies $S_{\alpha }$ first rise as the subsystem gets entangled with the bath and then fall as the subsystem cools. We find that the peak of the min-entropy, ${lim}_{\alpha \to \infty }{S}_{\alpha }$, sharpens to a cusp in the thermodynamic limit at a well-defined time we call the Page time. We construct a hydrodynamic ansatz for the evolution of the entanglement Hamiltonian, which accounts for the sharp Page transition as well as the intricate dynamics of the entanglement spectrum before the Page time. Our results hold both when the bath has the same Hamiltonian as the system and when the bath is taken to be Markovian. Our ansatz suggests conditions under which the Page transition should remain sharp even for Rényi entropies of finite index $\alpha$.

Type-I clathrate solids have attracted significant interest because of their ultralow thermal conductivities and subsequent promise for thermoelectric applications, yet the mechanisms underlying these properties are not well understood. Here, we extend the framework of vibrational dynamical mean-field theory (VDMFT) to calculate temperature-dependent thermal transport properties of solids using a many-body Green's function approach. When applied to a coarse-grained description of $X_8{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$, where $X=\mathrm{Ba},\mathrm{Sr}$, we find that nonresonant scattering between cage acoustic modes and rattling modes leads to a reduction of acoustic phonon lifetimes and thus thermal conductivities. Moreover, we find that the moderate temperature dependence of conductivities above 300 K, which is consistent with experimental measurements, cannot be reproduced by textbook perturbation theory calculations, which predict a $T^{-1}$ dependence. Therefore, we suggest that nonperturbative anharmonic effects, including four- and higher-phonon scattering processes, are responsible for the ultralow thermal conductivities of type-I clathrates.

Multiferroic materials, characterized by the occurrence of two or more ferroic properties, hold potential in future technological applications and also exhibit intriguing phenomena caused by the interplay of multiple orders. One such example is the formation of spin-cycloid structures within multiferroic materials, which we investigate in this work by focusing on their magnon excitations and transport based on a general multiferroic Hamiltonian with an antiferromagnetic order. More specifically, we identify the ground state and explore the dynamics of magnon modes, revealing distinct in-plane and out-of-plane modes with anisotropic dispersion relations. The magnon modes include a massless excitation, known as the Goldstone boson, originating from the spontaneous breaking of the translational symmetry by the formation of the cycloid structures. By employing the Boltzmann transport formalism, the magnonic thermal conductivity with spin cycloids and low-temperature anisotropic behaviors is discussed. This work provides pathways to envision the spin-textured multiferroics, which may serve as a fertile ground to look for novel thermal and spin transport with the rich interplay of quasiparticles such as magnons and phonons.

A growing list of Ce-based magnets have shown an extra and heretofore unexplained crystal electric field (CEF) mode at high energies. We describe a process whereby an optical phonon can produce a split CEF mode well above the phonon energy. We use density functional theory and point-charge model calculations to estimate the phonon distortions and coupling to model this effect in ${\mathrm{KCeO}}_2$, showing that it accounts for the extra CEF mode observed. This mechanism is generic and may explain the extra modes observed on a variety of ${\mathrm{Ce}}^{3+}$ compounds.

Motivated by experimental developments in non-Kramers spin-ice materials and the unclear role of disorder therein, we study the impact of random transverse fields on the dynamics of correlated magnetic systems. We model the effect of dilute, randomly placed transverse fields on quantities such as magnetic noise/susceptibility and the diffusivity of topological excitations. We consider a random ferromagnetic Ising chain (RTFIC) as well as three-dimensional spin ice. At low temperatures, both exhibit (sub-)diffusive defect dynamics, i.e., of domain walls and magnetic monopoles, respectively. Introducing sparse transverse fields leads to the emergence of an additional timescale on the order of the single-spin-flip time. We develop a Lindbladian framework that combines Monte Carlo simulations and exact diagonalization which allows us to characterize the dynamics and develop an analytical understanding of the phenomenon. This framework can be benchmarked in detail for the RTFIC. Our findings provide insights into the magnetization dynamics of disordered non-Kramers oxides, such as oxygen-diluted ${\mathrm{Ho}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$, and offer a framework for interpreting experimental observations in these systems.

Chiral bound states in the continuum (BICs) play a crucial role in manipulating circularly polarized waves with ultrahigh quality (Q) factors. However, intrinsic chirality has predominantly been achieved through symmetry-protected BICs, which require structural symmetry breaking. Here, we propose a universal yet simple design strategy to achieve intrinsic chirality using accidental BICs. By tuning the air hole radius of the photonic crystal or introducing an external magnetic field to break time-reversal $\left(\mathcal{T}\right)$ symmetry, the doubly degenerate accidental BICs with topological charge −1 can transition into quasi-BICs. Consequently, the high-Q quasi-BICs can be realized without breaking structural symmetry. Under an external magnetic field, the nonradiative vortex singularities (V points) split into a pair of circularly polarized states (C points) at the Γ point, enabling the realization of intrinsic chirality that preserves structural symmetry. In addition, these chiral quasi-BICs can be further tuned into magneto-optical (MO) BICs by tailoring the air hole radius of the photonic crystal. More interestingly, the location of the MO BICs can be accurately determined by theoretically solving the characteristic equation of the coupling Hamiltonian. As a result, we further demonstrate switchable nonreciprocal transmission for circularly polarized waves at a given magnetic field strength. This work enriches the current research on BICs, significantly advancing the design of chiral photonic devices that are magnetically perturbed but still structurally symmetric.

In the field of spintronics and quantum information, the realization and control of the quantum anomalous Hall (QAH) effect stands as a crucial development. Incorporating multiple degree of freedom, van der Waals (vdW) heterostructures based on two-dimensional (2D) topological axion antiferromagnet (AFM) and ferroelectric materials offer an excellent platform for harnessing the QAH effect. In this work, we proposed a unique mechanism to tune the intrinsic layer polarization anomalous Hall effect (LPAHE) in an axion AFM based on the balance of the work function difference and electrostatic potential difference, which was demonstrated in a real vdW heterostructure material with two septuple $\mathrm{MnB}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$ layers and one ferroelectric $\mathrm{I}{\mathrm{n}}_2\mathrm{T}{\mathrm{e}}_3$ layer by using first-principles calculations. The electron injection induced by ferroelectric polarization drives a magnetic phase transition to obtain one nonzero net Hall conductivity and a reasonably high Curie temperature (18 K). In this work, we suggest a strategy for exploring the ferroelectric control topological properties in layered AFMs.

We consider the finite-time quench dynamics in the quantum transverse field Ising model which exhibits a second-order phase transition from a paramagnetic to a ferromagnetic phase, as the transverse magnetic field is decreased. These dynamics have been thoroughly investigated in previous studies when the critical point is crossed during the quench; here, we quench the system from deep in the paramagnetic phase to just above the critical field so that the system remains in the gapped phase throughout the quench duration. On linearly quenching the infinitely large system, we find that the behavior of mean longitudinal defect density and mean transverse magnetization at the end of the quench falls into three distinct scaling regimes as the quench time is increased. For sufficiently small quench times, these observables remain roughly constant, but for larger quench times, a crossover occurs from the Kibble-Zurek scaling law to the quadratic quench rate law when the Kibble-Zurek time is of the order of relaxation time at the final quench field. These results are shown analytically using power series and uniform asymptotic expansions of the exact solution of the model, and also compared with an adiabatic perturbation theory in the third regime. We find that the above mentioned scaling regimes hold for quenches within the ferromagnetic phase also, and provide a general scaling argument for crossover from the Kibble-Zurek regime to an adiabatic regime for slow quenches within a gapped phase.

Altermagnetism, an unconventional collinear magnetic state, has gained significant attention in the last few years, and the underlying mechanisms driving this quantum phase are still evolving. Going beyond the group theoretical analyses, which focus on providing a binary description of the presence or absence of the altermagnetic state, in this work we explore the role of crystal chemical bonding. As the latter successfully integrates the crystal and orbital symmetries and is tunable, it provides a quantitative and realistic mechanism to explain the formation of altermagnetism. From the first principles calculations and tight-binding models within the framework of the linear combination of atomic orbitals on NiS, we establish a set of selection rules for the formation of altermagnetism in the NiAs prototype compounds (e.g., CrSb, MnTe, etc.). Broadly, if single orbitals from Ni and S sites are involved in the bonding, the second-neighbor interaction between the nonmagnetic atoms is a must to modulate the intrasublattice interactions differently for the opposite spin sublattices so the antiferromagnetic sublattice band degeneracy is lifted and momentum-dependent altermagnetic spin split (AMSS) appears. However, when multiple orbitals are involved from the Ni and S sites in the chemical bonding, altermagnetism is naturally present. Together they amplify the AMSS. Further, we propose 12 antinodal regions in the NiAs type hexagonal crystals, where AMSS is maximum. The electron correlation can tune the AMSS. Specific to NiS, for the edge valence band, the AMSS increases with correlation and can go beyond 1eV. The present study opens pathways to design chemical bonding driven selection rules in addition to the existing crystal symmetry criteria to tailor tunable altermagnetism.

Sample homogeneity on the microscopic scale is critical for the reliable interpretation of x-ray absorption spectra collected in transmission mode. Unfortunately, it is not always easy to ensure it in practice. Especially in operando studies of catalysts and functional materials, the microstructure of the sample can evolve during its operation and even become the key descriptor for understanding structure-property relationships of the material, as exemplified by the transformations taking place in technical iron-based catalysts for ammonia synthesis under operating conditions. Here we present a simple approach for the identification and quantification of the material's microgranular structure effect on its x-ray absorption spectrum. We demonstrate that the quantitative information on the sizes of microscopic sample particles can be extracted from the observed distortions in the x-ray absorption near-edge structure spectra. The obtained insight can also be used to correct for the artifacts in extended x-ray absorption fine structure fitting, associated with the presence of microscopic inhomogeneities in the sample.

Two-dimensional organic-inorganic hybrid perovskites (OIHPs) hold great promise for energy conversion applications, yet their potential is limited by the scarcity of antiferroelectric materials. Our machine learning accelerated molecular dynamics simulations predict intricate phase transitions in ${\left(\mathrm{PMA}\right)}_2\mathrm{Pb}{\mathrm{Br}}_4$, progressing from a wavelike ferroelectric (FE) to a normal FE, and ultimately to an antiferroelectric (AFE) phase as the temperature increases. Correlation analyses indicate that the FE-AFE transition is primarily driven by the structural transformation of the inorganic framework, from distorted to undistorted octahedra, which influences the molecular orientation through steric effects, while maintaining the stacking pattern of benzylammonium (PMA) molecules. The hydrogen bonds connecting the organic and inorganic components are essential for stabilizing both FE and AFE phases. Furthermore, an increased number of hydrogen bonds induces the unique wavelike pattern observed at low temperatures. This work offers insights into optimizing and designing FE and AFE phases in OIHPs by tuning steric effects and hydrogen bonds.

We study parametric instability in a magnomechanical system, specifically examining magnon tunneling between moving ferromagnetic insulators. Our analysis reveals that quantum fluctuations generate spin currents above a critical velocity threshold, while no spin currents occur below this threshold at low temperatures. The critical velocity depends on magnon stiffness and Zeeman energy. Approaching the threshold, the spin current becomes divergent, linked to the $\mathcal{PT}$-symmetry-breaking transition. This enhanced behavior could offer high-sensitivity measurements and efficient spin-current generation in magnon-based quantum technology.

Recent studies reveal that $\mathcal{T}$-odd spin currents generated via the nonrelativistic altermagnetic spin splitting effect (ASSE) exhibit significant potential for spintronics applications, with both computational and experimental validations. Addressing the scarcity of conductive altermagnets, we propose strain engineering as a reliable method for inducing altermagnetism. Focusing on rutile-structured ${\mathrm{OsO}}_2$, first-principles calculations show that minor equibiaxial tensile strain $({\mathcal{E}}_{\mathrm{ts}}=3\%)$ induces nonmagnetic-to-altermagnetic transitions, achieving an ASSE-driven spin-charge conversion ratio $\left({\theta }_{\text{AS}}\right)$ of $\sim 7\%$—far surpassing conventional spin Hall angles $\left({\theta }_{\text{IS}}\right)$. Calculations reveal that substantial ${\theta }_{\text{AS}}$ persists even in the absence of spin-orbit coupling, with its magnitude positively correlating to nonrelativistic spin splitting magnitude, which further confirms the strain-induced ASSE's nonrelativistic origin. Further investigation reveals that ${\mathrm{RuO}}_2$ exhibits analogous phenomena, which may resolve recent controversies regarding its magnetic properties. Our research opens new simple pathways for developing next-generation altermagnetic spintronics devices.

This study presents a detailed spin-polarized scanning tunneling microscopy (SP-STM) analysis on the structural, electronic, and magnetic properties on europium (Eu) films epitaxially grown on a W(110) substrate. Utilizing optimized growth parameters, we conduct a thickness-dependent series ranging from the submonolayer regime to films as thick as 650 AL. Atomically resolved STM images of a 130 AL Eu film unveil lateral periodic sequences of bcc(110)-ordered dislocation lines sandwiched between adjacent hcp(0001) segments, effectively relieving stress within the films. These dislocation lines exhibit a periodicity of $p_{\text{topo}}=(3.36\pm 0.11)$ nm. Tunneling spectroscopy reveals that the surface of Eu films hosts a pronounced double-peak structure at about $U_{\mathrm{bias}}\approx +0.30$ V and $\approx +0.48$ V, corresponding to unoccupied sample states. It is interpreted as an exchange-split $d_{z^2}$-like surface state which remains robust even within the bcc(110) structure of the dislocation lines. Magnetically sensitive data reveal a spin spiral with a surface periodicity of $p_{\text{mag}}=(2.76\pm 0.19)$ nm. The results are discussed in terms of bulk-terminated spin spirals in hcp Eu which propagate along $\langle \overline{1}\overline{1}23\rangle$ directions in the surface-near region.

Inducing magnetic order in topological insulators (TIs) is significant for developing next-generation novel spintronics. Among many TIs, ${\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$ has been reported to possess a large spin Hall angle and the highest spin Hall conductance. We experimentally realize strong perpendicular magnetic anisotropy (PMA) and very large magnetoresistance in ${\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$ induced through interface coupling with yttrium iron garnet. Particularly, by optimizing the thickness of ${\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$, we observe a large enhancement in interfacial magnetic anisotropy while simultaneously preserving the topological surface state (TSS), which suggests that the TSS plays a dominant role in enhancing the interfacial PMA. Furthermore, we detect a very large anomalous Hall resistance in ${\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$, serving as compelling evidence of robust interfacial PMA.

We report specific heat, ac/dc magnetic susceptibility as well as static and pulsed field magnetization studies on the distorted kagome magnet ${\mathrm{Pr}}_3{\mathrm{BWO}}_9$ down to 0.4 K and up to high magnetic fields. The low-temperature thermodynamic properties are found to be governed by an electronic quasidoublet ground state, the energy splitting of which amounts to ${\mathrm{\Delta }}_1\simeq 18$ K and exhibits a quadratic field dependence with $g_{\mathrm{eff}}=2.6$. Fitting of the specific heat data implies that the next excited state is strongly gapped at ${\mathrm{\Delta }}_2=430$ K and threefold degenerate in zero field. Our dc and ac susceptibility studies down to 0.4 K do not detect signatures of distinct spin glass behavior. Pulsed field magnetization measurements up to 60 T confirm the Ising-like paramagnetic nature of the magnetic ground state, which is characterized by $m_J=\pm 4$ and the anisotropy energy $E_a\simeq 950$ K.