In this study, MnP single crystals were synthesized and comprehensively characterized to elucidate their structural quality, magnetic behavior, magnetocaloric response, and field-dependent critical phenomena along the easy $c$ axis. High-resolution x-ray diffraction confirmed the orthorhombic MnP-type crystal structure with excellent crystallinity. At the same time, magnetization measurements revealed a sharp ferromagnetic transition near room temperature. To further understand the underlying physics governing these behaviors, the critical exponents β, γ, and δ were systematically extracted in three distinct magnetic-field regimes, low, medium, and high, thus enabling a detailed assessment of universality and crossover effects in this anisotropic itinerant ferromagnet. In the low-field regime, we obtained a Curie temperature $T_{\mathrm{C}}=288.69\pm 10.01\mathrm{K}$, with critical exponents $\beta =0.355\pm 0.016, \gamma =1.208\pm 0.021$, and $\delta =4.407\pm 0.167$. For medium fields, the transition sharpened and shifted toward higher temperature, yielding $T_{\mathrm{C}}=294.52\pm 4.08\mathrm{K}, \beta =0.368\pm 0.022, \gamma =0.995\pm 0.010$, and $\delta =3.701\pm 0.031$. In the high-field regime, the system displayed a pronounced crossover from nearly second-order to more mean-field-like behavior, with $T_{\mathrm{C}}=300.26\pm 2.00\mathrm{K}, \beta =0.490\pm 0.049, \gamma =1.058\pm 0.035$, and $\delta =3.158\pm 0.227$. These systematic variations indicate strong field sensitivity of the magnetic interactions and highlight a continuous evolution of the critical behavior across the three regimes. The intrinsic thermodynamic $T_{\mathrm{C}}$ is approximately 296 K, while the field-dependent values extracted from modified Arrott plot/Kouvel-Fisher analyses represent effective crossover temperatures. This work provides a unified picture of the structural, magnetic, magnetocaloric, and critical properties of MnP single crystals. The field-dependent critical exponents demonstrate that MnP exhibits nonuniversal scaling governed by magnetic anisotropy and external-field strength, offering valuable insight into both fundamental studies of criticality and the optimization of MnP-based magnetocaloric materials near room temperature.

In this work, we investigate the bi-isotropic effects in the formation and tunability of hybrid surface polaritons in bilayer configurations. To do that, we consider a heterostructure constituted with layers formed by a TI medium endowed with bi-isotropic constitutive relations and an AFM medium. Using transfer matrix formalism, we derive general dispersion relations for surface polaritonic modes including the bi-isotropic coupling parameter, and analyze their coupling to bulk magnon-polaritons in the AFM layer. As an illustration, we consider a heterostructure formed with ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ interfaced with antiferromagnetic (AFM) materials that support terahertz-frequency magnons. In the non-null bi-isotropic coupling regime, the surface Dirac plasmon-phonon-magnon polariton (DPPMP) dispersion undergoes a pronounced redshift, accompanied by the suppression of the characteristic anticrossing between the Dirac plasmon and the phonon. This effect, observed for all AFM materials considered, suggests a weakening of the hybrid interaction, possibly due to saturation or detuning mechanisms induced by the increased $\alpha$ parameter. The latter yields a redshift that partially compensates the blueshift induced by a higher Fermi level, restoring the system to a weak-coupling regime analogous to that observed at lower Fermi energies. Our findings reveal that both the Fermi level and the bi-isotropic response offer independent and complementary control parameters for tuning the strength of light-magnon coupling in TI/AFM heterostructures, with potential implications for reconfigurable THz spintronic and photonic devices.

The variational quantum eigensolver (VQE) has been widely used to find the ground state energy of different Hamiltonians with no analytical solutions that are classically difficult to compute. In our work, we use the VQE to identify the phase transition boundary for an infinite-order phase transition. Typically, in a finite-order phase transition, finite-order derivatives of the ground state energy would signal the phase transition. However, that is not the case for infinite-order phase transitions, for which a global-range order parameter is required. In this work, we use a long-range XXZ (LRXXZ) chain for our study. It has been observed that two types of phase transitions for this model exist. One is a first-order phase transition, straightforwardly evaluated using the gradient of the ground energy. The second is an infinite-order phase transition, which is conventionally unfeasible to evaluate using the ground state energy. Therefore, it has been observed that the ground state energy is not sufficient to probe both of these transition boundaries. However, we propose a simple technique to utilize the ground state energy from the VQE to identify both phase transitions. The idea stems from the argument that the VQE requires an ansatz circuit; therefore, the accuracy of the VQE relies on this ansatz circuit. We have designed the ansatz circuit such that the estimated ground state energy is sensitive to the phase it is evaluated in. It is achieved by applying the constraint that the net spin remains constant throughout the optimization process. Consequently, the ansatz works in a certain phase in which it gives a relatively small random error, as it should, when compared to the error in the ground state energy calculations of the other phases, in which the ansatz fails. Identifying these changes in the behavior of the error in the ground state energy evaluation using the VQE, we are able to identify the phase boundaries. Using Exact Diagonalization (ED), we also compare the behavior of the energy gradient and energy gap across both phase transition boundaries for this model. Further, by increasing the depth of the optimization circuit, we also accurately evaluate the ground energy of the LRXXZ chain for $J>0$ and $J<0$ in the paramagnetic region.

All-inorganic lead halide perovskites $\mathrm{CsPb}{\mathrm{X}}_3$ (X = Cl, Br, I) exhibit rich structural dynamics, with vibrational properties and electron-lattice interactions still under active investigation due to strong lattice anharmonicity and structural phase transitions. Here we present a first-principles study of $\mathrm{CsPbB}{\mathrm{r}}_3$ across its orthorhombic, tetragonal, and cubic phases. We analyze the impact of the structural phases on the phonon dispersions, by including lattice anharmonicity. We discuss the validity of the semiclassical Fröhlich Hamiltonian, by quantifying the electron-phonon coupling strength for individual polar optical phonons, analyzing the mixing induced by long-range polar interactions and the relative contributions to the dielectric spectrum, tracing their symmetry evolution using group theory and a band folding approach. Despite pronounced structural transformations and enhanced anharmonicity at elevated temperatures, the long-range polar coupling mechanism associated with a single longitudinal optical mode lying at high frequency remains dominant throughout the entire temperature range. Furthermore, we show that, in the absence of symmetry-breaking effects, effective cubic models accurately capture long-range field behavior in low-temperature phases. This work establishes a microscopic foundation for a better understanding of polarons and exciton-polarons in bulk $\mathrm{CsPbB}{\mathrm{r}}_3$ and related nanostructures.

Critical states in quasiperiodic systems defy the conventional dichotomy between extended and localized states. In this work, we demonstrate that non-Hermiticity fundamentally reshapes this paradigm by giving rise to a class of quasiperiodic skin criticality. We introduce a non-Hermitian quasiperiodic lattice based on a modulated Hatano-Nelson model and uncover a universality class of quasiperiodic skin criticality, in which all eigenstates share an identical multifractal spatial structure. Through a nonunitary gauge transformation, the system is mapped onto a disorder-free lattice, enabling exact analytical solutions for the full spectrum and eigenstates. As a consequence, the inverse participation ratio is strictly energy independent and controlled solely by a global phase. We further show that these collective critical features persist in multiband lattices, establishing a general and analytically controlled framework for non-Hermitian quasiperiodic criticality.

We investigate the influence of correlations and plasmonic excitation on the valence band satellite of $\alpha$-Fe, along with magnetic and spectral properties as a function of temperature. Coulomb interaction parameters are obtained by systematically employing various schemes within the constrained random-phase approximation (cRPA). This study identifies the presence of valence band satellite in Fe at $\sim 6\mathrm{eV}$ binding energy supported by (i) substantial incoherent spectral weight in the valence band spectra obtained from Density Functional Theory plus Dynamical Mean Field Theory $(\mathrm{DFT}+\mathrm{DMFT})$ and (ii) plasmonic excitations in the frequency range $\sim 6–8\mathrm{eV}$ suggested by $G_0{W}_0$ calculations. We note a significant contribution from the temperature-dependent Pauli spin susceptibility, indicating a competing degree of itinerancy. $e_g$ state shows a strong temperature-driven non-Fermi-liquid behavior emerging near $T_c$. Our results reveal that a high-temperature orbital-selective loss of coherence eventually leads to an orbital-selective collapse of magnetization at $T_c$, suggesting a ferromagnetic phase characterized by strong correlation- and temperature- dependent spectral features.

Photoluminescence measurements confirmed a direct band gap of ∼1.41 eV for the cubic ${\mathrm{Na}}_2\mathrm{KSb}$ phase. At the highest excitation powers, a secondary emission peak emerged alongside the original band-edge peak, indicating the formation of a Fermi-degenerate electron-hole plasma. Polarization- and temperature-resolved Raman spectroscopy, supported by density functional theory (DFT), revealed the vibrational and structural properties of multialkali antimonide high-vacuum photocathode thin films. Polycrystalline ${\mathrm{Na}}_2\mathrm{KSb}$ cubic phase of the as-grown film was explicitly identified by its characteristic transverse optical (TO - 147 $\mathrm{c}{\mathrm{m}}^{-1}$) and longitudinal optical (LO - 179 $\mathrm{c}{\mathrm{m}}^{-1}$) phonon modes. These modes exhibited exceptional thermal stability, while the LO mode intensity showed a selective, temperature-dependent quenching attributed to a weakening of the Fröhlich interaction. DFT phonon calculations for the thermodynamically stable cubic ${\mathrm{Na}}_2\mathrm{KSb}$ phase and the hexagonal ${\mathrm{NaK}}_2\mathrm{Sb}$/${\mathrm{Na}}_3\mathrm{Sb}$ polymorphs confirmed the experimental assignment of the cubic ${\mathrm{Na}}_2\mathrm{KSb}$ phase as the intrinsic structure of the as-grown film. However, the analysis revealed that high laser power density in Raman spectroscopy can induce a local phase transformation from the cubic structure to partially hexagonal ${\mathrm{NaK}}_2\mathrm{Sb}$ phase, highlighting the metastability of the material under nonequilibrium conditions. These findings provide fundamental understanding into the lattice dynamics and phase stability essential for the performance and operational limits of high-efficiency photocathodes.

Extending hyperuniformity from classical to quantum fluctuations in electron systems yields a framework that identifies quantum phase transitions and reveals underlying gap structures through the quantum weight. We study long-wavelength fluctuations of many-body ground states through the charge-density structure factor by incorporating intrinsic quantum fluctuations into hyperuniformity. Although charge fluctuations at zero temperature are generally suppressed by particle-number conservation, their long-wavelength scaling reveals distinct universal behaviors that define quantum hyperuniformity classes. By exemplifying the Aubry-André model, we find that gapped and gapless phases, as well as localized, critical, and extended phases are sharply distinguished by the quantum hyperuniformity classes. Notably, at the critical point, multifractal wave functions generate anomalous scaling behavior. We further show that, in quantum-hyperuniform gapped phases, the quantum weight provides a quantitative measure of the gap size through a universal power-law scaling. Along with classical hyperuniformity, quantum hyperuniformity class serves a direct fingerprint of quantum criticality and a practical probe of quantum phase transitions in aperiodic electron systems.

Altermagnets exhibit momentum-dependent spin splitting without net magnetization, combining characteristics of both ferromagnets and antiferromagnets, making them highly interesting for spintronics applications. CrSb is a prime candidate with a high Néel temperature ($\sim 700\mathrm{K}$) and a large exchange-driven splitting of $\sim 0.6–1\mathrm{eV}$. Using ab initio calculations, we consider slabs of various orientations in the ultrathin limit. In (0001)-oriented slabs, the exchange-driven altermagnetic spin splitting collapses, but including spin-orbit coupling restores a residual anisotropic splitting of $\sim 70\mathrm{meV}$. The (100)-oriented slabs become fully spin degenerate due to symmetry reduction. In contrast, the (110)-oriented slabs show a strong altermagnetic spin splitting of $\sim 400\mathrm{meV}$, and thus emerges as a robust candidate for realizing large, exchange-driven altermagnetism.

The ferrimagnetic Blume-Emery-Griffiths one-dimensional model on the sawtooth chain with bilinear and biquadratic interactions between spins is studied exactly. Conditions at which the characteristic feature of spin ices, the remnant entropy at zero magnetic field appears, are studied. On the other hand, we determine at which set of parameters the model manifests quasiordering. That quasiordering reveals itself in almost nondecaying correlation functions below the quasicritical temperature, the jumplike temperature behavior of the entropy, and the quasipeculiarity in the temperature behavior of the specific heat at the quasicritical temperature. We show that the temperature behavior of magnetic moments of spins and the total magnetization drastically change its properties at the quasicritical temperature. The magnetic Grüneisen parameter manifests the most dramatic changes at the temperature of the quasiordering if the latter exists and in the ground state otherwise.

The pursuit of high-temperature quantum anomalous Hall (QAH) insulators faces fundamental challenges, including narrow topological gaps and low Curie temperatures ($T_{\text{C}}$) in existing materials. Here, we propose a transformative strategy using bilateral hydrogenation to engineer a robust QAH state in the topologically trivial ferromagnetic semiconductor ${\mathrm{Cr}}_{\text{2}}{\mathrm{Ge}}_{\text{2}}{\mathrm{Te}}_{\text{6}}$ via covalent orbital reconstruction. First-principles calculations reveal that by fundamentally rewiring the underlying orbital hybridization network, hydrogenation alters orbital occupations to shift preexisting Dirac points—originally embedded in the conduction bands—to the vicinity of the Fermi level in ${\mathrm{Cr}}_{\text{2}}{\mathrm{Ge}}_{\text{2}}{\mathrm{Te}}_{\text{6}}{\mathrm{H}}_{\text{6}}$. This electronic restructuring, coupled with spin-orbit coupling, opens a global topological gap of 118.1 meV, establishing a robust QAH state with Chern number $C=$ 3. Concurrently, this same orbital reconstruction effectively tunes the energy difference between the ligand $p$ and transition metal $d$ orbitals. This specific energy shift enhances ferromagnetic superexchange via the $d_{z^2}\text{−}{p}_z\text{−}{d}_{xz}$ channel, significantly strengthening the nearest-neighbor coupling $J_{\text{1}}$ by 3.06 times and switching $J_{\text{2}}$ from antiferromagnetic to ferromagnetic. Monte Carlo simulations based on the extracted exchange parameters indicate a pronounced enhancement of ferromagnetic stability compared with pristine ${\mathrm{Cr}}_{\text{2}}{\mathrm{Ge}}_{\text{2}}{\mathrm{Te}}_{\text{6}}$, and we stress that the absolute Curie temperature depends on the mapping to an effective spin model and thus should be interpreted primarily in terms of relative trends. The comparative enhancement of ferromagnetic stability after hydrogenation is a salient effect of this orbital tuning. This work establishes targeted orbital reconstruction driven by surface hydrogenation as a powerful route to simultaneously control topology and magnetism in 2D materials, providing a general route to engineer QAH phases with large gaps and high Chern numbers in van der Waals ferromagnetic semiconductors.

In this work, we report coherent perfect absorption (CPA) of anti-modes in an indirectly coupled magnon–polariton system. By examining both single and indirectly coupled cases, we experimentally distinguish the modal decay rate $\gamma$ from the effective decay rate ${\gamma }_{\mathrm{eff}}$. At CPA, ${\gamma }_{\mathrm{eff}}=0$, leading to a vanishing output and a visually narrow spectrum in the dB scale, while the intrinsic linewidth set by $2\gamma$ remains unchanged, demonstrating that the effective decay rate dictates the spectral amplitude rather than the physical loss. Furthermore, in the indirectly coupled system, CPA persists over a broad, magnetically tunable detuning range, in contrast to the single-detuning CPA observed in the directly coupled case, thereby enabling magnetically reconfigurable and frequency-selective microwave absorbers.

We incorporate spin-orbit coupling (SOC) into effective Kugel-Khomskii models for the $n=1$ and $n=2$ members of the Ruddlesden-Popper series ${\mathrm{Sr}}_{n+1}{\mathrm{Cr}}_n{\mathrm{O}}_{3n+1}$. These models contain interacting spins 1 and pseudospins 1/2 at each site describing spin and orbital degrees of freedom, respectively. We solve the models at zero temperature using pseudospin bond operators and spin waves. We find that for realistic parameters, SOC dominates the physics of the compound ${\mathrm{Sr}}_2{\mathrm{CrO}}_4$ with almost decoupled single ${\mathrm{CrO}}_2$ planes. The spin ordering is antiferromagnetic, with nearest-neighbor Cr spins aligned antiparallel. The corresponding orbital configuration is $d_{xy\uparrow }^1(d_{xz\uparrow }^1-i{d}_{yz\uparrow }^1)$ or $d_{xy\downarrow }^1(d_{xz\downarrow }^1+i{d}_{yz\downarrow }^1)$ depending on the spin of the site. In contrast, for the bilayer compound ${\mathrm{Sr}}_3{\mathrm{Cr}}_2{\mathrm{O}}_7$ we find that the effect of the SOC is weak and the system prefers to form pseudospin singlets in the $z$ direction perpendicular to the planes. The spin order is antiferromagnetic within each plane and ferromagnetic between planes, in agreement with previous studies.

We develop a general theory of crystal truncation rod (CTR) scattering from vicinal surfaces with a coherently strained heteroepitaxial film. The formalism incorporates film-induced interference fringes, full elastic lattice distortion, terrace ordering, surface reconstruction, and real-time growth evolution within a unified description. Comparison between the Nagai model and the elasticity-based model shows that the lattice tilt is nearly identical in the two approaches, whereas the elasticity-based model predicts an additional triclinic deformation arising from shear strain. This deformation has little effect on specular CTRs but strongly modifies nonspecular rods, making them a sensitive probe of the full elastic state of coherent epitaxial films. We further show that the characteristic sensitivity of vicinal CTRs to terrace ordering, surface reconstruction, and terrace-resolved compositional modification remains robust in the presence of a coherent film. Representative calculations for InGaN/GaN demonstrate that the framework enables quantitative interpretation of both static and real-time CTR measurements and provides access to step- and terrace-resolved structural and kinetic information during heteroepitaxial growth.