Magnetoresistive materials have been tremendously important for the development of magnetic memory storage and spintronic devices. Recently, the antiferromagnetic Eu $\text{Eu}{X}_2{Pn}_2$ compounds, with $X$ being a transition metal and $\mathit{Pn}$ being a pnictogen, have seen intensive research interest due to their unusual anomalous Hall effect behavior and pronounced resistive anomaly near the Néel temperature ($T_{\text{N}}$). These magnetotransport phenomena have been interpreted in the context of short-ranged ferromagnetic fluctuations, magnetic polaron formation, canted spin configurations, and temperature-dependent metal-insulator transitions in the electronic structure. Here, we report the observation of such a pronounced resistivity anomaly in ${\mathrm{EuZn}}_2{\mathrm{As}}_2$ near $T_{\text{N}}=19$ K. We demonstrate the suppression of this anomaly using applied magnetic fields, both in plane and out of plane. To further interpret the origin of the observed transport behavior, we studied the temperature-dependent electronic structure using combined angle-resolved photoemission spectroscopy and first-principles density functional theory calculations, which exhibits limited modifications to the bands across $T_{\text{N}}$ away from the Fermi energy. This lack of involvement of the electronic structure indicates a spin-scattering origin of the aforementioned transport properties, rather than a reconstruction of the Fermi surface.

${\mathrm{CeRh}}_2{\mathrm{As}}_2$ has been receiving considerable attention due to its unusual two-phase superconductivity. The superconducting (SC) phase appears at $T_{\mathrm{c}}=0.35$ K in an ordered state (phase I) of the $\mathrm{Ce}\text{−}4f$ moments, which develops below $T_0=0.55$ K. The microscopic nature of phase I has not been fully established yet. We report a single-crystal study of the effect of La substitution on these low-temperature phases in ${\mathrm{Ce}}_{1-\mathit{x}}{\mathrm{La}}_{\mathit{x}}{\mathrm{Rh}}_2{\mathrm{As}}_2$ up to $\mathit{x}=0.1$. The lattice parameters increase monotonically with $x$, corresponding to an effective negative pressure of approximately $-0.3$ GPa for $x=0.1$. While the ${\mathrm{Ce}}^{3+}$ local valence state and the non-Fermi-liquid behavior are preserved, the resistivity coherence maximum $T_{\max }^{*}\approx 45$ K in the pristine sample shifts to lower temperatures with increasing $x$, indicating a suppression of the Kondo energy scale upon lattice expansion. On the other hand, both $T_{\mathrm{c}}$ and $T_0$ are rapidly suppressed to below 0.1 K for $x>0.05$. Notably, such a rapid decrease of $T_{\mathrm{c}}$ under moderate negative pressure is unexpected, but is rather consistent with a substitution-induced disorder effect which leads to strong pair breaking in unconventional superconductors. The observed fragility of phase I under both pressure and disorder may imply its itinerant origin.

Ultrafast optical control of magnetization is well established in ferromagnets, yet its realization in nonmagnetic semiconductors, where spin degeneracy typically precludes net magnetization, remains a significant challenge. Here, using real-time, time-dependent density functional theory (RT-TDDFT), we investigate the ultrafast spin dynamics in monolayer InSe, where spin-orbit coupling and crystal symmetry enable light-induced magnetization through spin-flip torque. Under an in-plane circularly polarized pulse, spin-flip transitions dominate at low intensities, generating a substantial out-of-plane magnetization. With increasing field strength, saturation-like behavior emerges in the spin-flip channels, suppressing this pathway and making competing excitation channels more accessible, leading to suppression or even reversal of the net magnetization. Furthermore, we show that strong linearly polarized pulses break time-reversal symmetry via carrier population imbalance, producing a residual magnetization. These results reveal a nonperturbative regime of light-matter interaction, where magnetization is induced purely by ultrafast carrier dynamics without invoking lattice or thermal effects, and offer new pathways for all-optical spin control in nonmagnetic quantum materials.

The excitation spectrum of Kitaev quantum spin liquids consists of itinerant Majorana fermions, which can be gapless or gapped, and vortices of a ${\mathbb{Z}}_2$ gauge field, known as visons, which are gapped within a stable ${\mathbb{Z}}_2$ spin liquid phase. In this work, we investigate visons in Kitaev-type models where the Majorana fermions form a Fermi surface. In this case, the creation of a vison pair is analogous to introducing a local impurity potential in a metal. Since the gapless modes lead to strong finite-size effects, we compare the numerical calculation of the two-vison gap on finite lattices with the result from an analytical approach based on Green's function techniques. We find that the two-vison gap decreases as the size of the Fermi surface increases, signaling an instability of the quantum spin liquid ground state. We also show that larger Fermi surfaces tend to suppress the change in local spin correlations due to the Majorana-vison scattering potential.

Noncoplanar spin textures act on double-exchange (DE) electrons as an emergent magnetic flux. For short-period spin crystals in frustrated magnets, the resulting band topology is set by the full Bloch Hamiltonian, not by the skyrmion charge alone. Here, we classify the DE band topology of field-selected noncoplanar crystals on a triangular-lattice $K\text{−}\mathrm{\Gamma }\text{−}{\mathrm{\Gamma }}^{\prime }$ magnet (with 7-, 20-, and 36-site magnetic cells), alongside canonical reference textures. Two distinct classes emerge, distinguished by the net emergent flux through the magnetic cell. Crystals with a net flux (20-site cells, skyrmion charge $Q_{\text{sk}}=\pm 4$) are Hofstadter-type Chern insulators whose global gaps persist down to weak Hund couplings of $J_H\approx 0.7t$ (where $t$ is the hopping amplitude), well below the bandwidth. In contrast, the zero-net-flux 7-site crystal realizes a Haldane-type band with $Q_{\text{sk}}=0$ yet $C=+1$. Its gap, generated solely by flux modulation, is narrow ($0.04–0.17t$) and is closed by minority-spin admixture unless $J_H$ reaches $8–38t$. The zero-net-flux 36-site crystals behave as Chern metals even in the strong-Hund limit. In both classes, the topological robustness is dictated by the strong-Hund global gap—an electronic-structure property that local texture diagnostics fail to capture. The bulk topology of the net-flux class is further confirmed by a quantized anomalous Hall plateau and a chiral edge mode. Finally, the applied field acts as a topological switch: its direction selects the topological class, while its magnitude drives the zero-net-flux branch from a Chern insulator to a Chern metal.

We investigate the transient response to photodoping of $\mathrm{Sn}/\mathrm{Si}\left(111\right)\text{−}\left(\surd 3\times \surd 3\right) \mathrm{R}{30}^{\circ }$, a simple and prototypical two-dimensional Mott-Hubbard insulator with a small gap on a triangular lattice, by time- and angle-resolved photoemission with a 120 fs time resolution. A transient metallic state forms nearly instantaneously after photoexcitation and persists for a few hundred femtoseconds, consistent with theoretical predictions and previous studies of small-gap Mott systems in one and three dimensions. The temperature dependence of the doublon lifetime indicates that the dominant relaxation mechanism involves coupling between charge and spin degrees of freedom. On a longer timescale, a small energy shift of the lower Hubbard band persists for more than 1 ns. We attribute this long-lived modification to energy renormalization of the Hubbard bands induced by the photoexcited electron-hole plasma in the Si substrate. Our results further demonstrate that substrate excitations and the dynamics of the three-dimensional electron-hole plasma play a significant role in ultrafast studies of two-dimensional materials supported on semiconducting or insulating substrates, while also pointing to a possible route for controlling transient electronic states.

Identifying endpoint criticality is challenging because pseudo-first-order signatures can persist over accessible system sizes and obscure the underlying scaling behavior. This difficulty is especially acute in the frustrated square-lattice $J_1–J_2$ Ising model, where the location and even the nature of the stripe-ordering endpoint have remained controversial for decades. Here we treat this endpoint as a relevant-marginal two-field scaling problem and develop a generalized field-mixing construction to resolve the endpoint ambiguity. Mixed-histogram symmetry defines a finite-size pseudotransition manifold, transforming pseudo-first-order finite-size structure into a scaling trajectory on which the normal relevant detuning is removed and the residual marginal drift is exposed. Along this manifold, Binder analysis locates the endpoint as a distinct singular point, while mixed-histogram scaling, comparison with the Ashkin-Teller Potts point, and complementary Binder scaling establish four-state Potts endpoint criticality with logarithmic corrections.

The recent interest in non-Hermitian systems has significantly broadened their application across condensed-matter physics, offering a unique framework to explore out-of-equilibrium phenomena. Simultaneously, altermagnets have emerged as a distinct magnetic class, characterized by unconventional spin-split bands protected by crystal symmetries. In this work, we investigate the interplay between non-Hermitian dynamics and spin transport in these materials, focusing on the Edelstein effect. We demonstrate that the introduction of non-Hermiticity in $d$-wave altermagnets and $p$-wave unconventional magnets opens novel susceptibility components that are inaccessible in Hermitian counterparts. Fundamentally, the dissipation breaks standard momentum selection rules, dynamically converting previously asymmetric channels into even-parity configurations under spatial inversion to allow macroscopic spin accumulation. Crucially, our results show that this nonconservative nature leads to the selective gain and loss of specific spin components, which can be finely tuned by the interplay between dissipation, the magnetic order parameter, and the Néel vector orientation. This phenomenon provides a new route for manipulating spin degrees of freedom through controlled nonconservative processes in emerging unconventional magnetic materials.

The Kitaev spin liquid provides a rare example of exactly solvable quantum spin liquid states. Intensive research over the past two decades has identified a variety of its candidate materials. In real materials, however, the Kitaev interaction is inevitably accompanied by additional magnetic interactions such as the Heisenberg and $\mathrm{\Gamma }$ interactions. These interactions often induce magnetic ordering at low temperatures, making it essential to clarify their effects in the search for and design of Kitaev spin liquid candidate materials. In this study, we revisit the ground-state phase diagram of the Kitaev–Heisenberg–$\mathrm{\Gamma }$ model from both classical and quantum perspectives, using state-of-the-art numerical techniques. In the classical case, we reveal a zoo of noncollinear orders, where a variety of noncollinear multiple-$Q$ magnetic orders with and without incommensurate modulations emerge. In the quantum case, we unravel that quantum fluctuations suppress many of the competing orders found in the classical case, resulting in a reduced number of dominant incommensurate orders. We further identify highly frustrated regions, where spiral spin liquid states as well as new magnetically ordered states are potentially stabilized by additional magnetic interactions. Our results provide a comprehensive perspective on the Kitaev–Heisenberg-$\mathrm{\Gamma }$ model for both classical and quantum spins and offer a valuable guide not only for interpreting experimental results on candidate materials, but also for searching and designing new materials to realize the Kitaev spin liquid.

Three-dimensional topological insulators have garnered significant attention in scientific research due to their unique electronic properties. An in-depth study has been conducted to explore the influence of iron (Fe) doping on both the magnetic properties and the topological insulating behavior of $\mathrm{S}{\mathrm{b}}_2\mathrm{T}{\mathrm{e}}_3$. Magnetization measurements indicate a magnetic phase transition in the Fe-doped $\mathrm{S}{\mathrm{b}}_2\mathrm{T}{\mathrm{e}}_3$ sample, along with the emergence of superparamagnetic behavior at low temperatures, characterized by an enhanced magnetic moment. Low-temperature $M-H$ curves fitted with the Langevin equation suggest the formation of Fe-induced magnetic clusters within the $\mathrm{S}{\mathrm{b}}_2\mathrm{T}{\mathrm{e}}_3$ matrix. Temperature-dependent muon spin resonance measurements also support the enhancement of magnetic ordering in the doped sample. The low-temperature, low-field magnetoresistance data of the Fe-doped material suggests weak antilocalization (WAL) behavior of the carriers. The signature of WAL is further supported by the Hikami-Larkin-Nagaoka fitting of the low-temperature magnetoconductance data. Density functional theory calculations for both undoped and Fe-doped samples corroborate with the experimental study and reveal an increase in the spin-orbit interaction upon Fe doping. The observation of these phenomena induced by Fe doping underlines the potential of this approach for the development of intrinsic magnetic topological insulators for a broad range of application.

The study of mechanisms for enhancing superconductivity has been a central topic in condensed matter physics because of the combination of fundamental and technological interests. One promising route is to exploit nonequilibrium effects in the steady state. Efforts in this direction have so far focused on enhancing the pairing mechanism known from thermal equilibrium through modified distributions for the electrons or the bosons mediating the electron–electron interaction. In this work, we identify an additional pairing mechanism that is active only outside thermal equilibrium. By generalizing Eliashberg theory to nonequilibrium steady states using the Keldysh formalism, we derive a set of Eliashberg equations that capture the effect of this genuinely nonthermal pairing glue even in the weak-coupling regime. We discuss two examples where this mechanism has a major impact. First, in a temperature-bias setup, we find that superconductivity is enhanced when the boson mediator is colder than the electrons. Second, we find that an incoherent drive of the boson mediator at energies much greater than the temperature pushes the system far from thermal equilibrium but leaves the critical coupling essentially unchanged, owing to a competition between electron heating and the enhancement of pairing by the nonthermal glue.

Collective modes in superconductors, such as the Higgs mode, offer deep insights into the nature of condensates. Third-harmonic generation (THG) is a primary tool for probing the Higgs mode, but its signal competes with that of quasiparticle excitations depending on impurity scattering rates. In particular, in the clean regime the standard BCS theory generally predicts the dominance of quasiparticle contributions. Here, we propose and demonstrate that the quantum geometry of electronic bands can be a key mechanism governing this competition. By developing a formalism that explicitly incorporates the quantum metric, and applying it to a tunable model of a dispersive-band superconductor, we show that the quantum metric can dramatically amplify the nonlinear light-Higgs coupling by several orders of magnitude. Our results establish that a large quantum metric can cause the Higgs mode to dominate the THG response, resolving the puzzle of Higgs and quasiparticle competition in the clean regime and identifying band geometry as a crucial ingredient for designing and understanding the nonlinear response of superconductors.

We investigate the effect of weak interband impurity scattering on the intertype (IT) domain between type-I and type-II superconductivity in diffusive two-band superconductors. Our results show that the significant broadening of the IT domain with increasing band diffusivity ratio, previously established in the absence of interband scattering, persists under weak interband scattering. However, depending on the microscopic parameters, weak interband scattering can either slightly narrow or further expand the IT domain. Consistent with the case of negligible interband scattering, we identify two distinct IT regimes in the presence of weak interband scattering. The first variant (here referred to as IT-$\alpha$) has the upper boundary controlled by a sign change of the short-range vortex-vortex interaction, while the lower boundary is governed by a sign change of the long-range interaction. This ordering is reversed in the second variant, here referred to as IT-$\beta$. In both regimes, the vortex-vortex interaction is nonmonotonic: long-range repulsive and short-range attractive in the IT-$\alpha$ domain, and short-range repulsive and long-range attractive in the IT-$\beta$ regime. We also find that weak interband scattering tends to suppress the IT-$\alpha$ regime in favor of IT-$\beta$. Our findings establish the stability and tunability of the intertype regime in dirty multiband superconductors, which is crucial for harnessing its unique magnetic properties.

Departing from the conventional method of coupling soft and hard magnetic phases to improve remanence, a novel paradigm is proposed, in which exchange coupling is engineered between an amorphous (Am) soft magnetic phase and a nanocrystalline (NG) hard magnetic phase. By tailoring the amorphous-to-nanocrystalline ratio, the remanence and maximum energy product $\left[{\left(BH\right)}_{\max }\right]$ were concurrently adjusted. Micromagnetic simulations reveal that the ${\mathrm{SmCo}}_5$ amorphous-nanocrystalline structure effectively facilitates the pinning of the amorphous phase by the hard magnetic nanocrystals during the demagnetization process, leading to a remarkable remanence enhancement. The simulated remanence ratio $(M_{\mathrm{r}}/M_{\mathrm{s}})$ increased by over 70%, from 0.52 to 0.89. Experimentally, SmCo bulk magnets with varying amorphous content were fabricated and characterized. The results show that the amorphous-nanocrystalline magnets exhibit an enhanced remanence ratio and improved $({BH)}_{\max }$ compared to the fully nanocrystalline samples. The underlying mechanism was investigated through a combination of theoretical and experimental techniques, including micromagnetic simulations of the magnetization reversal process, first-order reversal curve (FORC) analysis, and in situ Lorentz microscopy for domain observation. All results consistently indicate that the significant remanence enhancement originates from strong interphase exchange coupling between the amorphous and nanocrystalline phases. This approach offers a potential pathway for optimizing the performance of rare-earth permanent magnets.

The interplay between low-dimensional quantum correlations and collective ordering is a central issue in strongly correlated quantum matter. Here, we report the magnetic properties of the verdazyl-based Ni complex $\left[\mathrm{Ni}\right(p\text{−}\mathrm{Py}\text{−}\mathrm{V}\text{−}p\text{−}\mathrm{Br}\left){}_2\right(\mathrm{EtOH}){}_2{\left({\mathrm{H}}_2\mathrm{O}\right)}_2]{\left({\mathrm{NO}}_3\right)}_2$, which realizes a three-dimensionally coupled frustrated square lattice. Magnetization and specific-heat measurements reveal antiferromagnetic ordering at low temperatures and a field-induced phase transition. High-field ESR measurements indicate field-induced decoupling of the $S=1$ spins that mediate the three-dimensional magnetic couplings, resulting in an effective spin-$1/2$ frustrated square lattice. Although the resulting lattice contains both Haldane-type and Tomonaga–Luttinger liquid (TLL) building blocks, no clear Haldane-gap behavior is observed. Instead, pronounced nonlinear magnetization persists up to high fields, suggesting an unusual regime in which Haldane and TLL correlations coexist and compete. These results demonstrate a route toward field-controlled dimensional reduction and emergent quantum states in frustrated square lattices.

We investigate the magnonic properties of a one-dimensional antiferromagnetic chain incorporating Dzyaloshinskii-Moriya interaction (DMI) and cross damping. By analyzing the magnetization dynamics in the linear regime, we show that the system can be mapped onto an effective modified non-Hermitian Su-Schrieffer-Heeger model. This mapping enables the application of non-Hermitian band theory, including topological invariants and the generalized Brillouin zone, to characterize the system. Within this framework, we uncover rich non-Hermitian and topological magnonic phenomena induced by the interplay of DMI and dissipative coupling. In particular, the system exhibits a bipolar non-Hermitian skin effect, where distinct magnon modes accumulate at opposite boundaries, as well as topological edge states arising from asymmetric DMI across interfaces. We further show that nonreciprocal cross damping breaks the symmetry between left- and right-localized modes and can selectively suppress edge states. Importantly, the strength of cross damping provides an effective tuning knob to control both the emergence and spatial localization of skin modes and topological edge states. Since such dissipative coupling can be engineered, for example, via spin pumping, our results establish a route toward dynamic manipulation of non-Hermitian magnonic excitations and offer a platform for designing tunable topological magnonic devices.

We establish an exact Bogoliubov sum rule for any Hermitian single-particle operator $O$: at each momentum, its particle-hole and particle-particle matrix-element weights sum to the single-particle trace ${\mathrm{Tr}}_s\left(O^2\right)$. The result follows solely from Hilbert–Schmidt-norm invariance under a canonical Bogoliubov transformation and contains neither excitation-energy denominators nor occupations; physical response identities therefore require additional assumptions. At zero field, a fully gapped helicity-diagonal state with both helicity sheets present and a spin-orbit splitting asymptotically larger than the gap obeys ${\chi }_{\mu \nu }\left(0\right)/{\chi }_N={\delta }_{\mu \nu }-{\mathrm{\Pi }}_{\mu \nu }+o\left(1\right)$, where ${\chi }_N$ is the normal-state Pauli susceptibility and $\mathrm{\Pi }={\langle {\widehat{\mathbf{n}}}_{\mathbf{k}}{\widehat{\mathbf{n}}}_{\mathbf{k}}\rangle }_{\mathrm{FS}}$ is the Fermi-surface average of the unit spin-locking texture. The eigenvalues of $\mathrm{\Pi }$ form a simplex, while the normalized spin Knight-shift tensor defines an ellipsoid whose semiaxes are the residual principal responses. Full cubic invariance of both the superconducting state and locking texture fixes $\mathrm{\Pi }=\mathbb{I}/3$ and hence $\chi \left(0\right)/{\chi }_N=2\mathbb{I}/3+o\left(1\right)$; cubic crystal symmetry alone does not. For zero-field $s$-wave pairing in the reference-Fermi-surface regime, we obtain the exact closed-form kernel $F_s\left(\lambda \right)=1-asinh\lambda /\left[\lambda \sqrt{1+{\lambda }^2}\right]$, valid for arbitrary $\lambda =\left|\mathbf{g}\right|/\mathrm{\Delta }$. In a finite Zeeman field, the zero-field helicity reduction generally fails, so the equilibrium magnetization and differential response require a self-consistent BdG calculation rather than a field-dependent locking-tensor substitution. Applied to the ${}^{75}\mathrm{As}$ data on ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$, the framework identifies a field-dependent axial suppression pattern at 8–16 T. Both its placement near the $\widehat{c}$-axis vertex and the resulting tension with a specified decoupled-pocket spin-orbit-texture baseline require an additional fixed-tensor $T\to 0$ and zero-field extrapolation; no unique microscopic pairing state follows.

Metal intercalation and stacking engineering provide effective routes to enhance superconductivity in two-dimensional borophene-based materials. Here we focus on the $\mathit{AA}$-stacked Sr-intercalated coloring-triangle-lattice (CTL) bilayer borophene ($AA\text{−}{\mathrm{SrB}}_{18}$), identified from a systematic first-principles screening of metal-intercalated CTL bilayers. Among 20 dynamically stable metallic $M{\mathrm{B}}_{18}$ phases derived from 17 intercalated bilayers with $\mathit{AA}$ or ${AA}^{\prime }$ stacking, isotropic electron-phonon coupling calculations identify $AA\text{−}{\mathrm{SrB}}_{18}$ as the most promising superconducting candidate. We subsequently examine $AA\text{−}{\mathrm{SrB}}_{18}$ using fully anisotropic Migdal–Eliashberg calculations, which yield a $T_{\text{c}}$ of 22.2 K and reveal a weakly separated two-gap superconducting state associated predominantly with B-$\sigma$- and B-$\pi$-derived Fermi-surface sheets. The enhanced superconductivity relative to pristine CTL bilayer borophene originates mainly from Sr-induced strengthening of the electron–phonon coupling, dominated by low-frequency Sr vibrations and intermediate-frequency out-of-plane B phonon modes. In addition, $AA\text{−}{\mathrm{SrB}}_{18}$ hosts symmetry-protected Dirac crossings that are essentially unaffected by spin-orbit coupling, indicating robust topological metallic characteristics. These results establish $AA\text{−}{\mathrm{SrB}}_{18}$ as a promising two-dimensional platform exhibiting the coexistence of phonon-mediated superconductivity and nontrivial electronic topology, and highlight intercalant selection and stacking engineering as effective strategies for designing boron-rich superconducting materials.