Although quantum corrections (e.g., weak localization and electron-electron interaction) due to disorder, coherence, and interactions have been intensively studied for decades, understanding the magnon-electron interaction effect on quantum transport properties in magnetic systems still remains a challenge. Thus, the role of spin waves in the quantum transport of magnetic materials has not yet been fully understood. Driven by the miniaturization of spintronics devices possibly moving forward to quantum transport dimensions, in this work, we investigate spin wave mediated quantum transport in epitaxial antiferromagnetic ${\mathrm{Cr}}_2\mathrm{Al}$ films. Temperature($T$)-dependent conductance measurements reveal an additional linear $T$ contribution in the low-temperature range ($T<$ 30 K), which can be ascribed to the spin wave mediated electron-electron interactions in antiferromagnets. Brillouin light scattering confirms an antiferromagnetic resonance at near 80 GHz, consistent with the spin-flop field $H_{\mathrm{SF}}\sim$ 30 kOe derived from magnetoresistance measurements. Furthermore, the anomalous Hall effect in 2 nm ${\mathrm{Cr}}_2\mathrm{Al}$ films exhibits $G_{\mathrm{AH}}\propto$ ln $T$ and $G_{\mathrm{AH}}\propto G_{xx}^{0.9}$ ($T<$ 100 K), indicating that electron-electron Coulomb interactions contribute to the anomalous Hall effect through the extrinsic skew scattering mechanism, while the spin wave mediated electron-electron interactions show no contribution. These results provide critical insights into the effect of spin waves on the quantum transport properties of magnetic materials.

Nonlinear optical processes involving sum and difference frequency generation in solids offer powerful opportunities to gain deeper insight into fundamental light-matter interaction mechanisms, many of which have important technological applications. The efficiency of these interactions is closely linked to electronic states and increases significantly under resonance conditions. We report on resonant second-harmonic generation (SHG) on Frenkel excitons with sizes comparable to the crystal unit cell. The SHG study was done in the magnetoelectric antiferromagnet ${\mathrm{Cr}}_2{\mathrm{O}}_3$ at $1.4\mathrm{K}$, within the spectral range of 1.7–1.8 eV, where Frenkel excitons exhibit narrow spectral linewidths. High-resolution SHG spectra of these excitons reveal a strong polarization dependence and pronounced changes in SHG rotational anisotropies under an external magnetic field. A detailed theoretical analysis indicates that the magnetic-field-induced SHG spectral features originate from the combined Davydov and Zeeman splitting of exciton states in ${\mathrm{Cr}}_2{\mathrm{O}}_3$. We observe strong SHG nonreciprocity, arising from the interference between spontaneous antiferromagnetic and magnetic-field-induced nonlinear contributions to the SHG process. A magnetoelectric mechanism for magnetic-field-induced SHG is proposed. Additionally, the field-induced spin-flop transition from an easy-axis to an easy-plane state near $6\mathrm{T}$ generates a spin toroidal dipole moment, drastically modifying the SHG rotational anisotropy pattern. These experimental and theoretical results provide crucial insights into the fundamental mechanisms of nonlinear light-matter interactions in magnetoelectric antiferromagnets and pave the way for nonlinear optical devices.

We report on the electron spin resonance (ESR), heat capacity, magnetization, nuclear magnetic resonance (NMR), magnetic circular and linear dichroism (XMCD, XMLD), as well as the electrical resistivity of ${\mathrm{EuMn}}_2{\mathrm{P}}_2$ single crystals. Antiferromagnetic order of Eu was observed in several quantities at $T_{\mathrm{N}}^{\mathrm{Eu}}=18$ K. The temperature dependencies of ESR linewidth and resonance shift show, when approaching the Eu-ordered state, a divergence towards $T_{\mathrm{N}}^{\mathrm{Eu}}$, indicating the growing importance of magnetic correlations and the build-up of internal magnetic fields. An additional temperature scale of $\approx 47$ K has considerable impact on linewidth, resonance field and intensity. This points to the presence of weak Mn-based ordering. The observed ESR line is interpreted as an ${\mathrm{Eu}}^{2+}$ resonance, which probes the weak magnetic background of the Mn subsystem. Such a picture is suggested by the line shape which keeps to be Lorentzian across the 47 K scale and by the ESR intensity which can be described by the same Curie-Weiss temperature above and below 47 K. In the same temperature range, anomalies were observed at 48.5 and 51 K in the heat capacity data as well as a pronounced broadening of the NMR signal of the ${\mathrm{EuMn}}_2{\mathrm{P}}_2$ samples. In XMCD and XMLD measurements, this weak magnetic order could not be detected in the same temperature range which might be due to the small magnetic moment, with a potential $c$ component or frustration.

Altermagnets are a newly identified type of collinear antiferromagnetism with vanishing net magnetic moment, characterized by lifted Kramers' degeneracy in parts of the Brillouin zone. Their time-reversal symmetry-broken band structure has been observed experimentally and is theoretically well understood. On the contrary, altermagnetic fluctuations and the formation of the corresponding instabilities remains largely unexplored. We establish a correspondence between the quantum metric of normal and the altermagnetic spin-splitting of ordered phases. We analytically derive a criterion for the formation of instabilities and show that the quantum metric favors altermagnetism. We recover the expression for conventional $q=0$ instabilities where the spin-splitting terms of the normal-state model are locally absent. As an example, we construct an effective model of MnTe and illustrate the relationship between quantum geometry and altermagnetic fluctuations by explicitly computing the quantum metric and the generalized magnetic susceptibility.

Since the discovery of cuprates, the origin of high-$T_c$ superconductivity has been an outstanding puzzle. Recently, high-$T_c$ superconductivity was observed in a bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under pressure, whose structure hosts the apical oxygen between two layers, distinct from multilayer cuprates. Motivated by this discovery, we investigate its electronic structure using first-principles calculations and superconducting instabilities from both weak-coupling and strong-coupling perspective. Based on the first-principles band structures, we construct a bilayer two-orbital model on a square lattice, consisting of $d_{x^2-y^2}$ and $d_{z^2}$ orbitals, which accurately captures the low-energy electronic properties. Within this model, we study pairing instability using both functional renormalization group approach and multiorbital $t\text{−}J$ model. An $s_{\pm }$-wave pairing with sign-reversal gaps on different Fermi surfaces is revealed, reminiscent of iron-based superconductors. The Ni-$d_{z^2}$ orbital and its associated interlayer and intralayer exchange couplings are found to be crucial for the high-$T_c$ superconductivity. Our study provides valuable insights into the unique nature of electronic structure and superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ and contributes to the understanding of unconventional superconductivity.

We consider a superconductor under external perturbation, which forces Cooper pairs to develop with a finite total momentum $q$. The condensation energy of such a state decreases with $q$ and vanishes at a critical $q_c$. We analyze how superconducting order evolves at $q\approx q_c$. In three dimensions, the result is well known: the pairing susceptibility diverges at $q=q_c+0$, and the gap amplitude $\mathrm{\Delta }\left(q\right)$ gradually increases as $q$ decreases below $q_c$ and reaches its largest value ${\mathrm{\Delta }}_0$ at $q=0$. In two dimensions (2D), we find different behavior. Namely, for a parabolic dispersion, the pairing susceptibility also diverges at $q=q_c+0$, but at $q=q_c-0$, the gap amplitude jumps to the maximal ${\mathrm{\Delta }}_0$ and remains equal to it for all $q<q_c$. For a nonparabolic dispersion ${\varepsilon }_k=c{k}^{2\alpha }$, we find that for $\alpha >1$ the transition becomes second order, but the gap evolution is rather sharp, whereas for $\alpha <1$ it becomes first order, but $\mathrm{\Delta }\left(q\right)$ is nonmonotonic. This is similar, but not identical, to the behavior of magnetization near a Stoner transition in 2D.

The effect of high-energy electron irradiation on the temperature dependences of the resistivity ρ(T), fluctuation conductivity (FLC), and pseudogap (PG) Δ*(T) of $\mathrm{YB}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{7-\delta }$ (YBCO) single crystals containing virtually no twins was studied. A linear increase in the resistivity and a linear decrease in the superconducting (SC) transition temperature $T_c$ with increasing irradiation doses φ were observed. For relatively small φ, the linear $T_c$ can be described by the Abrikosov-Gorkov (AG) pair breaking theory, and for large φ, by the Emery-Kivelson (EK) theory, which takes into account the suppression of $T_c$ by quantum phase fluctuations caused by irradiation defects. As FLC shows, at the average value of ${\phi }_3=2.5\times {10}^{19}\mathrm{e}/\mathrm{c}{\mathrm{m}}^2$, which corresponds to the AG-EK crossover, the distance between the conducting $\mathrm{Cu}{\mathrm{O}}_2$ planes, $d_{01}$, as well as the coherence lengths along the $c$ axis, ${\xi }_{\mathrm{c}}$(0), and the region of SC fluctuations, $\mathrm{\Delta }{T}_{\mathrm{fl}}$, increase sharply, and the two-dimensional contribution of the Maki-Thompson fluctuations (2D-MT) unexpectedly changes to the two-dimensional contribution of the Aslamazov-Larkin (2D-AL). Surprisingly, no features in ρ(φ) and $T_c$(φ) indicating the AG-EK crossover are observed. At the same time, at ${\phi }_3$, a sharp increase in the opening temperature of PG, T*, as well as the value of PG, Δ*, is observed, which indicates a possible decrease in DOS under the influence of defects. With a further increase in φ, all the parameters of PG and its dimensions are greatly reduced, and an unusual shape of Δ*(T) is found. However, quite unexpectedly, at ${\phi }_5=5.6\times {10}^{19}\mathrm{e}/\mathrm{c}{\mathrm{m}}^2$ the temperature dependences of both FLC and PG demonstrate curves typical for well-structured YBCO, regardless of the number of defects.

In recent years, measurement induced entanglement transitions (MIETs) have attracted significant attention. However, the dynamical transition associated with the feedback induced skin effect, which exhibits a wealth of intriguing phenomena, has not been fully understood. In this work, we investigate a dynamical phase transition in a tilted free-fermion chain under measurement-feedback protocols, emphasizing the particle density and entanglement entropy dynamics. We reveal a feedback induced skin effect, enhanced by the Wannier-Stark ladder potential, that creates localization at one boundary and generates an effective pseudoedge under periodic conditions. The observables show a two-stage evolution: a rapid initial logarithmic growth followed by decay into an area-law steady state. Using a rescaling analysis, we pinpoint the critical behavior and offer an intuitive physical picture that links it to the feedback-driven suppression of quantum jump fluctuations. The resulting entanglement dynamics appear to be governed by a system-size-dependent delay, followed by a size-independent relaxation process. This behavior is consistent with the ballistic propagation of free fermions toward a domain-wall-like steady state and does not exhibit any signatures of nontrivial criticality. This work provides an effective supplement to the dynamical transition. It provides valuable references for linking the dynamical understanding of the role feedback plays in MIETs.

Metamaterials with Landau levels induced by synthetic pseudomagnetic fields present an exciting avenue for manipulating elastic waves. Traditionally, these Landau levels in elastic metamaterials are generated by out-of-plane pseudomagnetic fields, resulting in flat-band dispersions with limited bandwidth. In this study, we develop an elastic metamaterial with broadband ultrasonic chiral Landau levels induced by in-plane pseudomagnetic fields, which are synthesized by introducing linearly increased effective Dirac mass via locally breaking the inversion symmetry of each unit cell. We experimentally observe broadband zeroth-order chiral Landau levels for ultrasonic energy transmission. Additionally, we report the experimental observation of snake states, arising from the interaction between zeroth-order and first-order Landau levels. The excellent robustness of the chiral Landau levels is also experimentally validated. Our work suggests a way for realizing broadband ultrasonic chiral Landau levels in elastic systems, with promising potential for applications in engineering devices for integrated communication of elastic waves.

Understanding and predicting the anharmonic lattice dynamics of strongly anharmonic crystals remain significant challenges in condensed-matter physics and materials science. The high-entropy strategy offers a promising pathway in realizing “phonon glass electron crystal” (PGEC), yet the mechanisms underpinning the ultralow lattice thermal conductivity $\left({\kappa }_{\mathrm{L}}\right)$ are still largely intuitive and lack a clear physical picture. Here, we investigate the anharmonic lattice dynamics and the microscopic mechanism of the ultralow ${\kappa }_{\mathrm{L}}$ in ${\mathrm{AgSnSbTe}}_3$ single crystals leveraging the Wigner formalism, the compressed sensing lattice dynamics, and the anharmonic phonon renormalization. Neuroevolution potential is developed for homogeneous nonequilibrium molecular dynamics simulations to evaluate the effectiveness of the Wigner transport theory in describing the thermal transport of overdamped phonons. Our findings reveal that the off-centering effect significantly scatters the low-frequency optical phonon branches, while the large displacement vibrational modes of the Ag atoms result in extreme values of the Grüneisen parameters (γ). This study provides physical confirmations that the off-centering effect can attenuate the phonon intensity, and the vibration or diffusion of the weakly interacted atoms can enhance the anharmonicity. We also supply fundamental insights into the realization of the stable PGEC by employing the high-entropy strategy.

The anomalous Hall effect (AHE) is an efficient tool for detecting the Néel vector in collinear compensated magnets with spin-split bands, known as altermagnets (AMs). Here, we establish design principles for obtaining nonzero anomalous Hall conductivity in the recently proposed two-dimensional (2D) AMs using spin and magnetic group symmetry analysis. We show that only two of the seven nontrivial spin layer groups exhibit an unconventional in-plane AHE in which the Néel vector lies within the plane of the Hall current. Through first-principles simulations on bilayers of ${\mathrm{MnPSe}}_3$ and MnSe, we demonstrate the validity of our group theoretic framework for obtaining AHE with $d$- and $i$-wave altermagnetic orders, depending on the stacking of the bilayers. We find that the spin group symmetry is successful in determining the linear and cubic dependence of anomalous Hall conductivity in Néel vector space, although AHE is a relativistic effect. This work shows that the AHE in 2D AMs can probe the altermagnetic order and Néel vector reversal, thereby facilitating the miniaturization of altermagnetic spintronics.

We report the discovery of several classes of novel topological insulators (TIs) with hybrid-order boundary states generated from the first-order TIs with additional crystalline symmetries. Unlike the current studies on hybrid-order TIs where different-order topology arises from merging different-order TIs in various energy, these novel TIs exhibit unique properties, featuring a remarkable coexistence of first-order gapless modes and higher-order Fermi arc states, behaving as a hybrid between the first-order TIs and higher-order topological semimetals within a single bulk gap. Our findings establish a profound connection between these novel $d$-dimensional ($d\mathrm{D}$) TIs and ($d-1$)D higher-order TIs (HOTIs), which can be understood as a result of stacking $(d-1)\mathrm{D}$ HOTIs to $d\mathrm{D}$ with $d=3,4$, revealing unconventional topological phase transitions by closing the gap in certain first-order boundaries rather than the bulk. The bulk-boundary correspondence between these higher-order Fermi arcs and bulk topological invariants associated with additional crystallline symmetries is also demonstrated. We then address the conventional topological phase transitions from these novel TIs to nodal-line/nodal-surface semimetal phases, where the gapless phases host new kinds of topological responses. Meanwhile, we present the corresponding tolopogical semimetal phases by stacking these unique TIs. Finally, we discuss potential ways to realize these novel phases in synthetic and real materials, with a particular focus on the feasible implementation in optical lattices using ultracold atoms.

The multifunctional properties of $RTX$ ($R$ = lanthanide element, $T$ = Pd, Pt, and $X$ = Sb, Bi) half-Heusler compounds have attracted substantial attention for both fundamental research and potential applications. Within this series, we have investigated the electronic structure and physical properties of the TbPdSb single crystal, which crystallizes in the hexagonal structure with space group $P{6}_{3}mc$ (No. 186). The field and temperature dependence of the magnetization data reveal a strong magnetocrystalline anisotropy, and magnetic susceptibility for $B\parallel c$ shows two broad humps at $\sim 14$ and 125 K due to the presence of the crystal electric field (CEF) effect. The magnetic susceptibility data are well explained by the CEF analysis based on the point charge model, suggesting the $J$ = 6 multiplet of the ${\mathrm{Tb}}^{3+}$ ion splits into one singlet and six doublets with an overall splitting of $\sim 431$ K. The transverse magnetoresistance (MR) displays a crossover at the critical field $B{}^{*}$ from semiclassical $B^2$ dependence at low field to unsaturated linear $B$ dependence at high field up to 50 K. The critical field $B{}^{*}$ is proportional to the quadratic temperature dependence, which confirms the existences of Dirac fermions. The longitudinal MR also exhibits a rapid increase at low fields and a nonsaturating behavior with $B^2$ dependence at high fields. The Hall resistivity data suggest that electrical transport in TbPdSb is governed by the predominance of hole-type charge carriers. We have observed a large anomalous Hall conductivity of $\sim 1620 {\mathrm{\Omega }}^{-1}{\mathrm{cm}}^{-1}$ at 2 K and 3 T. Our Hall data analysis shows that the anomalous Hall effect in TbPdSb likely originates from the Berry curvature due to spin textures. The extensive first-principles calculations characterize TbPdSb as a topologically nontrivial nodal-line semimetal, showcasing the robustness of its Dirac points in the presence of the spin-orbit coupling effect. These findings offer valuable insights into its electronic and magnetic properties, unveiling its distinctive behavior at a fundamental level.

The quantized Thouless pumping charge in a spinless Rice-Mele model originates from a degeneracy point in the parameter space and cannot be detected when open boundary conditions are applied. In this work, we investigate the topological features of a spinful Rice-Mele model. We demonstrate that spin-orbit coupling facilitates the transition of a single degenerate point into a degenerate loop, which is anticipated to be the source of the topological characteristics. When periodic boundary conditions are considered, we find that the pumping spin is zero for an adiabatic loop within the nodal loop and is 2 (in units of $\hslash /2$) for an adiabatic passage enclosing the nodal loop. When open boundary conditions are considered, the boundary-bulk correspondence is demonstrated by quantized pumping spin flips at the edges, which can be obtained by completing double periods of a closed passage, rather than a single cycle. Our findings reveal an alternative dynamic manifestation of the boundary-bulk correspondence.

We report on the angle-resolved polarized Raman spectroscopy and estimation of the Raman tensor elements using both classical and quantum treatments to analyze the polarized Raman spectra of single crystal $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$. The observed polar patterns and systematic variations in the relative intensities of four characteristic Raman-active modes indicate a higher differential polarizability along the $c$ axis, accompanied by anisotropic photon-phonon interactions. This interplay of electron-photon-phonon interactions is crucial for understanding the lattice dynamics of $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$, which underpin its thermoelectric performance and topological properties.

Point-contact studies of interfacial chemical reactions have revealed that activation barriers can depend strongly on applied stress. However, discrepancies exist in reported values of the activation volume $\mathrm{\Delta }V$—the rate at which stress alters activation barriers—hindering its physical interpretation. We show that two contact mechanics effects—the spatially nonuniform stress, and the effect of load on reaction area—can lead to large errors. We derive a corrected model for Hertzian contacts as an example, and validate it using the growth kinetics of zinc dialkyldithiophosphate tribofilms. The model fully resolves disagreements in $\mathrm{\Delta }V$ between microscale and nanoscale atomic force microscope experiments. Our findings permit more accurate measurement of $\mathrm{\Delta }V$, which is crucial for understanding the stress-assisted thermal activation kinetics involved in mechanochemistry and tribochemistry.

The recent discovery of magic angle twisted bilayer graphene (MATBG), in which two sheets of monolayer graphene are precisely stacked to a specific angle, has opened up new opportunities in the field of topology, superconductivity, and other strongly correlated effects. Most conventional ways of preparing twisted bilayer devices require the use of high process temperatures and solvents and are not well suited for preparing samples which need to be flipped to be compatible with characterization techniques like scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), piezoresponse force microscopy (PFM), scanning thermal microscopy (SThM), and magnetic force microscopy (MFM). Here, we demonstrate a very simple polymer-based method using polyvinyl chloride (PVC), which can be used for making flipped twisted bilayer graphene devices. This allowed us to produce flipped twisted samples without the need of any solvents and with high quality as confirmed by PFM. We believe that this dry flip technique can be readily extended to twist 2D materials beyond graphene, especially air-sensitive materials which require operation under inert atmosphere, where often solvents cannot be used.