Within the family of altermagnets, CrSb is a metallic, collinearly ordered material that exhibits particularly strong symmetry-induced spin splitting in its band structure. In this study, we combine electrical magnetotransport measurements up to 68 T on microfabricated single-crystalline CrSb with first-principles calculations to investigate its Fermi surface. Notably, we study the temperature and field-orientation dependence of magnetic quantum oscillations observed in the magnetoresistance. The observed frequency spectrum agrees well with results from density functional theory calculations that take spin-orbit coupling into account, without invoking significant ad hoc band shifts. Our results confirm the predicted electronic band structure of altermagnetic CrSb and highlight the importance of high magnetic fields for accurately mapping the Fermi surfaces of unconventional emergent materials.

Period-averaged electromagnetic spin angular momentum is a well-established quantity for monochromatic fields, governing phenomena such as light-matter interactions with chiral particles and spin-orbit coupling effects. In contrast, the spin angular momentum of nonmonochromatic fields remains unexplored. Here, we extend the concept of optical spin to the domain of nonmonochromatic electromagnetic fields. Through this formulation, we uncover the precessional dynamics of electromagnetic spin in specific polychromatic configurations, including the superposition of circularly and linearly polarized plane waves propagating orthogonally at different frequencies, as well as fields generated by a precessing magnetic dipole. We discover that the dynamics of the electromagnetic spin in these cases obeys a Landau-Lifshitz-like equation, establishing a profound parallel between the dynamics of magnetization and photonic spin.

Elucidating the site symmetry of lanthanide dopants in micro/nanocrystals is essential for a comprehensive understanding of upconversion luminescence (UCL). Here, we report an excitation-wavelength-dependent polarization response in individual $\mathrm{E}{\mathrm{r}}^{3+}$-doped $\beta \text{−}\mathrm{NaY}{\mathrm{F}}_4$ microrods, where the degree of excitation polarization is tunable from 0 to 1 and the polarization orientation can be rotated by π/2. Further investigations reveal that subsequent excited-state absorption inherits the polarization orientation established by the initial ground-state absorption, with the degree of excitation polarization increasing as more excited-state absorption steps are involved in the upconversion process. Based on the Stark emission peaks of the ${}^4\mathrm{S}_{3/2}$ multiplet, polarization-verified crystal field calculations indicate that $\mathrm{E}{\mathrm{r}}^{3+}$ occupies spectroscopic sites with approximately ${\mathrm{C}}_3$ symmetry in the host. By assigning irreducible representations to all Stark levels, we establish a correlation between the macroscopic polarized UCL properties of $\mathrm{E}{\mathrm{r}}^{3+}$ and its local symmetry in a $\beta \text{−}\mathrm{NaY}{\mathrm{F}}_4$ lattice via point-group selection rules. Our work provides valuable insights into the polarization origins of UCL, offering an approach to optimize upconversion and realize diverse applications in polarized photonics.

The spin quantum Hall effect is a relative of the integer quantum Hall effect, characterized by integer quantized spin Hall conductance. In this work, we formulate and investigate a quantum network model consisting of $N$ channels per chiral link, preserving the fundamental symmetries of the spin quantum Hall effect. We demonstrate that, in the general case, the triplet sector of the theory remains coupled to the singlet sector. In the large-$N$ limit, we systematically derive the effective long-distance, low-energy field theory, identified as a nonlinear sigma model. Our analysis reveals that while triplet modes are typically massive and do not influence the large-$N$ nonlinear sigma model, specific conditions exist where these modes become soft, thereby increasing the diffusive length scale, which is the ultraviolet cutoff length of the effective theory. Furthermore, by calculating the bare longitudinal and spin Hall conductances, we show that the standard saddle-point approximation fails in regimes with significant tunneling asymmetry between even and odd links. Finally, we establish that the introduction of a Zeeman field not only breaks the SU(2) symmetry of the nonlinear sigma model action but also generates a term that explicitly violates inversion symmetry.

The discovery of ${\mathrm{LaSc}}_2{\mathrm{H}}_{24}$ represents an advance in the quest for room-temperature superconductivity, yet the microscopic mechanism underlying its high-temperature superconductivity remains unclear. Through a comprehensive revisit of theoretical analysis, we uncover a pivotal transition from the anisotropic two-gap superconductivity of ${\mathrm{LaH}}_{10}$ to an isotropic single-gap superconductivity in ${\mathrm{LaSc}}_2{\mathrm{H}}_{24}$ upon the introduction of scandium, thereby enhancing the superconducting critical temperature $\left(T_{\mathrm{c}}\right)$. This enhancement is rooted in a critical dual role of Sc $3d$ electrons: (i) the Sc-derived Jahn-Teller effect promotes hydrogen metallization via the elongation of specific interlayer H-H bonds and enhances electron-phonon coupling (EPC) through the softening of associated phonon modes; (ii) Sc $3d$ electrons reconstruct the electronic structure into an ${\mathrm{MgB}}_2$-like configuration, generating Sc-H-Sc $\sigma$- and $\delta$-bonding states with EPC strengths comparable to ${\mathrm{LaH}}_{10}$. Crucially, the pronounced orbital overlap between Sc and the hydrogen cages effectively unifies these two contributions on the Fermi surface. This Sc-induced gap unification bridges the high-EPC H-H states with widespread Sc-H states, establishing an isotropic single-gap nature with a large overall EPC strength. Our findings identify this Sc-induced gap unification as the fundamental mechanism for achieving room-temperature superconductivity in ${\mathrm{LaSc}}_2{\mathrm{H}}_{24}$, offering a theoretical blueprint for the future design of superior superconducting hydrides.

${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, a bilayer nickelate with Ruddlesden-Popper structure, undergoes a pressure-induced structural transition from a tilted Amam phase to an untilted Fmmm (or I4/mmm) phase near 10–15 GPa, concomitant with the emergence of high-$T_c$ superconductivity $(T_c\sim 80\mathrm{K})$. Despite intense interest, the phase boundaries and the impact of structural changes on the electronic properties remain unclear. Here, we combine high-pressure and high-temperature Raman and synchrotron-based infrared spectroscopies to map the structural and electronic evolutions. Raman measurements confirm the pressure-driven structural transition and reveal the emergence of Fano line shapes, indicating enhanced electron-phonon coupling. High-temperature data show analogous spectral signatures above 544 K, suggesting an upper temperature limit of the Amam phase within the T-P phase diagram of this system. Infrared reflectivity measurements evidence a concomitant enhanced metallicity, with a tremendous two-order-of-magnitude increase in carrier density, marking a crossover from a weakly to highly metallic state. These results establish a unified picture of the structural transition and its strong coupling to the electronic properties.

Pair-density-wave (PDW) correlations have been proposed as an important ingredient in the complex phase diagram of high-$T_{\mathrm{c}}$ cuprates, yet bulk-sensitive experimental signatures remain scarce. Here, we report resonant x-ray scattering measurements revealing a subharmonic charge-density-wave (CDW) scattering response in Sr-doped $1/8{\text{−}\text{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_4$ (LBCO). The subharmonic response appears at approximately half the primary CDW ordering wave vector and emerges within a physically relevant temperature regime associated with the development of in-plane superconducting correlations. Comparable subharmonic behavior is also observed in a chemically distinct La-based cuprate, ${\mathrm{La}}_{1.87}{\mathrm{Sr}}_{0.13}{\mathrm{Cu}}_{0.99}{\mathrm{Fe}}_{0.01}{\mathrm{O}}_4$ (LSCO), within the same stripe-ordered, layer-decoupled regime. Together, these observations identify a bulk-sensitive scattering signature that is consistent with PDW correlations in La-based superconducting cuprates.

Despite extensive studies of epitaxial Fe(110) films on GaAs(110), the magnetic properties of films thicker than 20 nm remain largely unexplored, even though this thickness range exhibits rich and unconventional magnetic behavior. In this work, we investigate epitaxial, Ag-capped bcc Fe(110) films with thicknesses ranging from 5 to 100 nm grown by molecular beam epitaxy. Their magnetic and structural properties are characterized using ferromagnetic resonance, vibrating sample magnetometry, x-ray diffraction, and microfocused Brillouin light scattering. Our measurements reveal the coexistence of cubic and uniaxial magnetic anisotropies, that in combination generate an easy axis aligned along the in-plane $\langle 001\rangle$ directions, which persists throughout the film volume even for thicknesses as large as 100 nm, having a magnitude comparable to that of the cubic anisotropy. To quantify the uniaxial volume anisotropy in thicker films, we fit the experimental data using a layer-resolved magnetic model that allows for a depth-dependent variation of magnetic properties across the film thickness. The precession-amplitude profiles of the perpendicular standing spin-wave modes across the film thickness lead to a depth-selective sensitivity of different modes, enabling the sensing of the local anisotropy landscape, from which a depth profile of anisotropy can be retrieved. X-ray diffraction measurements demonstrate that anisotropic strain—characterized by lateral anisotropic expansion accompanied by vertical compression—is the microscopic origin of the observed in-plane uniaxial anisotropy, persisting even in films with thicknesses up to 100 nm.

Gyromorphs are a new class of disordered systems that combine an amorphous-like absence of translational order with quasilong-range rotational order. Gyromorphs can outperform quasicrystals or hyperuniform arrangements in forming isotropic band gaps, suggesting an avenue to realize robust disordered topological phases. However, gyromorphs lack exact rotational symmetry, which is only realized on average, posing an obstacle for existing real-space invariants to correctly diagnose topological gyromorphs. In this work, we show that gyromorphs can host higher-order topological insulating phases protected by average rotational symmetry, and we develop and systematically compare tools for diagnosing topological phases protected by such symmetry. We introduce symmetry indicators of the effective Hamiltonian based on average rotational symmetries which, when combined with the spectral localizer and a scattering invariant, draw a consistent topological phase diagram. Our work unlocks gyromorphs as a novel platform to study topological phases beyond crystals, quasicrystals, and amorphous materials.

We provide a rigorous proof of the absence of nontrivial local conserved quantities in all spin-$\frac{1}{2}$ chains with symmetric nearest-neighbor interaction, except for known integrable systems. This result shows that there are no further integrable systems to be discovered. Our finding also implies that there are no intermediate systems with a finite number of nontrivial local conserved quantities. In addition, we clarify all short-support conserved quantities in nonintegrable systems, which we need to take into account in analyses of thermalization and level statistics.

We present a symmetry-based classification for superconducting pairing states, organized by the exchange properties of the anomalous correlation function rather than by a specific microscopic pairing mechanism. The classification is built from the pairwise permutation of spin, orbital, spatial, and temporal indices, leading to the fermionic constraint $\mathcal{S}{\mathcal{P}}^{*}\mathcal{O}{\mathcal{T}}^{*}=-1$, and is further organized by separating relative and center-of-mass space-time coordinates. This construction defines what we call the Berezinskii-Abrahams hypercube, in which conventional Bardeen-Cooper-Schrieffer superconductivity, unconventional $p$- and $d$-wave pairing, odd-frequency superconductivity, Fulde-Ferrell-Larkin-Ovchinnikov states, pair-density-wave states, and time-modulated superconducting orders appear as different sectors of a unified framework. Beyond organizing known phases, the Berezinskii-Abrahams hypercube identifies symmetry-allowed hybrid orders that have received comparatively little attention, including odd-frequency Fulde-Ferrell-Larkin-Ovchinnikov or pair-density-wave states and odd-frequency time-modulated superconducting states. We discuss microscopic routes, candidate platforms, experimental signatures, and stability constraints for these sectors, emphasizing the distinction between symmetry allowance and physical realizability. We also present the proximity-induced odd-frequency pair-density-wave state and its driven analog as two new examples of states that naturally emerge in the Berezinskii-Abrahams hypercube. The resulting framework provides a guide for connecting established superconducting phenomena with unexplored symmetry-allowed forms of order.

We investigate magnetization dynamics and spin-charge conversion in $\mathrm{NiFe}/{\mathrm{MnBi}}_2{\mathrm{Te}}_4$ heterostructures using broadband, temperature-resolved ferromagnetic resonance spectroscopy and inverse spin-Hall effect (ISHE) measurements over the 20–290 K range. A Landau-Lifshitz-Gilbert-based model simultaneously fits the temperature-dependent effective Gilbert damping ${\alpha }_{\mathrm{eff}}$ and the ISHE voltage, yielding the spin-Hall angle ${\theta }_{\mathrm{ISHE}}$. We find that ${\theta }_{\mathrm{ISHE}}$ remains nearly constant ($\approx 0.12–0.3$) at approximately 120–130 K. Above this temperature, ${\alpha }_{\mathrm{eff}}$ and $V_{\mathrm{ISHE}}$ decouple: the voltage drops while the damping increases, indicating that parasitic spin-rectification and a slight temperature drift of intrinsic NiFe damping dominate the signal and obscure direct spin-charge conversion. These results establish $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ as a robust platform for low-temperature spintronics and define the thermal boundaries above which secondary voltage contributions must be carefully managed.

We investigate the spin-$1/2$ Heisenberg antiferromagnet on the ruby lattice with uniform first- and second-neighbor interactions, which forms a two-dimensional network of corner-sharing tetrahedra. Using infinite projected entangled pair states (iPEPS), we study the ground state of the system to find that it is consistent with a gapped, threefold-degenerate simplex crystal phase, characterized by strong singlets formed on pairs of neighboring triangles. We argue that the formation of the simplex singlet ground state at the isotropic point relates to the weak intertriangle coupling limit, where an effective spin-chirality Hamiltonian on the honeycomb lattice exhibits an extensively degenerate ground state manifold of singlet coverings at the mean-field level. Under an applied Zeeman field, the iPEPS simulations uncover magnetization plateaus at $m/m_s=0,1/3,1/2,$ and $2/3$, separated by intermediate candidate supersolid phases, with partial reduction of the sixfold rotational symmetry of the lattice. Unlike the checkerboard lattice, these plateaus cannot be described by strongly localized magnons.

I-III-VI quantum dots are potential candidates for light-emitting and light-harvesting applications due to their heavy-metal–free composition and chemical tunability. Despite their potential, the investigation of intrinsic exciton and excitonic many-body dynamics has often been complicated because of their extensive defect energy landscape. Here, we investigate bright band-gap-emitting ${\mathrm{AgInS}}_2$ quantum dots of sizes ranging from $\sim 4$ to 7 nm using femtosecond pump-probe spectroscopy to link quantum confinement to exciton formation and many-body interactions. The exciton formation time is governed by inter-valence-band hole relaxation. This increases by more than a factor of 4 with decreasing quantum dot size, reflecting size-dependent exciton-phonon scattering efficiency. By temporally correlating hole relaxation with induced absorption dynamics, we identify different exciton-to-biexciton transitions originating from different exciton states. Excitation-fluence-dependent measurements reveal a biexciton decay time that scales with the quantum dot volume. Smaller quantum dots show fast decay of <100 ps, primarily governed by exciton-exciton annihilation. In larger quantum dots, the biexciton lifetime exceeds 400 ps, indicating reduced annihilation efficiency. Complementary streak-camera photoluminescence experiments provide direct spectroscopic evidence that these long-lived biexcitons are partially emissive. Collectively, we report an in-depth ultrafast-optical study yielding fundamental insights into the complex landscape of exciton formation and biexciton physics, which advances the understanding of intrinsic optical processes in ${\mathrm{AgInS}}_2$ quantum dots among I-III-VI materials.

Four-phonon scattering is widely regarded as the leading higher-order anharmonic correction to conventional three-phonon description of anharmonic scattering and lattice thermal transport. Here, we show that diagrammatic perturbation theory contains another phonon linewidth contribution of the same perturbation order, arising from the coupling between cubic and quintic anharmonic vertices. We derive and implement this contribution from first principles and identify it as a quintic-anharmonicity-assisted three-phonon scattering channel. Although this process shares the energy-conservation structure of the conventional three-phonon process, its perturbative order and temperature dependence resemble those of the conventional four-phonon process. For Si, we find that phonon scattering from this additional channel is comparable to four-phonon scattering over a broad frequency and temperature range, leading to a similar accelerated reduction of lattice thermal conductivity at high temperatures. We further show that in strongly anharmonic AgCl, this channel can become comparable to the ordinary three-phonon scattering even at room temperature. These results demonstrate that the commonly observed high-temperature enhanced scattering and suppression of lattice thermal conductivity might not be attributed uniquely to the four-phonon process, and establish quintic-anharmonicity-assisted three-phonon scattering as a previously overlooked same-order channel in anharmonic lattice dynamics, which may be leveraged to uncover hidden microscopic thermal transport mechanisms.

We study the phase of the coupling between magnons and surface acoustic wave (SAW) phonons in magnetic thin films. The coupling constant changes from a real to a complex number as the external magnetic field is reduced. Below a transition field, the imaginary coupling constant allows SAW phonons to couple to overdamped magnons whose resonance frequency is close to zero and far from the SAW resonance. The strength of the imaginary coupling constant and the magnitude of the transition field both scale with magnetic damping. We find the coupling produces a broad, pronounced minimum in the SAW transmittance spectrum near zero magnetic field in a Ni/Ru/Ni synthetic antiferromagnet with large magnetic damping. These results demonstrate that the phase of the complex magnon-phonon coupling constant can be tuned via magnetic field in strongly damped magnets, offering a platform to explore novel regimes of magnon-phonon interactions.

Magnetic noise spectroscopy provides direct access to spontaneous time-dependent magnetization fluctuations in correlated magnetic systems, including spin liquids, spin ices, and spin glasses. Here we investigate how demagnetizing fields shape the magnetic noise spectra measured in spin ice. By combining magnetic noise and ac susceptibility measurements on single-crystal spin ice samples with different sizes and shapes, we show that magnetic noise, like linear response, is strongly renormalized by sample geometry. As a consequence, measured noise spectra do not directly yield the intrinsic fluctuation spectrum, and demagnetization corrections cannot in general be determined from noise data alone. Instead, sample geometry must be treated as a central experimental control parameter for accessing intrinsic dynamics. These results establish the role of boundary conditions in fluctuation spectroscopy and provide a framework for quantitatively comparing noise measurements with microscopic theories of spin dynamics.

The bond-dependent anisotropic Kitaev interactions are the key for the Kitaev model, which has attracted intense interest for its potential to host quantum-spin-liquid states and fractional excitations. However, experimental realizations of such interactions remain scarce. Here, we investigate the magnetic excitations of ${\mathrm{NiI}}_2$, a van der Waals magnet with spin $S=1$. By combining inelastic neutron scattering, magnetization measurements, magnetic structure analysis, first-principles calculations, and linear-spin-wave simulations, we identify a minimal model that features substantial Kitaev and off-diagonal $\mathrm{\Gamma }$ interactions, which together stabilize the canted magnetic ground state and open a gap in the spin-wave spectrum. Notably, these interactions arise from strong spin-orbit coupling on the ligand ions, despite the quenched orbital moment of the magnetic ${\mathrm{Ni}}^{2+}$ ions. Our results provide compelling experimental evidence for the ligand-driven Kitaev mechanism. This demonstrates a concrete pathway to generating strong bond-dependent anisotropy in systems where the magnetic ions themselves have weak spin-orbit coupling, thereby substantially broadening the range of potential Kitaev materials.

Over the past decades, high harmonic spectroscopy (HHS) has emerged as a powerful tool for all-optical probing of topological properties of solids. There are outstanding questions regarding the universal nature of the spectral features of harmonics and their relationship to the nontrivial topological properties. Here, we present a systematic theoretical study of HHS in topological materials, including lower-order and higher-order topological insulators (LOTIs and HOTIs), focusing on observables such as helicity, circular dichroism, ellipticity dependence, and channel-resolved intensity yields. Using the Haldane, Kane-Mele, and breathing kagome lattice models, we theoretically extend all-optical approaches from the LOTI to the HOTI regime by explicitly incorporating contributions from bulk, edge, and corner states. Depending on the crystalline system, our calculations suggest that these observables can encode topological information through distinct modifications of the HHG spectra in topological phases. In particular, we identify significant enhancements of the harmonic intensity yields, reaching up to two orders of magnitude relative to trivial phases, together with distinct spectral signatures associated with edge and corner contributions revealed through channel-resolved intensity yields. These results show that channel-resolved HHS provides a promising route for probing topological states in both LOTIs and HOTIs.

Coherent control of quantum emitters is essential for scalable quantum photonic technologies. The recently proposed swing up of the quantum emitter population (SUPER) scheme allows efficient and coherent state preparation via off-resonant, red-detuned laser pulses, simplifying laser suppression and enhancing photon collection. We present a systematic study of SUPER excitation applied to a single GaAs quantum dot in a low-$Q$ micropillar cavity. We first identify the optimal excitation conditions for SUPER, and then compare the key figures of merit against the well-established two-photon excitation (TPE). Despite requiring higher excitation powers, SUPER achieves near-unity population inversion of the exciton state ($\sim 95\%$) and high single-photon purity ($g^{\left(2\right)}=0.03$) comparable to that under TPE, while also exhibiting a shortened decay time ($\sim 200$ ps) reducing the time jitter in the exciton population. A polarization-resolved analysis reveals that when both excitation and collection are aligned with one of the exciton dipoles, SUPER results in highly polarized single-photon emission, exceeding the resonant TPE saturation by a factor of 1.45. Under optimized excitation conditions, we also observe biexciton preparation via a distinct SUPER resonance, constituting an experimental demonstration of biexciton preparation using SUPER. These findings are in good agreement with a proposed four-level theoretical model that incorporates the biexciton state. Furthermore, we report that, strikingly, a slight misalignment of laser polarization induces an additional SUPER resonance that selectively populates the orthogonal exciton dipole, without altering the nominal excitation polarization. This unexpected behavior reveals a new degree of freedom for coherent state preparation. Our findings establish the SUPER scheme as a versatile tool for state-selective exciton and biexciton control, with strong potential for quantum photonic applications.