Physical Review B

Here, the authors determine the extreme-ultraviolet optical constants of monolayer and bilayer MoS${}_2$ through a combined experimental and first-principles study. They establish a consistent connection between two-dimensional conductivity and an effective three-dimensional refractive index, demonstrating that the optical response scales linearly with thickness. Unlike in the visible spectral range, they find that the XUV response is dominated by local-field effects, largely suppressing distinct excitonic signatures and providing benchmark data for future XUV and attosecond spectroscopies.

In trilayer transition metal dichalcogenides, strong quantum fluctuations stabilize quadrupolar excitons. This study reveals how this state breaks down due to strong correlations at high exciton densities. Attractive interactions drive antiparallel dipolar correlations, explaining the redshift to blueshift transition observed in recent experiments. Furthermore, the authors predict novel correlation driven quantum phases, specifically an exciton droplet and a staggered dipolar crystal, and detail their distinct experimental signatures to guide future experimental explorations.

We usually understand a critical point as occurring at a phase transition separating two distinct phases. Certain quantum many-body systems host unusual critical points that are entirely contained in a single phase of matter but are nonetheless protected for topological reasons. Here, the authors give general conditions when such “diabolical” critical points should exist and explore new types of classical phase transitions in which they might occur.

Here, the author develops a symmetry-based framework that explains why certain centrosymmetric antiferromagnets exhibit a finite anomalous Hall effect (AHE). In antipolarly distorted lattices, the inversional invariance of the spin-orbit interaction allows the antiferromagnetic state to be represented as an effective ferromagnet in a suitable local frame. This mapping naturally accounts for the emergence of conventionally ferromagnetic responses, including the AHE and a net orbital magnetization, even though the spin magnetization vanishes globally.

Three-dimensional topological insulators exhibit a quantized magnetoelectric effect described by a topological response theory. This hallmark result raises the question whether magnetoelectric effects rooted in topology also exist in lower dimensions. Here, the authors demonstrate a (quasi)topological magnetoelectric response in a class of two-dimensional antiferromagnets, which is similarly described by a topological response theory, yet in two dimensions and derived from topological semimetals. As such, the effect ultimately originates from a crystalline topological index in one dimension.

Helimagnets naturally host odd-parity spin splitting — spin locked antisymmetrically to momentum — but their theoretical description is hindered by large, sometimes incommensurate magnetic supercells. Here, the authors show that the generalized Bloch theorem removes this barrier: bands, spin polarization, and wavefunctions of any single-$q$ helimagnet can be obtained in the primitive cell and downfolded in reciprocal space. From first principles for MnI${}_2$, NiI${}_2$, and MnTe${}_2$, the authors find splitting maximized for $p$-orbital bands, and band spin texture that directly encodes the magnetic ordering vector.

Here, the authors propose a new concept of nonlinear pure spin current rooted in quantum geometry. A pure spin current carries electron spin sideways without a net charge current in the same direction, making it attractive for low-power devices. They predict a unique property that flipping the built-in electric polarization of a nonmagnetic material can reverse the pure spin current. This flipping behavior is absent in the conventional spin Hall effect, which has impeded potential applications of the spin Hall effect in spintronics for a long time. The systematic survey here identifies five crystal symmetry classes that allow this behavior, and quantum mechanical calculations predict it in five atomically thin ferroelectrics, paving the way for experimental detection and device application. The authors also propose an optical second-harmonic Kerr microscopy test with an estimated measurable signal, providing a practical route to verify electrically programmable, low-dissipation spin transport without magnetic order.

Recent numerical advances have renewed interest in the two-dimensional quantum $J_1$-$J_3$ Heisenberg antiferromagnet, but a detailed analytical theory has remained lacking. Here, the authors apply a semiclassical effective field theory and large-$N$ analysis. They show that previously overlooked interactions stabilize a quantum vestigial nematic phase at zero temperature, where discrete rotational symmetry is spontaneously broken despite the loss of long-range antiferromagnetic spiral order. This phase continues the known finite-temperature nematic phase, reflecting enhanced quantum fluctuations near the classical Lifshitz point.

Here, the authors use inelastic neutron scattering to investigate gapped Dirac magnons in the van der Waals ferromagnet CrI${}_3$. With high-quality single crystals, they directly resolve the characteristic winding of magnon spectral weight around the $K$ point of the hexagonal Brillouin zone, which provides a key signature of Dirac magnons. The authors further show that the magnon energies exhibit an approximately T${}^2$ thermal renormalization, consistent with magnon-magnon interactions.

Topological protection is weakened at armchair interfaces in quantum valley Hall systems because the two valleys mix and open a gap in the interface states. Here, the authors demonstrate that an adiabatic mass domain wall suppresses intervalley mixing, restoring robust propagation of topological interface modes throughout the bulk band gap. Experiments on silicon MEMS waveguides confirm efficient transmission through 90°, 120°, and 150° bends, establishing adiabatic geometry as a general strategy for designing versatile topological waveguides.

The interaction between surface acoustic waves and spin waves may open new routes for compact and efficient passive microwave devices. The design of such devices requires understanding of the magnetoacoustic phenomena. Here, the authors use phase-resolved micro-optical imaging to detect and discriminate both types of waves in their micropatterned device. By tuning the magnetic field, the authors directly image the resonant magnetoacoustic coupling and provide experimental evidence for the coherent excitation of spin waves by the traveling acoustic wave.

Spin-spin interactions of itinerant charge carriers in semiconductors are weak and rarely accessible for quantitative measurement. Here, the authors detect electron spin precession in a wide quantum well in an in-plane magnetic field through the spin Kerr effect at the exciton resonance of a narrow tunnel-coupled quantum well. Through theoretical modeling, they show that this effect is due to interwell electron-electron exchange. The narrow well exciton exchange splitting of only tens of microelectronvolts is measured from the Kerr signal.

Here, the authors revisit the question of the logarithmic renormalization of the Fermi velocity in graphene. Using large-scale Quantum Monte Carlo simulations of lattices with up to $2\times {10}^4$ interacting electrons, they directly connect experimental data with unbiased, nonperturbative calculations starting from a microscopic Hamiltonian. Their results reveal that even random-phase approximation corrections are quantitatively insufficient at realistic interaction strengths for suspended graphene, while continuum perturbation theory misses important lattice-scale effects. Remarkably, the optical conductivity still remains constant pointing to exact cancellation of different corrections.

Here, the authors reveal contrasting magnetoelastic effects in the metallic frustrated magnet CrB${}_2$: softening associated with Fermi surface nesting in compressive modes and spin-Jahn-Teller fluctuations in the shear mode. These results highlight the distinct roles of longitudinal and transverse magnetoelastic couplings in frustrated metallic magnetism.

The authors demonstrate here that the charge value of transport mechanisms impacts the validity of thermodynamic uncertainty relations (TURs) in the context of quantum transport in nanoscale junctions. They show that the recently established quantum TUR can be violated by the presence of transport processes that carry more than one charge, like Andreev reflection processes. To adequately address thermodynamic constraints in systems containing higher-order charge transport mechanisms, the authors propose a modified quantum TUR suitable for noninteracting electronic transport.

Far from equilibrium, heat flux profiles can exhibit complex and rapidly evolving shapes, hindering the formulation of macroscopic heat transport equations for energy currents in nanostructured semiconductors. Here, the authors address this challenge by decomposing the phonon distribution into a smooth component that captures its slowly evolving features and an arbitrarily complex component that accounts for higher-order corrections. Combined with the Boltzmann transport equation, this decomposition enables the prediction of heat transport under extreme confinement by modeling the slowly evolving component deterministically using the finite element method, while capturing the rapidly evolving component stochastically through a Monte Carlo scheme.

The authors analyze here the competition and coexistence of magnetic, charge, and $d$-wave superconducting orders in the two-dimensional Hubbard model using renormalization-group-improved Hartree–Fock calculations. The resulting phase diagram reveals superconductivity coexisting with Néel order on the electron-doped side and with spiral or stripe order on the hole-doped side. In the stripe phase, the superconducting gap is spatially modulated together with the charge order.

Four- or higher-order fermionic condensates can form in non-BCS multicomponent superconductors. Here, the authors present spectroscopic evidence for pairing correlations that appear well above the superconducting critical temperature in the highly overdoped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ system with broken time-reversal symmetry (BTRS). The NMR and $\mu$SR findings show that multicomponent superconductivity appears homogeneously throughout the entire sample volume and that the BTRS state is unrelated to conventional spin magnetism.

In single-crystal trigonal Te, the low-temperature Fano line shape of the Raman-active $A_1$ mode reflects interference between the phonon and an electronic continuum, whereas four-phonon scattering substantially shortens the lifetimes of low-frequency heat-carrying phonons and lowers the lattice thermal conductivity.

The authors present here results from electrical magnetotransport measurements on microstructures of altermagnetic CrSb in pulsed fields up to 68 T. They study the temperature and field-orientation dependence of magnetic quantum oscillations in combination with first-principles calculations. The observed frequency spectrum agrees well with density functional theory calculations that take spin-orbit coupling into account, without invoking significant $ad$ $hoc$ band shifts. The findings validate the predicted electronic band structure of CrSb hosting multiple semimetallic bands and a locally alternating spin polarization.

Here, the authors build a symmetry-based framework for rare-earth upconversion luminescence via deterministic polarization correlations among sequential absorption steps, previously assumed to be uncorrelated. Using polarization-resolved spectroscopy and crystal field modeling, they assign full Stark levels and irreducible representations for Er${}^{3+}$ in β-NaYF${}_4$ microrods and identify an approximate $C_3$ site symmetry. Since excited-state absorption inherits ground-state polarization constraints, both downshifting and upconversion luminescence exhibit excitation-wavelength-tunable, region-selective orthogonal excitation polarization responses.

Here, optical spin angular momentum is extended to nonmonochromatic electromagnetic fields, revealing that specific polychromatic configurations exhibit photonic spin precession governed by a Landau–Lifshitz-like equation. A precessing magnetic dipole realizes source-driven spin dynamics in the near field, while bichromatic two-wave interference additionally produces nutation. A generalized spin-continuity equation shows how sources act on optical spin through torque, establishing a direct link between photonic spin and magnetization dynamics.

The spin quantum Hall effect is the superconducting counterpart of the integer quantum Hall effect. Here, the authors derive the long-distance nonlinear sigma model for a quantum network with random tunneling between chiral links carrying $N$ channels. Strong even–odd tunneling asymmetry breaks the saddle point down. Also, the triplet sector stays coupled to the singlet one and can turn anomalously soft. The longitudinal and spin Hall conductances can be tuned independently, giving a flexible platform for class-$C$ localization.

Why does LaSc${}_2$H${}_{24}$ exhibit superior superconductivity compared with LaH${}_{10}$? Here, the authors indicate that scandium not only distorts the hydrogen cage structure but also creates MgB${}_2$-like Sc-H states at the Fermi level. This synergy enhances electron-phonon coupling, unifies strongly coupled H-H states with widely distributed Sc-H states on the Fermi surface, and leads to isotropic single-gap superconductivity with a higher superconductivity.

Here, the authors map the temperature-pressure evolution of the bilayer nickelate La${}_3$Ni${}_2$O${}_7$ and reveal that the suppression of tilts in oxygen octahedra is accompanied by a pronounced crossover toward a higher-carrier-density metallic state. By establishing the structural phase boundary over a broad temperature-pressure range, their results highlight the intimate interplay between lattice structure and electronic properties in this novel high-T${}_c$ superconductor.

Suggestive but indirect evidence for pair-density-wave correlations has been reported in several high-$T_{\mathrm{c}}$ cuprates, yet a bulk-sensitive scattering signature of the expected subharmonic charge response has remained elusive. Here, the authors use resonant soft x-ray scattering to identify a reproducible subharmonic charge density wave response near half the primary charge-ordering wave vector in two La-based cuprates. The response emerges in the stripe-ordered, layer-decoupled superconducting regime, where charge, spin, and superconducting correlations are intertwined.

Gyromorphs are disordered structures that retain quasi-long-range rotational order. They support unusually large, isotropic photonic band gaps, making them promising for technological applications. Here, the authors show that gyromorphs host higher-order topological insulating phases protected by rotational symmetry realized only on average, precisely where standard real-space diagnostics become ambiguous. They develop a diagnostic toolbox for average rotational symmetries that yields a consistent phase diagram, establishing gyromorphs as a new platform for statistical-symmetry-protected topology beyond crystals and quasicrystals.

The authors report here the coexistence of cubic and uniaxial magnetic anisotropies in thick epitaxial bcc Fe(110)/GaAs(110) films, with the latter having a magnitude comparable to that of the former. Their interplay stabilizes an in-plane easy axis along the ⟨001⟩ directions that persists throughout the film volume for thicknesses up to 100 nm. This unconventional behavior gives rise to a depth-dependent magnetic response, with perpendicular standing spin-wave modes exhibiting distinct sensitivities to different regions of the film thickness. The study further identifies anisotropic strain as the microscopic origin of the observed in-plane uniaxial anisotropy.

Integrable quantum spin chains are distinguished by infinitely many nontrivial local conserved charges, whereas generic systems are expected to have none. Here, the authors prove this expectation for spin-½ chains with symmetric nearest-neighbor interactions. Outside the known integrable families, no model has even one such charge. Thus, within this class, there is no intermediate possibility: a chain is either in a known integrable family, with infinitely many such charges, or has none.

Superconductivity begins when electrons bind into pairs. Because electrons are fermions, exchanging the two partners in a pair must flip the sign of its wavefunction — and that minus sign can be paid for in four different currencies: the pair’s spin, its spatial shape, its orbital character, and, less obviously, the relative time between the two electrons. Sharing one minus sign among four ± choices leaves exactly eight allowed kinds of Cooper pair. Balatsky and Banerjee show here that this eightfold rule is one face of a larger structure. A pair also has a center of mass — a place and a moment — and a superconductor can order in those as well. Taking internal shape (ρ), internal timing (τ), spatial modulation (R), and temporal modulation (T) as four independent axes builds the Berezinskii–Abrahams hypercube: a sixteen-corner map of superconducting order. BCS sits at the origin; each single axis recovers a familiar family — $p$- and $d$-wave gaps, odd-frequency pairing, FFLO and pair-density waves, driven superconductors. The corners in-between are hybrids. A few have been touched; most are empty, and the far corner, with all four switched-on at once, has never been visited. The hypercube is at once a classification and a search map.

The authors demonstrate here that the antiferromagnetic spin-½ Heisenberg model on the ruby lattice with second-neighbor interactions realizes a simplex valence-bond crystal state. Although singlet formation on the hexagonal plaquettes of the lattice appears to be a natural choice, the system instead selects simplices composed of two neighboring triangles. An effective spin-chirality description reveals how the interplay of spin and chiral degrees of freedom associated with individual triangles stabilizes simplex-based crystal order.

Here, the authors uncover size-dependent exciton formation and biexciton dynamics in AgInS${}_2$ quantum dots, an environmentally friendly I-III-VI semiconductor alternative. Exciton formation proceeds through phonon-mediated inter-valence-band hole relaxation. This process becomes progressively slower with decreasing quantum dot size, in contrast to the Coulomb-mediated relaxation characteristic of II-VI quantum dots. These dynamics govern the emergence of distinct exciton-to-biexciton transitions. The biexciton lifetime increases with crystallite size, with the largest quantum dots exhibiting partial biexciton emission.

Four-phonon scattering is widely viewed as the leading higher-order correction to anharmonic phonon dynamics. Here, the authors identify a previously overlooked scattering channel, in which cubic and quintic anharmonicity combine to produce three-phonon-like scattering at the same perturbative order. First-principles calculations show that this mechanism rivals four-phonon scattering in silicon and can approach ordinary three-phonon scattering in strongly anharmonic AgCl, reshaping the microscopic picture of lattice dynamics and thermal transport.

Pairing a ferromagnet with the MnBi${}_2$Te${}_4$ offers a promising route to efficient spin-to-charge conversion, but how well it performs across temperature had remained unmapped. Combining ferromagnetic resonance with inverse spin-Hall voltage measurements from 20–290 K, the authors show here that the spin-Hall angle stays nearly constant below approximately 130 K, then becomes unreliable as spin rectification and shifting damping take over. The results establish the material as a robust platform for cryogenic spin-orbit and topological spintronics.

Magnetic noise spectroscopy provides direct access to spontaneous magnetization fluctuations in correlated magnetic systems. Here, the authors investigate how demagnetizing fields influence magnetic noise spectra. By combining magnetic noise and ac susceptibility measurements across samples of different sizes and shapes, they show that sample geometry plays a decisive role in the measured fluctuations and must therefore be treated as a key experimental control parameter when probing intrinsic dynamics. Their results underscore the importance of boundary conditions and establish a framework for quantitatively comparing magnetic noise measurements with microscopic theories.

Kitaev interaction can generate unusual quantum states and is usually sought in compounds with strongly spin-orbit-coupled magnetic ions. Here, the authors combine neutron scattering with calculations of magnetic structure and excitations to establish sizable Kitaev and off-diagonal interactions in the spin-1 triangular magnet NiI${}_2$, with spin-orbit coupling supplied instead by surrounding iodine atoms. These interactions stabilize its canted proper-screw order and open an excitation gap. This finding extends the search for Kitaev physics into high‑spin systems with intrinsically weak ionic spin–orbit coupling.

Magnon-phonon coupling has attracted considerable interest because of its potential applications in hybrid quantum systems and magnonic devices. Here, the authors show that the coupling constant evolves from real to complex as the external magnetic field is reduced, thereby causing a pronounced minimum in phonon transmittance near zero field. The results demonstrate that the phase and magnitude of the complex coupling constant can be tuned with magnetic field in strongly damped magnets, offering a platform for exploring novel regimes of magnon-phonon interaction.

Edge transport is a powerful probe of anyons in fractional quantum Hall states. Here, the authors develop a nonequilibrium bosonization theory of interacting fractional quantum Hall edges, enabling a unified treatment of full counting statistics, anyon correlations, and tunneling transport far from equilibrium. For multimode edges, the theory reveals how interaction-induced fractionalization affects anyon dynamics through mutual braiding phases. It further predicts distinct signatures in experimentally accessible Fano factors, providing a route to probe anyonic braiding and fractionalization in nonequilibrium transport.

Here, the authors demonstrate that high-harmonic spectroscopy from lower-order to higher-order topological insulators reveals distinct contributions from bulk, edge, and corner electronic states. By systematically resolving these emission channels, they establish how topological features evolve across different classes of topological materials and clarify the microscopic origin of the emitted harmonics. Their results provide a unified framework for understanding and exploiting high-harmonic generation as a probe of topological quantum matter.