Time modulation introduces a dynamic degree of freedom for tailoring thermal radiation beyond the limits of static materials. Here, we investigate far-field thermal radiation from a periodically time-modulated SiC film under the Floquet nonequilibrium Green's function framework. We show that time modulation enables radiative energy transfer into the far field that surpasses the limit imposed by the equilibrium thermal fluctuations. This enhancement originates from the modulation-induced coupling between evanescent surface phonon polaritons and propagating modes, effectively bridging the energy and momentum mismatch through frequency conversion. Notably, even at zero temperature, the film emits a finite radiative heat flux due to nonequilibrium photon occupation generated by the modulation. The radiative output grows with increasing modulation strength, highlighting the role of external work in driving far-field emission. These results establish time modulation as an effective mechanism for bridging near-field and far-field regimes, opening different pathways for active thermal radiation control.

The consecutive magnetic ordering of the Ho and Ru ions in the pyrochlore ${\mathrm{Ho}}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$ and their interplay are investigated by neutron scattering, magnetic, and specific heat measurements. The Ru moments order at 95 K into a ${\mathrm{\Gamma }}_5$ easy-plane antiferromagnetic state. At 1.55 K, the Ho moments order into an unusual ${\mathrm{\Gamma }}_9$ ferromagnetic state with extensive ground state entropy and structured spin dynamics. It is shown how the internal fields with ${\mathrm{\Gamma }}_5$ and ${\mathrm{\Gamma }}_9$ geometry allow for two symmetry breaking transitions. The lower temperature ordering is driven by ruthenium mediated interactions between holmium moments as spin ice correlations develop. The unsaturated order is compatible with a fragmented ferromagnetic state equivalent to pyrochlore kagome ice.

We study two-dimensional massless Dirac fermions at neutrality, coupled to bosonic modes through a Yukawa interaction. We then examine the intriguing possibility that such a system, devoid of carriers at zero temperature, might nevertheless exhibit superconductivity. Remarkably, we find that superconductivity emerges in the vicinity of Gross-Neveu quantum criticality, provided the fermions cease to behave as well-defined quasiparticles, that is, once their anomalous dimension in the normal state becomes sufficiently large. In other words, well-defined fermions do not superconduct, whereas ill-defined ones do. We analyze four symmetry-distinct bosonic modes, each capable of driving normal-state criticality and, in three of the four cases, giving rise to a distinct superconducting phase. While phase fluctuations are strong in this regime, we argue that they do not destroy the superconducting state. We further characterize the resulting pairing states for a concrete Dirac model of spin-orbit coupled systems with orbitals of different parity. Our results are obtained using the Sachdev-Ye-Kitaev (SYK)-inspired framework for Dirac systems introduced by Kim et al. [Dirac fast scramblers, Phys. Rev. B 103, L081113 (2021)], which provides a controlled approach to the strongly coupled regime of Dirac fluids near Gross-Neveu criticality.

Measurements can detect errors in a decohered quantum memory allowing active error correction to increase the memory time. Previous understanding of this mechanism has focused on evaluating the performance of error-correction algorithms based on measurement results. In this work, we instead intrinsically characterize the information dynamics in a quantum memory under repeated measurements, using coherent information and relative entropy. We consider the dynamics of a $d$-dimensional stabilizer code subject to Pauli errors and noisy stabilizer measurements and develop a $(d+1)$-dimensional statistical mechanics model for the information-theoretic diagnostics. Our model is dual to the model previously obtained for the optimal decoding algorithm, and the potential decoding transition in the quantum memory again manifests as a thermal phase transition in the statistical mechanics model. We explicitly derive the model and study the phase transition in information encoding in three examples: surface codes, repetition codes, and the XZZX code.

The ongoing discoveries of graphene-based superconductors underscore the quest to understand the structure of new superconducting orders. We develop a theory that facilitates the use of the quantum twisting microscope (QTM) for that purpose. This work investigates momentum-conserving tunneling across a planar junction formed by a normal monolayer graphene tip and a superconducting graphene sample within the QTM setting. We show that the bias dependence of the zero-temperature tunneling conductance exhibits singularities that provide momentum-resolved information about the Bogoliubov quasiparticle spectra, including the superconducting gap. Using a model of superconducting twisted bilayer graphene (TBG), we illustrate that simultaneously tuning the tip doping level and the tip-sample twist angle allows for measuring the momentum-resolved superconducting gap in TBG. Our results indicate that momentum-conserving tunneling spectroscopy with the QTM is a promising method for exploring superconductivity in two-dimensional van der Waals materials.

We explore the constraints on the radiative properties of asymmetric open resonators imposed by energy conservation and time-reversal symmetry, identifying a connection between the bounds on scattering amplitude and the radiative phase difference between ports. Through this connection, we demonstrate that a radiative phase difference with nontrivial winding number is associated with fundamental scattering asymmetry bounds. When the scattering bound is applied to a zero-background reflection, the resonator supports degenerate coherent perfect absorption (CPA) states, yielding an exceptional point CPA. These bounds enable extreme light manipulation, connecting topological and non-Hermitian nanophotonic responses driven by broken symmetries.

Exchanging the positions of two non-Abelian anyons transforms between many-body wave functions within a degenerate ground-state manifold. This behavior is fundamentally distinct from fermions, bosons and Abelian anyons. Recently, quantum dot-superconductor arrays have emerged as a promising platform for creating topological Kitaev chains that can host non-Abelian Majorana zero modes. In this work, we propose a minimal braiding setup in a linear array of quantum dots consisting of two minimal Kitaev chains coupled through an ancillary, normal quantum dot. We focus on the physical effects that are peculiar to quantum dot devices, such as interdot Coulomb repulsion and residual single electron tunneling. We find that the errors caused by either of these effects can be efficiently mitigated by optimal control of the ancillary quantum dot that mediates the exchange of the non-Abelian anyons. Moreover, we propose experimentally accessible methods to find this optimal operating regime and predict signatures of a successful Majorana braiding experiment.

We introduce a class of dynamical field theories for $N$-component “Borromean” ($N\ge 3$) supercounterfluid order, naturally formulated in terms of interspecies bosonic fields ${\psi }_{\alpha \beta }$. Their condensation breaks the normal-state ${\left[\mathrm{U}\left(1\right)\right]}^N$ symmetry down to its diagonal U(1) subgroup, thereby encoding the arrest of the net superflow. This approach broadens our understanding of dynamical properties of supercounterfluids, at low energies capturing its universal properties, phase transition, counterflow vortices, and many of its other properties. Such supercounterfluid strikingly exhibits $N$ distinct flavors of energetically stable elementary vortex solutions, despite ${\mathbb{Z}}^{N-1}$ homotopy group of its $N-1$ independent Goldstone modes, with $N-1$ topologically distinct elementary vortex types, obeying modular arithmetic. The model leads to Borromean hydrodynamics as a low-energy theory, reveals the counterflow AC Josephson effect, and generically predicts a first-order character of the phase transitions into Borromean supercounterfluid state in dimensions greater than two.

We report the emergence of massless Dirac fermions in moiré-reconstructed bands of bilayer graphene (BLG) aligned with hexagonal boron nitride (hBN). Magnetotransport measurements reveal that while the primary BLG band retains a parabolic dispersion with a Berry phase of $2\pi$, the moiré-induced secondary bands at $n/n_0=\pm 4$ host chiral massless quasiparticles with a Berry phase $\pi$ and a Fermi velocity $v_m\approx 3.6\times {10}^5\mathrm{m}{\mathrm{s}}^{-1}$. This transition from massive to massless carriers arises from topological band reconstruction driven by the hBN moiré potential. Our results demonstrate that moiré engineering in BLG/hBN offers a powerful route to tune band topology and realize coexisting Dirac and massive fermions within a single crystalline platform.

Control of magnetic order in antiferromagnets is a central challenge in the development of next-generation spintronic devices. Here, we propose and analyze magnetization switching driven by the field-derivative torque (FDT), a torque that originates from the time derivative of an applied THz pulse acting on the staggered order parameter. Using atomistic spin simulations, we show that the field-derivative torque couples efficiently to the Néel vector, enabling deterministic switching without net spin accumulation. Further, we show that using the circularly polarized THz pulse, the FDT-induced magnetization switching reduces the required THz magnetic field by twofold. To this end, we compute the switching and nonswitching areas as a function of THz pulse width, THz magnetic field, and damping of the antiferromagnetic material. We find that the switching and nonswitching areas are completely deterministic in antiferromagnets. Moreover, the switching area increases by about 55% when the FDT is considered.

Topological kagome magnets offer a rich landscape for exploring the intricate interplay of quantum interactions among geometry, topology, spin, and correlation. ${\mathrm{GdTi}}_3{\mathrm{Bi}}_4$ crystallizes in layered Ti-based kagome nets intertwined with zigzag Gd chains along the $a$ axis and orders antiferromagnetically below $\sim 15\mathrm{K}$. Here, we present the temperature- and field-dependent electrical transport of ${\mathrm{GdTi}}_3{\mathrm{Bi}}_4$ in different directions. The material exhibits anomalous Hall conductivity (AHC) of $410{\mathrm{\Omega }}^{-1}\mathrm{c}{\mathrm{m}}^{-1}$ at 2 K for ${\mu }_{0}H\parallel c$, and it is completely absent for ${\mu }_{0}H\parallel a$, despite the similar magnetizations observed in both orientations. This behavior is quite contradictory, as the anomalous Hall effect (AHE) typically scales with the magnetization. Through first-principles calculations, it is demonstrated that in the presence of time-reversal symmetry broken by the Gd $4f$ sublattice and spin-orbit coupling, the magnetization direction controls the orbital mixing in the Ti $t_{2g}$ bands, relocating Berry-curvature hot spots and producing the observed orientation-selective AHC. The results establish ${\mathrm{GdTi}}_3{\mathrm{Bi}}_4$ as a platform for investigating new avenues of the AHE, such as directional AHE, and thus shed light on the intricate coupling between magnetic and electronic structures, paving the way for exploring novel quantum phenomena.

Tantalum (Ta)-based superconducting circuits have been demonstrated to enable ultrahigh qubit quality factors ($Q$), motivating a careful study of the microscopic origin of the remaining losses that limit their performance. We have recently shown that the losses in Ta-based resonators are dominated by two-level systems at low microwave powers and millikelvin temperatures. We also observe that some devices exhibit loss that is exponentially activated at a lower temperature inconsistent with the superconducting critical temperature (${\mathrm{T}}_c$) of the constituent film. Specifically, dc resistivity measurements show a ${\mathrm{T}}_c$ of over 4 K, while microwave measurements of resonators fabricated from these films show losses that increase exponentially with temperature with an activation energy as low as 0.3 K. Here, we present a comparative study of the structural and thermodynamic properties of Ta-based resonators and identify vortex motion-induced loss as the source of thermally activated microwave loss. Through careful magnetoresistance and x-ray diffraction measurements, we observe that the increased loss occurs for films that are in the clean limit, where the superconducting coherence length ($\xi$) is shorter than the mean free path ($l$). Vortex motion-induced losses are suppressed for films in the dirty limit, which show evidence of structural defects that can pin vortices. We verify this hypothesis by explicitly pinning vortices via patterning, and we find that we can suppress the loss by microfabrication.

Resonance Raman scattering is widely regarded as a powerful technique for probing material properties, since it provides access not only to the vibrational spectrum but also to the interplay between electronic structure and lattice vibrations. In order to obtain such information, however, it is necessary to tune the excitation energy to match a specific electronic transition of the material under investigation. In this paper, we investigate electron-phonon interactions in bulk $2\mathrm{H}\text{−}{\mathrm{MoTe}}_2$ near the indirect bandgap using a custom-built Raman microscope operating with an excitation laser in the infrared regime at 0.8 eV (1550 nm), a wavelength that has been rarely used in previous studies. Our experimental results, supported by ab initio calculations, demonstrate the scattering pathways responsible for the resonant enhancement of the second-order Raman peaks at 0.8 eV, while the first-order Raman scattering remains off-resonant at this excitation energy.

We present direct observation of the ringdown dynamics in the rotating frame of a resonantly driven single-mode nonlinear nanomechanical resonator. An additional close-to-resonance harmonic force excites nonlinear oscillations about the fixed point in the rotating frame. When the secondary drive is removed, we measure decay of the in-phase and quadrature components toward this fixed point. We show that the decay of the in-phase signal is nonexponential, even though the vibration amplitude decays exponentially if both forces are switched off, revealing an unexpected interplay between conservative nonlinearity and dissipation. A minimalistic model captures these dynamics as well as the spectrum of the vibrations excited by the additional force, relating them to the dissipation-induced symmetry breaking of the dynamics in the rotating frame.

We study the thermal transport properties of a mesoscopic device comprising two metallic islands embedded in a two-dimensional electron gas in the integer quantum Hall regime. It is shown that the $2M$ ballistic edge channels connecting the islands to the external reservoirs and the $N$ interisland channels play a central role in the phenomenon of heat Coulomb blockade. Unlike the single-island case, where the heat flux is reduced by exactly one quantum of thermal conductance, we predict an additional suppression proportional to the factor $M^2/{(2N+M)}^2$. We further examine a configuration in which the islands are placed between electrodes at different temperatures and identify the conditions under which the Wiedemann-Franz law is violated.

Recently the topic of altermagnetism has attracted tremendous attention, and ${\mathrm{RuO}}_2$ has been demonstrated to be one of the most promising altermagnetic candidates. However, disputes still remain on the existence of magnetic order in ${\mathrm{RuO}}_2$. Here in this work, we employ x-ray linear dichroism (XLD), a widely utilized technique for characterizing antiferromagnets, in conjunction with photoemission electron microscopy and multiple scattering calculation to provide clear evidence of the absence of magnetic order in epitaxial ${\mathrm{RuO}}_2$ films. The observed XLD signal is nearly invariant with temperature and independent of cooling-field direction, in stark contrast to the substantial magnetic-order-related XLD signal predicted by multiple scattering calculation. This finding strongly suggests a nonmagnetic origin for ${\mathrm{RuO}}_2$. Furthermore, we observed significantly distinct XLD signals at the Ru $M_3$ and O $K$ edges in ${\mathrm{RuO}}_2$ films grown on ${\mathrm{TiO}}_2$ substrate with different surface orientations, which can be attributed to the low-symmetry crystal field. These results unequivocally demonstrate the absence of magnetic order in ${\mathrm{RuO}}_2$ and establish XLD measurement as a robust technique for probing the low-symmetry magnetic materials.

To investigate the phonon dynamics of iron in the heavily hydride-ion-substituted region of ${\mathrm{LaFeAsO}}_{1-x}{\mathrm{H}}_x$ ($x>0.2$), ${}^{57}\mathrm{Fe}$ nuclear resonant inelastic scattering measurements were performed over a wide temperature range from 5 to 300 K on two polycrystalline samples with $x=0.35$ and 0.51, which exhibit superconducting and antiferromagnetic ground states, respectively. The resulting inelastic scattering spectra revealed distinct differences between the two compositions. The Fe phonon density of states (PDOS) exhibits a pronounced peak at 15 meV for $x=0.35$, whereas this peak is absent in $x=0.51$. Density functional theory calculations support the interpretation that the PDOS peak at 15 meV is associated with the optical vibrational modes of Fe atoms along the nearest-neighbor direction, mediated by As atoms. The calculations further suggest that the suppression of the PDOS peak at 15 meV for $x=0.51$ originates from in-plane electronic inequivalence. These findings suggest that signatures of electronic nematicity may persist over a wide temperature range in the $x=0.51$ composition, which exhibits magnetic and structural order, whereas such signatures are almost absent in the superconducting $x=0.35$ composition.

The origin of superconductivity in twisted bilayer graphene—whether phonon-driven or electron-driven—remains unresolved, in part due to the absence of a quantitative and efficient model for electron-phonon coupling (EPC). In this work, we develop a first-principles-based microscopic theory to calculate EPC in twisted bilayer graphene for arbitrary twist angles without requiring a periodic moiré supercell. Our approach combines a momentum-space continuum model for both electronic and phononic structures with a generalized Eliashberg-McMillan theory beyond the adiabatic approximation. Using this framework, we find that the EPC is strongly enhanced near the magic angle. The superconducting transition temperature induced by low-energy phonons peaks at $1.1^{\circ }$ around 1 K, and remains finite for a range of angles both below and above the magic angles. We predict that superconductivity persists up to $\sim 1.4^{\circ }$, where superconductivity has been recently observed despite the dispersive electronic bands [Finney et al., Proc. Natl. Acad. Sci. USA 119, e2118482119 (2022); Gao et al., arXiv:2412.01578]. Beyond a large density of states, we identify a key condition for strong EPC: resonance between the electronic bandwidth and the dominant phonon frequencies. We also show that the EPC strength of a specific phonon corresponds to the modification of the moiré potential. In particular, we identify several $\mathrm{\Gamma }$-phonon branches that contribute most significantly to the EPC, which are experimentally detectable via Raman spectroscopy.

The unexpected discovery of ordered magnetism in two-dimensional van der Waals materials at the monolayer limit [B. Huang et al., Nature (London) 546, 270 (2017)] challenges the Mermin-Wagner theorem [N. D. Mermin and H. Wagner, Phys. Rev. Lett. 17, 133 (1966)], which forbids spontaneous breaking of continuous symmetries in two dimensions at finite temperatures. The persistence of static magnetism in low dimensions is fundamentally influenced by magnetic anisotropy which is tied to the local single-ion crystalline electric field. Crucially, spin-orbit coupling connects the structural properties with spin degrees of freedom. We investigate the magnetic single-ion properties in the two-dimensional van der Waals magnet ${\mathrm{VI}}_3$. Utilizing neutron and x-ray diffraction, we map out the symmetry breaking phase transitions in ${\mathrm{VI}}_3$ and argue for the presence of a single structural transition at ${\mathrm{T}}_S\sim 80$ K, driven by an orbital degeneracy, followed by a ferromagnetic transition at a lower temperature, ${\mathrm{T}}_C\sim 50$ K. Through a comparative analysis of samples prepared under varying conditions, we suggest that lower temperature transitions reported near $\sim 30$ K are not intrinsic to ${\mathrm{VI}}_3$. A group theoretical analysis suggests a structural transition from rhombohedral $R\overline{3}$ to triclinic $P\overline{1}$ or $P1$. This transition is significant as it suggests the formation of two distinct crystallographically inequivalent ${\mathrm{V}}^{3+}$ sites on the honeycomb lattice, each with distinct spin-orbital properties. Neutron spectroscopy provides evidence for dominant magnetic exchange coupling only between symmetry-equivalent sites in the triclinic unit cell. We suggest this breaks up the low-temperature two-dimensional honeycomb ${\mathrm{VI}}_3$ lattice into two interpenetrating approximately hexagonal planes resulting in a fragmentated honeycomb. Our findings highlight the critical role of magnetoelastic coupling in determining the magnetic and structural phases in two-dimensional van der Waals magnets.

Inelastic neutron scattering in the chiral magnet ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ reveals strong nonreciprocal effects on magnon propagation at the boundary of the nuclear Brillouin zone. The nonreciprocal response is strongest at a central position between the zone corner and the edge midpoint. We explain these results using an effective linear spin-wave model. While directional effects in chiral magnets have so far only been known to exist at low momenta close to the center of the Brillouin zone, the present study shows that nonreciprocity persists at the highest possible reduced momenta. The observed magnons show very little damping within the limits of our experimental resolution, making them of great interest for the fundamental research on compact, high-frequency magnonic applications.