Nonmagnetic kagome metals and superconductors AV3Sb5 (A = K, Rb, Cs) host unconventional charge density wave (CDW) and superconducting (SC) phases accompanied by multiple electronic symmetry breaking. Due to the centrosymmetric crystal structure, inversion symmetry has generally been assumed to hold. Here, using scanning tunneling microscopy complemented by atomic force microscopy and optical second-harmonic generation, we directly reveal that inversion symmetry in the kagome plane is spontaneously broken in the CDW state. The mixed-parity CDW state exhibits ferroelectric dipolar and nematic quadrupolar ordered moments. The coexistence and coupling between the dipole and quadrupole favor noncollinear ferro-polar and nematic alignment that breaks all mirror symmetries and gives rise to robust electronic chirality in the 3Q CDW. The multipolar coupling to in-plane electric field enables electric field control and manipulation of the chiral polar-nematic CDW state, including its chirality. Below the SC transition, we observe parity-violating pair density modulations at both the original and the CDW lattice wavevectors. Our findings of parity-violating electronic chiral multipolar order provide microscopic insights into the magnetoelectric and nonreciprocal transport, loop current order, pairing density waves, and unconventional superconductivity in kagome metals and related quantum materials.

We investigate superconductivity in a two-band t-J model consisting of an itinerant orbital (orbital-0) and a quasi-localized orbital (orbital-1) using variational Monte Carlo. A robust orbital-selective d-wave superconducting state is found to emerge exclusively from the itinerant orbital. An analysis of the superexchange energy hierarchy shows that the quasi-localized orbital-1 competes with superconductivity by favoring local inter-orbital bound states, which act as energy defects and disrupt phase coherence. Consistently, the superconducting order parameter is monotonically suppressed as the occupancy of orbital-1 increases. Motivated by superconductivity in nickelate La_3Ni_2O_7, these results highlight the essential role of multi-orbital physics beyond the single-band t-J framework and point to a concrete route to enhance T_c: suppressing the involvement of localized d_z^2-derived orbitals.

Controlled generation of topological spin textures, such as merons and their bound state, the bimerons, is essential for advancing spintronic technologies and elucidating soliton physics in condensed matter. Using in situ Lorentz transmission electron microscopy coupled with femtosecond laser pulse, we demonstrate the creation of two distinct Bloch-type bimeron states in chiral magnet Co8Zn8Mn4 thin plates at room temperature. Magnetic imaging and micromagnetic simulations reveal that bimeron density varies with applied magnetic field strength, enabling dynamic topological control. We further establish that the topological classification of laser-generated bimerons is invariant with specimen thickness. Field-driven reversible transformations between elongated and circular bimeron morphologies are observed, governed by the competition of Zeeman energy and magnetic shape anisotropy. Micromagnetic simulations quantitatively reproduce these metastable states, validating a unified meron-skyrmion topological framework. This work establishes a single-pulse protocol for optical manipulation of topological spin textures.

We present a systematic study of the electronic structure of strained La_3Ni_2O_7 thin films. We show that biaxial compressive strain mainly elongates the outer apical Ni-O bond while leaving the inner apical Ni-O bond nearly unchanged. As a result, the Jahn-Teller splitting Δ_JT is strongly enhanced, whereas the interlayer d_z^2 hopping t_⊥^z changes only weakly. Since superconductivity is widely believed to emerge only below a critical in-plane lattice constant, our results identify the strain-enhanced Δ_JT as the relevant microscopic tuning parameter. Consistently, the calculated Fermi surfaces and Hall response for LaAlO_3 and SrLaAlO_4 substrates agree with ARPES and Hall measurements. Our results identify Jahn-Teller distortion as a key tuning parameter in strained La_3Ni_2O_7 and support its central role in optimizing superconductivity in bilayer nickelates.

The recent discovery of superconductivity in La_5Ni_3O_11 extends the family of superconducting Ruddlesden–Popper nickelates beyond La_3Ni_2O_7. Unlike conventional members of a single Ruddlesden–Popper series, La_5Ni_3O_11 contains an intercalated La_2NiO_4 layer between La_3Ni_2O_7 blocks, raising the question of whether this additional layer participates in the low-energy electronic structure. Here, we combine density functional theory, Wannier-based tight-binding modeling, and rotationally invariant slave-boson calculations to investigate the electronic role of the intercalated layer. We find that realistic electronic parameters place the La_2NiO_4 layer in gapped insulating regimes rather than a paramagnetic metallic state. Furthermore, realistic interlayer hybridization fails to generate any appreciable La_2NiO_4-derived spectral weight at the Fermi level. Our results demonstrate that the low-energy electronic structure of La_5Ni_3O_11 is governed primarily by the La_3Ni_2O_7 block, with the intercalated La_2NiO_4 layer remaining electronically inactive. This establishes a minimal low-energy description of La_5Ni_3O_11 and provides a unified framework for understanding superconductivity in intercalated Ruddlesden–Popper nickelates.

Hopfions are three-dimensional (3D) topological solitons predicted to exist in diverse magnetic systems, yet their practical utility has been largely restricted to cryogenic environments. Here, we overcome this temperature constraint by demonstrating stable magnetic hopfions in the chiral magnet Co8Zn8Mn4 at and above room temperature. Using a transmission electron microscope equipped for in situ optical excitation, we generate magnetic hopfions with femtosecond laser pulses. Long-term observations further reveal Brownian-like motion at room temperature and thermally activated collapse upon approaching the high-temperature regime. Together with micromagnetic simulations and homotopy group analysis, our experimental observations uncover the hopfion formation mechanism through the fusion of bimeron pairs. These findings establish room-temperature magnetic hopfions and provide a framework for their further studies under technologically relevant conditions.

ABSTRACT Topological magnetic skyrmions with nanoscale particle‐like characteristics and high manipulability have been intensively studied as promising candidates for next‐generation high‐density information units. Besides the chiral skyrmions determined by Dzyaloshinskii‐Moriya interaction (DMI), the energy competition between magnetic anisotropy and dipolar interactions has demonstrated rich freedoms for generating various topological spin configurations. Normally, circular configurations are favored for topological particles, leaving the square configuration only rarely observed in chiral antiskyrmions due to the anisotropic DMI so far. Here, we found that magnetoelectric manipulation can stabilize a variety of squarelike skyrmion bubbles at zero field in centrosymmetric DyFe 11 Mo magnet. Furthermore, by combining analysis of in situ Lorentz transmission electron microscopy (L‐TEM) images and micromagnetic simulations, the configuration transition between squarelike and circular skyrmion bubbles has been realized with the underlying mechanism clarified . The magnetic competition mediated by significant 3d‐4f electron interactions between rare‐earth and transition‐metal (RE‐TM) elements serves as the microscopic origin for magnetic texture manipulation, highlighting the extended application of the RE‐TM based magnets in exploring multiple topological spin textures and spintronic functions.

Moiré transition metal dichalcogenides have served as a versatile platform for simulating Hubbard physics. Recent experiments have identified robust superconductivity in moiré bilayer WSe_2 for certain twist angles. Here, we propose the gossamer nature of the superconductivity recently discovered at half-filling and zero displacement field in twisted WSe_2. By mapping the moiré continuum system to an effective extended single-orbital Hubbard model on the triangular lattice, we employ renormalized mean-field theory to investigate the strong-coupling phase diagram. We find that a moderate Coulomb repulsion partially suppresses charge fluctuations while preserving a finite density of mobile doublons and holes. In this regime, the interplay between extended kinetic hoppings and antiferromagnetic superexchange stabilizes a chiral d+id superconducting phase. Our results naturally account for the twist-angle-dependent evolution from a Mott insulator to a superconductor and eventually to a correlated metal. Furthermore, the model demonstrates that this half-filled pairing state vanishes rapidly upon density doping, consistent with experimental observations.

Skyrmion systems have been regarded as potential candidates for versatile energy-efficient information processing due to the intrinsic topological properties. In emerging skyrmion-based reservoir computing concepts, history-dependent spin state evolution constitutes a key physical ingredient, highlighting the importance of controllable collective dynamics in response to external stimuli. Antiskyrmions, as antiparticles of skyrmions, are expected to offer additional configurational degrees of freedom and enhanced thermal stability. However, experimental visualization of their field-dependent collective evolution remains scarce. Here we report a continuous, field-history-dependent antiskyrmion transition from a triangular to square lattice, accompanied by a sequence of intricate intermediate states in Mn1.4PtSn chiral magnet. Coordinated variations in antiskyrmion shape, size, and position are directly demonstrated, thereby offering experimentally multiple accessible degrees of freedom under controlled magnetic-field inputs. Systematic micromagnetic simulations reveal that the competition among Dzyaloshinskii-Moriya, dipolar, and Zeeman interactions governs the sequential reconfiguration of local spin textures underlying the observed lattice evolution. Our results provide a controllable and history-dependent antiskyrmion lattice platform with rich intermediate configuration states to explore multi-level information encoding and reservoir-computing applications.

Effectively implementing quantum algorithms on noisy intermediate-scale quantum (NISQ) processors is a central task in modern quantum technology. NISQ processors feature tens to a few hundreds of noisy qubits with limited coherence times and gate operations with errors, so NISQ algorithms naturally require employing circuits of short lengths via quantum compilation. Here, we evaluate a reinforcement learning (RL)-based quantum compiler on a superconducting processor. Our experiments reveal that for two-qubit circuits, the RL-based compiler surpasses conventional methods, demonstrating its ability to discover hardware-amenable circuits with near-optimal lengths. However, for three-qubit circuits, the RL-based compiler does not achieve unity theoretical fidelity. To address this limitation, we integrate a variational strategy with the RL-based compiler, highlighting their complementary strengths. Systematic experiments show that this variational RL-based compiler consistently identifies near-optimal circuits, even under stringent hardware constraints, outperforming conventional techniques. Furthermore, we analyze the impact of decoherence and gate errors, providing critical insights into the practical performance of RL-based compilers on quantum hardware. These findings exemplify the codesign of the software with hardware for efficient quantum compilation, offering valuable insights for the advancement of RL-based compilers.

Motivated by the evidence for time-reversal symmetry (TRS) breaking in nonmagnetic kagome metals AV3Sb5, a novel electronic order of persistent orbital loop-current (LC) has been proposed for the observed charge density wave (CDW) state. The LC order and its impact on the succeeding superconducting (SC) state are central to the new physics of the kagome materials. Here, we show that the LC order fundamentally changes the nature of the pairing instability and the SC state, leading to an extraordinary topological superconductor, dubbed as a roton superconductor. In a single-orbital model on the kagome lattice near van Hove filling, the LC CDW is a Chern metal, realizable in concrete models, with a partially filled Chern band hosting three Chern Fermi pockets (CFPs). We show that Cooper pairing of quasiparticles on the CFPs is described by three SC components coupled by complex Josephson couplings due to LC. The pairing instability is determined by the eigenvalues of the complex representation of the cubic group. We show that the Josephson phase is controlled by the discrete quantum geometry associated with the sublattice permutation group. A small LC can produce a large Josephson phase that drives the leading SC instability to a roton superconductor, where the internal phases of the three SC components are locked at 120^∘and loop supercurrents circulate around an emergent vortex-antivortex lattice with pair density modulations. We demonstrate by self-consistent calculations the properties of the roton superconductor and make theoretical predictions related to the recent experimental evidence for an exotic SC state in CsV3Sb5 exhibiting TRS breaking, anisotropic SC gap, pair density wave modulations, and charge-6e flux quantization. These findings are also relevant for the interplay between the orbital-driven anomalous Hall and SC states in other systems such as the moire structures.

The bilayer structure of the recently discovered high-temperature superconducting nickelate La3Ni2O7 provides a new platform for investigating correlation and superconductivity.Starting from a bilayer Hubbard model,we show that there is a molecular Mott insulator limit formed by the bonding band owing to Hubbard interaction U and large inter-layer coupling.This molecular Mott insulator becomes self-doped due to electrons transferred to the anti-bonding bands at a weaker inter-layer coupling strength.The self-doped molecular Mott insulator is similar to the doped Mott insulator studied in cuprates.We propose La3Ni2O7 to be a self-doped molecular Mott insulator,whose molecular Mott limit is formed by two nearly degenerate anti-symmetric dx2-y2 and dz2 orbitals.Partial occupation of the higher-energy symmetric dx2-y2 orbital leads to self-doping,which may be responsible for high-temperature superconductivity in La3Ni2O7.The effects of Hund's coupling JH on the low-energy spectra are also studied via exact diagonalization.The proposed low-energy theory for La3Ni2O7 is found to be valid for a wide range of U and JH.

The kagome metals and superconductors hosting rich correlated and topological electronic states have captivated quantum materials research. These states are triggered by an unconventional chiral charge density wave (CDW) wherein a chiral superconductivity emerges at low temperatures, yet the origin of this chiral CDW order, the parent state, is unresolved. Here, we report the discovery of a parent chiral-nematic Fermi liquid state in kagome metals and superconductors. We use spectroscopic-imaging scanning tunneling microscopy to study Ti-doped CsV3Sb5 where the CDW is suppressed, and find that multiorbital Fermi surfaces break all mirror reflections and exhibit handedness. We observe the chiral low-energy quasiparticle dispersions, providing direct evidence for a chiral-nematic electronic structure. We further observe the direct transition from the parent state to a chiral-nematic superconducting state. Moreover, in the samples with chiral CDW, we also observe the residual chiral-nematic QPI features, demonstrating that the CDW-triggered exotic states descend from the chiral-nematic Fermi liquid. Our findings not only provide a plausible chiral-nematic parent state, but also establish a new conceptual framework for exploring the emergence and consequences of such exotic quantum phases.

The discovery of high-T_c superconductor in Ruddlesden-Popper nickelate materials represented by La_3Ni_2O_7 has opened new directions in the quest for unconventional superconductivity. A central unresolved issue concerns the pairing symmetry of the superconducting order. In this paper, we model the superconducting order of La_3Ni_2O_7 using the established Fermi surface structure together with phenomenological pairing functions belonging to s_± and d-wave symmetry classes, which are the leading possibilities in the current debate. We compute several experimentally accessible observables-including tunneling density of states, point contact spectroscopy, superfluid density, and Raman spectroscopy-each of which exhibits distinct characteristics for different gap symmetries. These quantities provide a concrete and experimentally testable route for identifying the pairing symmetry of La_3Ni_2O_7 and for clarifying the microscopic nature of nickelate superconductivity.

We theoretically study the quantum spin Hall insulator (QSHI) in a perpendicular magnetic field. In the noninteracting case, the QSHI with space inversion and/or uniaxial spin rotation symmetry undergoes a topological transition into a normal insulator phase at a critical magnetic field B_{c}. The exciton condensation in the lowest Landau levels is triggered by Coulomb interactions in the vicinity of B_{c} at low temperature and spontaneously breaks the inversion and the spin rotation symmetries. We propose that the electron spin resonance spectroscopy with the ac magnetic field also aligned in the perpendicular direction can directly probe the exciton condensation order. Our results should apply to QSHIs such as the InAs/GaSb quantum wells and monolayer transition-metal dichalcogenides.

Fine-grained and anisotropic Alnico magnets were prepared by powder bed fusion using a laser beam. The as-built magnets were treated by solution treatment (ST) at 1250 °C, magnetic heat treatment (MHT) at 835 °C, and three-stage aging treatment (TSA) at 600 − 500 °C, respectively. The phase transition, microstructure evolution, and magnetic characteristics of the magnets were investigated. The findings demonstrate that as-built magnets are composed of equiaxed grains with a fine grain size of ∼1.5 µm and exhibit crystalline and magnetic anisotropy. After ST-MHT-TSA treatment, the magnets are composed of equiaxed grains with an average grain size of 12.1 − 15.5 µm, and every grain exhibits a spinodal structure consisting of the FeCo-type α1 phase and the Fe2NiAl-type α2 phase as well as enhanced < 211 > orientation. The orientation relation between α1 and α2 mainly forms {110}α1//{220}α2, {200}α1//{400}α2, and the atoms at the interface have a strong coherent matching. The spinodal structure in ST-MHT-TSA magnets mainly displays checkerboard-like. Both α1 and α2 phases exhibit a single domain structure; their interface is the magnetic domain wall. High α1 aspect ratio and anisotropy give Alnico magnet exceptional magnetic performance with Hc= 1363.1 Oe, Br= 9.0 kGs, and (BH)max= 6.2 MGOe. Furthermore, micro-magnetic simulations were used to disclose how some defect structures in the micro-regions affect the magnetic properties.

Magnetic skyrmions are promising as next-generation information units. Their antiparticle-the antiskyrmion-has also been discovered in chiral magnets. Here we experimentally demonstrate antiskyrmion sliding in response to a pulsed electric current at room temperature without the requirement of an external magnetic field. This is realized by embedding antiskyrmions in helical stripe domains, which naturally provide one-dimensional straight tracks along which antiskyrmion sliding can be easily launched with low current density and without transverse deflection from the antiskyrmion Hall effect. The higher mobility of the antiskyrmions in the background of helical stripes in contrast to the typical ferromagnetic state is a result of intrinsic material parameters and elastic energy of the stripe domain, thereby smearing out the random pinning potential, as supported by micromagnetic simulations. The demonstration and comprehensive understanding of antiskyrmion movement along naturally straight tracks offers a new perspective for (anti)skyrmion application in spintronics. Electric current pulses are used to move antiskyrmions, by coupling them with a helical track.

In superconducting qubit systems, microwave crosstalk among the qubit control lines is a prominent source of errors for gate operations, particularly when implemented simultaneously in a multiqubit system. In this work, we present an experimental study of crosstalk mitigation for the case of single-qubit gate operation, which involves the universal U3 gate decomposition into two Xπ/2 gates and three virtual Z gates. We demonstrate that by optimizing the virtual Z gate parameters, the crosstalk can be effectively mitigated, with the single-qubit gate fidelity recovered to the level comparable to that in the absence of crosstalk.

Bloch oscillations (BOs) are oscillations of electrons under external constant forces in a lattice, revealing the wavelike behavior of electrons. BOs lead to the localization of the wave packet that is called Wannier-Stark localization (WSL), resulting in the inhibition of conductivity. We simulate BOs experimentally in a one-dimensional superconducting circuit with nine qubits. The nine qubits form a one-dimensional lattice and an electron is mapped to a photon. We experimentally realize the coherent control of BOs by applying a well-controlled driving force with a frequency close to BOs. We observe the competition between localization and delocalization of the wave pocket by changing the drive parameters. Our study demonstrates the visualized wave behavior of electrons and proves a way to modulate electron transport in a perfect lattice.

The concept of Maxwell demon plays an essential role in connecting thermodynamics and information theory, while entanglement and non-locality are fundamental features of quantum theory. Given the rapid advancements in the field of quantum information science, there is a growing interest and significance in investigating the connection between Maxwell demon and quantum correlation. The majority of research endeavors thus far have been directed towards the extraction of work from quantum correlation through the utilization of Maxwell demon. Recently, a novel concept called Maxwell demon-assistant Einstein-Podolsky-Rosen (EPR) steering has been proposed, which suggests that it is possible to simulate quantum correlation by doing work. This seemingly counterintuitive conclusion is attributed to the fact that Alice and Bob need classical communication during EPR steering task, a requirement that does not apply in the Bell test. In this study, we demonstrate Maxwell demon-assistant EPR steering with superconducting quantum circuits. By compiling and optimizing a quantum circuit to be implemented on a 2D superconducting chip, we were able to achieve a steering parameter of $S_{2} = 0.770 \pm 0.005$ in the case of two measurement settings, which surpasses the classical bound of $1/\sqrt{2}$ by 12.6 standard deviations. In addition, experimental observations have revealed a linear correlation between the non-locality demonstrated in EPR steering and the work done by the demon. Considering the errors in practical operation, the experimental results are highly consistent with theoretical predictions. Our findings not only suggest the presence of a Maxwell demon loophole in the EPR steering, but also contribute to a deeper comprehension of the interplay between quantum correlation, information theory, and thermodynamics.