Suppressing lattice thermal conductivity ( κ _lat ) is pivotal for thermoelectric efficiency. While traditional strategies rely heavily on phonon scattering from mass- and size-mismatches, we demonstrate a robust κ _lat suppression mechanism driven by dopant-induced lattice stiffness modulation. Through a comparative analysis of p-type (Mn) and n-type (Co, Ir) doping in the β-FeSi2 model system, we show that Co and Ir doping significantly reduce κ _lat . Notably, Co doping achieves a ∼71
The local magnetic moments of atoms in a molecule or solid can be designated by different colors. Magnetic groups, or 2-color groups, or black-and-white groups have been applied in crystallography to classify different magnets. Despite its successes in the past decades, the recent advent of altermagnets and p-wave magnets raises new challenges to this long-standing framework, which calls for a new and unified one. Here we develop a multicolor group classification framework to classify nonmagnetic materials and magnets with collinear or non-collinear magnetism, and with or without spin-orbit coupling (SOC), including the recently identified altermagnets and p-wave magnets. Especially, altermagnetic topological matter with SOC and p-wave magnets can also be diagnosed with multicolor groups, a task which cannot be accomplished by magnetic space groups and spin space groups. Moreover, insufficiencies and misconceptions of conventional magnetic group classification can be supplemented through this new framework. Multicolor group will serve as a new stage in the symmetry classification of matter.
Tightly focused Bessel beams exhibit significantly higher intensity and non-diffractive three-dimensional micro-scale features compared to conventional fundamental Gaussian beams under the same optical power. These unique characteristics make Bessel beams particularly advantageous for enhancing photon pair generation in periodically poled nonlinear crystals. In this work, we experimentally demonstrate a compact pumping system using an asymmetric convex-convex lens and a plano-convex lens to generate Bessel beams. A broadband continuous-wave (CW) laser diode with a full-width at half-maximum (FWHM) of 0.54 (nm) is used to pump a periodically poled potassium titanyl phosphate (PPKTP) crystal configured in a type-II phase-matched dual-path Sagnac loop. Our setup achieves a record-high coincidence-to-single-photon (CSP) ratio of 25 810 (nm) , demonstrates exceptional performance metrics, including a brightness of 9.3 (kcps/mW) and a coincidences-to-accidentals ratio (CAR) of approximately 1091. Furthermore, the entanglement quality is verified through high visibility measurements: 99.2 (2.7 ± 0.04) , corresponding to a state fidelity of 0.95. In comparison, the Gaussian-pumped configuration yields a CSP ratio of 11.27 4.46 (kcps/mW) , and a CAR of approximately 500. Measured polarization visibilities are 99.1 S = 2.6 ± 0.03 . These comparative results underscore the substantial advantages of utilizing Bessel beams for high-performance entangled photon pair generation.
Anderson localization transition is a universal wave phenomenon characterized by a disorder-induced quantum phase transition from extended to localized states, whereas the non-Hermitian skin effect is a generic feature of non-Hermitian systems that causes bulk states to localize at the boundaries. Here, we report an unexpected skin-Anderson localization transition arising from the interplay between these two phenomena in hybrid-nonreciprocal systems that exhibit both reciprocity and nonreciprocity in different spatial directions. In the weak-disorder regime, the states are boundary-extended, meaning they are extended in reciprocal spatial dimensions but localized at the boundaries in nonreciprocal dimensions due to the non-Hermitian skin effect. As disorder increases, these boundary-extended states transition to boundary-localized states at a critical disorder strength. Remarkably, the corresponding critical points exhibit universal characteristics akin to those of the Anderson localization transition in its Hermitian counterpart, including identical critical exponents within numerical errors. When disorder exceeds a higher critical threshold, a second transition occurs in which boundary-localized states become bulk-localized, thereby eliminating the non-Hermitian skin effect. Thus, the skin-Anderson localization transition establishes a new framework for controlling state localization by unifying the physics of Anderson localization transitions with non-Hermitian topology.
The pursuit of geometrically frustrated lattices beyond conventional paradigms remains a central challenge in the design of quantum materials. Herein, we report the discovery of the A_3 V9Te13 (A = Cs, Rb) family of vanadium-based intermetallic compounds, which host a unique two-dimensional Mosaic lattice derived from the Kagome network, composed of an ordered tessellation of triangles, squares, and pentagons. The Cs compound (CVT) exhibits strong electronic correlations, characterized by non-Fermi liquid behavior at low temperatures, an exceptionally large Sommerfeld coefficient, and a bulk phase transition at T* ≈ 47 K with a possible charge- or spin-related origin. Inspired by pressure-tuning in related Kagome systems, we demonstrate that the electronic ground state of this lattice is exquisitely tunable via chemical pressure. Systematic substitution of Cs with smaller Rb ions suppresses the T^* phase transition and the correlated electronic response, ultimately driving the system into a highly frustrated semiconducting ground state without long-range magnetic order down to 60 mK. This work unveils a new structural platform for exploring the interplay between geometric frustration and strong electron correlations, providing a chemically controllable platform for exploring the phase space between distinct correlated electronic states.
Negative Differential Conductance (NDC) is a hallmark anomalous phenomenon in transport measurements, which is relatively rare in scanning tunneling microscopy due to its direct association with the local density of states. In this work, we constructed an ultrathin two-dimensional metal/semiconductor heterostructure by epitaxially growing a bilayer bismuth (Bi) film on a tin selenide (SnSe) substrate, revealing a unique moiré pattern arising from lattice mismatch. Spatially resolved tunneling spectroscopy detected a prominent NDC feature at approximately −650 meV. Both the energy position and depth of the NDC dip are strictly modulated by the periodicity of the moiré pattern. Our work not only establishes a novel Bi/SnSe material platform exhibiting NDC but also reports the visualization of NDC spatially modulated by a two-dimensional moiré superlattice, providing insight for the moiré electronics.
Strong electron correlation drives 1T-TaS2 from a half-filled metallic state into a Mott insulating phase, coexisting with a charge density wave at low temperatures. Under external stimuli such as pressure or ionic gating, superconductivity emerges in 1T-TaS2, exhibiting an intricate relationship of competition and coexistence with the charge density wave order. In the two-dimensional (2D) limit, enhanced quantum fluctuations can stabilize a quantum spin liquid (QSL) state in the Mott insulator. This review summarizes recent advances in understanding these quantum states in 2D 1T-TaS2 from the perspective of angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM), with a focus on the dimensionality effect on its electronic structure. We outline the signatures of QSL state in electronic spectra and discuss how this state can be revealed in the family of this material through experimental approaches beyond conventional probes such as neutron scattering. The role of Kondo effect in detecting spinon excitations is further discussed. Finally, we suggest future experimental directions and highlight how external perturbations such as gating and light excitation offer versatile pathways to control and exploit these intertwined quantum states.
Kagome materials have recently emerged as a versatile platform for exploring the intricate interplay among lattice, charge, spin, and orbital degrees of freedom, giving rise to a rich variety of quantum phenomena. While early studies predominantly focused on bulk kagome crystals, recent efforts have increasingly shifted toward their thin-film counterparts, motivated by the pursuit of enhanced tunability and potential device integration. Compared to bulk crystals, thin films offer distinct advantages such as precise control over strain, substrate-induced interactions, and reduced dimensionality, which together enable the modulation of electronic structures and the stabilization of emergent states. In particular, the ability to fine-tune key band features relative to the Fermi level provides a powerful route for engineering exotic states, including flat-band-driven magnetism, topological phases, and correlated electron phenomena. In this review, we provide a comprehensive overview of recent advances in the synthesis, characterization, and electronic structure studies of kagome thin films. We highlight key experimental breakthroughs that reveal how their topological and correlated properties evolve and discuss their broader significance within the landscape of quantum materials. Given the rapid convergence of experimental observations across diverse kagome systems, this review aims to offer timely guidance for future efforts toward unraveling the microscopic mechanisms of these unconventional electronic states.
Topological wave-packet dynamics provide a powerful framework for studying quantum transport in topological materials. However, extending this approach to non-Hermitian quantum systems presents several important challenges, primarily due to ambiguities in defining the Berry phase and the non-unitary evolution of the wave-packets when 𝒫𝒯 symmetry is broken. In this work, we adopt the complex Berry phase definition using the bi-orthogonal formalism and derive the semiclassical equations of motion (EOM) for a wave-packet in a non-Hermitian topological system. Interestingly, we find that the complex Berry curvature introduces both an anomalous velocity and a non-Hermitian Hall-like force into the semiclassical EOM. To validate the derived EOM, we design a non-Hermitian Haldane model featuring non-reciprocal next-nearest-neighbor (NNN) hopping, where the imbalance in the NNN hopping amplitudes gives rise to an emergent ‘complex chirality’. We reveal that the real and imaginary components of the complex chirality dictate the signs of both the real and imaginary parts of the complex Berry curvature, as well as the direction and dissipation rate of the edge states. Our analytical findings are confirmed by direct numerical simulations of the wave-packet dynamics. Finally, we suggest a potential experimental realization of this complex Haldane model using a non-Hermitian optical chiral cavity, providing a promising platform for testing our theoretical predictions.
Recently, gate-defined Josephson junctions based on magic-angle twisted bilayer graphene (MATBG) have been fabricated. In such a junction, local electrostatic gating can create two superconducting regions connected by an interaction-driven valley-polarized state as the weak link. Due to the spontaneous time-reversal and inversion symmetry breaking of the valley-polarized state, novel phenomena such as the Josephson diode effect have been observed without applying external fields. Importantly, when the so-called nonreciprocity efficiency (which measures the sign and strength of the Josephson effect) changes sign, the energy-phase relation of the junction is approximate $F(\phi) \approx \cos(2\phi)$ where $F$ is the free energy and $\phi$ is the phase difference of the two superconductors. In this work, we show that such a MATBG-based Josephson junction, when shunted by a capacitor, can be used to realize the long-sought-after $0$-$\pi$ qubits which are protected from local perturbation-induced decoherence. Interestingly, by changing the junction parameters, transmon-like qubits with large anharmonicity can also be realized. In short, by utilizing the novel interaction-driven valley-polarized state in MATBG, a single gate-defined Josephson junction can be used to replace complicated superconducting circuits for realizing qubits that are protected from local perturbations.
We report the superconducting properties of tensile-strained infinite-layer cuprate Sr 1− x Eu x CuO 2+ y thin films fabricated on KTaO 3 substrates via molecular beam epitaxy. The doping-dependent superconducting phase diagram shows an optimal doping level of $x\ \sim $ x ∼ 0.184 and a broader dome shifting to higher doping range due to reduced intralayer hopping and enhanced interlayer magnetic coupling. The characteristic of two-dimensional superconductivity is observed by Berezinskii-Kosterlitz-Thouless transition and the angle-resolved magnetoresistance measurements. Moreover, the temperature-dependent upper critical field and thermally-activated vortex motion under the in-plane and out-of-plane magnetic fields exhibit strong anisotropy, which further reveal the anisotropic nature of the superconductivity in infinite-layer cuprates.
The physical world is inherently out of equilibrium, and understanding the non-equilibrium behavior of quantum many-body systems remains a key open challenge in condensed matter physics. Recent advances in quantum computing platforms, such as Rydberg atoms and superconducting qubits, have opened promising avenues for studying non-equilibrium dynamics of many-particle systems using quantum simulators. In this work, we propose a benchmark scheme for validating the dynamical evolution outcomes of future large-scale qubit systems, which far exceeds the capability of classical numerical benchmark. Based on the J_1-J_2 Heisenberg model, we provide tunable analytical results including quantum walk dynamics, the out-of-time-ordered correlator (OTOC), and the butterfly velocity. Furthermore, taking IBM’s programmable quantum platform as an example, we design a scheme for simulating quantum walk dynamics and experimentally demonstrate the feasibility of benchmarking with our proposed dynamical observables.
The kagome lattice, with its unique geometric structure, has emerged as a leading platform for exploring quantum many-body physics, particularly in the study of quantum spin liquids (QSLs) and unconventional superconductivity. This review highlights recent advancements in the investigations of QSLs, fractional magnetization plateau phases in kagome antiferromagnets, and unconventional superconductivity in vanadium-based kagome superconductors. We begin by examining the classical ground-state properties of the nearest-neighbor kagome antiferromagnetic Heisenberg model and introducing recent experimental progress in the study of QSLs and fractional magnetization plateau phases. Next, we discuss the fermionic description of the QSL states, along with related gauge theory and the variational Monte Carlo (VMC) method. We then focus on discussing the VMC studies of QSLs and magnetization plateau phases in kagome antiferromagnets. For superconductivity in kagome systems, we first analyze the characteristics of the electronic structure and the possible associated electronic instabilities. Finally, we review recent experimental advances in unconventional superconductivity in AV3Sb5 (A = K, Rb, Cs), with a particular focus on chiral superconductivity and pairing density waves.
Elemental ferroelectrics, composed of a single element, have emerged as a new class of functional materials that offer distinct advantages of structural simplicity and compositional purity. Though elemental systems are typically stabilized in nonpolar, high-symmetry structures, ferroelectricity can be induced through various mechanisms including lattice distortions and interlayer charge redistribution that break centrosymmetry and drive the system into a polarized state. Both theoretical predictions and experimental demonstrations have revealed ferroelectric behavior in diverse elemental systems, with some exhibiting unique properties, including significant negative piezoelectric effects and stable charged domain walls. These findings not only advance fundamental understanding of ferroelectric mechanisms but also open new opportunities for novel ferroelectric applications.
The Gibbs free energy $(\Delta {G})$ ( Δ G ) of key intermediates has long served as the gold standard descriptor for evaluating catalytic activity in energy conversion reactions such as the hydrogen evolution reaction (HER). However, this thermodynamic criterion cannot explain why certain catalysts display exceptional activity at high overpotentials, far from equilibrium, despite possessing highly negative Gibbs free energies. Here, we demonstrate that for Pt-rare earth alloys with quantum confinement effects, negative adsorption energies can enhance surface hydrogen coverage and sustain rapid hydrogen evolution under large current densities through the Volmer-Heyrovsky (VH) mechanism. In the PtGd 3 alloys, quantum confinement effects emerge due to the large atomic radius and low electronegativity of Gd, which expand the Pt-Pt bond length and reduce d - d orbital overlap. This weak hybridization narrows the Pt d-band and shifts its center upward toward the Fermi level. The resulting redistribution of electronic density produces a more negative Δ G value compared with pure Pt. As a result, PtGd 3 exhibits lower HER activity near equilibrium but surpasses Pt under high overpotentials when kinetic factors dominate. These findings reveal how quantum confinement-induced electronic reconstruction can break the conventional thermodynamic equilibrium paradigm and offer a new design strategy for industrial-scale electrocatalysis.
We report the superconducting properties of tensile-strained infinite-layer cuprate Sr1−xEuxCuO2+y thin films fabricated on KTaO3 substrates via molecular beam epitaxy. The doping-dependent superconducting phase diagram shows an optimal doping level of x ∼ 0.184 and a broader dome shifting to higher doping range due to reduced intralayer hopping and enhanced interlayer magnetic coupling. The characteristic of two-dimensional superconductivity is observed by Berezinskii-Kosterlitz-Thouless transition and the angle-resolved magnetoresistance measurements. Moreover, the temperature-dependent upper critical field and thermally-activated vortex motion under the in-plane and out-of-plane magnetic fields exhibit strong anisotropy, which further reveal the anisotropic nature of the superconductivity in infinite-layer cuprates.
The nickelates present two distinct subfamilies: the square-planar nickelates, which are structural and electronic analogs to the single-orbital, strongly correlated cuprates; and the Ruddlesden-Popper nickelates, which exhibit a multi-orbital character reminiscent of the iron-based superconductors. This duality uniquely positions the nickelate family as a bridge between the two canonical systems, offering an unprecedented opportunity to comparatively study the physics of both within a single material platform. While the thermodynamic metastability of their superconducting phases presents significant synthesis challenges, shifting the focus to atomic-scale engineering of thin films, the nickelates provide a versatile new laboratory for deciphering the puzzle of unconventional superconductivity and exploring pathways to higher transition temperatures.
Quantum Hall effect (QHE) in graphene has been widely studied due to its simple device architecture, modest cryogenic requirements, and the unique non-equidistant Landau-level spectrum of Dirac carriers. Real-space visualization of the QHE in graphene is essential both for elucidating fundamental physics and for guiding graphene-based device design. Here, we present a novel scanning approach termed parallel EFM-sMIM imaging (PEMI) mode, which combines electrostatic force microscopy (EFM) and scanning microwave impedance microscopy (sMIM) to investigate the spatially distributed QHE in graphene. Comparative analysis reveals that the single-pass EFM mode demonstrates superior spatial resolution and signal-to-noise ratio compared to the constant-height EFM mode. PEMI measurements reveal that graphene’s electrical conductance manifests as discrete island-like domains exhibiting remarkable stability against magnetic field variations, and spatially distributed QHE states demonstrate independent emergence and evolution within these conductance islands. Notably, while tip-bias compensation demonstrates effectiveness in mitigating crosstalk interference, this technique inherently presents a trade-off by compromising the resolution of EFM signals. Finally, we employ contact-mode sMIM to measure carrier density and determine carrier type. This framework establishes a novel paradigm for parallel characterization of QHE textures and demonstrates promising extensibility to diverse 2D electronic systems through its adaptable architecture.
Molybdenum ditelluride (MoTe2) has recently emerged as a quantum material platform, especially exhibiting the fractional quantum anomalous Hall (FQAH) effect and unconventional superconductivity in its twisted bilayer configuration. However, a deep understanding of the strong many-body correlations and superconductivity in this system requires systematic real-space studies of the electronic and structural properties of few-layer MoTe2 by scanning tunneling microscopy (STM). This remains challenging due to the high air-sensitivity of MoTe2 and the difficulties associated with STM device fabrication. Here, we adopted an encapsulation strategy employing monolayer hexagonal boron nitride (hBN) that enabled atomic-scale characterization of air-sensitive MoTe2 devices via scanning probe techniques. This approach allowed us to probe both natural and twisted bilayer MoTe2 (tMoTe2) (with twist angle θ = 2.35^∘ ) directly while preserving their intrinsic electronic states. Our high-resolution scanning tunneling spectroscopy (STS) measurements detected the extremely weak valence band at the K-valley, in agreement with large-scale density functional theory (DFT) calculations. This work not only establishes a framework for studying air-sensitive quantum materials but also provides fundamental insights into moiré-engineered correlated and topological states in van der Waals heterostructures.
