Transition metal dichalcogenide homobilayers unite two frontiers of quantum materials research: sliding ferroelectricity, arising from rhombohedral stacking, and moiré quantum matter, emerging from small-angle twisting. The spontaneous polarization of ferroelectric rhombohedral stacked homobilayers produces a highly tunable band structure, which, together with strain-induced piezoelectricity, governs the topology and correlated electronic phases of twisted bilayers. Here we present a systematic low-temperature optical spectroscopy study of rhombohedral stacked bilayer WSe2 to quantitatively establish its fundamental electronic and ferroelectric properties. Exciton and exciton-polaron spectroscopy under doping reveals a pronounced electron-hole asymmetry that confirms type-II band alignment, with the conduction and valence band edges located at the Λ and K valleys, respectively. Through distinct excitonic responses and tunable interlayer-intralayer exciton hybridization under displacement fields, we uncover the coexistence of AB and BA ferroelectric domains. Using exciton-polarons as a probe, we directly measure the intrinsic polarization field and extract the interlayer potential. Finally, we demonstrate electric-field-driven symmetric switching of the valence band maximum, attributed to ferroelectric domain switching. These results provide a complete experimental picture of the band alignment, spontaneous polarization field, and domain dynamics of rhombohedral stacked WSe2, establishing key parameters to understand twisted bilayers and enabling new ferroelectric and excitonic device opportunities.

Twisted trilayer (Tt) transition metal dichalcogenides with multiple rotational degrees of freedom offer unprecedented opportunities for constructing large-wavelength moiré superlattices to maximize the effect of correlated behaviors. Precisely stacking trilayer structures to realize ultra-large moiré superlattices remains a significant challenge, hindering investigations of moiré-tuned excitonic properties. Here we fabricate Tt MoS2 via chemical vapor deposition, in which two commensurate twists of 2.7° and 21.9° are sequentially introduced from the top to middle, and to bottom layers. An unprecedented super-moiré structure with an ultra-large periodicity of around 24nm is achieved, 30 times larger than that of 21.9°-bilayer MoS2, hierarchically composed of periodical mirror-symmetric triangular tessellation patterns consisting of five kinds of high-symmetric stacking registrations and the relaxation regions resulting from the interlayer gliding. This robust ultra-large-period superstructure generates a deep moiré potential to effectively suppress intralayer moiré excitons recombination and be against intervalley exchange interaction at the magnetic field up to 9T, associated with the enhanced layer-valley-locked polarization by two-fold larger than that of the trilayer systems with incommensurate angles. Our work presents angle-dependent super-moiré architectures in Tt systems as a versatile platform for designing moiré quantum materials with tailored optoelectronic responses, advancing applications in valleytronic and excitonic devices.

Much ado about MOFs: metal-organic-frameworks as quantum materials

Conventional Raman spectroscopy faces inherent limitations in detecting interlayer layer-breathing (LB) vibrations with inherently weak electron-phonon coupling or Raman inactivity in two-dimensional materials, hindering insights into interfacial coupling and stacking dynamics. Here, we demonstrate a universal plasmon-enhanced Raman spectroscopy strategy using gold or silver nanocavities to strongly enhance and detect LB modes in multilayer graphene, hBN, and their van der Waals heterostructures. Plasmonic nanocavities even modify the linear and circular polarization selection rules of the LB vibrations. By developing an electric-field-modulated interlayer bond polarizability model, we quantitatively explain the observed intensity profiles and reveal the synergistic roles of localized plasmonic field enhancement and interfacial polarizability modulation. This model successfully describes the behavior of plasmon-enhanced LB vibrations across different material systems and nanocavity geometries. This work not only overcomes traditional detection barriers but also provides a quantitative framework for probing interlayer interactions, offering a versatile platform for investigating hidden interfacial phonons and advancing the characterization of layered quantum materials.

From Synthesis to Superconductivity: Hands-On Learning of Quantum Materials through YBCO Doping

In pursuit of a practical quantum advantage1, analogue quantum systems provide an invaluable way to simulate the physics of quantum materials2-4, quantum systems out of equilibrium5,6 or interaction-induced localization7. Notable recent progress to realize such systems has been achieved in ultracold atoms8-12, superconducting circuits13-15 and twisted van der Waals materials16-19. However, so far, these platforms have struggled to simulate large-scale strongly interacting fermionic systems at low temperatures, at which electronic correlations dominate materials properties and numerical simulations remain restricted in accuracy and scope20,21. Here we demonstrate the realization of a new platform consisting of large-scale 2D arrays of sub-nanometre precision-engineered atom-based quantum dots (15,000 sites) to simulate strongly interacting, low-temperature physics. By observing a metal-insulator (MI) transition on a 2D square lattice of atom-based quantum dots, we demonstrate independent and precise control of the on-site interaction U and tunnelling t. Magneto-transport measurements further indicate the formation of an insulating state driven by Mott-Hubbard/Anderson physics and promising signatures of correlated electron physics. These precision-engineered analogue quantum simulators provide a unique platform to simulate quantum materials on arbitrary 2D lattices and to explore many unanswered questions in the formation of quantum magnetism, interacting topological quantum matter and unconventional superconductivity.

ConspectusCoordination polymers (CPs) and metal-organic frameworks (MOFs) are highly valued for applications in gas storage, separation, and catalysis, but their electronic applications have been limited by low electrical conductivity and charge mobility. The rise of conjugated coordination polymers (c-CPs) has changed this scenario entirely. c-CPs utilize planar, conjugated ligands with ortho-donor coordination groups (-OH, -SH, -NH2, -SeH) to form extended lattices with transition metals, enabling strong d-π conjugation and exceptional charge transport properties.In this Account, we trace our decade-long efforts to develop a distinctive family of c-CPs: those based on the small yet versatile ligand, benzenehexathiol (BHT). We highlight how the small BHT ligand and its soft -SH donors, compared with hexahydroxytriphenylene (HHTP) and hexaaminotriphenylene (HATP) used in conducting CPs and MOFs, promote stronger metal-ligand coupling, enhanced charge delocalization, and richer coordination chemistry, underpinning the high conductivity and structure diversity of BHT-based c-CPs. We detail the innovative synthetic strategies, such as interfacial synthesis and redox modulation, that enable us to obtain a series of high-crystalline, high-conductivity BHT-based c-CPs. This family of materials has consistently broken records, achieving metallic conductivities exceeding 103 S·cm-1 and charge mobilities up to 400 cm2·V-1·s-1. Notably, they provide a versatile platform for discovering exotic quantum phenomena that are rare in framework materials. Our exploration led to the first CP-based superconductor, Cu3BHT, and has revealed candidates for topological phases such as Weyl semimetal in Ag3BHT and Kondo lattice in CuAg4BHT.We conclude by emphasizing how the structure diversity of BHT-based c-CPs dictates their exceptional chemical and physical properties. This Account is more than a summary. It is a blueprint for the design of the next generation of electrically conducting CPs, illustrating how rational ligand design and synthetic control are able to not only advance electronic material exploration but also open new frontiers in quantum materials research.

Abstract The complex phase diagram of 1T-TiSe 2 consists of a charge density wave (CDW) below 200 K, and CDW fluctuations of still unknown origin at higher temperatures. Here, we use time-resolved extreme ultraviolet momentum microscopy and density functional perturbation theory to uncover the formation mechanism of CDW fluctuations and their spectral features at 295 K. We investigated the transient dynamics of fluctuations upon nonresonant ultrafast photoexcitation, and directly correlate it with the CDW soft-phonon hardening. Surprisingly, our results show that the coherent amplitude mode modulating ultrafast CDW recovery persists above T CDW , and reveal that CDW fluctuations are dominated by the electron-phonon interaction rather than excitonic correlations as commonly believed. Our findings on these microscopic CDW fluctuations clarify the complex interplay between electronic and lattice degrees of freedom at elevated temperatures and, therefore, could be useful in understanding the nature of the CDW phase transition in 1T-TiSe 2 and similar quantum materials.

Isosbestic point formation on transverse magnetoresistance curves for strongly correlated quantum matter

Local shot noise spectroscopy with scanning tunneling microscopy (STM) has proven to be a powerful technique to investigate the electronic properties of quantum materials. It provides direct and non-invasive insight into the tunneling charge quanta or dynamics at the atomic scale. Due to the typically weak noise signal and the presence of low frequency spurious noise, local noise experiments require a high-resolution measurement amplifier. Here, we present a newly developed high-resolution noise amplifier that we implemented in three different STMs. Compared to our previous generation, we obtain more than a 20-fold improvement in the noise resolution, allowing us to resolve values of the effective charge as small as 0.01e. Our amplifier opens new possibilities for studying electronic properties in novel materials such as d-wave superconductors. In addition to this, it can give direct information about the local electron temperature in STM experiments.

ABSTRACT Landau levels are cornerstones of a wide range of quantum phenomena and applications. Understanding the impact of the gauge field, or pseudomagnetic field, on the electronic structure of 2D materials is critical for manipulating Landau electrodynamics. Although extensive theoretical and experimental studies have been carried out to probe pseudomagnetic field in graphene, most of them have been focused on the strain‐ and substrate‐engineering methods and magnetotransport properties. Here, we present using graphite as a unique material testbed for realizing isotope‐induced pseudomagnetic field. Using magneto‐Raman spectroscopy, we show that pure graphite and ‐doped graphite both exhibit graphene‐like Landau level transitions. Remarkably, we demonstrate that ‐doping leads to splitting of the Landau level transitions, a signature of pseudomagnetic field on the scale of 0.2 T. Moreover, the split Landau level transitions selectively couple with the G band phonon in distinct energy ranges. Our results highlight isotope doping as a feasible material engineering method of creating pseudomagnetic field and tuning magneto‐optical properties in 2D quantum materials.

Magnetoelectric coupling enables the manipulation of magnetization by electric fields and polarization by magnetic fields. While typically found in heavy element materials with large spin-orbit coupling, recent experiments on rhombohedral-stacked pentalayer graphene have demonstrated a longitudinal magnetoelectric coupling (LMC) without spin-orbit coupling. Here, we develop a microscopic theory of LMC in layered quantum materials and identify how it is controlled by a "layer-space" quantum geometry. Focusing on rhombohedral multilayer graphene systems, we find that the interplay between LMC and valley-polarized order produces a butterfly shaped magnetic hysteresis controlled by out-of-plane electric field: a signature of LMC and a multiferroic valley order. Furthermore, we identify a nonlinear LMC in rhombohedral multilayer graphene under time-reversal symmetry, while the absence of centrosymmetry enables the generation of a second-order nonlinear electric dipole moment in response to an out-of-plane magnetic field. Our theoretical framework provides a quantitative understanding of LMC, as well as the emergent magnetoelectric properties of rhombohedral multilayer graphene.

Optical control offers a non-contact, high-precision and ultrafast route to manipulating quantum material properties1-5. Fractional Chern ferromagnetic states in moiré superlattices are apromisingplatform by whichto pursue topological quantum computing6-10, but an effective optical control protocol has remained elusive. Here we demonstrate robust optical switching of integer and fractional Chern ferromagnets in twisted molybdenum ditelluride (MoTe2) bilayers using continuous-wave circularly polarized light. Highly efficient optical manipulation of spin orientations in the topological ferromagnet regime is realized at zero field using a pump light power as low as 28 nW µm-2. Using this optically induced transition, we also demonstrate magnetic bistate cycling and spatially resolved writing of ferromagnetic domain walls. This work establishes a reliable and efficient optical control scheme for moiré Chern ferromagnets, paving the way for dissipationless spintronics and quantized Chern junction devices.

ABSTRACT Freestanding complex oxide membranes enable the release and transfer of epitaxial films, offering new design freedoms for next‐generation electronics. While the LaAlO 3 /SrTiO 3 (LAO/STO) heterostructure exhibits remarkable tunable conductivity at its interface, the active interface remains buried beneath the substrate, limiting access to this functionality. Here, we demonstrate how the LAO/STO heterostructure, in membrane form, can be flipped and precisely positioned on silicon and other platforms using polymer‐free micromanipulation. The transferred membranes preserve atomically smooth surfaces, high crystallinity, and key electronic properties. Through the 44‐nm insulating STO layer, ultra‐low‐voltage electron‐beam lithography (ULV‐EBL) writes conductive nanostructures at the now‐accessible STO/LAO interface, offering the potential to function as programmable local gates that modulate charge carriers in the underlying silicon. The platform establishes a general strategy for integrating complex oxide heterostructures with semiconductors, quantum materials, and flexible substrates, enabling new architectures for reprogrammable nanoelectronic devices.

Studying nanoscale dynamics is essential for understanding quantum materials and advancing quantum-chip manufacturing. Still, it remains a major challenge to measure nonequilibrium properties such as current and dissipation, and their relationship to structure. Scanning nanoprobes utilizing superconducting quantum interference devices (SQUIDs) are uniquely suited here due to their unparalleled magnetic and thermal sensitivity. Here, we introduce tapping-mode SQUID-on-tip, which combines atomic force microscopy with nanoSQUID sensing. Our probes minimize the nanoSQUID-sample distance, provide in-plane magnetic sensitivity, and operate on realistic, highly corrugated nanostructures. Frequency multiplexing enables simultaneous imaging of currents, magnetism, dissipation, and topography. The large voltage output of our proximity-junction nanoSQUIDs allows us to resolve nanoscale currents as small as 100 nA using a simple four-probe electronic readout. By capturing local magnetic, thermal, and electronic response without external radiation, our technique offers a powerful noninvasive route to study dynamic phenomena in exotic materials and delicate quantum circuits.

Abstract 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.

Field-tailoring quantum materials via magneto-synthesis: metastable metallic and magnetically suppressed phases in a trimer iridate

van der Waals (vdW) layered semiconductors have emerged as a unique class of quantum materials distinguished from their bulk counterparts by reduced dielectric screening, strong Coulomb interactions, large exciton binding energies, strong spin-orbit coupling, and pronounced thickness-dependent band structures. These fundamental attributes have enabled the exploration of exotic many-body physics and a broad spectrum of device applications, ranging from field-effect transistors and ferroelectric switches to optoelectronics, magnetic semiconductors, neuromorphic computing, and energy harvesting systems. Despite remarkable advances, critical challenges remain in the controlled synthesis of high-quality crystals, formation of low-resistance contacts, integration of stable and scalable gate dielectrics, and reliable device performance at the wafer scale. In this mega-review, we provide a comprehensive overview of contemporary challenges and future opportunities in vdW-layered semiconductors, structured across nine themes: growth and heterostructures of transition metal dichalcogenides, Ohmic contacts, emerging gate dielectrics, high-performance low-power field-effect transistors (FETs), diluted magnetic semiconductors, plasmonics and exciton propagation, hot-carrier solar cells, bioinspired neuromorphic computing, and electrocatalytic/photocatalytic energy conversion. By consolidating fundamental insights and device-level perspectives, this review aims to chart a roadmap for advancing vdW semiconductors from laboratory-scale discoveries to transformative technologies in electronics, optoelectronics, spintronics, and sustainable energy systems.

Abstract Quantum memory devices are essential components of integrated quantumphotonic circuits with applications in quantum computing and quantum information processing. The comprehension and quantification of critical properties such as fidelity, coherence time, storage time, and efficiency of quantum memory are insufficient in the extant literature. In this review, we examine the development and characteristics of various types of quantum memories. Although diverse approaches to storing quantum information are described in detail, we emphasize solid-state quantum memory. Furthermore, we discuss the fabrication and characterization of defects of quantum materials, including two-dimensional materials, for quantum memory applications. We survey theoretical tools such as density functional theory for studying defects to evaluate quantum properties.

Photoexcitation provides a versatile route to drive quantum materials into nonequilibrium states, opening opportunities for phase engineering beyond conventional tuning parameters such as temperature, magnetic field, pressure, or chemical doping/substitution. VO2, a prototypical correlated oxide, has long served as a model system for understanding photoinduced insulator-metal transitions, yet the sequence of structural and electronic transitions remains intensely debated. Here, we uncover a hidden photoinduced transition pathway in epitaxially strained VO2 thin films, in which the structural transition precedes the electronic insulator-metal transition, reversing the canonical temporal order. Femtosecond X-ray diffraction reveals a transient structural state characterized by the disappearance of vanadium dimers generating dynamic tensile strain, while time-resolved terahertz spectroscopy shows that the electronic gap closes only after the strain relaxation. This lattice-driven transition highlights the pivotal role of Mott correlations in dictating electronic properties under nonequilibrium conditions. Our findings establish strain-light coupling as a design principle for ultrafast control of phase transitions, offering new avenues for reconfigurable electronic and photonic devices based on correlated oxides.