arXiv subjects

Eli Rotenberg

Publications and source records attributed to Eli Rotenberg.

At least 19 recordsLinked to original sources

arXiv2026

Direct observation of flat bands in near-magic-angle twisted bilayer CVD graphene

Advances in chemical vapor deposition (CVD) growth have driven graphene crystal quality to unprecedented levels, yet it is still unknown whether this route can realize the fragile flat-band and correlated states of the magic-angle (MA) twisted bilayer graphene (TBG). Here, we report on the experimental observation by room-temperature nano-angle-resolved photoemission spectroscopy (nano-ARPES) of flat bands in a TBG sample close to the MA, assembled via a grow-and-stack protocol based on low-pressure CVD of graphene on copper. Our study indicates electronic bands fully comparable to those measured in exfoliation-based samples and determines the size of the largest near-MA domain to be compatible with electronic transport experiments, motivating further experiments on flat band physics in CVD-graphene.

cond-mat.mes-hall↗

arXiv2026

Electronic and chemical phase identification in photoemission experiments using unsupervised machine learning

Vacuum ultraviolet photoemission spectroscopies are very information-rich experiments, but due to their surface sensitivity, data are often collected on an initially uncharacterized surface. Traditional raster-grid approaches for locating optimal measurement regions can be time-consuming. In this work, we introduce AARDVARK, a generalizable framework for sample exploration that leverages dimensionality reduction and Gaussian process regression to guide initial sample searches in spatially-resolved photoemission experiments. By utilizing UMAP as a target for a Gaussian process, the algorithm efficiently identifies boundaries of spectroscopically distinct regions, dynamically adapting to variations in sample characteristics. The algorithm enables real-time decision making in measurement selection, optimizes data acquisition, and presents a robust framework for future autonomous sample exploration in photoemission experiments.

cond-mat.mes-hall↗

arXiv2026

Electrically tunable interfacial thermal conduction via electronic structure engineering in ${Au}$/$Bi_{1-x}$$Sb_{x}$ topological insulators

This work provides direct experimental evidence for the role of topological interface states in thermal conduction across a metal/topological insulator junction. It also shows that this conduction can be reversibly modulated by electrical current injection, offering a new approach toward active control of heat flow at solid-state interfaces. Specifically, the interfacial thermal conductance of ${Au}$/$Bi_{89}$$Sb_{11}$ and ${Au}$/$Bi_{87}$$Sb_{13}$ junctions demonstrates distinct temperature- and bias-dependent behavior. Both responses are attributed to carrier redistribution between topological interface and bulk band states, driven thermally by Fermi-Dirac broadening and electrically by quasi-Fermi-level shifts and WKB tunneling into nearby bulk bands. Control experiments using trivial semimetals and insulating interlayers further confirm the topological specificity of the effect. Such electrically tunable interfacial heat conduction positions interface electronic structure engineering as a promising route for active thermal management. In doing so, it lays the groundwork for a mechanically robust alternative to conventional structure-driven thermal control compatible with increasingly dense, high-power solid-state devices.

cond-mat.mes-hall↗

arXiv2026

Bulk Superconductivity driven by Disorder-Induced Delocalization in 4Hb-Ta(S$_{1-x}$Se$_x$)$_2$

The unconventional superconductor 4Hb-TaS$_2$ is a natural heterostructure that can be broadly understood as interleaving Mott-like and metallic layers. We study the properties of this material as a function of quenched disorder in the form of Se/S substitution and find that while disordered samples show bulk superconductivity, clean samples do not. We show that a disorder-driven delocalization of carriers in the Mott-like ($1T$-) layer forms a new Fermi surface that is absent in the cleanest samples. This suggests that one of the primary drivers for superconductivity is the fragility of the Mott state, whose delocalization brings to life a sea of strongly correlated electrons.

cond-mat.supr-con↗

arXiv2026

p-Wave Orbital Angular Momentum Texture in a Chiral Crystal

The spin and orbital angular momentum (SAM and OAM) are conceptually analogous, yet their roles in condensed matter systems have not been often treated on equal footing. While SAM has been extensively explored, OAM has long been regarded as quenched in crystalline environments and thus largely overlooked. Recent experimental and theoretical advances, however, have demonstrated that OAM can drive a variety of novel electronic phenomena, highlighting the importance of probing OAM textures in the electronic band structure. Here, we investigate the momentum-space OAM texture of (TaSe4)2I, a one-dimensional chiral crystal. Using circular-dichroism angle-resolved photoemission spectroscopy (CD-ARPES), we uncover a p-wave OAM texture accompanied by OAM dipole structures. This orbital p-wave texture is intimately connected to, and thus controllable by the chirality of the host lattice. Complementary spin-resolved ARPES measurements and first-principles calculations reveal that the OAM polarization overwhelmingly dominates the low-energy electronic properties of (TaSe4)2I, far exceeding the SAM polarization. These observations represent the experimental verification of a new type of OAM texture in crystalline materials. Most importantly, these findings underscore a promising material platform for spinless orbitronics applications and lay the foundation for realizing multipolar OAM textures-orbital counterparts of the spin texture in unconventional magnets.

cond-mat.mtrl-sci↗

arXiv2026

Visualization of Tunable Electronic Structure of Monolayer TaIrTe$_4$

Monolayer TaIrTe$_4$ has emerged as an attractive material platform to study intriguing phenomena related to topology and strong electron correlations. Recently, strong interactions have been demonstrated to induce strain and dielectric screening tunable topological phases such as quantum spin Hall insulator (QSHI), trivial insulator, higher-order topological insulator, and metallic phase, in the ground state of monolayer TaIrTe$_4$. Moreover, charge dosing has been demonstrated to convert the QSHI into a dual QSHI state. Although the band structure of monolayer TaIrTe$_4$ is central to interpreting its topological phases in transport experiments, direct experimental access to its intrinsic electronic structure has so far remained elusive. Here we report direct measurements of the monolayer TaIrTe$_4$ band structure using spatially resolved micro-angle-resolved photoemission spectroscopy (microARPES) with micrometre-scale resolution. The observed dispersions show quantitative agreement with density functional theory calculations using the Heyd-Scuseria-Ernzerhof hybrid functional, establishing the insulating ground state and revealing no evidence for strong electronic correlations. We further uncover a pronounced electron-hole asymmetry in the doping response. Whereas hole doping is readily induced by electrostatic gating, attempts to introduce electrons via gating or alkali metal deposition do not yield a rigid upward shift of the Fermi level. Fractional charge calculations demonstrate that added electrons instead drive band renormalization and shrink the band gap. Taken together, our experimental and theoretical results identify the microscopic mechanism by which induced charges reshape the band topology of monolayer TaIrTe$_4$, showing that doping can fundamentally alter the electronic structure beyond the rigid band behaviour that is typically assumed.

cond-mat.str-el↗

arXiv2025

Influence of Bi Alloying on GaAs Valence Band Structure

Bi alloying is predicted to transform GaAs from a semiconductor to a topological insulator or semi-metal. To date, studies of the GaAs$_{1-x}$Bi$_x$ alloy band structure have been limited, and the origins of Bi-induced enhancement of the spin-orbit splitting energy, $\Delta_\mathrm{SO}$, are unresolved. Here, we present high-resolution angle-resolved photoemission spectroscopy (ARPES) of droplet-free epitaxial GaAs$_{1-x}$Bi$_x$ films with $x_{\mathrm{Bi}}$ = 0.06. In addition to quantifying the Bi-induced shifts of the light-hole and heavy-hole valence bands, we probe the origins of the Bi-enhanced $\Delta_\mathrm{SO}$. Using exact-two-component density functional theory calculations, we identify the key role of Bi p-orbitals in the upward shift of the light-hole and heavy-hole bands that results in the Bi-enhanced $\Delta_\mathrm{SO}$.

cond-mat.mtrl-sci↗

arXiv2025

Direct visualization of gate-tunable flat bands in twisted double bilayer graphene

The symmetry-broken correlated states in twisted double bilayer graphene (TDBG) can be tuned via several external knobs, including twist angle, displacement field, and carrier density. However, a direct, momentum-resolved characterization of how these parameters reshape the flat-band structure remains limited. In this study, we employ micro focused angle-resolved photoemission spectroscopy to investigate the flat-band dispersion of TDBG at a twist angle of 1.6, systematically varying the displacement field and carrier density via electrostatic gating. We directly observe multiple flat moir'e minibands near charge neutrality, including a flat remote valence band residing below the low-energy flat-band manifold. Furthermore, the dominant Coulomb repulsive energy over the flat- band bandwidth suggests favorable conditions for the emergence of interaction-driven correlated phenomena in TDBG. These findings establish that the formation and evolution of flat bands in TDBG arises from the interplay between the electron filling and the displacement field.

cond-mat.mes-hall↗

arXiv2025

Strain-tunability of the multipolar Berry curvature in altermagnet MnTe

The anomalous Hall effect describes the generation of a transverse voltage by a longitudinal current even in the absence of an external magnetic field. While typically observed in ferromagnets, it has also been predicted to arise in altermagnets, materials characterized by rotational symmetries that enable broken time reversal symmetry despite compensated collinear magnetic ordering. These symmetries enforce band (anti)crossings that can generate significant contributions to the Berry curvature that drives the anomalous Hall effect. This Berry curvature is predicted to exhibit a characteristic multipolar order, resulting in a symmetry-enforced distribution at or near net compensation which is highly sensitive to perturbations that distort this balance. However, exploring the predicted multipolar Berry curvature of altermagnets and its reversible manipulation remains challenging. Here, we demonstrate evidence for the multipolar nature of the altermagnetic Berry curvature in MnTe by tuning the anomalous Hall effect via uniaxial stress. Upon straining, the magnitude of the anomalous Hall conductivity changes and, at a critical strain of 0.14%, the sign is reversed. Symmetry analysis and density functional theory calculations reveal that this tunability is a direct consequence of the altermagnetic multipolar Berry curvature. Our results provide insight into the role of crystal and magnetic symmetries in the realization of higher-order Berry curvature distributions and their unique tunability.

cond-mat.mtrl-sci↗

arXiv2025

Spin-polarised surface fermiology of ohmic WSe$_2$/NbSe$_2$ interfaces

Discovering and engineering spin-polarised surface states in the electronic structures of condensed matter systems is a crucial first step in development of spintronic devices, wherein spin-polarised bands crossing the Fermi level can facilitate information transfer. Here, we show how the spin-orbit split K-point valleys of monolayer WSe$_2$ can be made potentially suitable for this purpose, despite the semiconducting ground state. By interfacing with metallic 2H-NbSe$_2$, these valence band extrema are shifted by $\sim$800~meV to produce a surface-localised Fermi surface populated only by spin-polarised carriers. By increasing the WSe$_2$ thickness, the Fermi pockets can be moved from K to $\Gamma$, demonstrating tunability of novel semi-metallic phases that exist atop a substrate additionally possessing charge density wave and superconducting transitions. Together, this study provides spectroscopic understanding into $p$-type, Schottky barrier-free interfaces, which are of urgent interest for bypassing the limitations of current-generation vertical field effect transistors, in addition to longer-term spintronics development.

cond-mat.mtrl-sci↗

arXiv2025

Visualizing Electronic Structure of Twisted Bilayer MoTe2 in Devices

The pursuit of emergent quantum phenomena lies at the forefront of modern condensed matter physics. A recent breakthrough in this arena is the discovery of the fractional quantum anomalous Hall effect (FQAHE) in twisted bilayer MoTe2 (tbMoTe2), marking a paradigm shift and establishing a versatile platform for exploring the intricate interplay among topology, magnetism, and electron correlations. While significant progress has been made through both optical and electrical transport measurements, direct experimental insights into the electronic structure - crucial for understanding and modeling this system - have remained elusive. Here, using spatially and angle-resolved photoemission spectroscopy ({\mu}-ARPES), we directly map the electronic band structure of tbMoTe2. We identify the valence band maximum, whose partial filling underlies the FQAHE, at the K points, situated approximately 150 meV above the {\Gamma} valley. By fine-tuning the doping level via in-situ alkali metal deposition, we also resolve the conduction band minimum at the K point, providing direct evidence that tbMoTe2 exhibits a direct band gap - distinct from all previously known moire bilayer transition metal dichalcogenide systems. These results offer critical insights for theoretical modeling and advance our understanding of fractionalized excitations and correlated topological phases in this emergent quantum material.

cond-mat.mes-hall↗

arXiv2025

Non-monotonic band flattening near the magic angle of twisted bilayer MoTe$_2$

Twisted bilayer MoTe$_2$ (tMoTe$_2$) is an emergent platform for exploring exotic quantum phases driven by the interplay between nontrivial band topology and strong electron correlations. Direct experimental access to its momentum-resolved electronic structure is essential for uncovering the microscopic origins of the correlated topological phases therein. Here, we report angle-resolved photoemission spectroscopy (ARPES) measurements of tMoTe$_2$, revealing pronounced twist-angle-dependent band reconstruction shaped by orbital character, interlayer coupling, and moir\'e potential modulation. Density functional theory (DFT) captures the qualitative evolution, yet underestimates key energy scales across twist angles, highlighting the importance of electronic correlations. Notably, the hole effective mass at the K point exhibits a non-monotonic dependence on twist angle, peaking near 2{\deg}, consistent with band flattening at the magic angle predicted by continuum models. Via electrostatic gating and surface dosing, we further visualize the evolution of electronic structure versus doping, enabling direct observation of the conduction band minimum and confirm tMoTe$_2$ as a direct band gap semiconductor. These results establish a spectroscopic foundation for modeling and engineering emergent quantum phases in this moir\'e platform.

cond-mat.mes-hall↗

arXiv2025

Investigating the Electrical Transport Properties and Electronic Structure of Zr2CuSb3

The checkerboard lattice has been proposed to host topological flat bands as a result of destructive interference among its various electronic hopping terms. However, it has proven challenging to realize experimentally due to the difficulty of isolating this structure from any significant out-of-plane bonding while maintaining structural integrity. Here, single crystals of Zr2CuSb3, a potential candidate for the checkerboard lattice, were synthesized using the solution (self-flux) method, and their structure was confirmed via X-ray diffraction. Electrical transport measurements indicate metallic behavior with electron-dominated carriers. Angle-resolved photoemission spectroscopy reveals multiple electron pockets and significant kz broadening due to its large c-axis and low dispersion features in k z. Density functional theory calculations further disentangle the contributions from each high-symmetry plane, providing a comprehensive characterization of electronic behavior.

cond-mat.mtrl-sci↗

arXiv2025

Mesoscale variations of chemical and electronic landscape on the surface of Weyl semimetal Co$_3$Sn$_2$S$_2$ visualized by ARPES and XPS

The multiple crystalline terminations in magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ display distinct topological and trivial surface states, which have successfully been distinguished experimentally. However, a model of pure terminations is known to be inadequate because these surfaces exhibit a high degree of spatial heterogeneity and point disorder. Here we perform a spectromicroscopy study of the surface chemistry and surface electronic structure using photoemission measurements in combination with first-principles calculations of core levels. We identify an intermediate region with properties distinct from both the sulfur and tin terminations, and demonstrate that the spectral features in this region can be associated with a disordered termination with a varying density of surface tin vacancies. This work establishes heuristics for identifying variable surface disorder using photoemission, an important prerequisite to experimentally establishing the behavior of momentum-space topological surface features subject to variable surface disorder on a single cleave.

cond-mat.mtrl-sci↗

arXiv2025

Local interface effects modulate global charge order and optical properties of 1T-TaS$_2$/1H-WSe$_2$ heterostructures

1T-TaS$_2$ is a layered charge density wave (CDW) crystal exhibiting sharp phase transitions and associated resistance changes. These resistance steps could be exploited for information storage, underscoring the importance of controlling and tuning CDW states. Given the importance of out-of-plane interactions in 1T-TaS$_2$, modulating interlayer interactions by heterostructuring is a promising method for tailoring CDW phase transitions. In this work, we investigate the optical and electronic properties of heterostructures comprising 1T-TaS$_2$ and monolayer 1H-WSe$_2$. By systematically varying the thickness of 1T-TaS$_2$ and its azimuthal alignment with 1H-WSe$_2$, we find that intrinsic moir\'e strain and interfacial charge transfer introduce CDW disorder in 1T-TaS$_2$ and modify the CDW ordering temperature. Furthermore, our studies reveal that the interlayer alignment impacts the exciton dynamics in 1H-WSe$_2$, indicating that heterostructuring can concurrently tailor the electronic phases in 1T-TaS$_2$ and the optical properties of 1H-WSe$_2$. This work presents a promising approach for engineering optoelectronic behavior of heterostructures that integrate CDW materials and semiconductors.

cond-mat.mtrl-sci↗

arXiv2025

Dark states of electrons in a quantum system with two pairs of sublattices

A quantum state of matter that is forbidden to interact with photons and is therefore undetectable by spectroscopic means is called a dark state. This basic concept can be applied to condensed matter where it suggests that a whole band of quantum states could be undetectable across a full Brillouin zone. Here we report the discovery of such condensed matter dark states in palladium diselenide as a model system that has two pairs of sublattices in the primitive cell. By using angle-resolved photoemission spectroscopy, we find valence bands that are practically unobservable over the whole Brillouin zone at any photon energy, polarisation, and scattering plane. Our model shows that two pairs of sublattices located at half-translation positions and related by multiple glide-mirror symmetries make their relative quantum phases polarised into only four kinds, three of which become dark due to double destructive interference. This mechanism is generic to other systems with two pairs of sublattices, and we show how the phenomena observed in cuprates, lead-halide perovskites, and density wave systems can be resolved by the mechanism of dark states. Our results suggest that the sublattice degree of freedom, which has been overlooked so far, should be considered in the study of correlated phenomena and optoelectronic characteristics.

cond-mat.supr-con↗

arXiv2025

Pseudogap in a crystalline insulator doped by disordered metals

A key to understand how electrons behave in crystalline solids is the band structure that connects the energy of electron waves to their wavenumber (k). Even in the phase of matter with only short-range order (liquid or amorphous solid), the coherent part of electron waves still possesses a band structure. Theoretical models for the band structure of liquid metals were formulated more than 5 decades ago, but thus far, bandstructure renormalization and pseudogap induced by resonance scattering have remained unobserved. Here, we report the observation of this unusual band structure at the interface of a crystalline insulator (black phosphorus) and disordered dopants (alkali metals). We find that a conventional parabolic band structure of free electrons bends back towards zero k with the pseudogap of 30-240 meV from the Fermi level. This is k renormalization caused by resonance scattering that leads to the formation of quasi-bound states in the scattering potential of alkali-metal ions. The depth of this potential tuned by different kinds of alkali metal (Na, K, Rb, and Cs) allows to classify the pseudogap of p-wave and d-wave resonance. Our results may provide a clue to the puzzling spectrum of various crystalline insulators doped by disordered dopants, such as the waterfall dispersion in cuprates.

cond-mat.str-el↗

arXiv2025

Electronic rotons and Wigner crystallites in a two-dimensional dipole liquid

A key concept proposed by Landau to explain superfluid liquid helium is the elementary excitation of quantum particles called rotons. The irregular arrangement of atoms in a liquid forms the aperiodic dispersion of rotons that played a pivotal role in understanding fractional quantum Hall liquid (magneto-rotons) and the supersolidity of Bose-Einstein condensates. Even for a two-dimensional electron or dipole liquid in the absence of a magnetic field, their repulsive interactions were predicted to form a roton minimum that can be used to trace the transition to Wigner crystals and superconductivity, but it has not been observed. Here, we report the observation of such electronic rotons in a two-dimensional dipole liquid of alkali-metal ions doping charges to surface layers of black phosphorus. Our data reveal a striking aperiodic dispersion of rotons characterized by a local minimum of energy at a finite momentum. As the density of dipoles decreases, where interactions dominate over kinetic energy, the roton gap reduces to 0 as in crystals, signalling Wigner crystallisation. Our model shows the importance of short-range order arising from repulsion between dipoles, which can be viewed as the formation of Wigner crystallites (bubbles or stripes) floating in the sea of Fermi liquids. Our results reveal that the primary origin of electronic rotons (and the pseudogap) is strong correlations.

cond-mat.str-el↗