arXiv subjects

Kenneth S. Burch

Publications and source records attributed to Kenneth S. Burch.

At least 19 recordsLinked to original sources

arXiv2026

A Strategy Toward Room Temperature Topological Hall Effect via Local Moment Magnetism

Topological spin textures in local moment systems hold great promise for technological applications due to their large magnetic moments, strong spin-orbit coupling (SOC), and high tunability. Finding new spin textures that are stable near room temperature is paramount to maximizing their potential for applications. Here, we provide a strategy for realizing topological spin textures at high temperatures by identifying rare earth ($R$) magnets ordering at or near room temperature. We demonstrate the feasibility of this strategy in one of these magnets, hexagonal Gd$_5$Pb$_3$, which orders at $T_C$ = 285 K. The indication for topological spin textures comes from topological Hall effect (THE), which, in Gd$_5$Pb$_3$, occurs between $T$ = 100 - 200 K, an order of magnitude higher temperature than in other reported $R$-based systems. Our results present an opportunity to explore the role of SOC, anisotropic exchange, geometric frustration, and magnetic interactions in stabilizing topological spin textures, and provide a pathway toward realizing them near room temperature in $R$-based magnets.

cond-mat.mtrl-sci↗

arXiv2026

Scalable, Simple, and Versatile Encapsulation of 2D Materials and Devices

Air-sensitive 2D materials present a fundamental challenge for device integration. Encapsulation is often required to preserve intrinsic properties, yet conventional protection strategies often fail for thicker layers and complicate fabrication. Here, we demonstrate that electron-beam (e-beam) evaporated aluminum oxide ($\mathrm{AlO}_x$) serves as both an effective encapsulation layer and a platform for direct device fabrication. Unlike transfer-based approaches, this scalable method is compatible with thicker flakes and full device or wafer coverage. It requires no stacking procedures and enables contacts without post-encapsulation etching. Using rare-earth tritellurides ($\mathrm{RTe}_3$, R = La, Er), semimetallic $\mathrm{WTe}_2$, and superconducting $\mathrm{FeTe}_x\mathrm{Se}_{1-x}$, we show that $\mathrm{AlO}_x$ suppresses oxidation and preserves intrinsic optical and electronic properties. We establish substrate-dependent optimization of encapsulation across a range of flake thicknesses, demonstrate that ultrathin $\mathrm{AlO}_x$ preserves $\mathrm{WTe}_2$'s plasmonic response and maintains superconducting performance in $\mathrm{FeTe}_x\mathrm{Se}_{1-x}$. Thus we overcome the longstanding tradeoff between encapsulation and straightforward device fabrication in fragile quantum materials.

cond-mat.mes-hall↗

arXiv2026

Nontrivial Boundary-Mediated Superconducting Transport in a TRSB Topological Iron-Based Superconductor

The interplay of superconductivity, band topology, and spontaneous time-reversal-symmetry breaking (TRSB) is expected to enable topological superconducting boundary states. FeTe0.55Se0.45 provides a promising single-material platform because it combines superconductivity, nontrivial band topology, and spontaneous magnetization in the superconducting state. Here we report evidence for a boundary-mediated superconducting transport response in exfoliated Fe(Te,Se) devices. Polar Kerr measurements show that TRSB emerges below TKerr < Tc and coexists with superconductivity across multiple compositions, providing an independent symmetry-breaking scale for transport. Using crystallographically sharp, continuous edges and side-surface-dominant contacts, we find that topological FeTe0.55Se0.45 exhibits an anomalous conductance plateau absent in topologically trivial FeTe0.40Se0.60 and Fe1.02Te0.55Se0.45 under comparable measurements. This plateau requires uninterrupted sharp edges connecting source and drain, persists over micrometer-scale separations far exceeding the bulk coherence length, shows strongly suppressed thermal broadening, and collapses when the drain is moved to the top surface. Its temperature evolution follows the TRSB scale: the plateau remains weakly broadened below T*Kerr and disappears near TKerr rather than Tc. These doping-selective, edge-geometry-dependent, TRSB-correlated, and long-range nonlocal signatures establish experimental criteria for identifying boundary-mediated superconducting transport in FeTe0.55Se0.45 and motivate phase-sensitive and theoretical studies of its microscopic origin.

cond-mat.supr-con↗

arXiv2026

Suppression of Metallic Transport in Nitrogen-rich Two-Dimensional Transition Metal Nitrides

The recent experimental realization of two-dimensional (2D) transition metal nitrides (TMNs, e.g., Mo5N6, {\delta}-MoN, and W5N6) opens new opportunities for exploring their fundamental physical properties at the two-dimensional limit. In this work, we propose a unified picture of transport phenomena in the nitrogen-rich 2D W5N6 and Mo5N6, and the stoichiometric 2D {\delta}-MoN based on several observations and first-principles calculations. Temperature coefficient of resistance (TCR) and magnetoresistance (MR) from Hall measurements consistently suggest disorder-induced transport mechanism at low temperatures (10-30 K). Notably, we observe a transition from metal to semimetal driven by the variation of nitrogen content in TMNs, supported by the suppressed density of states at the Fermi energy in nitrogen-rich TMNs (e.g. Mo5N6) from first-principle calculations. Carrier density calculations of bulk TMNs and 2D TMNs with -NH termination groups further reveal the switching of majority carrier type of Mo5N6 at reduced thickness, which is in great agreement with Hall measurement results. Our findings demonstrate that high nitrogen content in metallic molybdenum nitrides can induce the transition to a semimetallic phase at the 2D limit, shedding light on both the fundamental aspects of these materials and directions in future material design.

cond-mat.mtrl-sci↗

arXiv2026

Programmable, Spontaneous Superlattice Memory in a Monolayer Topological Insulator

Memory is a foundational concept across disciplines, from neurobiology and electronics to artificial intelligence and quantum gravity. In materials, memory effects typically arise from ferroic orders, such as ferroelectricity and ferromagnetism, where information is stored in charge or spin degrees of freedom. Here, we report a surprising discovery of a nonvolatile superlattice memory effect in monolayer TaIrTe4, a dual quantum spin Hall insulator, where information is encoded through sharply contrasting lattice periodicities. In particular, in a pristine monolayer, we observe the spontaneous emergence of a long-period superlattice that can be programmed ON and OFF in a nonvolatile manner by electrostatic tuning of low-energy electronic states. This switching toggles the system between two structural configurations with unit cell areas differing by nearly two orders of magnitude. Mechanistically, our results reveal two independent and distinct instabilities, one in the lattice and the other in the QSH electrons, which are coupled, leading to electrostatic control of lattice configurations with nonvolatile memory. This finding is enabled by combining linear and nonlinear transport measurements, Raman spectroscopy, and scanning tunneling microscopy, which probe complementary aspects of the underlying orders. Remarkably, this nonvolatile memory effect stabilizes a spontaneous superlattice with a periodicity on the few-nanometer scale that remains robust across a wide doping range, persists over days, and survives above 70 K. Combined with the QSH topology, this stability offers a promising route to nonvolatile memory control of topological flat bands and their filling enabled quantum states. Our preliminary data indeed show the emergence of new insulating states at fractional superlattice fillings, which can be clearly switched ON and OFF together with the superlattice.

cond-mat.mes-hall↗

arXiv2026

Transverse Photoresistivity from Photothermal Current Deflection in Metal Films

Quantum geometry in centrosymmetric systems has motivated the search for photocurrent responses beyond second order. In particular, electric field-induced nonlinear responses may also enable intrinsic polarization-sensitive optical detectors. Despite numerous efforts, clear methods are still needed to remove experimental artifacts, separating intrinsic from extrinsic effects, and disentangling linear responses from their higher-order counterparts. Here, we provide a systematic study of fabrication and measurement techniques to remove external artifacts in photoelectronic responses. This reveals a previously hidden photothermoelectric response in the transverse photoresistivity of symmetric thin films of simple metals. We identify its origin in thermal gradients producing current deflection and determine the device design and measurement parameters to minimize extrinsic effects that arise in photoinduced electronic responses.

cond-mat.mtrl-sci↗

arXiv2025

Electrical Readout Strategies of GFET Biosensors for Real-World Requirements

Graphene Field-Effect Transistors (GFETs) are increasingly employed as biochemical sensors due to their exceptional electronic properties, surface sensitivity, and potential for miniaturization. A critical challenge in deploying GFETs is determining the optimal electrical readout strategy. GFETs are typically operated with either of two modalities: one measuring current in real time (amperometric) and the other monitoring the change in voltage for charge neutrality (potential potentiometric). Here, we undertake a systematic study of the two modalities to determine their relative advantages/disadvantages towards guiding the future use of GFETs in sensing. We focus on viral proteins in wastewater, given the matrix's complexity and the growing interest in the field of wastewater surveillance. Our results show that transconductance offers far superior limits of detection (LOD) but suffers from limited reproducibility, a narrower dynamic range, and is ineffective for some viral proteins. In comparison, we find that Dirac point tracking offers higher reproducibility and superior robustness, but at a higher LOD. Interestingly, both techniques exhibit similar sensitivity, highlighting the importance of the aptamers employed. Systematic experiments also help explain differences in dynamic range and limited functionality in detecting some proteins, resulting from hidden electrophoresis, and shifting the high transconductance point away from the active region. Thus, our findings provide crucial considerations for designing and operating resilient graphene biosensors suitable for real-time pathogen monitoring in environmental scenarios.

cond-mat.other↗

arXiv2025

Weyl-Superconductivity revealed by Edge Mode mediated Nonlocal Transport

Topological superconductivity (TSC) hosts exotic modes enabling error-free quantum computation and low-temperature spintronics. Despite preliminary evidence of edge modes, unambiguous signatures remain undetected. Here, we report the first observation of protected, non-local transport from the edge modes of the potential Weyl-superconductor \ch{FeTe_{0.55}Se_{0.45}}. Namely resonant charge injection, ballistic transport, and extraction via edge modes. An anomalous conductance plateau emerges only when topological, superconducting, and magnetic phases coexist, with source-drain contacts coupled via the edge. Moving the drain to the bulk switches the non-local transport process to a local Andreev process, generating a zero-bias conductance peak (ZBCP). The edge mode's topological protection is confirmed by its insensitivity to external magnetic fields and increasing temperatures until the spontaneous magnetization is substantially suppressed. Our findings provide a new methodology to demonstrate TSC edge states in \ch{FeTe_{0.55}Se_{0.45}} via topologically protected non-local transport.

cond-mat.supr-con↗

arXiv2024

Uncovering the Hidden Ferroaxial Density Wave as the Origin of the Axial Higgs Mode in RTe$_3$

The recent discovery of an axial amplitude (Higgs) mode in the long-studied charge density wave (CDW) systems GdTe$_3$ and LaTe$_3$ suggests a heretofore unidentified hidden order. A theoretical study proposed that the axial Higgs results from a hidden ferroaxial component of the CDW, which could arise from non-trivial orbital texture. Here, we report extensive experimental studies on ErTe$_3$ and HoTe$_3$ that possess a high-temperature CDW similar to other RTe$_3$ (R = rare earth), along with an additional low-temperature CDW with an orthogonal ordering vector. Combining Raman spectroscopy with large-angle convergent beam electron diffraction (LACBED), rotational anisotropy second-harmonic generation (RA-SHG), and muon-spin relaxation ($\mu$SR), we provide unambiguous evidence that the high-temperature CDW breaks translation, rotation, and all vertical and diagonal mirror symmetries, but not time-reversal or inversion. In contrast, the low-temperature CDW only additionally breaks translation symmetry. Simultaneously, Raman scattering shows the high-temperature CDW produces an axial Higgs mode while the low-temperature mode is scalar. The weak monoclinic structural distortion and clear axial response in Raman and SHG are consistent with a ferroaxial phase in RTe$_3$ driven by coupled orbital and charge orders. Thus, our study provides a new standard for uncovering unconventional orders and confirms the power of Higgs modes to reveal them.

cond-mat.str-el↗

arXiv2024

La$_2$O$_3$Mn$_2$Se$_2$: a correlated insulating layered d-wave altermagnet

Altermagnets represent a new class of magnetic phases without net magnetization that are invariant under a combination of rotation and time reversal. Unlike conventional collinear antiferromagnets (AFM), altermagnets could lead to new correlated states and important material properties deriving from their non-relativistic spin-split band structure. Indeed, they are the magnetic analogue of unconventional superconductors and can yield spin polarized electrical currents in the absence of external magnetic fields, making them promising candidates for next-generation spintronics. Here, we report altermagnetism in the correlated insulator, magnetically-ordered tetragonal oxychalcogenide, La$_2$O$_3$Mn$_2$Se$_2$. Symmetry analysis reveals a $\mathit{d}_{x^2 - y^2}$-wave type spin momentum locking, which is supported by density functional theory (DFT) calculations. Magnetic measurements confirm the AFM transition below $\sim$166 K while neutron pair distribution function analysis reveals a 2D short-range magnetic order that persists above the N\'eel temperature. Single crystals are grown and characterized using X-ray diffraction, optical and electron microscopy, and microRaman spectroscopy to confirm the crystal structure, stoichiometry, and uniformity.

cond-mat.mtrl-sci↗

arXiv2024

Directionally Locked Heteroepitaxy with a Structurally Modulated van der Waals Material

Precise orientation of symmetry-mismatched epilayers on van der Waals (vdW) substrates via heteroepitaxy has commonly been achieved through surface treatment processes to accommodate weak interlayer registry and bonding strength, thereby limiting the range of material combinations for heterostructure design. In this study, we investigate the influence of lattice instabilities in a structurally modulated vdW TaCo2Te2 substrate on the growth and alignment of a symmetry-mismatched bulk CoxTey epilayer using in situ heating in a transmission electron microscope (TEM). We show that a Peierls-like lattice instability occurs in TaCo2Te2 at a transition temperature of ~523 K, which was corroborated by phonon calculations. Post-heat-treated samples reveal a thermally induced surface diffusion process and the dominant lateral growth of the CoxTey epilayer on the TaCo2Te2 vdW layers, as observed in cross-sectional TEM images. Temperature-dependent selected area electron diffraction (SAED) patterns reveal that the quasi-vdW CoxTey/TaCo2Te2 heterointerface acquires directional locking by aligning larger interlayer lattice mismatch along the lattice instability axis of TaCo2Te2, while preserving a strong lattice matching along the orthogonal direction. This heterostructure exhibits precise interlayer registry with one-dimensional lattice incommensuration along the lattice instability axis, resulting from structural distortion to accommodate lattice-mismatch strain. Moreover, the interfacial reconstruction of TaCo2Te2 back to the distorted phase stabilizes the lattice-locking of the quasi-vdW heterointerface at elevated temperatures. These findings encourage the expansion of material diversity for designing and predicting novel multi-dimensional heterostructures by leveraging lattice instabilities to guide epitaxy.

cond-mat.mtrl-sci↗

arXiv2024

Insulator-to-Metal Transition and Anomalously Slow Hot Carrier Cooling in a Photo-doped Mott Insulator

Photo-doped Mott insulators can exhibit novel photocarrier transport and relaxation dynamics and non-equilibrium phases. However, time-resolved real-space imaging of these processes are still lacking. Here, we use scanning ultrafast electron microscopy (SUEM) to directly visualize the spatial-temporal evolution of photoexcited species in a spin-orbit assisted Mott insulator {\alpha}-RuCl3. At low optical fluences, we observe extremely long hot photocarrier transport time over one nanosecond, almost an order of magnitude longer than any known values in conventional semiconductors. At higher optical fluences, we observe nonlinear features suggesting a photo-induced insulator-to-metal transition, which is unusual in a large-gap Mott insulator. Our results demonstrate the rich physics in a photo-doped Mott insulator that can be extracted from spatial-temporal imaging and showcase the capability of SUEM to sensitively probe photoexcitations in strongly correlated electron systems.

cond-mat.str-el↗

arXiv2024

Optical contrast analysis of {\alpha}-RuCl$_3$ nanoflakes on oxidized silicon wafers

{\alpha}-RuCl$_3$, a narrow-band Mott insulator with large work function, offers intriguing potential as a quantum material or as a charge acceptor for electrical contacts in van der Waals devices. In this work, we perform a systematic study of the optical reflection contrast of {\alpha}-RuCl$_3$ nanoflakes on oxidized silicon wafers and estimate the accuracy of this imaging technique to assess the crystal thickness. Via spectroscopic micro-ellipsometry measurements, we characterize the wavelength-dependent complex refractive index of {\alpha}-RuCl$_3$ nanoflakes of varying thickness in the visible and near-infrared. Building on these results, we simulate the optical contrast of {\alpha}-RuCl$_3$ nanoflakes with thicknesses below 100 nm on SiO$_2$/Si substrates under different illumination conditions. We compare the simulated optical contrast with experimental values extracted from optical microscopy images and obtain good agreement. Finally, we show that optical contrast imaging allows us to retrieve the thickness of the RuCl$_3$ nanoflakes exfoliated on an oxidized silicon substrate with a mean deviation of -0.2 nm for thicknesses below 100 nm with a standard deviation of only 1 nm. Our results demonstrate that optical contrast can be used as a non-invasive, fast, and reliable technique to estimate the {\alpha}-RuCl$_3$ thickness.

cond-mat.mtrl-sci↗

arXiv2024

Observation of the dual quantum spin Hall insulator by density-tuned correlations in a van der Waals monolayer

The convergence of topology and correlations represents a highly coveted realm in the pursuit of novel quantum states of matter. Introducing electron correlations to a quantum spin Hall (QSH) insulator can lead to the emergence of a fractional topological insulator and other exotic time-reversal-symmetric topological order, not possible in quantum Hall and Chern insulator systems. However, the QSH insulator with quantized edge conductance remains rare, let alone that with significant correlations. In this work, we report a novel dual QSH insulator within the intrinsic monolayer crystal of TaIrTe4, arising from the interplay of its single-particle topology and density-tuned electron correlations. At charge neutrality, monolayer TaIrTe4 demonstrates the QSH insulator that aligns with single-particle band structure calculations, manifesting enhanced nonlocal transport and quantized helical edge conductance. Interestingly, upon introducing electrons from charge neutrality, TaIrTe4 only shows metallic behavior in a small range of charge densities but quickly goes into a new insulating state, entirely unexpected based on TaIrTe4's single-particle band structure. This insulating state could arise from a strong electronic instability near the van Hove singularities (VHS), likely leading to a charge density wave (CDW). Remarkably, within this correlated insulating gap, we observe a resurgence of the QSH state, marked by the revival of nonlocal transport and quantized helical edge conduction. Our observation of helical edge conduction in a CDW gap could bridge spin physics and charge orders. The discovery of a dual QSH insulator introduces a new method for creating topological flat minibands via CDW superlattices, which offer a promising platform for exploring time-reversal-symmetric fractional phases and electromagnetism.

cond-mat.mes-hall↗

arXiv2023

Enhanced Ferromagnetism in Monolayer Cr2Te3 via Topological Insulator Coupling

Exchange-coupled interfaces are pivotal in exploiting two-dimensional (2D) ferromagnetism. Due to the extraordinary correlations among charge, spin, orbital and lattice degrees of freedom, layered magnetic transition metal chalcogenides (TMCs) bode well for exotic topological phenomena. Here we report the realization of wafer-scale Cr2Te3 down to monolayer (ML) on insulating SrTiO3(111) and/or Al2O3(001) substrates using molecular beam epitaxy. Robust ferromagnetism persists in the 2D limit. In particular, the Curie temperature TC of 2 ML Cr2Te3 increases from 100 K to ~ 120 K when proximitized to topological insulator (TI) (Bi,Sb)2Te3, with substantially boosted magnetization as observed via polarized neutron reflectometry. Our experiments and theory strongly indicate that the Bloembergen-Rowland interaction is likely universal underlying TC enhancement in TI-coupled magnetic heterostructures. The topological-surface-enhanced magnetism in 2D TMC enables further exchange coupling physics and quantum hybrid studies, including paving the way to realize interface-modulated topological electronics.

cond-mat.mtrl-sci↗

arXiv2023

Engineering Anomalously Large Electron Transport in Topological Semimetals

Anomalous transport of topological semimetals has generated significant interest for applications in optoelectronics, nanoscale devices, and interconnects. Understanding the origin of novel transport is crucial to engineering the desired material properties, yet their orders of magnitude higher transport than single-particle mobilities remain unexplained. This work demonstrates the dramatic mobility enhancements result from phonons primarily returning momentum to electrons due to phonon-electron dominating over phonon-phonon scattering. Proving this idea, proposed by Peierls in 1932, requires tuning electron and phonon dispersions without changing symmetry, topology, or disorder. This is achieved by combining de Haas - van Alphen (dHvA), electron transport, Raman scattering, and first-principles calculations in the topological semimetals MX$_2$ (M=Nb, Ta and X=Ge, Si). Replacing Ge with Si brings the transport mobilities from an order magnitude larger than single particle ones to nearly balanced. This occurs without changing the crystal structure or topology and with small differences in disorder or Fermi surface. Simultaneously, Raman scattering and first-principles calculations establish phonon-electron dominated scattering only in the MGe$_2$ compounds. Thus, this study proves that phonon-drag is crucial to the transport properties of topological semimetals and provides insight to further engineer these materials.

cond-mat.mtrl-sci↗

arXiv2023

The effect of surface oxidation and crystal thickness on magnetic properties and magnetic domain structures of Cr2Ge2Te6

Van der Waals (vdW) magnetic materials such as Cr2Ge2Te6 (CGT) show promise for novel memory and logic applications. This is due to their broadly tunable magnetic properties and the presence of topological magnetic features such as skyrmionic bubbles. A systematic study of thickness and oxidation effects on magnetic domain structures is important for designing devices and vdW heterostructures for practical applications. Here, we investigate thickness effects on magnetic properties, magnetic domains, and bubbles in oxidation-controlled CGT crystals. We find that CGT exposed to ambient conditions for 5 days forms an oxide layer approximately 5 nm thick. This oxidation leads to a significant increase in the oxidation state of the Cr ions, indicating a change in local magnetic properties. This is supported by real space magnetic texture imaging through Lorentz transmission electron microscopy. By comparing the thickness dependent saturation field of oxidized and pristine crystals, we find that oxidation leads to a non-magnetic surface layer which is thicker than the oxide layer alone. We also find that the stripe domain width and skyrmionic bubble size are strongly affected by the crystal thickness in pristine crystals. These findings underscore the impact of thickness and surface oxidation on the properties of CGT such as saturation field and domain/skyrmionic bubble size and suggest a pathway for manipulating magnetic properties through a controlled oxidation process.

cond-mat.mtrl-sci↗

arXiv2023

Ultrafast Dynamics of the Topological Semimetal GdSb$_{x}$Te$_{2-x-δ}$ In the Presence and Absence of a Charge Density Wave

Time-resolved dynamics in charge-density-wave materials have revealed interesting out-of-equilibrium electronic responses. However these are typically only performed in a single material possessing a CDW. As such, it is challenging to separate subtle effects originating from the CDW. Here, we report on the ultrafast dynamics of the GdSb$_{x}$Te$_{2-x-δ}$ series of materials where E$_{F}$ can be tuned, resulting in a change from an undistorted tetraganal phase to a CDW with a wavevector that depends on $x$. Using mid-infrared, near-infrared, and visible excitation, we find the dynamics are sensitive to both E$_{F}$ and the presence of the CDW. Specifically, as the Sb content of the compounds increases, transient spectral features shift to higher probe energies. In addition, we observe an enhanced lifetime and change in the sign of the transient signal upon removing the CDW with high Sb concentrations. Finally, we reveal fluence- and temperature-dependent photo-induced responses of the differential reflectivity, which provide evidence of transient charge density wave suppression in related telluride materials. Taken together our results provide a blueprint for future ultrafast studies of CDW systems.

cond-mat.mtrl-sci↗