We measure magneto-transport and critical currents in Bi_2Sr_2CaCu_2O_8+x Hall bar devices. Above critical current in an applied magnetic field, we observe longitudinal differential voltage along one edge comparable in magnitude but opposite in sign to the other edge. This phenomenon is unaffected by reversal of the applied field, and seems unique to devices with invasive voltage contacts. We attribute the source of this behavior to particle-hole symmetry breaking in moving vortices and the formation of opposite Bernoulli potentials due to opposing vortex velocities at the edges where the invasive contacts create hotspots for rapid vortex nucleation and flux flow. These results are fundamental to the composition and flow of dissipative currents in layered superconductors.

In this work, we demonstrate the exfoliation and transfer of metal oxide thin films from sacrificial polyvinyl alcohol (PVA) substrates to target surfaces. The films were deposited directly onto PVA using a standard amorphous Al[Formula: see text]O[Formula: see text] (alumina) atomic layer deposition (ALD) process and subsequently transferred to SiO[Formula: see text] or Au. The resulting transferred films are 32 nm-thick and continuous over millimeter-scale lateral dimensions. They exhibit angstrom-scale surface roughness and are structurally robust, remaining physically intact after multiple exfoliations. Our results address not only the transferred films but also the sacrificial PVA substrates-specifically their interaction with chemical vapor deposition processing at elevated temperatures. Most practically relevant, thermal analysis of the PVA reveals a well-defined melting temperature and no observable glass transition, motivating a recommended maximum processing temperature of 226 [Formula: see text]C. Additional thermal factors affecting ALD growth and final film quality, such as the mismatch in thermal coefficient of expansion between PVA and the metal oxide layer, are also discussed. Finally, at the interface between the transferred films and target substrates, we identify residual PVA-derived carbon contamination despite extensive O[Formula: see text] plasma processing. This finding is consistent with the observed degradation of the transferred films' dielectric properties, likely due to conductive pathways formed by residual carbon. Addressing this carbon contamination is therefore a critical direction for future work.

Resolving nanoscale light-matter interactions requires both high spatial resolution and anisotropic sensitivity to in-plane and out-of-plane optical responses. We introduce torsional force microscopy-infrared microscopy, a new optical imaging technique that combines cantilever torsional dynamics with a nonlinear frequency-mixing scheme to map both in-plane and out-of-plane photothermal signals. Using birefringent mica as a model system, we resolve distinct in-plane and out-of-plane vibrational responses and reconstruct the anisotropic strain distribution of nanobubbles, in excellent agreement with simulation. Furthermore, we demonstrate near-nanometer ( ~ 1 nm) spatial resolution in optical imaging of twisted bilayer graphene, enabling site-resolved spectroscopy within individual moiré cells. Energy-dependent imaging further reveals intra-unit cell optical features, highlighting the role of competing physical processes in a moiré lattice modulating its optical properties. By providing a direct, anisotropy-resolved view of nanoscale optical heterogeneities, this emerging infrared torsional force microscopy establishes a powerful platform for probing, understanding, and ultimately engineering light-matter interactions in complex quantum materials.

We report magnetotransport evidence of a hybridized Weyl semimetal (WSM) Fermi arc/topological insulator (TI) surface state at the interface of a ferromagnetic Mn_3+xSn_1-x/Bi_0.85Sb_0.15 heterostructure. High target utilization sputtering (HiTUS) was used to grow polycrystalline Mn_3+xSn_1-x films and Mn_3+xSn_1-x/Bi_0.85Sb_0.15 heterostructures on thermally oxidized Si/SiO_2 (100) substrates that exhibit the negative coefficient anomalous Hall effect (AHE) resulting from topological Weyl node transport. When various defects and impurities are introduced into these Mn_3+xSn_1-x films, a ferromagnetic (FM) phase develops that practically eliminates the topological Weyl node conduction. These FM Mn_3+xSn_1-x films exhibit large exchange bias effects below T=200 K that we attribute to the coexistence of a FM phase and the triangular antiferromagnetic (AFM) WSM phase. When Bi_0.85Sb_0.15 overlayers are grown on the FM Mn_3+xSn_1-x, the magnetotransport signal of Weyl node topological transport is restored, an effect we do not observe when replacing the Bi_0.85Sb_0.15 TI with heavy metal overlayers. We attribute the restoration of the Weyl node topological transport to the formation of a hybridized topological state at the WSM/TI interface.

Control over the position, orientation, and stacking order of two-dimensional (2D) materials within van der Waals heterostructures is crucial for applications in electronics, spintronics, optics, and sensing. The most popular strategy for assembling 2D materials uses purpose-built stamps with working surfaces made from one of several different polymers. However, these stamps typically require tedious preparation steps and suffer from poor durability, contamination, and limited applicability to specific 2D materials or surfaces. Here, we demonstrate significant improvements upon current 2D flake transfer and assembly practices by using mechanically durable stamps made from polyvinyl chloride (PVC) thin films. These stamps are simpler to prepare compared with existing methods and can withstand multiple transfer cycles without significant degradation, enabling greater reusability and flexibility during 2D flake assembly. We use two commercially available PVC films with distinct pick-up and release temperatures. Together, these films also enable polymer-to-polymer flake transfers and stack-and-flip fabrication of inverted heterostructures in one seamless process. Systematic comparisons of cleaning processes confirm the removal of PVC-derived residue from the assembled structures to create atomically clean interfaces. We demonstrate the utility and versatility of these polymer films and transfer process by fabricating graphene/hexagonal boron nitride heterostructure devices with high-performance electrical characteristics. Further, we demonstrate the ability to pick up and to deposit bulk aluminum gallium arsenide nanostructured films, enabling the creation of heterogeneously integrated devices. These advances enable faster and more versatile assembly of 2D materials than previously reported polymer-assisted methods. Accordingly, this technique increases fabrication rates, improves device quality, and enables more complex structures, thereby facilitating nanomaterial assembly in a broad range of applications.

Iron-rhodium (FeRh) has a first-order phase transition near room temperature between antiferromagnetic (AFM) and ferromagnetic (FM) phases, making it a promising material for magnetic memory technologies like heat-assisted magnetic recording (HAMR). It has a comparatively sharper phase transition and lower writing temperature than alternative materials, implying less thermal engineering constraints and an increase in write/read head lifetime. Despite great effort, however, AFM-based magnetic memory using FeRh has not yet been realized. Here, we employ both wide-field and scanning nanoscale quantum diamond microscopes (QDMs) to image directly the magnetic field of a patterned FeRh thin film structure under ambient conditions, demonstrating a magnetic recording technique that is reliable and robust. We experimentally identify coupling between the Néel and magnetization vector directions; and also, that the magnetic orientation of the FM phase uniquely determines the Néel vector in the AFM phase, due to pinned uncompensated magnetic moments (UMMs) in the FeRh structure. Thus, the magnetic orientation is maintained when the system is cycled between AFM and FM phases, providing the foundation for a practical, AFM-based magnetic memory.

Modulation doping, a well-established technique for traditional semiconductor heterostructures, is a promising approach for tailoring carrier concentration in 2D materials devices. In this letter we report on photoinduced modulation doping in hBN-graphene-hBN-SiO2 heterostructures utilizing standard white light sources and no additional fabrication complexity. We establish the use of this technique to both dope the channel material and to photoanneal devices, providing control over electronic doping and disorder in the graphene channel. We analyze the transport properties by employing Drude and Landauer transport models, highlighting the ability to reversibly tune the mobility and mean scattering length of the graphene with a high degree of accuracy. This tunability allows us to switch our device between the diffusive and quasi-ballistic transport regimes in situ. We utilize the exceptional control our technique provides over local disorder to realize quantum Hall isospin ferromagnetic states in a device whose initial quality would otherwise leave such states unobservable. These results demonstrate precise manipulation of carrier density and charge disorder in van der Waals heterostructures, providing a highly accessible approach to creating high-quality devices capable of realizing correlated electronic states.

While superconductors are highly attractive for energy-efficient computing, fundamental limitations in their logic circuit integration have hindered scaling and led to increased energy consumption. We therefore propose and experimentally demonstrate a novel superconducting switching device utilizing the proximity magnetization from a spin-orbit torque-switched magnet to control the resistivity of a superconductor. We further propose a complete logic family comprised solely of these devices. This novel implementation has the potential to drastically outperform existing superconducting logic families in terms of energy efficiency and scalability.

Doped semiconductors are a central and crucial component of all integrated circuits. By using a combination of white light and a focused laser beam, and exploiting hexagonal boron nitride (hBN) defect states, heterostructures of hBN/Graphene/hBN are photodoped in-operando, reproducibly and reversibly. We demonstrate device geometries with spatially-defined doping type and magnitude. After each optical doping procedure, magnetotransport measurements including quantum Hall measurements are performed to characterize the device performance. In the unipolar (p+-p-p+ and n-n+-n) configurations, we observe quantization of the longitudinal resistance, proving well-defined doped regions and interfaces that are further analyzed by Landauer-Buttiker modeling. Our unique measurements and modeling of these optically doped devices reveal a complete separation of the p- and n-Landau level edge states. The non-interaction of the edge states results in an observed 'insulating' state in devices with a bi-polar p-n-p configuration that is uncommon and has not been measured previously in graphene devices. This insulating state could be utilized in high-performance graphene electrical switches. These quantitative magnetotransport measurements confirm that these doping techniques can be applied to any two-dimensional materials encapsulated within hBN layers, enabling versatile, rewritable circuit elements for future computing and memory applications.

We report charge-to-spin conversion in a hybrid heterostructure comprised of atomically thin bismuth (Bi) confined between a silicon carbide (SiC) substrate and epitaxial graphene (EG). We confirm the composition, the dimensionality, and a 96.5% intercalation coverage using x-ray photoelectron spectroscopy, scanning transmission microscopy, low-energy electron diffraction, and Raman spectroscopy. Electrical transport measurements show signs of weak antilocalization in the heterostructure. Spin-torque ferromagnetic resonance measurements in Permalloy/EG/2D-Bi heterostructures probe charge-to-spin conversion, revealing an in-plane polarization of the spin current, perpendicular to the charge current. The ratio of the in-plane to out-of-plane torque is 3.75 times higher than in hydrogenated graphene control samples.

Next generation magnetic memories rely on novel magnetic phases for information storage. Novel spin textures such as skyrmions provide one possible avenue forward due to their topological protection and controllability via electric fields. However, the common signature of these spin textures, the topological Hall effect (THE), can be mimicked by other trivial effects. Competing anomalous Hall effect (AHE) components can produce a peak in the Hall voltage similar to that of the THE, making clear identification of the THE difficult. By applying the first-order reversal curve (FORC) technique to the Hall effect in candidate topological Hall systems we can clearly distinguish between the THE and AHE. This technique allows for quantitative investigation of the THE and AHE in magnetic materials and heterostructures with topologically non-trivial spin textures. We demonstrate the technique and apply it to several examples.

The competition between intrinsic spin-orbit physics, magnetic phenomena, and the quality of materials and interfaces governs the charge-to-spin conversion processes that are essential to the implementation of spintronic devices. Direct comparisons of spin parameters, which serve as metrics of device quality, obtained by different measurement techniques are scarce, leading to uncertainty regarding discrepancies and the reliability of the methods. Here, we directly compare the spin Hall coefficient (θ_SH) in molecular beam epitaxy grown films of (Bi_1-xSb_x)_2Te_3-ySe_y (BSTS, x = 0.58, y = 1) at room temperature using two complementary techniques: a static method using non-local voltage (NLV) measurements in BSTS Hall bars with DC charge current, and a dynamic method using spin-torque ferromagnetic resonance (ST-FMR) measurement in BSTS/Ni_80Fe_20 heterostructures at GHz frequencies. We obtain comparable spin Hall coefficients in angular-dependent ST-FMR (θ_SH=4.7±1.1) and in NLV (θ_SH=2.8±0.6). The complex effects of ferromagnetic interfaces while determining spin Hall coefficients using static or dynamic techniques becomes evident by contrasting our results to literature.

Two-dimensional (2D) 1T-VSe2 has prompted significant interest due to the discrepancies regarding alleged ferromagnetism (FM) at room temperature, charge density wave (CDW) states, and the interplay between the two. We employed a combined Diffusion Monte Carlo (DMC) and density functional theory (DFT) approach to accurately investigate the magnetic properties, CDW states, and their responses to strain in monolayer 1T-VSe2. Our calculations show the delicate competition between various phases, revealing critical insights into the relationship between their energetic and structural properties. We performed classical Monte Carlo simulations informed by our DMC and DFT results and found the magnetic transition temperature (Tc) of the undistorted (non-CDW) FM phase to be 228 K and the distorted (CDW) phase to be 68 K. Additionally, we studied the response of biaxial strain on the energetic stability and magnetic properties of various phases of 2D 1T-VSe2 and found that small amounts of strain can increase the Tc, suggesting a promising route for engineering and enhancing magnetic behavior. Finally, we synthesized 1T-VSe2 and performed Raman spectroscopy measurements, which were in close agreement with our calculated results, validating our computational approach. Our work emphasizes the role of highly accurate DMC methods in advancing the understanding of monolayer 1T-VSe2 and provides a robust framework for future studies of 2D magnetic materials.

Advancements in fabrication methods have shaped new computing device technologies. Among these methods, depositing electrical contacts to the channel material is fundamental to device characterization. Novel layered and 2D materials are promising for next-generation computing electronic channel materials. Direct-write printing of conductive inks is introduced as a surprisingly effective, significantly faster, and cleaner method to contact different classes of layered materials, including graphene (semi-metal), MoS2 (semiconductor), Bi-2212 (superconductor), and Fe5GeTe2 (metallic ferromagnet). Based on the electrical response, the quality of the printed contacts is comparable to what is achievable with resist-based lithography techniques. These devices are tested by sweeping gate voltage, temperature, and magnetic field to show that the materials remain pristine post-processing. This work demonstrates that direct-write printing is an agile method for prototyping and characterizing the electrical properties of novel layered materials.

Topological insulators (TIs) are intriguing materials for advanced computing applications based on spintronics because they can host robust spin effects. For instance, TIs have intrinsically large spin generation enabled by their large spin–orbit coupling. Furthermore, topological surface states (TSS) with spin-momentum locking and Dirac dispersion lead to long spin diffusion. Future spintronic device technology will require scalable film growth of high-quality material. We grow epitaxial films of (Bi1−xSbx)2Te3−ySey (BSTS, x = 0.58, y = 1) and confirm the gapless band structure with optimal doping using angle-resolved photoemission spectroscopy. The temperature dependence of the longitudinal resistivity shows that bulk transport is suppressed as the temperature is decreased, and at low temperature, surface transport dominates. We evaluate the spin transport properties in BSTS without using ferromagnetic tunnel contacts via a non-local resistance experiment as a function of temperature and applied charge current. As expected, these experiments reveal the necessity of decreasing the bulk conduction to best enhance the spin transport. In the TSS, we find a charge-to-spin conversion efficiency (spin Hall angle, θSH∼1) and spin diffusion over several micrometers. Further development of high-quality TIs will make them viable candidates for efficient and lossless spintronics.

RuO_2 has been proposed as the prototypical altermagnetic material. However, several reports have recently questioned its intrinsic magnetic ordering, leading to conflicting findings, especially in thin film heterostructures pointing to possible interface effects being convoluted with supposed antiferromagnetic/altermagnetic signatures. Here, extensive magnetometry measurements were performed on two independently grown thin film heterostructures of RuO_2 interfaced with either NiFe or Fe acting as the ferromagnetic layer. Below about 15 K, both samples exhibit exchange bias fields when cooled to approximately 2 K in a +1 T field, and a spin transitional feature is observed around 31 K. Magneto-Raman measurements on RuO_2 thin films only reveal a magnon mode when there is a NiFe layer, suggesting that RuO_2 does not intrinsically possess long range magnetic ordering.. When in contact with a ferromagnet, RuO_2 displays effects that could be ascribed to antiferromagnetism. However, the lack of intrinsic magnon modes points toward possible diffusion between the layers or spin disorder at the interface as seen by density functional theory (DFT) calculations.

Comparing spin transport parameters obtained by different measurement techniques can alleviate discrepancies in reported values and highlight the reliability of methods. Here, we directly compare the spin Hall coefficient (θSH) in molecular beam epitaxy grown films of (Bi1–xSbx)2Te3–ySey (BSTS, x = 0.58, y = 1) at room temperature using two complementary techniques: a static method using non-local voltage (NLV) measurements in BSTS Hall bars with DC charge current and a dynamic method using spin-torque ferromagnetic resonance (ST-FMR) measurement in BSTS/Ni80Fe20 heterostructures at GHz frequencies. We obtain comparable spin Hall coefficients in angular-dependent ST-FMR (θSH=4.7±1.1) and in NLV (θSH=2.8±0.6). The complex effects of ferromagnetic interfaces while determining spin Hall coefficients using static or dynamic techniques become evident by contrasting our results to the literature.