Broadband Light Harvesting from Scalable Two-Dimensional Semiconductor Multi-Heterostructures.

Broadband absorption in the visible spectrum is essential in optoelectronic applications that involve power conversion such as photovoltaics and photocatalysis. Most ultrathin broadband absorbers use parasitic plasmonic structures that maximize absorption using surface plasmons and/or Fabry-Perot cavities, which limits the weight efficiency of the device. Here, we show the theoretical and experimental realization of an unpatterned/planar semiconductor thin-film absorber based on monolayer transition-metal dichalcogenides.

Optically induced quantum transitions in direct probed mesoscopic NbSe for prototypical bolometers.

Superconducting transition-edge sensors (TES) have emerged as fascinating devices to detect broadband electromagnetic radiation with low thermal noise. The advent of metallic transition metal dichalcogenides, such as NbSe, has also created an impetus to understand their low-temperature properties, including superconductivity. Interestingly, NbSe-based sensor within the TES framework remains unexplored.

On-Chip Synthesis of Quasi-2D Semimetals from Multi-Layer Chalcogenides.

Reducing the dimensions of materials from three to two, or quasi-two, provides a fertile platform for exploring emergent quantum phenomena and developing next-generation electronic devices. However, growing high-quality, ultrathin, quasi2D materials in a templated fashion on an arbitrary substrate is challenging. Here, the study demonstrates a simple and reproducible on-chip approach for synthesizing non-layered, nanometer-thick, quasi-2D semimetals.

Giant Hall Switching by Surface-State-Mediated Spin-Orbit Torque in a Hard Ferromagnetic Topological Insulator.

Topological insulators (TI) and magnetic topological insulators (MTI) can apply highly efficient spin-orbit torque (SOT) and manipulate the magnetization with their unique topological surface states (TSS) with ultrahigh efficiency. Here, efficient SOT switching of a hard MTI, V-doped (Bi,Sb)Te (VBST), with a large coercive field that can prevent the influence of an external magnetic field, is demonstrated. A giant switched anomalous Hall resistance of 9.

Single-Phase L1-Ordered High Entropy Thin Films with High Magnetic Anisotropy.

The vast high entropy alloy (HEA) composition space is promising for discovery of new material phases with unique properties. This study explores the potential to achieve rare-earth-free high magnetic anisotropy materials in single-phase HEA thin films. Thin films of FeCoNiMnCu sputtered on thermally oxidized Si/SiO substrates at room temperature are magnetically soft, with a coercivity on the order of 10 Oe.

Isotopic effects on in-plane hyperbolic phonon polaritons in MoO.

Hyperbolic phonon polaritons (HPhPs), hybrids of light and lattice vibrations in polar dielectric crystals, empower nanophotonic applications by enabling the confinement and manipulation of light at the nanoscale. Molybdenum trioxide (α-MoO) is a naturally hyperbolic material, meaning that its dielectric function deterministically controls the directional propagation of in-plane HPhPs within its reststrahlen bands. Strategies such as substrate engineering, nano- and heterostructuring, and isotopic enrichment are being developed to alter the intrinsic die ectric functions of natural hyperbolic materials and to control the confinement and propagation of HPhPs.

Metrology for 2D materials: a perspective review from the international roadmap for devices and systems.

The International Roadmap for Devices and Systems (IRDS) predicts the integration of 2D materials into high-volume manufacturing as channel materials within the next decade, primarily in ultra-scaled and low-power devices. While their widespread adoption in advanced chip manufacturing is evolving, the need for diverse characterization methods is clear. This is necessary to assess structural, electrical, compositional, and mechanical properties to control and optimize 2D materials in mass-produced devices.

Novel nanocomposite-superlattices for low energy and high stability nanoscale phase-change memory.

Data-centric applications are pushing the limits of energy-efficiency in today's computing systems, including those based on phase-change memory (PCM). This technology must achieve low-power and stable operation at nanoscale dimensions to succeed in high-density memory arrays. Here we use a novel combination of phase-change material superlattices and nanocomposites (based on GeSbTe), to achieve record-low power density ≈ 5 MW/cm and ≈ 0.

Observation of Sub-10 nm Transition Metal Dichalcogenide Nanocrystals in Rapidly Heated van der Waals Heterostructures.

Two-dimensional materials, such as transition metal dichalcogenides (TMDCs), have the potential to revolutionize the field of electronics and photonics due to their unique physical and structural properties. This research presents a novel method for synthesizing crystalline TMDCs crystals with <10 nm size using ultrafast migration of vacancies at elevated temperatures. Through and processing and using atomic-level characterization techniques, we analyzed the shape, size, crystallinity, composition, and strain distribution of these nanocrystals.

Emergent ferromagnetism with superconductivity in Fe(Te,Se) van der Waals Josephson junctions.

Ferromagnetism and superconductivity are two key ingredients for topological superconductors, which can serve as building blocks of fault-tolerant quantum computers. Adversely, ferromagnetism and superconductivity are typically also two hostile orderings competing to align spins in different configurations, and thus making the material design and experimental implementation extremely challenging. A single material platform with concurrent ferromagnetism and superconductivity is actively pursued.

Edge-Confined Excitons in Monolayer Black Phosphorus.

Quantum confinement of two-dimensional excitons in van der Waals materials via electrostatic trapping, lithographic patterning, Moiré potentials, and chemical implantation has enabled significant advances in tailoring light emission from nanostructures. While such approaches rely on complex preparation of materials, natural edges are a ubiquitous feature in layered materials and provide a different approach for investigating quantum-confined excitons. Here, we observe that certain edge sites of monolayer black phosphorus (BP) strongly localize the intrinsic quasi-one-dimensional excitons, yielding sharp spectral lines in photoluminescence, with nearly an order of magnitude line width reduction.

Rydberg Excitons and Trions in Monolayer MoTe.

Monolayer transition metal dichalcogenide (TMDC) semiconductors exhibit strong excitonic optical resonances, which serve as a microscopic, noninvasive probe into their fundamental properties. Like the hydrogen atom, such excitons can exhibit an entire Rydberg series of resonances. Excitons have been extensively studied in most TMDCs (MoS, MoSe, WS, and WSe), but detailed exploration of excitonic phenomena has been lacking in the important TMDC material molybdenum ditelluride (MoTe).

CoTe : A Quantum Critical Dirac Metal with Strong Spin Fluctuations.

Quantum critical points separating weak ferromagnetic and paramagnetic phases trigger many novel phenomena. Dynamical spin fluctuations not only suppress the long-range order, but can also lead to unusual transport and even superconductivity. Combining quantum criticality with topological electronic properties presents a rare and unique opportunity.

Nitrogen-Based Magneto-ionic Manipulation of Exchange Bias in CoFe/MnN Heterostructures.

Electric field control of the exchange bias effect across ferromagnet/antiferromagnet (FM/AF) interfaces has offered exciting potentials for low-energy-dissipation spintronics. In particular, the solid-state magneto-ionic means is highly appealing as it may allow reconfigurable electronics by transforming the all-important FM/AF interfaces through ionic migration. In this work, we demonstrate an approach that combines the chemically induced magneto-ionic effect with the electric field driving of nitrogen in the Ta/CoFe/MnN/Ta structure to electrically manipulate exchange bias.

Distinct Contact Scaling Effects in MoS Transistors Revealed with Asymmetrical Contact Measurements.

2D semiconducting materials have immense potential for future electronics due to their atomically thin nature, which enables better scalability. While the channel scalability of 2D materials has been extensively studied, the current understanding of contact scaling in 2D devices is inconsistent and oversimplified. Here physically scaled contacts and asymmetrical contact measurements (ACMs) are combined to investigate the contact scaling behavior in 2D field-effect transistors.

Energy Efficient Neuro-Inspired Phase-Change Memory Based on Ge Sb Te as a Novel Epitaxial Nanocomposite.

Phase-change memory (PCM) is a promising candidate for neuro-inspired, data-intensive artificial intelligence applications, which relies on the physical attributes of PCM materials including gradual change of resistance states and multilevel operation with low resistance drift. However, achieving these attributes simultaneously remains a fundamental challenge for PCM materials such as Ge Sb Te , the most commonly used material. Here bi-directional gradual resistance changes with ≈10× resistance window using low energy pulses are demonstrated in nanoscale PCM devices based on Ge Sb Te , a new phase-change nanocomposite material .

Electrical Manipulation of Topological Phases in a Quantum Anomalous Hall Insulator.

Quantum anomalous Hall phases arising from the inverted band topology in magnetically doped topological insulators have emerged as an important subject of research for quantization at zero magnetic fields. Though necessary for practical implementation, sophisticated electrical control of molecular beam epitaxy (MBE)-grown quantum anomalous Hall matter have been stymied by growth and fabrication challenges. Here, a novel procedure is demonstrated, employing a combination of thin-film deposition and 2D material stacking techniques, to create dual-gated devices of the MBE-grown quantum anomalous Hall insulator, Cr-doped (Bi,Sb) Te .

Distinguishing the Two-Component Anomalous Hall Effect from the Topological Hall Effect.

In transport, the topological Hall effect (THE) presents itself as nonmonotonic features (or humps and dips) in the Hall signal and is widely interpreted as a sign of chiral spin textures, like magnetic skyrmions. However, when the anomalous Hall effect (AHE) is also present, the coexistence of two AHEs could give rise to similar artifacts, making it difficult to distinguish between genuine THE with AHE and two-component AHE. Here, we confirm genuine THE with AHE by means of transport and magneto-optical Kerr effect (MOKE) microscopy, in which magnetic skyrmions are directly observed, and find that genuine THE occurs in the transition region of the AHE.

BiSe Growth on (001) GaAs Substrates for Terahertz Integrated Systems.

Terahertz (THz) technologies have been of interest for many years due to the variety of applications including gas sensing, nonionizing imaging of biological systems, security and defense, and so forth. To date, scientists have used different classes of materials to perform different THz functions. However, to assemble an on-chip THz integrated system, we must understand how to integrate these different materials.

Are 2D Interfaces Really Flat?

Two-dimensional (2D) van der Waals materials are subject to mechanical deformation and thus forming bubbles and wrinkles during exfoliation and transfer. A lack of interfacial "flatness" has implications for interface properties, such as those formed by metal contacts or insulating layers. Therefore, an understanding of the detailed properties of 2D interfaces, especially their flatness under different conditions, is of high importance.

Spatially Resolved Band Gap and Dielectric Function in Two-Dimensional Materials from Electron Energy Loss Spectroscopy.

The electronic properties of two-dimensional (2D) materials depend sensitively on the underlying atomic arrangement down to the monolayer level. Here we present a novel strategy for the determination of the band gap and complex dielectric function in 2D materials achieving a spatial resolution down to a few nanometers. This approach is based on machine learning techniques developed in particle physics and makes possible the automated processing and interpretation of spectral images from electron energy loss spectroscopy (EELS).

Thermomagnetic properties of BiTe single crystal in the temperature range from 55 K to 380 K.

Magneto-thermoelectric transport provides an understanding of coupled electron-hole-phonon current in topological materials and has applications in energy conversion and cooling. In this work, we study the Nernst coefficient, the magneto-Seebeck coefficient, and the magnetoresistance of single-crystalline Bi2Te3 under external magnetic field in the range of -3 T to 3 T and in the temperature range of 55 K to 380 K. Moreau's relation is employed to justify both the overall trend of the Nernst coefficient and the temperature at which the Nernst coefficient changes sign.

Mobility Extraction in 2D Transition Metal Dichalcogenide Devices-Avoiding Contact Resistance Implicated Overestimation.

Schottky barrier (SB) transistors operate distinctly different from conventional metal-oxide semiconductor field-effect transistors, in a unique way that the gate impacts the carrier injection from the metal source/drain contacts into the channel region. While it has been long recognized that this can have severe implications for device characteristics in the subthreshold region, impacts of contact gating of SB in the on-state of the devices, which affects evaluation of intrinsic channel properties, have been yet comprehensively studied. Due to the fact that contact resistance (R ) is always gate-dependent in a typical back-gated device structure, the traditional approach of deriving field-effect mobility from the maximum transconductance (g ) is in principle not correct and can even overestimate the mobility.

Substrate-mediated hyperbolic phonon polaritons in MoO.

Hyperbolic phonon polaritons (HPhPs) are hybrid excitations of light and coherent lattice vibrations that exist in strongly optically anisotropic media, including two-dimensional materials (e.g., MoO).