Magnetic Field-Induced Spin Nematic Phase Up to Room Temperature in Epitaxial Antiferromagnetic FeTe Thin Films Grown by Molecular Beam Epitaxy.

Electronic nematicity, where strong correlations drive electrons to align in a way that lowers the crystal symmetry, is ubiquitous among unconventional superconductors. Understanding the interplay of such a nematic state with other electronic phases underpins the complex behavior of these materials and the potential for tuning their properties through external stimuli. Here, we report magnetic field-induced spin nematicity in a model system tetragonal FeTe, the parent compound of iron chalcogenide superconductors, which exhibits a bicollinear antiferromagnetic order.

Interlayer Exciton-Phonon Bound State in BiSe/Monolayer WS van der Waals Heterostructures.

The ability to assemble layers of two-dimensional (2D) materials to form permutations of van der Waals heterostructures provides significant opportunities in materials design and synthesis. Interlayer interactions can enable desired properties and functionality, and understanding such interactions is essential to that end. Here we report formation of interlayer exciton-phonon bound states in BiSe/WS heterostructures, where the BiSe A surface phonon, a mode particularly susceptible to electron-phonon coupling, is imprinted onto the excitonic emission of the WS.

Room-Temperature Oxygen Transport in Nanothin BiOSe Enables Precision Modulation of 2D Materials.

Oxygen conductors and transporters are important to several consequential renewable energy technologies, including fuel cells and syngas production. Separately, monolayer transition-metal dichalcogenides (TMDs) have demonstrated significant promise for a range of applications, including quantum computing, advanced sensors, valleytronics, and next-generation optoelectronics. Here, we synthesize a few-nanometer-thick BiOSe compound that strongly resembles a rare 3 bismuth oxide (BiO) phase and combine it with monolayer TMDs, which are highly sensitive to their environment.

Spin-Sensitive Epitaxial InSe Tunnel Barrier in InSe/BiSe Topological van der Waals Heterostructure.

Current-generated spin arising from spin-momentum locking in topological insulator (TI) surface states has been shown to switch the magnetization of an adjacent ferromagnet (FM) via spin-orbit torque (SOT) with a much higher efficiency than heavy metals. However, in such FM/TI heterostructures, most of the current is shunted through the FM metal due to its lower resistance, and recent calculations have also shown that topological surface states can be significantly impacted when interfaced with an FM metal such as Ni and Co. Hence, placing an insulating layer between the TI and FM will not only prevent current shunting, therefore minimizing overall power consumption, but may also help preserve the topological surface states at the interface.

Emergent electric field control of phase transformation in oxide superlattices.

Electric fields can transform materials with respect to their structure and properties, enabling various applications ranging from batteries to spintronics. Recently electrolytic gating, which can generate large electric fields and voltage-driven ion transfer, has been identified as a powerful means to achieve electric-field-controlled phase transformations. The class of transition metal oxides provide many potential candidates that present a strong response under electrolytic gating.

Large magneto-optical Kerr effect and imaging of magnetic octupole domains in an antiferromagnetic metal.

When a polarized light beam is incident upon the surface of a magnetic material, the reflected light undergoes a polarization rotation. This magneto-optical Kerr effect (MOKE) has been intensively studied in a variety of ferro- and ferrimagnetic materials because it provides a powerful probe for electronic and magnetic properties as well as for various applications including magneto-optical recording. Recently, there has been a surge of interest in antiferromagnets (AFMs) as prospective spintronic materials for high-density and ultrafast memory devices, owing to their vanishingly small stray field and orders of magnitude faster spin dynamics compared to their ferromagnetic counterparts.

Room-Temperature Spin Filtering in Metallic Ferromagnet-Multilayer Graphene-Ferromagnet Junctions.

We report room-temperature negative magnetoresistance in ferromagnet-graphene-ferromagnet (FM|Gr|FM) junctions with minority spin polarization exceeding 80%, consistent with predictions of strong minority spin filtering. We fabricated arrays of such junctions via chemical vapor deposition of multilayer graphene on lattice-matched single-crystal NiFe(111) films and standard photolithographic patterning and etching techniques. The junctions exhibit metallic transport behavior, low resistance, and the negative magnetoresistance characteristic of a minority spin filter interface throughout the temperature range 10 to 300 K.

Hydrogenated Graphene as a Homoepitaxial Tunnel Barrier for Spin and Charge Transport in Graphene.

We demonstrate that hydrogenated graphene performs as a homoepitaxial tunnel barrier on a graphene charge/spin channel. We examine the tunneling behavior through measuring the IV curves and zero bias resistance. We also fabricate hydrogenated graphene/graphene nonlocal spin valves and measure the spin lifetimes using the Hanle effect, with spintronic nonlocal spin valve operation demonstrated up to room temperature.

Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport.

The coupled imperatives for reduced heat dissipation and power consumption in high-density electronics have rekindled interest in devices based on tunnelling. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, layer uniformity, interface stability and electronic states that severely complicate fabrication and compromise performance. Two-dimensional materials such as graphene obviate these issues and offer a new paradigm for tunnel barriers.

Graphene as a tunnel barrier: graphene-based magnetic tunnel junctions.

Graphene has been widely studied for its high in-plane charge carrier mobility and long spin diffusion lengths. In contrast, the out-of-plane charge and spin transport behavior of this atomically thin material have not been well addressed. We show here that while graphene exhibits metallic conductivity in-plane, it serves effectively as an insulator for transport perpendicular to the plane.

Electrical spin injection from an n-type ferromagnetic semiconductor into a III-V device heterostructure.

The use of carrier spin in semiconductors is a promising route towards new device functionality and performance. Ferromagnetic semiconductors (FMSs) are promising materials in this effort. An n-type FMS that can be epitaxially grown on a common device substrate is especially attractive.