This is version 1. We add "Full Original Raw Data.zip" in version 2. Zip files: Paper Figures.zip: This zip file contains all datasets necessary for plotting the paper figures. MTX datasets are named the same as corresponding figures. DAT datasets (raw data) with a figure - filename map (Figure-rawdata map.xlsx). Jupyter notebooks for interactive graphing. Data Summaries.zip: Plotted extended data beyond paper figures, in ppt and measurement logs (laboratory notebooks) TEM.zip: TEM results. Full Original Raw Data.zip: Full Original Raw Data for each cooldown. See "Data Summaries.zip" for device information. See "Paper Figures.zip" for visualization. Data formats: MTX: A simple 2D/3D matrix format developed for Spyview (https://nsweb.tn.tudelft.nl/~gsteele/spyview/). DAT: Original spreadsheet data. SET: Instrument settings. PY: Measurement scripts.
Motivated by observations of extreme magnetoresistance (XMR) in bulk crystals of rare-earth monopnictide (RE-V) compounds and emerging applications in novel spintronic and plasmonic devices based on thin-film semimetals, we have investigated the electronic band structure and transport behavior of epitaxial GdSb thin films grown on III-V semiconductor surfaces. The Gd3+ ion in GdSb has a high spin S=7/2 and no orbital angular momentum, serving as a model system for studying the effects of antiferromagnetic order and strong exchange coupling on the resulting Fermi surface and magnetotransport properties of RE-Vs. We present a surface and structural characterization study mapping the optimal synthesis window of thin epitaxial GdSb films grown on III-V lattice-matched buffer layers via molecular beam epitaxy. To determine the factors limiting XMR in RE-V thin films and provide a benchmark for band structure predictions of topological phases of RE-Vs, the electronic band structure of GdSb thin films is studied, comparing carrier densities extracted from magnetotransport, angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations. ARPES shows hole-carrier rich topologically-trivial semi-metallic band structure close to complete electron-hole compensation, with quantum confinement effects in the thin films observed through the presence of quantum well states. DFT predicted Fermi wavevectors are in excellent agreement with values obtained from quantum oscillations observed in magnetic field-dependent resistivity measurements. An electron-rich Hall coefficient is measured despite the higher hole carrier density, attributed to the higher electron Hall mobility. The carrier mobilities are limited by surface and interface scattering, resulting in lower magnetoresistance than that measured for bulk crystals.
New properties can arise at van der Waals (vdW) interfaces hosting a moiré pattern generated by interlayer twist and strain. However, achieving precise control of interlayer twist/strain remains an ongoing challenge in vdW heterostructure assembly, and even subtle variation in these structural parameters can create significant changes in the moiré period and emergent properties. Characterizing the rate of interlayer twist/strain relaxation during thermal annealing is critical to establish a thermal budget for vdW heterostructure construction and may provide a route to improve the homogeneity of the interface or to control its final state. Here, we characterize the spatial and temporal dependence of interfacial twist and strain relaxation in marginally-twisted hBN/hBN interfaces heated under conditions relevant to vdW heterostructure assembly and typical sample annealing. We find that the ferroelectric hBN/hBN moiré at very small twist angles (θ≤0.1°) relaxes minimally during annealing in air at typical assembly temperatures of 170°C. However, at 400°C, twist angle relaxes significantly, accompanied by a decrease in spatial uniformity. Uniaxial heterostrain initially increases and then decreases over time, becoming increasingly non-uniform in direction. Structural irregularities such as step edges, contamination bubbles, or contact with the underlying substrate result in local inhomogeneity in the rate of relaxation.
We study a Cooper-pair transistor realized by two Josephson weak links that enclose a superconducting island in an InSb-Al hybrid nanowire. When the nanowire is subject to a magnetic field, isolated subgap levels arise in the superconducting island and, due to the Coulomb blockade,mediate a supercurrent by coherent co-tunneling of Cooper pairs. We show that the supercurrent resulting from such co-tunneling events exhibits, for low to moderate magnetic fields, a phase offset that discriminates even and odd charge ground states on the superconducting island. Notably,this phase offset persists when a subgap state approaches zero energy and, based on theoretical considerations, permits parity measurements of subgap states by supercurrent interferometry. Such supercurrent parity measurements could, in a new series of experiments, provide an alternative approach for manipulating and protecting quantum information stored in the isolated subgap levels of superconducting islands.
Heusler compounds are an exciting class of materials due to the diverse and tunable electronic and magnetic properties. In this work, the transition of semiconducting CoTiSb to a ferromagnet is examined in the substitutionally alloyed series of CoTi${}_{1-x}$Fe${}_{x}$Sb and Co${}_{1-y}$Fe${}_{y}$TiSb, grown by molecular beam epitaxy. The electronic band structure and magnetic moment depend strongly on Fe content and in particular the site it is substituted on. This coupled with its compatibility with other Heusler and III-V compounds and the expected half-metallic behavior in this quaternary Heusler compound system, make it promising for the development of future spintronic heterostructures and devices.
We report the formation of Mn-rich regions at the interface of Co2FexMn1-xSi thin films grown on GaAs substrates by molecular beam epitaxy (MBE). Scanning transmission electron microscopy (STEM) with electron energy loss (EEL) spectrum imaging reveals that each interfacial region: (1) is 1-2 nm wide, (2) occurs irrespective of the Fe/Mn composition ratio and in both Co-rich and Co-poor films, and (3) displaces both Co and Fe indiscriminately. We also observe a Mn-depleted region in each film directly above each Mn-rich interfacial layer, roughly 3 nm in width in the x = 0 and x = 0.3 films, and 1 nm in the x = 0.7 (less Mn) film. We posit that growth energetics favor Mn diffusion to the interface even when there is no significant Ga interdiffusion into the epitaxial film. Element-specific X-ray magnetic circular dichroism (XMCD) measurements show larger Co, Fe, and Mn orbital to spin magnetic moment ratios compared to bulk values across the Co2FexMn1-xSi compositional range. The values lie between reported values for pure bulk and nanostructured Co, Fe, and Mn materials, corroborating the non-uniform, layered nature of the material on the nanoscale. Finally, SQUID magnetometry demonstrates that the films deviate from the Slater-Pauling rule for uniform films of both the expected and the measured composition. The results inform a need for care and increased scrutiny when forming Mn-based magnetic thin films on III-V semiconductors like GaAs, particularly when films are on the order of 5 nm or when interface composition is critical to spin transport or other device applications.
Reconfigurable Mie resonator metasurfaces may give rise to new classes of programmable optical devices. Large phase and amplitude modulations can be achieved with high-Q resonances that are tunable by at least one line-width. We experimentally demonstrate narrow linewidth, reconfigurable Mie resonators comprising undoped InSb wires embedded inside a highly doped InSb Epsilon-Near-Zero (ENZ) cavity. We demonstrate a Q-factor increase of 400% by embedding a high index resonator within, instead of atop, an ENZ substrate. Systematic studies of varying width resonators reveal significant differences in coupling to the ENZ media for TM and TE resonators. A large refractive index modulation (Δn ≥1.5) is achieved with heating (80-575K), stemming from variations in the effective mass of free-carriers. Thermally tuning the ENZ wavelength of the cavity by >2μm (13-15.5μm) emables reconfigurable tuning by multiple line-widths. This ultra-wide thermal tunability of high-Q embedded resonators may enable new class of active metadevices in the mid-infrared wavelength regime.
Zip files: Paper Figures.zip: This zip file contains all datasets necessary for plotting the paper figures. MTX datasets are named the same as corresponding figures. DAT datasets (raw data) with a figure - filename map (Figure-rawdata map.xlsx). Jupyter notebooks for interactive graphing. Data Summaries.zip: Plotted extended data beyond paper figures, in ppt and measurement logs (laboratory notebooks) TEM.zip: TEM results. Full Original Raw Data.zip: Full Original Raw Data for each cooldown. See "Data Summaries.zip" for device information. See "Paper Figures.zip" for visualization. Data formats: MTX: A simple 2D/3D matrix format developed for Spyview (https://nsweb.tn.tudelft.nl/~gsteele/spyview/). DAT: Original spreadsheet data. SET: Instrument settings. PY: Measurement scripts.
