Publications
Exchange magnetostriction in two-dimensional antiferromagnets
Magnetostriction, coupling between the mechanical and magnetic degrees of freedom, finds a variety of applications in magnetic actuation, transduction and sensing1,2. The discovery of two-dimensional layered magnetic materials3–8 presents a new platform to explore the magnetostriction effects in ultrathin solids. Here we demonstrate an exchange-driven magnetostriction effect in mechanical resonators made of two-dimensional antiferromagnetic CrI3. The mechanical resonance frequency is found to depend on the magnetic state of the material.
Full flight envelope and trim map of flapping-wing micro aerial vehicles
Controlling agile and complex air-vehicle maneuvers requires knowledge of the full flight envelope and dominant modes of motion. This paper presents a comprehensive approach for determining the full flight envelope and trim map of minimally actuated flapping-wing micro aerial vehicles that are capable of a broad range of coupled longitudinal–lateral–directional aerobatic maneuvers. By this approach, a representative set of realizable set points and trim conditions can be determined from the flight dynamic model, including asymmetric and unstable maneuvers.
Imaging and control of critical fluctuations in two-dimensional magnets
Strong magnetization fluctuations are expected near the thermodynamic critical point of a continuous magnetic phase transition. Such critical fluctuations are highly correlated and in principle can occur at any time and length scales1; they govern critical phenomena and potentially can drive new phases2,3. Although critical phenomena in magnetic materials have been studied using neutron scattering, magnetic a.c. susceptibility and other techniques4–6, direct real-time imaging of critical magnetization fluctuations remains elusive.
Subterahertz Momentum Drag and Violation of Matthiessen's Rule in an Ultraclean Ferromagnetic SrRuO3 Metallic Thin Film
SrRuO3, a ferromagnet with an approximately 160 K Curie temperature, exhibits a T2-dependent dc resistivity below ≈30 K. Nevertheless, previous optical studies in the infrared and terahertz range show non-Drude dynamics at low temperatures, which seem to contradict Fermi-liquid predictions. In this work, we measure the low-frequency THz range response of thin films with residual resistivity ratios, Ï300K/Ï4K≈74.
Correlated insulating states at fractional fillings of moiré superlattices
Quantum particles on a lattice with competing long-range interactions are ubiquitous in physics; transition metal oxides1,2, layered molecular crystals3 and trapped-ion arrays4 are a few examples. In the strongly interacting regime, these systems often show a rich variety of quantum many-body ground states that challenge theory2. The emergence of transition metal dichalcogenide moiré superlattices provides a highly controllable platform in which to study long-range electronic correlations5–12.
Severe Dirac Mass Gap Suppression in Sb2Te3-Based Quantum Anomalous Hall Materials
The quantum anomalous Hall (QAH) effect appears in ferromagnetic topological insulators (FMTIs) when a Dirac mass gap opens in the spectrum of the topological surface states (SSs). Unaccountably, although the mean mass gap can exceed 28 meV (or 320 K), the QAH effect is frequently only detectable at temperatures below 1 K. Using atomic-resolution Landau level spectroscopic imaging, we compare the electronic structure of the archetypal FMTI Cr0.08(Bi0.1Sb0.9)1.92Te3to that of its nonmagnetic parent (Bi0.1Sb0.9)2Te3, to explore the cause.
Superconductivity, pseudogap, and phase separation in topological flat bands
Superconductivity is a macroscopic quantum phenomenon that requires electron pairs to delocalize over large distances. A long-standing question is whether superconductivity can exist even if the electrons' kinetic energy is completely quenched, as is the case in a flat band. This is fundamentally a nonperturbative problem, since the interaction energy scale is the only relevant energy scale, and hence it requires going beyond the traditional Bardeen-Cooper-Schrieffer theory of superconductivity, which is perturbative by nature.
Characterization of an architecture for front-end pixel binning in an integrating pixel array detector
Optimization of an area detector involves compromises between various parameters like frame rate, read noise, dynamic range and pixel size. We have implemented and tested a novel front-end binning design in a photon-integrating hybrid pixel array detector using the MM-PAD-2.0 pixel architecture. In this architecture, the pixels can be optionally binned in a 2 × 2 pixel configuration using a network of switches to selectively direct the output of 4 sensor pixels to a single amplifier input. Doing this allows a trade-off between frame rate and spatial resolution.
Observation of Strong Bulk Damping‐Like Spin‐Orbit Torque in Chemically Disordered Ferromagnetic Single Layers
Strong damping-like spin-orbit torque (τDL) has great potential for enabling ultrafast energy-efficient magnetic memories, oscillators, and logic. So far, the reported τDL exerted on a thin-film magnet must result from an externally generated spin current or from an internal non-equilibrium spin polarization in non-centrosymmetric GaMnAs single crystals. Here, for the first time a very strong, unexpected τDL is demonstrated from current flow within ferromagnetic single layers of chemically disordered, face-centered-cubic CoPt.
The MM-PAD-2.1: A Wide-Dynamic-Range Detector for High-Energy X-Ray Imaging
We have fabricated 128×128 pixel readout ASICs for the MM-PAD-2.1, a wide-dynamic-range photon-integrating detector intended for high-energy x-ray imaging (>20 keV). Design specifications include a signal-to-noise ratio of 10 for measurement of a single 20-keV photon, a maximum measureable signal of 108 20-keV photons/pixel/frame, and the ability to accurately measure sustained photon rates of ≥ 109 20-keV photons/pixel/s. The pixel pitch is 150 µm, resulting in an active area of 19.2 mm × 19.2 mm per single-chip module. ASICs have been bonded to both Si and CdTe sensors.