Publications
Nonlinear anomalous Hall effect in few-layer WTe 2
The Hall effect occurs only in systems with broken time-reversal symmetry, such as materials under an external magnetic field in the ordinary Hall effect and magnetic materials in the anomalous Hall effect (AHE) 1 . Here we show a nonlinear AHE in a non-magnetic material under zero magnetic field, in which the Hall voltage depends quadratically on the longitudinal current 2–6 . We observe the effect in few-layer T d -WTe 2 , a two-dimensional semimetal with broken inversion symmetry and only one mirror line in the crystal plane.
Strong damping-like spin-orbit torque and tunable Dzyaloshinskii-Moriya interaction generated by low-resistivity Pd1−xPtx alloys
Despite their great promise for providing a pathway for very efficient and fast manipulation of magnetization, spin-orbit torque (SOT) operations are currently energy inefficient due to a low damping-like SOT efficiency per unit current bias, and/or the very high resistivity of the spin Hall materials. This work reports an advantageous spin Hall material, Pd 1− x Pt x , which combines a low resistivity with a giant spin Hall effect as evidenced with three independent SOT ferromagnetic detectors.
Carrier confinement effects observed in the normal-state electrical transport of electron-doped cuprate trilayers
SrCuO2/Sr0.9La0.1CuO2/SrCuO2 trilayers were grown by oxide-molecular beam epitaxy. The thicknesses of the top and bottom SrCuO2 layers were fixed, while the thickness of the infinite-layer electron-doped cuprate Sr0.9La0.1CuO2 central layer was systematically changed. Transmission electron microscopy, x-ray reflectivity and x-ray diffraction measurements were performed to assess the sample quality and the abruptness of the interfaces.
Non-Abelian bosonization and modular transformation approach to superuniversality
Quantum Hall inter-plateau transitions are physical exemplars of quantum phase transitions. Near each of these transitions, the measured electrical conductivity scales with the same correlation length and dynamical critical exponents, i.e., the critical points are superuniversal. In apparent contradiction to these experiments, prior theoretical studies of quantum Hall phase transitions within the framework of Abelian Chern-Simons theory coupled to matter found correlation length exponents that depend on the value of the quantum critical Hall conductivity.
Three-dimensional character of the Fermi surface in ultrathin LaTiO3/SrTiO3 heterostructures
LaTiO3 films on SrTiO3 single crystal substrates exhibit metallic behavior attributed to the LaTiO3 film, the interface as well as part of the SrTiO3. In the limit of ultrathin LaTiO3 films on SrTiO3, the contribution to the metallicity from strain-induced electronic structure modification of the LaTiO3 film is minimized so that the dominant contribution to metallicity is from the interface and part of the SrTiO3 due to charge transfer of 3d electrons from LaTiO3 to SrTiO3.
Exploring bias in mechanical engineering students’ perceptions of classmates
Gender disparity in science, technology, engineering, and math (STEM) fields is an ongoing challenge. Gender bias is one of the possible mechanisms leading to such disparities and has been extensively studied. Previous work showed that there was a gender bias in how students perceived the competence of their peers in undergraduate biology courses. We examined whether there was a similar gender bias in a mechanical engineering course. We conducted the study in two offerings of the course, which used different instructional practices.
Electronic structure of SnSe2 films grown by molecular beam epitaxy
SnSe2 is a layered main-group metal dichalcogenide that has exhibited gate-tunable interfacial superconductivity as well as promising optoelectronic applications. Here, we synthesize SnSe2 films by molecular beam epitaxy and investigate their electronic structure with angle-resolved photoemission spectroscopy (ARPES). A comparison between density functional theory calculations and ARPES data from a thick film reveals the importance of spin-orbit coupling and out-of-plane dispersion in the SnSe2 valence bands, which were neglected in previous studies of its electronic structure.
Evidence of pair-density wave in spin-valley locked systems
Cooper pairs with a finite center-of-mass momentum form a remarkable state in which the superconducting order parameter is modulated periodically in space. Although intense interest in such a “pair-density wave” (PDW) state has emerged due to recent discoveries in high T c superconductors, there is little theoretical understanding of the mechanism driving this exotic state. The challenge is that many competing states lie close in energy in seemingly simple models, such as the Hubbard model, in the strongly correlated regime.
Fixed-Target serial oscillation crystallography at room temperature
A fixed-Target approach to high-Throughput room-Temperature serial synchrotron crystallography with oscillation is described. Patterned silicon chips with microwells provide high crystal-loading density with an extremely high hit rate. The microfocus, undulator-fed beamline at CHESS, which has compound refractive optics and a fast-framing detector, was built and optimized for this experiment.
Evidence for a Spatially Modulated Superfluid Phase of He 3 under Confinement
In superfluid He3-B confined in a slab geometry, domain walls between regions of different order parameter orientation are predicted to be energetically stable. Formation of the spatially modulated superfluid stripe phase has been proposed. We confined He3 in a 1.1 μm high microfluidic cavity and cooled it into the B phase at low pressure, where the stripe phase is predicted. We measured the surface-induced order parameter distortion with NMR, sensitive to the formation of domains. The results rule out the stripe phase, but are consistent with 2D modulated superfluid order.