Publications
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.
Thermodynamic Signatures of Weyl Fermions in NbP
We present a high magnetic field study of NbP—a member of the monopnictide Weyl semimetal (WSM) family. While the monoarsenides (NbAs and TaAs) have topologically distinct left and right-handed Weyl fermi surfaces, NbP is argued to be “topologically trivial†due to the fact that all pairs of Weyl nodes are encompassed by a single Fermi surface. We use torque magnetometry to measure the magnetic response of NbP up to 60 tesla and uncover a Berry paramagnetic response, characteristic of the topological Weyl nodes, across the entire field range.
Magnetoresistance Scaling Reveals Symmetries of the Strongly Correlated Dynamics in BaFe2 (As1-x Px)2
The phenomenon of T-linear resistivity commonly observed in a number of strange metals has been widely seen as evidence for the breakdown of the quasiparticle picture of metals. This study shows that a recently discovered H/T scaling relationship in the magnetoresistance of the strange metal BaFe2(As1-xPx)2 is independent of the relative orientations of current and magnetic field. Rather, its magnitude and form depend only on the orientation of the magnetic field with respect to a single crystallographic axis: the direction perpendicular to the magnetic iron layers.
Chiral spin order in some purported Kitaev spin-liquid compounds
We examine recent magnetic torque measurements in two compounds, γ-Li2IrO3 and RuCl3, which have been discussed as possible realizations of the Kitaev model. The analysis of the reported discontinuity in torque, as an external magnetic field is rotated across the c axis in both crystals, suggests that they have a translationally invariant chiral spin order of the form (Si·Sj×Sk)≠0 in the ground state and persisting over a very wide range of magnetic field and temperature.
Resonant torsion magnetometry in anisotropic quantum materials
Unusual behavior in quantum materials commonly arises from their effective low-dimensional physics, reflecting the underlying anisotropy in the spin and charge degrees of freedom. Here we introduce the magnetotropic coefficient k = ∂2F/∂θ2, the second derivative of the free energy F with respect to the magnetic field orientation θ in the crystal. We show that the magnetotropic coefficient can be quantitatively determined from a shift in the resonant frequency of a commercially available atomic force microscopy cantilever under magnetic field.
Scale-invariant magnetoresistance in a cuprate superconductor
The anomalous metallic state in the high-temperature superconducting cuprates is masked by superconductivity near a quantum critical point. Applying high magnetic fields to suppress superconductivity has enabled detailed studies of the normal state, yet the direct effect of strong magnetic fields on the metallic state is poorly understood. We report the high-field magnetoresistance of thin-film La2–xSrxCuO4 cuprate in the vicinity of the critical doping, 0.161 ≤ p ≤ 0.190.
Quantum limit transport and destruction of the Weyl nodes in TaAs
Weyl fermions are a recently discovered ingredient for correlated states of electronic matter. A key difficulty has been that real materials also contain non-Weyl quasiparticles, and disentangling the experimental signatures has proven challenging. Here we use magnetic fields up to 95 T to drive the Weyl semimetal TaAs far into its quantum limit, where only the purely chiral 0th Landau levels of the Weyl fermions are occupied.
Nonzero Berry phase in quantum oscillations from giant Rashba-type spin splitting in LaTiO3/SrTiO3 heterostructures
The manipulation of the spin degrees of freedom in a solid has been of fundamental and technological interest recently for developing high-speed, low-power computational devices. There has been much work focused on developing highly spin-polarized materials and understanding their behavior when incorporated into so-called spintronic devices. These devices usually require spin splitting with magnetic fields. However, there is another promising strategy to achieve spin splitting using spatial symmetry breaking without the use of a magnetic field, known as Rashba-type splitting.
Pseudogap temperature T∗ of cuprate superconductors from the Nernst effect
We use the Nernst effect to delineate the boundary of the pseudogap phase in the temperature-doping phase diagram of hole-doped cuprate superconductors. New data for the Nernst coefficient ν(T) of YBa2Cu3Oy (YBCO), La1.8-xEu0.2SrxCuO4 (Eu-LSCO), and La1.6-xNd0.4SrxCuO4 (Nd-LSCO) are presented and compared with previously published data on YBCO, Eu-LSCO, Nd-LSCO, and La2-xSrxCuO4 (LSCO).
Erratum: Broken rotational symmetry on the Fermi surface of a high-Tc superconductor (npj Quantum Materials (2017) DOI: 10.1038/s41535-017-0013-z)
The original version of this Article contained the following errors in the legend of Figure 3, where: "The right hand panels are projections of this surface into the ka-kb plane," Now reads: "b-e are projections of this surface into the ka-kb plane," In addition, "The upper two panels involve two anisotropic CDWs, with Q2 = (δ,0,1/2)" Now reads: "The upper two panels involve two anisotropic CDWs, with Q1 = (δ,0,1/2) In addition, "followed by uni-axial CDW reconstruction with Q2 = (δ,0,0)," Now reads: "followed by uni-axial CDW reconstruction with Q = (δ,0,0)," In addition, "The simplest