Engineering topics

Vishik, Inna M.

Publications and source records attributed to Vishik, Inna M..

4 records

DOE OSTI2023

Correlating Tomographic Chemical Inhomogeneity and Low Energy Electronic Structure in Layered Quantum Materials

Photoemission spectroscopy (PES) is a suite of experimental tools to learn about the electronic and chemical structure of materials and surfaces. Normally implemented in a surface-sensitive manner, the research performed under this grant focused on pushing PES into less explored regimes, to reveal bulk electronic structure, to reveal tomographic (layer-resolved) chemistry and electronic structure of layered materials and heterostructures, and to reveal interface phenomena at the junction of two different materials. Standing wave (SW) spectroscopies have also been applied to PdCoO2, a material of interest due to its high conductivity and electron-hydrodynamic tendencies. This material can be modeled as an alternating layered structure consisting of metallic Pd layers and insulating CoO2 layers. Using SW XPS, the total electronic structure has been decomposed into contributions from the two layers, and computations highlighted the different many-body interactions in the two layers (Comm. Phys. 4, 143 (2021)). We have also used hard-x-ray angle-resolved photoemission spectroscopy (ARPES), to investigate LaB6, a technologically important material with widespread application as a cathode material for electron microscopes. We measured the bulk electronic structure of this material and found that the one-step model of photoemission better captured the electronic structure and correlations. This model treats the three steps of the photoemission process—excitation, transport of the photoelectron to the crystal surface, and escape into the vacuum—as a single quantum mechanically coherent process (Phys. Rev. Mater. 5, 055002 (2021)). We also applied x-ray photoelectron spectroscopy, implemented in a near total reflection grazing incidence geometry to elucidate technologically relevant interfaces, such as those between a substrate and photoresist (J. Phys. D: Appl. Phys. 54 464002 (2021)).

36 MATERIALS SCIENCE↗

DOE OSTI2022

Dirac lines and loop at the Fermi level in the time-reversal symmetry breaking superconductor LaNiGa 2

Unconventional superconductors have Cooper pairs with lower symmetries than in conventional superconductors. In most unconventional superconductors, the additional symmetry breaking occurs in relation to typical ingredients such as strongly correlated Fermi liquid phases, magnetic fluctuations, or strong spin-orbit coupling in noncentrosymmetric structures. In this article, we show that the time-reversal symmetry breaking in the superconductor LaNiGa 2 is enabled by its previously unknown topological electronic band structure, with Dirac lines and a Dirac loop at the Fermi level. Two symmetry related Dirac points even remain degenerate under spin-orbit coupling. These unique topological features enable an unconventional superconducting gap in which time-reversal symmetry can be broken in the absence of other typical ingredients. Our findings provide a route to identify a new type of unconventional superconductors based on nonsymmorphic symmetries and will enable future discoveries of topological crystalline superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Electronic structure and topology across T c in the magnetic Weyl semimetal Co 3 Sn 2 S 2

Co 3 Sn 2 S 2 is a magnetic Weyl semimetal, in which ferromagnetic ordering at 177 K is predicted to stabilize Weyl points. We perform temperature and spatial dependent angle--resolved photoemission spectroscopy measurements through the Curie temperature (T c ), which show large band shifts and renormalization concomitant with the onset of magnetism. We argue that Co 3 Sn 2 S 2 evolves from a Mott ferromagnet below T c to a correlated metallic state above T c . To understand the magnetism, we derive a tight-binding model of Co-3d x 2 -y 2 orbitals on the kagome lattice. At the filling obtained by first-principles calculations, this model reproduces the ferromagnetic ground state, and results in the reduction of Coulomb interactions due to cluster effects. Using a disordered local moment simulation, we show how this reduced Hubbard U leads to a collapse of the bands across the magnetic transition, resulting in a correlated state which carries associated characteristic photoemission signatures that are distinct from those of a simple lifting of exchange splitting. Finally, the behavior of topology across T c is discussed in the context of this description of the magnetism.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2020

Two phase transitions driven by surface electron doping in WTe 2

WTe 2 is a multifunctional quantum material exhibiting numerous emergent phases in which tuning of the carrier density plays an important role. In this work, we demonstrate two nonmonotonic changes in the electronic structure of WTe 2 upon in situ electron doping. The first phase transition is interpreted in terms of a shear displacement of the top WTe 2 layer, which realizes a local crystal structure not normally found in bulk WTe 2 . The second phase transition is associated with stronger interactions between the dopant atoms and the host, both through hybridization and electric field. These results demonstrate that electron doping can drive structural and electronics changes in bulk WTe 2 with implications for realizing nontrivial band-structure changes in heterointerfaces and devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗