Publications by authors named "Arun Bansil"

In contrast to the Dirac-cone materials in which the low-energy spectrum features a pseudospin-1/2 structure, Lieb and Dice lattices both host triply degenerate low-energy excitations. Here, we discuss moiré structures involving twisted bilayers of these lattices, which are shown to exhibit a tunable number of isolated flat bands near the Fermi level due to the bipartite nature of their structures. These flat bands remain isolated from the high-energy bands even in the presence of small higher-order terms and chiral-symmetry-breaking interlayer tunneling.

View Article and Find Full Text PDF

Probing ground-state quantum geometry and topology through optical responses is not only of fundamental interest, but it can also offer several practical advantages. Here, using first-principles calculations on thin films of the antiferromagnetic topological insulator MnBiTe, we demonstrate how the generalized optical weight arising from the absorptive part of the optical conductivity can be used to probe the ground-state quantum geometry and topology. We show that three-septuple-layer MnBiTe film exhibit an enhanced, almost-perfect magnetic circular dichroism for a narrow photon energy window in the infrared region.

View Article and Find Full Text PDF
Article Synopsis
  • Recent discoveries in superconductivity involving infinite-layer nickelates, specifically LaNiO₂, have sparked new research into electronic interactions impacting these materials.
  • Using first-principles simulations, the study reveals that LaNiO₂ displays competing low-energy stripe phases, akin to those found in doped cuprates, driven by complex electronic mechanisms and distortions.
  • The findings highlight the significant role of strong electronic correlations and electron-phonon coupling in the behavior of nickelates, offering insights into electronic inhomogeneity and the absence of long-range order.
View Article and Find Full Text PDF

The interplay of topology, magnetism, and correlations gives rise to intriguing phases of matter. In this study, through state-of-the-art angle-resolved photoemission spectroscopy, density functional theory, and dynamical mean-field theory calculations, we visualize a fourfold degenerate Dirac nodal line at the boundary of the bulk Brillouin zone in the antiferromagnet YMnGe. We further demonstrate that this gapless, antiferromagnetic Dirac nodal line is enforced by the combination of magnetism, space-time inversion symmetry, and nonsymmorphic lattice symmetry.

View Article and Find Full Text PDF

The enigmatic mechanism underlying unconventional high-temperature superconductivity, especially the role of lattice dynamics, has remained a subject of debate. Theoretical insights have long been hindered due to the lack of an accurate first-principles description of the lattice dynamics of cuprates. Recently, using the r2SCAN meta-generalized gradient approximation (meta-GGA) functional, we have been able to achieve accurate phonon spectra of an insulating cuprate YBa2Cu3O6 and discover significant magnetoelastic coupling in experimentally interesting Cu-O bond stretching optical modes [Ning et al.

View Article and Find Full Text PDF

The Materials Genome Initiative (MGI) has streamlined the materials discovery effort by leveraging generic traits of materials, with focus largely on perfect solids. Defects such as impurities and perturbations, however, drive many attractive functional properties of materials. The rich tapestry of charge, spin, and bonding states hosted by defects are not accessible to elements and perfect crystals, and defects can thus be viewed as another class of "elements" that lie beyond the periodic table.

View Article and Find Full Text PDF

The family of transition-metal dipnictides has been of theoretical and experimental interest because this family hosts topological states and extremely large magnetoresistance (MR). Recently,TaAs2, a member of this family, has been predicted to support a topological crystalline insulating state. Here, by using high-resolution angle-resolved photoemission spectroscopy (ARPES), we reveal both closed and open pockets in the metallic Fermi surface (FS) and linearly dispersive bands on the (2‾01) surface, along with the presence of extreme MR observed from magneto-transport measurements.

View Article and Find Full Text PDF

Understanding the nature and origin of collective excitations in materials is of fundamental importance for unraveling the underlying physics of a many-body system. Excitation spectra are usually obtained by measuring the dynamical structure factor, S(Q, ω), using inelastic neutron or x-ray scattering techniques and are analyzed by comparing the experimental results against calculated predictions. We introduce a data-driven analysis tool which leverages 'neural implicit representations' that are specifically tailored for handling spectrographic measurements and are able to efficiently obtain unknown parameters from experimental data via automatic differentiation.

View Article and Find Full Text PDF

Quantum geometry in condensed-matter physics has two components: the real part quantum metric and the imaginary part Berry curvature. Whereas the effects of Berry curvature have been observed through phenomena such as the quantum Hall effect in two-dimensional electron gases and the anomalous Hall effect (AHE) in ferromagnets, the quantum metric has rarely been explored. Here, we report a nonlinear Hall effect induced by the quantum metric dipole by interfacing even-layered MnBiTe with black phosphorus.

View Article and Find Full Text PDF

Recent experiments report a charge density wave (CDW) in the antiferromagnet FeGe, but the nature of the charge ordering and the associated structural distortion remains elusive. We discuss the structural and electronic properties of FeGe. Our proposed ground state phase accurately captures atomic topographies acquired by scanning tunneling microscopy.

View Article and Find Full Text PDF

The spacetime light cone is central to the definition of causality in the theory of relativity. Recently, links between relativistic and condensed matter physics have been uncovered, where relativistic particles can emerge as quasiparticles in the energy-momentum space of matter. Here, we unveil an energy-momentum analogue of the spacetime light cone by mapping time to energy, space to momentum, and the light cone to the Weyl cone.

View Article and Find Full Text PDF
Article Synopsis
  • Using circularly polarized light to manipulate quantum materials presents significant possibilities in physics and chemistry, especially in areas like asymmetric synthesis and spintronics.
  • The study highlights the unexpected ability to control antiferromagnetic order in MnBiTe, an unusual material without chirality or magnetization.
  • The findings suggest that optical control and a special form of light interaction, called antiferromagnetic circular dichroism, stem from a concept known as optical axion electrodynamics, which may enable new optical technologies in various anti-symmetric materials.
View Article and Find Full Text PDF

Photocathodes-materials that convert photons into electrons through a phenomenon known as the photoelectric effect-are important for many modern technologies that rely on light detection or electron-beam generation. However, current photocathodes are based on conventional metals and semiconductors that were mostly discovered six decades ago with sound theoretical underpinnings. Progress in this field has been limited to refinements in photocathode performance based on sophisticated materials engineering.

View Article and Find Full Text PDF

The interplay of nontrivial topology and superconductivity in condensed matter physics gives rise to exotic phenomena. However, materials are extremely rare where it is possible to explore the full details of the superconducting pairing. Here, we investigate the momentum dependence of the superconducting gap distribution in a novel Dirac material PdTe.

View Article and Find Full Text PDF

Magnetic materials exhibiting topological Dirac fermions are attracting significant attention for their promising technological potential in spintronics. In these systems, the combined effect of the spin-orbit coupling and magnetic order enables the realization of novel topological phases with exotic transport properties, including the anomalous Hall effect and magneto-chiral phenomena. Herein, we report experimental signature of topological Dirac antiferromagnetism in TaCoTe via angle-resolved photoelectron spectroscopy and first-principles density functional theory calculations.

View Article and Find Full Text PDF

Interest in topological materials continues to grow unabated in view of their conceptual novelties as well as their potential as platforms for transformational new technologies. Electronic states in a topological material are robust against perturbations and support unconventional electromagnetic responses. The first-principles band-theory paradigm has been a key player in the field by providing successful prediction of many new classes of topological materials.

View Article and Find Full Text PDF
Article Synopsis
  • - In one-dimensional systems, electron interactions disrupt Fermi liquid theory, giving rise to a special state called Tomonaga-Luttinger Liquid (TLL), characterized by a dimensionless parameter known as the Luttinger parameter K, which measures the balance between kinetic and electrostatic energies among electrons.
  • - Recent findings indicate that TLL behavior has been observed in topological edge states of quantum spin Hall insulators, which feature 1D structures with a linear dispersion and unique spin properties.
  • - This study reveals that the many-body interactions in these helical Luttinger Liquids can be adjusted by their surrounding dielectric environment, allowing for precise control of the Luttinger parameter K, with implications for exploring non-Abelian paraferm
View Article and Find Full Text PDF

We present an in-depth discussion of the magnetic ground state of α''-FeN within the framework of the density functional theory (DFT). The exchange-correlation effects are treated using a variety of schemes, including the local-spin-density approximation, the generalized-gradient approximation, and the Strongly-Constrained-and-Appropriately-Normed (SCAN) scheme. We also delineate effects of adding an on-site interaction parameter on the Fe sites.

View Article and Find Full Text PDF

Breaking time-reversal symmetry by introducing magnetic order, thereby opening a gap in the topological surface state bands, is essential for realizing useful topological properties such as the quantum anomalous Hall and axion insulator states. In this work, a novel topological antiferromagnetic (AFM) phase is created at the interface of a sputtered, c-axis-oriented, topological insulator/ferromagnet heterostructure-Bi Te /Ni Fe because of diffusion of Ni in Bi Te (Ni-Bi Te ). The AFM property of the Ni-Bi Te interfacial layer is established by observation of spontaneous exchange bias in the magnetic hysteresis loop and compensated moments in the depth profile of the magnetization using polarized neutron reflectometry.

View Article and Find Full Text PDF

Being atomically thin and amenable to external controls, two-dimensional (2D) materials offer a new paradigm for the realization of patterned qubit fabrication and operation at room temperature for quantum information sciences applications. Here we show that the antisite defect in 2D transition metal dichalcogenides (TMDs) can provide a controllable solid-state spin qubit system. Using high-throughput atomistic simulations, we identify several neutral antisite defects in TMDs that lie deep in the bulk band gap and host a paramagnetic triplet ground state.

View Article and Find Full Text PDF

Whereas ferromagnets have been known and used for millennia, antiferromagnets were only discovered in the 1930s. At large scale, because of the absence of global magnetization, antiferromagnets may seem to behave like any non-magnetic material. At the microscopic level, however, the opposite alignment of spins forms a rich internal structure.

View Article and Find Full Text PDF

The electrification of heavy-duty transport and aviation will require new strategies to increase the energy density of electrode materials. The use of anionic redox represents one possible approach to meeting this ambitious target. However, questions remain regarding the validity of the O/O oxygen redox paradigm, and alternative explanations for the origin of the anionic capacity have been proposed, because the electronic orbitals associated with redox reactions cannot be measured by standard experiments.

View Article and Find Full Text PDF

Novel magnetic topological materials pave the way for studying the interplay between band topology and magnetism. However, an intrinsically ferromagnetic topological material with only topological bands at the charge neutrality energy has so far remained elusive. Using rational design, we synthesized MnBi8Te13, a natural heterostructure with [MnBiTe] and [BiTe] layers.

View Article and Find Full Text PDF

The rare-earth monopnictide family is attracting an intense current interest driven by its unusual extreme magnetoresistance (XMR) property and the potential presence of topologically non-trivial surface states. The experimental observation of non-trivial surface states in this family of materials are not ubiquitous. Here, using high-resolution angle-resolved photoemission spectroscopy, magnetotransport, and parallel first-principles modeling, we examine the nature of electronic states in HoSb.

View Article and Find Full Text PDF

The topological nodal-line semimetal (TNS) is a unique class of materials with a one dimensional line node accompanied by a nearly dispersionless two-dimensional surface state. However, a direct observation of the so called drumhead surface state within current nodal-line materials is still elusive. Here, using high-resolution angle-resolved photoemission spectroscopy (ARPES) along with first-principles calculations, we report the observation of a topological nodal-loop (TNL) in SrAs, whereas CaAs exhibits a topologically trivial state.

View Article and Find Full Text PDF