A5088178081- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Topological Materials and Phenomena
- Iron-based superconductors research
- Rare-earth and actinide compounds
- Magnetic and transport properties of perovskites and related materials
- Graphene research and applications
- 2D Materials and Applications
- Quantum and electron transport phenomena
- Electronic and Structural Properties of Oxides
- Superconductivity in MgB2 and Alloys
- Quantum Mechanics and Non-Hermitian Physics
- Superconducting Materials and Applications
- Chemical Thermodynamics and Molecular Structure
- Magnetic properties of thin films
- High-pressure geophysics and materials
- Inorganic Fluorides and Related Compounds
- Quantum many-body systems
- Thermodynamic and Structural Properties of Metals and Alloys
- Theoretical and Computational Physics
- Organic and Molecular Conductors Research
- Quantum, superfluid, helium dynamics
- Advanced Chemical Physics Studies
- Nuclear Materials and Properties
- Cold Atom Physics and Bose-Einstein Condensates
Indian Institute of Science Bangalore
2015-2024
Indian Institute of Technology Kharagpur
2022
University of Burdwan
2020
National University of Singapore
2014-2017
Los Alamos National Laboratory
2009-2016
Institute of Physics, Bhubaneshwar
2016
Northeastern University
2006-2014
Center for Integrated Nanotechnologies
2012
Tampere University
2012
Indian Institute of Technology Bombay
2005
The first-principles band theory paradigm has been a key player not only in the process of discovering new classes topologically interesting materials, but also for identifying salient characteristics topological states, enabling direct and sharpened confrontation between experiment. We begin this review by discussing underpinnings theory, which basically involves layer analysis interpretation assessing properties structures beyond standard construct. Methods evaluating invariants are...
Topological insulators (TIs) are a new type of electronic materials in which the nontrivial insulating bulk band topology governs conducting boundary states with embedded spin-momentum locking. Such edge more robust two-dimensional (2D) TI against scattering by nonmagnetic impurities than its three-dimensional (3D) variant, because 2D two helical protected from only possible backscattering. This makes family better candidate for coherent spin transport and related applications. While several...
Both theoretical and experimental studies of topological phases in non-Hermitian systems have made a remarkable progress the last few years research. In this article, we review key concepts pertaining to Hamiltonians with relevant examples realistic model setups. Discussions are devoted both adaptations invariants from Hermitian systems, as well origins new latter setup. Unique properties such exceptional points complex energy landscapes lead including winding number/vorticity defined solely...
Ultrathin ferroelectric semiconductors with high charge carrier mobility are much coveted systems for the advancement of various electronic and optoelectronic devices. However, in traditional oxide insulators, transition temperature decreases drastically decreasing material thickness ceases to exist below certain critical owing depolarizing fields. Herein, we show emergence an ordered ground state ultrathin (∼2 nm) single crystalline nanosheets Bi2O2Se at room temperature. Free-standing...
We use first-principles electronic structure calculations to predict a new class of two-dimensional (2D) topological insulators (TIs) in binary compositions group III elements (B, Al, Ga, In, and Tl) bismuth (Bi) buckled honeycomb structure. identify band inversions pristine GaBi, InBi, TlBi bilayers, with gaps as large 560 meV, making these materials suitable for room-temperature applications. Furthermore, we demonstrate the possibility strain engineering that phase transition BBi AlBi...
In the present study, we explore superconductivity in NdNiO$_2$ and LaNiO$_2$ employing a first-principles derived low-energy model Hamiltonian, consisting of two orbitals: Ni $x^{2}$-$y^{2}$, an {\it axial} orbital. The orbital is constructed out Nd/La $d$, 3$z^{2}$-$r^{2}$ $s$ characters. Calculation superconducting pairing symmetry eigenvalue spin-fluctuation mediated interaction underlines crucial role inter-orbital Hubbard superconductivity, which turns to be orbital-selective. axial...
Recently developed parity (P) and time-reversal (T) symmetric non-Hermitian systems govern a rich variety of new characteristically distinct physical properties, which may or not have direct analog in their Hermitian counterparts. We study here non-Hermitian, PT-symmetric superconducting Hamiltonian that possesses real quasiparticle spectrum the PT-region Brillouin zone. Within single-band mean-field theory, we find energies are possible when order parameter itself is either anti-Hermitian....
Unconventional superconductivity often arises from Cooper pairing between neighboring atomic sites, stipulating a characteristic symmetry in the reciprocal space. The twisted bilayer graphene (TBG) presents new setting where emerges on flat bands whose Wannier wavefunctions spread over many unit cells, forming so-called Moir\'e pattern. To unravel how states form pairs, we study interplay electronic, structural, and instabilities TBG. For comparisons, also boron-nitride (GBN) possessing...
We calculate RPA-BCS-based spin resonance spectra of the newly discovered iron-selenide superconductor by using two-orbital tight-binding model in a 1-Fe-unit cell. The slightly squarish electron pocket Fermi surfaces at $(\ensuremath{\pi},0)/(0,\ensuremath{\pi})$ momenta produce leading interpocket nesting instability incommensurate vector $q\ensuremath{\sim}(\ensuremath{\pi},0.5\ensuremath{\pi})$ normal-state static susceptibility, pinning strong stripe-like spin-density wave or...
We review the intermediate coupling model for treating electronic correlations in cuprates. Spectral signatures of scenario are identified and used to adduce that cuprates fall rather than weak or strong limits. A robust, 'beyond local-density approximation' framework obtaining wide-ranging properties via a GW-approximation based self-consistent self-energy correction incorporating correlation effects is delineated. In this way, doping- temperature-dependent spectra, from undoped insulator...
We use a first-principles based self-consistent momentum-resolved density fluctuation (MRDF) model to compute the combined effects of electron-electron and electron-phonon interactions describe superconducting dome in correlated MoS2 thin flake TiSe2. find that without including interaction, coupling transition temperature (Tc) are overestimated both these materials. However, once full angular dynamical fluctuations spin charge induced quasiparticle self-energy included, Tc reduced...
LaTe3 is a non-centrosymmetric material with time reversal symmetry, where the charge density wave hosted by Te bilayers. Here, we show that hosts Kramers nodal line-a twofold degenerate line connecting reversal-invariant momenta. We use angle-resolved photoemission spectroscopy, functional theory an experimentally reported modulated structure, effective band structures calculated unfolding, and symmetry arguments to reveal line. Furthermore, calculations confirm imposes gapless crossings...
Abstract Describing systems with non-Hermitian (NH) operators remains a challenge in quantum theory due to singularities (e.g., exceptional points and decoherence) arising from interactions the environment. We introduce well-defined computational basis for representing NH Hamiltonian eigenstates, wherein are shifted states expansion coefficients, simplifying mathematical treatment of open systems. Furthermore, we local `space-time' transformation on that defines generic dual space mapping....
Topological insulators represent a new class of quantum phase defined by invariant symmetries and spin-orbit coupling that guarantees metallic Dirac excitations at its surface. The discoveries these states have sparked the hope realizing nontrivial novel effects such as magnetoelectric effect topological Majorana excitations. Here we develop theoretical formalism to show three dimensional insulator can be designed artificially via stacking bilayers two-dimensional Fermi gases with opposite...
A determination of the superconducting (SC) electron pairing symmetry forms basis for establishing a microscopic mechanism superconductivity. For iron pnictide superconductors, ${s}^{\ifmmode\pm\else\textpm\fi{}}$-pairing theory predicts presence sharp neutron spin resonance at an energy below sum hole and SC gap energies ($E\ensuremath{\le}2\ensuremath{\Delta}$) ${T}_{c}$. On other hand, ${s}^{++}$-pairing expects broad excitation enhancement above $2\ensuremath{\Delta}$ Although has been...
We propose two complementary design principles for engineering three-dimensional (3D) Weyl semimetals and superconductors in a layer-by-layer setup which includes even- odd-parity orbitals alternating layers---dubbed an orbital selective superlattice. Such structure breaks mirror symmetry along the superlattice growth axis which, with help of either basal plane spin-orbit coupling or spinless $p+ip$ superconductivity, stabilizes 3D Dirac node. To explore this idea, we develop generalization...
The emergence of multiple Dirac cones in hexagonal boron nitride (hBN)–graphene heterostructures is particularly attractive because it offers potentially better landscape for higher and versatile transport properties than the primary cone. However, coefficients cloned yet not fully characterized many open questions, including evolution charge dynamics impurity scattering responsible them, have remained unexplored. Noise measurements, having potential to address these been performed date...
The newly discovered noncentrosymmetric superconductor ${\mathrm{ThCoC}}_{2}$ exhibits numerous types of unconventional behavior in the field dependent heat capacity data. Here we present first measurement gap symmetry by muon spin rotation and relaxation ($\ensuremath{\mu}\mathrm{SR}$) measurements. temperature dependence magnetic penetration depth measured using transverse $\ensuremath{\mu}\mathrm{SR}$ experiment reveals evidence a nodal pairing symmetry. To understand this finding, carry...
Employing first-principles density functional theory calculations and Wannierization of the low-energy band structure, we analyze electronic structure undoped, infinite-layer nickelate compounds ${\mathrm{NdNiO}}_{2},$ ${\mathrm{PrNiO}}_{2},$ ${\mathrm{LaNiO}}_{2}$. Our study reveals important role nonzero $f$-ness Nd Pr atoms, as opposed to ${f}^{0}$ occupancy La. The becomes effective in lowering energy rare-earth $5d$ hybridized axial orbital, thereby enhancing electron pockets...
Angle-dependent studies of the gap function provide evidence for coexistence two distinct gaps in hole-doped cuprates, where near nodal direction scales with superconducting transition temperature ${T}_{c}$, while that antinodal pseudogap temperature. We present model calculations which show most characteristic features observed recent angle-resolved photoemission spectroscopy (ARPES) as well scanning tunneling microscopy (STM) two-gap are consistent a scenario has nonsuperconducting origin...
The high-energy kink or the waterfall effect seen in photoemission spectra of cuprates is suggestive coupling quasiparticles to a bosonic mode with implications for mechanism superconductivity. Recent experiments, however, indicate that this may be an artifact produced entirely by matrix element effects, i.e., way photoemitted electron couples incident photons emission process. In order address issue directly, we have carried out realistic computations photointensity...
We present first-principles calculations to predict several three dimensional (3D) topological insulators in quaternary chalcogenide compounds which are made of I$_2$-II-IV-VI$_4$ compositions and ternary I$_3$-V-VI$_4$ famatinite compounds. Among the large members these two families, we give examples naturally occurring mainly Cu-based chalcogenides. show that materials candidates 3D or can be tuned obtain phase transition by manipulating atomic number other cation anion elements. A band...
We present a theoretical framework for quantitative understanding of the full doping dependence optical spectra cuprates. In accord with experimental observations, computed show how high-energy Mott features continue to persist in overdoped regime even after mid-infrared (MIR) peak originating from pseudogap has collapsed quantum critical point. this way, we reconcile opposing tendencies MIR and peaks shift opposite directions increasing doping. The competition between gap also results rapid...
We employed {\it in-situ} pulsed laser deposition (PLD) and angle-resolved photoemission spectroscopy (ARPES) to investigate the mechanism of metal-insulator transition (MIT) in NdNiO$_3$ (NNO) thin films, grown on NdGaO$_3$(110) LaAlO$_3$(100) substrates. In metallic phase, we observe three dimensional hole electron Fermi surface (FS) pockets formed from strongly renormalized bands with well-defined quasiparticles. Upon cooling across MIT NNO/NGO sample, quasiparticles lose coherence via a...