A5040266534- Physics of Superconductivity and Magnetism
- Ionosphere and magnetosphere dynamics
- Advanced Condensed Matter Physics
- Iron-based superconductors research
- Topological Materials and Phenomena
- Rare-earth and actinide compounds
- Earthquake Detection and Analysis
- Solar and Space Plasma Dynamics
- High-pressure geophysics and materials
- GNSS positioning and interference
- Geomagnetism and Paleomagnetism Studies
- Quantum, superfluid, helium dynamics
- Graphene research and applications
- Quantum and electron transport phenomena
- Cold Atom Physics and Bose-Einstein Condensates
- Atmospheric Ozone and Climate
- Geophysics and Gravity Measurements
- Magnetic and transport properties of perovskites and related materials
- Geophysics and Sensor Technology
- Superconductivity in MgB2 and Alloys
- Organic and Molecular Conductors Research
- Plasma Diagnostics and Applications
- Atomic and Subatomic Physics Research
- Quantum many-body systems
- Electronic and Structural Properties of Oxides
Ames National Laboratory
2024-2025
Iowa State University
2024-2025
Rice University
2021-2024
University of Florida
2019-2023
University of Milan
2022
University of Illinois Urbana-Champaign
2016-2021
Florida Museum of Natural History
2020
Urbana University
2016
Purdue University West Lafayette
2012-2015
Sri Sathya Sai Institute of Higher Learning
2009
We devise a model to explain why twisted bilayer graphene exhibits insulating behavior when ν = 2 or 3 charges occupy unit moiré cell, feature attributed Mottness per previous work but not for 1, clearly inconsistent with Mott insulation. compute rs EU/ EK, where EU and EK are the potential kinetic energies, respectively, show that (i) criterion lies at density larger than experimental values by factor of 104 (ii) transition series Wigner crystalline states exists as function ν. find that,...
Kagome materials often host exotic quantum phases, including spin liquids, Chern gap, charge order, and superconductivity. Existing scanning microscopy studies of the kagome order have been limited to non-kagome surface layers. Here we tunnel into lattice FeGe uncover features order. Our spectroscopic imaging identifes a 2x2 in magnetic lattice, resembling that discovered superconductors. Spin-mapping across steps unit-cell-height demonstrates this emerges from spin-polarized electrons with...
In the preceding paper by Schmerling & Thomas (1956) it was shown how, from experimental h'{f) records, is possible to deduce electron distributions in F layer appropriate an average magnetically quiet day any one month; and some account given of these at Slough, Huancayo Watheroo for different times day, seasons epochs solar cycle. this are used as facts which rates production loss electrons deduced. Use also made determined, rapid succession, near sunrise Cambridge. It here recognized...
Strange-metal behavior has been observed in materials ranging from high-temperature superconductors to heavy fermion metals. In conventional metals, current is carried by quasiparticles; although it suggested that quasiparticles are absent strange direct experimental evidence lacking. We measured shot noise probe the granularity of current-carrying excitations nanowires metal YbRh
Lattice symmetries are central to the characterization of electronic topology. Recently, it was shown that Green's function eigenvectors form a representation space group. This formulation has allowed identification gapless topological states even when quasiparticles absent. Here we demonstrate profundity framework in extreme case, interactions lead Mott insulator, through solvable model with long-range interactions. We find both poles and zeros subject symmetry constraints, relate...
There is extensive current interest in electronic topology correlated settings. In strongly systems, contours of Green's function zeros may develop frequency-momentum space, and their role has increasingly been recognized. However, whether how the contribute to properties a matter uncertainty. Here we address issue an exactly solvable model for Mott insulator. We show that several physically measurable correlation functions way does not run into inconsistencies. particular, physical remain...
Abstract Phonon softening is a ubiquitous phenomenon in condensed matter systems which often associated with charge density wave (CDW) instabilities and anharmonicity. The interplay between phonon softening, CDW superconductivity topic of intense debate. In this work, the effects anomalous soft on are studied based recently developed theoretical framework that accounts for damping within Migdal–Eliashberg theory. Model calculations show form sharp dip dispersion relation, either acoustic or...
Abstract The role of anharmonicity on superconductivity has often been disregarded in the past. Recently, it recognized that anharmonic decoherence could play a fundamental determining superconducting properties (electron–phonon coupling, critical temperature, etc) large class materials, including systems close to structural soft-mode instabilities, amorphous solids and metals under extreme high-pressure conditions. Here, we review recent theoretical progress effects, particular certain...
Abstract Non-volatile phase-change memory devices utilize local heating to toggle between crystalline and amorphous states with distinct electrical properties. Expanding on this kind of switching two topologically phases requires controlled non-volatile symmetries. Here, we report the observation reversible stable closely related crystal structures, remarkably electronic in near-room-temperature van der Waals ferromagnet Fe 5− δ GeTe 2 . We show that is enabled by ordering disordering site...
Abstract In weakly coupled BCS superconductors, only electrons within a tiny energy window around the Fermi energy, E F , form Cooper pairs. This may not be case in strong coupling superconductors such as cuprates, FeSe, SrTiO 3 or cold atom condensates where pairing scale, B becomes comparable even larger than . for example, plausible candidate pseudogap state at low doping is fluctuating pair density wave, but no microscopic model has yet been found which supports state. this work, we...
Bogoliubov Fermi surfaces (BFSs) are topologically protected regions of zero energy excitations in a superconductor whose dimension equals that the underlying normal state surface. Examples Hamiltonians exhibiting this ``ultranodal'' phase known to preserve charge-conjugation ($C$) and parity ($P$) but break time-reversal ($T$). In work, we provide examples model do not necessarily symmetry pattern have well-defined sign-changing Pfaffians yielding BFSs. While their topological character has...
Pair density waves (PDWs) are superconducting states formed by Cooper pairs of electrons containing a nonzero center-of-mass momentum. They characterized spatially modulated order parameter and may occur in variety emerging quantum materials such as cuprates, transition-metal dichalcogenides (TMDs), Kagome metals. Despite extensive theoretical numerical studies seeking PDWs lattices interacting settings, there is currently no exact mechanism that spontaneously favors solution the parameter....
Rare-earth magnets with parent cubic symmetry exhibit unique topological properties. However, the origin of these behaviors presently remains unclear. Here, we develop minimal models for Dirac semimetals (DSMs) accidental band crossings and higher-order topology in systems, incorporating candidate magnetic order to analyze bulk, surface, hinge state characteristics. In certain cubic-symmetric DSMs, identify an effective <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi...
A bstract We study an anisotropic holographic bottom-up model displaying a quantum phase transition (QPT) between topologically trivial insulator and non-trivial Weyl semimetal phase. analyze the properties of chaos in critical region. do not find any universal property Butterfly velocity across QPT. In particular it turns out to be either maximized or minimized at point depending on direction propagation. observe that instead butterfly velocity, is dimensionless information screening length...
A theory of superconductivity is presented where the effect anharmonicity, as entailed in acoustic, or optical, phonon damping, explicitly considered pairing mechanism. The gap equation solved including diffusive Akhiezer damping for longitudinal acoustic phonons Klemens optical phonons, with a coefficient which, either case, can be directly related to Gr\"uneisen parameter and hence anharmonic coefficients interatomic potential. results show that increase anharmonicity has strikingly...
We present a minimal theory of superconductivity enhancement in ferroelectric-type materials. Simple expressions for the optical mode responsible soft transition are assumed. A key role is played by anharmonic phonon damping which modulated an external control parameter (electron doping or mechanical strain) causing appearance mode. It shown that superconducting critical temperature Tc upon approaching ferroelectric from either side due to Stokes electron-phonon scattering processes promoted...
The interplay of topological electronic band structures and strong interparticle interactions provides a promising path towards the constructive design robust, long-range entangled many-body systems. As prototype for such systems, we here study an exactly integrable, local model fractionalized insulator. Using controlled perturbation theory about this limit, demonstrate existence bands zeros in exact fermionic Green’s function show that they do affect invariant system, but not quantized...
Abstract Bogoliubov Fermi surfaces are contours of zero-energy excitations that protected in the superconducting state. Here we show multiband superconductors with dominant spin singlet, intraband pairing spin-1/2 electrons can undergo a transition to state if spin-orbit coupling, interband and time reversal symmetry breaking also present. These latter effects may be small, but drive topological for appropriate nodal structure intra-band pair. Such should display nonzero zero-bias density...
The pairing of two electrons on a Fermi surface due to an infinitesimal attraction between them always results in superconducting instability at zero temperature ($T=0$). equivalent question Luttinger (LS) -- contour zeros the propagator instead leads quantum critical point (QCP) that separates non-Fermi liquid (NFL) and superconductor. A surprising little understood aspect pair fluctuations this QCP is their thermodynamics maps Sachdev-Ye-Kitaev (SYK) model strong coupling limit. Here, we...
Electron-phonon superconductors at high pressures have displayed the highest values of critical superconducting temperature ${T}_{c}$ on record, now rapidly approaching room temperature. Despite importance high-$P$ superconductivity in quest for room-temperature superconductors, a mechanistic understanding effect pressure and its complex interplay with phonon anharmonicity is missing, as numerical simulations can bring only system-specific details, clouding out key players controlling...