A5078429551- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- Advanced Condensed Matter Physics
- Quantum and electron transport phenomena
- Rare-earth and actinide compounds
- Cold Atom Physics and Bose-Einstein Condensates
- Magnetic and transport properties of perovskites and related materials
- Theoretical and Computational Physics
- Corporate Taxation and Avoidance
- Magnetic properties of thin films
- Quantum, superfluid, helium dynamics
- Organic and Molecular Conductors Research
- Topological Materials and Phenomena
- Graphene research and applications
- Quantum many-body systems
- Superconductivity in MgB2 and Alloys
- Superconducting Materials and Applications
- Intellectual Capital and Performance Analysis
- Magnetism in coordination complexes
- Surface and Thin Film Phenomena
- Inorganic Fluorides and Related Compounds
- High-pressure geophysics and materials
- Advanced Thermodynamics and Statistical Mechanics
- Quantum chaos and dynamical systems
- Advanced Chemical Physics Studies
University of Minnesota System
2021-2025
University of Minnesota
2015-2024
Los Alamos National Laboratory
2019
Twin Cities Orthopedics
2017
University of Wisconsin–Madison
2006-2015
Ruhr University Bochum
2014
Max Planck Society
2002-2009
Max Planck Institute for the Physics of Complex Systems
2002-2009
University of Maryland, College Park
2005-2006
Argonne National Laboratory
2001
We analyze antiferromagnetism and superconductivity in novel Fe-based superconductors within the itinerant model of small electron hole pockets near (0,0) $(\ensuremath{\pi},\ensuremath{\pi})$. argue that effective interactions both channels logarithmically flow toward same values at low energies; i.e., must be treated on equal footing. The magnetic instability comes first for sizes two pockets, but loses to upon doping. superconducting gap has no nodes, changes sign between Fermi surfaces...
I review recent works on the symmetry and structure of superconducting gap in Fe-based superconductors (FeSCs) underlying pairing mechanism these systems. The experimental data superconductivity show very rich behavior, with potentially different a state for compositions same material. variety states raises issue whether physics FeSCs is model dependent or universal, governed by single mechanism. argue that universal all obtained so far can be understood within scenario are well described...
We present the full analysis of normal state properties spin-fermion model near antiferromagnetic instability in two dimensions. The describes low-energy fermions interacting with their own collective spin fluctuations, which soften at transition. argue that 2D, system has typical energies—an effective interaction g¯ and an energy ωsf below behaves as a Fermi liquid. ratio determines dimensionless coupling constant for λ2 ∝ g¯/ωsf. show λ scales correlation length diverges criticality. This...
We present the general theory of clean, two-dimensional, quantum Heisenberg antiferromagnets which are close to zero-temperature transition between ground states with and without long-range N\'eel order. While some our discussion is more general, bulk will be restricted in order described by a three-vector parameter. For N\'eel-ordered states, ``nearly critical'' means that ground-state spin stiffness, ${\mathrm{\ensuremath{\rho}}}_{\mathit{s}}$, satisfies...
Starting from a microscopic itinerant model, we derive and analyze the effective low-energy model for collective magnetic excitations in iron pnictides. We show that stripe order is generally preempted by an Ising-nematic which breaks $C_{4}$ lattice symmetry but preserves O(3) spin-rotational symmetry. This leads to rich phase diagram as function of doping, pressure, elastic moduli, displaying split nematic tri-critical points. The transition may instantly bring system verge transition, or...
The authors show that cuprate pseudogap physics can be well understood within the same spin-fermion model which yields $d$-wave superconductivity and non-Fermi-liquid in normal state. Thus, re-emerges as a strong candidate for theoretical of cuprates.
The reorientation process in a magnetic field two-dimensional isotropic and XY quantum Heisenberg antiferromagnets is shown to occur through the intermediate phase with unbroken continuous symmetry constant magnetization equal one third of saturation value. same also found more complicated classical models.
A Heisenberg antiferromagnet on a kagom\'e lattice is highly degenerate in the classical limit. I show that quantum fluctuations lift degeneracy and yeild low-energy branch of spin-wave excitations with velocity which factor ${\mathit{S}}^{\mathrm{\ensuremath{-}}1/3}$ smaller than for conventional spin waves. The relevance these results to experiments stacked ${\mathrm{SrCr}}_{8\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{4+\mathit{x}}$${\mathrm{O}}_{19}$ discussed.
A phase diagram of the one-dimensional S=1/2 frustrated ferromagnetic Heisenberg model in a magnetic field is studied via bosonization technique. Besides phase, two different nematiclike phases with additional symmetry breaking reflections about bond or site are mapped out. The prediction made possible fourfold degeneracy ground state at H=0 for sufficiently strong second-neighbor coupling.
We argue that the resonant peak observed in neutron scattering experiments on superconducting cuprates and peak/dip/hump features ARPES measurements are byproducts of same physical phenomenon. both due to feedback effects damping spin fluctuations a $d-$wave superconductor. consider spin-fermion model at strong coupling, solve set coupled integral equations for fermionic bosonic propagators show dynamical susceptibility below $T_c$ possesses resonance $\Omega_{res} \propto \xi^{-1}$. The...
We consider the problem of fermions interacting with gapless long-wavelength collective bosonic modes. The theory describes, among other cases, a ferromagnetic quantum-critical point (QCP) and QCP towards nematic ordering. construct controllable expansion at in two steps: we first create non-Fermi-liquid ``zero-order'' Eliashberg-type theory, then demonstrate that residual interaction effects are small. prove this approach is justified under conditions: should be smaller than fermionic...
We analyze spin density wave (SDW) order in iron-based superconductors and electronic structure the SDW phase. consider an itinerant model for Fe-pnictides with two hole bands centered at $(0,0)$ electron $(0,\pi)$ $(\pi,0)$ unfolded BZ. A such a is generally combination of components momenta $(\pi,0)$, both yield $(\pi,\pi)$ folded zone. Neutron experiments, however, indicate that only one component present. show or selected if we assume band involved mixing bands. 3-band highly degenerate...
Magnetism and nematic order are the two non-superconducting orders observed in iron-based superconductors. To elucidate interplay between them ultimately unveil pairing mechanism, several models have been investigated. In with quenched orbital degrees of freedom, magnetic fluctuations promote stripe magnetism which induces order. spin charge spontaneous magnetism. Here we develop an unbiased approach, treat on equal footing. Key to our approach is inclusion character low-energy electronic...
We analyze the evolution of superconducting gap structure in strongly hole-doped Ba${}_{1\ensuremath{-}x}$K${}_{x}$Fe${}_{2}$As${}_{2}$ between $x=1$ and $x\ensuremath{\sim}0.4$ (optimal doping). In latter case, pairing state is most likely $s\ifmmode\pm\else\textpm\fi{}$, with different signs on hole electron pockets, but same two $\ensuremath{\Gamma}$-centered pockets (a $++$ pockets). a pure KFe${}_{2}$As${}_{2}$ ($x=1$), which has only laser ARPES data suggested another...
We present a detailed description of two-band quasi-two-dimensional metals with $s$-wave superconducting (SC) and antiferromagnetic spin-density-wave (SDW) correlations. general approach use it to investigate the influence difference between shapes areas two Fermi surfaces on phase diagram. In particular, we determine conditions for coexistence SC SDW orders at different temperatures dopings. argue that conventional order coexists only very low $T$ in tiny range parameters. An extended...
Using general symmetry arguments and model calculations we analyze the superconducting gap in materials with multiple Fermi-surface pockets, applications to iron pnictides. We show that pnictides has an extended $s$-wave but is either nodeless or nodes, depending on interplay between intraband interband interactions. argue nodes emerge without a phase transition as tendency toward spin-density-wave order gets weaker. These findings provide way reconcile seemingly conflicting results of...
We introduce an effective low-energy pairing model for Fe-based superconductors with $s$- and $d$-wave interaction components a small number of input parameters use it to study the doping evolution symmetry structure superconducting gap. argue that describes entire variety states found so far in allows one understand mechanism attraction ${s}^{\ifmmode\pm\else\textpm\fi{}}$ ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ channels, competition between solutions, origin superconductivity heavily doped...
Pairing symmetry in recently discovered Fe-based metallic superconductors AFe$_2$Se$_2$ (A = K, Rb, Cs) with high transition temperature $T_c \sim 40$ K is currently a subject of intensive debates. These systems contain only electron pockets, according to photoemission, and differ from the majority which both hole pockets are present. Both d-wave s-wave pairing symmetries have been proposed for AFe$_2$Se$_2$, but gap generally has nodes, while experiments clearly point no-nodal behavior,...
Iron-based superconductors were discovered seven years ago, in 2008. This short review summarizes what we learned about these materials over the last years, are open questions, and new physics expect to extract from studies of this class high-temperature superconductors.
Twisted bilayer graphene displays insulating and superconducting phases caused by exceptional flattening of its lowest energy bands. Superconductivity with highest $T_c$ appears at hole electron dopings, near half-filling for valence or conduction In the hole-doped case, data show that three-fold lattice rotation symmetry is broken in phase, i.e., a superconductor also nematic. We present mechanism nematic superconductivity. take as an input fact relevant dopings Fermi lies vicinity...
We analyze incommensurate charge-density-wave (CDW) and pair-density-wave (PDW) orders with transferred momenta (±Q,0)/(0,±Q) in underdoped cuprates within the spin-fermion model. Both appear due to an exchange of spin fluctuations before magnetic order develops. argue that ordered state lowest energy has nonzero CDW PDW components same momentum. Such a breaks C_{4} lattice rotational symmetry, time-reversal mirror symmetries. feedback from CDW/PDW on fermionic dispersion is consistent ARPES...