A5039082727- Physics of Superconductivity and Magnetism
- Quantum and electron transport phenomena
- Quantum many-body systems
- Topological Materials and Phenomena
- Rare-earth and actinide compounds
- Advanced Condensed Matter Physics
- Graphene research and applications
- Theoretical and Computational Physics
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum, superfluid, helium dynamics
- Quantum chaos and dynamical systems
- Iron-based superconductors research
- Advanced Thermodynamics and Statistical Mechanics
- Magnetic and transport properties of perovskites and related materials
- Surface and Thin Film Phenomena
- Retinal Imaging and Analysis
- Spectral Theory in Mathematical Physics
- Advanced Physical and Chemical Molecular Interactions
- Advanced Chemical Physics Studies
- Carbon Nanotubes in Composites
- Magnetic properties of thin films
- Quantum Chromodynamics and Particle Interactions
- Thermal properties of materials
- Quantum Mechanics and Applications
- Organic and Molecular Conductors Research
Flatiron Health (United States)
2022-2025
Flatiron Institute
2023-2025
University of California, Berkeley
2020-2023
Stanford University
2022
Harvard University
2013-2020
University of California, Santa Barbara
2018
Lancaster University
2012-2013
Indian Institute of Technology Kanpur
2012-2013
University of Pittsburgh
2005-2007
Using a general symmetry-based approach, we provide classification of generic miniband structures for electrons in graphene placed on substrates with the hexagonal Bravais symmetry. In particular, identify conditions at which first moir\'e is separated from rest spectrum by either one or group three isolated mini Dirac points and not obscured dispersion surfaces coming other minibands. such cases, Hall coefficient exhibits two distinct alternations its sign as function charge carrier density.
We show how Majorana end modes can be generated in a one-dimensional system by varying some of the parameters Hamiltonian periodically time. The specific model we consider is chain containing spinless electrons with nearest-neighbor hopping amplitude, $p$-wave superconducting term, and chemical potential; this equivalent to spin-$\frac{1}{2}$ anisotropic $XY$ couplings between nearest neighbors magnetic field applied $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{z}$ direction. that potential...
Strange metals-ubiquitous in correlated quantum materials-transport electrical charge at low temperatures but not by the individual electronic quasiparticle excitations, which carry ordinary metals. In this work, we consider two-dimensional metals of fermions coupled to critical scalars, latter representing order parameters or fractionalized particles. We show that (T), such generically exhibit strange metal behavior with a T-linear resistivity arising from spatially random fluctuations...
We study scrambling, an avatar of chaos, in a weakly interacting metal the presence random potential disorder. It is well known that charge and heat spread via diffusion such disordered metal. In contrast, we show within perturbation theory chaos spreads ballistic fashion. The squared anticommutator electron field operators inherits light-cone like growth, arising from interplay growth (Lyapunov) exponent scales as inelastic scattering rate diffusive piece due to two spatial dimensions,...
Significance All high-temperature superconductors exhibit a remarkable “strange metal” state above their critical temperatures. A theory of the strange metal is prerequisite for deeper understanding superconductivity, but ubiquitous quasiparticle normal metals cannot be extended to metal. Instead, many-body chaos over shortest possible time allowed by quantum theory. We characterize in model fermions at nonzero density coupled an emergent gauge field. find universal relationship between...
We present a lattice model of fermions with N flavors and random interactions that describes Planckian metal at low temperatures T→0 in the solvable limit large N. begin quasiparticles around Fermi surface effective mass m^{*} then include lead to fermion spectral functions frequency scaling k_{B}T/ℏ. The resistivity ρ obeys Drude formula ρ=m^{*}/(ne^{2}τ_{tr}), where n is density fermions, transport scattering rate 1/τ_{tr}=fk_{B}T/ℏ; we find f order unity essentially independent strength...
Despite much theoretical effort, there is no complete theory of the 'strange' metal state high temperature superconductors, and its linear-in-temperature, $T$, resistivity. Recent experiments showing an unexpected linear-in-field, $B$, magnetoresistivity have deepened puzzle. We propose a simple model itinerant electrons, interacting via random couplings with electrons localized on lattice quantum 'dots' or 'islands'. This solvable in large-$N$ limit, can reproduce observed behavior. The key...
We describe the large $N$ saddle point, and structure of fluctuations about a theory containing sharp, critical Fermi surface in two spatial dimensions. The describes onset Ising order liquid, closely related theories apply to other cases with surfaces. employ random couplings flavor space between fermions bosonic parameter, but there is no randomness: consequently, $G$-$\Sigma$ path integral expressed terms fields bilocal spacetime. exponents saddle-point are same as well-studied non-random...
A Fermi surface coupled to a scalar field can be described in $1/N$ expansion by choosing the fermion-scalar Yukawa coupling random $N$-dimensional flavor space, but invariant under translations. We compute conductivity of such theory two spatial dimensions for critical scalar. find Drude contribution, and verify that proposed $1/\omega^{2/3}$ contribution optical at frequency $\omega$ has vanishing co-efficient convex surface. also describe influence impurity scattering fermions, while self...
We introduce an effective theory for quantum critical points (QCPs) in heavy fermion systems, involving a change carrier density without symmetry breaking. Our new captures strongly coupled metallic QCP, leading to robust marginal Fermi liquid transport phenomenology, and associated linear temperature ($T$) "strange metal" resistivity, all within controlled large $N$ limit. In the parameter regime of strong damping emergent bosonic excitations, QCP also displays near-universal "Planckian"...
A pair density wave (PDW) is a superconductor whose order parameter periodic function of space, without an accompanying spatially uniform component. Since PDWs are not the outcome weak-coupling instability Fermi liquid, generic pairing mechanism for PDW has remained elusive. We describe and solve models having robust phases. To access intermediate coupling limit, we invoke large-N limits liquids with repulsive BCS interactions that admit saddle point solutions. show requirements long-range...
The theory for the onset of spin density wave order in a metal two dimensions flows to strong coupling, with interactions not only at ``hot spots,'' but on entire Fermi surface. We advocate computation dc transport regime where there is rapid relaxation local equilibrium around surface by processes which conserve total momentum. resistivity then controlled weaker perturbations do consider variations position quantum-critical point, induced long-wavelength disorder, and find contribution...
The strange metal phase of correlated electrons materials was described in a recent theory by model Fermi surface coupled two-dimensional quantum critical bosonic field with spatially random Yukawa coupling. With the assumption self-averaging randomness, similar to that Sachdev–Ye–Kitaev model, numerous observed properties were obtained for wide range intermediate temperatures, including linear temperature resistivity. Harris criterion implies spatial fluctuations local position point must...
The Sachdev-Ye-Kitaev (SYK) model describes electrons with random and all-to-all interactions, realizes a many-body state without quasiparticle excitations, non-vanishing extensive entropy $S_0$ in the zero temperature limit. Its low energy theory coincides of near-extremal charged black holes Bekenstein-Hawking $S_0$. Several mesoscopic experimental configurations realizing SYK quantum dynamics over significant intermediate scale have been proposed. We investigate thermoelectric transport...
Kohn's theorem places strong constraints on the cyclotron response of Fermi liquids. Recent observations a doping dependence in mass ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ [Legros et al., Phys. Rev. B 106, 195110 (2022)] are therefore surprising because can only be renormalized by large momentum umklapp interactions, which not expected to vary significantly with doping. We show that version continues apply disorder-free non-Fermi-liquids critical boson near...
We solve a model of electrons with Hubbard-U Coulomb repulsion and random Yukawa coupling to two-dimensional bosonic bath, using an extended dynamical mean field theory scheme. Our exhibits quantum critical point, at which the repulsive component electron interactions strongly enhances effects fluctuations on electrons, leading breakdown Fermi liquid physics formation strange metal "Planckian" [O(kBT/ℏ)] quasiparticle decay rates low temperatures T→0. Furthermore, eventual Mott transition...
We find a systematic reappearance of massive Dirac features at the edges consecutive minibands formed magnetic fields ${B}_{p/q}=\frac{p}{q}{\ensuremath{\phi}}_{0}/S$ providing rational flux through unit cell moir\'e superlattice created by hexagonal substrate for electrons in graphene. The Dirac-type $B={B}_{p/q}$ determine hierarchy gaps surrounding fractal spectrum and show that these have topological insulator properties. Using additional $q$-fold degeneracy ${B}_{p/q}$, we trace to...
Building upon techniques employed in the construction of Sachdev-Ye-Kitaev (SYK) model, which is a solvable $0+1$ dimensional model non-Fermi liquid, we develop solvable, infinite-ranged random-hopping fermions coupled to fluctuating U(1) gauge fields. In specific large-$N$ limit, our realizes gapless liquid phase, combines effects hopping and interaction terms. We derive thermodynamic properties phase realized by this charge transport an infinite-dimensional version with spatial structure.
A mysterious incoherent metallic (IM) normal state with T-linear resistivity is ubiquitous among strongly correlated superconductors. Recent progress microscopic models exhibiting IM transport has presented the opportunity for us to study new that exhibit direct transitions into a superconducting out of states within framework connected Sachdev-Ye-Kitaev "quantum dots." Here, local interactions dot produce in state, while attractive drive superconductivity. Through explicit calculations, we...
We develop a theory for light-induced superconductivity in underdoped cuprates which the competing bond-density wave order is suppressed by driving phonons with light. Close to instability system small Fermi surface, such as fractionalized liquid, we show that coupling of electrons strongly enhanced at ordering wavevectors, leading strong softening these wavevectors. For model classical anharmonic couplings, combination and can lead large phonon oscillations. When coupled phenomenological...
The hyperscaling property implies that spatially isotropic critical quantum states in $d$ spatial dimensions have a specific heat which scales with temperature as $T^{d/z}$, and an optical conductivity frequency $\omega^{(d-2)/z}$ for $\omega \gg T$, where $z$ is the dynamic exponent. We examine spin-density-wave fixed point of metals $d=2$ found by Sur Lee (Phys. Rev. B 91, 125136 (2015)) expansion $\epsilon = 3-d$. find contributions "hot spots" on Fermi surface to obey (up logarithms),...
We extend the theory of shot noise in coherent metals to strange without quasiparticle excitations. This requires a generalization Boltzmann equation with source distribution functions which depend independently on excitation momentum and energy. apply this model metal linear temperature ($T$) resistivity, describing Fermi surface spatially random Yukawa coupling critical boson. find suppression Fano factor metal, describe dependence applied voltage. At low temperatures, we obtain equal...
The two-dimensional Yukawa-Sachdev-Ye-Kitaev (2D-YSYK) model provides a universal theory of quantum phase transitions in metals the presence quenched random spatial fluctuations local position critical point. It has Fermi surface coupled to scalar field by spatially Yukawa interactions. We present full numerical solutions self-consistent disorder averaged analysis 2D-YSYK both normal and superconducting states, obtaining electronic spectral functions, frequency-dependent conductivity,...