Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session RR09: V: Strongly Correlated Systems, Including Quantum Fluids and Solids IV |
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Sponsoring Units: DCMP Chair: Néstor Massa, CONICET-Univ Nac of La Plata Room: Virtual Room 9 |
Tuesday, March 21, 2023 11:30AM - 11:42AM |
RR09.00001: Symplectic topological Kondo effect Guangjie Li, Elio J König, Jukka Vayrynen Strongly correlated systems with the ability to harbor anyonic quasi-particles are of primary importance both for fundamental scientific interest and for quantum information technology. Specifically, the multi-channel and the topological Kondo effects were advocated in this context, however they require either perfect channel symmetry or the use of Majorana fermions. Here we propose a Majorana-free mesoscopic setup which implements the Kondo effect of the symplectic Lie group and can harbor emergent anyons (including Majorana fermions, Fibonacci anyons, and $mathbb Z_3$ parafermions) even in the absence of perfect channel symmetry. In addition to the detailed prescription of the implementation, we present the strong coupling solution by mapping the model to the multi-channel Kondo effect associated to an internal SU(2) symmetry and exploit conformal field theory (CFT) to predict the non-trivial scaling of a variety of observables, including conductance, as a function of temperature. This work does not only open the door for robust Kondo-based topological quantum computation, but also sheds light on the physics of strongly correlated materials with competing order parameters. |
Tuesday, March 21, 2023 11:42AM - 11:54AM |
RR09.00002: Revisting the bosonization and scaling of the single-impurity Kondo model Aleksandar Ljepoja, Carlos J Bolech, Nayana Shah Capitalizing on recent work that clarifies the consistent use of bosonization methods to study quantum impurity models, we revise the refermionization of the multichannel Kondo model and uncover some hidden approximations that limit its range of validity. This complements and extends beyond previous results for the Toulouse limit and reinforces the need for the use of an extended calculational framework. We carry out a number of exact and scaling-analysis comparisons between the different model formulations to show that consistency considerations can lead to a full agreement on all aspects of the physics |
Tuesday, March 21, 2023 11:54AM - 12:06PM |
RR09.00003: Phase transitions of the Dicke model Pragna Das, Auditya Sharma We revisit the three main phase transitions of the Dicke model: quantum phase transition (QPT), thermal phase transition (TPT) and excited state quantum phase transition (ESQPT). It is known that in the QPT the system goes from the normal phase (NP) to the super-radiant phase (SP). We show here that in the SP, the ground state participation ratio scales as square root of the total Hilbert space dimension, indicating multifractal behavior of the system. The TPT is studied with the aid of the mutual information between two spins - this yields a striking signature in excellent agreement with the analytical expression for the critical temperature Tc, above which the system comes back from the SP to the NP for a sufficiently large coupling strength. The ESQPT which is traditionally understood as a property of the spectrum is here studied also with the aid of eigenstate properties. We find that not only is there a lower cut-off energy but also there exists an upper cutoff energy, which is signalled by a number of eigenstate properties: von-Neumann entanglement entropy between spins and bosons, the boson particle number, concurrence between two spins and the participation ratio. |
Tuesday, March 21, 2023 12:06PM - 12:18PM |
RR09.00004: Phase diagram and critical behaviour of disordered quantum clock model Vishnu Pulloor Kuttanikkad, Gaurav R Khairnar, Thomas Vojta, Rajesh Narayanan We investigate the critical behaviour of the phase transitions in the disordered quantum clock model using large-scale Monte Carlo simulations. We recast the model via the quantum-to-classical mapping onto a higher-dimensional classical spin Hamiltonian with the columnar disorder. The quasi-long-range ordered (QLRO) phase that separates the clock-ordered phase and paramagnetic phase survives at weak disorder but shrinks as the strength of the disorder increases. The QLRO phase vanishes at a tricritical point, beyond which there is a direct transition from the clock-ordered phase to the paramagnetic phase. The transition from the QLRO phase to the paramagnetic phase displays a crossover from clean-XY critical behaviour to disorder-dependent critical behaviour, similar to the behaviour observed in the (1+1) d disordered XY model [1]. However, the critical behaviour of the transition from the clock-ordered phase to the QLRO phase appears to be independent of the disorder strength. The direct transition between the clock-ordered and paramagnetic phases above the tricritical point also shows a disorder-dependent critical behaviour. At very high disorder strengths, we see signatures of the infinite randomness fixed-point as predicted by the strong disorder renormalization group calculations [2]. |
Tuesday, March 21, 2023 12:18PM - 12:30PM |
RR09.00005: Terminable Transitions in a Topological Fermion Ladder Yuchi He, Dante M Kennes, Christoph Karrasch, Roman Rausch Interacting fermion ladders are believed to exhibit various Mott-insulator regions as quantum |
Tuesday, March 21, 2023 12:30PM - 12:42PM |
RR09.00006: Ransom Magnetic Field and the Dirac Fermi Surface Chao-Jung Lee, Michael Mulligan We study a single 2d Dirac fermion at finite density, subject to a quenched random magnetic field. Applications of this theory include graphene when restricted to a single valley, the gapless surface states of a 3d time-reversal topological insulator, an integer quantum Hall plateau transition, and the (mean-field) Dirac composite fermion description of the half-filled lowest Landau level. At low energies and sufficiently weak disorder, the theory maps onto an infinite collection of 1d chiral fermions (associated to each point on the Fermi surface) coupled by a random vector potential. This low-energy theory exhibits an exactly solvable random fixed line, along which we directly compute various disorder-averaged observables without the need for the usual replica, supersymmetry, or Keldysh techniques. We find the longitudinal dc conductivity in the collisionless ω/T → ∞ limit to be nonuniversal and to vary continuously along the fixed line. |
Tuesday, March 21, 2023 12:42PM - 12:54PM |
RR09.00007: Observation of the Gurzhi Effect in Ultra-high Mobility Corbino Rings Sujatha Vijayakrishnan, Frederik Poitevin, Oulin Yu, Matei Petrescu, Zachary Berkson-Korenberg, Thomas Szkopek, Ken West, Loren N Pfeiffer, Guillaume Gervais In 1963, based on theoretical considerations, Gurzhi predicted that a decrease in resistance with increasing temperature should be observable when a clean conductor is confined to a constricted geometry. This effect, now known as the “Gurzhi effect” [1,2] is the result of hydrodynamic effects occurring in a highly interacting system with low disorder. In this talk, I will show our observation of the Gurzhi effect (below 1K) in an annular ring formed in an ultra-high mobility GaAs/AlGaAs two-dimensional electron gas system (2DEG). A four-terminal Corbino geometry was used since it only probes the bulk properties of the 2DEG, hence eliminating any potential spurious effects due to edges and/or geometry of the sample. The effect observed is fully consistent with recent calculations of various lengthscales by Anh and Das Sarma [3], and it provides a direct observation of hydrodynamic effects in the transport properties of an ultra-high electron mobility system. |
Tuesday, March 21, 2023 12:54PM - 1:06PM |
RR09.00008: Breaking down the magnonic Wiedemann-Franz law in the hydrodynamic regime Ryotaro Sano Quantum transport has attracted a profound growth of interest owing to its fundamental importance and many applications in condensed matter physics. Recent developments in experimental techniques have boosted the study of quantum transport. Notably in ultraclean systems, strong interactions between quasi-particles drastically affect the transport properties, resulting in an emergent hydrodynamic behavior. The most-studied example is the hydrodynamic charge transport in metals, which gives rise to an active research field called electron hydrodynamics. This concept has revealed various unconventional transport phenomena such as the violation of the Wiedemann-Franz (WF) law. |
Tuesday, March 21, 2023 1:06PM - 1:18PM |
RR09.00009: Electronic Poiseuille Flow in Hexagonal Boron Nitride Encapsulated Graphene FETs Tathagata Paul, Wenhao Huang, Mickael Perrin, Michel Calame In most conductors, diffusive scattering from defects and phonons leads to an Ohmic transport. Charge carriers traveling across the channel suffer many momentum relaxing collisions leading to a constant drift velocity along the direction of the applied electric field. Alternatively, transport is ballistic, when the channel dimensions are the smallest length scale in the system. However, a third and relatively unexplored transport regime emerges when electron-electron interactions are sufficiently strong to induce a correlated and momentum-conserving charge flow similar to the Hagen-Poiseuille flow of a classical fluid. In the current work, we investigate the electronic signatures of such a viscous charge flow in high-mobility graphene FETs. In two complementary measurement schemes, we monitor differential resistance of graphene for different channel widths and for different effective electron temperatures. We observe a width dependence of channel conductivity and a minimum resistivity at elevated electron temperatures, indicative of the presence of charge hydrodynamics. By combining both approaches, the presence of viscous effects is verified in a temperature range starting from 178K and extending upto room temperature. Our experimental findings are supported by finite element calculations of the graphene channel. The presence of viscous effects at room temperature opens up avenues for functional hydrodynamic devices such as geometric rectifiers and charge amplifiers. |
Tuesday, March 21, 2023 1:18PM - 1:30PM |
RR09.00010: Hydrodynamic thermoelectric transport in Corbino geometry Songci Li, Alex Levchenko, Anton Andreev We study hydrodynamic electron transport in Corbino graphene devices. Due to the irrotational character of the flow, the forces exerted on the electron liquid are expelled from the bulk. We show that in the absence of Galilean invariance, force expulsion produces qualitatively new features in thermoelectric transport: (i) it results in drops of both voltage and temperature at the system boundaries and (ii) in conductance measurements in pristine systems, the electric field is not expelled from the bulk. We obtain thermoelectric coefficients of the system in the entire crossover region between charge neutrality and high electron density regime. The thermal conductance exhibits a sensitive Lorentzian dependence on the electron density. The width of the Lorentzian is determined by the fluid viscosity. This enables determination of the viscosity of electron liquid near charge neutrality from purely thermal transport measurements. In general, the thermoelectric response is anomalous: It violates the Matthiessen's rule, the Wiedemann-Franz law, and the Mott relation. We also obtain analytic expressions for magnetoransport coefficients of Corbino devices, and obtain estimates for the electrical and thermal magnetoresistances for monolayer and bilayer systems at charge neutrality. Magnetoresistance becomes strong (of order 100%) at relatively weak fields, at which the kinetic coefficients of the electron liquid are practically unaffected by the magnetic field. |
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