publications

2024

1. PhysRevLett

   Irrational Moments and Signatures of Higher-Rank Gauge Theories in Diluted Classical Spin Liquids

   R. Flores-Calderón, Owen Benton, and Roderich Moessner

   Phys. Rev. Lett., Sep 2024

2023

1. PhysRevB

   Time-reversal invariant finite-size topology

   R. Flores-Calderon, Roderich Moessner, and Ashley M. Cook

   Phys. Rev. B, Sep 2023

   Abs

   We report finite-size topology in the quintessential time-reversal (TR) invariant systems, the quantum spin Hall insulator (QSHI) and the three-dimensional, strong topological insulator (STI)—previously-identified helical or Dirac cone boundary states of these phases hybridize in wire or slab geometries with one open boundary condition for finite system size, and additional, topologically protected, lower-dimensional boundary modes appear for open boundary conditions in two or more directions and coexist with the response signatures of the higher-dimensional topological bulk. We explicitly demonstrate this coexistence for both the QSHI in a ribbon geometry and the STI in a slab geometry. For the quasi-one-dimensional (q(2-1)D) QSHI, we find topologically protected, quasi-zero-dimensional (q(2-2)D) boundary states within the hybridization gap of the helical edge states, determined from q(2-1)D bulk topology characterized by topologically nontrivial Wilson loop spectra. We show this finite-size topology furthermore occurs in 1T"-WTe2 in ribbon geometries with sawtooth edges, based on analysis of a tight-binding model derived from density-functional theory calculations, motivating experimental investigation of our results. In addition, we find quasi-two-dimensional (q(3-1)D) finite-size topological phases occur for the STI, yielding helical boundary modes distinguished from those of the QSHI by a nontrivial magneto-electric polarizability linked to the original 3D bulk STI. Finite-size topological phases therefore exhibit signatures associated with the nontrivial topological invariant of a higher-dimensional bulk, clearly distinguishing them from previously-known topological phases. Finally, we find the q(3-2)D STI also exhibits finite-size topological phases, finding the first signs of topologically protected boundary modes of codimension greater than one due to finite-size topology. Finite-size topology of four- or higher-dimensional systems is therefore possible in experimental settings without recourse to thermodynamically large synthetic dimensions.

2. PhysRevB

   Time-reversal invariant topological skyrmion phases

   R. Flores-Calderon, and Ashley M. Cook

   Phys. Rev. B, Dec 2023
3. EPL

   Electrochemical transport in Dirac nodal-line semimetals

   R. Flores-Calderón, Leonardo Medel, and A. Martín-Ruiz

   Europhysics Letters, Jun 2023

   Publisher: EDP Sciences, IOP Publishing and Società Italiana di Fisica

   Abs

   Nodal-line semimetals are topological phases where the conduction and the valence bands cross each other along one-dimensional lines in the Brillouin zone, which are symmetry protected by either spatial symmetries or time-reversal symmetry. In particular, nodal lines protected by the combined symmetry exhibits the parity anomaly of 2D Dirac fermions. In this letter, we study the electrochemical transport in Dirac nodal-line semimetals by using the semiclassical Boltzmann equation approach. We derive a general formula for the topological current that includes both the Berry curvature and the orbital magnetic moment. We first evaluate the electrochemical current by introducing a small mass term (which could be induced by inversion-breaking uniaxial strain, pressure, or an external electric field) and apply it to the hexagonal pnictide CaAgP. The electrochemical current vanishes in the zero-mass limit. Introducing a tilting term that does not spoil symmetry that protects the nodal ring, we obtain a finite electrochemical current in the zero-mass limit, which can be regarded as a direct consequence of the parity anomaly. We show that the parity-anomaly–induced electrochemical transport is also present at nonzero temperatures.

2021

1. PhysRevB

   Quantized electrochemical transport in Weyl semimetals

   R. Flores-Calderón, and A. Martı́n-Ruiz

   Phys. Rev. B, Jan 2021

   Abs

   We show that under the effect of an external electric field and a gradient of chemical potential, a topological electric current can be induced in Weyl semimetals without inversion and mirror symmetries. We derive analytic expressions for the nonlinear conductivity tensor and show that it is nearly quantized for small tilting when the Fermi levels are close to the Weyl nodes. When the Van Hove point is much larger than the largest Fermi level, the band structure is described by two linearly dispersing Weyl fermions with opposite chiralities. In this case, the electrochemical response is fully quantized in terms of fundamental constants and the scattering time, and it can be used to measure directly the topological charge of Weyl points. We show that the electrochemical chiral current may be derived from an electromagnetic action similar to axion electrodynamics, where the position-dependent chiral Fermi level plays the role of the axion field. This posits our results as a direct consequence of the chiral anomaly.

2. CSF

   Soliton dynamics of a high-density Bose-Einstein condensate subject to a time varying anharmonic trap

   R. Flores-Calderón, J. Fujioka, and A. Espinosa-Cerón

   Chaos, Solitons & Fractals, Jan 2021

   Abs

   In this paper we study the soliton dynamics of a high-density Bose-Einstein condensate (BEC) subject to a time-oscillating trap. The behavior of the BEC is described with a modified Gross-Pitaevskii equation (mGPE) which takes into account three-body losses, atomic feeding and quantum fluctuations (up to a novel high-density term). A variational approximation (VA) is used to study the behavior of a Gaussian pulse in a static double-well potential. Direct numerical solutions of the mGPE corroborate that the center of the pulse exhibits an oscillatory behavior (as the VA predicts), and show a novel phenomenon of fragmentation and regeneration (FR). It is shown that this FR process is destroyed if we consider a potential with a time-dependent quadratic term, but the FR survives if the time dependence is introduced in a cubic term. Comparison between the VA and the numerical solution revealed an excellent agreement when the oscillations of the pulse remain in one of the potential wells. The effects of the quantum fluctuating terms on the FR process are studied. Finally, variational results using a supergaussian trial function are obtained.