arXiv subjects

T. H. Hansson

Publications and source records attributed to T. H. Hansson.

At least 19 recordsLinked to original sources

arXiv2026

A field theory approach to Breit-type Hamiltonians in gapped Dirac systems

We develop a path-integral-based field theory for deriving Breit-type low-energy Hamiltonians for gapped Dirac systems coupled to both vector and axial gauge fields. Treating the mass gap as the large energy scale, we integrate out the high-energy component of the Dirac spinor and obtain a canonical Schrödinger description for the remaining low-energy degrees of freedom. For the ordinary Dirac equation, our method reproduces the conventional Breit Hamiltonian order by order. In the presence of axial gauge fields, however, the resulting Hamiltonian contains additional vector-axial couplings that have no analogue in the traditional electromagnetic case. We illustrate the method using three- and two-dimensional Dirac models and discuss its relevance to gapped Weyl systems, where dynamical axial fields can generate distinctive low-energy transport signatures.

cond-mat.mes-hall↗

arXiv2026

Quantum Hall Liquids Coupled to Dynamical Electromagnetism

We investigate the effect on a Quantum Hall (QH) liquid of its coupling to 3+1 dimensional dynamical electromagnetism, which renders the system gapless. We calculate both the Hall and longitudinal resistances, $ρ_H$ and $ρ_L$, in the context of a minimal model of the electromagnetic environment, with a small three dimensional conductivity ${\tildeσ}$, that allows for a counter-flow current. In the thermodynamic limit, we show that $ρ_H$ is quantized, while $ρ_L$ approaches a non-zero limit, $ρ_L \sim α\, R_K$, where $α$ and $R_K=2π/e^2$ are the fine structure and the Klitzing constant. In contrast, the QH conductance, $σ_H$, is smaller than the expected quantized value by a correction $\sim α^2/R_K$. The electromagnetic interaction also generates corrections of order $α^2$ to the quasiparticle charges and statistics, in a way that is consistent with general arguments based on gauge invariance. In addition, we present an intuitive argument that relates the flux attachment associated with the composite boson representation of the electron liquid to the empirically observed %persistence of approximate quantization of $ρ_H$, even in circumstances in which $ρ_L$, and the deviation of $σ_H$ from its quantized value, are substantial.

cond-mat.mes-hall↗

arXiv2026

Fractionalized anyons in counterflowing Quantum Hall Liquids

A key property of topologically ordered systems, such as Quantum Hall states, is the existence of excitations obeying fractional quantum statistics - anyons. We develop a theory for multicomponent counterflow states where an ordinary Laughlin quasiparticle can split into fractional vortices carrying fractions of its charge and statistical angle. There are two phases, separated by a quantum phase transition, where in the first, although observable, the fractionalized charges are asymptotically confined. In the second phase, they are unconfined anyons and the topological order is different from that of the Laughlin state.

cond-mat.str-el↗

arXiv2025

On the relation between fractional charge and statistics

We revisit an argument, originally given by Kivelson and Roček, for why the existence of fractional charge necessarily implies fractional statistics. In doing so, we resolve a contradiction in the original argument, and in the case of a $ν= 1/m$ Laughlin holes, we also show that the standard relation between fractional charge and statistics is necessary by an argument based on a t'Hooft anomaly in a global one-form ${\mathcal Z}_m$ symmetry.

cond-mat.str-el↗

arXiv2025

Dynamics of "Classical" Bosons, Fermions, and beyond

We study the classical mechanics and dynamics of particles that retains some memory of quantum statistics. Our work builds on earlier work on the statistical mechanics and thermodynamics of such particles. Starting from the effective classical manifold associated with two-particle bosonic and fermionic coherent states, we show how their exchange statistics is reflected in the symplectic form of the manifold. We demonstrate the classical analogues of exclusion or bunching behavior expected in such states by studying their trajectories in various quadratic potentials. Our examples are two-particle coherent states in one dimension and two-particle vortex motion in the lowest Landau level. We finally compare and contrast our results with previous simulations of the full quantum system, and with existing results on the geometric interpretations of quantum mechanics.

quant-ph↗

arXiv2022

Quantum Field Theory Anomalies in Condensed Matter Physics

We give a pedagogical introduction to quantum anomalies, how they are calculated using various methods, and why they are important in condensed matter theory. We discuss axial, chiral, and gravitational anomalies as well as global anomalies. We illustrate the theory with examples such as quantum Hall liquids, Fermi liquids, Weyl semi-metals, topological insulators and topological superconductors. The required background is basic knowledge of quantum field theory, including fermions and gauge fields, and some familiarity with path integral and functional methods. Some knowledge of topological phases of matter is helpful, but not necessary.

cond-mat.str-el↗

arXiv2021

Mean Field Theories of Quantum Hall Liquids Justified: Variations on the Greiter Wilczek Theme

We present a field theoretic variant of the Wilczek - Greiter adiabatic approach to Quantum Hall liquids. Specifically, we define a Chern-Simons-Maxwell theory such that the flux-attachment mean field theory is exact in a certain limit. This permits a systematic way to justify a variety of useful approximate approaches to these problems as constituting the first term in a (still to be developed) systematic expansion about a solvable limit.

cond-mat.str-el↗

arXiv2020

Geometric Induction in Chiral Superconductors

We consider a number of effects due to the interplay of superconductivity, electromagnetism and elasticity, which are unique for thin membranes of layered chiral superconductors. Some of them should be within the reach of present technology, and could be useful for characterizing materials. More speculatively, the enriched control of Josephson junctions they afford might find useful applications.

cond-mat.supr-con↗

arXiv2020

Microscopic derivation of Ginzburg-Landau theories for hierarchical quantum Hall states

We propose a Ginzburg-Landau theory for a large and important part of the abelian quantum Hall hierarchy, including the prominently observed Jain sequences. By a generalized "flux attachment" construction we extend the Ginzburg-Landau-Chern-Simons composite boson theory to states obtained by both quasielectron and quasihole condensation, and express the corresponding wave functions as correlators in conformal field theories. This yields a precise identification of the relativistic scalar fields entering these correlators in terms of the original electron field.

cond-mat.str-el↗

arXiv2019

From coupled-wire construction of quantum Hall states to wave functions and hydrodynamics

In this paper we use a close connection between the coupled wire construction (CWC) of Abelian quantum Hall states and the theory of composite bosons to extract the Laughlin wave function and the hydrodynamic effective theory in the bulk, including the Wen-Zee topological action, directly from the CWC. We show how rotational invariance can be recovered by fine-tuning the interactions. A simple recipe is also given to construct general Abelian quantum Hall states desceibed by the multi-component Wen-Zee action.

cond-mat.str-el↗

arXiv2018

Screening and Topological Order in Thin Superconducting Films

We derive an effective two-dimensional low-energy theory for thin superconducting films coupled to a three-dimensional fluctuating electromagnetic field. Using this theory we discuss plasma oscil- lations, interactions between charges and vortices and extract the energy of a vortex. Having found that the effective theory properly describes the long distance physics, we then use it to investigate to what extent the superconducting film is a topologically ordered phase of matter.

cond-mat.supr-con↗

arXiv2018

Proposed Spontaneous Generation of Magnetic Fields by Curved Layers of a Chiral Superconductor

We demonstrate that two-dimensional chiral superconductors on curved surfaces spontaneously develop magnetic flux. This geometric Meissner effect provides an unequivocal signature of chiral super- conductivity, which could be observed in layered materials under stress. We also employ the effect to explain some puzzling questions related to the location of zero-energy Majorana modes.

cond-mat.supr-con↗

arXiv2017

Quantum Hall Physics - hierarchies and CFT techniques

The fractional quantum Hall effect, being one of the most studied phenomena in condensed matter physics during the past thirty years, has generated many groundbreaking new ideas and concepts. Very early on it was realized that the zoo of emerging states of matter would need to be understood in a systematic manner. The first attempts to do this, by Haldane and Halperin, set an agenda for further work which has continued to this day. Since that time the idea of hierarchies of quasiparticles condensing to form new states has been a pillar of our understanding of fractional quantum Hall physics. In the thirty years that have passed since then, a number of new directions of thought have advanced our understanding of fractional quantum Hall states, and have extended it in new and unexpected ways. Among these directions is the extensive use of topological quantum field theories and conformal field theories, the application of the ideas of composite bosons and fermions, and the study of nonabelian quantum Hall liquids. This article aims to present a comprehensive overview of this field, including the most recent developments.

cond-mat.str-el↗

arXiv2016

Edge Majoranas on locally flat surfaces - the cone and the Möbius band

In this paper, we investigate the edge Majorana modes in the simplest possible $p{}_{x}+ip_{y}$ superconductor defined on surfaces with different geometry - the annulus, the cylinder, the Möbius band and a cone (by cone we mean a cone with the tip cut away so it is topologically equivalent to the annulus and cylinder)- and with different configuration of magnetic fluxes threading holes in these surfaces. In particular, we shall address two questions: Given that, in the absence of any flux, the ground state on the annulus does not support Majorana modes, while the one on the cylinder does, how is it possible that the conical geometry can interpolate smoothly between the two? Given that in finite geometries edge Majorana modes have to come in pairs, how can a $p{}_{x}+ip_{y}$ state be defined on a Möbius band, which has only one edge? We show that the key to answering these questions is that the ground state depends on the geometry, even though all the surfaces are locally flat. In the case of the truncated cone, there is a non-trivial holonomy, while the non-orientable Möbius band must necessarily support a domain wall.

cond-mat.str-el↗

arXiv2014

Hall Viscosity of Hierarchical Quantum Hall States

Using methods based on conformal field theory, we construct model wave functions on a torus with arbitrary flat metric for all chiral states in the abelian quantum Hall hierarchy. These functions have no variational parameters, and they transform under the modular group in the same way as the multicomponent generalizations of the Laughlin wave functions. Assuming the absence of Berry phases upon adiabatic variations of the modular parameter $τ$, we calculate the quantum Hall viscosity and find it to be in agreement with the formula, given by Read, which relates the viscosity to the average orbital spin of the electrons. For the filling factor $ν=2/5$ Jain state, which is at the second level in the hierarchy, we compare our model wave function with the numerically obtained ground state of the Coulomb interaction Hamiltonian in the lowest Landau level, and find very good agreement in a large region of the complex $τ$-plane. For the same example, we also numerically compute the Hall viscosity and find good agreement with the analytical result for both the model wave function and the numerically obtained Coulomb wave function. We argue that this supports the notion of a generalized plasma analogy that would ensure that wave functions obtained using the conformal field theory methods do not acquire Berry phases upon adiabatic evolution.

cond-mat.str-el↗

arXiv2012

Topological Field Theory for p-wave Superconductors

We propose a topological field theory for a spin-less two-dimensional chiral superconductor that contains fundamental Majorana fields. Due to a fermionic gauge symmetry, the Majorana modes survive as dynamical degrees of freedom only at magnetic vortex cores, and on edges. We argue that these modes have the topological properties pertinent to a p-wave superconductor including the non-abelian braiding statistics, and support this claim by calculating the ground state degeneracy on a torus. We also briefly discuss the connection to the Moore-Read Pfaffian quantum Hall state, and extensions to the spinful case and to three-dimensonal topological superconductors.

cond-mat.supr-con↗

arXiv2010

A general approach to quantum Hall hierarchies

The abelian hierarchy of quantum Hall states accounts for most of the states in the lowest Landau level, and there is evidence of a similar hierarchy of non-abelian states emanating from the ν = 5/2 Moore-Read state in the second Landau level. Extending a recently developed formalism for hierarchical quasihole condensation, we present a theory that allows for the explicit construction of the ground state wave function, as well as its quasiparticle excitations, for any state based on the abelian hierarchy. We relate our construction to structures in rational conformal field theory and stress the importance of using coherent state wave functions which allows us to formulate an extension of the bulk - edge correspondence that was conjectured by Moore and Read. Finally, we study the proposed ground state wave functions in the limiting geometry of a thin torus and argue that they coincide with the known exact results.

cond-mat.str-el↗

arXiv2010

Quasihole condensates in quantum Hall liquids

We develop a formalism to describe quasihole condensates in quantum Hall liquids and thereby extend the conformal field theory approach to the full hierarchy of spin-polarized Abelian states, and to several classes of non-Abelian hierarchical states. Most previously proposed spin-polarized quantum Hall wave functions appear as special cases. In this paper we explain the physical motivations for the approach, and exemplify it by explicitly constructing the level-two quasihole condensate state at filling fraction 2/3, and the two level-three states at 5/13 and 5/7 which are built from combinations of quasielectron and quasihole condensates.

cond-mat.str-el↗