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arXiv:2305.16511 · Physical review. B./Physical review. B

Kardar-Parisi-Zhang universality at the edge of Laughlin states

Gustavo M. Monteiro, Dylan Reynolds, Paolo Glorioso, Sriram Ganeshan

Published Jan 14, 2025• 2 citations
arXivHTMLPDF

Abstract

In this Letter, we investigate the dissipative dynamics at the edge of Laughlin fractional quantum Hall (FQH) states starting from the hydrodynamic framework of the composite boson theory recently developed by G. M. Monteiro et al. [Phys. Rev. B 109, 174525 (2024)]. Critical to this description is the choice of boundary conditions, which ultimately stems from the choice of hydrodynamic variables in condensate degrees of freedom. Given the gapped nature of bulk, one would expect dissipation effects to play an important role only near the FQH edge. Thus, one envisions a scenario where the bulk hydrodynamic equations remain unmodified, while the dissipation effects are introduced at the edge via boundary conditions. We have recently shown that the anomaly requirements fix the boundary conditions of the FQH fluid to be no-penetration and no-stress boundary conditions. In this work, we introduce energy dissipation in the no-stress boundary condition leading to charge diffusion at the boundary. The resulting dissipative edge dynamics is quite rigid from a hydrodynamic perspective, as it has to preserve the edge charge continuity and the anomaly structure. We show that the diffusive edge dynamics with fluctuation-dissipation relations within a power counting scheme belong to the Kardar-Parisi-Zhang universality class.

DOI
10.1103/physrevb.111.l041108

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In this Letter, we investigate the dissipative dynamics at the edge of Laughlin fractional quantum Hall (FQH) states starting from the hydrodynamic framework of the composite boson theory recently developed by G. M. Monteiro et al. [Phys. Rev. B 109, 174525 (2024)]. Critical to this description is the choice of boundary conditions, which ultimately stems from the choice of hydrodynamic variables in condensate degrees of freedom. Given the gapped nature of bulk, one would expect dissipation effects to play an important role only near the FQH edge. Thus, one envisions a scenario where the bulk hydrodynamic equations remain unmodified, while the dissipation effects are introduced at the edge via boundary conditions. We have recently shown that the anomaly requirements fix the boundary conditions of the FQH fluid to be no-penetration and no-stress boundary conditions. In this work, we introduce energy dissipation in the no-stress boundary condition leading to charge diffusion at the boundary. The resulting dissipative edge dynamics is quite rigid from a hydrodynamic perspective, as it has to preserve the edge charge continuity and the anomaly structure. We show that the diffusive edge dynamics with fluctuation-dissipation relations within a power counting scheme belong to the Kardar-Parisi-Zhang universality class.
This paper investigates the bulk and boundary dynamics of Laughlin states, which are modeled using composite boson theory within a fluid dynamics framework. In this work, we adopt an alternative starting point based on a hydrodynamic action with topological terms, which fleshes out the fluid aspects of the Laughlin state manifestly. For a particular choice of the velocity field, the fluid equation for this action is akin to first-order hydrodynamic equations, supplemented with an additional constitutive equation known as the Hall constraint. When a hard wall boundary is present, one of the topological terms in the fluid action triggers anomaly inflow, indicating the presence of gauge anomaly at the edge. The first-order hydrodynamic equations require a second boundary condition, which, in the absence of dissipation, can be either a no-slip or a no-stress condition. We find that the no-slip condition, where the fluid adheres to the wall, is incompatible with the chiral edge dynamics. On the other hand, the no-stress condition, which allows the fluid to move along the wall without friction, is consistent with the expected chiral edge dynamics of the Laughlin state. Furthermore, our work derives this modified no-stress boundary condition within a variational principle. This is accomplished by incorporating a chiral boson action within the boundary action that is nonlinearly coupled to the edge density, thus systematically extending the edge chiral Luttinger liquid theory.
We show that dirty quantum Hall systems exhibit large hydrodynamic fluctuations at their edge that lead to anomalously damped charge excitations in the Kardar-Parisi-Zhang universality class ω≃ck-iDk^{3/2}. The dissipative optical conductivity of the edge is singular at low frequencies σ(ω)∼1/ω^{1/3}. These results are direct consequences of the charge continuity relation, the chiral anomaly, and thermalization on the edge-in particular translation invariance is not assumed. Diffusion of heat similarly breaks down, with a universality class that depends on whether the bulk thermal Hall conductivity vanishes. We further establish the theory of fluctuating hydrodynamics for surface chiral metals, where charge fluctuations give logarithmic corrections to transport.
Abstract Advancing a microscopic framework that rigorously unveils the underlying topological hallmarks of fractional quantum Hall (FQH) fluids is a prerequisite for making progress in the classification of strongly-coupled topological matter. We present a second-quantization framework that reveals an exact fusion mechanism for particle fractionalization in FQH fluids, and uncovers the fundamental structure behind the condensation of non-local operators characterizing topological order in the lowest-Landau-level. We show the first exact analytic computation of the quasielectron Berry connections leading to its fractional charge and exchange statistics, and perform Monte Carlo simulations that numerically confirm the fusion mechanism for quasiparticles. We express the sequence of (bosonic and fermionic) Laughlin second-quantized states, highlighting the lack of local condensation, and present a rigorous constructive subspace bosonization dictionary for the bulk fluid. Finally, we establish universal long-distance behavior of edge excitations by formulating a conjecture based on the DNA, or root state, of the FQH fluid.
A distinguishing feature of fractional quantum Hall (FQH) states is a singular behavior of equilibrium densities at boundaries. In contrast to states at integer filling fraction, such quantum liquids posses an additional dipole moment localized near edges. It enters observable quantities such as universal dispersion of edge states and Lorentz shear stress. For a Laughlin state, this behavior is seen as a peak, or overshoot, in the single-particle density near the edge, reflecting a general tendency of electrons in FQH states to cluster near edges. We compute the singular edge behavior of the one-particle density by a perturbative expansion carried out around a completely filled Landau level. This correction is shown to fully capture the dipole moment and the major features of the overshoot observed numerically. Furthermore, it exhibits the Stokes phenomenon with the Stokes line at the boundary of the droplet, decaying like a Gaussian inside and outside the liquid with different decay lengths. In the limit of vanishing magnetic length, the shape of the overshoot is a singular double layer with a capacity that is a universal function of the filling fraction. Finally, we derive the edge dipole moment of Pfaffian FQH states. The result suggests an explicit connection between the magnitude of the dipole moment and the bulk odd viscosity.
The universality of dynamical scaling laws constitutes a cornerstone in the theoretical understanding of quantum many-body systems, particularly in non-equilibrium settings. Recent advancements have proposed a phenomenological ansatz based on spontaneous symmetry breaking (SSB) to unify the description of charge transport in open quantum systems. However, it remains unclear under which conditions it fails to capture the emergent hydrodynamics and if it does break down, whether nontrivial dynamics emerge. In this work we show that Kardar-Parisi-Zhang (KPZ) dynamics in an open integrable model (the B3 model), rather than diffusion from SSB, emerges. We find that the B3 model is equivalent to two interacting asymmetric XXZ spin chains and the ansatz can only capture the influence of the inter-chain interactions. When the initial state is appropriate, the asymmetric XXZ structure dominates the dynamics, which gives KPZ scaling behavior even when the hopping rate becomes negative. Our work motivates theory of charge transport in open systems beyond the ansatz based on SSB.
The edge of the electronic fractional quantum Hall (FQH) system obeys the law of the chiral Luttinger liquid theory due to its intrinsic topological properties and the relation of bulk-edge correspondence. However, in a realistic experimental system, such as the usual Hall bar setup, the softening of the background confinement potential can induce the reconstruction of the edge spectrum, which breaks the chirality and universality of the FQH edge. The entanglement spectrum (ES) of the FQH ground state has the same counting structure as that of the energy spectrum indicating the topological characters of the quantum state. In this work, we report that the ES can also have an edge reconstruction while sweeping the area of the subsystem in real space cut. Moreover, we found that the critical area of the subsystem matches accurately with the intrinsic building block of the FQH liquids, namely the correlation hole of the FQH liquids. The above results seem to be universal after our study of a series of typical FQH states, such as two Laughlin states at $\ensuremath{\nu}=1/3$ and 1/51/51/5, and the Moore-Read state for $\ensuremath{\nu}=5/2$.