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Title: Loop current fluctuations and quantum critical transport

Abstract

We study electrical transport at quantum critical points (QCPs) associated with loop current ordering in a metal, focusing specifically on models of the “Hertz-Millis” type. At the infrared (IR) fixed point and in the absence of disorder, the simplest such models have infinite DC conductivity and zero incoherent conductivity at nonzero frequencies. However, we find that a particular deformation, involving N N species of bosons and fermions with random couplings in flavor space, admits a finite incoherent, frequency-dependent conductivity at the IR fixed point, \sigma(\omega>0)\sim\omega^{-2/z} σ ( ω > 0 ) ω 2 / z , where z z is the boson dynamical exponent. Leveraging the non-perturbative structure of quantum anomalies, we develop a powerful calculational method for transport. The resulting "anomaly-assisted large N N expansion" allows us to extract the conductivity systematically. Although our results imply that such random-flavor models are problematic as a description of the physical N = 1 N = 1 system, they serve to illustrate some general conditions for quantum critical transport as well as the anomaly-assisted calculational methods. In addition, we revisit an old result that irrelevant operators generate a frequency-dependent conductivity, \sigma(\omega>0) \sim \omega^{-2(z-2)/z} σ ( ω > 0 ) ω 2 ( z 2 ) / z , in problems of this kind. We show explicitly, within the scope of the original calculation, that this result does not hold for any order parameter.

Authors:
 [1];  [2];  [1];  [1]
  1. Massachusetts Institute of Technology
  2. Harvard University
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1973725
Grant/Contract Number:  
SC0008739
Resource Type:
Published Article
Journal Name:
SciPost Physics
Additional Journal Information:
Journal Name: SciPost Physics Journal Volume: 14 Journal Issue: 5; Journal ID: ISSN 2542-4653
Publisher:
Stichting SciPost
Country of Publication:
Netherlands
Language:
English

Citation Formats

Shi, Zhengyan Darius, Else, Dominic V., Goldman, Hart, and Senthil, Todadri. Loop current fluctuations and quantum critical transport. Netherlands: N. p., 2023. Web. doi:10.21468/SciPostPhys.14.5.113.
Shi, Zhengyan Darius, Else, Dominic V., Goldman, Hart, & Senthil, Todadri. Loop current fluctuations and quantum critical transport. Netherlands. https://doi.org/10.21468/SciPostPhys.14.5.113
Shi, Zhengyan Darius, Else, Dominic V., Goldman, Hart, and Senthil, Todadri. Mon . "Loop current fluctuations and quantum critical transport". Netherlands. https://doi.org/10.21468/SciPostPhys.14.5.113.
@article{osti_1973725,
title = {Loop current fluctuations and quantum critical transport},
author = {Shi, Zhengyan Darius and Else, Dominic V. and Goldman, Hart and Senthil, Todadri},
abstractNote = {We study electrical transport at quantum critical points (QCPs) associated with loop current ordering in a metal, focusing specifically on models of the “Hertz-Millis” type. At the infrared (IR) fixed point and in the absence of disorder, the simplest such models have infinite DC conductivity and zero incoherent conductivity at nonzero frequencies. However, we find that a particular deformation, involving N N species of bosons and fermions with random couplings in flavor space, admits a finite incoherent, frequency-dependent conductivity at the IR fixed point, \sigma(\omega>0)\sim\omega^{-2/z} σ ( ω > 0 ) ∼ ω − 2 / z , where z z is the boson dynamical exponent. Leveraging the non-perturbative structure of quantum anomalies, we develop a powerful calculational method for transport. The resulting "anomaly-assisted large N N expansion" allows us to extract the conductivity systematically. Although our results imply that such random-flavor models are problematic as a description of the physical N = 1 N = 1 system, they serve to illustrate some general conditions for quantum critical transport as well as the anomaly-assisted calculational methods. In addition, we revisit an old result that irrelevant operators generate a frequency-dependent conductivity, \sigma(\omega>0) \sim \omega^{-2(z-2)/z} σ ( ω > 0 ) ∼ ω − 2 ( z − 2 ) / z , in problems of this kind. We show explicitly, within the scope of the original calculation, that this result does not hold for any order parameter.},
doi = {10.21468/SciPostPhys.14.5.113},
journal = {SciPost Physics},
number = 5,
volume = 14,
place = {Netherlands},
year = {Mon May 15 00:00:00 EDT 2023},
month = {Mon May 15 00:00:00 EDT 2023}
}

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