Quantum criticality in a Kondo quantum dot coupled to helical edge states of interacting 2D topological insulators

Chung-Hou Chung, Salman Silotri

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3 Scopus citations

Abstract

We investigate theoretically the quantum phase transition (QPT) between the one-channelKondo (1CK) and two-channelKondo (2CK) fixed points in a quantum dot coupled to helical edge states of interacting 2Dtopological insulators (2DTI)with Luttinger parameter 0 < K < 1.Themodelwas studied by Lawet al (2010 Phys.Rev.B81 041305(R)), andwasmapped onto an anisotropic two-channelKondomodel via bosonization. For K < 1, the strong coupling 2CKfixed pointwas argued to be stable for infinitesimally weak tunnelings between the dot and the 2DTI based on a simple scaling dimensional analysis (Lawet al 2010 Phys.Rev.B81 041305(R).We re-examine thismodel beyond the bare scaling dimension analysis via a one-loop renormalization group (RG) approach combined with bosonization and re-fermionization techniques nearweak-coupling and strong-coupling (2CK) fixed points. We find for a fixed value of K < 1 that the 2CKfixed point can be unstable towards the 1CKfixed point and the systemis expected to undergo a quantum phase transition between 1CKand 2CKfixed pointswith changingKondo couplings. OurRGapproach is controlled near K=1. Ingeneral, thisQPTcanalsooccurupon tuning theLuttinger parameterKto a critical value Kc smaller than unity (0 < Kc < 1) for fixed Konodo couplings. The QPT in ourmodel comes as a result of the combined Kondo and the helical Luttinger physics in 2DTI, and it serves as the first example of the 1CK-2CKQPT that is accessible by the controlled RG approach. We extract quantum critical and crossover behaviors fromvarious thermodynamical quantities near the transition. Our results are robust against particle-hole asymmetry for 1/2 < K < 1.

Original languageEnglish
Article number013005
JournalNew Journal of Physics
Volume17
DOIs
StatePublished - 9 Jan 2015

Keywords

  • Kondo effect
  • quantum criticality
  • quantum dot
  • topological insulators

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