Quantum phase transition between one-channel and two-channel Kondo states in a quantum dot coupled to helical edge states of interacting 2D topological insulators
Chung-Hou Chung1*, Salman Silotri1
1Department of Electrophysics, National Chiao-Tung University, HsinChu, Taiwan
* presenting author:Chung-Hou Chung, email:chung@mail.nctu.edu.tw
For two decades, the exotic quantum phase transition (QPT) between the one-channel Kondo (1CK) and two-channel Kondo (2CK) ground states has been predicted in a Kondo impurity coupled to electron-electron interacting 1D Luttinger liquid lead via varying the electron interactions in the lead, defined by the Luttinger parameter K with a value between 0 and 1. However, no rigorous theoretical approaches are available so far to access this new quantum critical point. We successfully address this long-standing issue of 1CK-2CK QPT in a modern context: in a Kondo quantum dot coupled to helical edge states of interacting 2D topological insulators, known as the helical Luttinger liquids. We examine the Kondo model of our setup via a controlled 1-loop perturbative renormalization group (RG) approach combined with bosonization and re-fermionization techniques. In the limit of strong electron interactions (K much smaller than 1), we find the 2CK phase is favored. However, for sufficiently weak interactions (K close 1), the 2CK state is unstable towards the 1CK fixed point again and the system undergoes a quantum phase transition between 1CK and 2CK quantum ground states. The quantum critical and crossover behaviors for various thermodynamic quantities near the transition are obtained. Our study serves as the first example of the 1CK-2CK QPT that is accessible by a controlled theoretical approach. Reference: Chung-Hou Chung* and Salman Silotri (to appear in New Journal of Physics, 2014).

Keywords: quantum phase transitions, Kondo effect in quantum dots, Luttinger liquid, topological insulators, helical edge states