Crossover between two different Kondo couplings in side-coupled double quantum dots

Abstract

We study the Kondo effect in side-coupled double quantum dots with particular focus on the crossover between two distinct singlet ground states, using the numerical renormalization group. The crossover occurs as the quantized energy level of the embedded dot, which is connected directly to the leads, is varied. In the parameter region where the embedded dot becomes almost empty or doubly occupied, the local moment emerging in the other dot at the side of the path for the current is screened via a superexchange process by the conduction electrons tunneling through the embedded dot. In contrast, in the other region where the embedded dot is occupied by a single electron, the local moment emerges also in the embedded dot, and forms a singlet bond with the moment in the side dot. Furthermore, we derive two different Kondo Hamiltonians for these limits carrying out the Schrieffer-Wolff transformation, and show that they describe the essential feature of the screening for each case.

Spin-polarized conductance in double quantum dots: Interplay of Kondo, Zeeman, and interference effects

“…3 and 4 by considering the limit where both dots are noninteracting. Equations (19) and (27) hold equally well for interacting and noninteracting problems. How-ever, the case U 1 = U 2 = 0 offers the advantage that A 1 (0, 0) can also be calculated directly from the imaginary part of…”

“…A telling example is the interplay of Kondo physics and quantum interference in "side-coupled" or "hanging-dot" configurations, [11][12][13][14][15][16][17][18][19] leading to a variety of interesting "Fano-Kondo" effects. 20 A rather unexpected situation arises when a small, strongly interacting "dot 1" is connected to external leads via a large "dot 2" that is tuned to have a single-particle level in resonance with the common Fermi energy of the leads.…”

Kondo effect in a quantum dot side-coupled to a topological superconductor

“…Consequently, the linear conductance G is reduced to a quantized value of 3e 2 /2h, which unambiguously proves the existence of the MFS. This fractionally quantized conductance is quite distinguished from the similar setup using the side coupling to fermionic excitations [35][36][37][38] in which a perfect antiresonance (G = 0) or imperfect screening (0 < G < 1) are expected. In addition, the quantized value is robust against small perturbations of parameters in contrast to the noninteracting counterpart 31 since the Kondo resonance level always aligns with the MFS at the Fermi level.…”

Real two-stage Kondo effect in parallel double quantum dot

“…Contrast to this result, in a Kondo box consisting of a large carbon nanotube [16], the second-stage Kondo temperature decreases with increasing the dot-lead coupling. Theoretical works were concentrated on side-coupled double quantum dot systems [18][19][20][21][22][23][24][25], in which only one of the dots (QD1) is coupled to the electrodes and the other dot (QD2) is side-coupled to the QD1. In the case where each of the dots is singly occupied, for small interdot hopping t, the local spin on the QD1 is screened first by the electrons of the leads at a higher temperature, and then the spin on the QD2 is screened at a lower temperature.…”