Suppression of Kondo screening by the Dicke effect in multiple quantum dots

Abstract

The interplay between the coupling of an interacting quantum dot to a conduction band and its connection to localized levels has been studied in a triple quantum dot arrangement. The electronic Dicke effect, resulting from quasi-resonant states of two side-coupled non-interacting quantum dots, is found to produce important effects on the Kondo resonance of the interacting dot. We study in detail the Kondo regime of the system by applying a numerical renormalization group analysis to a finite-U multi-impurity Anderson Hamiltonian model. We find an extreme narrowing of the Kondo resonance, as the single-particle levels of the side dots are tuned towards the Fermi level and "squeeze" the Kondo resonance, accompanied by a strong drop in the Kondo temperature, due to the presence of a supertunneling state. Further, we show that the Kondo temperature vanishes in the limit of the Dicke effect of the structure. By analyzing the magnetic moment and entropy of the three-dot cluster versus temperature, we identify a different local singlet that competes with the Kondo state, resulting in the eventual suppression of the Kondo temperature and strongly affecting the spin correlations of the structure. We further show that system asymmetries in couplings, level structure or due to Coulomb interactions, result in interesting changes in the spectral function near the Fermi level. These strongly affect the Kondo temperature and the linear conductance of the system.

Understanding resonant tunnel transport in non-identical and non-aligned clusters as applied to disordered carbon systems

“…Motivated by the previous theoretical models of resonant tunnelling in impurity clusters 17,19,20 as well as some of the experimental observations of tunnel current in various nanostructures, 13,15,21 this work finds some unusual features of tunnel transport in a multi-cluster system mixed with disorder. It is clear (from Sec.…”

“…A similar feature was suggested for two impurity dots having a very small asymmetry in positions. 17,20 The corresponding conductance spectra showed either one or two minima at different energy positions depending on the configurations [ Fig. 1(b)].…”

“…Since it is difficult to make either a perfect horizontal or a vertical configuration most of the cases, a triangular distribution of impurities can be expected. 20 In our previous report, we found that for a triangular structure formed by three QDs of similar size and inter-cluster distance, negative differential resistance (NDR) was very difficult to observe. 23 Here, we show that the NDR signature of current steps and NDR can be produced by using unequal distances between the QDs of different sizes and artificially controlling the coupling between the dots, which can explain the switching behavior in carbon structures observed experimentally.…”

“…13 Resonant tunnel features for aligned and random distribution of impurity centres have been theoretically calculated over several decades 14,15 as a single channel 16,17 to multi-channel effect. [18][19][20] Earlier, the quantum conductance features for two-impurity centres were described as a combination of two states; one a long lifetime (narrow peak) and the other of a short lifetime (broad peak), 17,18 which has been extended in various fields of application, recently in spintronics and high frequency devices 21 and to understand the electronic properties of graphene QDs. 22 This energy difference between two unequal clusters can be manipulated by a third cluster, which was studied extensively for three dots of finite and equal size in a symmetric configuration and also by breaking the symmetry of the configurations, 23 however further study is needed to improve understanding of quantum transport.…”

Kondo effect and continuous quantum phase transitions in double quantum dots with on-site and interdot repulsion and magnetic field

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In parallel double quantum dot (DQD) systems with strong on-site Coulomb repulsion, the ground state is a local spin triplet due to the effective interdot ferromagnetic Ruderman-Kittel-KasuyaYosida (RKKY) interaction mediated by the conduction electrons of the leads. 12 At low temperature the local spin is underscreened by the conduction electrons, and the Kondo resonance in the conductance is observed.…”