Kondo effect and bistability in a double quantum dot

Abstract

We study theoretically the out-of-equilibrium transport properties of a double quantum dot system in the Kondo regime. We model the system by means of a two-impurity Anderson Hamiltonian. The transport properties are characterized by Kondo effect properties, however, superimposed them, the system possesses novel non-linear bistability behavior.Recently experiments on quantum dots (QDs) at temperatures (T ) below the Kondo temperature (T k ) have shown that new physics emerges when their transport properties are studied. 1,2,? These experiments confirm that many of the phenomena that characterize strongly correlated metals and insulators, as it is the case of the Kondo effect, are present in QDs. The advantage of studying the quantum-coherent many-body Kondo state in QDs, in comparison with natural compounds, consists in the possibility of continuous tuning the relevant parameters governing the properties of this state, in an equilibrium and out-of-equilibrium situation. In particular, the problem of electrons tunnelling through doublequantum-dots (DQDs) in the Kondo regime has received much attention in recent years. [4][5][6][7][8][9] The DQD is the simplest system where it is possible to study the competition between the inter-dot antiferromagnetic spin-spin correlation and the dot-conduction spin-spin correlation present in its ground state. The type of coupling between the QDs determines the character of the electronic states and the transport properties of the artificial molecule. In the tunnelling regime, the electronics states are extended across the entire system and form a coherent state based on the bonding or anti-bonding levels of the QDs. In this context, recently Aguado and Langreth 4 studied the out-of-equilibrium transport properties of a DQD in the Kondo regime. They found that for inter-dot-coupling greater than the level broadening, there is a critical voltage above which the coherent configuration is unstable. This instability is reflected as a drastic drop of the current leading to a singular region of negative differential conductance. This behavior resembles the I-V characteristic of a double barrier structure in the accumulation of charge regime. 10 This system, due to non-linearities introduced by the Coulomb interactions, has a bistable behavior, characterized by two solutions for the current. In this work we report the existence of a similar bistable behavior in an out-of-equilibrium double quantum-dot in the Kondo regime.

Two-level quantum dot susceptibility and polarization in the presence of Coulomb correlations

“…7 Double QDs systems behavior is recently under careful investigation because of the variable inter-dot tunneling coupling, 8 which is the physical reason for non-linearity formation and consequently for existence of such phenomena as bifurcations, 910 and bi-stability, 11 . 12 Electron transport in QDs is strongly governed by Coulomb interaction between localized electrons, the ratios between tunneling transfer amplitudes, QDs coupling and of course by the initial conditions, 10 .…”

Transport electron through a quantum wire by side-attached asymmetric quantum-dot rings

“…Parameter of p indicates the distance between two-rings. The system assumed in equilibrium, is modeled by using a non interacting Anderson tunneling Hamiltonian [5][6] which can be written as: In this section, simulated results including the electronic conductance through quantum wire with side-coupled asymmetric QD-rings as a scatter system are presented and discussed. Figure2 shows, the dimensionless conductance (g = G/(2e2/h) = T) is plotted versus Fermi energy in units of μ ( ε / μ).…”

Quantum-wire conductance manipulating by asymmetric quantum dot-molecules

“…This is because coupling to the continuum states shows an even-odd parity effect in the conductance when the Fermi energy is localized at the center of the energy band [3][4][5][6][7][8][9]. The systems such as uniform QD array [10], nano-wires [11] and nano-ring [12] which are side-coupled to a QW act as a scatter system for electron transmission through the QW and have a major effect on electronic conductance of nano-device. For a uniform QD-chains array with M sites, it was shown that the transmission characteristic has M anti-resonances and M-1 resonance, M mini-gaps and M-1 allowed mini-bands arise [10].…”