Interference and interaction effects in multilevel quantum dots

Motivated by the recent discovery of a canyon of conductance suppression in a two-level equal spin quantum dot system [Phys. Rev. Lett. 104, 186804 (2010)] the transport through this system is studied in detail. At low bias and low temperature a strong current suppression is found around the electron-hole symmetry point independent of the couplings, in agreement with previous results. By means of a Schrieffer-Wolff transformation we are able to give an intuitive explanation to this suppression in the low-energy regime. In the general situation, numerical simulations are carried out using quantum rate equations. The simulations allow for the prediction of how the suppression is affected by the couplings, the charging energy, the position of the energy levels, the applied bias, and the temperature. We find that away from electron-hole symmetry, the parity of the couplings is essential for the current suppression. It is also shown how broadening, interference, and a finite interaction energy cause a shift of the current minimum away from degeneracy. Finally we see how an increased population of the upper level leads to current peaks on each side of the suppression line. At sufficiently high bias we discover a coherence-induced population inversion.

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“…As a result no current can flow through the quantum dot; see also Ref. 42. The effect of the coherence is thus to decrease the current.…”

Section: Current Suppression At Electron-hole Symmetrymentioning

confidence: 99%

Canyon of current suppression in an interacting two-level quantum dot

Karlström¹,

Pedersen²,

Samuelsson³

et al. 2011

Phys. Rev. B

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“…2(e). In that system the effective spin asymmetry (assumed by our model) is realized by the asymmetry in the coupling of two QD levels [19].…”

mentioning

confidence: 99%

Gate-controlled spin splitting in quantum dots with ferromagnetic leads in the Kondo regime

et al. 2005

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The effect of a gate voltage (Vg) on the spin-splitting of an electronic level in a quantum dot (QD) attached to ferromagnetic leads is studied in the Kondo regime using a generalized numerical renormalization group technique. We find that the Vg-dependence of the QD level spin-splitting strongly depends on the shape of the density of states (DOS). For one class of DOS shapes there is nearly no Vg-dependence, for another, Vg can be used to control the magnitude and sign of the spin-splitting, which can be interpreted as a local exchange magnetic field. We find that the spinsplitting acquires a new type of logarithmic divergence. We give an analytical explanation for our numerical results and explain how they arise due to spin-dependent charge fluctuations.PACS numbers: 75.20. Hr, 72.15.Qm, 73.23.Hk The manipulation of magnetization and spin is one of the fundamental processes in magneto-electronics and spintronics, providing the possibility of writing information in a magnetic memory [1], and also because of the possibility of classical or quantum computation using spin. In most situations this is realized by means of an externally applied, nonlocal magnetic field which is usually difficult to insert into an integrated circuit. Recently, it was proposed to control the magnetic properties, such as the Curie temperature of ferromagnetic semiconductors, by means of an electric field: In gated structures [2], due to the modification of carrier-density-mediated magnetic interactions, such properties can be modified by a gate voltage. In this Letter we propose to control the amplitude and sign of the spin-splitting of a quantum dot (QD) induced by the presence of ferromagnetic leads, only by using a gate voltage without further assistance of a magnetic field. To illustrate this effect we investigate the Kondo effect and its spin-splitting as a very sensitive probe of the spin state of the dot and the effective local magnetic field in the QD generated by exchange interaction with the ferromagnetic leads.Recently, the possibility of the Kondo effect in a QD attached to ferromagnetic electrodes was widely discussed [3,4,5,6,7,8,9], and it was shown, that the Kondo resonance is split and suppressed in the presence of ferromagnetic leads [7,8]. It was shown that this splitting can be compensated by an appropriately tuned external magnetic field, and the Kondo effect is thereby restored [7,8]. In all previous studies of QDs attached to ferromagnetic leads [3,4,5,6,7,8,9] an idealized, flat, spinindependent DOS with spin-dependent tunneling amplitudes was considered. However, since the spin-splitting arises from renormalization effects i.e. is a many-body effect, it depends on the full DOS-structure of the involved material, and not only on its value at the Fermi surface. In realistic ferromagnetic systems, the DOS shape is strongly asymmetric due to the Stoner splitting and the different hybridization between the electronic bands [1].In this Letter we demonstrate that the gate voltage dependence of the spin-splitting of ...

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“…For some purposes one may think of the orbital degree of freedom in the spinless double-dot problem as playing a similar role to that of the spin degree of freedom in a conventional single-orbital dot [36][37][38][39]. There is, however, a fundamental difference between the two systems: the coherence between the dots plays a key role in the double dot system, while it is typically zero or vanishes in the steady state of the aforementioned single-dot situations.…”

Section: Introductionmentioning

confidence: 99%

“…Despite its simple structure, the orbitally degenerate spinless Anderson model exhibits a rich variety of complex many-body phenomena including orbital/pseudospin-Kondo physics [36][37][38][39], population inversion [40][41][42][43], negative differential resistance (NDR) [44][45][46][47], Fano-line shapes [18,48], interaction-induced level repulsion [36,44] and resonances [40,[49][50][51].…”

Section: Introductionmentioning

confidence: 99%

Formation of nonequilibrium steady states in interacting double quantum dots: When coherences dominate the charge distribution

Härtle

Millis

2014

Phys. Rev. B

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We theoretically investigate the full time evolution of a nonequilibrium double quantum dot structure from initial conditions corresponding to different product states (no entanglement between dot and lead) to a nonequilibrium steady state. and an interaction-induced renormalization of energy levels. We find that when the system carries a single electron on average the formation of the steady state is strongly influenced by the coherence between the dots. The latter can be sizeable and indeed larger in the presence of a bias voltage than it is in equilibrium. Moreover, the interdot coherence is shown to lead to a pronounced difference in the population of the dots.

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Interference and interaction effects in multilevel quantum dots

Cited by 64 publications

References 23 publications

Canyon of current suppression in an interacting two-level quantum dot

Canyon of current suppression in an interacting two-level quantum dot

Gate-controlled spin splitting in quantum dots with ferromagnetic leads in the Kondo regime

Formation of nonequilibrium steady states in interacting double quantum dots: When coherences dominate the charge distribution

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