On the relation between the 0.7-anomaly and the Kondo effect: Geometric Crossover between a Quantum Point Contact and a Kondo Quantum Dot

Abstract

Quantum point contacts (QPCs) and quantum dots (QDs), two elementary building blocks of semiconducting nanodevices, both exhibit famously anomalous conductance features: the 0.7-anomaly in the former case, the Kondo effect in the latter. For both the 0.7-anomaly and the Kondo effect, the conductance shows a remarkably similar low-energy dependence on temperature $T$, source-drain voltage $V_{\mathrm{sd}}$ and magnetic field $B$. In a recent publication [F. Bauer et al., Nature, 501, 73 (2013)], we argued that the reason for these similarities is that both a QPC and a KQD feature spin fluctuations that are induced by the sample geometry, confined in a small spatial regime, and enhanced by interactions. Here we further explore this notion experimentally and theoretically by studying the geometric crossover between a QD and a QPC, focussing on the $B$-field dependence of the conductance. We introduce a one-dimensional model that reproduces the essential features of the experiments, including a smooth transition between a Kondo QD and a QPC with 0.7-anomaly. We find that in both cases the anomalously strong negative magnetoconductance goes hand in hand with strongly enhanced local spin fluctuations. Our experimental observations include, in addition to the Kondo effect in a QD and the 0.7-anomaly in a QPC, Fano interference effects in a regime of coexistence between QD and QPC physics, and Fabry-Perot-type resonances on the conductance plateaus of a clean QPC. We argue that Fabry-Perot-type resonances occur generically if the electrostatic potential of the QPC generates a flatter-than-parabolic barrier top.

References in corpus (15)

• Spin-charge separation and localization in one-dimension
• Orbital Kondo effect in carbon nanotubes
• Magnetic impurity formation in quantum point contacts
• A novel approach to transport through correlated quantum dots
• Fermi-liquid theory for the single-impurity Anderson model
• Singlet-triplet transition in a lateral quantum dot
• Renormalization-group analysis of the one-dimensional extended Hubbard model with a single impurity
• Conductance of a quantum point contact based on spin-density-functional theory
• The influence of device geometry on many-body effects in quantum point contacts: Signatures of the 0.7 anomaly, exchange and Kondo
• Electronic magnetization of a quantum point contact measured by nuclear magnetic resonance
• Statistical study of conductance properties in one-dimensional quantum wires focussing on the 0.7 anomaly
• Conductance Anomaly and Fano Factor Reduction in Quantum Point Contacts
• Kondo effect in a one-electron double quantum dot: Oscillations of the Kondo current in a weak magnetic field
• Suppression of Shot Noise in Quantum Point Contacts in the "0.7" Regime
• Tunable 0.7 conductance plateau in quantum dots

Cited by in corpus (13)

• Conductance through a helical state in an InSb nanowire
• Two-color Fermi liquid theory for transport through a multilevel Kondo impurity
• Spin fluctuations in the 0.7-anomaly in quantum point contacts
• Electron phase shift at the zero-bias anomaly of quantum point contacts
• Functional Renormalization Group Approach for Inhomogeneous One-Dimensional Fermi Systems with Finite-Ranged Interactions
• The effect of split gate size on the electrostatic potential and 0.7 anomaly within one-dimensional quantum wires on a modulation doped GaAs/AlGaAs heterostructure
• Electrostatic potential shape of gate defined quantum point contacts
• Fabry-Pérot interference in a triple-gated quantum point contact
• Influence of assisted hopping interaction on the linear conductance of quantum dot
• Dynamic nuclear polarization at high Landau levels in a quantum point contact
• Incipient singlet-triplet states in a hybrid mesoscopic system
• Coherent Electron Optics with Ballistically Coupled Quantum Point Contacts
• Helical and topological phase detection based on nonlocal conductance measurements in a three terminal junction