The influence of device geometry on many-body effects in quantum point contacts: Signatures of the 0.7 anomaly, exchange and Kondo

Abstract

The conductance of a quantum point contact (QPC) shows several features that result from many-body electron interactions. The spin degeneracy in zero magnetic field appears to be spontaneously lifted due to the so-called 0.7 anomaly. Further, the g-factor for electrons in the QPC is enhanced, and a zero-bias peak in the conductance points to similarities with transport through a Kondo impurity. We report here how these many-body effects depend on QPC geometry. We find a clear relation between the enhanced g-factor and the subband spacing in our QPCs, and can relate this to the device geometry with electrostatic modeling of the QPC potential. We also measured the zero-field energy splitting related to the 0.7 anomaly, and studied how it evolves into a splitting that is the sum of the Zeeman effect and a field-independent exchange contribution when applying a magnetic field. While this exchange contribution shows sample-to-sample fluctuations and no clear dependence on QPC geometry, it is for all QPCs correlated with the zero-field splitting of the 0.7 anomaly. This provides evidence that the splitting of the 0.7 anomaly is dominated by this field-independent exchange splitting. Signatures of the Kondo effect also show no regular dependence on QPC geometry, but are possibly correlated with splitting of the 0.7 anomaly.

arXiv commentSpinTech IV contribution; new version contains additional wafer info and minor modifications to content

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Cited by in corpus (14)

• What lurks below the last plateau: Experimental studies of the 0.7 x 2e^2/h conductance anomaly in one-dimensional systems
• Odd and even Kondo effects from emergent localisation in quantum point contacts
• Spin Accumulation and Spin Relaxation in a Large Open Quantum Dot
• On the relation between the 0.7-anomaly and the Kondo effect: Geometric Crossover between a Quantum Point Contact and a Kondo Quantum Dot
• Spin fluctuations in the 0.7-anomaly in quantum point contacts
• Extreme sensitivity of the spin-splitting and 0.7 anomaly to confining potential in one-dimensional nanoelectronic devices
• Dependence of the 0.7 anomaly on the curvature of the potential barrier in quantum wires
• Spin-dependent tunneling into an empty lateral quantum dot
• 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
• Split-gate quantum point contacts with tunable channel length
• Electrostatic potential shape of gate defined quantum point contacts
• Quantised conductance of one-dimensional strongly-correlated electrons in an oxide heterostructure
• Enhancement mechanism of the electron g-factor in quantum point contacts
• Magnetic Splitting of the Zero Bias Peak in a Quantum Point Contact with a Variable Aspect Ratio