Wigner and Kondo physics in quantum point contacts revealed by scanning gate microscopy

TL;DR

This study uses scanning gate microscopy to explore the microscopic origins of conductance anomalies in quantum point contacts, revealing alternating Kondo effects and evidence of Wigner crystallization.

Contribution

It demonstrates how in situ electrostatic tuning uncovers the interplay of Wigner crystal formation and Kondo physics in quantum point contacts.

Findings

Repetitive splittings of zero-bias anomaly correlated with 0.7 anomaly.

Observation of alternating equilibrium and non-equilibrium Kondo effects.

Simulation evidence of one-dimensional Wigner crystallization.

Abstract

Quantum point contacts exhibit mysterious conductance anomalies in addition to well known conductance plateaus at multiples of 2e^2/h. These 0.7 and zero-bias anomalies have been intensively studied, but their microscopic origin in terms of many-body effects is still highly debated. Here we use the charged tip of a scanning gate microscope to tune in situ the electrostatic potential of the point contact. While sweeping the tip distance, we observe repetitive splittings of the zero-bias anomaly, correlated with simultaneous appearances of the 0.7 anomaly. We interpret this behaviour in terms of alternating equilibrium and non-equilibrium Kondo screenings of different spin states localized in the channel. These alternating Kondo effects point towards the presence of a Wigner crystal containing several charges with different parities. Indeed, simulations show that the electron density in the channel is low enough to reach one-dimensional Wigner crystallization over a size controlled by the tip position.