Singlet-triplet transition in a single-electron transistor at zero magnetic field

TL;DR

This paper investigates sharp conductance peaks in a single-electron transistor at zero magnetic field, revealing a singlet-triplet transition driven by potential shape changes, with implications for quantum state control.

Contribution

It demonstrates the occurrence of a singlet-triplet transition in a SET at zero magnetic field, a phenomenon previously observed mainly under magnetic fields, highlighting new control mechanisms.

Findings

Observation of Kondo peaks at odd electron numbers.

Detection of Kondo-like excited state features at even electron numbers.

Evidence of a zero-field singlet-triplet transition driven by potential shape changes.

Abstract

We report sharp peaks in the differential conductance of a single-electron transistor (SET) at low temperature, for gate voltages at which charge fluctuations are suppressed. For odd numbers of electrons we observe the expected Kondo peak at zero bias. For even numbers of electrons we generally observe Kondo-like features corresponding to excited states. For the latter, the excitation energy often decreases with gate voltage until a new zero-bias Kondo peak results. We ascribe this behavior to a singlet-triplet transition in zero magnetic field driven by the change of shape of the potential that confines the electrons in the SET.