Non-equilibrium transport reveals energy level degeneracy

TL;DR

This paper introduces a novel non-equilibrium transport method to determine energy level degeneracies in quantum dots, providing a simpler alternative to existing techniques and revealing detailed degeneracy structures in graphene and GaAs systems.

Contribution

The paper presents a new, general approach to measure energy level degeneracies in quantum dots using non-equilibrium transport, avoiding complex calibration or real-time detection.

Findings

Resolved shell structure in bilayer graphene quantum dots.

Observed degeneracy doubling in double quantum dots.

Achieved detailed degeneracy measurements previously inaccessible.

Abstract

We demonstrate a method to determine energy level degeneracies using non-equilibrium electronic transport through voltage-biased quantum dots. We establish the general validity of this approach using single and double quantum dots in bilayer graphene and GaAs. Unlike established methods based on entropy measurements or time-resolved tunneling statistics, our approach achieves comparable precision without requiring calibrated electron heating or real-time charge detection. We resolve the predicted symmetric shell structure in bilayer graphene quantum dots, including a singlet ground state at half filling and the ground state degeneracies of the first 13 carriers. Extending the method to double quantum dots, we observe degeneracy doubling associated with bonding and antibonding orbitals for a single carrier and a fourfold degeneracy for two carriers, previously inaccessible with existing techniques. These results establish a conceptually general and experimentally straightforward approach for probing energy level degeneracies in complex quantum systems.