Half-levitons -- zero-energy excitations of a driven Fermi sea

TL;DR

This paper introduces half-levitons, zero-energy excitations in a driven Fermi sea created by Lorentzian voltage pulses, revealing fractional charge and unique energy distribution features.

Contribution

It demonstrates the existence of zero-energy, fractional charge excitations called half-levitons generated by specific voltage pulses in a Fermi sea, with analysis of their properties and experimental detection.

Findings

Half-levitons carry an effective fractional charge of e/2.

Energy distribution function has a peak at the Fermi energy with symmetric tails.

Zero-energy excitations coexist with electron-hole pairs due to the pulse.

Abstract

A voltage pulse of a Lorentzian shape carrying a half of the flux quantum excites out of a zero-temperature Fermi sea an electron in a mixed state, which looks like a quasi-particle with an effectively fractional charge $e/2$. A prominent feature of such an excitation is a narrow peak in the energy distribution function laying exactly at the Fermi energy $ \mu$. Another spectacular feature is that the distribution function has symmetric tails as above as below $ \mu$, which results in a zero energy of an excitation. This sounds improbable since at zero temperature all available states below $ \mu$ are fully occupied. The resolution is lying in the fact that such a voltage pulse excites also electron-hole pairs which free some space below $ \mu$ and thus allow a zero-energy quasi-particle to exist. I discuss also how to address separately electron-hole pairs and a fractionally charged zero-energy excitation in experiment.