Quantum chaos in quantum dots: the case of the transmission phase in quantum transport

Rodolfo A. Jalabert

IPCMS-DMONS

In a quantum coherent conductor, like a quantum dot, the transmission phase is a key transport property. Unlike the conductance, the transmission phase is not directly measurable. Nevertheless, phase-sensitive experiments have been performed by embedding a quantum dot, operating in the Coulomb blockade regime, in one of the arms of an Aharonov-Bohm interferometer. These experiments yielded a puzzling in-phase locking between consecutive Coulomb-blockade resonance peaks, stimulating a considerable theoretical activity. We show that the spatial wave-function correlations existing in a chaotic ballistic quantum dot provide a tendency for the emergence of large universal sequences of in-phase resonances in the short wavelength limit. We study the approach towards the universal behavior and relate it with the statistical distribution of the wave-function values in billiards exhibiting classically chaotic dynamics. We discuss the validation of our theoretical approach by a second-generation experiment unambiguously accessing the transmission phase, and we link our experimentally motivated investigation with the general question of the statistical properties of wave-function distributions.

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Stéphane Parola

Laboratoire de Chimie UMR 5182 CNRS-ENS-UCBL

École Normale Supérieure de Lyon

Abstract S-Parola_17janv2020

Filtering the photoluminescence spectra of atomically thin semiconductors with graphene

Stéphane Berciaud

IPCMS-DMONS

Atomically thin semiconductors made from transition metal dichalcogenides (TMDs) are model systems for investigations of strong light-matter interactions and applications in nanophotonics, opto-electronics and valley-tronics. However, the typical photoluminescence spectra of TMD monolayers display a large number of intrinsic and extrinsic features that are particularly challenging to decipher. On a practical level, monochromatic TMD-based emitters would be beneficial for low-dimensional devices but no solution has yet been found to meet this challenge. Here, using a counter-intuitive strategy that consists in interfacing TMD monolayers with graphene, a system known as an efficient luminescence quencher [1], we demonstrate bright, single and narrow-line photoluminescence arising solely from TMD neutral excitons. This observation stems from two effects: (i) complete neutralization of the TMD by the adjacent graphene leading to the absence of optical features from charged excitons (ii) selective non-radiative transfer of TMD excitons to graphene, that is sufficiently rapid to quench radiative recombination of long-lived excitonic species without significantly affecting bright excitons, which display much shorter, picosecond radiative lifetimes at low temperatures [2]. Our approach is systematically applied to four tungsten and molybdenum-based TMDs and establishes TMD/graphene heterostructures as a unique set of opto-electronic building blocks. As an outlook, the implications of our results for opto-valleytronics and chiral optics [3] will be discussed in light of our recent demonstration of large valley polarization and coherence in TMD-graphene heterostructures [4].

This work was done with E. Lorchat, L. E. Parra-Lopez and G. Froehlicher, S. Azzini, T. Chervy, T.W. Ebbesen and C. Genet at U. Strasbourg; C. Robert, D. Lagarde, and X. Marie at INSA Toulouse.

References:

[1] G. Froehlicher, E. Lorchat, S. Berciaud, Phys. Rev. X 8, 011007 (2018)

[2] E. Lorchat, L. E. Parra López et al., arXiv :1908.10690

[3] T. Chervy, S. Azzini, et al., ACS Photonics 5, 1281 (2018)

[4] E. Lorchat, S. Azzini, T. Chervy et al., ACS Photonics 5, 5047 (2018)