Emerging many-body effects in semiconductor artificial graphene with low disorder

Lingjie Du,Vittorio Pellegrini,Loren N Pfeiffer,Geoff C Gardner,Shalom J Wind,Diego Scarabelli,Sheng Wang,Ken W West,Saeed Fallahi,Aron Pinczuk,Michael J Manfra

doi:10.1038/s41467-018-05775-4

Lingjie Du, Vittorio Pellegrini + Show 9 more

Open Access

https://doi.org/10.1038/s41467-018-05775-4

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Abstract

The interplay between electron–electron interactions and the honeycomb topology is expected to produce exotic quantum phenomena and find applications in advanced devices. Semiconductor-based artificial graphene (AG) is an ideal system for these studies that combines high-mobility electron gases with AG topology. However, to date, low-disorder conditions that reveal the interplay of electron–electron interaction with AG symmetry have not been achieved. Here, we report the creation of low-disorder AG that preserves the near-perfection of the pristine electron layer by fabricating small period triangular antidot lattices on high-quality quantum wells. Resonant inelastic light scattering spectra show collective spin-exciton modes at the M-point's nearly flatband saddle-point singularity in the density of states. The observed Coulomb exchange interaction energies are comparable to the gap of Dirac bands at the M-point, demonstrating interplay between quasiparticle interactions and the AG potential. The saddle-point exciton energies are in the terahertz range, making low-disorder AG suitable for contemporary optoelectronic applications.

Highlights

The interplay between electron–electron interactions and the honeycomb topology is expected to produce exotic quantum phenomena and find applications in advanced devices
Dispersing Dirac bands have been reported in several artificial graphene (AG) systems, including molecular assemblies on copper[11], fermionic atoms trapped in optical lattices[12], photonic systems[13], and nanopatterned GaAs quantum wells (QWs)[14]
The capability of observing collective saddle-point spin excitons and the emergence of relatively large Coulomb interactions in the lowdisorder AG lattices demonstrate access to a regime in AG that is dominated by electron–electron interaction effects, allowing the exploration of intriguing many-body effects that are inaccessible in graphene

Summary

Introduction

The interplay between electron–electron interactions and the honeycomb topology is expected to produce exotic quantum phenomena and find applications in advanced devices. We fabricate small period triangular antidot lattices that significantly suppress the impact of processing disorder on electrons, and preserve the high-quality of states in as-grown QWs. The achievement enables observations of collective saddle-point spin excitons that are subject to exchange Coulomb interactions. The capability of observing collective saddle-point spin excitons and the emergence of relatively large Coulomb interactions in the lowdisorder AG lattices demonstrate access to a regime in AG that is dominated by electron–electron interaction effects, allowing the exploration of intriguing many-body effects that are inaccessible in graphene. Combining Coulomb interactions in a clean electron environment with a meV-energy gap at the M-point provides opportunities for experimental studies of many-body effects in honeycomb lattices such as chiral superconductivity[2]

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