Observation of Dirac bands in artificial graphene in small-period nanopatterned GaAs quantum wells

• Published in: Nature nanotechnology Vol. 13; no. 1; pp. 29 - 33
• Main Authors: Wang, Sheng, Scarabelli, Diego, Du, Lingjie, Kuznetsova, Yuliya Y., Pfeiffer, Loren N., West, Ken W., Gardner, Geoff C., Manfra, Michael J., Pellegrini, Vittorio, Wind, Shalom J., Pinczuk, Aron
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2018; Nature Publishing Group
• Subjects: 639/301/119/1000/1018; 639/925/927/1007; Band structure; Band structure of solids; Chemistry and Materials Science; Condensed matter physics; Current carriers; Density of states; Dispersion; Electron gas; Emergence; Energy; Fermions; Gallium arsenide; Graphene; Honeycomb construction; Inelastic scattering; Lattice parameters; Letter; Materials Science; Nanotechnology; Nanotechnology and Microengineering; Photonics; Quantum wells; Science & Technology - Other Topics; Topology
• ISSN: 1748-3387; 1748-3395
• DOI: 10.1038/s41565-017-0006-x

Charge carriers in graphene behave like massless Dirac fermions (MDFs) with linear energy-momentum dispersion 1 , 2 , providing a condensed-matter platform for studying quasiparticles with relativistic-like features. Artificial graphene (AG)—a structure with an artificial honeycomb lattice—exhibits novel phenomena due to the tunable interplay between topology and quasiparticle interactions 3 – 6 . So far, the emergence of a Dirac band structure supporting MDFs has been observed in AG using molecular 5 , atomic 6 , 7 and photonic systems 8 – 10 , including those with semiconductor microcavities 11 . Here, we report the realization of an AG that has a band structure with vanishing density of states consistent with the presence of MDFs. This observation is enabled by a very small lattice constant ( a  = 50 nm) of the nanofabricated AG patterns superimposed on a two-dimensional electron gas hosted by a high-quality GaAs quantum well. Resonant inelastic light-scattering spectra reveal low-lying transitions that are not present in the unpatterned GaAs quantum well. These excitations reveal the energy dependence of the joint density of states for AG band transitions. Fermi level tuning through the Dirac point results in a collapse of the density of states at low transition energy, suggesting the emergence of the MDF linear dispersion in the AG. Advanced nanoengineering of small-period AG lattices enables the observation of a vanishing density of states that suggests the presence of massless Dirac fermions.