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

Abstract

Charge carriers in graphene behave like massless Dirac fermions (MDFs) with linear energy-momentum dispersion , 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 . So far, the emergence of a Dirac band structure supporting MDFs has been observed in AG using molecular , atomic and photonic systems , including those with semiconductor microcavities . 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.

Symmetry breaking in molecular artificial graphene

“…The unique physics of Dirac quasiparticles can be mimicked in artificial graphene (AG) systems [1]. These AG systems include cold atom lattices [2][3][4][5][6], phononic crystals [7][8][9][10], photonic crystals [11][12][13][14][15][16], semiconductor nanopatterns [17][18][19][20][21][22] and molecular lattices assembled on metal surfaces, termed as molecular designers [23][24][25][26][27][28][29][30][31][32][33][34]. The tunability of the artificial systems makes them ideal playgrounds to exploit phenomena that are extremely challenging to access in real materials.…”

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

“…Artificial graphene (AG) 9 – 14 is a controllable platform for simulation of quantum behavior in the physics of 2D crystals 15 – 19 . Linearly dispersing Dirac bands have been reported in several 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 . AG systems with tunable honeycomb lattices should be suitable for explorations of quantum regimes of many-body effects in graphene-like band structures.…”

Majorana zero modes from topological kink states in the two-dimensional electron gas

“…Topological kink states and MZMs in 2DEG We start to construct an artificial graphene model [29,30] in 2DEG with periodic triangular antidot lattice, as displayed in Fig.1(b). The Hamiltonian reads:…”

“…For the purpose of comparison to experiments, lattice constant a = 5nm is used thus the typical size of a single antidot is about 30nm [29,30]. We set the width/length of the superconductor area (see Fig.1 (a)) as 0.85µm/4µm which includes 20/40 antidot supercells in the transverse/longitudinal direction.…”