Exciton-polariton condensates near the Dirac point in a triangular lattice

TL;DR

This paper demonstrates the direct mapping of Dirac-like linear dispersions in exciton-polariton condensates within a triangular lattice, revealing relativistic properties and quantum phenomena such as superfluidity and quantum Hall effects in a solid-state platform.

Contribution

It provides the first direct observation of Dirac dispersions in exciton-polariton condensates in a triangular lattice, linking condensed matter physics with relativistic quantum phenomena.

Findings

Linear dispersions near Dirac points with velocities ~10^8 cm/s

Observation of superfluidity in exciton-polariton condensates

Features analogous to quantum Hall effect in the system

Abstract

Dirac particles, massless relativistic entities, obey linear energy dispersions and hold important implication in particle physics. Recent discovery of Dirac fermions in condensed matter systems including graphene and topological insulators raises great interests to explore relativistic properties associated with Dirac physics in solid-state materials. In addition, there are stimulating research activities to engineer Dirac paricles to eludicte their physical properties in a controllable setting. One of the successful platforms is the ultracold atom-optical lattice system, whose dynamics can be manipulated in a clean environment. A microcavity exciton-polariton-lattice system provides an alternative route with an advantage of forming high-orbital condensation in non-equilibrium conditions, which enables to explore novel quantum orbital order in two dimensions. Here we directly map the liner dispersions near the Dirac points, the vertices of the first hexagonal Brillouin zone from exciton-polariton condensates trapped in a triangular lattice. The associated velocity values are ~ 0.9 - 2*10^8 cm/s, which are consistent with the theoretical estimate 1*10^8 cm/s with a 2 \mu m-lattice constant. We envision that the exciton-polariton condensates in lattices would be a promising solid-state platform, where the system order parameter can be accesses in both real and momentum spaces. We furthermore explore unique phenomena revealing quantum bose nature such as superfluidity and distinct features analogous to quantum Hall effect pertinent to time-reversal symmetry.