Ground State of a Two-Dimensional Coupled Electron-Hole Gas in $\mathrm{InAs}/\mathrm{GaSb}$ Narrow Gap Heterostructures

The contributions of wave function hybridization and spontaneous exciton formation to the ground state of closely spaced electron and hole gases in $\mathrm{In}\mathrm{As}/\mathrm{GaSb}$ heterostructures were investigated using cyclotron resonance (CR) spectroscopy. Strongly hybridized samples exhibit two electronlike CR absorptions at all perpendicular magnetic fields. The high frequency mode neither disappears at high temperatures $\left(\sim 100\mathrm{K}\right)$ nor is affected by changes in electron or hole density, but is eliminated by a high parallel magnetic field $\left(\sim 7\mathrm{T}\right)$. These effects can be understood as signatures of electron-hole wave function hybridization, and cannot be explained in terms of an excitonic gas.