Evidence from Quantum Monte Carlo Simulations of Large-Gap Superfluidity and BCS-BEC Crossover in Double Electron-Hole Layers

We report quantum Monte Carlo evidence of the existence of large gap superfluidity in electron-hole double layers over wide density ranges. The superfluid parameters evolve from normal state to BEC with decreasing density, with the BCS state restricted to a tiny range of densities due to the strong screening of Coulomb interactions, which causes the gap to rapidly become large near the onset of superfluidity. The superfluid properties exhibit similarities to ultracold fermions and iron-based superconductors, suggesting an underlying universal behavior of BCS-BEC crossovers in pairing systems.

Figure 1

DMC estimates of $ϵ(k)$ as a function of the magnitude $k$ of the wave vector of the additional electron, at $r_s/a_0^{*}=2$, 5, and 10. The solid lines are fits of the DMC data to Eq. (1).

Figure 2

Superfluid gap $\mathrm{\Delta }$, obtained by fitting the VMC and DMC data to Eq. (1), as a function of $r_s$, (a) in excitonic Hartree units, and (b) relative to $E_F$. The dotted lines interpolating the DMC results are intended as a guide to the eye.

Figure 3

(a) $\mu$, (b) $k_{\min }$, and (c) $m^{*}$, obtained by fitting the VMC and DMC data to Eq. (1), as functions of $r_s$. The dotted lines interpolating the DMC results are intended as a guide to the eye.

Figure 4

VMC and DMC values of (a) $c$ and (b) $r_{\text{ex}}$ as functions of $r_s$. The inset in the bottom panel shows $r_{\text{ex}}$ in excitonic Hartree units. The dotted lines interpolating the DMC results are intended as a guide to the eye.