Quantum Phases of Excitons and Their Detections in Electron-Hole Semiconductor Bilayer Systems

Abstract

We construct a quantum Ginsburg-Landau theory to study the quantum phases and transitions in electron hole bilayer system. We propose that in the dilute limit as distance is increased, there is a first order transition from the excitonic superfluid (ESF ) to the excitonic supersolid (ESS) driven by the collapsing of a roton minimum, then a 2nd order transition from the ESS to excitonic normal solid. We show the latter transition is in the same universality class of superfluid to Mott transition in a rigid lattice. We then study novel elementary low energy excitations inside the ESS. We find that there are two "supersolidon " longitudinal modes ( one upper branch and one lower branch ) inside the ESS, while the transverse mode in the ESS stays the same as that inside a ENS. We also work out various experimental signatures of these novel elementary excitations by evaluating the Debye-Waller factor, density-density correlation, specific heat and vortex -vertex interactions. For the meta-stable supersolid generated by photon pumping, we show that the angle resolved spectrum is dominated by the macroscopic super-radiance from its superfluid component, even it is just a very small percentage of the the whole system. This fact can be used to detect the metastable ESS state generated by photon pumping by a power spectrum experiment easily and without any ambiguity.I.

Supersolid in thermal phase diagram of symmetric electron-hole semiconductor bilayer

“…1 shows the phase diagram of parallel dipolar coupled quantum wells in the two-band symmetric quasiparticle model as a function of δ s and the temperature. The known Wigner crystal (WC), electron-hole plasma (eh-Plasma), and superfluid exciton condensate (SFEC) phases occupy regions delimited by δ s values in agreement with [7] and [8]. For a bilayer system with interlayer separation d = 1.0 nm, interlayer dielectric background, = 12.91, we find, in Fig.…”

“…Previously, both fixed-node diffusion quantum Monte Carlo [6], and mean-field approaches [7], [8] have been applied to the CQW system. While these approaches point to the existence of the supersolid phase in the CQW system, they are well-known to give poor estimates of thermal properties and phase transitions [9].…”

Quantum magnetism of spinor bosons in optical lattices with synthetic non-Abelian gauge fields

“…In 3d, the roton sphere is a 2d continuous manifold, so its dropping before touching zero signals a first order transition. Similarly, in a 2d electron-hole semi-conductor bilayer (EHBL) system [62] or 2d bilayer quantum Hall (BLQH) systems [63][64][65], the roton circle is a 1d continuous manifold tuned by the distance between the two layers, so its dropping before touching zero also signals a first order transition. In contrast, the C-IC magnons in Fig.2b are located at two isolated points (0, ±k 0 y ), they indeed touch zero at all the transitions shown in Fig.10, so it signals a second order phase transition.…”

Goldstone and Higgs modes of photons inside a cavity

“…The Goldstone modes have been detected in a quantum anti-ferromagnet7, a superfluid891011 and also in cold atom systems121314151617. However, the massive Higgs mode is much more difficult to detect in experiments.…”