Dark High Density Dipolar Liquid of Excitons

Area of Science:

• Condensed matter physics
• Quantum many-body systems
• Atomic physics

Background:

• Investigating phase transitions and particle correlations in two-dimensional (2D) interacting dipolar systems is a significant challenge in many-body physics.
• Understanding the collective behavior of particles with internal degrees of freedom, like spin, is key to exploring novel quantum states.

Purpose of the Study:

• To investigate the possible phases and nanoscale particle correlations in 2D interacting dipolar systems.
• To observe the spontaneous condensation of trapped 2D dipolar excitons with internal spin degrees of freedom.
• To characterize the nature of the condensed states and the underlying interactions.

Main Methods:

• Experimental observation of trapped 2D dipolar excitons with internal spin degrees of freedom.
• Analysis of phase transitions induced by varying excitation powers.
• Temperature-dependent measurements to identify critical temperatures (Tc).

Main Results:

• Observation of spontaneous condensation from an interacting gas into a high-density, closely packed liquid state of dark dipoles below Tc ≈ 4.8 K.
• Identification of a further phase transition into a bright, highly repulsive plasma at higher excitation powers.
• Evidence for attractive interactions contributing to the dark liquid state formation, beyond purely repulsive dipole-dipole forces.

Conclusions:

• A novel 2D atomic-like interacting dipolar liquid state has been realized.
• The coupling of light to internal spin degrees of freedom is crucial for the formation and nature of the condensed dark ground state.
• Quantum mechanical fluctuations are expected to play a significant role in this strongly correlated, long-lived dark liquid.