Conductivity Spectrum of Ultracold Atoms in an Optical Lattice

Area of Science:

• Condensed Matter Physics
• Quantum Simulation
• Ultracold Atoms

Background:

• Understanding charge transport in quantum systems is crucial.
• Neutral fermions in optical lattices offer a controllable platform for studying fundamental physics.
• Previous studies have explored static properties, but dynamic conductivity measurements are less common.

Purpose of the Study:

• To measure the dynamic conductivity of neutral fermions in a cubic optical lattice.
• To investigate the frequency-dependent conductivity across various experimental parameters.
• To relate conductivity measurements to thermodynamic properties and damping mechanisms.

Main Methods:

• Utilized in situ fluorescence microscopy to observe alternating current.
• Applied a single-frequency uniform force via displacement of a harmonic trap.
• Measured real and imaginary conductivity up to frequencies within the lowest band.

Main Results:

• Observed a neutral-particle analog of Ohm's law in the linear response regime.
• Found that conductivity decreases with increasing band-averaged effective mass.
• Identified a T-linear regime for conductivity at high temperatures.
• Demonstrated that current relaxation requires finite lattice depth, enabling damping through collisions.

Conclusions:

• The spectral width of conductivity indicates current dissipation rates.
• Integrated spectral weight relates to thermodynamic properties via a sum rule.
• Lattice depth is essential for breaking Galilean invariance and facilitating current damping in neutral fermion systems.