Metallic and Insulating Phases of Repulsively Interacting Fermions in a 3D Optical Lattice

Abstract

For strong interactions, we find evidence for an emergent incompressible Mott insulating phase.

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

“…The method of directly measuring the expansion dynamics can be used to detect complex quantum states including Mott-insulating states [10] or to possibly distinguish pseudogap [8] from superfluid states in the attractive Hubbard model. In addition, the effects of various disorder potentials on the two-dimensional dynamics can be studied.…”

“…Experimental sequence We use a balanced spin mixture of the two lowest hyperfine states |F , m F = |9/2, −9/2 and |9/2, −7/2 of fermionic potassium 40 K with N = 2−3 × 10 5 atoms at an initial temperature of T /T F = 0.13 (2). Starting in an harmonic trap, the atoms are loaded into a combination of a blue-detuned three-dimensional optical lattice with lattice constant a lat = λ/2 = 369 nm and a red-detuned dipole trap, using a sequence similar to the one applied in [10]. Once in the lattice, tunneling is strongly reduced by increasing the lattice depth to 20 E r (recoil energy E r = h 2 /(2mλ 2 )) and the interactions can be controlled via a Feshbach resonance without affecting the density distribution (see SI A).…”

“…The experiment starts with the preparation of a bandinsulating state of a balanced spin mixture of fermionic potassium 40 K, as described in previous work [10]: Through evaporative cooling in a red-detuned crossed dipole trap a quantum degenerate mixture of the two lowest hyperfine states of potassium was reached with atom numbers of N = 1−1.5 × 10 5 atoms per spin state at a temperature of T /T F = 0.13 (2), where T F denotes the Fermi temperature in the harmonic trap. The trapping frequencies of the dipole trap were then increased Subsequently, a simple-cubic blue-detuned 3D optical lattice (λ = 738 nm) is ramped up linearly to a depth of 8E r (1E r = h 2 /(2mλ 2 )) in 56 ms while the magnetic field is held at 209.1 G, which corresponds to vanishing interactions (see V H).…”

“…Using both bosonic and fermionic [8][9][10] atoms, it has become possible to simulate models of strongly interacting quantum particles, for which the Hubbard model [11] Initial State Free Expansion in lattice FIG. 1.…”

A cold-atom Fermi–Hubbard antiferromagnet

“…Ultracold fermions in optical lattices offer the potential to answer open questions on the lowtemperature regime of the doped Hubbard model [9][10][11], which is thought to capture essential aspects of the cuprate superconductor phase diagram but is numerically intractable in that parameter regime. Already, Mott-insulating phases and short-range antiferromagnetic correlations have been observed, but temperatures were too high to create an antiferromagnet [12][13][14][15]. A new perspective is afforded by quantum gas microscopy [16][17][18][19][20][21][22][23][24][25][26][27][28], which allows readout of magnetic correlations at the site-resolved level [25][26][27][28].…”