Fig. 1: Hole pairing in mixD ladders.
From: Magnetically mediated hole pairing in fermionic ladders of ultracold atoms
a, Binding mechanism in the t−J ladders. Depicted are ladder systems with spin exchange J⊥ ≫ J∥ that form strong singlet bonds along the rungs. When a single hole from (i) moves through the system, as illustrated in (ii), it breaks the spin order by displacing the singlet bonds. (iii) The magnetic energy cost can be avoided if the second hole restores the spin order by moving together with the first hole. b, Pauli blocking of holes. Owing to their fermionic nature, holes repel each other along all directions according to the tunnelling amplitudes t⊥ and t∥. Close-distance hole pairs are thus energetically unfavourable. In mixD systems, a potential offset Δ between the two legs suppresses tunnelling t⊥ and Pauli repulsion only occurs along the legs. Holes on the same rung can thus benefit from the binding mechanism, forming tightly bound pairs with a large binding energy. c, Average density of the mixD L = 7 ladder system with Δ ≈ U/2. d, Single experimental shot with two holes on the same rung, exemplifying the bunching of holes in the mixD system. a.u., arbitrary units.
