Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2000-06-14
Phys. Rev. B 63, 165110 (2001)
Physics
Condensed Matter
Strongly Correlated Electrons
12 pages, Part on (spinon) pair-hopping amplitude extended in Appendix A; To appear in PRB
Scientific paper
10.1103/PhysRevB.63.165110
We study two (very) weakly-coupled Hubbard chains in the half-filled case, and especially the situation where the intrachain Mott scale $m$ is much larger than the bare single-electron interchain hopping $t_{\perp}$. First, we find that the divergence of the intrachain Umklapp channel at the Mott transition results in the complete vanishing of the single-electron interchain hopping: This is significant of a strong confinement of coherence along the chains. Excitations are usual charge fermionic solitons and spinon pairs of the Heisenberg chain. Then, we show rigorously how the tunneling of spinon-pairs produces a magnetic interchain exchange $J_{\perp}={t_{\perp}}^2/m>0$. The result is an insulating state with spin-gapped excitations as in the delocalized limit (i.e. for rather large interchain hoppings), where the two-leg ladder is in the well-known D-Mott phase. Unlike for Bechgaard salts, the confinement/deconfinement transition at absolute zero is here a simple crossover: no metallic phase is found in undoped two-leg ladders. This statement might be generalized for N-leg ladders with N=3,4... (but not too large).
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