Physical nature of dimensional crossovers in weakly coupled Hubbard chains and ladders has been discussed within the framework of the perturbative renormalization-group approach. The difference between these two cases originates from different universality classes which the corresponding isolated systems belong to.
Effects of the interladder one-particle hopping, t⊥, on the low-energy asymptotics of a weakly coupled Hubbard ladder system have been studied, based on the perturbative renormalization-group approach. We found that for finite intraladder Hubbard repulsion, U, there exists a crossover value of the interladder one-particle hopping, t⊥c. For $0
Based on the perturbative renormalization group (PRG) approach, we have studied dimensional crossovers in Hubbard ladders coupled via weak interladder one-particle hopping, t⊥. We found that the one-particle crossover is strongly suppressed through growth of the intraladder scattering processes which lead the isolated Hubbard ladder system toward the spin gap metal (SGM) phase. Consequently when t⊥ sets in, there exists, for any finite intraladder Hubbard repulsion, U>0, the region where the two-particle crossover dominates the one-particle crossover and consequently the d-wave superconducting transition, which is regarded as a bipolaron condensation, occurs. By solving the scaling equations for the interladder one-particle and two-particle hopping amplitudes, we give phase diagrams of the system with respect to U, t⊥0 (initial value of t⊥) and the temperature, T. We compared the above dimensional crossovers with those in a weakly coupled chain system, clarifying the difference between them.
We present a systematic weak-coupling renormalization group (RG) technique for studying a collection of N coupled one-dimensional interacting electron systems, focusing on the example of N-leg Hubbard ladders. For N=2,3, we recover previous results, and find that also more generally broad regions of the phase space of these models are unstable to pairing, usually with approximate d-wave symmetry. We show how these instabilities can be understood in terms of a fairly conventional ``gap'' function \ensuremath{\Delta} at the discretized Fermi surface, and describe how this function is calculated. The dimensional crossovers as $N\ensuremath{\rightarrow}\ensuremath{\infty}$ and as many such ladders are weakly coupled together are also discussed.