A two-leg ladder with n -component fermionic fields in the chains has been considered using an analytic renormalization group method. The fixed points and possible phases have been determined for generic filling as well as for a half-filled system and for the case when one of the subbands is half filled. A weak-coupling Luttinger-liquid phase and several strong-coupling gapped phases have been found. In the Luttinger liquid phase, for the most general spin dependence of the couplings, all 2n modes have different velocities if the interband scattering processes are scaled out, while n doubly degenerate modes appear if the interband scattering processes remain finite. The role of backward scattering, charge transfer, and umklapp processes has been analyzed using their bosonic form and the possible phases are characterized by the number of gapless modes. As a special case the SU(n) symmetric Hubbard ladder has been investigated numerically. It was found that this model does not scale to the Luttinger liquid fixed point. Even for generic filling gaps open up in the spectrum of the spin or charge modes, and the system is always insulator in the presence of umklapp processes.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Oct 19 2006|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics