arXiv subjects

Hsiu-Hau Lin

Publications and source records attributed to Hsiu-Hau Lin.

57 records · Page 4Linked to original sources

arXiv1998

The N-chain Hubbard Model in Weak Coupling

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 $Δ$ at the discretized Fermi surface, and describe how this function is calculated. The dimensional crossovers as $N \to \infty$ and as many such ladders are weakly coupled together are also discussed.

cond-mat.str-el↗

arXiv1998

Correlation Effects of Single-Wall Carbon Nanotubes in Weak Coupling

Single-wall carbon nanotubes with on-site interaction $U \ll t$ are studied by a controlled renormalization group method. When formulated as a system of $N_{f}$ flavors of interacting Dirac fermions, the effective model at generic filling resembles a set of quasi-1D Hubbard chains. For the undoped $(N_{y}, N_{y})$-armchair and the $(N_{x}, -N_{x})$-zigzag with $N_x=3n$, specific mappings to the 2-chain Hubbard model at half filling with effective interaction $u_{eff}=U/N_{y}$ and $2U/N_{x}$ are found from this more general equivalence. The phase diagrams of the (3, 3)-armchair and the (6, -6)-zigzag at generic fillings are studied and compared as an example.

cond-mat.str-el↗

arXiv1998

Exact SO(8) Symmetry in the Weakly-Interacting Two-Leg Ladder

A perturbative renormalization group analysis of interacting electrons on a two-leg ladder reveals that at half-filling any weakly repulsive system scales onto an exactly soluble Gross-Neveu model with a hidden SO(8) symmetry. The half-filled ground state is a Mott insulator with short-range d-wave pair correlations. We extract the exact energies, degeneracies, and quantum numbers of *all* the low energy excited multiplets. One energy (mass) m octets contains Cooper pair, magnon, and density-wave excitations, two more octets contain single-particle excitations, and a mass \sqrt{3}m antisymmetric tensor contains 28 "bound states". Exact single-particle and spin gaps are found for the lightly-doped (d-wave paired one-dimension Bose fluid) system. We also determine the four other robust phases occuring at half-filling for partially attractive interactions. All 5 phases have distinct SO(8) symmetries, but share S.C. Zhang's SO(5) as a common subgroup.

cond-mat.str-el↗