Tuesday, October 2, 2012

Breakdown of the Luttinger liquid paradigm

At the Journal Club for Condensed Matter Patrick Lee has a helpful commentary on a recent preprint

Non-Fermi liquid d-wave metal phase of strongly interacting electrons
Hong-Chen Jiang, Matthew S. Block, Ryan V. Mishmash, James R. Garrison, D. N. Sheng, Olexei I. Motrunich, Matthew P. A. Fisher

The preprint presents numerical evidence that a t-J model on a ladder with a particular kind of ring exchange has an exotic ground state.

This state is particularly interesting for two reasons.

First, it falls outside the Luttinger liquid paradigm which is the one-dimensional version of Landau's Fermi liquid theory.

Second, this exotic state is well described by a variational wave function based on the  "parton" construction [a generalisation of slave bosons] where electron operators are replaced by a product of three fermion operators.
The million dollar question remains: is any of this relevant to two dimensions?

The authors state, "estimating the strength of K [ring exchange] .... in real materials such as La2-xSrxCuO4 is an interesting question."

This is particularly important because they require K larger than the hopping t to get the non-Fermi liquid phase.

I thought the ring exchange was the four spin ring exchange occurs in solid 3He and in a weak Mott insulator. However, it is different. As the figure above shows this "ring exchange" involves spatially rotating spin singlets. I thank Matthew Fisher for clarifying my confusion on this point.

For the parent Mott insulator La2CuO4 the magnitude of the 4-spin ring exchange was determined by inelastic neutron scattering a decade ago by Radu Coldea and collaborators. It is smaller than t.

Previously, I posted about nice related work by some of the same authors, on a Heisenberg model with 4 spin-ring exchange on a multi-leg ladder. This model is directly relevant to the possible spin liquid state in organic charge transfer salts.

No comments:

Post a Comment

Science job openings in sunny Brisbane, Australia

Bribie Island, just north of Brisbane. The University of Queensland has just advertised several jobs that may be of interest to readers of t...