Aug 16, 1999
RVB States and Spin Liquids in 2D
Claire L'Huillier, (Univ P & M Curie)
We display some characteristics of two distinct 2-dimensionnal "Quantum
Disordered phases" recently studied in Paris VI and Hannover. The results have
been obtained from a detailed analysis of finite size spectra ( exact
diagonalisations with sample sizes up to 36). In these two models the spin 1/2
interact through SU(2) invariant hamiltonians and the lattices are
"frustrating " (triangular based lattices). The Multi-Spin -Exchange
hamiltonian exhibits various phase transitions from ferromagnetism to three
subblattice long range order. For a very large window of coupling parameters it
exhibits a "Spin Liquid Phase" with a large gap and short range correlations.
The ground-state is unique (up to a topological degeneracy) . A singlet
bound state might be present just below the first magnetic excitations.
The second example is much more intriguing: the spin 1/2 Heisenberg hamiltonian
on
the kagome lattice has presumably gapless SINGLET excitations
that cannot be reduced to a "single mode picture". The spin 1/2 excitations of
this model may be deconfined and T-symmetry breaking.
cond-mat/9812329, cond-mat/9802168, cond-mat/9907220
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