Exact Ground States with Deconfined Gapless Excitations for the ThreeLeg Spin1/2 Tube
Abstract
We consider a spin1/2 tube (a threeleg ladder with periodic boundary conditions) with a Hamiltonian given by two projection operators—one on the triangles and the other on the square plaquettes on the side of the tube—that can be written in terms of Heisenberg and fourspin ring exchange interactions. We identify 3 phases: (i) for strongly antiferromagnetic exchange on the triangles, an exact ground state with a gapped spectrum can be given as an alternation of spin and chirality singlet bonds between nearest triangles; (ii) for ferromagnetic exchange on the triangles, we recover the phase of the spin3/2 Heisenberg chain; (iii) between these two phases, a gapless incommensurate phase exists. We construct an exact ground state with two deconfined domain walls and a gapless excitation spectrum at the quantum phase transition point between the incommensurate and dimerized phases.
 Publication:

Physical Review Letters
 Pub Date:
 January 2012
 DOI:
 10.1103/PhysRevLett.108.017205
 arXiv:
 arXiv:1107.5501
 Bibcode:
 2012PhRvL.108a7205L
 Keywords:

 75.10.Jm;
 05.30.Rt;
 75.10.Kt;
 75.30.Kz;
 Quantized spin models;
 Magnetic phase boundaries;
 Condensed Matter  Strongly Correlated Electrons
 EPrint:
 5 pages, 5 figures, paper revised, references added