Neel-dimer transition in an antiferromagnetic Heisenberg model and deconfinement of spinons at the critical point
- Department of Applied Physics, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, 466-8555 (Japan)
Quantum phase transition from the Neel to the dimer states in an antiferromagnetic (AF) Heisenberg model on square lattice is studied. We introduce a control parameter {alpha} for the exchange coupling that connects the Neel ({alpha}=0) and the dimer ({alpha}=1) states. We employ the CP{sup 1} representation of the s=(1/2) spin operator and integrate out the half of the CP{sup 1} variables at odd sites to obtain a CP{sup 1} nonlinear {sigma} model. The effective coupling constant is a function of {alpha}, and at {alpha}=0, the CP{sup 1} model is in the ordered phase that corresponds to the Neel state of the AF Heisenberg model. A phase transition to the dimer state occurs at a certain critical value of {alpha}{sub C} as {alpha} increases. In the Neel state, the dynamical composite U(1) gauge field in the CP{sup 1} model is in a Higgs phase, and low-energy excitations are gapless spin waves. In the dimer phase, a confinement phase of the gauge theory with s=1 excitations is realized. For the critical point, we argue that a deconfinement phase, which is similar to the Coulomb phase in three spatial dimensions, is realized and s=(1/2) spinons appear as low-energy excitations.
- OSTI ID:
- 20664945
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 70, Issue 17; Other Information: DOI: 10.1103/PhysRevB.70.174407; (c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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