U(1) symmetry breaking and violated axial symmetry in TlCuCl3 and other insulating spin systems
Abstract
We describe the Bose-Einstein condensate of magnetic bosonic quasiparticles in insulating spin systems using a phenomenological standard functional method for T=0 . We show that results that are already known from advanced computational techniques immediately follow. The inclusion of a perturbative anisotropy term that violates the axial symmetry allows us to remarkably well explain a number of experimental features of the dimerized spin-1/2 system TlCuCl3 . Based on an energetic argument we predict a general intrinsic instability of an axially symmetric magnetic condensate toward a violation of this symmetry, which leads to the spontaneous formation of an anisotropy gap in the energy spectrum above the critical field. We, therefore, expect that a true Goldstone mode in insulating spin systems, i.e., a strictly linear energy-dispersion relation down to arbitrarily small excitations energies, cannot be observed in any real material.
- Publication:
-
Physical Review B
- Pub Date:
- January 2009
- DOI:
- 10.1103/PhysRevB.79.014438
- arXiv:
- arXiv:0812.0535
- Bibcode:
- 2009PhRvB..79a4438D
- Keywords:
-
- 64.70.Tg;
- 75.10.Hk;
- 75.30.Gw;
- 75.45.+j;
- Quantum phase transitions;
- Classical spin models;
- Magnetic anisotropy;
- Macroscopic quantum phenomena in magnetic systems;
- Condensed Matter - Strongly Correlated Electrons
- E-Print:
- 6 pages, 3 figures