1990/08/01 by Uwe Grimm · 1 citation
Mathematics · Physics and Astronomy · #Algebraic structures and combinatorial models #Physics of Superconductivity and Magnetism #Quantum many-body systems #hep-th
paper · pdf · doi:10.1016/0550-3213(90)90462-m
published as Nucl.Phys. B340 (1990) 633-658 · 20 pages, old preprint from the pre-arXiv (but not pre-LaTeX) era, made available electronically because it may still be of interest
openalex publication_date 1990/08/01 · arxiv created 2003/10/09 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The finite-size scaling properties of the quantum Ising chain with different types of generalized defects are studied. These not only mean an alteration of the coupling constant as previously examined, but an additional arbitrary transformation in the algebra of observables at one site of the chain. One can distinguish between two classes of generalized defects: those which do not affect the finite-size integrability of the Ising chain, and on the other hand those that destroy this property. In this context, finite-size integrability is always understood as a synonym for the possibility to write the Hamiltonian of the finite chain as a bilinear expression in fermionic operators by means of a Jordan-Wigner transformation. Concerning the first type of defect, an exact solution for the scaling spectrum is obtained for the most universal defect that preserves the global Z2 symmetry of the chain. It is shown that in the continuum limit this yields the same result as for one properly chosen `ordinary' defect, that is changing the coupling constant only, and thus the finite-size scaling spectra can be described by irreps of a shifted u(1) Kac-Moody algebra. The other type of defect is examined by means of numerical finite-size calculations. In contrast to the first case, these suggest a non-continuous dependence of the scaling dimensions on the defect parameters. A conjecture for the operator content involving only one primary field of a Virasoro algebra with central charge c=1/2 is given.