Ian Affleck

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We study the critical two-dimensional Ising model with a defect line (altered bond strength along a line) in the continuum limit. By folding the system at the defect line, the problem is mapped to a special case of the critical Ashkin-Teller model, the continuum limit of which is the Z 2 orbifold of the free boson, with a boundary. Possible boundary states(More)
Boundary critical phenomena are studied in the 3-State Potts model in 2 dimensions using conformal field theory, duality and renormalization group methods. A presumably complete set of boundary conditions is obtained using both fusion and orbifold methods. Besides the previously known free, fixed and mixed boundary conditions a new one is obtained. This(More)
This article reviews the quantum entanglement in Valence-Bond-Solid (VBS) states defined on a lattice or a graph. The subject is presented in a self-contained and pedagogical way. The VBS state was first introduced in the celebrated paperbreviation AKLT is widely used). It became essential in condensed matter physics and quantum information(More)
The boundary conformal field theory approach to quantum impurity problems is used to study the Fermi edge singularity, occuring in the X-ray ad-sorption probablility. The deep-hole creation operator, in the effective low-energy theory, changes the boundary condition on the conduction electrons. By a conformal mapping, the dimension of such an operator is(More)
Using the density matrix renormalization group and a bosonization approach, we study a spin-1/2 antiferromagnetic Heisenberg chain with near-neighbor coupling J 1 and frustrating second-neighbor coupling J 2 , particularly in the limit J 2 >> J 1. This system exhibits both dimerization and incommensurate spiral spin correlations. We argue that this system(More)
A systematic field-theory approach to Electron Spin Resonance (ESR) in the S = 1/2 quantum antiferromagnetic chain at low temperature T (compared to the exchange coupling J) is developed. In particular, effects of a transverse staggered field h and an exchange anisotropy (including a dipolar interaction) δ on the ESR lineshape are discussed. In the lowest(More)
A scaling form for the local susceptibility, derived from renormalization group arguments, is proposed. The scale over which the uniform part of this scaling form varies can be viewed as a definition of the Kondo " screening cloud " ∼ ξ K. The proposed scaling form interpolates between Ruderman-Kittel-Kasuya-Yosida (RKKY) results in the high temperature(More)