Boundary resonances in S=1/2 antiferromagnetic chains under a staggered field.
We develop a boundary field theory approach to electron spin resonance in open S=1/2 Heisenberg antiferromagnetic chains with an effective staggered field. In terms of the sine Gordon effective field theory with boundaries, we point out the existence of boundary bound states of elementary excitations, and modification of the selection rules at the boundary. We argue that several "unknown modes" found in electron spin resonance experiments on KCuGaF(6) [I. Umegaki, H. Tanaka, T. Ono, H. Uekusa, and H. Nojiri, Phys. Rev. B 79, 184401 (2009)] and Cu-PM [S. A. Zvyagin, A. K. Kolezhuk, J. Krzystek, and R. Feyerherm, Phys. Rev. Lett. 93, 027201 (2004)] can be understood as boundary resonances introduced by these effects.
Department of Physics, University of Tokyo, Hongo, Tokyo 113-0033, Japan.
Shunsuke C
SC
Furuya
Masaki
M
Oshikawa