title: Zeeman levels with exotic field dependence in the high field phase of an S=1 Heisenberg antiferromagnetic chain.
abstract: We have performed electron spin resonance measurements over a wide frequency and magnetic field range on a single crystal of the S=1 quasi-one-dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(PF6). We observed gapped excitation branches above the critical field H(c) where the Haldane gap closes. These branches are analyzed by a phenomenological field theory using the complex-field phi(4) model. A satisfactory agreement between experiment and theory is obtained.
authors: RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan.
authors: M
authors: M
authors: Hagiwara
authors: Z
authors: Z
authors: Honda
authors: K
authors: K
authors: Katsumata
authors: A K
authors: AK
authors: Kolezhuk
authors: H-J
authors: HJ
authors: Mikeska