Spin gap in the weakly interacting quantum spin chain antiferromagnet KCuPOHO

Fujihara, Masayoshi ; Hagihara, Masato   ; Morita, Katsuhiro*; Murai, Naoki  ; Koda, Akihiro*; Okabe, Hirotaka*; Mitsuda, Setsuo*

The = 1/2 Heisenberg linear chain antiferromagnet is the simplest spin model; nevertheless it serves as a platform for various quantum many-body phenomena. Here, we report the magnetic behavior of a quasi-one-dimensional antiferromagnet KCuPOHO. A long-range commensurate antiferromagnetic order with ordered moment 0.31(1) per spin occurs at = 11.7(1) K. Above , the inelastic neutron excitation is characterized by a two spinon continuum. The intrachain interaction and interchain interaction are estimated to be 172 K and 4.25(4) K, respectively; thus the ratio of the / = 0.0247(3). At lower energies, below , a spin gap is observed in the dispersive excitations. These results are consistent with characteristics observed in weakly interacting = 1/2 Heisenberg chain system.