Ground state phase diagram of the asymmetric spin tube up to 6 legs

6-legまでの非対称スピンチューブの基底状態の相図

五十嵐 亮; 奥村 雅彦   ; 山田 進  ; 町田 昌彦  

Igarashi, Ryo; Okumura, Masahiko; Yamada, Susumu; Machida, Masahiko

We obtain the detailed ground state phase diagram of the asymmetric spin tube up to 6 legs using the two-dimensional density-matrix renormalization-group method. Spin gap is observed for the symmetric tube regardless of the leg size, but 3- and 5-leg system becomes gapless when one of the asymmetric interchain (rung) interaction is turned off. We determine the phase boundary between the spin gap phase and the gapless phase and discuss the leg-size dependence of the full gap region.