抄録
The ground state of the four-chain Heisenberg ladder model is numerically investigated. Hidden-order correlations suitable for the system are introduced and calculated with an emphasis on the spatially isotropic point, where a corresponding material exists.The existence of a long-range hidden-order correlation indicates formation of a short-range RVB state in the case of the antiferromagneticinter-chain coupling.A transition between the phase of the ferromagnetic inter-chain couplingand that of the antiferromagnetic one is discussed.