Ground-State of Spin-1/2 Alternating Heisenberg-XY Ferromagnet in One Dimension

清美 岡本, Kiyomi Okamoto

Donald D. Betts, J. Oitmaa

Chunhuan Xiang, Su Yao, Honglei Wang

Kiyomi Okamoto, Tadao Sugiyama

The ground state properties of the one-dimensional spin-1/2 alternating Heisenberg- XY ferromagnet are analytically investigated by the use of the phase Hamiltonian representation. To treat the non-harmonic terms in the phase Hamiltonian, both the self-consistent harmonic approximation (SCHA) and the renormalization group method are applied. The ground state is either the effective singlet (ES) state or the so-called spin-fluid state. The phase diagram is depicted on the Δ -δ plane, where Δ and δ are the anisotropy and alternation parameters, respectively. The longitudinal and transverse spin correlation functions (< S i z S j z > and < S i + S j - >) in the ES state are also discussed in the framework of the SCHA.

Kazuo Hida

The location of the XY phase in the ground-state phase diagram of the spin-1/2 anisotropic ferromagnetic-antiferromagnetic alternating Heisenberg chain is determined. This model reduces to the spin-1 XXZ chain if the ferromagnetic bond is infinitely strong. The phase boundary between the XY phase and the Haldane phase is determined from the analysis of the numerically obtained energy spectrum of finite-sized systems with the open boundary condition. Our results are consistent with the series-expansion results by Yamanaka et al . within their error bars. The boundary between the ferromagnetic phase and the XY phase is also determined by comparing the energy eigenvalues of these two phases.

清美 岡本, Kiyomi Okamoto

, Correlation Function <Siz Sjz> in Spin--1/2 Alternating Heisenberg-XY Antiferromagnets in One-Dimension in Spin-1/2 Alternating Heisenberg-XY Antiferromagnets in One-Dimension