Exactly solvable spin ladder model with degenerate ferromagnetic and singlet states

TL;DR

This paper introduces an exactly solvable spin ladder model featuring a degenerate ground state with singlet and ferromagnetic states, revealing complex spin correlations and gapless spectrum with special parameter conditions.

Contribution

It presents a new exactly solvable spin ladder model with a degenerate ground state and analyzes its unique spin correlations and spectral properties.

Findings

Degenerate singlet and ferromagnetic ground states.

Double-spiral spin correlation structure.

Gapless spectrum with asymptotic degeneracy at special parameters.

Abstract

We study the spin ladder model with interactions between spins on neighboring rungs. The model Hamiltonian with the exact singlet ground state degenerated with ferromagnetic state is obtained. The singlet ground state wave function has a special recurrent form and depends on two parameters. Spin correlations in the singlet ground state show double-spiral structure with period of spirals equals to the system size. For special values of parameters they have exponential decay. The spectrum of the model is gapless and there are asymptotically degenerated excited states for special values of parameters in the thermodynamic limit.