An Exactly Solvable Spin-1 Model under External Magnetic Field

R. Shankar

Cesur Ekiz

A two-fold Cayley tree with fully q-coordinated sites is constructed and the spin-1 Blume–Capel model in the presence of an external magnetic field is solved exactly. The relevant properties such as magnetization m and square magnetic moment q are investigated as functions of temperature and external magnetic field both for ferromagnetic and antiferromagnetic couplings. In the study, we propose a possible mechanism of the plateau based on the exchange couplings.

Andrei A. Zvyagin, Gleb A. Skorobagatko

We propose an exactly solvable quantum spin model, in which the alternation of the exchange interactions between neighboring spins is accompanied by the multiple spin exchange. The model permits us to obtain exactly thermodynamic characteristics of the considered quantum spin chain. In the ground state, depending on the strength of the three-spin coupling, the model manifests either the spin-gapped behavior of low-lying excitations at low magnetic fields, or the ferrimagnetic ordering with the spontaneous magnetization and with gapless low-lying excitations. The system undergoes second order or first order quantum phase transitions, governed by an external magnetic field and the multiple spin exchange coupling strength. Our exactly solvable quantum spin model demonstrates that multispin interactions in a dimerized quantum spin chain can produce a spontaneous magnetization. On the other hand, for quantum spin chains with a spontaneous magnetization, caused by multispin couplings, the alternation of nearest neighbor exchange interactions can be the reason for destroying of that magnetization and the onset of a spin gap for low-lying excitations.

Man Mohan

T. Morita, Tomoya Horiguchi

Krzysztof Byczuk

The spin-charge-separated Luttinger liquid in arbitrary spatial dimensions and in the applied external magnetic field is investigated within an exactly solvable model of correlated fermions. Exact eigenstates, eigenvalues, and correlation functions of this system are determined and its single-pseudoparticle properties are discussed. It is shown that strongly correlated fermions of spin one-half and charge one, which are described by the present model, can be mapped onto a system of noninteracting fermionlike pseudoparticles possessing continuous charge and spin. The charge and the spin of these pseudoparticles acquire arbitrary values between 0 and $e$ and 0 and $\ensuremath{\Elzxh}/2$, respectively, when the magnetic field is varied. These pseudoparticles represent quanta of exact elementary excitations in this system.