Magnetic catalysis effect in (2+1)-dimensional Gross--Neveu model with Zeeman interaction

Abstract

Magnetic catalysis of the chiral symmetry breaking and other magnetic properties of the (2+1)-dimensional Gross--Neveu model are studied taking into account the Zeeman interaction of spin-1/2 quasi-particles (electrons) with tilted (with respect to a system plane) external magnetic field $\vec{B}={\vec{B}}_{\perp }+{\vec{B}}_{\parallel }$. The Zeeman interaction is proportional to magnetic moment ${\mu }_B$ of electrons. For simplicity, temperature and chemical potential are equal to zero throughout the paper. We compare in the framework of the model the above mentioned phenomena both at ${\mu }_B=0$ and ${\mu }_B\ne 0$. It is shown that at ${\mu }_B\ne 0$ the magnetic catalysis effect is drastically changed in comparison with the ${\mu }_B=0$ case. Namely, at ${\mu }_B\ne 0$ the chiral symmetry, being spontaneously broken by $\vec{B}$ at subcritical coupling constants, is always restored at $|\vec{B}|\to \infty$ (even at ${\vec{B}}_{\parallel }=0$). Moreover, it is proved in this case that chiral symmetry can be restored simply by tilting $\vec{B}$ to a system plane, and in the region $B_{\perp }\to 0$ the de Haas -- van Alphen oscillations of the magnetization are observed. At supercritical values of coupling constant we have found two chirally non-invariant phases which respond differently on the action of $\vec{B}$. The first (at rather small values of $|\vec{B}|$) is a diamagnetic phase, in which there is an enhancement of chiral condensate, whereas the second is a paramagnetic chirally broken phase. Numerical estimates show that phase transitions described in the paper can be achieved at low enough laboratory magnetic fields.

Comments: v3;14 pages; 8 figures;minor changes of the text;published version