Eur. Phys. J. B (2015) 88: 2
https://doi.org/10.1140/epjb/e2014-50589-x

Regular Article

The spin-1/2 square-lattice J₁-J₂ model: the spin-gap issue

¹ Institut für Theoretische Physik, Universität Magdeburg, 39016 Magdeburg, Germany
² Institut für Apparate- und Umwelttechnik, Universität Magdeburg, 39016 Magdeburg, Germany
³ School of Dentistry, Cardiff University, Cardiff CF14 4XY, UK

^a e-mail: johannes.richter@physik.uni-magdeburg.de

Received: 31 August 2014
Received in final form: 7 October 2014
Published online: 2 January 2015

Abstract

We use the coupled cluster method to high orders of approximation in order to calculate the ground-state energy, the ground-state magnetic order parameter, and the spin gap of the spin-1/2 J₁-J₂ model on the square lattice. We obtain values for the transition points to the magnetically disordered quantum paramagnetic phase of J^c1₂ = 0.454J₁ and J^c2₂ = 0.588J₁. The spin gap is zero in the entire parameter region accessible by our approach, i.e. for J₂ ≤ 0.49J₁ and J₂> 0.58J₁. This finding is in favor of a gapless spin-liquid ground-state in this parameter regime.