Two-dimensional quantum-spin-1/2 XXZ magnet in zero magnetic field: Global thermodynamics from renormalisation group theory

ABSTRACT

Phase diagram, critical properties and thermodynamic functions of the two-dimensional field-free quantum-spin-1/2 XXZ model has been calculated globally using a numerical renormalisation group theory. The nearest-neighbour spin-spin correlations and entanglement properties, as well as internal energy and specific heat are calculated globally at all temperatures for the whole range of exchange interaction anisotropy, from XY limit to Ising limits, for both antiferromagnetic and ferromagnetic cases. We show that there exists long-range (quasi-long-range) order at low-temperatures, and the low-lying excitations are gapped (gapless) in the Ising-like easy-axis (XY-like easy-plane) regime. Besides, we identify quantum phase transitions at zero-temperature.

GRAPHICAL ABSTRACT

KEYWORDS:

• Quantum spin models
• magnetic anisotropy
• order-disorder transformations
• quantum phase transitions
• thermodynamic and entanglement properties
• renormalisation group theory

PACS CLASSIFICATION:

• 05.10.Cc
• 05.30.Rt
• 05.50.+q
• 64.60.ae
• 64.60.Cn
• 64.60.De
• 64.70.Tg
• 75.10.Jm
• 75.10.Kt
• 75.30.Gw
• 75.30.Kz
• 75.40.Cx

Acknowledgments

I would like to thank Dr. A. Nihat Berker of Kadir Has University, for suggesting this problem to me and for valuable discussions; and to Dr. Aykut Erbaş of Bilkent University for careful reading of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Ozan S. Sarıyer http://orcid.org/0000-0001-6064-392X

Additional information

Funding

This work was supported by The Scientific and Technological Research Council of Turkey under 2232 TÜBİTAK Reintegration Grant 115C135.