2008/05/20 by R. F. Bishop, P. H. Y. Li, R. Darradi +2 · 1 citation
Physics and Astronomy · #Advanced Condensed Matter Physics #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.78.054412
published as Phys. Rev. B 78, 054412 (2008) · 28 pages, 5 figures
arxiv created 2008/05/20 · openalex publication_date 2008/08/11 · arxiv updated 2009/12/01 · openalex created_date 2017/03/16 · openalex updated_date 2026/08/01
We study the zero-temperature phase diagram of the two-dimensional quantum J1XXZ--J2XXZ spin-1/2 anisotropic Heisenberg model on the square lattice. In particular, the effects of the anisotropy \ensuremathΔ on the z-aligned N'eel and (collinear) stripe states, as well as on the xy-planar-aligned N'eel and collinear stripe states, are examined. All four of these quasiclassical states are chosen in turn as model states, on top of which we systematically include the quantum correlations using a coupled cluster method analysis carried out to very high orders. We find strong evidence for two quantum triple points (QTPs) at (\ensuremathΔc=\ensuremath-0.10\ifmmode±\else\textpm\fi0.15, J2c/J1=0.505\ifmmode±\else\textpm\fi0.015) and (\ensuremathΔc=2.05\ifmmode±\else\textpm\fi0.15, J2c/J1=0.530\ifmmode±\else\textpm\fi0.015), between which an intermediate magnetically disordered phase emerges to separate the quasiclassical N'eel and stripe collinear phases. Above the upper QTP (\ensuremathΔ\ensuremath\gtrsim2.0) we find a direct first-order phase transition between the N'eel and stripe phases, exactly as for the classical case. The z-aligned and xy-planar-aligned phases meet precisely at \ensuremathΔ=1, also as for the classical case. For all values of the anisotropy parameter between those of the two QTPs there exists a narrow range of values of J2/J1, \ensuremathα^c1(\ensuremathΔ)<J2/J1<\ensuremathα^c2(\ensuremathΔ), centered near the point of maximum classical frustration, J2/J1=(1)/(2), for which the intermediate phase exists. This range is widest precisely at the isotropic point, \ensuremathΔ=1, where \ensuremathα^c1(1)=0.44\ifmmode±\else\textpm\fi0.01 and \ensuremathα^c2(1)=0.59\ifmmode±\else\textpm\fi0.01. The two QTPs are characterized by values \ensuremathΔ=\ensuremathΔc at which \ensuremathα^c1(\ensuremathΔc)=\ensuremathα^c2(\ensuremathΔc).