Influence of quantum fluctuations on zerotemperature phase transitions between collinear a.pdf

Influence of quantum fluctuations on zero-temperature phase transitions between collinear and noncollinear states in frustrated spin systems Sven E. Kr¨uger and Johannes Richter Institut f¨ur Theoretische Physik, Universit¨at Magdeburg, P.O.Box 4120, 39016 Magdeburg, Germany 1 (Dated: February 1, 2008) 0 0 We study a square-lattice spin-half Heisenberg model where frustration is introduced by competing 2 nearest-neighbor bonds of different signs. We discuss the influence of quantum fluctuations on the r nature of the zero-temperature phase transitions from phases with collinear magnetic order at small p A frustration to phases with noncollinear spiral order at large frustration. We use the coupled cluster method (CCM) for high orders of approximation (up to LSUB6) and the exact diagonalization of 7 finite systems (up to 32 sites) to calculate ground-state properties. The role of quantum fluctuations 2 is examined by comparing the ferromagnetic-spiral and the antiferromagnetic-spiral transition within ] the same model. We find clear evidence that quantum fluctuations prefer collinear order and that l e they may favour a first order transition instead of a second order transition in case of no quantum - fluctuations. r t s . t Introduction. While quantum fluctuations do not influ- disorder” phenomenon, see, e.g., Refs. 12,13). More- a m ence the critical properties of phase transitions at T 0 over quantum fluctuatio