Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 30: Correlated Electrons: Spin Systems and Itinerant Magnets 2
TT 30.4: Vortrag
Donnerstag, 28. Februar 2008, 11:15–11:30, EB 202
Quantum fluctuations in high field magnetisation of 2D squarelattice J1-J2 antiferromagnets (exchanged with TT 8.8) — Peter Thalmeier1, Michael Zhitomirsky2, •Burkhard Schmidt1, and Nic Shannon3 — 1Max-Planck-Institut für Chemische Physik fester Stoffe, Dresden, Germany — 2Commisariat à l’Energie Atomique, DSM/DRFCM/SPSMS, Grenoble, France — 3H H Wills Physics Laboratory, Bristol, United Kingdom
The square lattice J1–J2 Heisenberg model with spin S=1/2 has three magnetic and two nonmagnetic phases. It describes a number of recently found layered vanadium oxide perovskites. We discuss the magnetisation curve and high-field susceptibility using spin-wave theory and exact diagonalisation in the whole J1–J2 plane. We compare both results and find good overall agreement in the sectors of the phase diagram with magnetic order. Close to the nonmagnetic regions the magnetisation curve shows strong deviations from the classical linear behaviour caused by large quantum fluctuations and spin-wave approximation breaks down. On the FM side (J1<0) where one approaches the quantum gapless spin nematic ground state this region is surprisingly large. We find that inclusion of second order spin-wave corrections does not lead to fundamental improvement. Quantum corrections to the tilting angle of the ordered moments are also calculated. They may have both signs, contrary to the always negative first order quantum corrections to the magnetisation. Finally we investigate the effect of the interlayer coupling and find that the quasi-2D picture remains valid up to |J⊥/J1|∼ 0.3.