Thielemann, B.; Rüegg, Ch.; Kiefer, K; Rønnow, H.M.; Normand, B.; Bouillot, P.; Kollath, C.; Orignac, E.; Citro, R.; Giamarchi, T.; Läuchli, A.M.; Biner, D.; Krämer, K.; Wolff-Fabris, F.; Zapf, V.; Jaime, M.; Stahn, J,; Christensen, N.B.; Grenier, B.; McMorrow, D.F.; Mesot, J.: Field-controlled magnetic order in the quantum spin-ladder system (Hpip)2CuBr4. Physical Review B 79 (2009), p. 020408(R)/1-4
10.1103/PhysRevB.79.020408
Abstract:
Neutron diffraction is used to investigate the field-induced antiferromagnetically ordered state in the two-leg spin-ladder material Hpip2CuBr4. This “classical” phase, a consequence of weak interladder coupling, is nevertheless highly unconventional: its properties are influenced strongly by the spin Luttinger-liquid state of the ladder subunits. We determine directly the order parameter transverse magnetization, the ordering temperature, the spin structure, and the critical exponents around the transition. We introduce a minimal microscopic model for the interladder coupling and calculate the quantum fluctuation corrections to the mean-field interaction.