Thielemann, BeniRüegg, christianKiefer, KlausRønnow, Henrik M.Normand, BruceBouillot, PKollath, C.Orignac, E.Citro, R.Giamarchi, TLäuchli, A. M.Biner, D.Krämer, K. W.Wolff-Fabris, FZapf, V. S.Jaime, M.Stahn, J.Christensen, N. B.Grenier, B.McMorrow, D. F.Mesot, J.2009-03-122009-03-122009-03-12200910.1103/PhysRevB.79.020408https://infoscience.epfl.ch/handle/20.500.14299/35934WOS:000262978100013Neutron diffraction is used to investigate the field-induced, antiferromagnetically ordered state in the two-leg spin-ladder material (Hpip)(2)CuBr4. 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.antiferromagnetic materialscopper compoundscritical exponentsfluctuationsLuttinger liquidmagnetic momentsmagnetic structuremagnetisationmagnetocaloric effectsMonte Carlo methodsNeel temperatureneutron diffractionorganic compoundsX-Y modelCriticalityDynamicsChainstext::journal::journal article::research article