Controlling Luttinger liquid physics in weakly coupled spin ladders under magnetic field
Résumé
Luttinger liquid (LL) physics is a remarkable manifestation of strong correlations in one-dimensional (1D) systems. Physical properties of a LL are determined by two Luttinger parameters characterizing the power law decay of most observables. In addition to the difficulty in realising LLs, no precise control over Luttinger parameters is usually possible. Notable exception are gapless phases of 1D antiferromagnets (AFs), such as spin chains and ladders, where the Luttinger parameters can be directly tuned by an external magnetic field. Here we demonstrate that CuBr4(C5H12N)2 (BPCB), a material containing weakly coupled spin-1/2 Heisenberg AF ladders, is a unique system for controlling and probing the LL physics. Using 14N nuclear magnetic resonance we quantitatively characterize the variation of Luttinger parameters over the gapless phase of BPCB. This allows us to fully account for the phase transition to a 3D ordered phase at temperatures below 110 mK, which takes place due to weak inter-ladder exchange coupling, in terms of weakly coupled LLs.