Field-induced quantum criticality and universal temperature dependence of the magnetization of a spin- 1/2 Heisenberg Chain

Y. Kono, The University of Tokyo
T. Sakakibara, The University of Tokyo
C. P. Aoyama, College of Liberal Arts and Sciences
C. Hotta, The University of Tokyo
M. M. Turnbull, Clark University
C. P. Landee, Clark University
Y. Takano, College of Liberal Arts and Sciences

Abstract

High-precision dc magnetization measurements have been made on Cu(C4H4N2)(NO3)2 in magnetic fields up to 14.7 T, slightly above the saturation field Hs=13.97T, in the temperature range from 0.08 to 15 K. The magnetization curve and differential susceptibility at the lowest temperature show excellent agreement with exact theoretical results for the spin-1/2 Heisenberg antiferromagnet in one dimension. A broad peak is observed in magnetization measured as a function of temperature, signaling a crossover to a low-temperature Tomonaga-Luttinger-liquid regime. With an increasing field, the peak moves gradually to lower temperatures, compressing the regime, and, at Hs, the magnetization exhibits a strong upturn. This quantum critical behavior of the magnetization and that of the specific heat withstand quantitative tests against theory, demonstrating that the material is a practically perfect one-dimensional spin-1/2 Heisenberg antiferromagnet.