title: Field-induced quantum criticality and universal temperature dependence of the magnetization of a spin-1/2 heisenberg chain.
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=13.97  T, 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.
authors: Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.
authors: Y
authors: Y
authors: Kono
authors: Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.
authors: T
authors: T
authors: Sakakibara
authors: Department of Physics, University of Florida, Gainesville, Florida 32611-8440, USA.
authors: C P
authors: CP
authors: Aoyama
authors: Department of Basic Science, University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan.
authors: C
authors: C
authors: Hotta
authors: Carlson School of Chemistry and Department of Physics, Clark University, Worcester, Massachusetts 01610-1477, USA.
authors: M M
authors: MM
authors: Turnbull
authors: Carlson School of Chemistry and Department of Physics, Clark University, Worcester, Massachusetts 01610-1477, USA.
authors: C P
authors: CP
authors: Landee
authors: Department of Physics, University of Florida, Gainesville, Florida 32611-8440, USA.
authors: Y
authors: Y
authors: Takano