Quantum critical dynamics of a S = 1/2 antiferromagnetic Heisenberg chain studied by 13C-NMR spectroscopy

TL;DR

This study investigates the quantum critical behavior of a S=1/2 antiferromagnetic Heisenberg chain using 13C-NMR spectroscopy, revealing how magnetic excitations diverge near the critical field through experimental and quantum Monte Carlo analysis.

Contribution

It provides the first comprehensive experimental and theoretical analysis of quantum critical dynamics in a S=1/2 antiferromagnetic Heisenberg chain across a wide temperature and field range.

Findings

Good agreement between experiment and quantum Monte Carlo calculations.

Observation of a maximum in 1/T_1 near the critical field.

Finite-temperature evidence of diverging magnetic excitations at quantum critical point.

Abstract

We present a 13C-NMR study of the magnetic field driven transition to complete polarization of the S=1/2 antiferromagnetic Heisenberg chain system copper pyrazine dinitrate Cu(C_4H_4N_2)(NO_3)_2 (CuPzN). The static local magnetization as well as the low-frequency spin dynamics, probed via the nuclear spin-lattice relaxation rate 1/T_1, were explored from the low to the high field limit and at temperatures from the quantum regime (k_B T << J) up to the classical regime (k_B T >> J). The experimental data show very good agreement with quantum Monte Carlo calculations over the complete range of parameters investigated. Close to the critical field, as derived from static experiments, a pronounced maximum in 1/T_1 is found which we interpret as the finite-temperature manifestation of a diverging density of zero-energy magnetic excitations at the field-driven quantum critical point.