Impact of strong disorder on the static magnetic properties of the spin-chain compound BaCu2SiGeO7

TL;DR

This study combines experimental NMR and magnetization measurements with numerical simulations to demonstrate that the disordered spin-chain compound BaCu2SiGeO7 exhibits a random-singlet state consistent with the random Heisenberg chain model, revealing the effects of strong disorder.

Contribution

It provides the first comprehensive experimental and numerical evidence for the random-singlet state in BaCu2SiGeO7, highlighting the role of disorder and local transverse fields in this quasi-1D magnet.

Findings

Quantitative agreement with the random Heisenberg chain model.

Evidence for the formation of a random-singlet state at low temperatures.

Identification of a local transverse staggered field affecting low-temperature properties.

Abstract

The disordered quasi-1D magnet BaCu2SiGeO7 is considered as one of the best physical realizations of the random Heisenberg chain model, which features an irregular distribution of the exchange parameters and whose ground state is predicted to be the scarcely investigated random-singlet state (RSS). Based on extensive 29Si NMR and magnetization studies of BaCu2SiGeO7, combined with numerical Quantum Monte Carlo simulations, we obtain remarkable quantitative agreement with theoretical predictions of the random Heisenberg chain model and strong indications for the formation of a random-singlet state at low temperatures in this compound. As a local probe, NMR is a well-adapted technique for studying the magnetism of disordered systems. In this case it also reveals an additional local transverse staggered field (LTSF), which affects the low-temperature properties of the RSS. The proposed model Hamiltonian satisfactorily accounts for the temperature dependence of the NMR line shapes.