The study of quantum phase transitions, which are zero-temperature phase transitions between distinct states of matter, is of current interest in research since it allows for a description of low-temperature properties based on universal relations. Here we show that the crystal green dioptase Cu_6Si_6O_18 . 6H_2O, known to the ancient Roman as the gem of Venus, has a magnetic crystal structure, formed by the Cu(II) ions, which allows for a quantum phase transition between an antiferromagnetically ordered state and a quantum spin liquid.
@article{arxiv.cond-mat/0208106,
title = {Quantum phase transition in the dioptase magnetic lattice},
author = {C. Gros and P. Lemmens and K. -Y. Choi and G. G"untherodt and M. Baenitz and H. H. Otto},
journal= {arXiv preprint arXiv:cond-mat/0208106},
year = {2009}
}