Quantum spin: liquid assets

A quantum spin liquid is a hypothetical system of spins (such as those carried by electrons), the orientations of which continue to fluctuate even at absolute zero. The evidence for the existence of such states remains tentative. Zi Yang Meng et al. have developed a microscopic model of correlated electrons arranged on a honeycomb lattice (like that in, for example, graphene), and identify the conditions under which a quantum spin liquid is realized in such a system. This unexpected state of matter is a resonating valence bond state, akin to that proposed for high-temperature superconductors, raising the possibility of unconventional superconductivity through doping.

Article: Quantum spin liquid emerging in two-dimensional correlated Dirac fermions

Z. Y. Meng, T. C. Lang, S. Wessel, F. F. Assaad & A. Muramatsu

doi:10.1038/nature08942

Abstract | Full Text | PDF (766K) | Supplementary information

Nature 464, 847-851 (8 April 2010) | doi:10.1038/nature08942; Received 30 October 2009; Accepted 17 February 2010

Quantum spin liquid emerging in two-dimensional correlated Dirac fermions

Z. Y. Meng¹, T. C. Lang², S. Wessel¹, F. F. Assaad² & A. Muramatsu¹

Institut für Theoretische Physik III, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

Correspondence to: Z. Y. Meng¹ Correspondence and requests for materials should be addressed to Z.Y.M. (Email: meng@theo3.physik.uni-stuttgart.de).

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At sufficiently low temperatures, condensed-matter systems tend to develop order. A notable exception to this behaviour is the case of quantum spin liquids, in which quantum fluctuations prevent a transition to an ordered state down to the lowest temperatures. There have now been tentative observations of such states in some two-dimensional organic compounds, yet quantum spin liquids remain elusive in microscopic two-dimensional models that are relevant to experiments. Here we show, by means of large-scale quantum Monte Carlo simulations of correlated fermions on a honeycomb lattice (a structure realized in, for example, graphene), that a quantum spin liquid emerges between the state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator. This unexpected quantum-disordered state is found to be a short-range resonating valence-bond liquid, akin to the one proposed for high-temperature superconductors: the possibility of unconventional superconductivity through doping therefore arises in our system. We foresee the experimental realization of this model system using ultra-cold atoms, or group IV elements arranged in honeycomb lattices.