Dresden 2011 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 6: Focused Session: Frontiers in Classical and Quantum Spin Liquids
TT 6.3: Hauptvortrag
Montag, 14. März 2011, 15:45–16:30, HSZ 03
Disorder in a quantum spin liquid: flux binding and local moment formation — Adam Willans1, •John Chalker1, and Roderich Moessner2 — 1Theoretical Physics, Oxford University, UK — 2Max-Planck-Institut für Physik komplexer Systeme, Dresden
We study the consequences of disorder in the Kitaev honeycomb model, using this exactly solvable spin liquid as a laboratory for the exploration of impurity effects in strongly fluctuating quantum magnets. The clean system has fermionic excitations and Z2 fluxes as its degrees of freedom, and this remains the case with disorder. As a function of model parameters, it displays gapless and gapped phases.
We examine the effects of site dilution and exchange randomness in both phases. We show that a single vacancy binds a flux and induces a local moment. This moment is polarised by an applied field h: in the gapless phase, for small h the local susceptibility diverges as χ(h) ∼ ln(1/h); for a pair of nearby vacancies on the same sublattice, this even increases to χ(h) ∼ 1/(h[ln(1/h)]3/2). By contrast, weak exchange randomness does not qualitatively alter the susceptibility but has its signature in the heat capacity, which in the gapless phase is power law in temperature with an exponent dependent on disorder strength.