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dc.contributor.advisorYoung S. Lee.en_US
dc.contributor.authorHan, Tianheng, Ph. D. Massachusetts Institute of Technologyen_US
dc.contributor.otherMassachusetts Institute of Technology. Department of Physics.en_US
dc.date.accessioned2013-07-10T14:51:05Z
dc.date.available2013-07-10T14:51:05Z
dc.date.copyright2012en_US
dc.date.issued2012en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/79516
dc.descriptionThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.en_US
dc.descriptionCataloged from PDF version of thesis.en_US
dc.descriptionIncludes bibliographical references (p. 183-200).en_US
dc.description.abstractNew physics, such as a quantum spin liquid, can emerge in systems where quantum fluctuations are enhanced due to reduced dimensionality and strong frustration. The realization of a quantum spin liquid in two-dimensions would represent a new state of matter. It is believed that spin liquid physics plays a role in the phenomenon of high-Tc superconductivity, and the topological properties of the spin liquid state may have applications in the field of quantum information. The Zn-paratacamite family, ZnCu₃(OH)₆Cl₂ for x > 0.33, is an ideal system to look for such an exotic state in the form of antiferromagnetic Cu2+ kagome planes. The x = 1 end member, named herbertsmithite, has shown promising spin liquid properties from prior studies on powder samples. Here we show a new synthesis by which high-quality centimeter-sized single crystals of Zn-paratacamite have been produced for the first time. Neutron and synchrotron x-ray diffraction experiments indicate no structural transition down to T = 2 K. The magnetic susceptibility both perpendicular and parallel to the kagome plane has been measured for the x = 1 sample. A small, temperature-dependent anisotropy has been observed, where Xz / Xp > 1 at high temperatures and Xz / Xp < 1 at low temperatures. Fits of the high-temperature data to a Curie-Weiss model also reveal anisotropies for [Theta]cw's and g-factors. By comparing with theoretical calculations, the presence of a small easy-axis exchange anisotropy can be deduced as a primary perturbation to the dominant Heisenberg nearest neighbor interaction. These results have great bearing on the interpretation of theoretical calculations based on the kagome Heisenberg antiferromagnet model to the experiments on ZnCu₃(OH)₆Cl₂. Specific heat measurements down to dilution temperatures and under strong applied magnetic fields show a super linear temperature dependence with a finite linear term. Most importantly, we present neutron scattering measurements of the spin excitations on a large deuterated single crystal sample of herbertsmithite. Our observation of a spinon continuum in a two-dimensional magnet is unprecedented. The results serve as a key fingerprint of the quantum spin liquid state in herbertsmithite.en_US
dc.description.statementofresponsibilityby Tianheng Han.en_US
dc.format.extent200 p.en_US
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582en_US
dc.subjectPhysics.en_US
dc.titleThermodynamic and neutron scattering study of the spin- 1/2 kagome antiferromagnet ZnCu₃(OH)₆Cl₂ : a quantum spin liquid systemen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Department of Physics
dc.identifier.oclc849747344en_US


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