Entanglement defines the essential non-classical features of quantum mechanics, and long-range entanglement engenders exotic phenomena such as fractional quantum numbers and emergent topological excitations. Theoretically, the exemplars of such massive long-range entanglement are quantum spin liquids (QSLs), states of quantum magnets in which electronic spins reside in macroscopic superpositions of infinitely many microstates. QSLs have been elusive experimentally, in part because disorder induces competing local glassy states instead of entangled ones. However, recently it has been shown that for spin-ice materials, such as holmium titanate, it is possible to tune to QSLs via the controlled introduction of structural disorder.
We have grown large single crystals of holmium titanate in which we are able to control the structural disorder through doping. We now propose to study the structural defects and the spin correlations using the diffuse scattering of neutrons. The student will measure the defect structures using x-ray diffraction at Royal Holloway, and neutron Laue diffraction using SXD at ISIS. The defect structures will be compared with first-principles density-functional calculations, and the effects on the single-ion magnetic properties will be determined. The spin correlations will then be measured using the diffuse scattering of polarized neutrons using D7 at the ILL. By studying samples with different levels of disorder it will be possible to test the theoretical predictions that this system will change from a classical spin ice to a true QSL.
The PhD project will be located in Grenoble (France), at the ILL, and at Royal Holloway, University of London. Applicants should have a degree in a Physics discipline. Academic knowledge of condensed matter physics will be an advantage. A cover letter, a detailed CV, and the names and contacts of two referees should be sent to the two supervisors: Professor Jon Goff (Royal Holloway) Tel: +44(0)1784443485, E-mail: [email protected]; Dr Lucile Mangin-Thro (ILL), Tel: +33(0)476207571, E-mail: [email protected].
The successful candidate will be employed for three years (starting from October 2019), with a gross salary of around 2400 €/month.