At the forefront of modern materials research is the pursuit of novel quantum states of matter, in which quantum mechanical effects determine the collective physical properties observable at a macroscopic level.1 A prime example in the context of magnetic materials is the quantum spin liquid (QSL). A QSL represents a unique magnetic state of matter that fails to undergo conventional long-range magnetic order at any temperature and instead is characterised by its highly quantum-entangled, quantum-superpositional nature.2 Not only are these features fascinating from a fundamental perspective, but they may also hold the key to future quantum technologies, such as quantum computing and information security.3 Despite this, materialisations of the QSL remain scarce, making the discovery and exploration of new materials that may host this quantum state of matter compelling scientific challenges.
In this context, materials such as the layered metal oxide, YbMgGaO4, are attracting considerable attention.4 YbMgGaO4 is composed of triangular layers of magnetic YbO6 octahedra separated by non-magnetic double layers of Mg/GaO5 trigonal bipyramids.5 The Mg2+ and Ga3+ cations are disordered within these double layers, which interestingly, represents an example of chemical frustration, as the non-magnetic trigonal bipyramidal sites form a network of edge-sharing triangles. Simultaneously, there is a magnetic frustration associated with the antiferromagnetic triangular system of YbO6 octahedra which, coupled with the effective quantum S = ½ moment of the Yb3+ ion, makes YbMgGaO4 a prime candidate in which to seek exotic QSL behaviour. Indeed, studies have identified key hallmarks of a QSL state in YbMgGaO4.6 However, a crucial outstanding scientific question is, what is the effect of the Mg2+/Ga3+ cation disorder on the magnetic properties of this system and, more generally, how robust are quantum states of matter such as the QSL to quenched chemical disorder?
The purpose of this PhD studentship is to unravel the effect of chemical disorder on the magnetic ground state selection in YbMgGaO4 by seeking and exploring new, cation-ordered derivatives to reveal the intrinsic physics of the triangular YbO6 layers. Our principle scientific aim is to test the hypothesis that by seeking alternative cation couples within the disordered Mg2+/Ga3+ layers we can drive cation ordering via control of ionic charge and stoichiometry to reveal the ground state of the frustrated quantum magnetic layers of YbO6 octahedra in the absence of chemical disorder. This will be achieved by combining and developing computer-aided materials design, high-throughput inorganic materials synthesis, and neutron and X-ray scattering measurements.
Requirements and Eligibility:
Applications are encouraged from highly motivated candidates who have, or expect to have at least a 2:1 degree or equivalent in Chemistry, Physics, Materials Science, or a related discipline. Previous experience in the synthesis or characterisation of inorganic materials is highly desirable.
Applications should be made as soon as possible but no later than 31st March 2019. Informal enquiries are strongly encouraged and should be addressed to Dr Lucy Clark at [email protected]
Some teaching duties may be required.
The Department of Chemistry at the University of Liverpool is a world-leading centre for advanced materials research, ranked 1st for outputs and 3rd for impact in REF2014. Advanced materials research is further enhanced by the recently opened Materials Innovation Factory (MIF), a £68 M project part-funded by HEFCE and Unilever that co-locates academic materials research with partners in industry. The Clark Group at the University of Liverpool is based within the MIF and focuses on the discovery and characterisation of a range of quantum materials7 with access to a range of cutting-edge equipment for materials synthesis and characterisation.
The Institut Laue-Langevin (ILL) is the world’s leading facility in neutron science and is situated in Grenoble, France. The ILL hosts 2000 user visits every year for neutron scattering scientists from around the world, leading to an annual research output of 600 scientific publications. The ILL PhD Graduate School provides high-quality supervision and tailored support, owing to the strengths of the instrument suite and the expertise of the staff at the facility.
1N. Samarth, Nature Mater. 16, 1068 (2017), 2L. Balents, Nature 464, 199 (2010), 3T. Tokura et al., Nature Phys. 13, 1056 (2017), 4Y. Li et al., Sci. Rep. 5, 16419 (2015), 5R. Grajczyk and M. A. Subramanian, J. Prog. Solid State Chem. 43, 37 (2015), 6J. A. M. Paddison et al., Nature Phys. 13, 117 (2017), 7K. Tustain et al., Phys. Rev. Mater. 2, 111405(R) (2018).