Tuning order from disordered ground states in geometrically frustrated classical "non-hbar" materials

Condensed matter physics has developed a relatively complete theory of common phases in materials leading to many technologically important devices including electronic screens, memory storage, and switching devices. Landau, or mean-field theory, has provided a framework to model, predict, and understand phases and transitions in a surprisingly diverse variety of materials and also dynamical systems. While these conventional ground states have proven technologically important and the underlying theory represents a major success for scientists, these phases have proven incredibly difficult to suppress and often emerge when new materials properties are sought or engineered.

To discover novel phases that will lead to a new materials revolution, these common phases need to be suppressed to allow exotic and unconventional properties to emerge. The most common vehicle to turn off conventional phases in materials has been through the introduction of disorder through chemical doping resulting in strong random fields. Many important theories have been formulated and tested to describe the effects of random fields and in particular to account for the fine balance between surface and bulk free energy. However, the use of disorder has proved limiting as properties are often templated into the material and not directly controllable and also the resulting ground state of the material is difficult to understand.

Another route, which has more recently been explored in the last decade, to suppress conventional phases is by introducing strong fluctuations. While this can be trivially done with temperature, new phases have emerged by studying quantum systems where the physics are governed by quantum mechanics and the Heisenberg uncertainty principle. The study of quantum systems has resulted in the discovery of many new phases of matter including high temperature superconductors and also quantum spin-liquids where the magnetism is dynamic at any temperature.

A limitation of quantum fluctuations is that the properties do not carry over directly to ferroelectric based systems and also multiferroics where magnetic and structural properties are strongly coupled. Also, owing to the strong fluctuating nature of the ground state, the properties have not been found to be easily tunable limiting immediate use for applications. This proposal aims to therefore take a different route by studying classically frustrated systems where a large ground state degeneracy is introduced naturally through the lattice and quantum mechanical effects are small. Emphasis will be placed on lattices based upon a triangular geometry. The lack of strong fluctuations (that exists in quantum systems) provides the ability to controllably tune between different ground states making this route a potential means of creating new switching devices or novel memory storage systems.

The proposal aims to investigate classically frustrated magnets and ferroelectrics. These systems can be described within a common framework and will be studied using scattering techniques to provide a bulk real space image of the ground state. The properties will be tuned with magnetic and electric fields supplying a direct route for discovering a new route towards technologically applicable materials. The combined approach of investigating ferroelectrics and magnets will result in a complete understanding applicable to immediate industrial applications. These new materials will lead to the discovery of new phases including new high temperature multiferroics, classical spin liquids, or localized controllable boundaries or defects.

Impact will be achieved through 1) publication and communication; 2) outreach; 3) making contact with industry; 4) training highly qualified people.

1) The results of the science proposed here will be published in highly cited journals and advertised at international conferences. Manuscripts will also be posted on the publicly available "cond-mat" website based at Cornell University. The PI has an established track record of doing this with over 55 publications posted on this site.

The proposal requests funds for the PI and PDRA to attend international and UK based conferences such as the APS March meeting also the BCA meeting. This is important for advertising the work and maximizing academic impact. The requested travel time to large scale facilities will also allow more informal means of communications including meetings and seminars at host institutions.

2) Part of the proposal will include involving undergraduate students in projects based on the science proposed here. Specifically, this will include hosting 2-3 undergraduates in a real neutron/x-ray experiment every year during innovative learning week (ILW) in the winter semester. Also, undergraduate students will be directly involved with larger projects through the masters and specialist physics routes. Offering these projects will introduce undergraduate students to large scale facility science and allow them to develop skills in the area of computing, materials preparation in the lab, and also project management through organizing a large scale facility experiment. Such skills are important regardless of the career path chosen by the student.

In terms of graduate outreach, a ~6 hour neutron scattering lecture series will be given through the SUPA framework every year as part of the "Probes for Condensed Matter" course offered by the DTC. It is through these efforts that large scale facilities will be advertised and also students introduced to the science involved with this type of research.

CSEC also hosts public outreach events which the PI will remain actively involved in. These events include Erskine Williamson day and also open days at Edinburgh and are aimed at high school students and the general public.

3) Contact will be maintained with the industrial representative at the School of Physics as well as the knowledge transfer officer at CSEC. This will aid in exploiting links with industry that can be made throughout the project. Through the use of speciality equipment manufactured by UK based companies (such as Oxford Instruments) feedback will be provided through groups at large scale facilities to further develop new instruments. Intellectual property will be protected through contact with Edinburgh's knowledge transfer office and ERI (Edinburgh Research and Innovation).

4) The project will involve a graduate student funded through the DTA allocation at the University of Edinburgh and will also involve undergraduate students through masters and senior undergraduate projects. Through the highlighted international collaborations facilitated by this proposal the PDRA and students will learn new skills in materials preparation unique to Edinburgh. The proposal requests funds to travel to unique equipment at NIST (particularly the MACS instrument at the NIST Center for Neutron Research) in Maryland and also for the use of unique sample environments at PSI - Switzerland. It is anticipated that these experiments will be combined with visits to labs based in the University of Maryland and also Rutgers in New Jersey to gain knowledge of new crystal growth techniques. Both universities are within driving distance of NIST. The proposal also requests funds for a PDRA which will aid in launching an independent research career based upon UK based large scale facilities. These combined efforts will help in training individuals to make significant contributions to the UK economy and research.