project . 2015 - 2019 . Closed

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

UK Research and Innovation
Funder: UK Research and InnovationProject code: EP/M01052X/1
Funded under: EPSRC Funder Contribution: 731,953 GBP
Status: Closed
01 Jan 2015 (Started) 31 Dec 2019 (Ended)

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.

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