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Details of Grant 

EPSRC Reference: EP/N027671/1
Title: Novel X-ray methods for studying correlated quantum matter in the strong spin-orbit coupling limit
Principal Investigator: McMorrow, Professor DF
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Diamond Light Source European Synch Radiation Facility - ESRF German Elektronen Synchrotron (DESY)
IFW Dresden
Department: London Centre for Nanotechnology
Organisation: UCL
Scheme: EPSRC Fellowship
Starts: 01 June 2016 Ends: 31 May 2021 Value (£): 1,210,990
EPSRC Research Topic Classifications:
Condensed Matter Physics Magnetism/Magnetic Phenomena
Quantum Fluids & Solids
EPSRC Industrial Sector Classifications:
Electronics
Related Grants:
Panel History:
Panel DatePanel NameOutcome
19 Apr 2016 EPSRC Physical Sciences Fellowship Interview 19 and 20 April 2016 Announced
18 Feb 2016 EPSRC Physical Sciences Physics - February 2016 Announced
Summary on Grant Application Form
Although it is one of the most prosaic properties of a material, the response to an applied electrical voltage can be one of its most profound. Initial insight into why some materials are electrical conductors while others are insulators came from the early application of quantum mechanics. In this view, electrons in "simple" materials are treated as independent, and solids are classified according to the number of electrons filling the quantum states: for an even number the states are filled, resulting in an insulator, whereas for an odd number the states are partly filled allowing the electrons to conduct. Although this rule of thumb works for many "simple" materials, including e.g. aluminum and silicon on which a large fraction of our current technologies are based, it fails spectacularly for others. Simple oxides of transition metals, for example, exist with partially filled electron states. Mott first proposed that it was only by including electron interactions, which in materials such as oxides can be dominant, that the metal-insulator transition can be understood. Hubbard later proposed a deceptively simple model with just two parameters, describing the tendency of electrons either to localize (insulating behaviour) or delocalize (metallic). For more than 50 years, the Mott-Hubbard paradigm has provided the abiding theoretical framework for rationalizing the electronic and magnetic properties of "complex" quantum solids defined as those that exhibit explicit collective quantum effects, such as high-temperature superconductivity.

More recently, the relativistic coupling of an electron's intrinsic spin with its orbital motion - the spin-orbit interaction (SOI) - has come sharply into focus with the discovery that it can lead to qualitatively new types of electronic state. It has been shown that even for certain "simple" materials the SOI leads to surface metallic states on materials that in the bulk are insulating. These surface states are non-trivial, in that they are protected by symmetries - or topology - and therefore cannot be easily destroyed. The question then naturally arises as to the consequences of including relativistic effects in "complex" quantum materials in which the electrons interact strongly. The answer requires developing a new paradigm - beyond the Mott-Hubbard one - that treats interactions and the SOI on an equal footing. This proposal is to perform experiments that will be key to establishing this new paradigm. This new frontier has attracted considerable theoretical attention, and a plethora of predictions have been made for exotic electronic and magnetic states, some of which in the long run may lead to new technologies. Examples include novel types of insulators, metals, superconductors, quantum spin liquids, etc. However, history shows that although theory provides a useful guide, it cannot anticipate all possibilities, and many exciting discoveries will no doubt be made through experimentation.

Revealing the nature of the electronic and magnetic correlations in complex "quantum matter" through experimentation is very challenging, requiring techniques with extremely high sensitivity and specificity. A major theme of this proposal is the development of novel X-ray techniques which will offer unprecedented insights into the atomic scale order and excitations in solids. The techniques will be developed at large-scale central facilities, both nationally and internationally, which have dedicated particle accelerators for producing ultra intense X-ray beams. The recent advent of X-ray laser sources represent the pinnacle of this technology which deliver 20 orders of magnitude higher intensity than conventional sources in femto-second pulses (i.e. the time taken for light to transit a molecule). These sources are transformational enabling novel non-equilibrium electronic and magnetic states to be created and their evolution to be studied in real-time.

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