51吃瓜黑料

Quantum thermodynamics

This area of research focusses on the interplay of quantum and thermal fluctuations in quantum systems, and the extension of thermodynamics to the quantum regime.

Quantum thermodynamics research group

Material design for energy and business

Research leads: ,

Energy

In the 21st century, the quest for new materials to combat the problems of climate change and improve the quality of life requires cutting edge understanding of the fundamentals of material science.

At 51吃瓜黑料, we have researchers looking into the fundamental theory and design of materials. We use this for energy storage, where we use first principles theory and structure search tools in an effort to discover the perfect battery and ultra capacitors where materials with a colossal permittivity have been touted for use as a high energy density capacitor.

We also apply this to energy harvesting technologies such as solar and thermoelectrics. Finally, we also study water splitting using semiconductors in the presence of light (the so-called artificial photosynthesis) to custom design materials suitable for enhanced conversion.

Business

Our research team is also experienced in helping companies in developing the material solutions for their problems.

We simulate and understand the electronic, optical and thermal properties of materials and help both small companies and large address key issues in their device production. We develop models for characterising materials, how their manufacture (or “growth”) affects them to understand how to make better materials.

We create a list of measurable characteristics of materials, to enable rapid identification of what factors dominant in a material. We do this theoretically using multiple techniques ranging from analytic continuum models to full atomic scale simulation using ab initio calculations with researchers in a vast range of theoretical expertise in materials.

Current projects

• Better batteries – sponsored by Deregallera Ltd (CEO Martin Boughtwood)
• 2D batteries
• Patterned thermoelectrics– sponsored by Deregallera Ltd (CEO Martin Boughtwood)
• Oxide solar cells - sponsored by Solaris
• Two-dimensional metamaterial thermoelectrics
• The origins of colossal permittivity

Condensed matter theory

Research leads: ,

We work on the analytical theory of correlated system in reduced dimensionality, with particular emphasis on atomically thin materials and topological metasurfaces.

In this vast area of research we are currently active in:

• Electronic quantum transport in graphene and other atomically thin materials
• Nano-electromechanical systems (NEMS) and superconducting suspended resonators
• Dirac metasurfaces and topological polaritonics
• Plasmonic resonances in metallic nanoparticles.

We also work on ab inito and semi-ab initio investigations of the physics of electrons and phonons in bulk (3D), surface (2D) and nanocomposite structures.

Specific topics include:

• electronic band structure
• phonon dispersion relations
• electron-electron, electron-phonon and phonon-phonon interactions
• thermal transport
• thermoelectric properties
• BCS superconductivity.

Theory of magnetosensitivity

Research lead:

Dipolarly coupled spin-radicals

We have recently shown that in systems of three or more radicals, remarkable magnetic field effects can be induced by the electron-electron dipolar interaction alone – without involvement of hyperfine interactions, in stark contrast to what applies to radical pairs [1]. By considering the role of symmetries and energy level crossings, we have presented a model that demonstrates a directional sensitivity to fields weaker than the geomagnetic field. We achieve remarkable spikes in the reaction yield as a function of the magnetic field intensity that can be tuned by the exchange interaction. These results further our current understanding of weak-field reaction magnetosensitivity and could be particularly relevant to magnetic field effects on lipid autoxidation or the understanding of the putative effects of extremely low frequency (ELF) magnetic fields on biological systems.

[1] R. H. Keens, S. Bedkihal, and D. R. Kattnig, Phys. Rev. Lett. 2018, 121, 096001.

Magnetic field effects (MFEs) in three-radical systems

In the figure below, we have assumed that two radicals (white semicircles) are located at a distance of 2 nm and varied the position of the third radical on a plane comprising the inter-radical axes of the first two radicals. Assuming a lifetime of 1 μs, we predict astonishing magnetic field effects for the singlet recombination yield of radical 1 and 2. For weak magnetic fields comparable to the Earth’s magnetic field (top), we predict MFEs of more than 8 %; more than 20 % are found for high magnetic fields (bottom). Remarkably, large effects are expected even if the distance of closest approach to the third radical approaches 5 nm, i.e. if the third radical assumes the function of a “casual bystander”.

The avian quantum magnetic compass and magnetic field effects in cryptochromes

Evidence is accumulating that in certain birds (like the European Robin) and a few other animals, a magnetic inclination compass is based on a radical pair reaction in blue light-sensitive flavoproteins called cryptochromes. These magneto-sensors are supposed to be located in the retinae of the animals, where they possibly give rise to a magnetic-field dependent visual impression.

A possible reaction scheme (top right of the figure above) entails photo-excitation of the flavin cofactor, the formation of a spin-correlated radical ion pair by a succession of electron transfer reactions involving a triad or, in animals, tetrad of highly conserved tryptophan residues, its coherent interconversion between overall singlet and triplet states, and, eventually, spin selective recombination or spin-insensitive formation of a signalling state, possibly followed by the stabilisation of the flavin radical by proton transfer reactions and release of a C-terminal domain.

This reaction scheme is not the only possible reaction scheme discussed in the context of magnetoreception. However, it is the only scheme that is currently supported by in vitro experiments on the purified cryptochromes of the fruit fly and Arabidopsis thaliana. For these systems, the effect is known to originate from the radical pair involving the flavin anion radical and the radical cation of the third tryptophan of the triad or tetrad (see the insert at the bottom of the figure).

There are many unsolved enigmas associated with the radical pair hypothesis of magnetoreception, which we try to assess and resolve:

• How can the small effects induced by an Earth-strength magnetic field be amplified in order for the sensor to work with only 1 photon/s per cone outer segment?
• What process provides the remarkable acuity?
• Why is the effect sensitive to weak monochromatic or broadband radio-frequency magnetic fields, which would suggest a remarkable resilience to decoherence – much better than most man-made quantum device but operating at elevated temperatures in a noisy, biological environment?
• How does the sensor deals with the detriment of inter-radical interactions?

The chemical Zeno effect

Surprisingly, magnetic field effects can be vastly amplified if one of the radicals of the primary pair undergoes a spin-selective electron transfer reaction with a spin-bearing scavenger (chemical Zeno effect). This leads us to suggest new, extended reaction schemes for the putative magnetosensory protein cryptochrome [1,2]. The new mechanism offers clear and important benefits such as a greatly enhanced sensitivity to the orientation of a 50 μT magnetic field (by up to two orders of magnitude in the relative anisotropy) and magnetosensitivity for radicals that are more than 2 nm apart.

This means that radical pairs too distant to undergo spin-selective recombination reactions could also be viable magnetic compass sensors and that the detrimental effects of inter-radical exchange and dipolar interactions can be minimized. Even more surprisingly, the effect immunizes the sensor to fast decoherence processes in one of the radicals [2]. Consequently, magnetic field effects on radical pairs involving swiftly spin-relaxing species, such as superoxide, are no longer to be precluded [2].

[1] D. R. Kattnig and P. J. Hore, Sci. Rep. 7, 11640 (2017).
[2] D. R. Kattnig, J. Phys. Chem. B 121, 10215 (2017).

Oxidative degradation of lipids

A common denominator of the effects of weak magnetic fields on biological systems appears to be a modulation of reactive oxygen species and oxidative decay processes such as those associated with lipid autoxidation. This raises the question of the possibility of an inherent magnetic field effect on lipid peroxidation in general and the recombination of peroxyl radicals, the main chain carriers in the oxidative degradation of polyunsaturated fatty acids, in particular. We study the spin dynamics that could underlie these processes. Preliminary calculations suggest that magnetic field effects in these systems could be markedly enhanced through three-radical effects. These effects are predicted to give rise to magnetic field effect that, unlike the well-known effects due to radial pairs, depend on radical concentration. Furthermore, a peculiar dependence on field intensity in predicted.

Change of the recombination yield as a function of the magnetic field excluding (top, partly hidden) and including three-radical effects (right). The change in the recombination yield of the latter depends on the location of the third radical relative to the encountering pair and lies between the blue and red line. Under favourable conditions the magnetic field effects are predicted to be markedly larger than for the hyperfine induced effect in radical pairs.

Magnonics theory

Research lead:

Spin waves in graded magnonic media

Wave excitations of the magnetic order (so called spin waves, quanta of which are called magnons) have an extremely rich and peculiar dispersion, which is nonlinear, anisotropic and non-reciprocal. The spin wave dispersion is very sensitive to the sample’s magnetic properties and micromagnetic state, so that spin waves are rarely observed to propagate in uniform media. Inspired by and feeding from other fields of wave physics, we are developing the theory of spin wave excitation, propagation and control in media with continuously varying properties, i.e. media with a graded magnonic index. This research is not only full of exciting fundamental challenges but may also enable a new, spin wave based technology for data and signal processing.

Electromagnetic to spin wave coupling

Spin waves are traditionally excited by electromagnetic waves at frequencies of few to hundreds of GHz.  This is however difficult to a huge gap between the wavelength (and therefore momentum) of electromagnetic and spin waves at the same frequency.  We are tackling this challenge by developing a theory of spin-wave excitation in media with broken translational symmetry, i.e. via exploiting compositional, geometrical or micromagnetic non-uniformities that my either naturally exist or artificially created in magnonic media or devices.  Such non-uniformities are, in fact, ubiquitous in realistic magnonic samples.  Hence, our theory also provides insights into how and why spin waves may be unintentionally excited in dynamic magnetic measurements.