School of Physics and Astronomy

Search site

School Research Seminars

The School is introducing a new set of research seminars given by all new members of academic staff. It will be an opportunity to learn more about the varied areas of research going on in the School. These are primarily open to just members of Physics and Astronomy, lunch will be provided.

All seminars, unless stated otherwise, will run from 12-1pm.

Monday 16th May, 7.73

Dr Peter Adams

Exploring functional biomembranes: supported lipid bilayers, toxins and light-harvesting proteins

In this seminar I will present some of my previous and ongoing research into biological soft materials, including lipid membranes, proteins and photosynthesis. Supported lipid bilayers (SLBs) are established as simplified models for biological membrane amenable to microscopy and biophysical techniques. Firstly, I will describe the interaction with SLBs with lipopolysaccahride (LPS), a structural component of bacterial outer membranes and a potent human toxin. I will reveal how LPS spontaneously inserts into supported lipid bilayers causing major reorganization and dynamic change to the membrane depending on its local ionic environment. Lipid membrane tubules, perforations and multi-layers are observed by fluorescence microscopy and atomic force microscopy. These findings have important implications about the physical interaction of LPS and lipids relevant to its toxicity.

 

Secondly, I will highlight research into (re)designing biological membranes involved in absorbing solar energy. In natural photosynthesis, light harvesting (LH) membrane proteins absorb photons of light by their embedded chromophores (chlorophylls, carotenoids) and transfer that energy to downstream proteins. In ongoing research, the membrane protein LHC-II and various lipids are used as building blocks for designing new membranes with controlled composition, organisation and optical properties. Furthermore, I will show micro- and nano-scale patterning of LHCII protein into array structures on solid substrates.

 

In other research, we generated an artificial LH system comprised of amphiphilic diblock polymers acting as a matrix for the organisation of synthetic energy donor and acceptor chromophores. This was found to provide a highly modular system allowing high efficiency energy transfer. Alternatively, natural LHC-II protein can be coupled to synthetic donors, including lipid-linked dyes and quantum dots, in order to modulate the absorption profile of the protein-based system. Novel polymer/chromophore and lipid/protein/chromophore systems improve our understanding of fundamental energy transfer processes as well as generating new materials with tuneable optical properties.

 

Monday 13th June, 7.70

Dr Mamatha Nagaraj

Liquid Crystals: From Molecular and Supramolecular Structures to Novel Devices

We are all familiar with the concept of materials as solids, liquids and gases. There is a fourth state of matter that exist between solid and liquid states known as liquid crystalline state. The most familiar application of liquid crystals is the liquid crystal displays or LCDs. Although usually associated with rod and disk-like molecules, liquid crystallinity has been observed in organic molecules with a variety of different and unconventional anisotropic shapes. Amongst these, mesogens having V-shape or banana-shape have been considered as one of the most fascinating classes. This is due to the wide range of unique mesophases and unusual physical properties, for example enhanced cybotacticity, anomalous elastic constants, large flexoelectricity and spontaneous deracemization in achiral materials, they exhibit compared to conventional liquid crystals.

In this talk, I will outline some of the amazing complex molecular and supramolecular self-assembled structures formed by mesogens of unconventional architectures. I will present recent results on unusual electric field-driven transformations and reorganizations seen in the nanostructure of the lamellar and 3D mesophases formed by such mesogens and their prospects for a range of novel applications and devices.

Monday 20th June, 8.60

Dr Zlatko Papic

Strongly-entangled quantum matter

 

One of the ultimate goals in physics is to understand and classify all possible phases of matter and their generic types of behaviour. For example, early on we are taught that matter can exist in four basic entities as solid, liquid, gas or plasma. Later, by studying quantum mechanics and condensed matter physics, we learn that matter can organise into more subtle forms, such as superfluids and superconductors, and the variety of possible  phases of matter is seemingly much bigger than in classical physics. How can one build a library of all phases of matter? Since the work of Landau in the 1950s, people have been classifying phases of matter according to what symmetries they break --an approach known as the theory of symmetry breaking and "order parameters". The thermodynamic properties of such systems are then computed by invoking the principles of Boltzmann/Gibbs equilibrium statistical mechanics and "ensemble averaging".In the 1980s, however, we first realised that certain quantum systems can also give rise to ordered phases which fall outside the basic "classification" principles of symmetry and statistical mechanics. This is because these systems are strongly quantum, and quantum mechanics allows for non-local correlations between particles. This phenomenon, known as "entanglement", allows these systems to display new types of order and dynamical behaviour without analogs in classical physics. The interest in such systems is two-fold. Firstly, they can exhibit novel kinds of "vacua" whose elementary excitations are richer than allowed by the Standard Model of high-energy physics, yet they can be realised in "table top" condensed matter experiments. Secondly, their unique physics is being applied to design more robust quantum devices for information processing.   

 

In this talk I will present an overview of my research into the two kinds of physical systems that exemplify the new paradigm of quantum entangled matter mentioned above. First, I will discuss the fractional quantum Hall effect which manifests as an anomaly in transport on 2D semiconductor heterostructures. This effect stems from the formation of some of the most strongly-entangled quantum phases known in nature, which have a new kind of order -- topological order -- that can be described as resilience to any local perturbations. I will discuss some recent theoretical as well as experimental activity on studying such phenomena in new graphene-based materials and systems of quantum spins. In the second part, I will focus on the out-of-equilibrium dynamics of interacting systems in the presence of disorder. Such systems can display a type of behaviour called "many-body localisation", which has recently emerged as a generalisation of the famous problem of single electron localisation [Anderson, 1958]. Many-body localised systems currently generate much theoretical interest due to the fact they break ergodicity, and hence cannot be described by equilibrium statistical mechanics. Their practical relevance lies in the fact that they avoid thermalisation even at infinitely long times, which may allow them to sustain and "protect" quantum ordered phases of matter at high temperatures.

Monday 19th September, 8.90 (2-3pm)

Dr Satoshi Sasaki

Topological quantum phases of matter: From topological insulators to topological superconductors

 

It is almost a decade ago that the first-generation topological insulators (TIs) with nontrivial electronic band structures were discovered from real materials. Since then, the search for ideal topological materials (TMs) has been intensified and the topic of the topological quantum phase of matter in solid state physics became of great interest. Why? There are at least the following two reasons:

 

1) The helical (or chiral) spin texture in topological surface states protected by particular symmetries of TIs (or topological Weyl semimeatls) can be a promising platform for topotronics; an extended concept of spintronics.

2) TMs with a strong spin-orbit coupling that can superconduct are candidates for topological superconductors (TSCs) hosting Majorana fermions (MFs) at their edges/surfaces. MFs are predicted to be mysterious uncharged quasiparticles of TSCs with similar properties to the undiscovered elemental particles. Proposals for MF-based topological quantum computations are probably the strongest motivation for our research: The MFs that locate on TSCs could be useful for storage of quantum information and fault-tolerant computation because of the nonlocality and robustness of the MFs against dephasing.

 

In my talk, I will introduce the concept of the topological phase of matter and try to convince you why it is of interest to explore the TMs, in particular TIs and TSCs. Then I would like to review my work on topological materials and discuss challenging ideas for the future research that fit well and compliment to the expertise and infrastructure present in our school and university.

 

Monday 10th October

Dr Zhan Ong

Monday 21st November

Dr Sally Peyman

Past seminars

Monday 12th October (1-2pm), 8.60 EC Stoner

Dr Jung-uk Shim

Microfluidic approach to facilitate novel way to biology

Abstract

I will discuss a microfluidic technology to probe the specific activity of protein expressed by single cells by simultaneously monitoring the amount of expressed protein and its enzymatic activity. This approach allows the analysis of cells that were exposed to identical environmental condition [1]. The permeability of the device material, poly-dimethylsiloxane, can be exploited to deliver hormone-like small molecules to droplets encapsulating cells. [2] This capability enables the study of the response of individual cells to different regulators by deliberately changing the chemical environment of droplets. In further miniaturization the study of much smaller individual species was made possible by single molecule fluorescence detection in microfluidic droplets. This study has enabled us to detect and characterize single biological molecules.[3] To this end I have performed single molecule FRET measurement and shown that the time-dependent kinetics of conformational change (unfolding/refolding) of proteins can be followed by encapsulating protein molecules in droplets of denaturant. A microfluidic immunoassay will be discussed, which enabled quantification of a very low abundance biomarker by the ability of a droplet assay to directly count individual enzyme molecules in a bead-based antibody binding assay. This approach is able to identify the presence of a cancer biomarker significantly more sensitively than the standard ELISA [4].

References

[1] Shim, J.U. J. Am. Chem. Soc., 2009. 131(42): p. 15251-15256.

[2] Shim, J.U. Lab Chip, 2011. 11(6): p. 1132-1137.

[3] Horrocks, M.H. Anal. Chem., 2012. 84(1): p. 179-185.

[4] Shim, J.-u. ACS Nano, 2013. 7(7): p. 5955-5964.

 

 

Monday 16th November, 7.83 EC Stoner

Dr Sven Van Loo

Filaments in the interstellar medium

Molecular clouds exhibit a hierarchical density structure with stars forming in their densest regions. Often, these star-forming complexes have an elongated, filamentary shape. Recent Herschel observations of such filaments show a column density profile that deviates from hydrostatic equilibrium. Several explanation have been proposed, but have not elucidated the formation process. 

I will discuss the formation of filaments by self-gravitating layers by gravitational instabilities. Self-gravitating layers are unstable to perturbations and fragment into clumps or thin filaments. When the layers are threaded by magnetic fields, fragmentation is still possible. Numerical simulations of the gravitational instability in magnetised layers produce density structures similar to observed ones. The filament network that forms is either a hub-filament or a parallel-filament network depending on the magnitude of the magnetic field. Although the filaments are collapsing, the central region of the filament can be perfectly described by an equilibrium density distribution. Excess mass accumulates at radii larger than the scale height resulting in a density and column density distribution that is flatter than for an equilibrium cylinder. I do not reproduce the quasi-constant filament width because no additional support is provided even though I include magnetic fields. Using SMA polarization observations, I will interpret the filamentary network of the massive star forming complex G14.225-0.506 in terms of the gravitational instability model.

While this talk will mainly focus on star formation, I will also briefly discuss some non-astrophysical research I am involved in such as the development of a AMR Vlasov code and the impact of the quality of CO2 on transport and storage.