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Viewing upcoming talks containing the keyword: 8
Cond Mat Seminars
Speaker: Bernd Braunecker (St Andrews)
A Cooper pair splitter extracts Cooper pairs from a superconductor and sends the two constituent electrons into two different leads. This process should preserve the Cooper pair's spin singlet entanglement, but to date no experimental proof could be provided. I will show that attaching spin filters to the Cooper pair splitter can be used to implement an entanglement detector that relies on the measurement of conductance rather than on higher order noise correlators. A practical setup was proposed in  for a carbon nanotube based Cooper pair splitter, making use of the spin-orbit interaction which due to the nanotube curvature is substantially larger than in flat graphene and produces perfect spin filtering. To bridge from the theory proposal to a proper realisation, I will discuss very recent experiments  in which the spin filtering properties of the nanotubes could be verified. B. Braunecker, P. Burset, and A. Levy Yeyati, Phys. Rev. Lett. 111, 136806 (2013). M. C. Hels, B. Braunecker, K. Grove-Rasmussen, and J. NygÃ¥rd, Phys. Rev. Lett. 117, 276802 (2016).
On: February 8, 2017 From: 12h00 To: 13h00View talk
Speaker: Chris Kay (University College London)
Applications of Paramagnetism in Structural Biology & Materials Research Chris Kay University College London In order to investigate the structure and function of molecular machines (i.e. enzymes) and novel materials and we are using continuous -wave and p ulsed EPR spectroscopy . The paramagnetic states employed are either stable radicals (e.g. nitroxide spin labels) or transient species (e.g. triplet states) . In this talk, I will discuss a few examples from our work.
In structural biology, X -ray crystallog raphy and increasingly cryo -EM are the methods of choice for high -resolution structural studies. Nevertheless, these are augmented by spectroscopic approaches including EPR spectroscopy that provide constraints for molecular modeling of intermediate conf ormations. As proteins are mostly diamagnetic, nitroxide spin labels are engineered into specific positions using site directed mutagenesis. Here I present some results from our recent studies into the binding of a peptide to a protein  and the structure and dynamics of a coiled coil .
Surfaces with built -in antimicrobial activity have the potential to reduce hospital -acquired infections. One promising strategy is to create functionalized surfaces which, following illumination with visible light, are able to generate singlet oxygen under aerobic conditions. W e considered five commercially available organic photosensitizer dyes encapsulated in silicone polymer and correlate d density functional theory calculations with UV -Vis spectroscopy, time -resolved EPR spectroscopy and singlet oxygen production measurements. Our approach forms the basis for the rational in silico design and spectroscopic screening of simple and efficient self -sterilizing surfaces made from cheap, low toxicity photosensitizer dyes enc apsulated in silicone [3 ].
Although randomly oriented samples are useful for many applications , sometimes it is preferable to use ordered samples. For example, s ingle crystals of pentacene in p-terphenyl have long been considered an ideal model system by EPR spectroscopists. One example of an application that mak es use of the remarkable properties of this system is as the gain medium in a MASER working at room temperature and i n the earth’s magnetic field .
 Papaioannou,D., Geibel,S., Kunze,M.B.A., Kay,C.W.M., Waksman,G. (2016). Structural and biophysical investigation of the interaction of a mutant Grb2 SH2 domain (W121G) with its cognate phosphopeptide , Protein Science 25, 627 -637.
 Bagnéris,C., Rogala,K.B., Baratchian,M., Zamfir,V., Kunze,M.B .A, Dagless,S., Pirker,K.F., Collins , M., Hall, B.A., Barrett,T.E., Kay, C.W.M. (2015). Probing the Solution Structure of IκB Kinase (IKK) Subunit γ and its Interaction with Kaposi's Sarcoma Associated Herpes Virus Flice Interacting Protein and IKK Subunit β by EPR Spectroscopy . Journal of Biological Chemistry 290, 16539 -16549.
 Noimark S., Salvadori E., Gómez -Bombarelli R., MacRobert A.J., Parkin I.P. , Kay C.W.M., (2016 ) Comparative study of singlet oxygen production by photosensitiser dyes encapsulate d in silicone: towards rational design of anti -microbial surfaces PCCP 18, 28101 -28109.
 Salvadori,E., Breeze,J.D., Tan, K. -J., Sathian,J. Richards,B., Fung,M.W., Wolfowitz,G., Oxborrow,M., Alford,N. , Kay,C.W.M. (2017 ) Nanosecond time -resolved character ization of a pentacene -based room -temperature MASER . Scientific Reports 7, 41836; doi: 10.1038/srep418362016 Download PDF
On: February 10, 2017 From: 12h00 To: 13h00View talk
Speaker: David Parker (Durham)
Euro Tracker Dyes and Probes David Parker Department of Chemistry, Durham University South Road, Durham DH1 3LE, UK firstname.lastname@example.org Highly emissive , sensitised lanthanide complexes based on macrocyclic ligands have been used extensively in vitro as a nalytical probes and in cellulo to stain cell compartments or study biological function. They are bright, possess long -lived, sharp emission bands and exhibit high photo stability , and have been used to assess pH, pM and pX. 1 Such favourable photophysical properties make the m promising candidates for other applications, such as security labelling or as anti - counterfeiting tools. The annual cost of counterfeiting to the global economy is estimated to be $1.7 trillion, and in the last 10 years, the Bank of En gland has withdrawn >5 million counterfeit banknotes from circulation , with a value of nearly £100 million. 2 Chiral europium complexes, may be resolved by chiral HPLC. Each enantiomer gives rise to mirror -image circularly polarised luminescence (CPL). Thi s fingerprint can be exploited as a security feature for the labelling of authentic items. Simple methods of detection of the resolved complexes have been developed , using band pass filters attached to a commercially available DSLR camera or CCD detector . Chiral image contrast has also been explored in microscopy , selecting the sign of the circularly polarised light, over a given wavelength range . 3 Figure 1 . Structure of the RRR -Λ-(δδδ ) enantiomer and CPL spectra of enantiomeric complexes. 1. S. J. Butler, M. Delbianco, L. Lamarque, B. K. McMahon, E. R. Neil, R. Pal, D. Parker, J. W. Walton and J. M. Zwier, Dalton Trans. , 201 5, 44 , 4791 -4803. 2. Roles and responsibilities of inter mediaries: Fighting counterfeiting and piracy in the supply chain, International Chamber of Commerce, Paris, 2015. 3. A. T. Frawley, R. Pal and D. Parker Chem. Commun . 2016, in press; DOI 10.1039/c6cc07313a . Download PDF
On: February 15, 2017 From: 15h30 To: 16h30View talk
Speaker: Neil Robertson (Edinburgh)
New Materials for Hybrid Photovoltaics and Photocatalysis The talk will give an account of our recent work in the development of new materials for solar energy conversion, including photovoltaics and photocatalysis. Perovskite solar cells (PSCs) have brought about a paradigm shift in efficiencies of solution -processed photovoltaics, rising recently to around 22%. Triarylamine (TAA) -based materials, especially spiro -OMeTAD, have been the most promising hole -transport m aterials (HTM) for these devices, however Spiro -OMeTAD is one of the most costly layers of the PSCs. Considering this, we have prepared novel triarylamines with varying oxidation potentials based on a low -cost alternative to the spiro core of spiro -OMeTAD. Studies in PSCs give excellent performance comparable to that of spiro -OMeTAD and also show straightforward redox tuning of the HTMs. One potential problem with perovskite solar cells is the use of a soluble lead complex in the APbX3 absorber layer (A = e .g. CH3NH3, X = I, mixed I/Br, mixed I/Cl), leading to concerns around toxicity. A possible alternative is to use the non -toxic alternative bismuth, however the Bi(III) oxidation state will lead to different, non -perovskite, stoichiometries compared with P b(II). Strategies are therefore required to achieve 3 -dimensional charge transfer without the perovskite structure. We have explored ABiI4 absorbers featuring edge -sharing BiI6 octahedra forming a chain structure with A = an aromatic anion. Short I…I and I …A contacts give rise to pseudo 3 -dimensional structure. Preliminary studies of these as absorbers in solar cells show working cells with efficiency that, although low, is comparable with the best among the other small number of Bi -halide materials studied so far. Using materials related to these photovoltaic systems, we have also studied photocatalysis, aimed at the purification of water. According to the World Health Organisation, 748 million people rely on unimproved water sources, and The United Nations has stated that in 15 years there will be a global fresh water shortfall of 40%. Photocatalysis can lead to the mineralisation of organic pollutants and the destruction of bacteria through high -energy holes and electrons generated under irradiation leadin g to reactive oxygen species such as the hydrolyl radical. The most common photocatalyst TiO2 however, only absorbs in the UV region, shows rapid electron -hole recombination and is typically used in a powder form necessitating separation at the end of its use. To address these issues we use a TiO2 -BiOI thin -film heterojunction structure and have successfully demonstrated the destruction of model organic pollutants. Download PDF
On: February 22, 2017 From: 15h30 To: 16h30View talk
Cond Mat Seminars
Speaker: S. Taylor / D. Biwas / J. Feng (St Andrews)
We have 3 speakers from St Andrews giving their March Meeting talks.
Correlated Noise in Cold Atom Quantum Simulation
We point out that, when a Hubbard model is simulated by an optical-lattice system with noise in the laser controller, there is generically a correlation between the fluctuations of the hopping amplitude, J, and those of the on-site repulsion, U. We analyse a toy model of such correlated noise. We also show, in a more realistic model, that such correlations lead to a non-trivial ramp-time-independent value of the fidelity in the case of strong noise.
Anisotropic electronic structure of ReS2
The recent discovery that the optical properties of the group VIIB transition metal dichalcogenides (TMDCs), ReX2 (X=Se,S) depend only weakly on material thickness has opened the possibility to achieve optical response from bulk ReX2 which can only be realised by fabrication of single-layer samples in group VIB semiconducting TMDCs such as MoS2 and WSe2 . While anisotropy in the optical and electronic properties of ReX2 has been extensively studied, the electronic structure which underpins this remains almost completely unexplored experimentally to date. We present direct measurements of the electronic structure of ReS2 from angle resolved photoelectron spectroscopy. Through this, we uncover an intriguing energy dependence of the underlying electronic structure anisotropy. Particularly we find that the states at the valence band top are rather three dimensional, with the fundamental band gap located away from the Brillouin zone centre. At higher binding energies, the electronic bands become quasi one- dimensional, reflecting the Re chains which form due to a pronounced structural distortion in ReS2.
 S. Tongay, et. al., Nat. Commun. 5, 3252 (2014).
Electronic structure of semi-metallic PtSe2 investigated with spin- and angle-resolved photoemission
The observation of extremely high and non-saturating magnetoresistance has sparked a renewed interest in compensated electron and hole pocket semimetals . Here, we will present direct electronic structure measurements of 1T-structured PtSe2, a transition-metal dichalcogenide (TMD) compound. This was previously predicted to be semi-metallic with co-existing electron and hole pockets making up its the Fermi surface , but the details of its band structure have remained elusive to date. Unlike more intensely studied TMDs such as NbSe2/MoS2, its low-energy electronic structure is predicted to be dominated by chalcogen p-orbital, rather than transition-metal d-orbital, derived states. Nonetheless, we will show how spin-orbit coupling in the chalcogen shell still plays a major role in shaping its underlying electronic structure. Combining spin- with angle-resolved photoemission spectroscopy, we uncover its bulk electronic structure as well as revealing the formation of a number of topologically-protected states in this system.
 M. N. Ali, et al. Nature 514, 205208 (2014).
 D. Dai, et al. J. Solid State Chem. 173, 114 (2003).
On: March 8, 2017 From: 12h00 To: 13h00View talk
Speaker: Polly Arnold (Edinburgh)
The activation of small, traditionally inert molecules by metal complexes contributes to our fundamental understanding of metal -ligand bonding and can open up new areas of catalysis. We rece ntly reported the first molecules that combine two strongly reducing U III centres in the same molecule, using pyrrole - based macrocycles. Here, we will present new 4f - and 5f -metal complexes of these, and their binding and reductive activation of small mole cules. We will compare their reactivity and present new alternative O -donor systems that can support two -metal -based small molecule reactivity.
References 1. M. S. Dutkiewicz, J. H. Farnaby, C. Apostolidis, E. Colineau, O. Walter, N. Magnani, M. G. Gardiner, J. B. Love, N. Kaltsoyannis, R. Caciuffo, P. L. Arnold Nature Chem. 2016 , 8, 797. 2. J. A. L. Wells, M. L. Seymour, M. Suvova and P. L. Arnold, Dalton Trans. , 2016 , 45 , 16026. 3. J. A. Hlina, J. R. Pankhurst, N. Kaltsoyannis, P. L. Arnold. J. Am. Chem. Soc. 2016 , 138 , 3333. 4. P. L. Arnold, C. J. Stevens, J. H. Farnaby, M. G. Gardiner, G. S. Nichol, J. B. Love, J. Am. Chem. Soc. 2014 , 136 , 10218. 5. P. L. Arnold, J. H. Farnaby, R. C. White, N. Kaltsoyannis, M. G. Gardin er, J. B. Love, Chem. Sci. 2014 , 5, 756. 6. P. L. Arnold, S. M. Mansell, D. McKay, and L. Maron, Nature Chem. , 2012 , 4, 668 . 7. S. M. Mansell, N. Kaltsoyannis, P. L. Arnold, J. Am. Chem. Soc. 2011 , 133 , 9036. Download PDF
On: March 15, 2017 From: 15h30 To: 16h30View talk