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Viewing upcoming talks containing the keyword: 3
Physics and Astronomy Colloquia
Speaker: Dr Amalia Coldea (University of Oxford)
Iron-based superconductors have attracted significant scientific interest in condensed matter physics  due their potential practical application and theoretical challenge in unifying their superconducting properties origination from a multi-band electronic system under a single overarching theory. Among the different classes of compounds, FeSe is structurally the simplest iron-based superconductor but one of the most intriguing electronically, with extreme tunability in its electronic and superconducting properties. With a superconducting transition of 9K, FeSe undergoes a structural transition around 87K but does not order magnetically at any temperature. Furthermore, it shows a strong increase of its superconducting transition temperature towards 40K under applied pressure, or by intercalating with various organic and non-organic elements between its van-der Waals layers as well as by doping its surface.
I will discuss the evolution of the electronic structure of FeSe and provide evidence that its structural transition is electronically driven. Using high-resolution ARPES data, we track the Fermi surface deformation from four-fold to two-fold symmetry across the structural transition, as a result of the dramatic splitting of bands with dxz and dyz character in the presence of strong electronic interactions . Our elastoresistance measurements on FeSe show the divergence of the nematic susceptibility, when approaching the structural transition, supporting the electronically-driven scenario for this transition . I will present the details of the multi-band Fermi surface of FeSe based on ARPES, quantum oscillations and magnetotransport data in high magnetic fields [2,3]. I will also discuss the effect of chemical pressure on FeSe, using isovalent substitution of S onto the Se site, which subtly modifies the electronic structure of FeSe and induces a suppression of the structural transition temperature using ARPES  and quantum oscillations studies.
On: November 6, 2015 From: 10h00 To: 11h00View talk
What are Extrasolar planets made of? Molecular line lists for hot atmospheres (Joint EaStCHEM/Physics Colloquium)
Speaker: Jonathan Tennyson (UCL)
Over two thousand extrasolar planets (exoplanets) have been discovered and they appear to be ubiquitous. Attention is therefore turning to questions concerning what are their chemical and thermal composition and, ultimately, whether they might support life. Methods are now available to probe exoplanet atmospheres using the light of their host star. However most of the exoplanets detected so far are hotter than the earth. This means that understanding and characterising their atmospheres requires a detailed knowledge of how the molecules in their atmospheres absorb light over an extended temperature range. The European Research Council-funded ExoMol project aims to produce comprehensive line lists for all molecules thought to be important in the atmospheres and appropriate over an extended range of temperatures. For many systems these line lists are huge so the task can only attempted theoretically. Our method is to use high quality first principles quantum, where appropriate tuned to laboratory experimental data. Progress on this project and the related topic of obtaining high resolution exoplanet spectra will be discussed.
On: November 13, 2015 From: 10h00 To: 11h00View talk
Speaker: Sir Fraser Stoddart (Northwestern)
The Nature of the Mechanical Bond
Department of Chemistry, Northwestern University, Evanston, IL 60208
The emergence of the mechanical bond during the past 25 years is giving chemistry a fillip in more ways than one. While its arrival on the scene is already impacting materials science and molecular nanotechnology, it is also providing a new lease of life to chemical synthesis where mechanical bond formation occurs as a consequence of the all-important templation orchestrated by molecular recognition and self-assembly processes. The way in which covalent bond formation activates noncovalent bonding interactions, switching on molecular recognition that leads to self-assembly and the template-directed synthesis of mechanically interlocked molecules—of which the so-called catenanes and rotaxanes may be regarded as the prototypes—has introduced a level of integration into chemical synthesis that has not previously been attained jointly at the supramolecular and molecular levels. The challenge now is to carry this level of integration, already achieved during molecular synthesis, beyond relatively small molecules into the realms of precisely functionalized extended molecular structures and aggregated superstructures that perform functions in a collective manner as the key sources of instruction, activation and performance in multi-component integrated devices.
Following a general introduction to the mechanical bond, my lecture will highlight the following topics – namely (1) radical chemistry, involving multiple viologens, and how it has been exploited in more recent times to template the formation of foldamers and mechanical bonds in both rotaxanes and catenanes leading, in some instances, to the formation of persistent organic radicals in mechanically interlocked molecules (MIMs) and (2) artificial molecular pumps based on flashing ratchet mechanisms that rely on the formation of radical and mixed valence dimers in a reducing medium and subsequently Coulombic repulsions on oxidation in order to perform work away-from-equilibrium on their environments. My lecture will conclude with (a) a discussion of how stereochemistry controls hydrogel formation, (b) a description of how a lock-and-key fit provides a new way to isolate gold and (c) how covalent capture leads to the development of a supramolecular encryption procedure and the formation of 2D-supramolecular polymer films.
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“From supramolecular to systems chemistry: Complexity emerging out of simplicity,” Angew. Chem. Int. Ed. 2012, 51, 12902–12903.
“Putting mechanically interlocked molecules (MIMs) to work in tomorrow’s world,” Angew. Chem. Int. Ed. 2014, 53, 11102–11104.
“Radically enhanced molecular recognition,” Nature Chem. 2010, 2, 42–49.
“Folding of oligoviologens induced by radical-radical interactions,” J. Am. Chem. Soc. 2015, 137, 876–885.
“Mechanical bond formation by radical templation,” Angew. Chem. Int. Ed. 2010, 49, 8260–8265.
“A radically configurable six-state compound,” Science 2013, 339, 429–433.
“Great expectations: Can artificial molecular machines deliver on their promise?” Chem. Soc. Rev. 2012, 41, 19–30.
“Relative unidirectional translation in an artificial molecular assembly fueled by light,” J. Am. Chem. Soc. 2013, 135, 18609–18620.
“An artificial molecular pump,” Nature Nanotech. 2015, 10, 547–553.
“Assembly of supramolecular nanotubes from molecular triangles and 1,2-dihalohydrocarbons,” J. Am. Chem. Soc. 2014, 136, 16651–16660.
“A rigid naphthalenediimide triangle for organic rechargeable lithium-ion batteries,” Adv. Mater. 2015, 27, 2907–2912.
“Selective isolation of gold facilitated by second-sphere coordination by α-cyclodextrin,” Nat. Commun. 2013, 4, Article 1855.
“Quantitative emergence of heterorotaxanes by template-directed click chemistry,” Angew. Chem. Int. Ed. 2013, 52, 381–387.
“Tunable solid-state fluorescent materials for supramolecular encryption,” Nat. Commun. 2015, 6, Art
On: November 20, 2015 From: 16h00 To: 17h00View talk
Physics and Astronomy Colloquia
Speaker: Professor Jo Dunkley (University of Oxford)
The Cosmic Microwave Background provides us with a wealth of information about the universe, most recently via measurements of its polarization. It allows us to probe the physics of the early universe, as well as tracing the cosmic web of dark matter through its gravitational lensing signal. I will describe the Atacama Cosmology Telescope in northern Chile, show early results from the experiment and discuss the prospects with upcoming data for testing inflation, neutrino physics, and dark energy. I will also discuss preparations for the upcoming upgrade to Advanced ACTPol, which will map the CMB polarization over half the sky at multiple wavelengths, overlapping many other large optical surveys.
On: November 20, 2015 From: 10h00 To: 11h00View talk