- EaStCHEM Colloquia
- Physics and Astronomy Colloquia
- Irvine Lectures
- Photonics Seminar
- Special Seminars
- Synthesis Seminars
- Cond Mat Seminars
- Organic Semiconductor Centre
- Theoretical Physics Discussion Group
- ScotCHEM Colloquia
- History of Mathematics
- RSC Award Lectures
- Toy List
Viewing upcoming talks containing the keyword: 4
Cond Mat Seminars
Speaker: Kasper Grove-Rasmussen (Niels Bohr Institute, Copenhagen)
I will present a review of our current understanding of the quantum states in a carbon nanotube quantum dot deduced from low temperature transport measurements in parallel and perpendicular magnetic fields. The observed energy spectrum is shown to be ordered in shells of two doublets consistent with a single-particle four-state model including spin-orbit interaction, valley mixing and an orbital g-factor . Furthermore, for certain shells, the two doublets are observed to be differently coupled to the leads, resulting in gate-dependent level renormalization. By comparison to the shell model this is shown to be a consequence of intra-shell valley mixing in the nanotube. Moreover, a parallel magnetic field is shown to reduce this mixing and thus suppress the effects of tunnel-renormalization .
Finally, I will give an idea of our on-going effort on nanotube Cooper pair splitters. We are particular interested in utilizing our understanding of the level structure and spin-orbit coupling presented above to fabricate devices, which are predicted to be ideal for testing the spin entanglement of split Cooper pairs . Experimental results on a bent nanotube Cooper pair splitters will be compared to the requirement for ultimately demonstrating entanglement.
 T. Sand Jespersen, K. Grove-Rasmussen, J. Paaske, K. Muraki, T. Fujisawa, J. Nygård, and K. Flensberg, Nat. Phys. 7, 348 (2011).
 K. Grove-Rasmussen, S. Grap, J. Paaske, K. Flensberg, S. Andergassen, V. Meden, H. I. Jørgensen, K. Muraki, and T. Fujisawa, Phys. Rev. Lett. 108, 176802 (2012).
 B. Braunecker, P. Burset, and A. Levy Yeyati, Phys Rev. Lett. 109, 166403 (2012)
On: November 4, 2015 From: 13h00 To: 14h00View talk
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.
“Mechanostereochemistry,” Pure Appl. Chem. 2010, 82, 1569–1574.
“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
Photoprotection and photoactivation of biomolecules: lessons learned from femtosecond spectroscopy (Video Conference from Edinburgh)
Speaker: Vas Stavros (Warwick)
Photoprotection from harmful UV radiation occurs in many shapes and forms. For example eumelanins in skin provide a natural defence to UV radiation exposure in humans; sunscreens on the other hand provide artificial photoprotection. Combined, detrimental effects such as damage to DNA are largely prevented. However, even when photodamage does occur, photoactivated prodrugs can inhibit further photodamage. The flow of energy involved in photoprotection and photoactivation processes occurs on very short timescales. This talk will introduce some of the techniques that have been developed in our group to probe this energy flow in real time. Example systems recently studied will be presented, ranging from photodissociation of eumelanin building blocks in the gas- and solution-phase, electronic and vibrational dynamics in sunscreens and solvolysis of ruthenium prodrugs.
On: November 25, 2015 From: 15h30 To: 16h30View talk