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Viewing upcoming talks containing the keyword: 17
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
Mechanistic Insights into the Structure-Property Relationship through detailed Crystallographic Studies
Speaker: Mark Senn (University of Oxford )
Engineering a ground state structure to produce a desired physical property is becoming more widespread, particularly in the field of ferroelectrics where the symmetry of the paraelectric parent phase may be intentionally broken by chemical design to lead to a polar distortion, e.g., Ref. 1. Here it is our ability to characterise the structure via crystallographic methods and qualify its average symmetry which allows us to inform the structure-property relationship which underpins this work. I will give two examples from my own research where symmetry analysis of the ground state crystallographic structure has led to mechanistic insight into metal-insulator phase transitions2 and improper ferroelectric mechanisms3.
However, despite the success of this approach, several limitations exist. Firstly, many physical properties such as thermal expansion and superconductivity do not arise solely from the ground state crystal structure but due to excitations and lattice dynamics. Secondly, not all functional materials are fully ordered and their physical properties often arise from so called order-disorder phase transitions. Here, long-range crystallographic symmetry does not reflect the local underlying microscopic mechanism, and it is unclear what insight conventional crystallography can bring. In the second half of my talk I will extend the application of symmetry analysis further to tackle these problems. I will show how we can gain insight into negative thermal expansion though the study of closely competing ground state structures3 and how in the archetypal ferroelectric Barium Titanate we can reconcile the observed order-disorder phase transitions with its long range crystallographic symmetry and its observed macroscopic properties4.
1) A. T. Mulder, N. A. Benedek, J. M. Rondinelli, C. J. Fennie, Adv. Funct. Mater. 23, 4810–4820 (2013).
2) M.S. Senn, J.P. Wright, and J.P. Attfield, Nature 481, 173 (2012).
3) M.S. Senn, A. Bombardi, C.A. Murray, C. Vecchini, A. Scherillo, X. Luo, and S.W. Cheong, Phys. Rev. Lett. 114, 23 (2015).
4) M.S. Senn, D.A. Keen, T.C.A. Lucas, J.A. Hriljac, and A.L. Goodwin, http://arxiv.org/abs/1512.03643 (2015).
On: January 22, 2016 From: 14h00 To: 15h30View talk
Physics and Astronomy Colloquia
Speaker: Dr Paul van Kampen (Dublin City University, Centre for Laser Plasma Research)
Electromagnetism is a challenging topic to teach and to learn. For example, students often find it difficult to distinguish between force and field, to understand electromagnetic induction. It is well known that many students struggle to apply mathematics in their study of physics in general and in electromagnetism in particular.
In this talk I will outline how systematic inquiry into how students learn physics (i.e., Physics Education Research) has identified common difficulties, and I will illustrate instructional materials that help students overcome them.
On: January 29, 2016 From: 10h00 To: 11h00View talk
Speaker: Elena Besley (Nottingham)
There are many instances in everyday life where small particles can acquire an electrical charge of the same sign. Examples include aerosol and water droplets in clouds, dust particles in space, toner particles in ink-jet printers, and suspensions of colloidal particles. As the particles carry a charge of the same sign, either positive or negative, they are expected to repel one another; however, under certain circumstances their interaction can be strongly attractive. For conducting particles, this effect was identified by William Thomson (later Lord Kelvin) who in 1845 developed a theory showing that the attraction is due to differences in the magnitude of the image charges induced in particles in cases where either their size or charge differs.1
Until recently there was no stable mathematical solution to the fundamental problem of calculating the electrostatic interaction between charged particles of dielectric material, mainly due to significant mathematical complexity of the problem. To date a variety of solutions have been offered, many of which present mathematical derivations with limited applicability, numerical complications or poor convergence at short particle separations.
I will report a comprehensive theory2,3 with universal relevance to the electrostatic properties of closely interacting particles of arbitrary size and charge.4-7 Calculations of surface charge density provide evidence of the physical effects, which cause polarisable particles carrying the same sign of charge to attract one another. The results show that attraction requires a mutual polarisation of charge, leading to regions of negative and positive surface density, at short separation distances. In this talk, the new theory will be discussed together with its relevance across multiple disciplines involving interactions of small particles. Our explanation of how particles interact with one another may also contribute to the design of thin films and surface assemblies with novel properties.
1. Thomson, W. (Lord Kelvin), J. Math. Pures Appl., 10: 364 (1845); J. Math. Pures Appl., 12: 256 (1847)
2. Bichoutskaia E., Boatwright A. L., Khachatourian A., Stace A. J., J. Chem. Phys., 133: 024105 (2010)
3. Khachatourian, A., Chan, H.-K., Stace, A. J., Bichoutskaia, E., J. Chem. Phys., 140: 074107 (2014)
4. Stace, A. J., Boatwright, A. L., Khachatourian, A., Bichoutskaia, E., J. Coll. Inter. Sci., 354: 417 (2011)
5. Stace, A. J., Bichoutskaia, E., Phys. Chem. Chem. Phys., 13: 18339 (2011)
6. Stace, A. J., Bichoutskaia, E., Soft Matter, 8: 6210 (2012)
7. B. Lindgren, E., Chan, H.-K., Stace, A. J., Besley, E. Perspective Article, Phys. Chem. Chem. Phys.
DOI: http://dx.doi.org/10.1039/C5CP07709E (2016)
On: March 9, 2016 From: 15h30 To: 16h30View talk