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Durham University

Centre for Materials Physics

Past Seminars

Seminars are usually held on (check the details for venue), but you should check the seminar details for exceptions.

Quantum effects in muon spin spectroscopy

Presented by Dr. Matjaž Gomilšek, Jožef Stefan Institute, Ljubljana, Slovenia

22 July 2020 13:00 in CMP seminar via Zoom

Muon spin relaxation and rotation (muSR) is a powerful technique for probing local magnetic fields in a variety of materials via the precession of an implanted muon’s spin. Among its many advantages is exquisite sensitivity to small internal fields and a unique, broad frequency window. However, the interpretation of experimental muSR results is often complicated by an a priori unknown muon position, possible distortions of the local crystal structure, as well as quantum muon effects such as muon zero-point motion and quantum tunnelling. While there has recently been a lot of work addressing these issues in the classical, point-particle approximation via large-scale ab initio density functional theory (DFT) calculations, the effects of quantum muon motion have received substantially less attention, even though they are often expected to be substantial.
In this talk I will present our recent progress towards incorporating the effects of fully-quantum muon motion into ab initio DFT calculations via path-integral molecular dynamics (PIMD). I will demonstrate that common quantum-muon approximation schemes such as the harmonic approximation, various adiabatic schemes, and even muon–nuclear separability ansätze (i.e. the assumption of no quantum entanglement between muon and nuclear positions) all fail to describe real quantum muon motion due to the low muon mass, which can strongly amplify quantum motion effects. I will also present some recent measurements of quadrupolar level-crossing resonance (QLCR) muon spectra on solid nitrogen and our ab initio modelling of them via DFT+PIMD, and demonstrate that the shifts of the observed resonances from classical predictions can be explained by incorporating the effects of fully-quantum muon motion.

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Spin crossover materials, a playground for many-body physics: antiferroelastic order, spin-state ice, deconfined quasiparticles, and emergent gauge fields

Presented by Prof. Ben Powell, The University of Queensland, Australia

15 July 2020 10:00 in
Meeting ID: 286 750 9085

Spin crossover occurs in molecules where two electronic states (high-spin and low-spin) are close enough in energy that one can change the electronic state by temperature, magnetic field, light-irradiation, etc. In crystals such molecules interact via elastic forces and form beautiful patterns of high- and low-spin molecules, known as antiferroelasticity. I will show that a simple model for this, based on balls and springs, can be mapped exactly to an Ising model with long-range interactions. Solving this model allows one to explain which different antiferroelastic orders are observed in which families of materials, and why [1]. On frustrated lattices we predict a new phase of matter: spin-state ice. The low-energy physics of this phase is described by an emergent U(1) gauge field (similar to electromagnetism) and the low-energy excitations carry a fractionalised spin midway between the high-spin and low-spin states (that behave analogously to charged particles) [2]. This is an example of a Coulomb phase. Unlike other Coulomb phases in spin ice, water ice, and some spin liquids, the unique nature of spin crossover compounds gives rise to multiple Coulomb phases in the same material that can be tuned between with temperature alone.

[1] J. Cruddas and B. J. Powell, Structure-property relationships and the mechanisms of multistep transitions in spin crossover materials and frameworks, arXiv:2006.03255

[2] J. Cruddas and B. J. Powell, Spin-state ice in elastically frustrated spin-crossover materials, J. Am. Chem. Soc 141, 19790 (2019).

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Nonlinear optics in dielectrics from first-principles

Presented by Dr Myrta Grüning, Queen's University, Belfast

12 December 2018 13:00 in PH30

I review a first-principles real-time approach to calculate nonlinear optical properties in dielectrics [1] and showcase results obtained with this approach for the second- and third-harmonic generation and two-photon absorption in bulk crystals, 2D materials and nanostructures [2,3,4,5] at different level of theory [6,7].

[1] C. Attaccalite and M. Grüning Phys. Rev. B 88, 235113 (2013)
[2] Claudio Attaccalite, Myrta Grüning, Hakim Amara, Sylvain Latil, François Ducastelle Phys. Rev. B 98, 165126
[3] C. Attaccalite, E. Cannuccia, and M. Grüning Phys. Rev. B 95, 125403
[4] C. Attaccalite, A. Nguer, E. Cannuccia, and M. Grüning Phys. Chem. Chem. Phys. 17 9533
[5] M. Grüning and C. Attaccalite Phys. Rev. B 89, 081102(R); Phys. Rev. B 90, 199901 (2014)
[6] M. Grüning, D. Sangalli, and C. Attaccalite Phys. Rev. B 94, 035149; M. Grüning and C. Attac-
calite Phys. Chem. Chem. Phys., 2016,18, 21179-21189
[7] C. Attaccalite, M. Grüning, and A. Marini Phys. Rev. B 84, 245110

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Presented by Prof. Eiji ÅŒsawa, Toyohashi University of Technology and NanoCarbon Research Institute, Ueda, Japan

Emeritus Professor of Computational Chemistry at Toyohashi University of Technology, Japan, noted for his prediction of the C60 molecule in 1970.

5 December 2018 13:00 in PH30

'One of the longest pending problems in science, identification of detonation nanodiamond (DND) discovered in 1963, is finally solved. The notorious tight aggregation in DND could be destroyed by attrition milling assisted by Wigner-Seitz theory of interparticle distance, Taguchi’s method of quality engineering and an interpretation of LDI-TOF-MS. The primary particles of DND, with diameter of 2.6±0.5nm, proved to have graphene oxide patches on the surface, extensively disordered diamond phase near the surface, and a cube-shaped diamond single crystal consisting of exactly 1000 carbon atoms. Total number of carbon atoms in a DND is predicted to be 1670 by both SCC-DFTB calculations and by mass analysis. DND is by no means a simple nano-version of large diamond crystals, but a novel hybrid nano-carbon consisting of "sp2, sp2+x (0 We are currently exploring its applications taking advantage of high sphericity, hardness and chemical stability in DND. In this lecture two of the most promising experiments will be mentioned: (1) toughening of solid materials by dispersing DND, (2) and generation of zero-friction lubrication liquid (DND dissolves well in water and a few organic solvents like ethylene glycol EG). Taking advantage of these remarkable results we will briefly talk about a realistic plan to reduce emission of green-house gases by stopping the abuse of steel for transportation equipment like cars and airplanes. This goal may be reached by replacing steel with, for an example, DND-dispersed plastics like PET. Moving machines made from the tough plastics may be lubricated by, for an example with dilute DND solution in EG, wherein DND particles work as rolling nano-spacers to produce virtually frictionless systems. Steel machines and lubrication oils are the last giant ‘necessity evils’ still wandering in our modern society.'

'Eiji Osawa is emeritus professor of computational chemistry at Toyohashi University of Technology, Japan, noted for his prediction of the C60 molecule in 1970. Osawa received his Masters of Engineering in chemistry from Kyoto University Department of Industrial Chemistry and then became an engineer at Teijin Co. Ltd. In 1964, he returned to Kyoto University and earned a Doctorate of Engineering in chemistry. After three years of postdoctoral work at the University of Wisconsin, Princeton University and the State University of New York at Stony Brook, in 1970 he became an assistant professor at Hokkaido University. In 1990, Osawa became a full professor at Toyohashi University of Technology, where he retired in 2001. Upon his retirement, assisted by Futaba, Co., Ltd., Osawa started the research and development company Nano-Carbon Research Institute, Ltd.'

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Presented by Dr. Laura Fumagalli, Manchester University

6 June 2018 13:00 in Ph8

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Presented by Dr Jonathan White, PSI

16 May 2018 13:00 in Ph8

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Presented by Prof. Feliciano Giustino, Oxford University and CornellUniversity

2 May 2018 13:00 in Ph8

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Carbon Nanotube-Based Lyotropic Liquid Crystal Microdroplets in Bulk and on Solid Surfaces

Presented by Prof. Paul van der Schoot, Department of Applied Physics, Eindhoven Technical University, Eindhoven (NL)

25 April 2018 13:00 in ph30

Dispersions of long, rod-like particles such as carbon nanotubes are known to form spindle-shaped,
cylindrically symmetric elongated nematic liquid crystalline droplets in coexistence with the isotropic phase.
Their shape and director field structure depends on the size of the drops, the interfacial tension, anchoring
strength and elastic constants. In contact with a wall, the droplets become more elongated due to the effects of line tension.
By visualising hundreds of nematic droplets of carbon nanotubes dissolved in chlorosulfonic acid and applying
elasticity theory to fit the data, we extract information on the elastic and surface properties of the droplets.
For sessile drops we find that the ratio of the line tension and the interfacial tension for this
particular system equals −0.84 ± 0.06 μm. This ratio is 2 orders of magnitude larger than what has been
reported for conventional fluids, in agreement with scaling arguments.

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Presented by Dr Ioanna Theodorakopoulos, NHRF Athens, Greece

21 March 2018 13:00 in TBA

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Presented by Prof. Hair Srikanth, University of Florida, USA

15 March 2018 13:00 in PH30

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Presented by Dr Isis Theophilou, MPI Hamburg, Germany

7 March 2018 13:00 in PH30

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Presented by Dr Aidan Brown, University of Edinburgh

28 February 2018 13:00 in PH30

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Presented by Dr Basile Curchod, Chemistry, Durham University

14 February 2018 13:00 in OC218

What happens to a molecule once it has absorbed UV or visible light? How does the molecule release or convert the extra-energy it just received? Answering these questions clearly goes beyond a pure theoretical curiosity, as photochemical and photophysical processes are central for numerous domains like energy conversion and storage, radiation damages in DNA, or atmospheric chemistry, to name a few.

Ab initio multiple spawning (AIMS) is a theoretical tool that aims at an accurate yet efficient in silico description of photochemical and photophysical processes in molecules. AIMS describes the excited-state dynamics of nuclear wavepackets using adaptive linear combinations of frozen Gaussians.[1] In this talk, I intend to survey some recent developments and applications of the AIMS technique.

An important feature of the AIMS formalism is its flexibility, which permits the addition of critical physical processes for a realistic simulation of photochemical processes. We for example recently included in AIMS spin-orbit coupling[2] and the effect of an external electric field,[3] leading to two new schemes called Generalized AIMS (GAIMS) and eXternal Field AIMS (XFAIMS). We also proposed a simple yet rational approximation to AIMS termed Stochastic-Selection AIMS (SSAIMS), which allows decreasing the computational cost of an AIMS dynamics substantially.[4]

To study the excited-state dynamics of large molecules, we also recently interfaced AIMS with the GPU-based electronic structure code TeraChem. Combining the accuracy of AIMS with the efficiency of GPU-accelerated electronic structure calculations (LR-TDDFT or SA-CASSCF) allows indeed for a significant step forward in the simulation of nonadiabatic events, as it pushes the boundaries of the well-known compromise between efficiency and accuracy imposed by the computational cost of such dynamics. Thanks to this new interface, we could investigate the nonadiabatic dynamics of different medium-size organic molecules important in biological chemistry, organic electronics, and atmospheric chemistry.[5-7]

[1] B. F. E. Curchod and T. J. Martínez, “Ab Initio Nonadiabatic Quantum Molecular Dynamics”, Chem. Rev., in press (2018).

[2] B. F. E. Curchod, C. Rauer, P. Marquetand, L. González, and T. J. Martínez, “GAIMS – Generalized Ab Initio Multiple Spawning for both Internal Conversion and Intersystem Crossing Processes”, J. Chem. Phys., 144, 101102 (2016).

[3] B. Mignolet, B. F. E. Curchod, and T. J. Martínez, “XFAIMS – eXternal Field Ab Initio Multiple Spawning for Electron-Nuclear Dynamics Triggered by Short Laser Pulses”, J. Phys. Chem, 145, 191104 (2016) .
[4] B. F. E. Curchod, W. J. Glover, and T. J. Martínez, “SSAIMS – Stochastic-Selection Ab Initio Multiple Spawning for Efficient Nonadiabatic Molecular Dynamics”, in preparation (2018).
[5] J. W. Snyder Jr., B. F. E. Curchod, and T. J. Martínez, “GPU-Accelerated State-Averaged CASSCF Interfaced with Ab Initio Multiple Spawning Unravels the Photodynamics of Provitamin D3”, J. Phys. Chem. Lett., 7, 2444 (2016).
[6] B. Mignolet, B. F. E. Curchod, and T. J. Martínez, “Rich Athermal Ground-State Chemistry Triggered by Dynamics through a Conical Intersection”, Angew. Chem. Int. Ed., 55, 14993 (2016).
[7] B. F. E. Curchod, A. Sisto, and T. J. Martínez, “Ab Initio Multiple Spawning Photochemical Dynamics of DMABN Using GPUs”, J. Phys. Chem. A, 121, 265 (2017).

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Electronics with sustainable materials

Presented by Prof. Elvira Fortunato , i3N/CENIMAT, Department of Materials Science from Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal

5 April 2017 13:00 in Ph8

10 years ago it was pure science fiction the notion of fully transparent, flexible and conformable displays, like those used by T. Cruise in the Minority Report movie fully based on materials away from silicon! Thanks to the Hollywood vision and the hard work of scientists this is now a reality. After the huge success and revolution of transparent electronics where we must highlight the low process temperatures that turn possible the use of low cost eco-friendly materials and substrates such biopolymer or paper, where CENIMAT is pioneer and with the worldwide interest in displays/smart interfaces where metal oxide thin films have proved to be truly semiconductors, display backplanes have already gone commercial due to the huge investment of several high profile companies such: SHARP, SAMSUNG, LG, BOE, in a very short period of time. In this presentation we will show some of the developments done in terms of metal oxide based-TFTs as well as TCOs produced either by conventional PVD techniques as well as by new low temperature solution processes. We can anticipate that the metal oxide based industry will be in the near future a so-called multi billion euro market similar to what is observed with the pharmaceutical industry, due to the number of different applications that can serve, ranging from information technology, biotechnology/life sciences and energy to food/consumer products.
On the other hand, 5 years ago paper electronics was also pure science fiction, but today we have already several paper-based electronics like integrated circuits, supercapacitors, batteries, fuel cells, solar cells, transistors, microwave electronics, digital logic/computation, displays, force-sensing MEMS, user interfaces, transparent substrates, substrates with high strength, wearable devices, and new rapid diagnostic test sensors. These devices with their associated physics and processing will play an important and relevant to our society ongoing efforts to in environmental sustainability, safety, communication and health.

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Ultrafast and Very Small: Discover Nanoscale Magnetism With Picosecond Time Resolution Using X-Rays

Presented by Dr Hendrik Ohldag, SLAC National Accelerator Laboratory, Menlo Park, California, USA

4 April 2017 13:00 in Sir James Knott Library Ph132

Today’s magnetic device technology is based on complex magnetic alloys or multilayers that are patterned at the nanoscale and operate at gigahertz frequencies. To better understand the behavior of such devices one needs an experimental approach that is capable of detecting magnetization with nanometer and picosecond sensitivity. In addition, since devices contain different magnetic elements, a technique is needed that provides element-specific information about not only ferromagnetic but antiferromagnetic materials as well. Synchrotron based X-ray microscopy provides exactly these capabilities because a synchrotron produces tunable and fully polarized X-rays with energies between several tens of electron volts up to tens of kiloelectron volts. The interaction of tunable X-rays with matter is element-specific, allowing us to separately address different elements in a device. The polarization dependence or dichroism of the X-ray interaction provides a path to measure a ferromagnetic moment and its orientation or determine the orientation of the spin axis in an antiferromagnet. The wavelength of X-rays is on the order of nanometers, which enables microscopy with nanometer spatial resolution. And finally, a synchrotron is a pulsed X-ray source, with a pulse length of tens of picoseconds, which enables us to study magnetization dynamics with a time resolution given by the X-ray pulse length in a pump-probe fashion.
The goal of this talk is to present an introduction to the field and explain the capabilities of synchrotron based X-ray microscopy, which is becoming a tool available at every synchrotron, to a diverse audience. The general introduction will be followed by a set of examples, depending on the audience, that may include properties of magnetic materials in rocks and meteorites, magnetic inclusions in magnetic oxides, interfacial magnetism in magnetic multilayers, and dynamics of nanostructured devices due to field and current pulses and microwave excitations.

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Presented by TBA,

20 June 2016 13:00 in PCL048 (Hogan Lovells lecture theatre, Palatine Centre)

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Is ITER the way? & Study of spin dependent transport for spintronic device applications

Presented by Francis Ridgeon, Oto-obong-Inyang,

6 June 2016 13:00 in OC218

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The physics behind the avian compass & The failure of predictability, and how only top-down descriptions have meaning

Presented by David Graves, Robert Schoonmaker,

23 May 2016 13:00 in OC218

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A beginner's guide to linear stability analysis & DNA (origami) nanotechnology as a powerful dynamic and tunable architecture for plasmonic structure

Presented by Ewan Hemingway, Luca Piantanida,

9 May 2016 13:00 in OC218

Ewan Hemingway: A beginner's guide to linear stability analysis
Luca Piantanida: DNA (origami) nanotechnology as a powerful dynamic and tunable architecture for plasmonic structure

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Confined networks of filaments to model the cytoskeleton

Presented by Kristian Müller-Nedebock, Stellenbosch University

4 May 2016 13:00 in Ph8

Prof. Kristian Müller-Nedebock, visiting as part of the Durham Centre for Soft Matter-Stellenbosch University Newton Fund scheme.

When both stiff polymer chains (and also networks of these chains) are formed in a confined space, the geometry leads to spatially varying segment densities and filament alignment. Molecular dynamics simulations have hinted at interesting related phenomena [Azari, Müller-Nedebock, EPL (2015)]. Insights on such systems might prove useful in scenarios ranging from the filamentous networks in cells to understanding the interactions of polymers with filler particles in rubbers, or copolymers with different flexibilities. In this talk a monomer ensemble technique will be presented [e.g., Pasquali, Percus, Molecular Physics (2009)] which leads to computable profiles for the orientation and density of chains. Moreover, one can merge the technique with a formalism that enables networking interactions [Fantoni, Müller-Nedebock, PRE (2011)], with control over the functionality of the network, ranging from standard cross-linking to tethering of chains to the confining wall. Some of these techniques can be extended to study the properties of non-equilibrium networks

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Presented by Mark Etherington, Rongjuan Huang,

14 March 2016 13:00 in Ph132

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Instabilities and Solitons on Soap Films

Presented by Dr Gareth Alexander, Warwick University

24 February 2016 13:00 in Ph8

Shape and form are hallmarks of soft materials, implicit in their name. I will describe our recent work on characterising morphology and transitions in soap films, both experimental and theoretical. It is well known that the static shapes of soap films can be characterised by minimal surfaces and has also been long appreciated that such surfaces exhibit generic instability. The nature, variety and consequences of these instabilities for the morphology has been studied in detail only for a small number of idealised cases -- the catenoid, helicoid and Meeks Möbius strip surfaces. It is a conjecture of Goldstein et al. that these are representative of all topological transitions. We have developed a series of experiments for soap films spanning (n,n) torus link frames that illustrates a broad range of topological transitions and provides general anecdotal support for their conjecture. On the theoretical side, I will outline a general program for the analysis of instabilities in terms of geometric properties of curves on the surface. In the case of non-orientable strips the instability leads generically to the formation of solitons analogous to those in scalar phi^4 theories, which can be readily demonstrated in simple experiments. This is joint work with Tom Machon, Ray Goldstein and Adriana Pesci.

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Presented by Alexander Blair, Subkhi Sadullah,

22 February 2016 13:00 in Ph132

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Presented by Rangarajan Radhakrishnan, Jack Panther,

8 February 2016 13:00 in Ph132

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Intergroup: Understanding the PhD thesis and viva: myths and regulations

Presented by Del Atkinson ,

25 January 2016 13:00 in Ph132

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CMP Seminar

Presented by Prof Jens Eisert, Free University of Berlin

9 December 2015 13:00 in Ph8

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Intergroup: TBA

Presented by Rahul Chakno, Ethan Miller,

7 December 2015 13:00 in Ph132

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CMP Seminar

Presented by Dr Helen He, University of Durham

2 December 2015 13:00 in Ph8

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CMP Seminar

Presented by Prof Glen McHale, University of Northumbria

25 November 2015 13:00 in Ph8

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Intergroup: TBA

Presented by Joe Troughton, David Hoyle,

23 November 2015 13:00 in Ph132

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CMP Seminar

Presented by Prof Rex Godby , University of York

11 November 2015 13:00 in Ph8

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Intergroup: Why silicon breaks the way it does & How to (try to) build a synthetic molecular motor

Presented by Brian Tanner, Lara Small,

9 November 2015 13:00 in Ph132

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Presented by Aidan Hindmarch,

26 October 2015 13:00 in Ph132

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Presented by Prof Matthew Turner, University of Warwick

14 October 2015 13:00 in Ph8

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Dynamic processes observed by scanning tunneling microscopes: vibrations, diffusions and reactions

Presented by Prof. Werner Hofer, Newcastle University Dean of Research & Innovation,

20 May 2015 13:00 in Ph8


WA Hofer1, JC Polanyi2 and HJ Gao3
1 School of Chemistry, Newcastle University
2 Department of Chemistry, Toronto University
3 Institute of Physics, Chinese Academy of Sciences, Beijing
Dynamic processes in scanning tunneling microscopy (STM) are increasingly the focus of cutting edge research due to their importance for energy conversion and reaction processes. It is in principle possible to study these processes by suitable adaptation of STM theory and a step-by-step analysis of the processes themselves. I shall give several examples where such a detailed understanding is indispensible for a comprehensive understanding e.g. in atomic switching and diffusion processes, in molecular growth processes, condensation reactions, and long range molecular propagation even on reactive surfaces. At the end of my talk I shall demonstrate that careful statistical analysis in combination with high-resolution STM can even lead to surprising new insights into fundamental physics.

Selected references:
WA Hofer, AS Foster and AL Shluger, Theories of Scanning probe Microscopes at the Atomic Scale, Reviews of Modern Physics 75, 1287-1331 (2003)
PG Piva et al., Field regulation of single-molecule conductivity by a charged surface atom, Nature 435, 658-661 (2005)
KR Harikumar et al., Dipole-directed assembly of lines of 1,5-dichloropentane on silicon substrates by displacement of surface charge, Nature Nanotechnology 3, 222-229 (2008)
KR Harikumar et al., Cooperative molecular dynamics in surface reactions, Nature Chemistry 1, 716-721 (2009)
KR Harikumar et al., Directed long-range molecular migration energized by surface reaction, Nature Chemistry 3, 400-408 (2011)
L Liu et al., Reversible Spin Control of Individual Magnetic Molecule by Hydrogen Atom Adsorption, Scientific Reports 3, 1210 (2013)
WA Hofer, Heisenberg, uncertainty, and the scanning tunnelling microscope, Frontiers of Physics 7, 218 - 222 (2012)

Colleagues are welcome to a buffet lunch before the talk, from 12:30 pm at the Bransden Coffee room, where they can meet with the speaker. If you want to meet Prof. Hofer, please email

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Polarisation of cells and soft objects driven by mechanical interactions: Consequences for migration and chemotaxis

Presented by Dr Marco Leoni, Institute Curie, Paris

25 March 2015 13:00 in PH8

We study a generic model for the polarisation and motility of self-propelled soft objects, biological cells or biomimetic systems, interacting with a viscous substrate. The active forces generated by the cell on the substrate are modelled by means of oscillating force multipoles at the cell-substrate interface. Symmetry breaking and cell polarisation for a range of cell sizes naturally "emerge"from long range mechanical interactions between oscillating units, mediated both by the intracellular medium and the substrate. However, the harnessing of cell polarisation for motility requires substrate-mediated interactions. Motility can be optimised by adapting the oscillation frequency to the relaxation time of the system or when the substrate and cell viscosities match. Cellular noise can destroy mechanical coordination between force-generating elements within the cell, resulting in sudden changes of polarisation. The persistence of the cell's motion is found to depend on the cell size and the substrate viscosity. Within such a model, chemotactic guidance of cell motion is obtained by directionally modulating the persistence of motion, rather than by modulating the instantaneous cell velocity, in a way that resembles the run and tumble chemotaxis of bacteria.

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Presented by Branton Campbell, Brigham Young University

11 March 2015 13:00 in PH8

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Presented by Paul Midgley, University of Cambridge

25 February 2015 13:00 in PH8

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Presented by Olivier Pierre-Louis, Universite Claude Bernard Lyon 1

11 February 2015 13:00 in PH8

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Presented by Oleg Kirichek, STFC Rutherford Appleton Laboratory

4 February 2015 13:00 in PH8

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Presented by Paola Verrucchi, Universita' di Firenze

28 January 2015 13:00 in PH8

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Presented by Mike Smith, University of Nottingham

14 January 2015 13:00 in PH8

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Molecular views of electrokinetic phenomena

Presented by Dr Laurent Joly, Institut Lumière Matière, Université Lyon 1, Villeurbanne, France

4 June 2014 13:00 in Ph8

During this presentation, I will give an overview of the work of our group on the description of electrokinetic (EK) phenomena at the molecular level, using molecular dynamics simulations and theoretical modeling [1]. This work enabled us to investigate the limitations of the traditional description of EK phenomena, which relies on the mean-field Poisson-Boltzmann theory of the electric double layer and continuum hydrodynamics for the flow fields. In particular, we showed the crucial contribution of interfacial hydrodynamics to the zeta potential, quantifying the amplitude of electrokinetic phenomena.

Firstly, I will show how the failure of the standard hydrodynamic no-slip boundary condition at the nanoscale can result in a large enhancement of the zeta potential [2,3]. I will then discuss how ionic specificity couples to hydrodynamic slip to generate anomalous EK effects [4,5]. Finally, I will illustrate our approach with a recent work on electrokinetic transport in a soap film covered with ionic surfactants [6].

1. D. M. Huang, L. Joly, C. Cottin-Bizonne, C. Ybert, E. Trizac, L. Bocquet: "Molecular views of electrokinetic phenomena", in "Surface Electrical Phenomena in Membranes and Microchannels", A. Szymczyk (Ed), Research Signpost (2008) ISBN 978-81-7895-326-7.

2. L. Joly, C. Ybert, E. Trizac, L. Bocquet, Phys. Rev. Lett. 93, 257805 (2004).

3. L. Joly, C. Ybert, E. Trizac, L. Bocquet, J. Chem. Phys. 125, 204716 (2006).

4. D. M. Huang, C. Cottin-Bizonne, C. Ybert, L. Bocquet, Phys. Rev. Lett. 98, 177801 (2007).

5. D. M. Huang, C. Cottin-Bizonne, C. Ybert, L. Bocquet, Langmuir 24, 1442 (2008).

6. L. Joly, F. Detcheverry, L. Bocquet, A.-L. Biance, in preparation.

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From physics of lipid membranes to host/pathogen biological processes

Presented by Dr Pietro Cicuta, Department of Physics, Cavendish Laboratory, University of Cambridge

14 May 2014 13:00 in Ph8

Phospholipids form the continuous phase of biological cell membranes; typically they exist as multi-component mixtures. Work over the last decade has highlighted that typical lipid compositions are close to a demixing transition, and this provides a general physical basis for the spontaneous emergence of concentration fluctuations. The first part of the seminar will overview recent work from our lab, showing emergence of non-equilibrium patterns in in-vitro vesicle systems; coexisting phases have different bending rigidities, and this can be exploited to co-localise the more disordered areas onto regions of induced high curvature. The second part of the talk will illustrate examples of complex biological situations that take place when micro-organisms contact the exterior membrane of cells, attempting to invade. We have studied two distinct systems: the malaria parasite invading red blood cells, and Salmonella bacteria invading macrophages (cells of the immune system). In both cases, we will highlight the importance of physical interactions between the small pathogen organisms and the membrane of the host cell.

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Seminar Cancelled.

Presented by Prof. Paul A. Midgley, Department of Materials Science and Metallurgy, University of Cambridge

30 April 2014 13:00 in Ph8

Buffet lunch from 12:30 pm in the Bransden coffee room

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Presented by Dr. Enrico Da Como, University of Bath

19 March 2014 13:00 in Ph8

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Presented by Dr. Steven McVitie, University of Glasgow

5 March 2014 13:00 in Ph8

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Presented by Dr. Johan Mattsson, University of Leeds

19 February 2014 13:00 in Ph8

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Presented by Dr Margarita Staykova, Durham University

5 February 2014 13:00 in Ph8

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The Quantum Mechanics of Nano-confined water

Presented by Prof George Reiter, University of Houston

22 January 2014 13:00 in Ph8

Water is usually regarded as a collection of molecules, weakly interacting through electrostatic forces. Recent work using neutron and x-ray Compton scattering to measure the momentum distribution of the electrons and protons in several systems in which the water is confined on the scale of 20Ã… demonstrate that the ground state of nano-confined water is qualitatively different from the weakly interacting molecule model prediction. The protons delocalize, sometimes in double wells, over distances of .2-.3 Ã…, and the momentum distribution of the valence electrons is profoundly perturbed. Pump probe experiments by others demonstrate that proton transport in the nano-confined ground state is not diffusive. The properties of this state are likely to be essential for the functioning of biological cells and the origins of life, as the distance between elements of the cell is typically 20 Ã….

Lunch in the James Knott Library beforehand at 12:30pm.

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Nanoscale organisation and dynamics of liquids at the interface with solids

Presented by Dr. Kislon Voitchovsky, Durham University

27 November 2013 13:00 in Ph8

Abstract: At the interface with solids, the behaviour of liquid molecules can be strongly affected by local interactions with the surface of the solid. The so-called interfacial liquid tends to be more ordered and denser than bulk liquid, depending on its local affinity for the solid. Interfacial liquid is a key to countless phenomena ranging from electrochemistry, heterogeneous catalysis, wetting, heat transfer, self-assembly processes, folding and function of biomolecules. Despite this ubiquitous importance, little is known about interfaces where the solid exhibit nanoscale complexity, mostly due to a lack of suitable investigation techniques.

Using a novel experimental approach based on atomic force microscopy (AFM), it has become possible to map the molecular organisation of the interfacial liquid and gather quantitative information about its local dynamics. The technique is applied to investigate the lateral arrangement of single ions at the surface of minerals in aqueous solution. Results show that interfacial water can drive ordering and correlation between single metal ions, suggesting intriguing possibilities for charge transfer at along the interface. Alternatively, it is possible to use external electric fields to control the structuring of the interfacial liquid, which in turns guides the organisation of ions at interfaces.

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Enhanced diffusion of tracers in a bath of self-propelled particles

Presented by Dr. Alexander Morozov, University of Edinburgh

13 November 2013 13:00 in Ph8

Recent experiments have shown that micron-size tracer particles in dilute suspensions of either swimming bacteria or synthetic self-propelled particles perform diffusive motion with the diffusion coefficient significantly larger than its thermal value. Several theories have been proposed to explain the origin and magnitude of the enhanced tracer diffusivity. There is now a general agreement that it is proportional to the so-called "active flux" - the product of the swimmers number density and their velocity, but there is no quantitative agreement between theory and experiments.

I will present a detailed theory and simulations of tracers diffusing in bacterial suspensions. Our work confirms the scaling with the active flux, but also unravels new important dependencies on the properties of the velocity field created by the swimmers and their kinematics. I will show how this solves the problem of quantitative disagreement with experimental observations. I will also discuss how the long-range hydrodynamic interaction could have helped the present-day bacterial kinematics to evolve.

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Soft incommensurate spin density wave fluctuations in Fe_{1+x}Te

Presented by Dr Chris Stock, University of Edinburgh

30 October 2013 13:00 in Ph8

Understanding the parent phases of iron based superconductors is a fundamental component towards deriving the mechanism of superconductivity in doped and fluctuating variants. While in the cuprates the high temperature superconducting phase universally derives from a Mott insulator, the case in the iron based systems is not as clear with the parent compounds displaying metallic or even semi metallic behavior. In this talk I will discuss the phase diagram and magnetic fluctuations in arguably one of the simplest iron based superconductors - the monolayer Fe_{1+x}Te system. We have previously mapped out the magnetic and structural phase diagram, as a function of x
using thermodynamic and neutron diffraction techniques and found two regions of collinear and incommensurate magnetic order separated by a tricritical-like point [1,2]. Near this multicritical point, the magnetic structure obtains an incommensurate spin density wave nature as demonstrated by us using polarized neutrons and a series of neutron studies have found that these excitations appear to compete with superconductivity in anion doped variants [3,4]. In this talk I will present neutron inelastic scattering results from reactor and spallation sources and discuss how these evolve with charge doping through interstitial iron x. These results demonstrate a soft incommensurate spin excitation associated the spin density wave vector discussed above which likely competes with superconductivity. Comparisons with doped iron based systems and other superconductors will be made.

[1] E. E. Rodriguez et al. Phys. Rev. B 84, 064403 (2011).
[2] E. E. Rodriguez et al. Phys. Rev. B 88, 165110 (2013).
[3] C. Stock et al. Phys. Rev. B 85, 094507 (2012).
[4] S. Chi et al. Phys. Rev. B 84, 214407 (2011).

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Two transitions in ferromagnets: The role of anisotropy

Presented by Dr. Martin Long, University of Birmingham

16 October 2013 13:00 in Ph8

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Interfacial Phenomena in Soft Matter and Biophysics

Presented by Halim Kusumaatmaja, Durham

26 June 2013 13:00 in Ph30

I will use this opportunity to provide a broad overview of my research interests, both in terms of topics and methods. With this in mind, I will discuss three separate problems. Firstly, I will speak about water-repellent surfaces, particularly how roughness may strongly influence the hydrophobicity of the surface. The second topic draws inspiration from biological membranes. The focus is on phase separation which may occur on the membrane surface or in the aqueous solution encapsulated by the membrane. Finally, colloidal particles trapped at liquid interfaces provide a "simple" model system to study defects on two-dimensional crystals. Interestingly, defects are often unavoidable (even in the ground state) when the interface is curved.

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The Role of Nanoscience and Nanotechnology in Addressing the World's Energy Challenges

Presented by James Dickerson, Brookhaven National Laboratory (US)

17 June 2013 13:00 in Ph30

Lunch will be provided beforehand at 12:30pm in the Bransden Room

Contact Del Atkinson for more information

Tooling Up for Nanoworld: The Magic of Molecular Machines

Presented by Professor David Leigh FRS, University of Manchester

7 May 2013 16:00 in Sir Arnold Wolfendale Lecture Theatre, Calman Learning Centre

Perhaps the best way to appreciate the technological potential of controlled molecular-level motion is to recognise that nanomotors and molecular-level machines lie at the heart of every significant biological process. Over billions of years of evolution nature has not repeatedly chosen this solution for achieving complex task performance without good reason. In stark contrast to biology, none of mankind’s fantastic myriad of present day technologies exploit controlled molecular-level motion in any way at all: every catalyst, every material, every polymer, every pharmaceutical, every chemical reagent, all function exclusively through their static or equilibrium dynamic properties. When we learn how to build artificial structures that can control and exploit molecular level motion, and interface their effects directly with other molecular-level substructures and the outside world, it will potentially impact on every aspect of functional molecule and materials design. An improved understanding of physics and biology will surely follow.

Professor Leigh is the Sir Samuel Hall Professor of Chemistry at The University of Manchester. He
has won a number of major international awards including the 2007 Izatt-Christensen Award for Macrocyclic Chemistry, the 2007 Descartes Prize and the 2007 Feynman Prize for Nanotechnology. He was elected to Fellowship of the Royal Society in 2009 and in 2013 gave the Bakerian Lecture, the Royal Society’s premier lecture in the physical sciences and an annual series that dates back to 1775.

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Room-temperature solid-state masers based on molecular intersystem crossing (ISC)

Presented by Dr Mark Oxborrow, Imperial College, London

1 May 2013 16:00 in Ph30

Like lasers, masers exploit the quantum mechanical process of stimulated emission to amplifier electromagnetic waves - though at microwave frequencies (i.e. around a few GHz) as opposed to optical ones (several hundreds of THz). Since microwave photons individually carry little energy, a maser can amplifier a weak signal whilst imparting very little deleterious (Schawlow-Townes) shot noise onto it. Masers made out of solid-state gain materials such as ruby were invented in the mid. 1950s. They became key to the success of NASA's deep space network, as used for receiving spectacular images of the rings of Saturn back from its distant Voyager 1 & 2 space probes, as well as supporting other missions (like those to Mars) since. But ruby masers can only operate advantageously at liquid-helium temperatures. This prevented their uptake in a great many applications that could have otherwise taken advantage of their superior noise performance. Compared to semiconductor-based amplifiers, which do work - albeit noisily - at room temperature, masers have languished in the backwaters.

In my talk, I shall describe a solid-state maser that does work at room temperature. In contrast to ruby, this new maser's gain medium is an organic mixed molecular crystal, namely p-terphenyl, which is lightly doped with pentacene. Upon photo-exciting the latter species with yellow pump light from a pulsed dye laser, molecular intersystem crossing (ISC) into pentacene's triplet ground state provides a strong population inversion across the upper and lower sub-levels of this state, sufficient for masing at ~1.45 GHz on the TE01δ mode of a high-Q sapphire-loaded cylindrical microwave cavity, with an output (saturation) power of around -10 dBm. As the ISC process provides negative spin temperatures of the order of a few tens of mK, microwaves can in principle be amplified at a residual noise temperature of this same order, even though the maser crystal is at room temperature. In other words: a cryogenic amplifier that isn't. The general prospects of organic masers based on ISC shall be discussed.

Contact Dr. Kevin Weatherill for more information