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Bristol, United Kingdom

Humpert A.,University of Warwick | Allen M.P.,University of Warwick | Allen M.P.,Hh Wills Physics Laboratory
Physical Review Letters | Year: 2015

We show, by molecular simulation, that for a range of standard, coarse-grained, nematic liquid crystal models, the director bend fluctuation is a propagating mode. This is in contrast to the generally accepted picture of nematic hydrodynamics, in which all the director modes (splay, twist, bend, and combinations thereof) are overdamped. By considering the various physical parameters that enter the equations of nematodynamics, we propose an explanation of this effect and conclude that propagating bend fluctuations may be observable in some experimental systems. © 2015 American Physical Society. Source


Foster D.,Hh Wills Physics Laboratory | Krusch S.,University of Kent
Nuclear Physics B | Year: 2015

In this paper, we present a detailed study of Skyrmion-Skyrmion scattering for two B=. 1 Skyrmions in the attractive channel where we observe two different scattering regimes. For large separation, the scattering can be approximated as interacting dipoles. We give a qualitative estimate when this approximation breaks down. For small separations we observe an additional short-range repulsion which is qualitatively similar to monopole scattering. We also observe the interesting effect of "rotation without rotating" whereby two Skyrmions, whose orientations remain constant while well-separated, change their orientation after scattering. We can explain this effect by following preimages through the scattering process, thereby measuring which part of an in-coming Skyrmion forms part of an out-going Skyrmion. This leads to a new way of visualising Skyrmions. Furthermore, we consider spinning Skyrmions and find interesting trajectories. © 2015 The Authors. Source


Berry M.V.,Hh Wills Physics Laboratory | Shukla P.,Indian Institute of Technology Kharagpur
European Journal of Physics | Year: 2011

The spin of a top can be regarded as a fast variable, coupled to the motion of the axis which is slow. In pure precession, the rotation of the axis round a cone (without nutation), can be considered as the result of a reaction from the fast spin. The resulting restriction of the total state space of the top is an illustrative example, at graduate-student level, of the general dynamical concept of the slow manifold. For this case, the slow manifold can be calculated exactly, and expanded as a series of reaction forces (ofmagnetic type) in powers of slowness, corresponding to a modified precession frequency. The forces correspond to a series for the Hannay angle for the fast motion, describing the location of a point on the top. © 2011 IOP Publishing Ltd. Source


Le Feber B.,FOM Institute for Atomic and Molecular Physics | Rotenberg N.,FOM Institute for Atomic and Molecular Physics | Beggs D.M.,FOM Institute for Atomic and Molecular Physics | Beggs D.M.,Hh Wills Physics Laboratory | Kuipers L.,FOM Institute for Atomic and Molecular Physics
Nature Photonics | Year: 2014

Control of light-matter interactions at the nanoscale has advanced fields such as quantum optics, photovoltaics and telecommunications. These advances are driven by an improved understanding of the nanoscale behaviour of light, enabled by direct observations of the local electric fields near photonic nanostructures. With the advent of metamaterials that respond to the magnetic component of light, schemes have been developed to measure the nanoscale magnetic field. However, these structures interact not only with the magnetic field, but also with the electric field of light. Here, we demonstrate the essential simultaneous detection of both electric and magnetic fields with subwavelength resolution. By explaining our measurements through reciprocal considerations, we create a route towards designing probes sensitive to specific desired combinations of electric and magnetic field components. Simultaneous access to nanoscale electric and magnetic fields will pave the way for new designs of optical nanostructures and metamaterials. © 2013 Macmillan Publishers Limited. All rights reserved. Source


Royall C.P.,Hh Wills Physics Laboratory | Royall C.P.,University of Bristol | Royall C.P.,Center for Nanoscience and Quantum Information | Williams S.R.,Australian National University
Physics Reports | Year: 2015

Amorphous solids, or glasses, are distinguished from crystalline solids by their lack of long-range structural order. At the level of two-body structural correlations, glassformers show no qualitative change upon vitrifying from a supercooled liquid. Nonetheless the dynamical properties of a glass are so much slower that it appears to take on the properties of a solid. While many theories of the glass transition focus on dynamical quantities, a solid's resistance to flow is often viewed as a consequence of its structure. Here we address the viewpoint that this remains the case for a glass. Recent developments using higher-order measures show a clear emergence of structure upon dynamical arrest in a variety of glass formers and offer the tantalising hope of a structural mechanism for arrest. However a rigorous fundamental identification of such a causal link between structure and arrest remains elusive. We undertake a critical survey of this work in experiments, computer simulation and theory and discuss what might strengthen the link between structure and dynamical arrest. We move on to highlight the relationship between crystallisation and glass-forming ability made possible by this deeper understanding of the structure of the liquid state, and emphasise the potential to design materials with optimal glassforming and crystallisation ability, for applications such as phase-change memory. We then consider aspects of the phenomenology of glassy systems where structural measures have yet to make a large impact, such as polyamorphism (the existence of multiple liquid states), ageing (the time-evolution of non-equilibrium materials below their glass transition) and the response of glassy materials to external fields such as shear. © 2014 Elsevier B.V. Source

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