Physics Colloquia

Rainbows are among the most beautiful sights of nature, and in this lecture I shall show how physics sheds light (literally) on some of their less well-known properties. As well as the origin of the bright primary and the weaker secondary bows, we shall understand their polarization, the dark sky outside, and why we never see a tertiary bow in addition to the primary and secondary rainbows, explained within the ray theory of light. When we introduce wave theory, we can also explain the weak supernumerary bows sometimes seen just inside the primary bow. Of the other optical phenomena we see in the sky, I discuss haloes caused by refraction through ice crystals in clouds, and the more mysterious glories due to scattering by mist. The talk will be illustrated with original (family!) photographs.

Giant gravitational wave detectors now operating in Europe and the USA are only the first step in an ambitious program to detect gravitational waves and use them to explore the universe. Gravitational waves convey the 'sounds' of the universe: vibrations in the fabric of spacetime created by the most exotic and powerful events in the universe, many of which will never be observed in any other way. I will review progress so far, near-term prospects, and long-term expectations for observations from the ground and from space.

In the first part of the talk, I will give a brief overview of different modelling techniques for ferromagnetic nanostructures (Heisenberg and micromagnetism & computational implementation) and their complementary strengths. The second part of the talk will focus on multi-physics micromagnetic simulations of these systems, and the corresponding ongoing work in Southampton.

In 1987, Eli Yablonovitch and Sajeev John independently proposed the idea of a photonic band gap, an event which initiated the burgeoning field of Nanophotonics. Eli's interest was to control spontaneous emission to improve semiconductor lasers, while Sajeev proposed to literally localize photons. Since then, photonic-crystals have become an important class of the large family of metamaterials. In this talk, I will present our latest insights and discuss how one can switch photonic band gap crystals in a fast way. We will also discuss spontaneous emission control with quantum dots, fabrication techniques and cavities in 3D crystals, or effects of unavoidable disorder.

Einstein's disagreements with the usual view of quantum theory were in two problem areas: (1) Realism, locality, determinism, and (2) The macroscopic limit. Both are discussed, together with their significance for more recent developments in quantum theory and quantum information theory, and their continuing relevance today. [from Einstein's struggles with quantum theory, Dipankar Home and Andrew Whitaker, Springer, 2007]

This talk will highlight recent work on star formation in nearby galaxies, with emphasis on the Spitzer SINGS and LVL Legacy surveys, and planned observations with the Herschel KINGFISH survey.

Carbon is an element that is unique in the variety, utility and individuality of its allotropes. Diamond and graphite each have several unique properties that have been exploited in twentieth century science and technology. Against the landscape of the rest of the periodic table, the discoveries of new elemental carbon materials, fullerenes (1985) and nanotubes (1991), stand out as substantial landmarks. Their beauty lies in the topological conversion of flat graphite sheets into curved molecular forms, which can be isolated, studied and exploited by chemists and physicists alike. Logic demands that other non-molecular, topological conversions must exist and could lead to interesting new materials. I shall show that graphite sheets can be engineered to buckle, fold and/or weld together when bombarded by high energy neutrons.

Graphene has recently taken the scientific world by storm since 2004, due to its rather exotic way in which charge carriers conduct electricity. We investigate carrier interference in graphene by studying weak localisation and conductance fluctuations, both in monolayers and bilayers. Although the two systems are different in their energy spectrum (massless fermions in monolayer and massive in bilayer), they both have chiral charge carriers. This makes interference very different from that in conventional 2D structures, controlled by elastic scattering mechanisms. Our study is complemented by atomic force microscope imaging of the graphene surface. We find that graphene is not flat but has ripples across the surface that can stretch the crystal bonds and contribute to the elastic scattering we see in the electrical measurements.