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Theory Group Lunchtime Seminars

Scheduled seminars are listed below.

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  • Theory Seminar
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Thu, Nov 23, '17
1pm - 2pm
Theory Seminar: Elsen Tjhung (Cambridge), Time reversal symmetry breaking in scalar field theory, 1300 in PS1.28

Active matter is a class of non-equilibrium systems where energy is injected to the system continuously by the constituent particles themselves. Many examples of active matter are biological in nature, for example, bird flocks, bacterial suspensions and biological tissues. In the case of bacterial suspensions, the fluid solvent is continuously stirred by the swimming motion of the bacteria, driving it out-of-equilibrium. Active matter is an interesting class of non-equilibrium systems because it often displays large-scale time reversal symmetry breakdown at steady state. For example, when we put an asymmetric gear into a bath full of bacteria, the gear will start to rotate in one direction at steady state. This is a manifestation of large-scale time reversal symmetry breaking because if we reverse the arrow of time, the gear will rotate in the other direction. In this talk, I will present a simple scalar field theory which can capture such large-scale time reversal symmetry breaking.

Thu, Nov 30, '17
1pm - 2pm
Theory Seminar: Stephen Powell (Nottingham), Non-equilibrium classical dynamics and quantum phases of dimer models, 1300 in PS1.28

Dimer models arise as effective descriptions in a variety of physical contexts, and provide paradigmatic examples of systems subject to strong local constraints. Their statistical mechanics exhibits unusual phenomena such as algebraic correlations and deconfinement of monomer excitations. I will first describe the classical non-equilibrium dynamics of the dimer model, where signatures of strong correlations are visible in both global and local observables, and can be understood in terms of one-dimensional strings of high mobility. I will then show how the classical dynamics can be used to study the corresponding quantum problem, and helps to resolve an outstanding puzzle about the structure of the phase diagram.

Thu, Dec 7, '17
1pm - 2pm
Theory Seminar: Paul Goddard (Warwick), Determining the Fermi surface of high-temperature superconductors and other low-dimensional materials, 1300 in PS1.28

I will discuss recent magnetotransport data on an underdoped high-temperature superconductor. To assist with the discussion I will first describe how one goes about mapping the Fermi surface of quasi-two-dimensional materials using high magnetic field measurements, focussing particularly on the technique of angle-dependent magnetoresistance. This will be illustrated using the results of earlier experiments on an organic superconductor, for which a full determination of the Fermi surface was possible. I then will contrast this with the more challenging measurements performed on YBa2Cu3O6+x and explain what conclusions can be drawn in this case.