## Events - Weekly

**April 2013 >>**

Sunday,
April 28 |
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Monday,
April 29 |

David Rand (Warwick U.) "Design principles and dynamics in clocks, cell cycles and signals." Joseph Henry Room · 12:00 p.m.– 1:00 p.m.Condensed Matter Seminar - Jeremy Levy, University of Pittsburgh, Oxide Nanoelectronics On Demand Electronic confinement at nanoscale dimensions remains a central means of science and technology. I will describe a novel method for producing electronic nanostructures at the interface between two normally insulating oxides, LaAlO3 and SrTiO3. These structures and devices are written by a conductive atomic force microscope probe in ambient conditions at room temperature, and can be erased and reconfigured. The spatial dimensions of these structures are comparable to the width of a single-wall carbon nanotube (~2 nm). A wide variety of devices can be created, including nanowires, tunnel junctions, diodes, field-effect transistors, single-electron transistors, superconducting nanowires, and nanoscale THz emitters and detectors. This new, on-demand nanoelectronics platform has the potential for widespread scientific and technological exploitation. PCTS Seminar Room · 1:15 p.m.– 2:30 p.m.High Energy Theory Seminar - Xi Yin, Harvard - A low temperature expansion for supersymmetric matrix quantum mechanics PCTS Seminar Room · 2:30 p.m.– 4:00 p.m. |

Tuesday,
April 30 |

High Energy Theory Seminar - Tolya Dymarsky, Cambridge - On the four-point correlation function of the stress-energy tensor in a CFT We discuss to what extent the full set of symmetries, i.e. conformal symmetry and general diffeomorphisms constraint the form of the four-point correlation functions of stress-energy tensors and conserved currents in a general conformal field theory. The conformal symmetry alone expresses the correlation function of four stress-energy tensors in terms of over six hundred scalar functions of the conformal cross-ratios. Imposing conservation restricts the number of the unconstrained degrees of freedom to 29 scalar function. Similarly, four-point function of the conserved currents depends on just 7 unconstrained scalar functions. The relatively small number of the surviving degrees of freedom raises hopes of formulating conformal bootstrap for these correlates in a self-contained practical way. PCTS Seminar Room · 2:00 p.m.– 3:30 p.m.Special Condensed Matter Seminar, Kai Sun, U of Michigan at Ann Arbor, Kondo insulators: insulator, metal or topological insulator? In the last few decades, various puzzles have emerged in the study of strongly-correlated materials. In a family of strongly-correlated insulators, known as Kondo insulators, one such long-standing puzzle has remained open for over 40 years. In particular, it has been found that some Kondo insulators display strange electrical transport that cannot be understood if one assumes that it is governed by the three-dimensional bulk. In this talk, I show that some Kondo insulators have the right ingredients to be topological insulators, which we called topological Kondo insulators. For a topological Kondo insulator, the low-temperature transport is dominated by the 2D surface rather than the 3D bulk, because the bulk of this material is an insulator while its surface is a topologically-protected 2D metal. This theoretical picture offers a natural explanation for the long-standing puzzle mentioned above. I will also discuss some recent experiments, which indicate that SmB$_6$ (a Kondo insulator) is indeed a bulk insulator with a conducting surface. PCTS Seminar Room · 3:30 p.m.– 5:00 p.m.Math Physics Seminar, Hugo Duminil, U of Geneva, Parafermionic observables in planar Potts models and Self Avoiding Walks In this talk, we will discuss the role of parafermionic observables in the study of several planar statistical physics models. These objects have been introduced recently by Smirnov and Cardy and have been instrumental in Smirnov's proof of conformal invariance of the Ising model. We will explain how they can be combined with combinatorial and probabilistic arguments to compute the connective constant for self-avoiding walks (the n=0 loop O(n)-model) on the hexagonal lattice, and to provide information on the critical phase of the Fortuin-Kasteleyn percolation (a graphical representation of Potts models). As an application of their use for FK percolation, we will show the absence of spontaneous magnetization for the critical planar Potts models with 2, 3 and 4 colors, thus proving part of the conjecture asserting that the planar Potts models undergo a discontinuous phase transition if and only if the number of colors is greater than 4. Jadwin A06 · 4:30 p.m.– 6:00 p.m. |

Wednesday,
May 1 |

Condensed Matter LUNCH Seminar, Chen Fang, PU and Suyang Xu, PU Chen Fang will discuss Crystalline Topological Insulators SuYang Xu will discuss Protected & Broken Symmetries in TIs Jadwin 111 · 12:00 p.m.– 1:00 p.m. |

Thursday,
May 2 |

Hamilton Colloquium Series - Eliot Quataert, University of California-Berkeley - "The Physics of Galaxy Cluster Plasmas" Galaxy clusters are among the largest gravitationally bound objects in the universe. The majority of the baryonic mass in clusters resides in a hot, low density plasma that pervades the intracluster medium (rather than in stars). The heating and cooling processes in this plasma must be understood in order to make progress on a number of key problems in galaxy formation, including the formation of the most massive galaxies and black holes in the universe. An understanding of galaxy cluster thermodynamics is also important for the use of clusters as cosmological probes into the nature of dark matter and dark energy. In this talk, I will describe new insights into the physics of galaxy cluster plasmas, focusing on (1) the physics of novel forms of convection that arise in dilute plasmas, and (2) the subtle imbalance between heating and cooling processes that leads to the development of cool gas embedded in the ambient hot plasma, which is the fuel for star formation and black hole growth at the centers of clusters. I will also describe the importance of this physics for galaxy formation and for the use of clusters as cosmological probes. Jadwin A10 · 4:30 p.m.– 5:30 p.m. |

Friday,
May 3 |

PCTS Series Nonequilibrium Physics with Strongly Interacting Matter and Light presents: Quantum quenches, dynamical transitions and off-equilibr Several mean-field computations have revealed the existence of an out of equilibrium dynamical transition induced by quantum quenching an isolated system starting from its symmetry broken phase. In this talk I shall present results obtained for the quantum O(N) field theory in the large N limit by taking into account dynamical fluctuations at the Hartree-Fock level. I shall derive the critical properties of the dynamical transition beyond mean-field theory and show the existence of diverging time and length-scales, dynamic scaling and aging. Finally, I will discuss a relationship with the coarsening dynamics induced by quenching from the symmetric toward the symmetry broken phase. Giulio Biroli IPhT, Saclay, Paris Jadwin A06 · 2:00 p.m.– 3:15 p.m. |

Saturday,
May 4 |