Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
Dark matter can be a thermal relic exponentially lighter than
the weak scale without being exponentially weakly coupled. I will present
three mechanisms to obtain light thermal dark matter with sizable
self-interactions and couplings to the Standard Model.
Recent findings on quantitative growth patterns have revealed striking generalities across the tree of life, and recurring over distinct levels of organization. Growth-mass relationships in 1) individual growth to maturity, 2) population reproduction, 3) insect colony enlargement and 4) community production across wholeecosystems of very different types, often follow highly robust near ¾ scaling laws. These patterns represent some of the most general relations in biology, but the reasons they are so strangely similar across levels of organization remains a mystery.
Quantum spin ice is a frustrated magnet that displays rich emergent phenomena. For example, the magnetic moments carried by the spins may separate into mobile magnetic charges, producing quantum fractional excitations known as spinons. The spinon moves in a background of disordered spins, and its motion is strongly coupled to the spin background. In this talk, I will demonstrate that the spinon dynamics can be described as a quantum walk with entropy-induced memory.
The ytterbium pyrochlores, Yb2B2O7, are a family of materials with a remarkable diversity in their low-temperature physics. At the heart of their interesting physics is the proximity of their ground states to numerous competing phases. These proximate phases make the Yb pyrochlores very sensitive to perturbations such as pressure and off-stoichiometry. I will present a study of the effects of chemical pressure on the ytterbium pyrochlores, in which substitution of a non-magnetic constituent alters the lattice size and consequently inflicts an internal pressure on the system.
We introduce a new classical spin liquid on the pyrochlore lattice by extending spin ice with further neighbour interactions. This disorder-free spin model exhibits a form of dynamical heterogeneity with extremely slow relaxation for some spins while others fluctuate quickly down to zero temperature. We thus call this state "spin slush", in analogy to the heterogeneous mixture of solid and liquid water.
In this talk, I will describe a new technique—stochastic resonance magnetic force microscopy (SRMFM)—developed in my group for imaging the vortex dynamics in multiply connected superconducting devices. Unlike existing techniques, which directly image vortices, our technique relies on the mechanism of stochastic resonance to image the fluctuations between different vortex configurations.
General relativity is invariant under diffeomorphisms, and
excitations of the metric corresponding to diffeomorphisms
are nonphysical. In the presence of a boundary, though --
including a boundary at infinity -- the Einstein-Hilbert
action with suitable boundary terms is no longer fully
invariant, and certain diffeomorphisms are promoted to
physical degrees of freedom. After briefly describing how
this happens in (2+1)-dimensional AdS gravity, I will
report on work in progress on the asymptotically flat case,
The kagome lattice in a mineral compound "Herbertsmithite" represents structurally the most ideal kagome Heisenberg antiferromagnet known to date. Herbertsmithite does not undergo a magnetic long-range order or spin freezing at least down to ~J/2000. We will present 17-Oxygen and 2-Deuterium single crystal NMR study of Herbertsmithite. We will demonstrate that the ground state of the kagome plane has a spin gap ~ 0.05J [1], and ~5% excess Cu2+ ions occupying the out-of-plane Zn2+ sites are the only defects [2].
A many-body quantum system on the verge of instability between competing ground states exhibits emergent phenomena. Interacting electrons on triangular lattices are likely subjected to multiple instabilities in the charge and spin degrees of freedom, affording diverse phenomena related to the Mott physics. The molecular conductors are superior model systems for studying the Mott physics because of the designability and controllability of material parameters such as lattice geometry and bandwidth by chemical substitution and/or pressure.
Current observations provide precise but limited information about inflation and reheating. Theoretical considerations, however, suggest that the early universe might be filled with a large number of interacting fields with unknown interactions. How can we quantitatively understand the dynamics of perturbations during inflation and reheating in such scenarios and when only limited
constraints are available from observations? Based on a precise