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.
The erbium and ytterbium rare earth pyrochlores exhibit local XY spin anisotropy. Experimental and theoretical investigations of XY pyrochlores have revealed a strong propensity for quantum magnetic phenomena, such as order-by-disorder and the quantum spin ice state. We have conducted a systematic investigation of the family of XY pyrochlores, Yb2B2O7 and Er2B2O7, spanning many non-magnetic B site cations (B = Ge, Ti, Pt, and Sn).
High quality single crystals of Yb2Ti2O7 synthesized using a traveling solvent floating zone method enable experiments that explore the anisotropic temperature-field phase diagram of this quantum spin ice candidate. We have examined the H//(111) orientation, which is interesting because a phase transition that breaks three fold rotation symmetry is possible in the presence of a magnetic field.
The pyrochlore magnet Yb2Ti2O7 has the remarkable property that it orders magnetically, but has no propagating magnons over wide regions of reciprocal space. Using inelastic neutron scattering we observe that at high magnetic fields, in addition to dispersive magnons there is also a two-magnon continuum, which grows in intensity upon reducing field, overlaps with one-magnon states at intermediate fields leading to strong dispersion renormalizations and magnon decays.
Harboring interpenetrating lattices of corner-sharing tetrahedra, materials with the pyrochlore structure type dominate exploration of the physics of quantum spin ices. Recent synthetic advances in the control of point defects, such as in Yb2Ti2O7 and Pr2Zr2O, have demonstrated that even sub-percent changes in the type and/or number of defects radically modulates the low temperature physics of these materials.
We aim to provide a concise review on theoretical background on emergent quantum electrodynamics in pyrochlore quantum spin ice. We first introduce elementary excitations in quantum spin ice using a simple model and then extend the discussion to more realistic systems. Implications to experiments are also discussed.
In this tutorial, we will review the microscopic aspects of rare-earth magnets relevant for quantum spin ice. We first discuss the single-ion properties of the variety of rare-earth atoms that appear in quantum spin ice candidate materials. Second, we consider the origin of the two-ion exchange interactions, including electric and magnetic multipolar interactions, super-exchange and virtual crystal field mediated interactions.
In this work we consider a recent proposal in which gravitational interactions are mediated via the exchange of classical information and apply it to a quantized Friedman-Robertson-Walker (FRW) universe with the assumption that any test particles must feel a classical metric. We show that such a model results in decoherence in the FRW state that manifests itself as a dark energy fluid that fills the spacetime.
Causal dynamical triangulations (CDT) is a sum-over-histories approach to quantum gravity which leverages the techniques developed in lattice quantum field theory. In this talk, I discuss the thick sandwich problem in CDT: Given initial and final spacelike hypersurfaces, each with a fixed geometry, what is the transition amplitude for one transitioning into the other? And what geometries dominate the associated path integral? I discuss preliminary studies performed in this direction. I also highlight open problems and interesting directions for future research.
I will discuss two ways in which revising the notion of time at the Big Bang will lead to testable predictions. I will then contrast these predictions against standard ΛCDM scenario, and cosmological observations. The first model, Holographic Cosmology, is based on a 3d quantum field theory without time, suggesting the possibility of nonperturbative effects on large angles (l
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