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 spin 1/2 Heisenberg model on a triangular lattice with interchain exchange, J', weaker than the intrachain exchange J, is a particularly well-studied frustrated magnet because of its relevance to Cs2CuCl4, which is thought to be in close proximity to a spin liquid phase. Although an incomensurate spiral state is stable for J'~J, a variet of theoretical studies find evidence for spin liquid behavior well before the decoupled chain limit, J'=0, is reached.
Very recently, it has been recognized that excitations out of the ground state of materials known as spin ice can be viewed as magnetic monopoles, the magnetic analog to electric charges. Like electrons and positrons,
these particles possess a charge of +Q or -Q and therefore attract or repel each other. Magnetic monopoles, however, can be accelerated using a magnetic field instead of an electric field. In this talk, I will report on
We begin with a fundamental approach to quantum mechanics based on the unitary representations of the group of diffeomorphisms of physical space (and correspondingly, self-adjoint representations of a local current algebra). From these, various classes of quantum configuration spaces arise naturally.
Geometrical frustration in magnetic systems provides a rich playground to study the emergence of novel ground states. In systems where not all magnetic couplings can be simultaneously satisfied, conventional long range magnetic order is often precluded, or pushed to much lower emperature scales than would be expected from the strength of the magnetic interactions. Dy2Ti2O7 has a pyrochlore lattice, where the magnetic Dy ions lie on the vertices of corner sharing tetrahedra.
Utilizing the Baym-Kadanoff formalism with the polarization function calculated in the random phase approximation, the dynamics of the ÃÂ½=0, ÃÂ±1, ÃÂ±2, ÃÂ±3, ÃÂ±4 quantum Hall states in bilayer graphene is analyzed. In particular, in the undoped graphene, corresponding to the ÃÂ½ =0 state, two phases with nonzero energy gap, the ferromagnetic and layer asymmetric ones, are found. The phase diagram in the plane (ÃÂ0,B), where ÃÂ0 is
The nature of the pairing mechanism in the recently discoverediron-pnictide family of superconductors remains an outstanding issue. To answer this question, it is instructive to know the symmetry of the superconducting energy gap. Low temperature thermal conductivity measurements provide a robust test of the presence or absence of low energy electronic quasiparticles that in turn can be used to characterise the symmetry of the gap function.
Direct visualization of the electronic structure within each crystalline unit cell of a solid is a new frontier in condensed matter physics (M.J.
Lawler et al, Nature 466, 347 (2010)). In this talk, I will introduce the
techniques of spectroscopic imaging scanning tunneling microscopy (SI-ÃÂÃ¢ÂÂSTM) and then explain how our new application of this technique allows
visualization of the intra-ÃÂÃ¢ÂÂunit-ÃÂÃ¢ÂÂcell electronic structure. We use this
Recently resonant elastic soft x-ray scattering (RSXS) has emerged as a powerful new tool to study electronic ordering in materials like cuprates and manganites. The power of this technique is to combine xray
scattering, which is sensitive to spatial order, with x-ray spectroscopy, which is sensitive to the valence, spin and orbital symmetry of specific atoms. This combination allows one to probe very directly and
Many of the most interesting electronic behaviors arise in materials with strong electron-electron correlations. Many of these same materials are disordered either intrinsically or due to doping. The combination of disorder and interactions generally gives rise to a feature in the density of states at the Fermi level, with two of the most influential examples being the Altshuler-Aronov anomaly and the Efros-Shklovskii Coulomb gap.
Mass, a concept familiar to all of us, is also one of the deepest mysteries in nature. Almost all of the mass in the visible universe, you, me and any other stuff that we see around us, emerges from QCD, a theory with a negligible microscopic mass content. How does QCD and the family of gauge theories it belongs to generate a mass? This class of non-perturbative problems remained largely elusive despite much effort over the years. Recently, new ideas based on compactification have been shown useful to address some of these.