# Colloquium

Unless otherwise noted, the physics colloquia are held in Room 307 of the Science and Engineering Research Facility. Refreshments are served at 3:00 p.m. with the talk following at 3:30. The colloquia are available via Webcast archives.

January 16: MLK Holiday |
NA |
NA |
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January 23 |
Bruce D. Gaulin |
Quantum Ground States in Real Frustrated Magnets | |

January 30 |
Greg Fiete |
Searching for New Topological Phases in Correlated Materials | |

February 6 |
Chris Tulk |
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February 13 |
Samindranath Mitra |
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February 20 |
Gail McLaughlin |
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February 27 |
Thomas Corbitt |
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March 6 |
Wouter Deconinck |
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March 13: Spring Break |
NA |
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NA |

March 20 |
Julia Velkovska |
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March 27 |
Alexander Fetter |
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April 3 |
Krzyztof Rykaczewski |
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April 10 |
Young Lee |
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April 17 |
Ariel Amir |
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April 24: Honors Day |

**Bruce D. Gaulin, McMaster University**

Quantum Ground States in Real Frustrated Magnets

The pyrochlore lattice, a network of corner-sharing tetrahedra, is one of the most pervasive crystalline architectures in nature that supports geometrical frustration. We and others have been interested in a family of rare earth pyrochlore magnets, that can display quantum S=1/2 magnetism on such a lattice. The ground states for these materials may be described by a model known as "spin ice", a model with the same frustration and degeneracy as solid ice (the kind you skate on), as well as by a quantum version of this model known as "quantum spin ice" that possesses an emergent quantum electrodynamics. I'll describe how this comes about and how we can understand these materials, with an emphasis on modern neutron scattering. I'll also briefly discuss how fragile some of these quantum ground states seem to be with respect to weak quenched disorder, which is hard to avoid in real materials.

**Greg Fiete, University of Texas**

Searching for New Topological Phases in Correlated Materials

Recent years have seen rapid advances in the theoretical understanding of materials with strong spin-orbit coupling, and experiments have identified new classes of materials exhibiting unusual electrical properties. Many of these discoveries fall in the class of "topological materials". In this talk, I will summarize some of the recent developments in this field and highlight some of our own work based on a combination of model Hamiltonian studies and first-principles approaches to guiding experimental discovery of these phases in transition metal oxides. Some potential device applications will also be described.