Re: [Aspuru-Guzik group list] [Aspuru-meetings-list] Group meeting by Sarah tomorrow

When: Friday June 30, 2011 from 11:30 AM to 12:30 PM Where: Cabot Division Room at Mallinckrodt What: Sarah is up for group meeting: "Title: Dynamics of Monopoles in Spin Ice First, I will give an introduction to spin ice and magnetic monopoles. Spin ices are frustrated ferromagnets which are recognized as a class of magnets exhibiting unusual behavior such as residual entropy. In spin ice, dipolar interaction dominates the nearest neighbor interaction. Thus the spin configuration at low temperature consists of two of the four spins in a tetrahedron pointing inwards, and the others outwards (2-in, 2-out state). The 2-in, 2-out constraint is called the ice rule. Violating the ice rules by flipping a spin out of a ground state configuration, leads to a pair of pointlike defects in the tetrahedra the spin belongs to. These two defects are deconfined: they can be separated to an arbitrarily large distance at a finite cost in energy. We study the diffusion annihilation process which occurs when spin ice in a [111] magnetic field is quenched from a fully magnetized phase deep into the spin ice regime, where the excitations - magnetic monopoles - are sparse." -- Joel Yuen-Zhou PhD candidate in Chemical Physics Harvard University CCB, 12 Oxford St. Mailbox 107, Cambridge, MA, USA.