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August, 08/30/2015
Events and times subject to change

September 3, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)


M. Zahid Hasan
Princeton University

Discovery of Weyl Fermion and Topological Fermi Arc Quasiparticles in Condensed Matter Systems

Topological matter can host Dirac, Majorana and Weyl fermions as quasiparticle modes on their boundaries. First, I briefly review the basic concepts defining insulators and superconductors where topological surface state (Dirac and Majorana) modes are robust only in the presence of a gap (Hasan and Kane; Rev. of Mod. Phys. 82, 3045 (2010)). In these systems topological protection is lost once the gap is closed turning the system into a trivial metal. A Weyl semimetal is the rare exception in this classification scheme which is a topologically robust metal (semimetal) whose low energy excitations are Weyl fermion quasiparticles. In a Weyl semimetal, the chiralities associated with the Weyl fermion nodes can be understood as topological charges, leading to split monopoles and anti-monopoles of Berry curvature in momentum space. This gives a measure of the topological strength of the system. Due to this topology a Weyl semimetal is expected to exhibit 2D Fermi arc quasiparticles on its surface. These arcs (“fractional” Fermi surfaces) are discontinuous or disjoint segments of a two dimensional Fermi contour, which are terminated onto the projections of the Weyl fermion nodes on the surface (Xu, Belopolski et.al., Science 349, 613 (2015)). I show that Fermi arc quasiparticles can only live on the boundary of a 3D crystal which collectively represents the realization of a new state of quantum matter.


October 1, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)


John Preskill
Caltech

TBA



October 8, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)


Daan Frenkel
University of Cambridge

TBA



November 5, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)


Misha Lukin
Harvard University

TBA



November 12, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)


Nuh Gedik
MIT

TBA



December 3, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)


Nima Arkani-Hamed
IAS

TBA



January 28, 2016 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)


Tim Mitchison
Harvard University

TBA