Condensed Matter Physics Seminar
Note Special Time and Place!
11 a.m., Monday, February 20, 2006
Room
2205, Physics Building
Possible New Physics at Quantum Critical Points: Nontrivial Topology in
2D Antiferromagnets
Zaira Nazario
(Stanford University)
Abstract: It has recently been proposed that there are degrees of
freedom intrinsic to quantum critical points that can contribute to quantum
critical physics. We point out that intrinsic critical degrees of freedom exist
quite generally below the upper critical dimension. We have recently shown that
despite the absence of a Hopf term and zero Berry phase terms, the Neel ordered
phase of 2+1 D quantum antiferromagnets have spin 1/2 excitations, i.e. spinons.
The spinons are skyrmion excitations of a topological nature. We have recently
shown that in 2+1 D antiferromagnets skyrmion excitations are stable at
criticality and identify them as the critical excitations. Hence, the critical
excitations are fractionalized. Since skyrmion gap is proportional to the spin
stiffness, quantum criticality corresponds to skyrmion gap collapse.

Host: Das Sarma
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