연사:  Professor Zohar Nussinov (Washington University)

일시: 2011년 11월 4일(금) 오전 11:00

장소:  물리학과 세미나실 (31355호실) 

초록:  I will briefly review the rudiments of orbital physics and then discuss several more recent results. Orbitals may be described by SU(2) operators. However, unlike spins, orbitals live real space and thus their interactions are highly frustrated and may lead to unconventional correlations. It will be shown that spatial orders of electronic orbital states in a crystal can be triggered by thermal fluctuations alone (contrary to earlier lore, no zero point quantum fluctuations are necessary to stabilize orders). It will be further shown how symmetry considerations alone give rise to dimensional reduction as well as topological order and selection rules that may be experimentally tested from scattering measurements. I will illustrate that in addition to charge and spin order driven quantum critical points, "Orbital Order Driven Quantum Criticality" can, as a matter of principle, also occur in the simplest orbital Hamiltonians. New predicted orbital nematic orders will be demonstrated in some of the best known orbital dependent Hamiltonians. Time permitting, I will briefly discuss an exact solution for a system directly derived from the Hubbard model on the pyrochlore lattice and illustrate how a similar dimensional reduction that occurs there triggers deconfined excitations at a quantum critical point.