Events - Daily
April 15, 2013 >>
|Monday, April 15|
King-Wai Yau (Johns Hopkins) "Responses to Single Photons in Vision and to Single Odorant Molecules in Olfaction, and Their Implications"
Joseph Henry Room · 12:00 p.m.– 1:00 p.m.
Condensed Matter Seminar, Young S. Lee, MIT, Two faces of the kagomé lattice: quantum spin liquids and topological flat bands
I will describe experimental studies of new states of magnetism on the S=1/2 kagomé lattice. In particular, I will discuss results on two materials: one with antiferromagnetic exchange (herbertsmithite) and one with ferromagnetic exchange (Cu(1,3-bdc)).
Quantum spin liquids are new states of matter that are characterized by long-range entanglement and support exotic excitations. This year marks the 40th anniversary of the original proposal for such a state by Anderson; however, they have only recently been realized in experiments. Herbertsmithite is a leading candidate for having a quantum spin liquid (QSL) ground state. A recent breakthrough in crystal growth has allowed us to uncover a hallmark signature of the QSL state. Inelastic neutron scattering measurements reveal that the spin excitations are fractionalized, a remarkable first. Additional measurements, made possible by the crystals, further corroborate the identification of a QSL.
In contrast to the antiferromagnetic case, ferromagnetic moments on the kagomé lattice are not highly frustrated. Our neutron scattering measurements on Cu(1,3-bdc) confirm that the spins order at low temperatures. However, inelastic scattering reveals an interesting flat band in the magnon dispersion relations. Moreover, each band is separated by a gap from the other bands. I will discuss the role of the Dzyaloshinsky-Moriya interaction and the prospects of measuring new physics with topologically non-trivial magnon bands.
PCTS Seminar Room · 1:15 p.m.– 2:30 p.m.