Condensed Matter Physics Seminar

Exploring Spin-Liquid Excitations

Matthew B. Stone
Condensed Matter Sciences Division
Oak Ridge National Laboratory

I will be presenting inelastic neutron scattering measurements of two quantum magnets, piperazinium hexachlorodicuprate (PHCC) and dimethyl ammonium copper chloride (MCCL). Both systems consist of coupled S=1/2 magnetic moments in an organo-mettalic crystal lattice. The resulting magnetic ground state of both materials does not possess long range order, but can be considered to consist of only short range spin correlations in a so-called quantum spin liquid ground state. However, differences in the microscopics of how the spins are coupled results in very different magnetic excitations in these materials. I will discuss measurements of the excitations in MCCL and how they are able to answer fundamental questions regarding the magnetic exchange in this material. The resulting model for the interactions places MCCL at a unique point in the phase diagram of quantum antiferromagnets. Measurements of excitations in PHCC reveal a peculiar point in the excitation spectrum known as the spectrum termination point heretofore only characterized experimentally in superfluid He4. Beyond this point, the character of the spectrum fundamentally changes and the excitations are found to have a finite lifetime.

Thursday, September 20, 2007
2:00 pm
Gant Science Complex
Materials Science Building
Room IMS20

(The seminar is followed by coffee/tea, cookies, and an informal discussions.)

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