, Oak Ridge National Laboratory
[Host: Seung-Hun Lee]
The lowest energy excitations in quantum disordered spin chains and ladders are a triplet of massive magnons. The stability of these quasiparticles depends critically on the symmetries of the actual spin Hamiltonian. When the spin system undergoes a quantum phase transition, for example one induced by a strong external magnetic field, the symmetry of the ground state changes, and so do the excitations. I will present a comparative inelastic neutron
scattering study of three distinct one-dimensional disordered spin systems: the S=1 quasi-1D bond-alternating antiferromagnet NTENP, the uniform anisotropic S=1-chain Haldane-gap compound
NDMAP and the uniform isotropic ``composite'' Haldane spin chain IPA-CuCl3. For each material I will discuss the field-induced condensation of magnons, and analyze the spectra measured below,
at and above the transition point. The high-field phase will be characterized either as a Bose-Einstein magnon condensate, with a
cartelistic gapless Goldstone mode, or as a gapped "quantum spin solid". The issue of magnon stability in each phase will be addressed in detail.
Condensed Matter Seminar
Thursday, October 26, 2006
Physics Building, Room 204
Note special time.
Note special room.
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