Thursday, March 17, 2011

A signature of deconfined spinons?

This week Jure Kokalj [currently a postdoc with me] gave a nice Quantum Sciences seminar at UQ where he discussed his Ph.D work with Peter Prelovsek about spinon deconfinement in frustrated quantum spin chains. [See this PRB]. They used a new numerical method to calculate finite temperature dynamical correlation functions for the Heisenberg spin chain with next-nearest neighbour exchange interactions J'.  When J' is large enough a gap opens in the spin excitation spectrum and there is spontaneous breaking of the discrete lattice symmetry and long range dimer spin correlations. The low lying excitations are deconfined spinons (spin-1/2 domain walls).
The new feature they found was that at non-zero temperature a large peak appears in the dynamical spin susceptibility at zero frequency and wave vector pi. I think the physics is that the finite temperature populates low lying triplet states which couple significantly to degenerate singlet excitations via spin flip operators. This peak should be observable with inelastic neutron scattering.

A few questions arise:

Is spinon deconfinement necessary for the appearance of this peak?

How does this compare to the dimerised Heisenberg spin chain in which the spinons are confined into triplons? (i.e. how does it related to this nice PRL by Kai Schmidt and Gotz Uhrig)?

Are there any two-dimensional analogues of this zero-frequency peak?

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