Starts 2 Feb 2012 11:30

Ends 2 Feb 2012 20:00

Central European Time

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Seminar on Disorder and strong electron correlations:
" Competing spin-disordered phases of the spin-1/2 Heisenberg antiferromagnet on the Kagome lattice "

Starts 2 Feb 2012 11:30

Ends 2 Feb 2012 20:00

Central European Time

ICTP

Leonardo da Vinci Building Luigi Stasi Seminar Room

Strada Costiera, 11
I - 34151 Trieste (Italy)

Despite years of intense theoretical attack from different directions, the ground state of the S = 1/2 Kagome Heisenberg antiferromagnet has remained elusive. I will revisit this question within the framework of Gutzwiller projected fermionic wave functions studied using Variational quantum Monte Carlo technique. We found the so called U(1) Dirac state, an exotic algebraic spin liquid, to have the best variational energy. While there were doubts concerning its stability, experiments have hinted towards a gapless, algebraic spin liquid behavior. Indeed we show that the U(1) Dirac spin liquid is remarkably stable w.r.t dimerizing towards a large class of Valence bond crystal perturbations.
This stability is also preserved upon addition of a weak 2nd NN exchange couplings. However we find, that upon addition of a weak 2nd NN ferromagnetic coupling, a non-trivial valence bond crystal is stabilized, and has the lowest energy. This VBC possesses a non-trivial flux pattern and is a strong dimerization of another competing U(1) gapless spin liquid with a large spinon Fermi surface, the so called uniform RVB state. The U(1) Dirac state and the uniform RVB state are shown to be remarkably stable w.r.t. destabilizing into the class of Z2 spin liquids.
I will also briefly touch upon my ongoing work dealing with a complete group theoretical classification of time-reversal invariant Valence bond crystals on the Kagome lattice, and present some results concerning the properties of the ground state on small clusters which are extracted using the Lanczos method on a given variational wave function.

- N. Ivanissevich