Regensburg 2002 – scientific programme

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TT: Tiefe Temperaturen

TT 7: Postersitzung I: Anwendungen der Supraleitung (1-6), Dünne Schichten, Josephsonkontakte, SQUIDs (7-17), Neue und unkonv. Supraleiter(18-23), Amorphe- und Tunnelsyst. (24-28), Quantenflüssigkeiten (29-30), Syst. korr. Elektr.: Theorie I (31-45)

TT 7.33: Poster

Monday, March 11, 2002, 14:30–18:00, A

Planar pyrochlore: a strong-coupling analysis — •Wolfram Brenig and Andreas Honecker — Institut für Theoretische Physik, Technische Universität Braunschweig, 38106 Braunschweig, Germany

Recently, the two-dimensional spin-1/2 checkerboard lattice has been proposed to form a valence bond crystal with long range quadrumer order. Starting from the limit of isolated quadrumers, we perform a complementary analysis of the evolution of the spin spectrum as a function of the inter quadrumer coupling j using both, exact diagonalization (ED) and series expansion (SE) by continuous unitary transformation. We compute (i) the ground state energy, (ii) the elementary triplet excitations, (iii) singlet excitations on finite systems and find very good agreement between SE and ED. In the thermodynamic limit we find a ground state energy substantially lower than documented in the literature. The elementary triplet excitation is shown to be gapped and almost dispersionless, whereas the singlet sector contains strongly dispersive modes. Evidence is presented for the low energy singlet excitations in the spin gap in the vicinity of j=1 to result from a large downward renormalization of local high-energy states.