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Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 38: CE: Quantum-Critical Phenomena 2

TT 38.4: Invited Talk

Friday, March 26, 2010, 11:00–11:30, H18

Neutron Scattering Studies of Spin-Ladders — •Bella Lake1,2, Alexei M. Tsvelik3, Susanne Notbohm1,4, D. Alan Tennant1,2, Toby G. Perring5,6, Manfred Reehuis1, Chinnathambi Sekar7,8, Gernot Krabbes7, and Bernd Büchner71Helmholtz-Zentrum Berlin, Germany. — 2Technische Universität Berlin, Germany. — 3Brookhaven National Laboratory, U.S.A. — 4University of St. Andrews, U.K. — 5Rutherford Appleton Laboratory, U.K. — 6University College London, U.K. — 7IFW-Dresden, Germany. — 8Periyar University, Salem, India.

This presentation will discuss magnetic excitations of two-leg spin-ladders with spin-1/2 moments and antiferromagnetic exchange interactions. Inelastic neutron scattering measurements will be presented for two ladders systems. La4Sr10Cu24O41 has a strong rung coupling and the excitations are found to consist of a gapped one-magnon mode and a two-magnon continuum. A large cyclic exchange is found which reduces the gap. In contrast CaCu2O3 has a weak rung interaction and a substantial cyclic exchange which drives the system gapless and quantum critical. At high energies the excitations are described well by the Bethe Ansatz and the field theory solution for a Luttinger liquid quantum critical point. At low energies a gap appears in the bonding susceptibility while the antibonding susceptibility remains gapless. The data is well described by a model where a gapped singlet bound-spinon mode is located at the bonding wavevector while a gapless triplet lies at the antibonding wavevctor. The antibonding susceptibility is critical and is at the Wess-Zumino-Novikov-Witten quantum critical point.

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