Regensburg 2010 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 38: CE: Quantum-Critical Phenomena 2

TT 38.4: Hauptvortrag

Freitag, 26. März 2010, 11:00–11:30, H18

Neutron Scattering Studies of Spin-Ladders — •Bella Lake^1,2, Alexei M. Tsvelik³, Susanne Notbohm^1,4, D. Alan Tennant^1,2, Toby G. Perring^5,6, Manfred Reehuis¹, Chinnathambi Sekar^7,8, Gernot Krabbes⁷, and Bernd Büchner⁷ — ¹Helmholtz-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.