Regensburg 2019 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 47: Quantum Magnets, Molecular Magnets and Skyrmions

TT 47.14: Talk

Wednesday, April 3, 2019, 18:30–18:45, H23

Winding up quantum spin helices: Avoided level crossing vs. topological protection — •Thore Posske and Michael Thorwart — I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, 20355 Hamburg, Germany

A magnetic helix can be wound into a classical Heisenberg chain by fixing one end while rotating the other one. We show that in quantum Heisenberg chains, the magnetization slips back to the trivial state beyond a finite turning angle. Avoided level crossings thus undermine classical topolog- ical protection. Yet, for special values of the axial Heisenberg anisotropy, stable spin helices form again, which are non-locally entangled. Away from these sweet spots, spin helices can be stabilized dynamically or by dissipation. For half-integer spin chains of odd length, a spin slippage state and its Kramers partner define a qubit with a non-trivial Berry connection.