Dresden 2014 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 37: Spin Torque and Spin Excitations I
MA 37.1: Vortrag
Donnerstag, 3. April 2014, 09:30–09:45, HSZ 401
Goldstone modes observed in a single-k weak chiral magnet — •Max Kugler1, Georg Brandl1, Robert Georgii1, Peter Böni2, Christian Pfleiderer2, Achim Rosch3, Markus Garst3, and Johannes Waizner3 — 1Heinz Maier-Leibnitz Zentrum (MLZ), TU München — 2Physik Department E21, TU München — 3Institute for Theoretical Physics, University of Cologne
The dispersion of the helimagnon modes in the weak chiral helimagnet MnSi has been measured in the momentum directions q parallel and perpendicular to the helix wave vector k using triple-axis neutron spectroscopy (TAS). In contrast to earlier measurements by Janoschek et al. [1], where the measurements were performed in a multi-domain state leading to the appearance of numerous modes, we applied a small magnetic field of 100 mT to enforce a single domain state thus reducing the number of modes drastically. Therefore, we succeeded to clearly identify the various magnetic modes and measure their dispersion. By inclusion of an energy gap all the data can be well reproduced by the theory on helimagnons by Belitz et al. [2]. However, the energy gap can neither be explained by dipolar interactions nor by the applied field because of the Goldstone theorem. For q ⊥ k, a multiple band structure develops in which we succeeded to resolve the first six bands. Furthermore, we investigated the renormalization of the helimagnons for both q-directions and achieved an excellent agreement with our magnetisation data and previous measurements in the field-induced ferromagnetic state.
[1] PRB 83, 214436 (2010) [2] PRB 73, 054431 (2006)