Magnetic heat transport in low-dimensional quantum magnets

PhD ceremony: Ms. M. Otter, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Magnetic heat transport in low-dimensional quantum magnets

Promotor(s): prof. P.H.M. van Loosdrecht

Faculty: Mathematics and Natural Sciences

In low-dimensional quantum magnets heat is mainly transported along one axis by the transport of magnetic energy. Furthermore, these materials are electrically insulating and the heat transport along the good axis is comparable to that of a metal. They offer new possibilities for smart cooling of microelectronics. When heat is transported along one axis, the density of components along other axes can be larger than when a three-dimensional heat conductor would be used.

This research concentrates on two materials; the spin chain SrCuO2, in which the magnetic structure forms a chain, and the spin ladder Ca9La5Cu24O41, in which it forms a ladder. A new technique to measure heat transport optically is developed, which has the advantages over a conventional technique that it is a very fast technique, that the minimum distance over which one can measure is orders of magnitude smaller and that one can measure in a time-resolved fashion. Apart from measurements on pure materials, measurements on a realistic ‘device’ configuration have been performed.

It turns out the heat transport in spin ladder materials is strongly time-dependent because of a weak interaction between the magnetic excitations and the lattice vibrations. This property can be used to measure the interaction between crystal vibrations and magnetic excitations in a direct way.