Dual seminar by dr. Matteo Savoini (ETH Zurich) and dr. Chiara Ciccarelli (University of Cambrigde) (Lecture)
- Friday 8 February 2019Add to my calendar
- from 13:45
dr. Matteo Savoini (ETH Zurich) and dr. Chiara Ciccarelli (University of Cambrigde)
Dr. Matteo Savoini: “Ultrafast control of ferroic order & related applications”
The interaction of ultrafast laser pulses with ferroic materials has developed into a fascinating research topic in the past 20 years. Here I report two very recent experiments we have performed using time-resolved hard X-ray radiation. This X-ray energy window allows us to directly assess the ultrafast dynamics induced in the lattice upon laser excitation and their influence on the ferroic properties of the sample (such as magnetization and/or ferroelectric polarization changes).
In more detail, we have performed an ultrafast hard X-ray diffraction experiment on Fe thin films, in which we were able to measure the signature of the Einstein-de Haas effect upon laser induced demagnetization. In particular we measured the excitation of ultrafast transverse phonons, which can account for the momentum loss occurring in the demagnetization process.
On another experiment we have attempted the control of the ferroelectric polarization through the direct excitation of phonon modes in an ionic semiconductor, Sn2P2S6. In this material the ferroelectric properties are determined by the Sn-atom positions, thus by a proper excitation (in the low THz region) a direct control of the ferroelectricity can be achieved. Once again time-resolved X-ray diffraction is a key tool to directly measure the atomic position, thus infer the induced changes.
Dr. Chiara Ciccarelli: “The wonders of symmetry in spintronics: manipulating spins with electric fields”
Until twenty years ago the possibility to manipulate magnetism electrically relied exclusively on the Ørsted field generated by a current-carrying wire, a phenomenon discovered more than two centuries ago but still employed to write magnetic bits in hard disk drives and solid-state magnetic RAMs. The observation in the recent past that an electrical current passed directly into a ferromagnet can induce magnetic switching led to the development of new prototypes of memories with great potential for enhancing the functionalities of electronic logic circuits in terms of speed and power dissipation . In this context the study of spin-orbit torques (SOTs) constitutes a fast moving field of experimental and theoretical physics.
SOTs emerge from the spin-charge locking established by the break of spacial inversion symmetry. This break can occur at the interface in a multilayer heterostructure or within the unit cell of a ferromagnet. In this talk I will discuss my studies on SOTs showing that the break of symmetry within the unit cell of a ferromagnet allows for the electrical switching of its magnetisation at room temperature  and the electrical readout of its magnetic excitations . I will also discuss some very recent results where the break of symmetry plays again a key role in coupling ferromagnetism and superconductivity, two states of matter otherwise considered incompatible .
- A. Brataas et al., Nature Materials 11, 372(2012).
- C. Ciccarelliet al., Nature Physics12, 855 (2016).
- C. Ciccarelli et al., Nature Nanotechnology 10, 50 (2015).
- K.R. Jean, C. Ciccarelli et al., Nature Materials 17, 499 (2018).
Alex Khajetoorians & Alexey Kimel