Time-Resolved Spectroscopy of Multifunctional Materials*

The ability to control and manipulate coherent vibrational degrees of freedom, i.e. Coherent Phonons

(CPs) on a nanoscale length and picosecond time scale promises to be crucial in the fields of quantum

phononics.  In this talk, we focus on magneto-optical measurements at high magnetic fields of two multifunction material systems for developing concepts for new device functionalities: Multiferroic BaTiO₃-BiFeO3 films and nanorods, and GaMnAs, a ferromagnetic semiconductor.

BaTiO₃-BiFeO₃ is a multiferroic material with strong magneto-electric (ME) properties. Specifically, by detecting coherent phonons (CP) we provided detailed spectroscopy information on coherent states in this material system. Our results provide new insights into the ME signatures in these heterostructures.

Additionally, we present our experimental and theoretical studies on the generation and propagation of longitudinal coherent acoustic phonons by ultrafast laser pulses in a ferromagnetic GaMnAs film at high external magnetic fields. Our observation provides new information, reporting an extremely large increase in the amplitude of the CP when an external magnetic field is applied. The ability to control and manipulate coherent vibrational degrees of freedom on a nanoscale length and picosecond time scale promises to be revolutionary in the fields of quantum phononics.