The TRR 227 kindly invites you to the joint TRR 227 & MLU Institute of Physics Colloquium.

Speaker: Dr. Andrea Eschenlohr (Faculty of Physics, University Duisburg-Essen)

Charge, spin and energy transfer at interfaces on femtosecond timescales

Femtosecond laser excitation of solids leads to a highly non-equilibrium state involving electronic, spin and lattice excitations. In heterostructures, transport processes across interfaces further become important, and the interface properties are expected to modify the spectrum of excitations. Understanding and controlling these ultrafast dynamics is a prerequisite for their application in future electronic or spintronic devices. I will discuss two cases where we have identified and analyzed the microscopic processes underlying these ultrafast dynamics at interfaces in the time domain:

At Co/Cu(001) interfaces, we identify the fundamental microscopic processes during optically induced, femtosecond charge and spin transfer by means of a direct comparison of interface-sensitive nonlinear magneto-optics and ab initio theory. We show that the ultrafast spin dynamics originates from spin-dependent charge transfer as well as back-transfer between Co and Cu. This femtosecond spin transfer competes with dissipation of spin angular momentum mediated by spin-orbit coupling already on timescales below 100 fs.

Element-sensitive, femtosecond time-resolved x-ray absorption spectroscopy allows to track the energy transfer in all constituents of a [Fe/MgO]8 metal/insulator heterostructure after localized optical excitation. We find a strong competition of local relaxation in Fe with phonon-mediated energy transfer across the Fe/MgO interface. Furthermore, we discuss a separation of bulk and interface dynamics via an absorption feature at the oxygen K edge assigned to hybridized interface states by ab initio theory.

Funding from the German Research Foundation within SPP 1840 QUTIF and Sfb 1242 is gratefully acknowledged.