Condensed Matter Physics Seminar: Lakshmi Das

Abstract: 
My research employs ultrafast pump-probe spectroscopy to investigate the charge
and spin dynamics in antiferromagnetic (AFM) materials on femtosecond timescales. By
studying the time-resolved changes in reflectivity and transmission, I aim to deepen our
understanding of ultrafast magnetization dynamics in AFM materials – systems where the
antiparallel alignment of spins results in zero net magnetization, presenting unique challenges
compared to conventional ferromagnetic (FM) materials. The inherently higher magnon
precession frequencies in AFMs (on the order of THz) make them promising candidates for
ultrafast spin control, which has significant implications for the development of nextgeneration spintronic and quantum devices.
I will also discuss briefly the new type of fundamental magnetism- altermagnetism (AM).
AM is a magnetic phase that breaks the combined PT symmetry (parity and time) with
compensated collinear/non collinear magnetic order. In real space, opposite spin sublattices
are connected by a rotational symmetry operation of the crystal (rather than translational). In
the momentum space, they exhibit momentum dependent spin polarization and band splitting
thus enabling a ferromagnetic like spin dependent phenomena despite having net zero
magnetization. In this sense, they are the best of both worlds- zero net magnetization of
antiferromagnets and strong spin dependent phenomena of the ferromagnets.
In this talk, I will provide an overview of ultrafast pump-probe measurements conducted on
various AFM materials of interest, which are explored in the Ultrafast Nanoscience group at
Umeå. I will also introduce my Marie Sklodowska-Curie postdoctoral project- ATOPS
(Ultrafast Optical Antiferromagnetic Topological Spintronics) which began in the summer of
2025. In this project, I will employ time resolved pump probe spectroscopy and time resolved
x-ray diffraction (Tr-XRD) to study Mn- based altermagnetic candidate material to uncover
their ultrafast lattice and spin dynamics.