Authors:	Pokharel, Amrit Raj
Title:	Time resolved spectroscopy of strongly correlated materials
Online publication date:	2-Mar-2023
Year of first publication:	2023
Language:	english
Abstract:	Strongly correlated materials are systems for which the complex interplay among the electrons, spin and lattice lead to the formation of different phase transitions and new orders with dramatically different electrical, optical, mechanical and thermal properties. Emergence of complex phases like- Charge Density Wave (CDW), Spin Density Wave (SDW), Superconductivity just to name a few, with remarkable properties offer great deal (such as an order of magnitude change in electrical conductivity) from fundamental research perspective and thought to shape our future technologies. Non-equilibrium spectroscopic techniques are ideal tools to investigate such correlated systems as the techniques offer simulta- neous spectroscopic and temporal information. In addition, driving the system out of equilibrium and tracking the relaxation dynamics and their couplings, one can disentangle the different degrees of freedom because of the different timescales that characterize the recovery of the initial ground state. The work described in this thesis utilizes the ultrafast spectroscopic tech- nique as a tool to investigate the solid state materials exhibiting Charge Density Wave (CDW) order, Kondo Insulating (KI) behavior and Mott Insulating (MI) ground state. All of these materials fall into the category of strongly correlated systems where multiple phases emerges due to correlation effects. In the Kondo Insulator YbB12 we track the photo-induced reflectivity dynamics at various temperatures and excitation densities and discuss the corresponding changes in the ow energy electronic structure. In CDW system BaNi2As2 we study the collec- tive amplitude modes of the CDW order and their temperature and excitation density dependence. These results provide valuable information on the nature of the CDW order and its relation to the observed structural phase transitions. In particular, the smooth evolution of several amplitude modes through the struc- tural phase transitions suggest that CDW may be responsible for the triclinic phase transition. Moreover, robustness of the CDW order against perturbation suggest an unconventional, non-Peierls nature of the CDW order. Last, but not least, we present the time-resolved study on photo-doping the Mott insulator La2CuO4. By tracking the time evolution of the complex dielectric function over the broad spectral range, we study the dynamics of the charge transfer gap and the appearance of the mid-infrared excitations. By varying the excitation densi- ties over three order of magnitude we demonstrate the extreme resilience of the Mott insulating ground state against perturbation.
DDC:	530 Physik 530 Physics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 08 Physik, Mathematik u. Informatik
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-8818
URN:	urn:nbn:de:hebis:77-openscience-0741be10-ab00-4a4c-9344-c4387554ae049
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	http://rightsstatements.org/vocab/InC/1.0/
Extent:	ix, 144 Seiten ; Illustrationen, Diagramme
Appears in collections:	JGU-Publikationen