Spectroscopic Studies of Iron-based Superconductors, Multi-ferroic Oxides and Double-perovskite: Phonons, Electronic and Spin Excitations

TL;DR

This thesis uses Raman spectroscopy to investigate phonons, electronic, and spin excitations in iron-based superconductors, multiferroic oxides, and double perovskites, revealing complex couplings crucial for understanding their exotic properties.

Contribution

It provides detailed spectroscopic insights into the coupling of phononic, magnetic, and orbital excitations in these complex materials, advancing understanding of their microscopic physics.

Findings

Identification of phonon modes and their coupling with magnetic excitations.

Observation of spin and electronic excitations in various materials.

Insights into the role of magnetism and coupling in exotic properties.

Abstract

Raman spectroscopy is a very powerful probe to study the nature of quasi-particle excitations in condensed matter physics. The work presented in this thesis is focused on two different families of novel materials, namely the iron-based superconductors (FeBS), multiferroic oxides and double perovskite. Although the properties of these two systems are quite different, some comparison can still be drawn between them. For instance, in both of these systems magnetism plays a crucial role and intricate coupling between phononic, magnetic and orbital degrees of freedom is crucial to understand their underlying physics responsible for their various exotic physical properties. Understanding the microscopic origin of quasi-particle excitations, such as phonons, magnons, orbitons, plasmons etc., and coupling between them in these complex materials, has been an intense field of research because it is believed that these excitations hold the key for explaining their rich physics. The systems studied in the thesis include (A) FeBS - (i) FeSe0.82 (ii) Ce1-zYzFeAsO1-xFx (z = 0, 0.4; x = 0.1, 0.2) (iii) Ca4Al2O5.7Fe2As2 (iv) Ca(Fe1-xCox)2As2 (x = 0.03, 0.05). (B) Multiferroic oxides - (i) AlFeO3 (ii) TbMnO3 and double perovskite (iii) La2NiMnO6.