Resonant(Inelastic) X-ray Scattering And Its Application In Strongly Correlated Systems

Understanding the electronic behaviour and electon-electron interaction has been one of the major challenges in condensed matter physics.To tackle the task,people have developed different kinds of experimental methods,such as angle-resolved photon-emission spectroscopy,scanning tunnelling microscopy,neutron scattering and other spectroscopies based on photon scattering.Among those,X-ray scattering,especially the resonant?inelastic?X-ray scattering is taking a pivotal role.In recent years,the advances in synchrotron techniques and the fast development of mechanics make the equipments for resonant?inelastic?X-ray scattering available,hence boostering the application of resonant X-ray scattering in condensed matter physics,especailly the strongly correlated systems.In this PhD thesis,we will explore four topics as shown below:?The ?21 beamline devoted to the resonant inelastic X-ray scattering?RIXS?in Diamond Light Source,UK.The brilliant design on optics and mechanics positions this beamline as one of the best RIXS facilities in the world,so we introduce the optical design of this beamline and the methods for commissioning the optics.In addition,we also develop a set of procedures to process the experimental data which are believed to be helpful for people to achieve a better understanding on the technique and also the data.? RIXS study of the orbital dynamics in KCuF₃.Thanks to a very high energy resolution??37 meV at Cu L₃-edge?,dispersive excitations below 100 meV are well separated from quasi-elastic peaks and found to follow the magnetic dynamics--spinon.Whereas no signatures from collective orbital excitation?orbiton?proposed by the super-exchange interaction are observed.Instead,excitations from different Cu²⁺3d orbitals are resolved in an energy range from 0.7 eV to 1.7 eV but not disperseng in the reciprocal space.Comparison to the ab initio calculation based on single cluster is found to be in good agreement on these orbital excitations,indicating either the orbiton signal is very weak in RIXS or the orbiton excitation is deemed to appear at too low energy?<?30 meV?to be observed currently.? Investigation of short-range charge order in Bi₂Sr_2-xLa_xCuO_6+?with RIXS.Unconventional high T_c superconductor-cupates can host diverse symmetry-breaking states,of which the charge order?CO?as the self-organization of doped carriers has been confirmed as a universal phase and found to show intimate interplay with other orderings,such as superconductivity and spin density wave.Here,we utilize the high energy resolution RIXS at both Cu L₃-edge and O K-edge to investigate the doping evolution of CO in Bi₂Sr_2-xLa_xCu₂O_6+?systematically.The observed CO wave vector at O K-edge is consistent with the results at Cu L₃-edge.Besides,the bond stretching phonon can be resolved clearly at Cu L₃-edge,which shows an anomaly around CO wave vector and persists up to room T when the CO has disappeared.On slightly over-doped sample?p=0.18?,no CO can be detected at both of edges,and at the same time,the bond stretching phonon presents a rather trivial behaviour.All these observations demonstrate an intimate interplay between charge instability and lattice degree of freedom in Bi₂Sr_2-xLa_xCu₂O_6+?.? Long-time recovering dynamics of laser-perturbed magnetic ordering in Sr₂IrO₄studied with resonant elastic X-ray scattering.The recovery dynamics relating to the J_eff=1/2 state isospins is found to be as slow as the lattice degree of freedom,extending up to 15ns.Moreover,it strongly fluctuates,different from the thermal dissipation of lattice heating which shows a smooth variation with time.We attribute this behaviour to the fluctuating formation of randomly distributed magnetic domains due to the strong magnetoelastic coupling inherited from the J_eff=1/2 states during the recovering process.