Investigations of magnetic ground and excited states emerging from spin-orbit coupling in strongly correlated electron system
일 시 : 2020년 11월 10일 화요일 16:00
연 사 : 천 세 환 박사 (포항가속기연구소 PAL-XFEL)
장 소 : 자연과학관 747호
초 록
Spin-orbit coupling is a relativistic interaction between spin and orbital motion of a particle. In strongly correlated electron system, the coupling between an electron’s spin and orbital degrees of freedom is responsible for unconventional magnetic phenomena such as magnetoelectric (ME) effects and topological magnetic orders. Hexaferrites feature a giant magnetoelectricity at room temperature enabling control of substantial electric and magnetic polarizations by magnetic and electric fields, respectively. Apart from these static effects, the hexaferrites host a novel dynamic ME effect, i.e. electromagnon – a magnon excited by modulating electric dipole. I will discuss investigation of both static and dynamic ME effects in Y-type and Z-type hexaferrites via multiple experimental techniques such as electric/magnetic transport and terahertz optical spectroscopy measurements. Magnetic ground states of honeycomb and pyrochlore iridates involve topological magnetic orders such as quantum spin liquid and Weyl semimetal states, respectively, constructed with spin-orbit entangled Jeff = 1/2 state. Their relevance to the topological orders are manifested in the magnetically excited states. Resonant inelastic x-ray scattering (RIXS) serves as an essential probe for the excited states allowing one to identify momentum dependence of the excitations. The RIXS studies of honeycomb Na2IrO3 and Li2IrO3, and pyrochlore Eu2Ir2O7 will be presented. Lastly, I will introduce progress in study of ultrafast magnetic dynamics using PAL-XFEL. X-ray free electron laser (XFEL) is a new generation x-ray source that has key features of femtoseconds pulse and high brightness. The capability of optical laser pump and XFEL probe experiment allows one to access in the time domain the intriguing magnon excitations. Our observation of coherent magnons in hexaferrites and iridates demonstrate a new capacity of magnetic spectroscopy opening a gateway to ultrafast magnetic dynamics in magnetic materials.