| Iridate Srn+1IrnO3n+1(n=1,2)is a typical 5d transition metal oxide,showing Jeff=1/2 insulation state.Because multiple degrees of freedom such as charge,spin,orbit,and lattice are coupled and competitive,Srn+1IrnO3n+1(n=1,2)exhibits a singular quantum state,in addition to the interaction of the spin orbit,the spin The interaction with the lattice has also been shown to have a non-negligible effect.In this study,in order to explore the characteristics of the sample spin lattice coupling in the non-equilibrium state,high-pressure ultrafast spectroscopy was carried out on the iridium salt Srn+1IrnO3n+1(n=1,2).Using pump light with a wavelength of 400 nm and probe light of 800 nm,an in-situ high-pressure ultrafast laser pump-detection device was built to effectively reduce the point-to-point error of the sample surface.For Srn+1IrnO3n+1(n=1,2)The non-equilibrium quasi-particles were subjected to in-situ high-pressure time-resolved ultrafast kinetic experiments.The Raman spectroscopy test of the sample Sr2lrO4 at room temperature examined the pressure point at which a phase transition may occur.Between 19.6 and 22.2 GPa,a new Raman peak appears at a wavenumber of 199 cm-1.Other Raman peaks also exhibit anomalies in this pressure range.These changes all point to the broken symmetry of the crystal structure.The phase transition occurs here,and it may be one of the important reasons for the change of spin magnetism at low temperature.Through the high-pressure ultrafast laser pump-probe experiment,the relaxation kinetics of Sr2IrO4 non-equilibrium quasi-particles after being excited were analyzed.At 18 to 20 GPa,it was found that the ultrafast kinetic signals of Sr2IrO4 fluctuated abnormally at the three time scales of fast component,slow component and slowest component.In particular,the relaxation time ?slow of the slow component appears divergent in this pressure range.This is because the narrowing of the energy gap causes the balance between non-equilibrium quasiparticles and high-energy phonons to be broken,resulting in the characteristic of phonon bottleneck effect.,Pointing to the structural phase change that occurs at this pressure point.The study also found anomalies at 32 GPa,as well as residual local spin fluctuations.The luminous flux dependence experiment proves that the experimental data is not affected by the thermal excitation effect.At the same time,the high-pressure ultrafast kinetics of the single crystal sample Sr3Ir2O7 was studied.Since the energy gap of Sr3Ir2O7 is much smaller than that of Sr2IrO4,the ultrafast relaxation process is faster than that of Sr2IrO4.At 14.3 GPa,the amplitude and time period of the ultrafast relaxation component of Sr3Ir2O7 show abnormal fluctuations.Not only does the amplitude drop rapidly to a minimum,but the relaxation time also exhibits a divergence phenomenon very similar to Sr2IrO4,which is in equilibrium with high pressure According to the experimental report,the energy gap at this pressure point shrinks rapidly,which will cause a phonon bottleneck.Our research innovatively promotes the application of high-pressure ultrafast time-resolved technology in experiments.A series of non-equilibrium ultrafast kinetic signals of 5d metal oxide Srn+1IrnO3n+1(n=1,2)were carried out The probe study confirmed the possible structural phase transition of the sample at room temperature and high pressure,and found the phonon bottleneck at the critical pressure point due to the change in energy gap.However,since Srn+1IrnO3n+1(n=1,2)is a system with very complex interactions and coupling of multiple degrees of freedom,the change of its internal quantum state under high pressure involves many factors.In ultrafast power The academic performance is also very complicated.In the future,more experimental research will be needed to gradually improve the understanding of the information in the non-equilibrium state of this system. |
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