| An exciton polariton is a new quasiparticle with boson characteristics formed by the strong coupling of semiconductor excitons and microcavity photons.Due to its small effective mass and strong interaction,theoretically,Bose-Einstein condensation(BEC)can be achieved at standard low temperature or even room temperature.In recent years,microcavity exciton polariton has become a research hotspot in condensed matter physics,and has received the enthusiastic attention of scientists.Its research has been extended to various small quantum systems,including quantum wells,thin films,quantum wires,and quantum dots.Many basic physical problems can be realized by microcavity exciton polariton,such as Bose-Einstein condensation,superfluidity,KPZ effect,vortex,etc.Vortex is a topological defect of a two-dimensional system.Under certain conditions,clockwise and counterclockwise vortices will form paired bound states.This is called the Berezinskii-Kosterlitz-Thouless(BKT)phase transition.In this study,we investigated the dynamics of vortices in the exciton polariton system,as well as the nature of BKT topological phase transitions caused by vortices.An exciton polariton is a semi-light and semi-hybrid quasi-particle produced by the coupling of an exciton and a microcavity photon in a semiconductor quantum well.It constitutes a typical type with external drive and internal dissipation.Non-equilibrium quantum fluid is a good platform for studying non-equilibrium vortices.Our theoretical study is based on the Gross-Pitaevskii(GP)equation,taking into account the effects of external driving and internal dissipation on the system.The random simulation method is used to study the properties of the vortex state.The results show that the vortex can also exist stably under non-equilibrium conditions,and the distribution of the vortex can be changed by changing the intensity of the P0 driving pump,so as to realize the pairing of the vortices,and thus cause the BKT phase transition.This work elucidates the effects of open environment on the dynamic properties and pairing mechanism of vortices,and also reveals the physical mechanism of non-equilibrium condensation.We calculate the density fluctuation distribution,first order coherence function,and scaling function.It is found that the correlation at short range agrees with the Bogoliubov linear theory.While the long range correlation is characterized by the nonlinear scaling behavior of Kardar-Parisi-Zhang(KPZ)universality class,especially when the interaction is weak.In this regime,a scaling analysis turns out to be necessary to capture the universal KPZ scaling features.In the KPZ regime,the vortex pairing effect is probably not relevant,but introducing vortex excitations can drive the system into a state close to spatiotemporal chaos.This article is organized as follows:In chapter one,the development and research significance of Bose-Einstein condensation,exciton polariton,exciton polariton and vortex in semiconductor microcavity are briefly introduced.The related basic physical concepts involved in this thesis are emphasized,including exciton,microcavity,exciton polariton,BKT phase transition,KPZ effect and vortex.In chapter two,the theoretical basis and numerical calculation methods of this article are introduced.The GP equation and the KPZ equation are mainly introduced.In Chapter Three.Our work is introduced in detail,that is,the vortex state and phase transition of a two-dimensional non-equilibrium quantum fluid.We investigated the dynamics of vortices in the exciton polariton system and the properties of BKT topological phase transitions caused by vortices.In Chapter four,we mainly introduce the space-time scale of two-dimensional weakly interacting exciton polariton.We perform a numerical study on the two-dimensional exciton-polariton systems based on the generalized stochastic Gross-Pitaevskii equation.We calculate the density fluctuation distribution,first order coherence function,and scaling function.It is found that the correlation at short range agrees with the Bogoliubov linear theory.While the long range correlation is characterized by the nonlinear scaling behavior of Kardar-Parisi-Zhang(KPZ)universality class,especially when the interaction is weak.In this regime,a scaling analysis turns out to be necessary to capture the universal KPZ scaling features.In the KPZ regime,the vortex pairing effect is probably not relevant,but introducing vortex excitations can drive the system into a state close to spatiotemporal chaos.In the last chapter,we briefly summarize this paper and look forward to the future research. |
