| As a non-conventional superconductor,copper oxide superconductor has many interactions and complex quantum phenomena,and its microscopic mechanism is still a hot research topic.We know that under the action of high pressure,low temperature,ultrafast laser and other conditions,substances will exhibit some unusual phenomena,which provides us with a new way to understand their complex mechanism.High pressure can compress the lattice spacing,which may increase the superconducting transition temperature of copper oxide superconductors;In the field of ultrafast experiments,copper oxide superconductors,as a kind of strongly interacting materials,are also popular research objects.Changing external parameters(such as pressure,temperature,etc.)will cause changes in the electronic states of these systems.Therefore,copper oxide superconductors are a good system for observing the ultrafast mechanism of substances dependent on pressure,temperature and other regulatory conditions.The study of ultrafast spectra at high pressure and low temperature will also reveal more physical information of copper oxide superconductors.So far,the experimental research combining these dimensions at the same time is still relatively blank.This paper integrates three kinds of experimental technologies: high pressure,low temperature and ultrafast,designs and builds a feasible experimental device for studying superconductors,establishes an experimental method for studying superconductivity by high pressure,low temperature and ultrafast spectroscopy,and explores the ultrafast properties of Cu-O superconductor Bi-2212,which provides new information for a deeper understanding of the mechanism of high-temperature superconductors in the future.The specific work is as follows:(1)An experimental device capable of conducting ultrafast spectral study of superconductors under extreme conditions of high pressure and low temperature has been designed and built.Through various adjustment methods such as pressure,temperature and dimension adjustment,the ultrafast information of materials under extreme conditions including superconducting state transition,phonon bottleneck and other phenomena has been explored,It can also eliminate the adverse effects on the experiment caused by the off-site experiment.(2)A series of atmospheric pressure characterization experiments were performed on Bi-2212 thin film.Then we have carried out ultrafast measurement of Bi-2212 film at atmospheric pressure in the temperature range of 85-300 K.We observed the data change between the possible pseudo-gap state and the normal state and an increase in the slow relaxation time of the phonon bottleneck phenomenon,which may be caused by the pseudo-gap closure.The absorption spectra of 77-300 K at 1.73 GPa,3.12 GPa and 4.7 GPa were obtained by using high pressure and low temperature absorption spectra.The optical absorption properties of Bi-2212 thin film material at high pressure and low temperature were studied.(3)The ultrafast optical measurements of 1.4 GPa and 2.2 GPa at 77-300 K for Bi-2212 thin film materials were carried out using the established high pressure and low temperature ultrafast device.The analysis of the measured results shows that the life of the slow component has a sudden change at 90 K(1.4 GPa)and 100 K(2.2 GPa),and its amplitude has a positive and negative sign transition at the same time,which strongly indicates that the sample has a superconducting transition at this temperature point,and the pressure can lead to the increase of the superconducting transition temperature.Other abnormal changes of fast components may indicate that pressure or temperature induce phonon bottlenecks and affect the intensity of spin fluctuations. |
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