Angle Resolved Photoemission Spectroscopy Study On Overdoped Bi2201 High Temperature Superconductor

High temperature superconductor is one of the greatest discoveries in the 20th century.The high transition temperature and high critical magnetic field hold great potential applications in the f'uture.As a macroscopic quantum phe-nomenon,high temperature superconductivity has attracted huge numbers of physicists to reveal its mechanism.Key insights into its electron paring mech-anism should definitely lie in the anomalous electronic structures.As a major tool in directly probing the electronic structure of materials,angle-resolved pho-toemission spectroscopy(ARPES)has been playing an important role in high tem-perature superconductivity research.In this thesis,the systematic investigations of'the electronic structures,Fermi surf'ace topology,scattering rates,Fermi liquid behavior of Bi2201 at its overdoped regime by ARPES will be presented.The main content of the thesis is the following:1.The basic properties and history of superconductivity are introduced.The discovery of unconventional superconductors,including cuprates,iron based superconductors and heavy Fermion superconductors,and the basic knowl-edge of the cuprates are introduced.At the end of the chapter,some im-portant ARPES results on high temperature cuprates are also discussed.2.The principle,related thoories and basic components of ARPES systems are introduced.The performance and testing results of our VUV Laser-based ARPES systems,including 6.994eV laser ARPES,tunable laser ARPES,Time-of-flight ARPES,spin resolved ARPES and He3 ARPES,are present-ed.A comparison between laser and other light sources,mainly synchrotron and discharged gas light sources,is made.3.High quality and large-sized single crystals,Pb doped Bi2Sr2Cu06+? have been grown using the traveling solvent floating zone method.Details of the growth and physical property characterizations of the single crystals are introduced.Samples covering from overdoped(Tc?22K,OD22K)to overdoped non-superconducting samples can be got by annealing samples under different atmospheres and different temperatures.4.The evolution ofthe Fermi surface topology with doping has been investigat-ed in the overdoped region of the Bi2201 superconductor.Our helium lamp data shows that,samples in the overdoped superconducting region(Tc?17K)exhibit hole-like Fermi surface centered around(?,?).The heavily overdope-d nonsuperconducting samples can be obtained by annealing samples under different atmospheres and different temperatures.5.The scattering rate of Bi2201,and its momentum and doping dependences,has been studied.By comparing the data of Laser-based and helium lamp-based ARPES measurements,we have proven the necessity of high instru-mental resolution in measuring intrinsic electron scattering in Bi2201.Our high resolution laser ARPES data show that,for the overdoped Bi2201,the scattering rate is anisotropic in momentum space.It reaches to its maxi-mum value at the nodal direction and reduces monotolically from nodal to antinodal regions.We also studied the doping dependence ofthe scattering rate in the nodal direction:it increases with doping from optimally doping to extremely overdoped region.6.Many-body effects in Bi2201 have been investigated by Laser-ARPES.We find that even in the heavily overdoped non-superconducting Bi2201 sample,a kink at?70meV can still be clearly seen in the nodal dispersion.Also there may exist other fine structure at 40meV,30meV and 17meV.We systemat-ically studied the doping and temperature dependence of the Fermi liquid behavior for the nodal direction in overdoped Bi2201.By fitting the imagi-nary part of the self energy?"(w)with a model that includes three terms:the electron-electron correlation self energy(?"e-e(?)=A*?n),the electron phonon coupling self energy(?"e-p(?)?erf(?-?D))and an impurity term(?"imp(?)= const),we find that the nodal imaginary part of the self energy can be well described.Furthermore,the nodal electron-electron self energy evolves from near linear dependence on energy in optimally-doped sample to the quadratical dependence in the overdoped non-superconducting sample.This indicates that,for the nodal direction,there is an evolution from the marginal Fermi liquid behavior(optimally-doped)to Fermi liquid behavior with increasing doping.