Electronic Phase Diagram Of Electron-doped Cuprate La_2-xCe_xCuO_4+? Thin Films

Since the discovery of cuprates about thirty years ago,many high-temperature superconductors have been uncovered.But the origin of superconductivity is still under debate.As a strongly correlated system,there are many unique properties and composite orders in the normal state,such as antiferromagnetic order,stripe order and charge order,etc.which are considered to be closely related to the for-mation of Cooper pairs.Compared with the hole-doped cuprates,there are lower upper critical field and disappearance of pseudogap in the electron-doped coun-terpart.So it is very convenient to suppress the superconductivity by magnetic field to study the properties and composite orders in the normal state,which is very meaningful to research the origin of superconductivity.In this thesis,we mainly focus on the electron-doped cuprate La2-xCexCuOo4±?(LCCO)which has high quality samples over a wide range of doping levels.Through the study of properties in normal state,we plan to give the interpre-tations on the unique properties and the relation between the antiferromagnetic order and superconductivity.The main contents are as follows:(1)Through the study of the in-plane magnetoresistance on the LCCO thin films with different Ce dopings and oxygen contents,we observe that there exist unique properties in the normal state,such as negative and linear magnetoresis-tance.Then we propose that the negative in-plane magnetoresistance is related to the static antiferromagnetic order.The linear in-plane magnetoresistance in the under-doped regime and near optimal doping level,is relevant to network and density wave transition,respectively.(2)By taking the transport measurements for LCCO thin films with different oxygen contents in high magnetic field up to 58 Tesla,we confirm the boundaries of static and dynamic antiferromagnetic order,and then establish a multidimen-sional phase diagram.We also give an illustration of the quantum critical point in this system:there are two quantum critical points in this system and they will move in different directions when the magnetic field is applied.Meanwhile,we also consider that the spin density wave competes with superconductivity.Since our results could be interpreted by the conducting nano-filament network,we give one possible explain on the superconductivity in the electron-doped cuprates.(3)The LCCO combinatorial thin films from x = 0.1 to x = 0.19 were successfully fabricated by the combi laser-MBE technique.Through the struc-tural,content and transport measurements,the distribution of gradient content is verified to be continuous.Meanwhile,we take simulations of the film growth and show that the deviation of composition from the linear distribution is smaller than 1.54x 10-4,which is good enough to study the quantum criticality in future.