The Single Crystal Growth,Transport Characteristic And Electronic Structure Research Of The Typical F-electron Materials

The significant progress of condensed matter physics theories which have been made by researchers for many years have made it possible to explain the physical properties of most solid materials and the microscopic mechanism.However,there are still many major issues that need to be discussed,including how to accurately describe strongly correlated electronic materials,a system with many novel quantum properties.The band theory which is based on the single-electron approximation and ignores the Coulomb repulsion between the electrons,can explain the micro-mechanics behavior of the ordinary metals,semiconductors and insulators.But in strongly correlated electronic materials,the single-electron approximation is no longer applicable.They show complicated and complex quantum characteristics because of the strong correlation between the quasi-particles including electrons,phonons and spins,and it's hard to describe the micro-mechanisms quantitatively.How to understand and accurately explain the electronic structure,magnetic properties,superconductivity and quantum phase transitions in these materials is of great value for us to explore new quantum phenomenoms and develop brand new technologies.As a main branch of the strongly correlated materials,the heavy-fermion system shows extremely low energy scale and researchers in our group already did many valuable explorations.We select the heavy-fermion system and felectron system to study the crystal growth,transportation property and electronic structure.Our mainly research objects are the typical antiferromagnetic uranium heavy fermion superconductor UPd2Al3 and Lanthanum to explore the transportation property and electronic structure,respectively.We hope that our work could make a contribution to develop the strongly correlated experiment and theory.In the present research,the discussion of UPd2Al3 mainly focused on its superconductivity and magnetic phase transition.People had conducted a comprehensive exploration of it in the early stage,and determined its magnetic structure,magnetic phase transition,field behavior,strongly correlated electron behavior,and possible superconducting parameters.But it is still unclear about how the 5f electrons behave differently by temperature changing.To understand the total physics in this novel antiferromagnetic-superconductivity co-existing material requires more sophisticated experiments and breakthrough theories.This article mainly focuses on the transport characteristics of UPCd2Al3:Firstly,we have grown up the UPd2Al3 single crystals by tri-arc pull-up furnace with part of them have been annealed by box furnace.Then we determined the single crystal quality,elemental composition,impurity matter and lattice plane index of UPd2Al3 by X-Ray Diffractometer(XRD),Energy Dispersion Spectroscopy(EDS).By the Physical Property Measurement System(PPMS)experiments,we got the resistance,magnetic susceptibility and magnetization experimental data of UPd2Al3.After analysis and data fitting,these transport informations lead the way to explore the magnetic structure,transport characteristic and 5f electron behavior characteristic of UPd2Al3.We grown the high quality single crystal samples with the residual resistivity RRR=164 and figured out the negative influence of the annealing.The magnetic susceptibility of UPd2Al3 shows the dual characteristic of 5f electrons in UPd2Al3 with effective magnetic moment 3.246 ?B/U which means there are pretty strong valence fluctuation in UPd2Al3.At 80 K,the 5f electrons start being coherent and gradually turn to the quasi-particles excitations.The short-range magnetic moment groups also start to interact with each others.The competition of these two correlated effects determines the ground state of UPd2Al3,and at 14 K,it transforms to antiferromagnetic state from paramagnetic state.Much lower temperature experiment with high magnetic field shows the relocation of magnetic domain at 0.6 T and electron spin flip at 4 T which may cause the fermion surface distortion.The metal La is an ancient system.It has been fully explored in the fields of application and basic research.But its electronic structure and whether there are surface states are still in controversial.So this part research starts from the ?-La single crystal thin film growth,then detects the electronic structure.We had grown the ?-La single crystal thin films by Molecular Beam Epitaxy(MBE)method.Then we check the thin films quality,two-dimensional property and surface reconstruction of the samples by Reflection High Energy Electron Diffraction(RHEED)and Low Energy Electron Diffraction(LEED).We chose the high quality samples to carry out the Angle Resolved Photoemission Spectroscopy(ARPES)to obtain the electronic structure,clear Fermi surface topology and surface states.The comparison between our first principle calculations and ARPES results found that there are strong d electrons correlation effects in ?-La thin film which may originate from the low dimensional effect and there is no surface state in ?-La which commonly agreed but from 5d electron bulk orbitals contribution.