Application Of Tunnel Diode Oscillator In Superconductivitv And Strong Correlated Materials

Tunnel diode oscillator(TDO)is a powerful radio frequency method,which can easily realize high resolution resistivity and susceptibility measurements using simple experimental setups.It is widely used in measuring superconducting order parameter,phase trasntions and quantum oscillations in extreme conditions.And it plays an important role in studying unconventional superconductivity and quantum phase transitions.This thesis is devoted to studying different properties of CeRh6Ge4,CeRhIn5 and Lu5-xRh6Sn18+x using TDO technique.The detailed experimental results are summarized into three main points as follow:1)The electronic structure study of heavy fermion material CeRh6Ge4 with ferromagnetic quantum criticality.Recently,our group found a pressure induced ferromagnetic quantum critical point(FM QCP)in heavy fermion ferromagnet CeRh6Ge4,which broke the consensus of no FM QCP in a clean system.Inorder to study the mechanism of FM QCP and the electronic structure of this material,we performed angle dependent quantum oscillation measurements using both TDO and cantilever.In the meantime,we also did band structure calculations assuming 4f electrons are fully localized or itinerant.By comparing experimental results and calculations,we found that the Fermi surfaces are quiet consist with the fully localized scenario.This discovery indicates that CeRh6Ge4 is distinct from the itinerant ferromagnetic systems and the localization of 4f electrons might be an important ingredient to having FM QCP in this material.Hence,we think CeRh6Ge4 is a local moment ferromagnet which is distinct from the itinerant ferromagnetic systems with quantum phase transitions.Our studies suggest the possibility of a local quantum critical point in CeRh6Ge4.2)The explorance of pressure-field phase diagram of antiferromagnetic heavy fermion material CeRhIn5.This thesis detected the pressure dependence of metamagnetic transitions in CeRhIn5 using TDO and found the metamagnetic transitions are anisotropic and can exist in superconducting state.Combining the high field transport results in the reference,we concluded that the metamagnetic transition field kept at around 2 T below 1 GPa but increased with pressure when above 1 GPa.This behavior of meta-magnetic transition might relate to the change of magnetic structure under pressure.Furthermore,the highly anisotropy of metamagnetic transition also indicates the possibility of anisotropic pressure-field phase diagram under different field orientations.3)The order parameter study of time reversal symmetry breaking superconductor Lu5_xRh6Sn18+x.We measured the magnetic penetration depth using TDO and found the exponential temperature dependence of penetration depth.By analyzing the absolute value of superconducting coherence length and penetration depth,this thesis found the superfluid density of this material can be well fitted by s-wave model.Moreover,our band structure calculations suggested the existence of 3D Fermi surfaces,which ruled out the possibility of all nodel gap structures from the symmetry analysis that allowing time reversal symmetry breaking.Hence,the unconvential time reversal symmetry breaking in Lu5-xRh6Sn18+x is very most likely due to the loop Josephson current recently proposed by theorists.