Manipulation On The Physical Properties Of Low Dimensional Manganites And Exploitation On The Topological Properties Of Weyl Semimetal

In condensed matter physics,the exotic behavior of electrons can usually excite a spectrum of intriguing quantum effects and emergent phenomena.Perovskite manganite is a typical kind of strongly correlated systems.Due to the coupling between the spin,charge,lattice,and orbital degrees of freedom,manganites possess rich electronic phase diagrams and physical properties,among which,the electronic phase separation(EPS)is one of the most important physical features.In this thesis,we modulate the magnetic and transport behaviors of low dimensional manganites through manipulation on its EPS in real space,via dimensionality engineering,Au particle capping and laser illumination.On the other hand,Weyl Semimetal has attracted widespread attentions in recent years due to its singular topological electronic structures in momentum space.In this thesis,we investigate the topological properties of Type-? Weyl Semimetal WP2 via angle-resolved photoemission spectroscopy(ARPES)and electronic transport measurements.The dissertation is composed of four parts:In the first chapter,we first introduce the research background of manganites,such as the crystal structures and distortions of perovskite manganites,several primary physical mechanisms for understanding its magnetic and electronic behaviors,and the current research progress about the manipulation of its electronic phases and physical properties.Then,we succinctly introduce the basic conceptions about topological semimetals,especially Weyl Semimetal-related topological protection,chirality,classification and its unique fingerprint effects:Fermi arc and chiral anomaly.In the second chapter,by using single-crystalline La0.33Pr0.34Ca0.33MnO3(LPCMO)/MgO core-shell nanowire as a model system,we demonstrate that the quasi-1D confinement on the electronically phase-separated manganites substantially enhances the sensitivity of transport to even probe the magnetic fluctuations,e.g.,the magnetic nanodroplets in the insulating matrix,which is the precursor to the FMM phase.More interestingly,the quasi-1D confinement can even modify the phase competition to stabilize thin insulating domains at low temperatures,which serve as tunneling barriers to form intrinsic tunneling junctions.Such tunneling effect survives even under magnetic field up to 14 T and essentially modifies the classic 1D percolation picture to stabilize a novel quantum percolation state.A new phase diagram for this model manganite system under quasi-1D confinement is thus established for the first time,which differs substantially from that for the bulk or thin films.Our findings inspire new insight into understanding and manipulation of the EPS and corresponding magneto-transport properties in electronically soft matters via dimensionality control and thus hold great promises toward electronic device applications.In the third chapter,cooperative effects of Au-nanodots capping and laser illumination on the transport properties of LPCMO thin films have been exploited.The local insulating domains are induced due to the extraction of oxygen from LPCMO thin films by Au nanodots,leading to a nonpercolating state at low temperatures.When the laser illumination is subsequently switched on,the nonpercolating state can be switched back to a percolating state in a nonvolatile way.Moreover,such a photo-induced percolating state can be easily erased by thermal cycling.Our findings would further promote the realization of engineering desired patterns of competing phases in manganites.Such a route for the manipulation of electronic phases will underpin the understanding of the coexistence and competition between various electronic phases,and further inspire novel functional applications.In the fourth chapter,extremely long and straight Fermi arcs are discovered for the first time at the(021)surface of the WP2 single crystal by ARPES measurements.Electronic transport reveals a butterfly-like AMR at low temperatures,arising from the anisotropic bow-tie-like electron FSs.Moreover,a highly tunable Berry phase is demonstrated from the angle-dependent SdH quantum oscillations,which can be attributed to the topological singularities,i.e.monopoles or band degenerate points in the momentum space.Our findings not only inspire deep insights into the understanding of the topological and Fermitronic properties of Weyl semimetals,but also promise potential applications in topological electronic and Fermitronic devices.