Studies On Novel Magnetism And Electronic Transport Properties In CoSn,FeGe,MnPt

The physical properties of solid-state materials depend largely on their electronic band structure.Compared with the common parabolic dispersive bands,the linearly dispersive Dirac/Weyl bands and the nondispersive flat bands are important platforms for generating new states and new effects.For example,in Dirac/Weyl bands,electrons have zero mass,which leads to novel relativistic and topological phenomena.The typical representatives are the exotic topological transport properties such as chiral anomaly and intrinsic anomalous Hall effect in Dirac/Weyl semimetals.In contrast,electrons in flat bands have infinite effective mass.For flat bands in which the kinetic energy of electrons is quenched,the Coulomb interaction will dominate and give rise to a variety of correlated electron phenomena,such as ferromagnetism,high temperature fractional quantum Hall effect and high temperature superconductivity,serving as an ideal platform for exploring strong correlation effect.The band structure of a material is usually closely related to its crystal structure.One representative example is the kagome lattice,theoretical studies show that there are naturally linear dispersive Dirac/Weyl bands and nondispersive flat bands in its band structure.In addition,in real kagome lattice materials,the kagome lattices are mainly composed of 3d transition metal elements,which leads to rich magnetic ground state.The coexistence of the above special electronic band structure and the rich magnetic ground state makes kagome lattice materials host exotic physical effects.In this dissertation,we mainly focus on kagome lattice materials,and systematically study the magnetism and electronic transport properties of three different materials,including CoSn,FeGe and MnPt.The main results achieved are as follows:(1)Study on flat-band physics in paramagnetic kagome lattice CoSnWe systematically studied the flat-band-induced physical properties by using the paramagnetic kagome lattice CoSn.By combination of first-principles calculations and angle-resolved photoemission spectroscopy measurements,we first reveal the existence of narrow flat bands around the Fermi level in CoSn.Electronic transport measurements indicate that the resistivity within the kagome lattice plane is 60 times larger than the interplane one,in sharp contrast with conventional(quasi-)two-dimensional layered materials.Moreover,macroscopic magnetic measurements indicate that the magnetic susceptibility under the out-of-plane magnetic field is much smaller as compared with the in-plane case,which is revealed to be arising from the introduction of a unique orbital diamagnetism through further nuclear magnetic resonance measurement.Systematic analyses reveal that these anomalous and giant anisotropies can be attributed to the localization of flat-band electrons in the kagome lattice.This work successfully reveals the macroscopic electronic behavior caused by the flat band in the kagome lattice and provides a new idea for further exploring the flat-band-induced correlated electronic properties.(2)Study on novel magnetotransport behaviors in antiferromagnetic kagome lattice FeGeWe systematically studied the characteristic magnetic transport behavior induced by rich magnetic ordered structure using antiferromagnetic kagome lattice FeGe.At low temperature,we first observe that the magnetic susceptibility of FeGe decreases first and then increases with the decrease of temperature,indicating that there may be a new type of magnetic ordered phase.Moreover,we observe the jump behavior of magnetoresistance and Hall resistance with the increase of magnetic field,which can be attributed to the the spin-flop of magnetic moment and the possible Lifshitz phase transition caused by the magnetic field,respectively.This work provides a candidate system for further exploring the deep correlation between spin symmetry and magnetic transport behavior.(3)Study on topological magnetism and topological transport behaviors in antiferromagnetic MnPt systemWe systematically studied the electronic transport properties of the antiferromagnetic material MnPt.We reveal the coexistence of parallel-field negative magnetoresistance and topological Hall effect at low temperature,indicating a possible coexistence of topology in both reciprocal space and real space.In addition,we also observe nonFermi liquid behavior at low temperature,which can be tuned to marginal Fermi liquid behavior with increasing magnetic field.This work not only provides a material candidate for experimentally exploring the coexistence and coupling of various topological magnetoelectric states,but also provides a new idea for designing new topological electronic devices and spintronic devices.