Exploration Of Exotic Quantum States In Rare-earth-based Correlated Materials

Correlated quantum materials are playing a significant role in condensed matter physics,exhibiting many exotic quantum states including high temperature superconductivity,Mott insulators,and heavy fermions,etc.These materials can also host topological electronic structure,revealing fascinating physical properties as observed in topological Kondo insulators.As typical correlated quantum materials,rare-earth based intermetallic componds attract much attention because of the strong interaction between 4f electrons and conduction electrons.In this thesis,aiming at discovery of new quantum states of correlated materials,we focus on sample exploration and physical properties investigation of rare-earth based quasi-one-dimesional and low-carrier concentration Kondo lattices,and potential magnetic topological semimetals.The main results obtained in this work are as follows:1.Based on the previous research,we found that CeAu2In4 is a new candidate of quasi-one-dimensional Kondo lattice compound.Needle-like single crystals of CeAu2In4 have been grown from In flux and characterized by crystallographic,magnetic,transport and specific heat measurements down to very low temperatures.This compound is found to undergo an antiferromagnetic transition at TN?0.9 K with a large Sommerfeld coefficient of the specific heat,?=369 mJ mol-1 K-2,and a highly non-mean-field profile of the specific heat peak.The Kondo temperature TK was estimated to be 1.1 K,being low and comparable to TN.While Fermi liquid behavior is observed deep into the magnetically ordered phase,the Kadowaki-Woods ratio is much reduced relative to the expected value for Ce compounds with Kramers doublet ground state.Markedly,this feature shares striking similarities to that of the prototypical quasi-one-dimensional compounds YbNi4P2 and CeRh6Ge4 that have tunable ferromagnetic quantum critical point.Given the shortest Ce-Ce distance along the needle direction,CeAu2In4 appears to be an interesting model system to investigate the unconditional antiferromagnetic quantum critical behavior in a quasi-one-dimensional Kondo lattice with enhanced quantum fluctuations.2.Exploration of low-carrier density Kondo lattice compounds is significant in studying the exotic properties of Kondo semiconductors,semimetals,and underscreeened Kondo compounds.The previous investigations on CeCuAs2 polycrystalline samples suggested it might be a low-carrier density Kondo system.Here we have synthesized Single crystals of CeCuAs2 by Bi-flux and solid state reaction method.Combined electric transport,magnetic,and specific heat measurements reveal it to be a heavy fermion semimetal.The two different grown techniques yield two kinds of samples with rather different physical properties.One type is metallic,with antiferromagnetic phase transition at 7.9 K.The other is semiconductor-like,with a clear feature of short-range magnetic interaction at low temperature observed in both susceptibility and specific heat.Single crystal x-ray diffraction analysis indicates the metallic sample employs a stoichioetric HfCuSi2 type structure.While the semiconductor-like sample forms a stuffed HfCuSi2 type structure with slight excess of Cu occuping the "2c" site.The above results suggest CeCuAs2 is an adjustable low-carrier Kondo system,which can be used to study Kondo screening effect by tuning carrier concentration.A key point in the future investigation is to smoothly tune this compound from a Kondo semimetal to a Kondo semiconductor.3.PrAlSi was predicted to be a potential ferromagnetic Weyl semimetal,which can be an ideal system to study the relationship of f-electron magnetism and topological electronic band.Here we have syntesized single crystral of PrAlSi and comprehensively investigated its structural,magnetic,transport,and thermodynamic properties,in comparison to its nonmagnetic analog LaAlSi.PrAlSi exhibits a ferromagnetic transition at Tc=17.8 K,which,however,is followed by two weak phase transitions at lower temperatures.The two reentrant magnetic phases can be suppressed by a small magnetic field of about 0.4 T and are proposed to be spin glasses or ferromagnetic cluster glasses based on dc and ac magnetic susceptibilities.At higher magnetic fields,PrAlSi show a large anomalous Hall conductivity amounting to?2000 ?-1 cm-1.Both PrAlSi and LaAlSi reveal large,nonsaturating magnetoresistance as a function of field.While Shubnikov-de Haas oscillations are absent in LaAlSi,they are clearly observed below about 25 K in PrAlSi,with an unusual temperature dependence of the dominating oscillation frequency F.It increases from F=18 T at 25 K to F=33 T at 2 K,hinting at an emerging Fermi pocket upon cooling into the ordered phase.These results suggest that PrAlSi is a interesting system where a small Fermi pocket is strongly coupled to local-moment magnetism.On the other hand,due to the complicated magnetic phase at low temperature and the comparable crystal electric field splitting energy to ordering temperature,PrAlSi exhibites a giant magnetocaloric effect,with-?SM=22.6 J/kg K near the Curie temperature under a magnetic field change of ?0?H=5 T along the magnetic easy c axis,and can be a promising magnetocaloric material.