Infrared Spectroscopy Study Of The Hybridization Effect On Yb Based Compounds

Heavy fermion metal is a strongly correlated class of electronic systems that began its research in the 1970 s which is also known as heavy electronic metal systems.This system comes from the study in the first half of the twentieth century on the magnetic impurity metal scattering effect.Surprisingly,the 10 k singular minimum observed in the resistance measurement of gold has opened up further research in this area.With the further development of materials related to the heavy fermions,much more abundant physical properties and complicated physical mechanisms have attracted more and more attention.In addition,the discovery of new heavy fermionic and mixed valence materials and the high-quality synthesis of known materials are of tremendous significance for the discovery and understanding of the properties in this system.Among various research methods,the infrared spectroscopy is able to provide a lot of meaningful information for the band structure,charge dynamics and related aspects.It plays a key role in revealing the energy level of the energy gap in strongly associated problems,exploring the effects of electron correlation,probing the lifetime of quasiparticle transport,then inferring its propagation,and increasing the mass of effective electrons in heavy fermion systems.We synthesized a number of Yb-based and Lu-based new single crystal materials and make physical characterization in PPMS system.In addition,the optical response of hybridization effects in heavy fermions and mixed valence compounds is mainly studied by the method of infrared spectroscopy,the corresponding physical phenomena are investigated and the physical mechanisms involved are explored.The main contents include the following:First of all,in the RT2Al10 system represented by Yb Fe2Al10(R stands for rare earth materials and lanthanides,and T stands for transition metal Fe,Ru and Os),we add the research results of single crystal Yb Fe2Al10.We explored the synthesis of high-quality single crystal,and succeed in synthesis of a large single crystal crystal and making detailed physical characterization.There is no sign of phase transition in the resistance measurement,reflecting a very good metallic behavior.In particular,the magnetic susceptibility is quite different from that of polycrystalline samples.There shows no magnetic order from room temperature to 1.8K,but it deviates from CurieWeiss behavior near 380 K and forms a broad peak.It implies obvious hybridization behavior within the material and also is the typical feature of mixed valent materials.The measured results of the optical spectroscopy showed a typical metallic response with a plasma frequency of 1.77 e V which was significantly reduced with temperature decrement or hybridization intensity increment.Based on the characteristics of opening a bandgap combined with the magnetic susceptibility of mix-valent compounds,we hypothesize that hybridization effect begins above room temperature throughout the single crystal sample and opens the hybrid gap.It also implies that the sample has a rather high coherent temperature.It is quite different from the previously reported polycrystalline nature.Our work helps to further understand the physical mechanisms underlying this system.Secondly,we have explored the self-flux method to synthesize Ybx Lu1-x Al3(x = 0,0.25,0.5,0.75 and 1)as a typical intermediate valent material.First,Yb Al3 appears a pseudogap around 540 cm-1(~ 67 me V),and this feature is suppressed in a sample with a doping concentration of about 0.25.The temperature dependent gap-formation is caused by hybridization between conduction electrons and 4f electrons of Yb irons.The strong mid-IR peak also originates from the transition across the direct hybridization bandgap.Although hybridization strength have been confirmed to increase with increasing Lu content,the mid-IR peaks gradually shift to lower energies as the Yb content decreases.This observation is completely contrary to the expectations of PAM.Through systematic analysis,we believe that the periodic effect of Kondo lattice still plays a prominent role in the doping process.Although random substitution of magnetic Yb with non-magnetic Lu will partially destroyed periodic Kondo lattice effect and results in a decrease in the mid-infrared hybridized energy gap as the hybridization strength increases.Finally,the A3T4X13 with cubic Yb3Rh4Sn13-type structure(A stands for a rare earth element,T for a transition metal,X represents Ge or Sn)has a wealth of physical properties: superconductivity,charge density wave,heavy Fermi metals and mixed valence behavior.The magnetic susceptibility characterization of single crystal Yb3Co4Ge13 and Yb3Rh4Ge13 indicates the two materials have a similar Kondo temperature as well as the hybridizion strength.The infrared spectroscopy study found that the two compounds have obvious spectral characteristics of heavy fermions.In the conductivity spectra of Yb3Rh4Ge13,the hybridization gap opens at 360 me V through the Drude-Lorentz fitting and for Yb3Co4Ge13 the gap shifts to 350 me V.Both materials have a similar electronic structure based on the spectroscopy,and there is no significant change in the hybridization effect or the electronic structure of the material with respect to the change of the transition metal from Co to Rh.The results of optical studies can provide a new insight in the nature of this system and the mechanism of the intermediate valence behaviors.