The Thermal Transport Properties Of Correlated Electron System

There are a variety of complex scattering mechanisms in the correlated electronsystems. Therefore, the thermal transport properties of the correlated electron systemare very intriguing. Reversely, research on the thermal transport properties help tounderstand complex scattering mechanism in the correlated electron material (e.g. theintermediate valence compound, the heavy-fermion compound, superconductingmaterial). With the development of cryogenic technology, transport propertiesmeasurement has a further breakthrough.The main work of this paper includes three parts. Firstly, we have designed twomeasurement devices for the thermal transport properties. Secondly, the Nernst effectand the thermoelectric properties of the intermediate valence compound YbAl3wasinvestigated. Thirdly，the thermoelectric properties of the strong correlated electroncompounds FeSi1-xGexwas studied.At present, commercial measurement systems for the thermal transport propertiesare very advanced and convenient. The sample holder, we used to call it “Puck”, isonly applicable to the big size sample. Thus, we can’t use this puck to measure a smallsize sample. In order to solve this problem, we design two distinctive sample holdersand a relevant data acquisition system. It is very convenient to use our sample holderand relevant data acquisition system to measure the thermal transport properties of asmall size sample.The recently research found that the Nernst coefficient and thermopower of theheavy-fermion compound CeCu2Si2are related by the anomalous Hall mobility due tothe local asymmetric Kondo scattering. We are interested in checking the applicabilityof this result in the prototypical intermediate valence compound YbAl3and finding the reason of the enhance thermopower of YbAl3. Single crystals of YbAl3are grownby the self-flux technique. Then the Nernst coefficient and the thermoelectricproperties of YbAl3were measured. We found that the relationship that wasdiscovered for CeCu2Si2is not applicable to YbAl3. Different to the thermopowerwhose absolute values are enhanced with increasing temperature and assume a broadmaximum at175K, the Nernst coefficient of YbAl3is enhanced only below T≈75K.Rather, the thermopower of YbAl3is well described by a simple narrow-band model.We discuss the reason for this in terms of the intermediate valence nature of YbAl3that is conceptually different from the local Kondo physics.FeSi is a prototypical narrow-gap Heavy-fermion semiconductor with enhancedthermopower. The resistivity of FeSi1-xGexwas researched previously. It is found thatthe resistivity of FeSi1-xGexdecreases with increasing of x. Base on the relationshipbetween ZT and the resistivity, thermal conductivity, thermopower, we want to makefurther research on the thermoelectric transport properties of FeSi1-xGex,aiming tofind enhanced thermopower and ZT in FeSi1-xGex.Firstly,the sample of FeSi1-xGexwasprepared by arc melting. The results of powder XRD for the FeSi1-xGexsamples showthat the XRD patterns shift to lower angles corresponding to a lattice expansion withincrease in Ge concentration. We measure the resistivity, thermal conductivity andthermopower of FeSi1-xGex, then found that these are decreases with the increase ofx.This result is different from what has been expected.