Exploration Of Carbon-based Superconductors And Properties Of A New Heavy Fermion Compound YbPtAs

Because of the novel properties and huge application potential,superconductivity is always a hot topic in condensed matter physics since its discovery.Up to now the superconductors can be sorted into four types of superconducting metals and alloys,organic superconductors,heavy fermion superconductors,unconventional high temperature superconductors includes cuprate superconductors and iron-based superconductors.Organic superconductors have great value in both research of superconducting mechanism and application due to the simple structure and small quality.The organic materials including graphite,carbon nanotube,fullerene C60,aromatic hydrocarbons,organic salts,can lead to superconductivity through doping or other methods.In this article,The glassy carbon?GC?reacted with a series of alkali and alkaline earth metals and the superconductivity was discovered in the GC doped with K and Ca.Graphene fiber and graphene film with high quality have been fabricated and show superconductivity after doping with Ca.Heavy fermion compounds,in which the local momentums couple to the conduction electrons resulting in novel phenomena,have been one of the important topics in condensed matter physics.The paring mechanism of heavy fermion compounds is not the conventional electron-phonon coupling.We prepared the YbPt As sample with an AlB2-type structure to study the physical properties.There is no occurance of superconductivity down to 1.8 K in the antiferromagnetic heavy fermion compound Yb PtAs.The main contents are listed as follows:1.Introduction of the development of superconductivity and the research status of the organic superconductors.The brief introduction of the heavy fermion compounds,Kondo effect and RKKY exchange action originate from the coupling of the local moments with conduction electrons.2.The phenol formaldehyde?PF?resin is first carbonized to glassy carbon?GC?,GC consists of disorder curly graphene,which is similar to the fragments of C60.Alkali and alkaline metals are doped into GC through solid state reaction,and KGC8 and CaGC6 with good superconductivity are recieved.The Tc?8 K?of KGC8 is much larger than the Tc?0.55 K?of graphite intercalated compounds?GIC?KC8.The difference of Tc value originate from the distinction of structure in GC and graphite.Tc?9.2 K?for CaGC6 is comparable to the Tc?11.5 K?for CaC6.This is the first time that superconductivity has been achieved in GC.3.The graphene fiber and graphene film with high quality are fabricated according to the wet pinning.Graphene fiber is assembled by folding the graphene along the axis disorderly and consists of much wrinkles.Graphene film is composed of graphene layers and covered with wrinkles and ripples.Ca intercalated graphene fiber and graphene film are synthesized via a facile vapor transport process,and superconductivity has been observed at 11 K.The color of graphene fiber and film evoled from silver gray to yellow due to the intercaltion of Ca.After reaction,graphene fiber and film show good flexibility and keep intact.These two superconductors have wide application prospects in the future.4.Polycrystalline YbPtAs was synthesized by solid state reaction and single crystal YbPtAs was grown from a lead flux.The structure of YbPtAs is noncentrosymmetrical AlB2-type similar to the Sr PtAs.The Yb ions are in a trivalent state in YbPtAs and order antiferromagneticlly at Neel temperatures TN1=6.5 K and TN2=2 K,respectively,deduced from the magnetic susceptibility and heat capacity measurements.The magnetic contribution in resistivity shows a broad maximum around 100 K indicates the presence of Kondo effect in YbPtAs.The Sommerfield value for YbPtAs obtained from the heat capacity result is?=213 mJmol^-1K^-2,which is much larger than?=3.4 mJmol^-1K^-2 of LuPtAs.YbPtAs is a new heavy fermion material.