The Search For Unconventional Superconductivity,Novel Magnetism And Topology In Equiatomic Arsenides

In this thesis,we concentrate on several rare-earth-/alkaline-earth-based equiatomic arsenides.We have synthesized high-quality crystalline samples,carefully characterized their physical properties,and searched for potential novel properties at low temperature.We mainly focus on the study of several typical ordered phases which are closely related to spin degrees of freedom,where the correlation and topology are also discussed.1.We have grown high-quality single crystals of YbAs,and performed a detailed study of the magnetotransport and electronic structure.Unlike Ce-monopnictides,we have found significant inconsistencies between our transport data and the proposed p-f mixing model.Our conclusion is that there is a lack of a heavy fermion state in YbAs,at least down to 0.275 K,and no band inversion is found.However,we have detected an anomalous extremely large magnetoresistance in YbAs(compared to nonmagnetic LuAs),which we confirmed is due to the short-ranged spin correlations which develop below 20 K.Furthermore,we observed a field-stabilized new phase in magnetic fields above 11 T,for which the order parameter remains to be determined2.We have synthesized both poly-and single-crystals of CaPtAs,which crystallizes in a tetragonal noncentrosymmetric(NC)structure(space group:I41md)with a lattice parameter c almost 10 times larger than a.We have confirmed bulk superconductivity in CaPtAs with a Tc of 1.47 K,and determined various superconducting parameters.In particular,by fitting the temperature dependence of the electronic specific heat and magnetic penetration depth at T<<Tc,we obtain evidence for point nodes in the superconducting gap.Furthermore,zero-field muon-spin relaxation measurements detect time-reversal symmetry breaking(TRSB)in CaPtAs at T ?Tc.All together,these results indicate that CaPtAs is a new unconventional superconductor with both TRSB and inversion symmetry breaking.3.We have synthesized both poly-and single-crystals of EuPtAs with a polar NC structure(space group:I41md).We carefully characterized the physical properties of EuPtAs and constructed the field-temperature phase diagrams for both H ? c and H ? c.Our results indicate that the local moments of Eu2+in EuPtAs undergo two magnetic transitions at low temperature.In the phase diagram for H ? c,we observed a new phase(phase ?)with a dome-shaped phase boundary,which shows similarities with the reported A-phase in EuPtSi,including additional jumps in both the MR and Hall resistivity inside this phase.These imply a potential topologically nontrivial magnetic structure in phase ?.Lastly,our preliminary neutron scattering experiments indicate incommensurate propagation vectors below TN in zero field.4.We have also synthesized poly crystal line YbPdAs with a hexagonal ZrNiAl-type NC structure(space group:P62m),in which the Yb-atoms form a distorted Kagome lattice.After a detailed characterization,we found that YbPdAs is a low-carrier Kondo lattice with a second-order phase transition below T*(?)6.5 K.More microscopic measurements are needed to reveal the order parameter below T*,and the potential frustration effects arising from the crystal structure.