Single Crystal Growth And Physical Properties Of Topological Materials

Recent years have seen the prosperous development of topological electronic materials and it has been an important part in condensed matter physics.The discovery for topological insulator,topological semimetal and other new topological states have opened up a new field for searching and studying novel fermions.There has formed a process of study topological materials as following by the route of theoretical prediction–materials synthesis–experimental confirm.Among this,single crystal growth plays an important role in the part of materials synthesis.In this dissertation,combined with single crystal growth,structural and physical properties and Angle resolved photoemission spectroscopy?ARPES?measurements,we observed the crystalline,electronic and magnetic properties and band structures of some new topological electronic materials.Main results are listed here:1.Single crystals of a nearly Dirac semimetal,EuMnSb₂,have been successfully grown.The structural and physical properties were studied in detail.Unlike EuMnBi₂and other AMnPn₂?A=Ca,Sr or Ba,Pn=Sb,Bi?materials that possessed square-net Sb or Bi layer,the Sb atoms in EuMnSb₂ formed a zig-zag layered structure.Specific heat capacity and magnetic properties exhibit an A-type antiferromagnetic ground state below²0 K.A characteristic hump appears in the temperature-dependent electrical resistivity curve at?25 K.Interestingly,EuMnSb₂ shows a negative magnetoresistance?up to-95%?in contrast to the positive magnetoresistances observed for EuMnBi₂ and AMnPn₂,providing a unique opportunity to study the correlation between electronic charges and spins in this class of materials.2.High-quality TiB₂ single crystals are grown via a flux method and its crystalline structure is observed.By using ARPES,we have systematically studied the electronic band structure of TiB₂.We find that two nodal-rings in the orthogonal k_z=0 and k_x=0planes,which connect with each other and form a remarkable nodal-chain structure along?38?-K direction.Furthermore,we observe the Dirac-cone-like surface states coming from both Ti and B terminations on the?001?cleaved surface,which are distinct from the drum-like surface states.3.We have successfully grown the KHgSb,ZrSiS and EuCd₂As₂ single crystals and studied their structural and physical properties.By using ARPES,we have discovered many novel topological electronic states in these samples.Interesting surface state with hourglass-shaped band dispersion is observed on the?010?surface of KHgSb.Remarkable nodal-line and nodal-surface band structures are observed in bulk electonic state of ZrSiS.The Weyl-cone-like band structure induced by strong ferromagnetic fluctuation in paramagnetic region is observed in EuCd₂As₂.These findings have broadened the research field of new topological electronic states.Nowadays,the investigation and development for new topological materials and topological states have entered a new chapter.The concepts of“Solid Universe”and“Topological Dictionary”are creating a new upsurge in condensed matter physics.