Studies Of Electronic Correlations,Magnetism And Topology In Rare-earth Pnictides

Strongly correlated materials can be tuned by pressure,external magnetic fields and chemical substitution which potentially lead to the realization of quantum phase transitions.On the other hand,changing the spin-orbital coupling strength in these systems could possibly modify their band structure and leads to topological phase transitions.Due to the limitations of present experimental and theoretical techniques,most studies focused on band topology are within the single particle picture.It turns out that materials with strong electronic correlations or unusual magnetic order exhibit even more fascinating behavior.Therefore,correlated topological materials have emerged to become one of the major focuses of band topology research in recent years.During my PhD,I dedicated myself to searching for ideal correlated topological material candidates,and systematically measuring their physical properties.Rare earth pnictides are correlated electronic system with large orbital angular momentum and therefore they exhibit rich ground states and high tunability.By combining different tuning parameters and various physical property measurements,we systematically studied the magnetism,electronic correlations and topological properties of these compounds.The results allow us to explore the interplay between magnetism,electronic correlations and topological properties.Ce2Sb/Bi are heavy fermion antiferromagnets which crystallize in a tetragonal structure.Band structure calculations show that these compounds are potential candidates for correlated topological materials.We successfully synthesized high quality single crystalline samples,systematically probed the magnetocrystal line anisotropy and completed the temperature-field phase diagrams.These results suggest that both materials possess field-induced tri-critical points at low temperatures.Based on the Ehrenfest equation,we predict that the tri-critical point of Ce2Sb can be suppressed to lower temperatures under pressure,eventually reaching a quantum tri-critical point.This study provides guidance for realizing quantum tri-criticality and understanding spin fluctuation theory.XSb/Bi(X=Ce,Pr,Sm)have face-centered cubic structures with rich magnetic ground states.Magnetotransport measurements show that all these compounds exhibit large magnetoresistance due to electron-hole compensation.The combination of quantum oscillation analysis,theoretical calculations and ARPES measurements leads to the systematic mapping of the topological properties of these materials.Based on these results,we have uncovered topological phase transitions with two possible tuning parameters:the spin orbital coupling strength and 4f-electron number.Moreover,we have systematically studied how the electronic structures of PrSb and PrBi respond to an external magnetic field.Some exotic behaviors in SmSb beyond the description of conventional Lifshitz-Kosevich theory are also reported.XPtBi(X=Ce,Sm)also crystallize in a cubic crystal structure yet with Pt atoms on the noncentrosymmetic sites.Such a special crystalline geometry forces the degeneracy of electron and hole bands at Kramer’s points.Detailed band structure calculations near the Fermi level show the existence of triple-degenerate points due to strong spin-orbital splitting.It is theoretically predicted that the triple-degenerate points naturally become pairs of Weyl nodes upon breaking time reversal symmetry,and therefore they contribute to the chiral anomaly effect.Angle-resolved magnetotransport measurements provide crucial evidence for the chiral current induced negative magnetoresistance,which only occurs when the field is applied along the current direction.These results not only identify the existence of field-induced Weyl nodes,but also provide a platform for studying the thermoelectric and optical responses of correlated topological materials.Meanwhile,the existence of long-range antiferromagnetic order in the XPtBi compounds makes them highly relevant for probing the topological response to magnetic ordering states.