Superconductivity In Noncentrosymmetric Mo₃P Single Crystal And The Phase Diagram In CsCo₂Se₂ Single Crystal

After the superconductor enters the superconducting state,it has attracted much attention from scientists due to its zero resistance and Meissner effect.Although the mechanism of superconductivity in conventional superconductors can be explained by the BCS theory,there are still many unconventional superconductors that so far cannot be described by a unified basic theory.Compared with conventional superconductors,unconventional superconductors exhibit many strange physical properties,such as multi-band effect,mixing of spin singlet and spin triplet pairs,and existence of superconducting energy gap nodes.Searching for unconventional superconductors and studying their strange physical properties has always been a hot topic in condensed matter physics theory and experimental research.In the first part,superconductivity in single crystallinehas been investigated by the measurement of electrical resistivity,magnetic susceptibility,and specific heat capacity.Its space group is I4-2 m with lattice parameters(6(6=(7(7=9.8084?2???and(8(8=4.8352?1??.A bulk superconductivity with a critical temperature of₍(8?8?=anisotropic behavior was discovered in the resistivity and upper critical fields.A clear upward curvature in Hc2 was observed,suggesting a multiband superconductivity in.The value of the Ginzburg-Landau parameter indicates thatis a type-II analyses indicate thatis a weak coupling Bardeen-Cooper-Schrieffer superconductor with fully gapped superconductivity.In the second part,the magnetic properties of Cs,possessing a Th,are systematically studied by using specific heat,resistivity,and torque measurements.Our results reveal that Csundergoes a paramagnetic state to antiferromagnetic order at?80at zero magnetic field.The TN is nearly independent of the external magnetic field for H?c-axis,and can be suppressed for H?ab-plane below 4 T,above which spin-flop phase transition sets in.A hump-like behavior in resistivity was discovered,which was ascribed to a field-induced spin-flop phase transition.The magnetoresistance results suggest that a crossover of spin-flop phase transition occurs at low temperatures in the field range of 2-4 T for H?ab-plane.Furthermore,the magnetic torque results reveal a novel ordered Co spin structure at low temperatures under 6 T for H?ab-plane.Finally,we summarize the magnetic phase diagram of Csbased on resistivity and torque results.