Abnormal Nernst Effect Of The Magntic Topological Semimetals

Thermoelectric effects,including Seebeck effect and Nernst effect,which can reflect the topological information of Fermi surface,have been used as a powerful means to detect and study topological/quantum phase transition,spin excitation,magnetic ordering and other strange physical phenomena in the field of condensed matter.For a conductor,the longitudinal temperature gradient can induce a longitudinal voltage,which is known as Seebeck effect.When a magnetic field is applied in the direction of a vertical temperature gradient,the conductor will induces an electric field transversely,which phenomenon is known as Nernst effect.In this paper,we studied two topological Ferromagnetic Semi-metallic materials by transport measurements which is including Magnetothermoelectric effect:?1?We emphatically studied the anomalous quantum transport properties of Co₃Sn₂S₂which is provided with quasi-two-dimensional Ferromagnetic Weyl Semi-metal with Kagome lattice and measured its anomalous Hall effect and anomalous Nernst effect.?2?We studied the two-dimensional ferromagnetic Nodal-line semimetal Fe_3-xGe Te₂system under different iron vacancies.?1?We studied the thermoelectric effect of quasi-two-dimensional ferromagnetic Weyl semi-metal Co₃Sn₂S₂.We found that the system showed a giant anomalous nernst signal?ANS?,reacheing the maximum value of 5?V/K at 70K.The value is much larger than that of the conventional Ferromagnets?less than 1?V/K?,where the origin of the large Nernst signal is ascribed to the Weyl point of the topology very different from that of the conventional Ferromagnets.In addition,the Nernst signal deviates from the conventional scale relation for the normal Ferromagnets,which implies the different mechanism in the present system.According to the first-principles calculations,we declare that the large ANE in the system is mainly due to the non-trivial Berry curvature near Weyl points.Our experimental results further confirm that the Co₃Sn₂S₂is the ferromagnetic topological Weyl semi-metal,and the Berry curvature near the Weyl points contributes greatly to the AHE and ANE.?2?We investigated the AHE/ANE in the 2D ferromagnetic Nodal-line semi-metal Fe_3-xGe Te₂?x=0.11-0.20?with different iron vacancies.Through the measurement of electric and thermal transports,we found that the iron vacancies could effectively change the Curie temperature from 165K of x?0.20 to 210K of x?0.11.Meanwhile,the saturation magnetic moment increases with the increasing Curie temperature.For all the samples with different iron vacancies,the AHE and the ANE are observed,but the size of AHE does not change too much with iron vacancies.On the contrary,iron vacancies can greatly affect the magnitude of ANE.With the increase of Fe vacancies,ANE single decreased rapidly.These results indicate that besides ferromagnetic ordering,the non-trivial topological band structure in the Fe_3-xGe Te₂system plays an important role in the magnitude of the anomalous Nernst effect.Non-trivial Berry curvature enhances greatly the abnormal Nernst signal in the present system.