2020, Galeski, S., Zhao, X., Wawrzyńczak, R., Meng, T., Förster, T., Lozano, P.M., Honnali, S., Lamba, N., Ehmcke, T., Markou, A., Li., Q., Gu, G., Zhu, W., Wosnitza, J., Felser, C., Chen, G.F., Gooth, J.

Interacting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three-dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response in the quantum limit of the bulk semimetal HfTe5, adjacent to the three-dimensional quantum Hall effect of a single electron band at low magnetic fields. The additional plateau-like feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikov-de Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the three-dimensional quantum Hall effect. Our findings are consistent with strong electron-electron interactions, stabilizing an unconventional variant of the Hall effect in a three-dimensional material in the quantum limit.

2020, Park, G.-H., Reichlova, H., Schlitz, R., Lammel, M., Markou, A., Swekis, P., Ritzinger, P., Kriegner, D., Noky, J., Gayles, J., Sun, Y., Felser, C., Nielsch, K., Goennenwein, S.T.B., Thomas, A.

We report a robust anomalous Nernst effect in Co2MnGa thin films in the thickness regime between 20 and 50 nm. The anomalous Nernst coefficient varied in the range of -2.0 to -3.0 μV/K at 300 K. We demonstrate that the anomalous Hall and Nernst coefficients exhibit similar behavior and fulfill the Mott relation. We simultaneously measure all four transport coefficients of the longitudinal resistivity, transversal resistivity, Seebeck coefficient, and anomalous Nernst coefficient. We connect the values of the measured and calculated Nernst conductivity by using the remaining three magnetothermal transport coefficients, where the Mott relation is still valid. The intrinsic Berry curvature dominates the transport due to the relation between the longitudinal and transversal transport. Therefore, we conclude that the Mott relationship is applicable to describe the magnetothermoelectric transport in Weyl semimetal Co2MnGa as a function of film thickness.