2021, Bannies, J., Razzoli, E., Michiardi, M., Kung, H.-H., Elfimov, I.S., Yao, M., Fedorov, A., Fink, J., Jozwiak, C., Bostwick, A., Rotenberg, E., Damascelli, A., Felser, C.

Several early transition metal dipnictides (TMDPs) have been found to host topological semimetal states and exhibit large magnetoresistance (MR). In this paper, we use angle-resolved photoemission spectroscopy (ARPES) and magnetotransport to study the electronic properties of a TMDP ZrP2. We find that ZrP2 exhibits an extremely large and unsaturated MR of up to 40 000% at 2 K, which originates from an almost perfect electron-hole (e-h) compensation. Our band structure calculations further show that ZrP2 hosts a topological nodal loop in proximity to the Fermi level. Based on the ARPES measurements, we confirm the results of our calculations and determine the surface band structure. This paper establishes ZrP2 as a platform to investigate near-perfect e-h compensation and its interplay with topological band structures.

2019, Haubold, E., Fedorov, A., Pielnhofer, F., Rusinov, I.P., Menshchikova, T.V., Duppel, V., Friedrich, D., Weihrich, R., Pfitzner, A., Zeugner, A., Isaeva, A., Thirupathaiah, S., Kushnirenko, Y., Rienks, E., Kim, T., Chulkov, E.V., Büchner, B., Borisenko, S.

We report experimental and theoretical evidence that GaGeTe is a basic Z2 topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the classic 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion at the T-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron and holelike carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material's application potential.