Abstract
Recent debates in the literature over the relationship between topology and Extreme Magnetoresistance (XMR) have drawn attention to the Lanthanum Monopnictide family of binary compounds. Angle resolved photoemission spectroscopy (ARPES) is used to measure the electronic structure of the XMR topological semimetal candidates LaBi, LaSb, and LaAs. The orbital content of the near-EF states in LaBi and LaSb are extracted using varying photon polarizations and both dominant d and p bands are observed near X. The measured bulk bands are shifted in energy when compared to the results of Density Functional Calculations. This disagreement is minor in LaBi, but large in LaSb and LaAs. The measured bulk band structure of LaBi shows a clear band inversion and puts LaBi in the υ = 1 class of Topological Insulators (or semimetals), as predicted by calculations and consistent with the measured Dirac-like surface states. LaSb is on the verge of a band inversion with a less-clear case for any distinctly topological surface states and in disagreement with calculations. Lastly, these same bands in LaAs are clearly non-inverted implying its topological triviality and demonstrating a topological phase transition in the Lanthanum monopnictides. Using a wide range of photon energies the true bulk states are cleanly disentangled from the various types of surface states which are present. These surface states exist due to surface projections of bulk states in LaSb and for topological reasons in LaBi.
Highlights
The binary compounds containing a single pnictogen element with La in a rock salt crystal structure have recently drawn attention in the literature for both demonstrating extreme magnetoresistance (XMR) as well as possible topological states and surface Dirac Fermions.1–6 Here magnetoresistance is defined by the ratio R(H)/R(0), where R is the electrical resistance and H is the applied magnetic field
We report a clear band inversion in LaBi, while LaSb is near a band inversion, and LaAs is clearly non-inverted
The consensus reached by refs.6,21,22 is that LaBi is topologically nontrivial
Summary
The binary compounds containing a single pnictogen element with La in a rock salt crystal structure have recently drawn attention in the literature for both demonstrating extreme magnetoresistance (XMR) as well as possible topological states and surface Dirac Fermions. Here magnetoresistance is defined by the ratio R(H)/R(0), where R is the electrical resistance and H is the applied magnetic field. The binary compounds containing a single pnictogen element with La in a rock salt crystal structure have recently drawn attention in the literature for both demonstrating extreme magnetoresistance (XMR) as well as possible topological states and surface Dirac Fermions.. Due to the spin-orbit coupling in both of these materials, electronic structure calculations predict mixing between the La d orbital and the pnictogen p orbital bands, which compose the pocket.. Due to the spin-orbit coupling in both of these materials, electronic structure calculations predict mixing between the La d orbital and the pnictogen p orbital bands, which compose the pocket.2,12 The mixing of these two bands, in turn, creates an orbital composition crossover at EF on this pocket. The existence of this crossover is found in many of the materials which exhibit XMR. topological surface states have been suggested as a necessary ingredient for XMR. Several of the materials which demonstrate XMR have been confirmed or predicted to be, topologically non-trivial indicating, at minimum, a correlation between the two phenomena
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