Abstract
Bulk Dirac electron systems have attracted strong interest for their unique magnetoelectric properties as well as their close relation to topological (crystalline) insulators. Recently, the focus has been shifting toward the role of magnetism in stabilizing Weyl fermions as well as chiral surface states in such materials. While a number of nonmagnetic systems are well known, experimental realizations of magnetic analogs are a key focus of current studies. Here, we report on the physical properties of a large family of inverse perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) in which we are able to not only stabilize 3D Dirac electrons at the Fermi energy but also chemically control their properties. In particular, it is possible to introduce a controllable Dirac gap, change the Fermi velocity, tune the anisotropy of the Dirac dispersion, and—crucially—introduce complex magnetism into the system. This family of compounds therefore opens up unique possibilities for the chemical control and systematic investigation of the fascinating properties of such topological semimetals.
Highlights
Three dimensional Dirac electrons in condensed matter physics have attracted significant interest1–3 due to a range of unusual electric and magnetic properties they display
Hall measurements are consistent with a holelike carrier concentration of the order of 1018 cm−3 with a Hall mobility of 4.4 × 104 cm2/V s,22 both comparable to other Dirac electron materials
What is surprising is the strong variation of the magnetism with carrier concentration that becomes apparent in our measurements on several batches of Sr3PbO [Fig. 1(d)]
Summary
Three dimensional Dirac electrons in condensed matter physics have attracted significant interest due to a range of unusual electric and magnetic properties they display. The most accessible phenomena are those arising from the unusual single particle excitation spectrum [Fig. 1(a)], combining a vanishing Fermi wave vector kF with a finite Fermi velocity vF. The ratio vF/kF is, for example, directly proportional to the mobility μ and diverges in the case of Dirac electrons upon approaching the Dirac point energy εD. Dirac electrons form the starting point for the creation of Weyl fermions lacking Kramers degeneracy via either (i) time reversal symmetry breaking or (ii) the combined effect of inversion symmetry breaking and spin orbit coupling.. A number of “clean” 3D Dirac and Weyl electron systems are known in which Dirac and A second more unique class of phenomena are those rooted in the Berry curvature, originating from the inherent pseudospin degree of freedom of Dirac dispersions. In addition, Dirac electrons form the starting point for the creation of Weyl fermions lacking Kramers degeneracy via either (i) time reversal symmetry breaking or (ii) the combined effect of inversion symmetry breaking and spin orbit coupling. A number of “clean” 3D Dirac and Weyl electron systems are known in which Dirac and
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