Two-dimensional mineral [Pb₂BiS₃][AuTe₂]: High-mobility charge carriers in single-atom-thick layers

Two-dimensional (2D) electronic systems are of wide interest due to their richness in chemical and physical phenomena and potential for technological applications. Here we report that [Pb₂BiS₃][AuTe₂], known as the naturally occurring mineral buckhornite, hosts 2D carriers in single-atom-thick layers. The structure is composed of stacking layers of weakly coupled [Pb₂BiS₃] and [AuTe₂] sheets. The insulating [Pb₂BiS₃] sheet inhibits interlayer charge hopping and confines the carriers in the basal plane of the single-atom-thick [AuTe₂] layer. Magneto-transport measurements on synthesized samples and theoretical calculations show that [Pb₂BiS₃][AuTe₂] is a multiband semimetal with a compensated density of electrons and holes, which exhibits a high hole carrier mobility of ∼1360 cm²/(V s). This material possesses an extremely large anisotropy, γ = ρ_c/ρ_ab ≈ 10⁴, comparable to those of the benchmark 2D materials graphite and Bi₂Sr₂CaCu₂O_6+δ. The electronic structure features linear band dispersion at the Fermi level and ultrahigh Fermi velocities of 10⁶ m/s, which are virtually identical to those of graphene. The weak interlayer coupling gives rise to the highly cleavable property of the single crystal specimens. Our results provide a novel candidate for a monolayer platform to investigate emerging electronic properties.