First discovered in 1975, heavy-fermion materials often have atypical correlated phases, such as multiple superconducting states (see Physics Today, November 2021, page 19). Their electronic behavior arises from quasiparticles of large effective mass, anywhere from 50 to 1000 electron masses, which in turn arise from the hybridization of conduction electrons and those in the 4f and 5f orbitals of their rare-earth or actinide ions. Exploring heavy fermions’ novel physics requires working with exotic materials—for example, uranium ditelluride—that offer limited ways to adjust their properties.
Peter Liljeroth, his graduate student Viliam Vaňo, and their colleagues at Aalto University in Finland are now the first to observe heavy-fermion behavior in a material without rare-earth or actinide elements. Their two-layer stack of tantalum disulfide is easy to make, handle, and tweak and will offer a method to explore the full range of heavy-fermion physics.
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