Publication Type:Journal Article
Source:Proceedings of the National Academy of Sciences (2018)
Correlated electron systems often show unexpected behavior that defies theoretical explanations. One such mystery is the universal presence of V-shaped gaps with surprisingly linear energy dependence, whose origins are as-yet unknown. Conventional wisdom implicates static order like charge density waves or fluctuations of a nearby order parameter like superconductivity or antiferromagnetism. However, adding dopants to correlated systems inevitably leads to the opposite of order—i.e., electronic disorder—which begs the question: Could disorder create well-defined signatures in electronic properties? By carefully choosing a material with no additional order, we show that order is not the only path to gaps and that disorder may play a surprising role in generating universal signatures in the density of states of disordered correlated systems.A correlated material in the vicinity of an insulator–metal transition (IMT) exhibits rich phenomenology and a variety of interesting phases. A common avenue to induce IMTs in Mott insulators is doping, which inevitably leads to disorder. While disorder is well known to create electronic inhomogeneity, recent theoretical studies have indicated that it may play an unexpected and much more profound role in controlling the properties of Mott systems. Theory predicts that disorder might play a role in driving a Mott insulator across an IMT, with the emergent metallic state hosting a power-law suppression of the density of states (with exponent close to 1; V-shaped gap) centered at the Fermi energy. Such V-shaped gaps have been observed in Mott systems, but their origins are as-yet unknown. To investigate this, we use scanning tunneling microscopy and spectroscopy to study isovalent Ru substitutions in Sr3(Ir1-xRux)2O7 (0 <= x <= 0.5) which drive the system into an antiferromagnetic, metallic state. Our experiments reveal that many core features of the IMT, such as power-law density of states, pinning of the Fermi energy with increasing disorder, and persistence of antiferromagnetism, can be understood as universal features of a disordered Mott system near an IMT and suggest that V-shaped gaps may be an inevitable consequence of disorder in doped Mott insulators.