Disorder induced power-law gaps in an insulator–metal Mott transition

Abstract

A correlated material in the vicinity of an insulator-metal transition (IMT) exhibits rich phenomenology and 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 drives 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.

Local Spectroscopies Reveal Percolative Metal in Disordered Mott Insulators

“…show that Mott physics is preserved in magnetically ordered regions, while increasingly disordered regions have enhanced spectral weight within the Hubbard gap with the formation of a V-shaped pseudogap. Such spectroscopic dependence on disorder has been observed experimentally in Mott insulating materials, where the pseudogap behavior is enhanced near impurity atoms [9].…”

“…Global properties -With increasing disorder fraction, the DOS N(ω) shows an evolution from a Mott gapped insulator to a gapless phase leading to a V-shaped suppression, a pseudogap, at the chemical potential [ Fig. 1(d,e)] [9,10]. To get some idea of whether these in-gap states are localized or extended, we plot the inverse participation ratio…”

Atomic fluctuations in electronic materials revealed by dephasing

“…The ideal behavior predicted by the Schottky-Mott limit was restored by the control of interfacial defects at a metal-semiconductor junction (16). The balance between competing phases in strongly correlated electronic materials, such as high-temperature superconductors and Mott insulators, is highly dependent on the presence and type of electronic disorder (17)(18)(19)(20)(21). Inhomogeneities in the energy of electronic states also provide both challenges and opportunities for quantum applications such as quantum information-processing and superfluorescence (22,23).…”

Doping and temperature evolutions of optical response of Sr3(Ir1-xRux)2O7

“…On the other hand, other studies report that the spin-orbit coupling is robust against Rh doping 36,37 and Rh is substituted as Rh 3+ (4d 6 ), leading to hole doping into the Ir sites [37][38][39] . In the Sr 3 (Ir 1-x Ru x ) 2 O 7 crystals, an X-ray absorption spectroscopy shows that the charge disproportionation does not occur 23 . STS studies of Sr 3 (Ir 1-x Ru x ) 2 O 7 further show that impurity bands do not form upon Ru doping and that the insulator-metal transition is a percolation type 22,23 .…”