Disorder-Induced Mottness in a Doped Mott Insulator

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• The persistence of the Mott insulating state away from integer filling is a long-standing problem.
• Existing theoretical models often attribute this to electronic phase separation, but predictions differ from experimental observations.
• Understanding the factors governing Mott insulator behavior is crucial for developing novel electronic materials.

Purpose of the Study:

• To investigate the role of intrinsic disorder in the persistence of the Mott insulating state in doped materials.
• To reconcile discrepancies between theoretical predictions and experimental results regarding critical doping levels.
• To elucidate the mechanisms by which defects influence the electronic structure of Mott insulators.

Main Methods:

• Scanning tunneling microscopy (STM) and spectroscopy (STS) were employed.
• Measurements were performed on Fe-intercalated 1T-TaS2 (an electron-doped Mott insulator) and the 1T-TaS2 layer within 4Hb-TaS2 (a hole-doped material).
• The electronic properties in the vicinity of point defects and domain boundaries were analyzed.

Main Results:

• Mott insulating regions were observed to nucleate at point defects and charge density wave domain boundaries in electron-doped 1T-TaS2.
• These defects function as local charge sinks, leading to sharp chemical potential differences and narrow Mott depletion plateaus.
• In contrast, similar impurities in the hole-doped 1T-TaS2 layer of 4Hb-TaS2 did not induce incompressible regions.
• This highlights a doping-dependent effect of disorder on the electronic structure.

Conclusions:

• Intrinsic disorder, rather than solely electronic phase separation, is a critical factor in maintaining the Mott insulating state away from integer filling.
• Local defects play a significant role in shaping the inhomogeneous electronic structure of doped Mott insulators by creating localized Mott regions.
• The contrasting behavior between electron- and hole-doped systems underscores the importance of disorder in compensating doping effects.