Avoided metallicity in a hole-doped Mott insulator on a triangular lattice

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Doping Mott insulators can lead to exotic emergent states like superconductivity and various orders.
• Understanding the physics of these emergent states is challenging due to complex doping chemistries.
• Delafossite PdCrO2 offers a unique Mott insulating CrO2 layer for studying doping effects.

Purpose of the Study:

• To investigate the effects of doping on the Mott insulating CrO2 layer in PdCrO2.
• To explore a clean doping route via an intrinsic polar catastrophe at the surface.
• To understand the nature of the emergent electronic states and their dynamics.

Main Methods:

• Scanning tunneling microscopy (STM) to probe surface structure and electronic properties.
• Angle-resolved photoemission spectroscopy (ARPES) to investigate electronic band structure.
• Density functional theory (DFT) calculations to model the electronic ground state.

Main Results:

• The CrO2 surface remains insulating, exhibiting a short-range ordered state.
• Charge disproportionation forms an insulating surface ground state, distinct from the bulk Mott insulator.
• Voltage pulses induce transient modifications to the surface state, indicating glassy charge order.

Conclusions:

• An intrinsic polar catastrophe provides a clean route to dope the surface of PdCrO2.
• The doped surface exhibits a novel insulating state driven by charge disproportionation.
• The observed glassy dynamics suggest a complex charge ordering mechanism at the surface.