Unveiling the electronic transformations in the semi-metallic correlated-electron transitional oxide Mo₈O₂₃

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Molybdenum oxide (Mo8O23) belongs to the MoO3-x family, exhibiting properties tunable from insulating to metallic.
• Previous studies suggested a charge density wave transition above room temperature, but low-temperature behavior remained unclear.

Purpose of the Study:

• To comprehensively investigate the electronic structure and ordering phenomena in Mo8O23.
• To elucidate the low-temperature electronic behavior and its implications for material properties and applications.

Main Methods:

• Density-functional theory (DFT) calculations to model electronic structure changes with temperature.
• Angle-resolved photoemission spectroscopy (ARPES) to confirm theoretical predictions like Dirac crossings.
• Tunneling spectroscopy (STS) to probe the electronic gap and identify transitions.

Main Results:

• DFT predicts a crossover from semi-metallic to narrow-gap semiconductor behavior with decreasing temperature.
• ARPES confirms a buried Dirac crossing, while STS reveals a gradual gap opening at 343 K, indicative of charge density wave (CDW) formation.
• Low-temperature experiments (Hall effect, STS, ARPES) contradict the simple CDW picture, showing metallic behavior, a non-trivial gap, and evidence for a correlated state onset at 70 K.

Conclusions:

• Mo8O23 exhibits complex electronic behavior driven by the interplay of electronic correlations and multiple narrow bands near the Fermi level.
• The observed phenomena, including metastability, suggest potential applications in memristors.
• The low-temperature behavior deviates from simple CDW models, pointing towards a more intricate correlated electronic state.