Universality class of the mott transition

Area of Science:

• Condensed matter physics
• Materials science
• Organic electronics

Background:

• The Mott transition describes a metal-insulator transition in materials driven by electron-electron interactions.
• Layered organic conductors, such as EtMe_{3}P[Pd(dmit)_{2}]_{2}, offer a unique platform to study fundamental electronic phase transitions.
• Understanding the critical behavior near the Mott transition is crucial for designing novel electronic materials.

Purpose of the Study:

• To investigate the pressure dependence of conductivity and thermoelectric power in EtMe_{3}P[Pd(dmit)_{2}]_{2}.
• To objectively determine the Mott-Hubbard transition using the critical behavior of thermoelectric effects.
• To analyze the relationship between the metal-insulator crossing and conductivity changes under pressure.

Main Methods:

• Isothermal pressure sweeps were performed on EtMe_{3}P[Pd(dmit)_{2}]_{2} samples.
• Electrical conductivity and thermoelectric power were measured as a function of pressure.
• Analysis focused on the critical exponents characterizing the Mott-Hubbard transition.

Main Results:

• The thermoelectric effect's critical behavior clearly identified the Mott-Hubbard transition during pressure sweeps.
• The metal-insulator crossing, determined by the thermoelectric minimum, did not coincide with the conductivity derivative maximum.
• Critical exponents for the Mott-Hubbard transition were found to be consistent with the Ising universality class.

Conclusions:

• Thermoelectric power provides a robust method for pinpointing Mott-Hubbard transitions in organic conductors.
• The observed critical exponents suggest a universal behavior of the Mott-Hubbard transition, independent of system dimensionality.
• Discrepancies in transition determination highlight the complexity of electronic phase transitions in these materials.