AC conductivity and correlation effects in nano-granular Pt/C.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Nano-granular metals exhibit complex electronic behavior due to quantum correlations, disorder, and finite-size effects.
• Charge transport in these materials is primarily governed by thermally-assisted tunneling between metallic grains.
• Understanding AC conductivity is crucial for characterizing transport regimes, especially near the insulator-metal transition.

Purpose of the Study:

• To investigate the frequency-dependent conductivity (AC conductivity) of nano-granular platinum (Pt) embedded in amorphous carbon (C).
• To explore the transport regime on the insulating side of the insulator-metal transition, focusing on correlated charge transport.
• To compare findings with previous studies on similar granular systems like nano-granular Palladium (Pd).

Main Methods:

• Fabrication of nano-granular Platinum/Carbon (Pt/C) samples with varying tunnel-coupling strengths.
• Measurement of AC conductivity across a range of frequencies.
• Analysis using a lumped-circuit model to relate AC conductivity to temperature-dependent DC conductivity.

Main Results:

• A universal behavior was observed in the frequency dependence of AC conductivity for nano-granular Pt/C.
• This universal behavior was directly traceable to the temperature-dependent DC conductivity.
• The observed transport regime showed minimal polarization contributions, highlighting pronounced correlation effects, contrasting with prior studies on Pd/SiO2.

Conclusions:

• Nano-granular metals, specifically Pt/C, exhibit a universal AC conductivity response linked to DC conductivity in the insulating regime.
• Correlation effects significantly influence charge transport in this regime, differing from weak-coupling systems.
• Potential applications for nano-granular metals include proximity impedance spectroscopy for dielectric materials.