Displaced Drude Peak: Optical Investigations of Dynamical Localization in Low-Dimensional Molecular Conductors

• Applicant: Professor Dr. Martin Dressel
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 567253715

The optical response of correlated electron systems often deviates from a simple metallic behavior because incipient localization causes a reduction of the low-frequency conductivity, resulting in a displaced Drude peak. With increasing temperature, the optical conductivity is significantly suppressed by electron-boson scattering due to dynamic randomness, which enables quantum localization even in the absence of static disorder. In order to experimentally verify these theoretical predictions, we plan systematic optical measurements on low-dimensional correlated electron systems with the particular emphasis on the appearance of a finite-frequency maximum in the optical conductivity. Our study will focus on well-characterized two-dimensional organic conductors with different electronically correlated ground states: weak anti-ferromagnetism, quantum spin liquid and charge order. Using a variety of compositions and substitution, the compounds have different strength of electronic interaction and band filling. Measurements of the optical response down to T = 4 K reveal the significant temperature evolution of the displaced Drude peak for each of the systems. An elaborate theory and numerically exact results that are produced to describe the materials under study will allow us to obtain insights in the relevant spin and charge fluctuations. We expect information on how the electrons feel these collective fluctuations and how these fluctuations increase with correlation strength and depend on the magnetic ground state.

• DFG Programme: Research Grants