Molecular quantum materials: electronic phases and charge dynamics in two-dimensional organic solids

Abstract

This review provides a perspective on recent developments and their implications for our understanding of novel quantum phenomena in the physics of two-dimensional organic solids. We concentrate on the phase transitions and collective response in the charge sector, the importance of coupling of electronic and lattice degrees of freedom and stress an intriguing role of disorder. After a brief introduction to low-dimensional organic solids and their crystallographic structures, we focus on the dimensionality and interactions and emergent quantum phenomena. Important topics of current research in organic matter with sizeable electronic correlations are Mott metal-insulator phase transitions, charge order and ferroelectricity. Highly frustrated two-dimensional systems are established model compounds for studying the quantum spin liquid state and the competition with magnetic long-range order. There are also unique examples of quantum disordered state of magnetic and electric dipoles. Representative experimental results are complemented by current theoretical approaches.

Modulated crystal structure of the atypical charge density wave state of single-crystal Lu2Ir3Si5

“…Coexistence and competition of multiple phase transitions observed in both inorganic and organic compounds have always attracted the attention of theorists and experimentalists [1][2][3][4]. For instance, charge density wave (CDW) ordering has been found to coexist with superconductivity or magnetism in a variety of rare-earth intermetallic compounds [5].…”

Dielectric Anomaly and Charge Fluctuations in the Non-Magnetic Dimer Mott Insulator λ-(BEDT-STF)2GaCl4

“…Strongly correlated electron systems attract much interest due to some novel magnetic, dielectric, and superconducting properties; both electron-electron interactions and quantum fluctuations are considered crucial for understanding these phenomena. Among these systems, the quasi-two-dimensional organic charge-transfer salts are renowned for their versatility and enormously rich phase diagrams, comprising superconducting, spin-liquid, antiferromagnetic, or charge-ordered phases that arise from the interplay of spin, charge, and lattice degrees of freedom [1][2][3][4][5]. Besides the most popular examples κ-(BEDT-TTF) 2 X, another dimerized family has drawn large attention, the λ-salts, where the lattice system consists of triangular and square tiling as depicted in Figure 1b.…”

Absence of Superconductivity in the Hubbard Dimer Model for κ-(BEDT-TTF)2X

“…Superconducting organic charge-transfer (CT) solids hold a special place in this context, as SC in CT solids was discovered significantly prior to the discovery of the phenomenon in the cuprates [10]. Despite intensive investigations over the past four decades, however, the mechanism of SC in CT solids remains a mystery, and organic SC continues to be an active research area, as illustrated by the appearance of many review articles on the subject over the past decade [11][12][13][14][15]. In the present paper, we report the results of our latest calculations that have probed a key question in the field of organic SC.…”