Theoretical Discovery of a Superconducting Two-Dimensional Metal–Organic Framework

Abstract

Superconductivity is a fascinating quantum phenomenon characterized by zero electrical resistance and the Meissner effect. To date, several distinct families of superconductors (SCs) have been discovered. These include three-dimensional (3D) bulk SCs in both inorganic and organic materials as well as two-dimensional (2D) thin film SCs but only in inorganic materials. Here we predict superconductivity in 2D and 3D organic metal-organic frameworks by using first-principles calculations. We show that the highly conductive and recently synthesized Cu-benzenehexathial (BHT) is a Bardeen-Cooper-Schrieffer SC. Remarkably, the monolayer Cu-BHT has a critical temperature (T) of 4.43 K, while T of bulk Cu-BHT is 1.58 K. Different from the enhanced T in 2D inorganic SCs which is induced by interfacial effects, the T enhancement in this 2D organic SC is revealed to be the out-of-plane soft-mode vibrations, analogous to surface mode enhancement originally proposed by Ginzburg. Our findings not only shed new light on better understanding 2D superconductivity but also open a new direction to search for SCs by interface engineering with organic materials.

Superconductivity in two-dimensional phosphorus carbide (β0-PC)

“…The in-plane modes of C atoms occupy the high frequencies above 860 cm −1 . Similar to Li-decorated monolayer graphene [25] and 2D Cu-benzenehexathial (Cu-BHT) [48], here, the vertical vibrations of C atoms are also lower than their horizontal modes. The phonon density of state (PhDOS), the Eliashberg electron-phonon spectral function α 2 F(ω), and the cumulative frequency-dependent of EPC λ (ω) are displayed in Figures 2b and 2c.…”

“…Actually, superconductivity has little been predicted for intrinsic 2D-monolayer systems. In Table I, we list the superconductive parameters of µ * , N (E F ), ω log , λ , and T c for some typical 2D phonon-mediated superconductors [48,[54][55][56][57][58][59][60]. All these systems have been predicted to appear superconductivity without external conditions of high pressure, strain, carrier doping, metal decorations/intercalations, and/or functional groups.…”

Two-Dimensional Band Structure in Honeycomb Metal–Organic Frameworks

“…Using low-temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM) complemented by density-functional theory (DFT) calculations, we show the formation of 2D band structure in the MOF decoupled from the substrate. These results open the experimental path towards MOF-based designer quantum materials with complex, engineered electronic structures with potential applications in devices with currently inaccessible and unforeseen functionalities [17].The synthetic flexibility and tuneable electronic properties of MOFs stem from the choice of metal atoms, organic molecules, the linker chemistry and electronic and magnetic interactions among the building blocks [5,8,10,11,18,19]. For example, it is possible to realize honeycomb and Kagome lattices that are expected to give rise to Dirac cones and flat bands in the band structure [5][6][7][8].…”

“…The synthetic flexibility and tuneable electronic properties of MOFs stem from the choice of metal atoms, organic molecules, the linker chemistry and electronic and magnetic interactions among the building blocks [5,8,10,11,18,19]. For example, it is possible to realize honeycomb and Kagome lattices that are expected to give rise to Dirac cones and flat bands in the band structure [5][6][7][8].…”

Crossband versus intraband pairing in superconductors: Signatures and consequences of the interplay

“…To date, multiband electronic structure is proven to be of crucial importance in rather versatile superconducting systems, such as MgB 2 [10], iron-based compounds [11][12][13][14][15][16], superconducting nanostructures [17][18][19][20][21], 2D electron gases at interfaces [22][23][24], metal-organic superconductors [25][26][27], etc. In such multiband superconductors, the pairing interaction and the proximity/hybridization of two or more bands can result in the formation of Cooper pairs with electrons originating from different bands, a phenomenon termed "cross-band pairing" or simply "crosspairing".…”