Striped Phase

While pursuing metal-organic frameworks, we stumbled on something unexpected but experimentally robust back in June of 2019. DCA molecules and Au adatoms on Ag111 form DCA-Au-DCA units, and the cyano groups aren’t involved as you’d intuitively expect.

It took some heroic effort and creative thinking from Adam & the team in Prague to “just run this one through the computer real quick”, but nonetheless we’re pleased to have this explanation of the selective C-H scisson necessary to justify the observed end products.

Lowe, B., et. al. (2022). Selective Activation of Aromatic C–H Bonds Catalyzed by Single Gold Atoms at Room Temperature. J. Am. Chem. Soc.

Kagome metal-organic framework

Dhaneesh Kumar has extensively studied the on-surface properties of the DCA molecule for his PhD. After getting a good handle on just the DCA on Ag111, we started sprinkling some Cu atoms into the mix.

We observed the same honeycomb kagome structure that forms on Cu111– as seen in an ncAFM force volume shown in the right image. It has also been synthesized on graphene.

The key difference we observed on Ag111 was the Kondo effect, an STS peak at Fermi we tracked up to 150 K!

The consistent spatial distribution of this feature across the MOF was another key observation.

ncAFM force volume of DCA (structure superimposed upper right) self-assembly on Cu111 surface. dZ denotes lift of sensor away from surface for each frame.

Bernard put in the hard yards with DFT/ +U calculations in conjunction with mean-field Hubbard modelling to rationalise our experimental observations as strong Coulomb interactions between electrons within the kagome MOF.

STS maps
dI/dV STS mapping at biases indicated upper left
DCA Cu Kagome schematic
Schematic of Kondo screened spin moments within the MOF. Blender by Dhaneesh

We’re excited by the possibilities for solid-state architectures to offer further access & control of these intriguing quantum states.

Kumar, D., et. al. (2021). Manifestation of Strongly Correlated Electrons in a 2D Kagome Metal–Organic Framework. Advanced Functional Materials, 2106474.

ArXiv link
FLEET blog

Thin-film Dirac semimetal review article

Iolanda DiBernardo reviewed the development of Na3Bi as a topological electronic material.

The physics of Dirac semimetals (“3d graphene”) is introduced, and the results from the last half decade are tied together in one narrative, in particular our work at Monash demonstrating that Na3Bi grows directly on insulators, and that indeed an electric field will open a topological gap, two key ingredients to achieving a working “topological transistor”.

“Progress in Epitaxial Thin‐Film Na3Bi as a Topological Electronic Material”, Advanced Materials, 2021. 10.1002/adma.202005897