MOF – Jack Hellerstedt

Mott transition in kagome MOF

Ben & Bernard’s work on the two-dimensional kagome metal-organic framework is out this week (26 April 2024) in Nature Comms.

It was fantastic to see interesting electronic properties emerge at relatively big energy scales for this sort of work, when we were finally able to get the 2d kagome MOF composed of Cu adatoms & DCA molecules, to self-assemble on insulating hexagonal boron nitride (hBN) supported by a Cu111 metallic substrate.

We teamed up with Ben Powell’s group at UQ for the many-body expertise required to understand the tunnel junction and substrate work function dependent modulations of the electronic gap in the language of Mott physics.

Lowe, B., Field, B., Hellerstedt, J. et al. Local gate control of Mott metal-insulator transition in a 2D metal-organic framework. Nat Commun 15, 3559 (2024). https://doi.org/10.1038/s41467-024-47766-8

2021 AIP summer meeting

The AIP summer meeting was a hybrid event this year 6-9 Dec. ’21 with the border restrictions still in place preventing us from travelling to Brisbane.

Iolanda kindly invited me to talk about Marina’s MgPc hybridization work as well as new results of orbital tomography performed at the Australian Synchrotron (in preparation).

Ben Lowe contributed a talk to the scanning probe microscopy focus session, with an update on how we’re closing in on understanding the mechanism of formation for some unusual metal-organic products identified with ncAFM measurements.

Thanks also to Peggy Schönherr, Peggy Zhang, Peter Jacobson, and Iolanda DiBernardo for contributing talks to the SPM focus session.

Bernard Field talked about how he’s pushing forward how we can rationalise our observations of self-assembled MOF structures, stemming from our recently published experimental results that Agustin talked about in the MOF focus session.

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. https://doi.org/10.1002/adfm.202106474

ArXiv link
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