Draft 1 - Condensed Matter & Materials Physics (CMMP)

The Condensed Matter & Materials Physics Group (CMMP)'s research combines experimental, theoretical and computational approaches. Systems studied include nanodevices, battery materials, multiferroics, chemical reactions, defects, surfaces, correlated electronic states, spin liquids, spin ice, ultrathin epitaxial films, heterostructures, biological systems and soft matter. Techniques applied include neutron and X-ray scattering, atomic-scale fabrication, scanning tunnelling microscopy, thermodynamic measurements, and computational modelling.

The CMMP consists of 19 research groups who cover a wide range condensed matter physics maintaining strong connections with the UK central facilities at Harwell, with the Thomas Young Centre for computational materials physics and with the London Centre for Nanotechnology.

Research Highlights:

Transiently delocalized states enhance hole mobility in organic molecular semiconductors

Samuele Giannini, Lucia Di Virgilio, Marco Bardini, Julian Hausch, Jaco J. Geuchies, Wenhao Zheng, Martina Volpi, Jan Elsner, Katharina Broch, Yves H. Geerts, Frank Schreiber, Guillaume Schweicher, Hai I. Wang, Jochen Blumberger, Mischa Bonn and David Beljonne

By combining terahertz photoconductivity measurements with non-adiabatic molecular dynamics simulation developed in Jochen Blumberger's group, Giannini et al show that charge transport in two organic semiconductors is mediated by holes surfing on extended electronic states with a temperature-dependent mobility that provides a sensitive fingerprint for the underlying density of states.

Giannini, S., Di Virgilio, L., Bardini, M. et al. Transiently delocalized states enhance hole mobility in organic molecular semiconductors. *Nat Mater* (2023). https://doi.org/10.1038/s41563-023-01664-4

Unveiling ultra-thin electron liquids in silicon

*Constantinou, P., Stock, T. J. Z., Crane, E., Kölker, A., van Loon, M., Li, J., Fearn, S., Bornemann, H., D'Anna, N., Fisher, A. J., Strocov, V. N., Aeppli, G., Curson, N. J., Schofield, S. R.*

Soft X-rays enable UCL and Swiss scientists to visualise non-invasively the electronic properties of ultra-thin dopant layers buried within semiconductor wafers. The ability to access this previously hidden information will give a boost to the design and development of quantum-electronic devices.

Constantinou, P. et al. Momentum-Space Imaging of Ultra-Thin Electron Liquids in δ-Doped Silicon. Adv. Sci. **2023**, 2302101. https://doi.org/10.1002/advs.202302101

Exciton transport in molecular organic semiconductors boosted by transient quantum delocalization

*Samuele Giannini, Wei-Tao Peng, Lorenzo Cupellini, Daniele Padula, Antoine Carof & Jochen Blumberger*

A novel non-adiabatic molecular dynamics simulation is introduced for time-propagation of electronic excitations in organic semiconductors, suggesting that exciton transport in these materials occurs via transient quantum delocalizations.

Giannini, S., Peng, WT., Cupellini, L. *et al*. Exciton transport in molecular organic semiconductors boosted by transient quantum delocalization. *Nat Commun* 13, 2755 (2022). https://doi.org/10.1038/s41467-022-30308-5

Simulating groundstate and dynamical quantum phase transitions on a superconducting quantum computer

*James Dborin, Vinul Wimalaweera, F. Barratt, Eric Ostby, Thomas E. O'Brien & A. G. Green*

Researchers from UCL, University of Massachusetts, and Google Quantum AI have demonstrated that tensor network methods give current quantum devices genuine potential for quantum advantage.

Dborin, J., Wimalaweera, V., Barratt, F. et al. Simulating groundstate and dynamical quantum phase transitions on a superconducting quantum computer. Nat Commun 13, 5977 (2022). https://doi.org/10.1038/s41467-022-33737-4

Origin of Ferroelectric Domain Wall Alignment with Surface Trenches in Ultrathin Films

*Jack S. Baker and David R. Bowler*

We used our large scale density functional theory code CONQUEST to study the alignment of ferroelectric domain walls with surface trenches in lead titanate thin films.

Baker, Jack S. and Bowler, David R. Origin of Ferroelectric Domain Wall Alignment with Surface Trenches in Ultrathin Films. Phys. Rev. Lett. **127**, 247601 (2021). https://link.aps.org/doi/10.1103/PhysRevLett.127.247601

Stable iPEPO Tensor-Network Algorithm for Dynamics of Two-Dimensional Open Quantum Lattice Models

*C. Mc Keever and M. H. Szymańska*

Being able to accurately describe the dynamics and steady states of driven and/or dissipative but quantum correlated lattice models is of fundamental importance in many areas of science: from quantum information to biology. An efficient numerical simulation of large open systems in two spatial dimensions is a challenge. In this work, we develop a new tensor network method, based on an infinite projected entangled pair operator ansatz, applicable directly in the thermodynamic limit.

McKeever, C. and Szymańska, M. H. Stable iPEPO Tensor-Network Algorithm for Dynamics of Two-Dimensional Open Quantum Lattice Models. Phys. Rev. X 11, 021035 (2021). https://doi.org/10.1103/PhysRevX.11.021035

Phosphorene Nanoribbon-Augmented Optoelectronics for Enhanced Hole Extraction

Thomas J. Macdonald, Adam J. Clancy, Weidong Xu, Zhongyao Jiang, Chieh-Ting Lin, Lokeshwari Mohan, Tian Du, Daniel D. Tune, Luis Lanzetta, Ganghong Min, Thomas Webb, Arjun Ashoka, Raj Pandya, Vasiliki Tileli, Martyn A. McLachlan, James R. Durrant, Saif A. Haque, and Christopher A. Howard

Phosphorene nanoribbons, first produced at UCL in 2019, have started to live up to their hype with the first demonstration of their properties in applications, dramatically improving the efficiency of perovskite solar cells.

T.J. Macdonald, et al. Phosphorene Nanoribbon-Augmented Optoelectronics for Enhanced Hole Extraction. *J. Am. Chem. Soc.* **2021**, 143(51), 21549-21559. https://doi.org/10.1021/jacs.1c08905

Pressure-induced Jahn-Teller switch in the homoleptic hybrid perovskite [...]

*Rebecca Scatena, Michał Andrzejewski, Roger D. Johnson, and Piero Macchi*

We discovered an unconventional pressure-induced orbital reordering phase transition above 5.2 GPa in the perovskite-like hybrid organic-inorganic material [(CH3)2NH2]Cu(HCOO)3], mediated by structural instabilities unique to the hybrid system.

Scatena, R. et al. Pressure-induced Jahn–Teller switch in the homoleptic hybrid perovskite [(CH3)2NH2]Cu(HCOO)3]: orbital reordering by unconventional degrees of freedom. *J. Mater. Chem. C*, 2021, 9, 8051-8056. https://doi.org/10.1039/D1TC01966J

Non-Fermi liquid behavior below the Néel temperature in the frustrated heavy fermion magnet UAu2

*Christopher D. O’Neill, Julian L. Schmehr, Harry D. J. Keen, Luke Pritchard Cairns, Dmitry A. Sokolov, Andreas Hermann, Didier Wermeille, Pascal Manuel, Frank Krüger, and Andrew D. Huxley*

In metals, identical Fermions in three dimensions invariably form a Fermi liquid or superconducting state at low temperature, except at quantum critical points separating differently ordered states. We report that uranium diauride (UAu2) breaks this paradigm, hosting a robust non-Fermi liquid within a magnetically ordered state.

O'Neill, Christopher D. et al. Non-Fermi liquid behavior below the Néel temperature in the frustrated heavy fermion magnet UAu2. *Proc. Natl. Acad. Sci. U.S.A.* **118**, e2102687118 (2021). https://doi.org/10.1073/pnas.2102687118

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