Watching patterns emerge in quantum materials

Abstract image or blue glowing technology lines in deep space

Discover how femtosecond snapshots of electron and ion motion are used to understand the behaviour of charge-density-wave transitions in quantum materials.

The Science and Technology Facilities Council’s (STFC) Central Laser Facility’s (CLF) Artemis facility celebrates its first published paper in its new, upgraded lab space at the Research Complex at Harwell.

A game-changing facility

Interactions between electrons and atoms in materials happen extremely fast; one billionth to one quadrillionth of a second (femtoseconds)! To understand these interactions, we need a facility capable of recording and capturing these processes.

STFC’s Artemis facility at the CLF (Artemis) is just such a facility, one of only a few in the world and can be seen as a game-changer in the exploration of new materials. Dedicated to tracking the ultrafast motion of electrons in molecules and novel materials, the new laboratory provides ultrafast laser sources, XUV beamlines and end-stations for molecular dynamics, condensed matter physics and imaging.

The results that Artemis can produce not only promote the developments of innovative technologies, but also expand our fundamental understanding of the complicated physics found in the interactions between light and matter.

Senior Experimental Scientist, Dr Charlotte Sanders at STFC’s CLF, says:

We are incredibly happy to have the new Artemis lab up and running and producing papers.

Not only are we enjoying the benefits of our new lab space, but with our new HiLUX upgrades over the next four years, our users can expect even more new capabilities in the near future.

It is an extremely exciting time.

The first published paper

Quantum materials are a fascinating area of research in condensed matter physics. In some two-dimensional materials, there are a range of phase transitions such as charge-density-waves (CDWs), Mott insulating phases and superconductivity. Understanding how and why these transitions occur is a major goal of the field.

The research is led by Dr Enrico Da Como from the University of Bath, in collaboration with:

  • Dr Charles James Sayers from the Polytechnic University of Milan
  • Dr Ettore Carpene from the Institute of Photonics and Nanotechnologies of the Italian National Research Council (CNR)

The research team have observed fundamental interactions inside quantum materials on a femtosecond timescale.

Dr Ettore Carpene, Researcher at the Institute of Photonics and Nanotechnologies of the CNR says:

One of the most important scientific questions surrounding quantum materials is the origin of phase transitions to ordered states of matter.

Significant attention

CDWs are a phenomenon where the electrons spontaneously bunch up into regular patterns across a layer of material. The study of CDWs in solids has garnered significant attention in condensed matter physics due to their connection to other electronic quantum states, and they have a complex interplay with superconductivity and with Mott insulating phases.

A recent study on tantalum diselenide 1T-TaSe2 showed that certain collective electronic states could be explained by a charge-transfer mechanism due to the lattice reconstruction that accompanies the charge ordering itself.

This finding highlights the role of the crystal lattice in driving and stabilising phase transitions in quantum materials. This understanding could lead to the design of materials with unique electronic properties.

The study employed short light pulses at the STFC CLF’s Artemis 1kHz beamline to investigate the behaviour of electrons and ions in quantum materials at the femtosecond timescale. It provided valuable insights into the complex behaviour of these materials.

Dr Charles James Sayers, Research Fellow in the ultrafast spectroscopy group at Polytechnic University of Milan, says:

Using ultrashort pulses of light on the order of femtoseconds, such as those available at the Artemis facility, allows us to directly visualise the motion of electrons and ions inside materials in real time, providing a great insight into the important interactions occurring inside these exotic materials.

Model system

The team focused on a model system that undergoes a CDW transition, which redistributes electrons and ions to form a wave-like pattern of charge on the material’s surface. The researchers found that the CDW transition was not driven by electron correlations, but rather by a tendency toward distortion in the crystal lattice.

This discovery underscores the importance of using short light pulses to study the behaviour of quantum materials and separate the effects of the crystal lattice and electrons. It has led to a better understanding of the origin of phase transitions in similar systems and the development of new materials with unique properties.

The work has been published in Physical Review Letters.

Dr Charlotte Sanders, STFC CLF, continues:

It was great to work with colleagues at the University of Bath, Politecnico di Milano, and CNR-IFN on this interesting project.

We look forward to a lot more top-notch science with them and the rest of our user community in the future.

Top image:  Credit: sakkmesterke, iStock, Getty Images Plus via Getty Images

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