Angulon: physics and applications of a new quasiparticle

Project Information

ANGULON

Grant agreement ID: 801770

DOI

10.3030/801770

Project closed

EC signature date 2 October 2018

Start date 1 February 2019

End date 31 January 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 588,00

EU contribution

€ 1 499 588,00

Coordinated by

INSTITUTE OF SCIENCE AND TECHNOLOGY AUSTRIA
Austria

Periodic Reporting for period 4 - ANGULON (Angulon: physics and applications of a new quasiparticle)

Reporting period: 2023-08-01 to 2024-01-31

Summary of the context and overall objectives of the project

The overarching goal of the project is to develop a theory describing the physics of rotating „impurities“, such as molecules interacting with a quantum environment, such as a liquid or a crystal. This problem is extremely challenging, since it involves a large number of interacting quantum particles (in principle, on the order of 10^23). Furthermore, in order to describe many physical and chemical processes, one needs to describe time-dynamics, which complicates the problem further.
When developed, the theory will allow to understand and, most important, to control chemical reactions in solvents, which is one of the key problems of chemical physics. Furthermore, we expect applications in other areas of quantum physics, involving angular momentum, such as solid-state magnetism.
As a result of the project, we have developed a theory of many-body processes involving angular momentum, with multifaceted applications – from molecules in helium nanodroplets to ultracold quantum gases to spin dynamics in solids. This laid a solid foundation for further developments at the interface of molecular and condensed-matter physics.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We achieved a substantial progress in describing the static and dynamical properties of molecules in quantum solvents. Together with the experimental group of Prof. Stapelfeldt (U Aarhus, Denmark), we described the dynamics of small molecules (I2, CS2, OCS) in superfluid helium nanodroplets following a low-intensity laser pulse. On the other hand, high-intensity laser excitation paved the way to studying highly excited rotational states in superfluids with rotational coherent spectroscopy, which was previously impossible for standard spectroscopic tools (microwave or IR).
Together with the Stapelfeldt group we demonstrated the first planar quantum rotor – a linear molecule trapped on the surface of a helium droplet whose rotation is confined to the plane – and studied its properties.
Furthermore, we developed the theory of intermolecular interactions mediated by a quantum solvent, demonstrated the possibility to generate synthetic spin-orbit coupling forces by means of such a solvent and applied parts of the generated knowledge in completely different fields, such as excitonic liquids in semiconductors and chiral organic molecules on surfaces. We studied topological properties of the angulon quasiparticles and theoretically showed the possibility to realize particles with fractional statistics with molecules in superfluid helium droplets.
As an aside, we developed a theory describing electron transport through chiral molecules adsorbed on a surface of a material. We evaluated the role of dissipation and of many-particle effects in the chiral induced spin selectivity.
In collaboration with the experimental group of Prof. Alpishchev (ISTA) we studied molecular rotation inside lead-halide perovskites – promising materials for solar-cell applications.
We have studied the dynamics of angular momentum in a molecule kicked by a periodic train of laser pulses. We showed that topological Dirac cones emerge in the effective band structure of a single molecule constructed in the Floquet space, which paves the way to bridging molecular physics with topological materials such as topological insulators and Weyl semimetals. As a necessary ingredient we provided a detailed study of the validity of the sudden approximation in laser-molecule interactions.
The project has achieved its main goals – to develop a theory of many-body angular momentum transfer and to apply it to a variety of molecular and solid-state systems. The results have already motivated several experimental developments which are going to involve the PI and his group as collaborators in the nearest future. The results of the project were published in numerous publications, presented at several conferences, covered by the press and popular magazines, and highlighted on social media and the PI’s YouTube channel.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Most of the results achieved during the reporting period are beyond the state of the art, since they involve quantum impurities with complex internal structure (such as molecules) immersed in a quantum bath. In addition, a substantial amount of work was concerned with developing time-dependent techniques to describe the dynamics of molecules in solvents, which pushes the limits of the state-of-the-art methods.
By the end of the project we established a reliable theoretical and computational machinery, describing quantum impurities with angular momentum (such as molecules) in various types of environments. Furthermore, we made substantial progress in the theory of electron transport through chiral molecules, with potential applications to spintronics, and in studying molecules rotating in lead-halide perovskites. Finally, we started a new direction of topological physics emerging in molecules kicked by periodic laser pulses, which can potentially allow for topological classification of chemical states in a similar way as it is done in condensed-matter physics.

An example of the angulon’s spectral function