A team of OPTOlogic researchers describes in Nature Quantum Materials a technique to probe the orbital texture of a metal using photoemission spectroscopy.
In the article, published in the journal Nature Quantum Materials, researchers from the Fritz Haber Institute of the Max Planck Society, together with researchers from the University of Bordeaux, the SLAC National Accelerator Laboratory, the University of Würzburg, the New Technologies Research Center of the University of West Bohemia and the Institute for Optics and Atomic Physics of the Technical University of Berlin, describe how to access the orbital texture – the momentum-dependent orbital character of crystalline solids – using novel a measurement method in photoemission spectroscopy.
Researchers also went through some of their latest publications. So far, the consortium members have published more than ten publications in peer-reviewed journals and have several in preprint. This is a remarkable achievement, considering that the project has been ongoing for about six months.
Samuel Beaulieu, the first author of the study, explains, “During my postdoc with Prof. Ralph Ernstorfer, I started to investigate the electronic structure of 2D materials using angle-resolved photoemission spectroscopy. I had the intuition that measuring the modulation of the photoemission intensity upon a specific crystal rotation could give us insight beyond the band structure”.
Using multidimensional photoemission spectroscopy
Angle-resolved photoemission spectroscopy (ARPES) is an experimental technique that allows measuring the momentum-resolved energy bands in crystalline solids. In this method, the electrons inside a solid absorb a photon with larger energy than the material’s work function and escape into the vacuum. A key aspect of this technique is that the energy- and momentum-dependence of the photoemission signal is proportional to the single-particle spectral function, giving key information about the many-body interactions inside the material.
In addition to being sensitive to the spectral function, the ARPES signal is modulated by the so-called matrix element effects, which encode information about the orbitals forming the energy bands. However, being a complex quantity, extracting information about orbitals from matrix element effects is not a trivial task.
First, the team used extreme ultraviolet angle-resolved photoemission spectroscopy, allowing us to access 3D photoemission intensities, resolved in energy and both momentum components of the electrons. In addition, they measured the photoemission intensity modulation upon sample rotation – a procedure that they recently developed- which allowed them to disentangle signatures of the orbital texture of a layered 2D metal (1T-TiTe2).
Then, to strengthen the robustness of the results, they compared the experimental measurements with the theoretical calculations performed by two theory research groups, which used two complementary approaches. The synergy between the novel experimental approach and these state-of-the-art theoretical calculations allowed linking the orbital texture of the material and the measured angle-resolved photoemission intensity modulation upon sample rotation.
The results represent a significant step towards moving from the typical band structure mapping to accessing the electronic wave function and the orbital texture of solids. In the future, this methodology could be used to investigate the ultrafast non-equilibrium modification of the orbital texture upon photoexciting materials using ultrashort light flashes.
“Our discovery could be used to generate very precise knowledge about the non-equilibrium behavior of nature, specifically quantum materials, upon absorption of light. Because light-matter interaction governs a great number of devices in our everyday life, who knows, maybe our discovery could one day have an impact on everyday life”, comments Beaulieu.
Cited article: Beaulieu, S., Schüler, M., Schusser, J. et al. Unveiling the orbital texture of 1T-TiTe2 using intrinsic linear dichroism in multidimensional photoemission spectroscopy. npj Quantum Mater. 6, 93 (2021). https://doi.org/10.1038/s41535-021-00398-3
