The project has established a state-of-the-art ultrafast spectroscopy laboratory at Tel Aviv University, equipped with multiple synchronized laser beamlines and a high-resolution photoemission spectrometer. This infrastructure forms the basis for the project’s main scientific achievements, which revolve around revealing new ways to probe and control photocurrents in topological materials.
Two central breakthroughs have been achieved so far:
1. Revealing the true origin of circular dichroism in photoemission (Sidilkover et al., Phys. Rev. Research 2025)
Circular dichroism (CD)—the difference in photoemission intensity between right- and left-circularly polarized light—has long been interpreted as a direct fingerprint of the orbital or spin texture of electronic states in topological insulators. The project’s work revisited this assumption using the prototypical topological material Bi2Se₃ and demonstrated that the observed CD signals are far more complex.
Through systematic experiments across a wide range of photon energies, combined with theoretical modeling, it was shown that CD arises not only from the intrinsic properties of the electronic bands but also from the photoemission process itself, including hidden atomic orbital contributions and interference between photoemission pathways. These findings clarify long-standing controversies in the field and provide a more accurate framework for interpreting dichroism in angle-resolved photoemission. The results highlight how even in seemingly simple systems, the measured light–matter interaction encodes subtle quantum mechanical effects.
2. Measuring the phase of an electronic wavefunction using interferometric photoemission (Gvishi et al., 2025, Nature Photonics, under review)
The project introduced a new interferometric approach that brings phase measurement—a quantity long considered inaccessible in solids—into the realm of condensed matter physics. By combining two optical excitation pathways within a trARPES experiment, the team created a quantum-path electron interferometer, enabling direct measurement of the phase of an electronic wavefunction as a function of energy and momentum.
This groundbreaking technique allowed, for the first time, the reconstruction of the phase of the Dirac topological state in a topological insulator. The results reveal phase inversions and resonant effects that are directly linked to the material’s topology, opening a new window into the quantum geometry of solids.
Together, these studies redefine how we probe and understand the interaction between light and electronic states in topological materials, transforming photoemission spectroscopy from an amplitude-based to a phase-sensitive technique.
