Band-resolved imaging and nonlinear optical control of currents in topological materials

Project Information

PhotoTopoCurrent

Grant agreement ID: 101078232

DOI

10.3030/101078232

EC signature date 13 February 2023

Start date 1 October 2023

End date 30 September 2028

Funded under

• European Research Council (ERC)

Total cost

€ 2 316 250,00

EU contribution

€ 2 316 250,00

Coordinated by

TEL AVIV UNIVERSITY
Israel

Periodic Reporting for period 1 - PhotoTopoCurrent (Band-resolved imaging and nonlinear optical control of currents in topological materials)

Reporting period: 2023-10-01 to 2026-03-31

Summary of the context and overall objectives of the project

The PhotoTopoCurrent project explores how light can be used to control and manipulate the quantum properties of advanced materials. Modern quantum materials, such as topological insulators and Weyl semimetals, host exotic electronic states that can conduct current without resistance or exhibit strong spin–orbit coupling, giving rise to new physical phenomena. However, the ability to actively control these states using light – a key step toward future quantum technologies – remains one of the central challenges in condensed matter physics.
The project’s central goal is to develop band-resolved coherent optical control of electronic currents in topological materials. To achieve this, the project combines three cutting-edge approaches:
1. Ultrafast laser spectroscopy, to excite and probe electrons on femtosecond (10⁻¹⁵ s) timescales;
2. Angle-resolved photoemission (ARPES), to directly image the electronic band structure in momentum and energy space; and
3. Coherent control techniques, inspired by atomic and optical physics, to steer electrons along specific quantum pathways.
By combining these methods into a single experimental framework—time- and angle-resolved photoemission (trARPES)—the project enables researchers to watch electrons move through materials in real time, observe how light modifies their energy and momentum, and ultimately control their behavior through interference and phase manipulation.
The overarching objective of PhotoTopoCurrent is to establish band-resolved coherent control of photocurrents in topological materials, bridging the gap between ultrafast optics and solid-state transport. Through this approach, the project aims to answer fundamental questions: How can light alter the quantum geometry of a material? Can we use interference between quantum pathways to direct current flow along specific bands? And can we access the phase of electronic wavefunctions—a quantity central to topology but long considered experimentally inaccessible in solids?
The broader impact of this work lies in paving the way for light-controlled quantum devices, linking fundamental research to potential applications in optoelectronics, information processing, and energy-efficient technologies.

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

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.

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)

The results of PhotoTopoCurrent go significantly beyond the current state of the art, both methodologically and conceptually.
• Redefining a widely used probe: The reinterpretation of circular dichroism provides a new understanding of one of the most widely used experimental signatures in photoemission studies. It establishes that dichroic patterns in topological insulators are not simple fingerprints of spin texture, but result from the interplay of local atomic structure, hidden orbital angular momentum, and interference effects. This finding resolves long-standing inconsistencies in the literature and sets a more reliable foundation for future spectroscopic research in the field.
• Introducing phase-resolved photoemission: The interferometric trARPES technique developed within the project brings phase—the key quantity governing coherence and topology—into direct experimental reach. This capability opens the door to studying how quantum geometric properties evolve under external stimuli and to designing new experiments where coherent light is used to manipulate electronic phases in solids.
• Creating a new experimental platform: The combination of multi-wavelength trARPES and interferometric control transforms the laboratory into one of the few facilities worldwide capable of exploring quantum interference and phase coherence in materials. This platform is expected to enable future discoveries at the intersection of ultrafast optics and condensed matter physics.
The broader potential impact of these results extends well beyond the specific materials studied. The ability to measure and control quantum phase and coherence in solids lays the groundwork for phase-engineered materials and light-driven quantum devices. Moreover, the insights gained from understanding how photoemission signals arise and how they can be manipulated are expected to influence the design of next-generation spectroscopic tools across Europe and internationally.
By combining innovative methodology with fundamental discoveries, PhotoTopoCurrent is helping to build a bridge between ultrafast optical control and quantum materials research, demonstrating how EU-funded frontier science can push the boundaries of what can be measured—and ultimately controlled—in the quantum world.