To unveil mobile excitons we use angle-resolved photoemission spectroscopy (ARPES) to detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide TaSe3. While screening usually suppresses exciton formation in metals, the low density of conduction electrons, the low dimensionality, and two many-body effects favor them. In this presentation I will introduce the idea how to...
Systematic strain studies with ARPES have long been notoriously difficult to achieve. Here, we report first results from strained Sr$_2$RuO$_4$ using a novel technique combining a thermally-actuated strain cell with a micro-structured tapered sample prepared by focused ion beam milling. For the first time, this allows the quasi-continuous variation of strain on a single sample. I will...
The recently discovered layered kagome metals AV${_3}$Sb${_5}$ (A=K, Rb, Cs) exhibit diverse correlated phenomena, which are intertwined with a topological electronic structure with multiple van Hove singularities (VHSs) in the vicinity of the Fermi level. As the VHSs with their large density of states enhance correlation effects, it is of crucial importance to determine their nature and...
RENiO3 (RE - Rare Earth elements) exhibit multifunctional physical phenomena related to the spin and orbital degrees of freedom of the transition metal d-states and their interplay with the lattice. Notably, the iso-structure of RENiO3 permits the realization of hetero-structures altering physical matters that are very different from their bulk form.
Our ARPES data demonstrates that...
In Fermi liquids, electron-boson coupling is (EBI) quantified through the Eliashberg function $\alpha^2F(\omega,\mathbf{k})$, which modifies their self-energy $\Sigma(\varepsilon,\mathbf{k})$ obtainable from ARPES. We present a combined ARPES, density-functional theory, and high-resolution electron energy-loss spectroscopy (HREELS) study on the EBI in CaTiO$_3$ (CTO) thin films. CTO hosts a...
Recent transport experiments revealed a correlated insulating phase and quantum criticality points in twisted transition metal dichalcogenides (TMDs) that were predicted to host non-dispersive Moiré mini-bands. Here, we report for the first time on the direct observation of flat bands in twisted TMDs investigating 57° twisted bilayer WSe$_2$ by micro-focused angle-resolved photoemission...
This work focuses on modulation of spin-orbit interaction (SOI) in 2H-MoSe2 induced by proximity effects at its interface with amorphous Pb, providing strong SO coupling. The key element of our approach is the formation of amorphous Pb overlayers, allowing us to overcome k-space mismatch of the wavefunctions across the interface. We use SX-ARPES, which allows reaching the interface region...
Misfit compounds are natural stacks of two-dimensional materials, forming a three-dimensional structure that is commensurate in one direction but incommensurate in the other. Here we show that the misfit structure can be used to strongly influence the electronic properties as in an artificial moire structure formed from two-dimensional materials. Using ARPES with a micron-scale light focus, we...
YNi$_2$B$_2$C is a borocarbide superconductor with a complex electronic band structure that has a very strong Ni character near the Fermi energy. We present density functional theory (DFT) and one-step model of photoemission results for YNi$_2$B$_2$C and compare them to experimental soft x-ray angle resolved photoemission spectroscopy (SX-ARPES) measurements.
We show that electron...
Chiral topological semimetals (which possess neither mirror nor inversion symmetries) are a new class of quantum materials that have been predicted to host novel phenomena, such as multifold fermions with large topological charge, long Fermi-arc surface states, unusual magnetotransport and lattice dynamics, unconventional superconductivity, and exotic optical effects, such as a quantized...
We present our recent results on the spin texture in chiral topological semimetals, which host multifold fermions, a higher spin-generalization of Weyl-fermions. While ordinary Weyl-fermions display arbitrary spin-textures, multifold fermions are predicted to exhibit spin-momentum locking [1]. We use spin- and angle resolved photoemission spectroscopy to reveal the spin polarization of the...
As one of the external stimuli, strain applied to the solids can trigger exotic quantum phenomena such as phase transitions. Strain tuning the band structure and its visualization in ARPES are therefore very attracting and important. Here, we present our recent results on tuning the band structure and visualizing the topological phase transition in a quasi-one-dimension superconductor TaSe3.
I will introduce our recent efforts exploiting some of the varied facets of ARPES. Exploiting synchrotron micro-ARPES we extracted the electronic structure of the spatially competing low-temperature phases in IrTe$_2$. Comparison with theory provides evidence for a molecular-type local bonding mechanism. Using femtosecond time-resolved ARPES at 21 eV photon energy we could extend band mapping...
The generation of spin current pulses by laser-driven demagnetization links the field of ultrafast magnetism to spintronics. We demonstrate that femtosecond spin injection can be observed by spin and time resolved photoemission experiments.
We study iron films which are excited by a 800 nm pump laser beam. Photoemission by a HHG source in combination with a spin polarimeter is used to...
Electrodes for photocatalytic water splitting have to fulfill several requirements like high light absorption and efficient carrier transport to the surface without energy loss. Cuprous oxide is a prime candidate due to the small, direct bandgap and to abundant and cheap constituents, but the photochemical conversion efficiencies found so far are well below the theoretically possible figures....
