An international team of scientists from Geneva, Barcelona, and Leiden have revealed what makes magic angle graphene so special. We combined different imaging techniques and angle-resolved photoemission with simultaneous real- and momentum-space resolution (nano-ARPES) to directly map the band dispersion in twisted bilayer graphene devices near charge neutrality. Our experiments reveal large areas with a…

We published in PRL a combined experimental and theoretical study of the electronic structure of bulk Pt2HgSe3. We show that this material is one of only a few known dual-topological insulators, featuring different surface states that are linked to crystalline symmetries rather than to the topological properties of the 2D monolayer, which is a quantum spin…

Experiments reveal that quasiparticle properties in the superconductor Sr2RuO4 have a significant angular dependence due to the combined effects of local electron interactions and spin-orbit coupling. We determine the variation of the mass enhancement along the entire Fermi surface, which shows a strong dependence on the direction of the quasiparticle momentum. This is often interpreted…

January 2019: We measured the electronic structure of exfoliated mono-, bi-, and few-layer 1T′-WTe2 by laser-based microfocus angle-resolved photoemission. This is achieved by encapsulating with monolayer graphene a flake of WTe2 comprising regions of different thickness. Our data support the recent identification of a quantum spin Hall state in monolayer 1T′-WTe2 and reveal strong signatures of…

October 2018: We studied the evolution of the k-space electronic structure of bulk Ca2RuO4, lightly doped with Pr, under uniaxial strain. Using ultrathin plate-like crystals, we achieve uniaxial strain levels up to−4.1%, sufficient to suppress the insulating Mott phase and access the previously unexplored electronic structure of the metallic state at low temperature. Nature Communications volume 9,…

We have identified a three-dimensional spin texture in the two-dimensional electron gas (2DEG) at the SrTiO3 (111) surface.  In a free-electron Rashba 2DEG system the induced spin polarization lies entirely in the plane of confinement. Our tight binding supercell calculations for the SrTiO3 (111) 2DEG reveal a Rashba spin-splitting with a significant out-of-plane component in…

September 2016: Using micro focused laser ARPES we have observed large Fermi arcs on both the top and bottom surface of WTe2. Our surface electronic structure calculations demonstrate that these Fermi arcs are topologically trivial and that their existence is independent of the presence of type-II Weyl points in the bulk band structure. Contrary to common…

We published in Phys. Rev. X a combined experimental and theoretical study of MoTe2, which provides new evidence for the existence of type-II Weyl semimetals. Using angle-resolved photoemission, we show that the inequivalent top and bottom (001) surfaces of MoTe2 host distinct Fermi arc surface states. Employing systematic electronic structure calculations, we show that some of these…

Alberto de la Torre has been awarded the “Prix Vacheron Constantin des Sciences 2016” for his doctoral thesis entitled Spectroscopic Studies of Layered Iridium Oxides and reporting “the doping evolution of the electronic structure of the single and bilayer iridates Sr2IrO4 and Sr3Ir2O7 from angle resolved photoemission (ARPES) experiments”. This prize encourage young students from…

April 2016: We publish in Nature Materials a study of electron-phonon interactions in the SrTiO3(001) two-dimensional electron liquid. The band insulator strontium titanate, SrTiO3, widely used as substrate for growing oxides films, is a highly fascinating material in its own right. Most notably, it becomes superconducting upon doping with less than 1 excess electron per…