arXiv subjects

Gianmarco Gatti

Publications and source records attributed to Gianmarco Gatti.

4 recordsLinked to original sources

arXiv2026

Bulk and surface electronic structure of MoAlB(010)

The bulk and surface electronic structure of MoAlB(010) is studied by a combination of angle-resolved photoemission spectroscopy and density functional calculations. The observed bulk Fermi-level crossings agree with the previously reported bulk Fermi surface of the material. Additionally, we find several surface states in the wide projected bulk band gaps around the Fermi energy. The surface states differ in their stability under residual-gas exposure in the vacuum system and in the magnitude of their Rashba-type spin-orbit splitting. We explain this in terms of their elemental and orbital character. A surface state arising from Al dangling bonds is sensitive to surface contamination, whereas a mainly Mo-derived surface state exhibits the stronger spin-orbit splitting. The surface states show symmetry-enforced crossings near the $\bar{\mathrm{S}}$ point of the surface Brillouin zone. These are protected by the mirror-symmetry elements of the p2mm wallpaper group.

cond-mat.mtrl-sci↗

arXiv2022

Observation of flat $Γ$ moiré bands in twisted bilayer WSe$_2$

The recent observation of correlated phases in transition metal dichalcogenide moiré systems at integer and fractional filling promises new insight into metal-insulator transitions and the unusual states of matter that can emerge near such transitions. Here, we combine real- and momentum-space mapping techniques to study moiré superlattice effects in 57.4$^{\circ}$ twisted WSe$_2$ (tWSe$_2$). Our data reveal a split-off flat band that derives from the monolayer $Γ$ states. Using advanced data analysis, we directly quantify the moiré potential from our data. We further demonstrate that the global valence band maximum in tWSe$_2$ is close in energy to this flat band but derives from the monolayer K-states which show weaker superlattice effects. These results constrain theoretical models and open the perspective that $Γ$-valley flat bands might be involved in the correlated physics of twisted WSe$_2$.

cond-mat.str-el↗

arXiv2019

Unveiling the electronic transformations in the semi-metallic correlated-electron transitional oxide Mo$_8$O$_{23}$

Mo$_8$O$_{23}$ is a low-dimensional chemically robust transition metal oxide coming from a prospective family of functional materials, MoO$_{3-x}$, ranging from a wide gap insulator $(x=0)$ to a metal $(x=1)$. The large number of stoichometric compounds with intermediate $x$ have widely different properties. In Mo$_8$O$_{23}$, an unusual charge density wave transition has been suggested to occur above room temperature, but its low temperature behaviour is particularly enigmatic. We present a comprehensive experimental study of the electronic structure associated with various ordering phenomena in this compound, complemented by theory. Density-functional theory (DFT) calculations reveal a cross-over from a semi-metal with vanishing band overlap to narrow-gap semiconductor behaviour with decreasing temperature. A buried Dirac crossing at the zone boundary is confirmed by angle-resolved photoemission spectroscopy (ARPES). Tunnelling spectroscopy (STS) reveals a gradual gap opening corresponding to a metal-to-insulator transition at 343 K in resistivity, consistent with CDW formation and DFT results, but with large non-thermal smearing of the spectra implying strong carrier scattering. At low temperatures, the CDW picture is negated by the observation of a metallic Hall contribution, a non-trivial gap structure in STS below $\sim 170$ K and ARPES spectra, that together represent evidence for the onset of the correlated state at $70$ K and the rapid increase of gap size below $\sim 30$ K. The intricate interplay between electronic correlations and the presence of multiple narrow bands near the Fermi level set the stage for metastability and suggest suitability for memristor applications.

cond-mat.str-el↗

arXiv2019

Orbitally selective breakdown of Fermi liquid quasiparticles in Ca$_{1.8}$Sr$_{0.2}$RuO$_4$

We present a comprehensive angle-resolved photoemission spectroscopy study of Ca$_{1.8}$Sr$_{0.2}$RuO$_4$. Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through a light polarization analysis and comparison to dynamical mean-field theory calculations. Bands assigned to $d_{xz}, d_{yz}$ orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions - associated with a predominantly $d_{xy}$ band character - are shown to display non-Fermi-liquid behavior. We thus demonstrate that Ca$_{1.8}$Sr$_{0.2}$RuO$_4$ is a hybrid metal with an orbitally selective Fermi liquid quasiparticle breakdown.

cond-mat.str-el↗