BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d25646a6c06 DTSTART:20230711T130000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium and Online (Teams) SUMMARY:ICFO | DAVID BARCONS RUIZ CLASS:PUBLIC DESCRIPTION:Graphene has revolutionized the field of condensed matter physi cs over the last two decades\, emerging as an outstanding research platfor m. This is because graphene electrons behave as massless Dirac fermions\, displaying properties typical of relativistic particles\, and because of i ts extraordinary opto-electronic characteristics\, such as an exceptional electron mobility\, high tunability with electrostatic gating and broadban d light absorption. More recently\, the discovery of correlated physics in graphene moiré\; superlattices has led to a torrent of new investig ations and results in the community. Moiré\; superlattices are gener ated by stacking Van der Waals layers with a relative twist\, originating a new and longer periodicity that modifies the electronic band structure. In principle\, one could also engineer artificially such superlattices\, w ith the benefit of a complete flexibility to create any kind of lattice. I n the first part of this Thesis\, we introduce a new nanopatterning techni que allowing us to pattern Van der Waals materials on a scale comparable t o moiré\; superlattices\, but with no restrictions in the lattice de sign. Our technique is based on ion-beam milling of suspended membranes an d is able to imprint periodic features in graphite electrodes with less th an 20 nm period. These periodic features serve to generate a superlattice potential in single layer graphene that modifies its band structure\, whic h is demonstrated through electronic transport measurements. We employ our nanopatterning process to study more complicated lattice structures\, whi ch are not accessible by twisting layers. Our technique allows us to propo se a feasible experimental setup to engineer isolated electronic flat band s\, that could potentially lead to correlated phenomena\, by inducing a su perlattice potential in gapped bilayer graphene. This will allow to engine er a new class of solid-state Fermi-Hubbard model simulators\, similar to those in moiré\; semiconductors.\nOwing to the long distances graphe ne electrons can propagate without loosing their momentum\, even at room t emperature\, it was recently shown that they can behave as a hydrodynamic fluid\, for a significant and experimentally accessible range of parameter s. This fluid-like behaviour is driven by the electron-electron collisions . Phenomena typical to liquids\, such as viscosity\, has been studied in g raphene devices\, drawing considerable interest from the scientific commun ity. In the second part of this Thesis\, we employ terahertz graphene plas mons &ndash\; a collective excitation of the electron density - to explore the transition from the collisionless regime\, where electron-electrons d o not play a role in the dynamical response of graphene\, to the hydrodyna mic regime. \; We demonstrate that the dynamical response of an electr on liquid to an oscillating electric potential is different depending on w hether the excitation frequency is larger or smaller than the frequency of electron-electron collisions. In electronic Fermi liquids\, this is the e quivalent of the zero to first sound transition observed in neutral Fermi liquids such as He-3. Finally\, we implement a phase-resolved THz scatteri ng nearfield system\, that allows high signal-to-noise ratio imaging in th e THz regime with few tens of nanometers resolution. We apply this techniq ue to image THz acoustic plasmons in charge neutral graphene\, for the fir st time.\nThesis Director: Prof Dr. Frank H.L. Koppens and Dr. Hanan Herzi g Sheinfux DTSTAMP:20260405T123206Z END:VEVENT END:VCALENDAR