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Seminars and Events

Seminars and Events

Thematic Seminars

Coordinador: Rafael Jiménez-Riobóo


21 February 2020, 12:00 h. Salón de Actos

Magic Angle Bilayer Graphene - Superconductors, Orbital Magnets, Correlated States and beyond

Dmitri Efetov
Professor at ICFO-The Institute of Photonic Sciences


When twisted close to a magic relative orientation angle near 1 degree, bilayer graphene has flat moire superlattice minibands that have emerged as a rich and highly tunable source of strong correlation physics, notably the appearance of superconductivity close to interaction-induced insulating states. Here we report on the fabrication of bilayer graphene devices with exceptionally uniform twist angles. We show that the reduction in twist angle disorder reveals insulating states at all integer occupancies of the four-fold spin/valley degenerate flat conduction and valence bands, i.e. at moire band filling factors nu = 0, +(-) 1, +(-) 2, +(-) 3, and reveals new superconductivity regions below critical temperatures as high as 3 K close to - 2 filling. In addition we find novel orbital magnetic states with non-zero Chern numbers. Our study shows that symmetry-broken states, interaction driven insulators, and superconducting domes are common across the entire moire flat bands, including near charge neutrality. We further will discuss recent experiments including screened interactions, fragile topology and the first applications of this amazing new materials platform.


03 February 2020, 12:00 h. Salón de Actos

SrTiO3-based 2-dimensional electron gases for ultralow power spintronics: Has oxide electronics finally found its “killer app”?

Dr. Manuel Bibes
Unité Mixte de Physique CNRS / Thales, Université Paris-Saclay, Orsay (FRANCE)



The ever increasing power consumption of Information and Communication Technology (ICT) systems currently largely based on CMOS technology is unsustainable in the mid-term1, which is driving major ICT manufacturers and the scientific community to actively search for alternative, more energy-efficient solutions for data storage and processing. One promising approach, proposed by Intel, is the so-called MESO transistor (for MagnetoElectric-Spin-Orbit), a spin-based non-volatile device in which magnetic information is written by a magnetoelectric element and read out by a spin-orbit element through the inverse spin Hall effect (ISHE) or the inverse Edelstein effect (IEE). The IEE occurs in systems with broken inversion symmetry such as the surface of topological insulators or in two-dimensional electron gases (2DEG) displaying Rashba spin-orbit coupling. The IEE is particularly attractive because of superior spin to charge conversion efficiencies and of the higher resistance of 2DEGs compared to metals showingISHE.
In this presentation, I will show that the 2DEG that forms at the interface of SrTiO3 (STO)4with LaAlO35 or reactive metals such as Al may be exploited to interconvert spin and charge currents through the direct and inverse Edelstein effects with high efficiencies. In a first part, I will present spin to charge conversion experiments using the spin-pumping technique to inject a spin current in the 2DEG. By applying a gate voltage, we tune the position of the Fermi level in the complex multi-orbital structure of STO, which results in a strong variation of the IEE amplitude with sign changes....




     

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