Forum DQMP – Auditoire Stückelberg, Ecole de physique

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Date(s) - 25/11/2014
13 h 00 min - 14 h 00 min

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Superconducting Properties of Two Coupled LaAlO3/SrTiO3 Interfaces
Denver Li (group of Prof. Triscone)
The discovery of a two-dimensional electron gas (2DEG), formed at the interface
between the two band insulators LaAlO3 and SrTiO3, has generated significant interest
partly because of the opportunity to realize oxide nanoscale devices. The 2DEG oxide
interface has revealed intriguing electronic properties, tunable superconductivity and a
rich phase diagram. This interface naturally provides a versatile system to artificially build
stacks of multiple 2D superconductors that would allow coupled 2D superconducting
layers to be studied.
However, one main obstacle is the realization of a fully metallic two-dimensional electron
gas (2DEG) at the interface between LaAlO3 and SrTiO3 thin films. We present here the
successful realization of a superconducting 2DEG at interfaces between artificially-grown
LaAlO3 and SrTiO3 thin films[1]. Our results highlight the importance of two factors – the
growth temperature and the SrTiO3 termination. By adopting an extremely high SrTiO3
growth temperature, we demonstrate a way to realize metallic, down to the lowest
temperature, and superconducting 2DEG at interfaces between LaAlO3 layers and SrTiO3
thin films. This study paves the way to build conducting LaAlO3/SrTiO3 multilayers.
Following this path, we demonstrate for the first time the realization of such functional biinterface
LaAlO3/SrTiO3 heterostructures with novel interesting superconducting
properties. [1] D. Li et al., APL Materials 2, 012102 (2014)
Interactions in Tetralayer Graphene Induce an Insulating State
Anya Grushina (group of Prof. Morpurgo)
Electron-electron interaction effects close to the charge neutrality in graphene cause
interesting effects, e.g. Fermi velocity renormalization in monolayer and spontaneous gap
opening in bilayer graphene. Devices with more graphene layers have been studied less
intensively and one would intuitively expect their properties to converge towards those of
graphite with weaker interaction effects. In this talk, I will show that thick graphene layers
of high quality can exhibit even stronger interactions effects than mono- or bilayer by
revealing a highly insulating state in suspended multi-terminal tetralayer graphene with
Bernal-stacking around the charge neutrality point in absence of magnetic field. This
highly insulating behavior cannot be explained within a single particle framework, strongly
indicating that the phenomenon originates from electron-electron interaction. By analogy
with bilayer graphene, a possible mechanism of spontaneous symmetry breaking is
proposed based on a staggered interlayer exchange potential. It can also naturally
explain a systematic even-odd effect of interactions on few-layer graphene of high quality
— only the stacks with even number of graphene layers exhibit spontaneous insulating
behavior.

Coffee and tea will be available from
12h50 at the entrance of the Auditoire
Forum Committee :
Laura Foini
Céline Lichtensteiger
Nicolas Ubrig
18.11.2014
DQMP, Ecole de Physique, 24 quai Ernest-Ansermet, CH-1211 Genève 4, http://dpmc.unige.ch

Réalisation : Sur Mesure concept