Proposition de stage M2
2015-2016
Responsable du stage
Nom : Christophe Brun, Tristan Cren
Localisation : 4 place Jussieu, 75005 Paris
Tour 2232 étage 2ème
Equipe : Spectroscopie des Nouveaux Etats Quantiques
Courriel : brun@insp.jussieu.fr
Téléphone : +33 (0)1 44 27 4675
Page web : http://www.insp.jussieu.fr/-Spectroscopie-des-nouveaux-etats-.html
Searching for and fabricating new high-Tc monolayer
superconductors
In a superconductor, electrons form pairs called Cooper pairs that can carry a current
without dissipation. A tremendous effort has been undertaken in order to understand the basic
mechanisms at play in superconductivity and to fabricate new materials with the highest possible
critical temperature. This effort has led to the discovery of high-critical temperature (abbreviated
HTc) superconductors in 1986, based on copper-oxide atomic planes. For the first time ever,
material chemists were able to synthetize new materials being superconducting above liquid
nitrogen temperature: 77K. This achievement is very important for applications involving
superconducting materials, because it enables avoiding the use of liquid helium which usually
requires complex and costly cryogenic infrastructures. More recently iron-based superconductors
were synthetized and were also shown to be superconductors. Nevertheless iron-based bulk
superconductors have a maximum critical temperature (much) below 77K. In the last ten years,
with the progress in combining surface science and low-temperature techniques, researchers
started to investigate the possibility of having HTc superconductivity in ultrathin materials by
engineering an appropriate coupling through the substrate. This effort has led to the discovery of
interface superconductivity between two different non superconducting materials [1], and to the
existence of superconductivity in a single atomic metallic plane (Pb, Sn) at the surface of an
insulating substrate [2]. Our team in UPMC has followed up on this research topic [3] and
discovered new properties of these monolayer superconductors. Unfortunately, the Tc’s of these
newly discovered ultrathin superconductors were below 4.2K so far. However, in 2012 a Chinese
group managed to fabricate and demonstrate that a single monolayer of FeSe (iron selenide) on a
SrTiO3 (strontium titanium oxyde) substrate is superconducting with a Tc that should be higher
than 77K [4]. The quality of the films were improved further. As a consequence, superconductivity
above 100K was reported this year in this system [5]. Theoretical works suggest that SrTiO3 plays
a very important role in the resulting HTc, because it has a huge dielectric constant at low
temperature. We propose during this master 2 internship to fabricate new metal on SrTiO3
systems, to search for new monolayers superconductors with potentially HTc. The growth will be
carried out in a new ultrahigh vacuum system equipped with surface science techniques. The
Sujet du stage
Unité mixte de recherche 7588 – CNRS / Université Pierre et Marie Curie
Campus Jussieu – Tours 22 et 23 – Case courrier 840
4 place Jussieu – 75252 Paris Cedex 5 – France
Tél. : +33 (0)1 44 27 63 72 – Fax : +33 (0)1 44 27 46 09 – www.insp.upmc.fr
newly synthetized films will be further studied by scanning tunneling microscopy/spectroscopy
(STM / STS) at very low temperature (300 mK) and high field (10 T), to investigate the
superconducting properties with a state-of-the-art experimental set-up unique in France and
having only few equivalent in the world.
[1] Reyren, N. et al. Science 317, 1196 (2007);
[2] Zhang, T. et al. Nature Phys. 6, 104 (2010);
[3] C. Brun, T. Cren et al. Nature Physics 10, 444 (2014);
[4] Q.Y Wang et al. 29, 037402 Chin. Phys. Lett. (2012);
[5] J.F. Ge et al. Nature Materials 14, 285 (2015);
Techniques utilisées : ultrahigh vacuum techniques, molecular beam epitaxy, low-energy-
electron diffraction, Auger spectroscopy, scanning tunneling microscopy/spectroscopy,
very low temperature, magnetic field, data analysis and modelling.
Stage rémunéré : 480 euros/mois
Ce stage pourra t-il se poursuivre en thèse : oui
Si oui, financement envisagé : bourse de l’école doctorale
Unité mixte de recherche 7588 – CNRS / Université Pierre et Marie Curie
Campus Jussieu – Tours 22 et 23 – Case courrier 840
4 place Jussieu – 75252 Paris Cedex 5 – France
Tél. : +33 (0)1 44 27 63 72 – Fax : +33 (0)1 44 27 46 09 – www.insp.upmc.fr