1) Pressure-induced superconductivity and its interplay with magnetism in CeAu2Si2 / 2) Mapping the phase diagram of BiFeO3-LaFeO3 superlattices by Zhi Ren / Benedikt Ziegler

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Date(s) - 06/05/2014
13 h 00 min - 15 h 00 min

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Auditoire Stückelberg, 24 quai Ernest-Ansermet

This seminar will be presented by Zhi Ren / Benedikt Ziegler (Ecole de physique – DPMC)

1) Pressure-induced superconductivity and its interplay with magnetism in CeAu2Si2 Zhi Ren (group of Prof. Jaccard) ! Pressure is a clean way to tune the ground state of heavy fermion compounds. Here we show that the antiferromagnet CeAu2Si2 (TN ≈ 10 K) exhibits pressure-induced heavy fermion superconductivity with a maximum Tc of 2.5 K. Superconductivity is found to interplay with magnetism over an unprecedentedly broad range of pressure (11.8 – 22.6 GPa). Remarkably, in almost half of this range, bulk superconducting and magnetic ordering are simultaneously enhanced, which is in contrast to all other known Ce-based pressure-induced superconductors. Although evidence for both critical spin and valence fluctuations are found in the vicinity of maximum Tc, neither of them seems to be responsible for the Cooper pairing. Alternatively, first-principle calculations suggest that orbital transitions and their associated fluctuations may play an important role.

2) Mapping the phase diagram of BiFeO3-LaFeO3 superlattices Benedikt Ziegler (group of Prof. Paruch) ! Recent experimental and theoretical studies on solid solutions of BiFeO3 and LaFeO3 show an extremely rich and complex phase diagram, with morphotropic-boundary-like characteristics, incommensurability and anomalous magnetostriction observed at different compositions. However, so far there have been no studies on BiFeO3-LaFeO3 superlattices. Combining structural and functional measurements, we map the phase diagram of such BiFeO3-LaFeO3 superlattices, grown by off-axis sputtering on (110) DyScO3 substrates. The phase diagram displays three distinct regions as a function of BiFeO3 fraction, with a BiFeO3-like ferroelectric phase and a LaFeO3-like paraelectric phase at its extremities, and a complex intermediate region, as supported by first principles calculations. Synchrotron X-ray diffraction measurements show three different superstructures demonstrating complex phase coexistence. Control of these competing phases could provide a route for the design of high response artificial materials!

Réalisation : Sur Mesure concept