Blanc SIMI 4 - Blanc - SIMI 4 - Physique des milieux condensés et dilués

Superconductors in high magnetic fields – SUPERFIELD

Submission summary

Understanding the normal state of cuprate high temperature superconductors is one of the leading challenges in condensed-matter physics. In the very recent years, a new twist has been given to the field. First, transport and nuclear-magnetic-resonance (NMR) experiments (by partners 1 and 2) in magnetic fields strong enough to significantly depress superconductivity have revealed that superconductivity is in close competition with stripe order (a state where electronic charges align into linear filaments called stripes) in the purest underdoped cuprate YBa2Cu3Oy. This series of experiments has received outstanding international recognition owing to its potential impact on our comprehension of high temperature superconductivity. Second, the widespread interpretation of the pseudogap phenomenon state in terms of preformed pairs has been challenged by a number of works, particularly that of partner 3 which has fundamentally changed our understanding of the Nernst effect in metals and superconductors.

Our project aims at understanding the stripe-ordered and the pseudogap states of high Tc superconductors. A substantial part of the experimental strategy lies in the use of high magnetic fields. Two main research directions will be followed:

1) Studies of the electronic properties of cuprates, especially in high magnetic fields.
Magnetotransport, quantum oscillation, ultrasound and NMR measurements will be performed, in clean single crystals of YBCO, Tl2201 and Hg1201. Our collaborative effort aims at determining whether charge order (static stripes) and/or nematic order (fluctuating stripes) play a central role in cuprate physics, including the mechanism of superconductivity. For this, the competition between superconductivity and charge-stripe order will be studied as a function of field, in order to arrive at a microscopic description. The doping and the material dependence of stripe order will be explored as a test of the ubiquity of this phenomenon. Possible connections between (probably fluctuating) charge stripes and the pseudogap will be investigated.

2) Studies of superconducting fluctuations in low density superconductors.
The question of superconducting and/or phase fluctuations is central in the debate on the pseudogap of cuprates. We consider, however, that this problem is better addressed in conventional superconductors where much remains to be understood. We will perform Nernst effect measurements superconductors (doped SrTiO3, CuxBi2Se3, YbPtBi) in which the low carrier density should cause strong phase fluctuations. We shall investigate whether phase fluctuations in these superconductors affect the validity of the standard theory of Gaussian fluctuations. Obviously, a better understanding of the Nernst effect in general and more specifically of the signatures of superconducting fluctuations in Nernst measurements, will be crucial for the interpretation of the highly controversial Nernst measurements in high-Tc cuprates.

This project will be managed by partner 1 (LNCMI-Grenoble, coordinator and scientific supervisor: M-H. Julien) in close collaboration with the principal partners 2 (LNCMI-Toulouse, C. Proust) and 3 (LPEM-Paris, K. Behnia). The consortium members are all recognized experts in studies of correlated metals and superconductors in extreme conditions. In their respective fields of expertise, they have demonstrated their capability to perform state-of-the-art experiments and to produce high impact results at the international level. An essential aspect of our work is a coordinated strategy between partners 1 and 2. Our collaboration relies on the strong belief that the combination of macroscopic and microscopic measurements on the same samples is essential for the understanding of high temperature superconductivity.

Project coordination

Marc-henri Julien (LNCMI Grenoble) –

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.



Help of the ANR 542,578 euros
Beginning and duration of the scientific project: October 2012 - 48 Months

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