Sven Badoux, Université de Sherbrooke

Jeudi 28 Septembre 2017 à 14h00
Amphi Urbain, Esc N
1ème etage

Transport signatures of charge density wave order
and the pseudogap critical point in cuprate superconductors

Since the discovery of cuprate superconductors 30 years ago, transport measurements in high magnetic fields have led to several major discoveries. The observation of quantum oscillations [1] revealed the existence of a small coherent Fermi surface in apparent contradiction with the prevailing picture of the electronic structure, guided by angle-resolved photoemission spectroscopy. Combined with the negative Hall and Seebeck coefficients measured in high fields at low temperature [2-3], the quantum oscillations revealed that the Fermi surface of cuprates undergoes a reconstruction in the underdoped side of the phase diagram. A few years later, the mechanism for this reconstruction was shown to be charge-density-wave (CDW) order by NMR and x-ray measurements [4,5].

Understanding the mechanism of superconductivity in cuprates requires that we understand the role of the different phases present in these materials. One of the biggest mysteries remains the nature of the pseudogap phase and its link to the CDW. In order to study this phase at low temperature, high magnetic fields are required to suppress superconductivity.

After a brief introduction to the cuprates, I will present recent transport measurements on three cuprate materials, YBCO [6], LSCO [7,8] and Nd-LSCO [9], performed in magnetic fields large enough to suppress superconductivity at low temperature. These measurements yielded two main findings. First, the pseudogap critical doping p* and the onset of the charge-density-wave order occur at different doping values. So the two phenomena are separate. Secondly, the carrier density n is observed to drop sharply at p*, going from n = 1+p above p* to n = p below p*. This signature imposes strong constraints on the possible nature of the pseudogap phase.

1. N. Doiron-Leyraud et al, Nature 447, 565 (2007).
2. J. Chang et al, PRL 104, 057005 (2010).
3. D. Leboeuf et al, Nature 450, 533 (2007).
4. T. Wu et al., Nature 477, 191 (2011).
5. G. Ghiringhelli et al., Science 337, 821 (2012).
6. S. Badoux et al, Nature 531, 210 (2016).
7. S. Badoux et al, PRX 6, 021004 (2016).
8. F. Laliberté et al, arXiv:1606.04491 (2016).
9. C. Collignon et al, PRB 95, 224517 (2017).

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