Rick Green,College Park, Maryland 20742, USA.

jeudi 28 Novembre 2019, Amphi Boreau ,escalier C, 2 eme ètage.

Quantum Materials Center and Department of Physics, University of Maryland,

Strange Metal Transport and Ferromagnetism in La2-xCexCuO4

I present measurements of resistivity, Hall Effect, magnetoresistance and thermopower in the electron-doped cuprate La2-xCexCuO4 for 0.19≥ x ≥0.08 as a function of temperature and magnetic field. The surprising new results are :
1) The normal state magnetoresistance exhibits an anomalous linear-in-H behavior [1] at the same doping and temperature where a linear-in-T resistivity was previously observed for H>Hc2 [2], i.e. above the Fermi surface reconstruction at x =0.14 up to the end of the superconducting dome (x 0.175). For doping above the dome conventional Fermi liquid behavior is found (except see (3)).
2) The normal state Seebeck coefficient, S/T, exhibits an unconventional low temperature –lnT dependence at the same doping where linear-in-T and linear-in-H resistivity is found [3]. Conventional S/T = constant behavior is found above the superconducting dome.
3) Itinerant ferromagnetism is found below 4K for doping beyond the SC dome, based on transport, magnetization and Kerr Effect experiments [4].
I conclude that conventional Fermi liquid theory cannot explain (1) and (2). Moreover, the magnitude of the anomalous magnetoresistance and thermopower scales with Tc, suggesting that the origin of the superconductivity is correlated with the anomalous normal state properties. The data suggest that there is a SC/FM Quantum Phase Transition at the end of the SC dome [5].
1. T. Sarkar et al., Sci. Adv. 5, eaav6753 (2019).
2. K. Jin et al. , Nature 476, 73 (2011).
3. P. R. Mandal et al., PNAS 116, 5991(2019).
4. T. Sarkar et al., arXiv:1902.11235.
5. Butch et al., PNAS 109, 8440 (2012) ;

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