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CNAM Colloquium: Richard Greene, UMD

Thu, Mar 28, 2019 2:00 pm - 3:30 pm
Room 1201 John S Toll Building


Title: The Strange Metal State of the Electron-Doped Cuprates
Speaker: Richard Greene, UMD
An understanding of the high-temperature copper oxide (cuprate) superconductors has eluded the
physics community for over 30 years, and represents one of the greatest unsolved problems in
condensed matter physics. Particularly enigmatic is the normal state from which the
superconductivity emerges, so much so that this phase has been dubbed a “strange metal”. In this
talk, I will review recent research into this strange metallic state as realized in the electron-doped
(n-type) cuprates with a focus on their transport properties. In particular, I will show and discuss
measurements of resistivity, Hall Effect, magnetoresistance and thermopower in the n-type
cuprate La 2-x Ce x CuO 4 for 0.19≥ x ≥0.08 as a function of temperature. The surprising new and
unconventional 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>H c2
[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 beyond the “dome” conventional Fermi liquid behavior is found
(with a surprising “spin”).
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) The normal state resistivity above Tc, from 80 K to 400 K, follows an anomalous ~A(x)T 2
behavior at zero field for all doping(x) [4].
I conclude that conventional Fermi liquid theory cannot explain any of these results and they
remain an outstanding challenge to theory. Moreover, the magnitude of the anomalous low
temperature resistivity, magnetoresistance and thermopower scales with Tc, suggesting that the
origin of the superconductivity is correlated with the anomalous normal state properties.
If time allows I will discuss our surprising discovery of static Ferromagnetism beyond the
superconducting dome [5].

Research done in collaboration with Drs. Tara Sarkar, Pampa Mandal, and Josh Higgins and
undergraduate Nick Poniatowski.

1. T. Sarkar et al., arXiv;1810.03499, accepted in Sci. Adv. 2019.
2. K. Jin et al. , Nature 476, 73 (2011).
3. P. R. Mandal et al., arXiv: 1810.06511, accepted in PNAS 2019.
4. T. Sarkar, R. L. Greene, and S. Das Sarma, Phys. Rev. B 98, 224503 (2018).
5. T. Sarkar et al., arXiv: 1902.11235, submitted to Science.
Host: Local

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