Title: The Strange Metal State of the Electron-Doped Cuprates Speaker: Richard Greene, UMD Abstract: 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  at the same doping and temperature where a linear-in-T resistivity was previously observed for H>H c2 , 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 . 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) . 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 .
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