Ferromagnetic order beyond the superconducting dome in a cuprate superconductor

Abstract

According to conventional wisdom, the extraordinary properties of the cuprate high-temperature superconductors arise from doping a strongly correlated antiferromagnetic insulator. The highly overdoped cuprates—whose doping lies beyond the dome of superconductivity—are considered to be conventional Fermi liquid metals. We report the emergence of itinerant ferromagnetic order below 4 kelvin for doping beyond the superconducting dome in thin films of electron-doped La2–xCexCuO4 (LCCO). The existence of this ferromagnetic order is evidenced by negative, anisotropic, and hysteretic magnetoresistance, hysteretic magnetization, and the polar Kerr effect, all of which are standard signatures of itinerant ferromagnetism in metals. This surprising result suggests that the overdoped cuprates are strongly influenced by electron correlations.

Universal scaling of the critical temperature and the strange-metal scattering rate in unconventional superconductors

“…where the resistivity decreases with decreasing temperature without any abrupt drop of resistance down to the lowest measured temperature of 2 K. The critical composition at which the superconductivity disappears corresponds to the doping level of x c ≈ 0.177, consistent with previous results 9,16 . For x > x c , the low-temperature dependence of resistivity obeys the Fermi liquid behavior, namely ρ = ρ 0 + A 2 T 2 (Fig.…”

Optical conductivity and superconductivity in highly overdoped La 2− x Ca x CuO 4 thin films

“…The precipitous decline of the superfluid density near the end of the superconducting dome (7,8) has been controversially discussed in terms of quantum-phase fluctuations (7,8) and dopant-induced disorder (9)(10)(11). The discoveries of charge-density waves (12) and ferromagnetism (13,14) have highlighted the potential influence of competing instabilities of the electron system, possibly enhanced by a van Hove singularity in the band structure. Very recently, superconductivity has been discovered far outside the superconducting dome established for well-known cuprates (1), for instance, in Ba2CuO 4−δ with Tc = 73 K at p ∼ 0.4 (15) and in Cu0.75Mo0.25Sr2YCu2O7.54 with Tc = 84 K at p ∼ 0.46 (16), suggesting that none of these effects necessarily obliterate superconducting correlations.…”

Density Wave Mediated Dzyaloshinskii-Moriya Interactions

“…Additionally, a two patch RG analysis of the U -V -J model indicates that triplet d x 2 −y 2 -density wave order is can be energetically favorable in a finite region of coupling space given J/U < 0. 15 Ferromagnetic ordering was also predicted 37 to emerge in the highly overdoped cuprates and experimentally confirmed 38 to exist in the CuO 2 planes of the cuprates. We find that the iσd x 2 −y 2 +d xy -density wave-induced DM interaction in a 2D ferromagnetic system generically produces a magnon spectrum with two branches with a characteristic d x 2 −y 2 gap.…”

“…It has previously been shown 15 via a one-loop renormalization group analysis of the extended U -V -J model that triplet d x 2 −y 2 -density wave condensation is energetically favorable for a range of interaction strengths given J/U < 0. Furthermore, it was theoretically predicted 37 and recently experimentally confirmed 38 that the highly overdoped cuprates show ferromagnetic ordering in the CuO 2 planes. Due to these reasons we investigate the mixed triplet-singlet density wave DMI effects on a twodimensional Heisenberg ferromagnet.…”