Competing ferromagnetism in high-temperature copper oxide superconductors

Abstract

The extreme variability of observables across the phase diagram of the cuprate high-temperature superconductors has remained a profound mystery, with no convincing explanation for the superconducting dome. Although much attention has been paid to the underdoped regime of the hole-doped cuprates because of its proximity to a complex Mott insulating phase, little attention has been paid to the overdoped regime. Experiments are beginning to reveal that the phenomenology of the overdoped regime is just as puzzling. For example, the electrons appear to form a Landau Fermi liquid, but this interpretation is problematic; any trace of Mott phenomena, as signified by incommensurate antiferromagnetic fluctuations, is absent, and the uniform spin susceptibility shows a ferromagnetic upturn. Here, we show and justify that many of these puzzles can be resolved if we assume that competing ferromagnetic fluctuations are simultaneously present with superconductivity, and the termination of the superconducting dome in the overdoped regime marks a quantum critical point beyond which there should be a genuine ferromagnetic phase at zero temperature. We propose experiments and make predictions to test our theory and suggest that an effort must be mounted to elucidate the nature of the overdoped regime, if the problem of high-temperature superconductivity is to be solved. Our approach places competing order as the root of the complexity of the cuprate phase diagram.quantum-phase transition ͉ non-Fermi liquid ͉ broken symmetry ͉ quantum order ͉ criticality T he superconducting dome (see Fig. 1), that is, the shape of the superconducting transition temperature T c as a function of doping (added charge carriers), x, is a clue that the high-T c superconductors are unconventional. Conventional superconductors, explained so beautifully by Bardeen, Cooper, and Schrieffer (52), have a unique ground state that is not naturally separated by any nonsuperconducting states. The electronphonon mechanism leads to superconductivity for arbitrarily weak attraction between electrons. To destroy a superconducting state requires a magnetic field or strong material disorder. In the absence of disorder or magnetic field, it is difficult to explain the sharp cutoffs at x 1 and x 2 within the Bardeen, Cooper, and Schrieffer theory. For high-T c superconductors, there is considerable evidence that competing order parameters are the underlying reason. Thus, x 1 and x 2 signify quantum phase transitions, most likely quantum critical points (QCPs) (1). Understanding high-T c superconductors therefore requires an understanding of possible competing orders (2, 3). The QCP at x 1 has been extensively studied (4-8), but little is known about x 2 . Recent work has also emphasized the importance of the maximum of the uniform susceptibility in defining the pseudogap line T* in Fig. 1 that ends at another QCP at x c (8). Here, we attempt, instead, at gaining insight from the possible existence of a QCP at x 2 .Complex materials (cuprates, heavy fermions, and organics)...

Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors

“…That the antiferromagnetic fluctuations (36) could have such long reach (37) and play a role in the uncovered field-induced QCP is quite extraordinary. We expect that the true nature of the quantum critical fluctuations that produce the n-FL state in the highly overdoped Tl 2 Ba 2 CuO 6ϩx is complex because here we are not far from the superconductivity's charge-doping end point (38). From our experiments, with salient similarities found between a cuprate and a heavy-Fermion compound, all evidence here points to a spin-controlled QCP universal to these strongly correlated electron systems.…”

Intermediate coupling model of the cuprates

“…40(a) at energies below 20 meV deserves comment. This dip reflects pair-breaking magnetic scattering (PBS) near Γ, which is related to earlier indications of ferromagnetic (FM) instabilities near the VHS [401,402]. A similar scenario of competing d-wave pairing vs pair-breaking effects has been discussed in the context of electron-phonon pairing [403].…”

Curie-like paramagnetism due to incomplete Zhang-Rice singlet formation in La2−xSrxCuOKaiser1, Huang2, Komiya3 et al. 2012Phys. Rev. B141191View full textAdd to dashboardCite

“…However, the origin of such localized moments has never been established, and more recently this has prompted alternative explanations for the Curie-like behavior of χ. 16 While often attributed to magnetic impurities or oxygen-disorder induced defects, the Curie-like susceptibility appears to be a universal property of heavilyoverdoped cuprates, which has persisted through significant improvements in sample quality. In fact Takagi et 10 have proposed that beyond x = 0.22 where a Curie-like term appears in their measurements of χ, that 1/4 of the overdoped Sr ions may create the paramagnetic moments either via direct substitution of Sr on the Cu sites, or as a more plausible scenario, the holes they add enter the Cu 3d x 2 −y 2 orbitals.…”