We propose that resistivity curvature mapping (RCM) based on the in-plane resistivity data is a useful way to objectively draw electronic phase diagrams of high-Tc cuprates, where various crossovers are important. In particular, the pseudogap crossover line can be conveniently determined by RCM. We show experimental phase diagrams obtained by RCM for Bi2Sr2-zLazCuO6+delta, La2-xSrxCuO4, and YBa2Cu3Oy, and demonstrate the universal nature of the pseudogap crossover. Intriguingly, the electronic crossover near optimum doping depicted by RCM appears to occur rather abruptly, suggesting that the quantum-critical regime, if it exists, must be very narrow.

Although the Hall coefficient RH is an informative transport property of metals and semiconductors, its meaning in the cuprate superconductors has been ambiguous because of its unusual characteristics. Here we show that a systematic study of RH in La2−xSrxCuO4 single crystals over a wide doping range establishes a qualitative understanding of its peculiar evolution, which turns out to reflect a two-component nature of the electronic structure caused by an unusual development of the Fermi surface recently uncovered by photoemission experiments.PACS numbers: 74.25. Fy, 74.72.Dn, 74.25.Jb During the past 17 years after the high-T c superconductivity was discovered in cuprates, virtually all measurable properties of their "normal state", the state in the absence of superconductivity, have been studied to understand the stage for novel superconductivity. However, there is yet no established picture for even such basic properties as the resistivity and the Hall coefficient [1], not to mention other more elaborate properties. The Hall coefficient R H of conventional metals is independent of temperature and signifies the Fermi surface (FS) topology and carrier density, but in cuprates R H shows strong, sometimes peaked, temperature dependences as well as a complicated doping dependence. An advance in understanding came when Chien, Wang and Ong found [2] that the cotangent of the Hall angle, cot Θ H (which is the ratio of the in-plane resistivity ρ ab to the Hall resistivity ρ H ), approximately shows a simple linear-in-T 2 behavior, which suggests the existence of a quasiparticlerelaxation rate that changes as ∼ T 2 . However, while it appears that the Hall problem in cuprates can be simplified when analyzed in terms of cot Θ H , it was argued by Ong and Anderson [3] that cot Θ H is after all a derived quantity and the central anomaly resides in the directly measured quantities ρ ab and R H .In this Letter, we address the notoriously difficult problem of the Hall effect with the recent knowledge on the physics of lightly-doped cuprates and the peculiar evolution of the FS recently elucidated by the angle-resolved photoemission spectroscopy (ARPES) experiments [4,5]. We first show that the behavior of R H and ρ ab in the lightly-doped cuprates mimics rather well the behavior of a conventional Fermi liquid, and discuss that this behavior signifies the physics on the "Fermi arc", a small portion of the FS near the Brillouin-zone diagonals. We then discuss that the peculiar hole-doping dependence and the temperature dependence of R H reflect a gradual participation of the "flatband" near (π, 0) of the Brillouin zone, which brings about a sort of two-band nature to the transport. The measurements of R H and ρ ab using a standard six-probe method are done on high-quality single crystals of La 2−x Sr x CuO 4 (LSCO) and YBa 2 Cu 3 O y (YBCO), the details of which have been described elsewhere [6].In slightly hole-doped LSCO and YBCO, which are usually considered to be antiferromagnetic insulators, it was demonstrated [6] th...

We present comprehensive neutron scattering studies of nonsuperconducting and superconducting electrondoped Pr 0.88 LaCe 0.12 CuO 4±␦ ͑PLCCO͒. At zero field, the transition from antiferromagnetic ͑AF͒ as-grown PLCCO to superconductivity without static antiferromagnetism can be achieved by annealing the sample in pure Ar at different temperatures, which also induces an epitaxial ͑Pr, La, Ce͒ 2 O 3 phase as an impurity. When the superconductivity first appears in PLCCO, a quasi-two-dimensional ͑2D͒ spin-density-wave ͑SDW͒ order is also induced, and both coexist with the residual three-dimensional ͑3D͒ AF state. A magnetic field applied along the ͓1 ,1,0͔ direction parallel to the CuO 2 plane induces a "spin-flop" transition, where the noncollinear AF spin structure of PLCCO is transformed into a collinear one. The spin-flop transition is continuous in semiconducting PLCCO, but gradually becomes sharp with increasing doping and the appearance of superconductivity. A c-axis aligned magnetic field that suppresses the superconductivity also enhances the quasi-2D SDW order at ͑0.5,0.5,0͒ for underdoped PLCCO. However, there is no effect on the 3D AF order in either superconducting or nonsuperconducting samples. Since the same field along the ͓1 ,1,0͔ direction in the CuO 2 plane has no ͑or little͒ effect on the superconductivity, ͑0.5,0.5,0͒ and ͑Pr, La, Ce͒ 2 O 3 impurity positions, we conclude that the c-axis field-induced effect is intrinsic to PLCCO and arises from the suppression of superconductivity.

We use neutron scattering to demonstrate that electron-doped superconducting Pr 0.88 LaCe 0.12 CuO 4−␦ in the underdoped regime is electronically phase separated in the ground state, showing the coexistence of a superconducting phase with a three-dimensional antiferromagnetically ordered phase and a quasi-two-dimensional spin-density wave modulation. The Néel temperature of both antiferromagnetic phases decreases linearly with increasing superconducting transition temperature ͑T c ͒ and vanishes when optimal superconductivity is achieved. These results indicate that the electron-doped copper oxides are close to a quantum critical point, where the delicate energetic balance between different competing states leads to microscopic heterogeneity.

It was recently demonstrated that the anisotropic phonon heat transport behavior is a good probe of the stripe formation in La(2-x)Sr(x)CuO(4) (LSCO) [Phys. Rev. B 67, 104503 (2003)]]. Using this probe, we examined an electron-doped cuprate Pr(1.3-x)La(0.7)Ce(x)CuO(4) (PLCCO) and found that essentially the same features as those in LSCO are observed. Moreover, the in-plane resistivity rho(ab) of lightly doped PLCCO shows metallic behavior (drho(ab)/dT>0) in the Néel ordered state with a mobility comparable to that in LSCO. It is discussed that these peculiar properties in common with LSCO signify the existence of stripes in electron-doped cuprates.