We present magnetotransport evidence for antiferromagnetism in films of the electron-doped cuprates Pr2−xCexCuO4. Our results show clear signature of static antiferromagnetism up to optimal doping x=0.15, with a quantum phase transition close to x=0.16, and a coexistence of static antiferromagnetism and superconductivity for 0.12≤x≤0.15. PACS numbers: 74.25.Fy, 73.43.Qt, 74.78.Bz In strongly correlated electron systems, quantum fluctuations close to a quantum critical point lead to many exotic properties of matter [1,2]. One example is the unconventional superconductivity (SC) and the non-Fermi liquid normal state properties, which appear close to a quantum phase transition (QPT). Such phenomena are found in many heavy Fermion [3,4] and organic [5] superconductors. However, attempts to apply quantum phase transition ideas to describe the properties of the high-T C cuprate superconductors are controversial. In the hole-doped (p-type) cuprates, whether a superconducting fluctuation scenario [6] or a competing order scenario [7,8,9] is an appropriate description of the pseudogap phenomena is still highly debated. In the electron-doped (n-type) cuprates, the existence of an antiferromagnetic to paramagnetic QPT is more plausible, but there is significant disagreement over if, and where, it occurs and its role in the physical properties [10,11,12,13,14,15,16,17,18,19,20,21].Several transport studies [10,11,12] on electron-doped Pr 2−x Ce x CuO 4 (PCCO) thin films suggest an antiferromagnetic QPT inside the superconducting dome at x≈0.16, which is slightly above the optimal doping. Angle resolved photoemission spectroscopy (ARPES) measurements on Nd 2−x Ce x CuO 4 (NCCO) [18] and optical measurements on NCCO and PCCO [19,20] revealed a normal-state gap which still exists at the optimal doping x=0.15. However, a recent inelastic neutron scattering (INS) measurement on NCCO single crystals suggests that long-range order antiferromagnetism (LROAF) does not coexist with SC and an antiferromagnetic QPT occurs just before the superconducting dome at x≈0.13 [21]. A recent ARPES work on superconducting Sm 2−x Ce x CuO 4 (SCCO) single crystals suggests a short-range order antiferromagnetism (SROAF) instead at x=0.14 [22]. In principle, neutron scattering (NS) and µSR could differentiate these different interpretations. But, so far, measurements from different groups are in significant disagreement [13,14,15,16,21,23]. The major experimental difficulty is likely caused by a high-temperature oxygen annealing, which is necessary to achieve superconductivity on the n-type cuprates, but also leads to spurious phases [15] or doping inhomogeneity/uncertainty [16] in large crystals. The controversy over the magnetic properties at high dopings, i.e., x≥0.13, leads to question the nature of the QPT proposed by the transport and optical measurements. In this report, we present an in-plane angular magnetoresistance (AMR) study of our PCCO thin films. A fourfold oscillation of the AMR, which is caused by the non-collinear antiferromagne...

We investigated the in-plane angular magnetoresistivity ( This twofold AMR below T D (x) is suggested to originate from an antiferromagnetic or spin density wave order.

We measured the high temperature (up to 800 K) resistivity of several dopings of SrFe2−x(Ni,Co)xAs2 (122) and compared the results with similar measurements on electron-doped cuprates. We find that the Sr-122 pnictide resistivity saturates above 500 K at around 400 − 700 µΩ·cm, consistent with the Mott-Ioffe-Regel (MIR) limit and in contrast to the MIR violating behavior of the hole-doped cuprates and our measurements on electrondoped cuprates. This supports the view that electronic correlations in the ferropnictides may be weaker than in the cuprates.

We present magneto-transport measurements performed on underdoped Pr2−xCexCuO4 at THz frequencies as a function of temperature and doping. A rapidly decreasing Hall mass is observed as the doping is reduced consistent with the formation of small electron Fermi pockets. However, both dc and infrared (IR) magneto-transport data strongly deviate from the predictions of transport theory in the relaxation time approximation (RTA) based on angular resolved photoemission data. The Hall mass is observed to increase continuously with increasing temperature with no signature at the Néel temperature. In the paramagnetic state, the temperature dependence of the Hall mass is consistent with current vertex corrections to the Hall conductivity due to magnetic fluctuations as observed in overdoped Pr2−xCexCuO4. Possible causal mechanisms for the discrepancy between transport theory within the RTA and the magneto-transport data are discussed.

The anomalous magneto-transport properties in electron doped (n-type) cuprates were investigated using Hall measurements at THz frequencies. The complex Hall angle was measured in overdoped Pr2−xCexCuO4 samples (x=0.17 and 0.18) as a continuous function of temperature above Tc at excitation energies 5.24 and 10.5 meV. The results, extrapolated to low temperatures, show that inelastic scattering introduces electron-like contributions to the Hall response. First principle calculations of the Hall angle that include current vertex corrections (CVC) induced by electron interactions mediated by magnetic fluctuations in the Hall conductivity reproduce the temperature, frequency, and doping dependence of the experimental data. These results show that CVC effects are the source of the anomalous Hall transport properties in overdoped n-type cuprates. PACS numbers: 74.72.Jt 78.20.Ls 71.18.+y 71.10.Ay 71.45.GmThe anomalous properties of the cuprates above the superconducting transition temperature have presented many puzzling challenges to the paradigms of condensed matter physics. In particular the unusual magnetotransport has often been cited as evidence that the cuprates are not Fermi liquids [1,2]. Despite the large simple convex hole-like Fermi surfaces observed by angular resolved photoemission (ARPES), both optimally doped n-and ptype cuprates exhibit anomalous and strongly temperature dependent Hall coefficients. In overdoped n-type cuprates, R H has zero crossings that suggest a mixed electron and hole response. Consensus on an explanation for the apparent non-Fermi liquid behavior of the cuprates has not been achieved despite much theoretical and experimental effort [1, 2].One proposed explanation involves current vertex corrections (CVC) to the standard relaxation time approximation (RTA) for the Hall conductivity [2]. In this Fermiliquid scenario, inelastic electron interactions mediated by antiferromagnetic (AF) fluctuations are the operative mechanism. In an alternative explanation thermally induced magnetic fluctuations at finite temperatures reconstruct the FS dynamically leading to fluctuating electron and hole-like Fermi surface segments over an area determined by the AF correlation length and a time scale associated with the AF correlation time [3]. In both of these scenarios, Fermi liquid behavior is recovered at T=0 where inelastic scattering and thermal fluctuations vanish.In this letter we directly address these issues by extending magnetotransport measurements into the frequency domain in the electron doped cuprates. We report temperature and doping dependent Hall data on overdoped Pr 2−x Ce x CuO 4 (PCCO) at THz frequencies 10 meV. At finite frequencies near zero temperatures where inelastic scattering is still operative but magnetic fluctuations are weak, we observe a strong suppression of the Hall response which corresponds to electronlike contributions coming into σ xy , even at T=0. Our experimental observations together with direct comparisons between our magnetotransport data and first-princip...