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28 pages including supplementary; It has long been recognized that the key to unlocking the mystery of cuprate high-Tc superconductivity lies in understanding the anomalous normal state from which pairs form and condense. While many of its defining properties have been identified, they are often considered either at a singular doping level or as an isolated phenomenon as a function of doping. As a result, their relation to each other and to the pseudogap (PG), strange metal (SM) and non-superconducting (non-SC) regimes that define the cuprate phase diagram has yet to be elucidated. Here, we report a high-field in-plane MR study on several cuprate families spanning all 3 regimes that reveal a complex yet nonetheless systematic evolution of the form of the MR, with each regime possessing its own distinct scaling behavior. In the PG regime, the MR exhibits pure H/T^2 scaling at low fields and H-linearity at the highest field strengths. While the H-linearity persists inside the SM regime, the scaling changes abruptly to H/T. The size of the H-linear slope, meanwhile, is found to be correlated with both the T-linear resistivity coefficient and Tc, strengthening the characterization of the SM regime as a quantum critical phase. We interpret the omnipresence of H-linear MR across both regimes as a signature of highly anisotropic, possibly discontinuous features on the Fermi surface. Finally, within the non-SC, Fermi-liquid regime, we observe a recovery of conventional Kohler scaling. This comprehensive study establishes the distinct nature of the magnetotransport within each regime and identifies power-law scaling of the normal state MR as a defining feature of SC hole-doped cuprates. The incompatibility of such power-law scaling with any known variant of Boltzmann transport theory motivates the quest for an altogether new theoretical framework, one in which the MR is entirely decoupled from elastic impurity scattering.

Hall effect and quantum oscillation measurements on high temperature cuprate superconductors show that underdoped compositions have a small Fermi surface pocket whereas when heavily overdoped, the pocket increases dramatically in size. The origin of this change in electronic structure has been unclear, but may be related to the high temperature superconductivity. Here we show that the clean overdoped single-layer cuprate Tl2Ba2CuO6+δ (Tl2201) displays CDW order with a remarkably long correlation length ξ ≈ 200 ˚A which disappears above a hole concentration pCDW ≈ 0.265. We show that the evolution of the electronic properties of Tl2201 as the doping is lowered may be explained by a Fermi surface reconstruction which accompanies the emergence of the CDW below pCDW. Our results demonstrate importance of CDW correlations in understanding the electronicproperties of overdoped cuprates.

We report Nernst effect measurements for some crystalline films of Ca and Zn-doped yttrium barium copper oxide grown by pulsed laser deposition. We argue that our results and most of the published data for LSCO are consistent with the theory of Gaussian superconducting fluctuations., Comment: 4 pages 4 figures

We report measurements of the magnetic susceptibility of twinned single crystals of YBa2Cu3O6+x from just above their superconducting transition temperatures to 300 K with magnetic fields of up to 5 T applied parallel and perpendicular to the CuO2 planes at seven values of x. Appropriate analysis allows the relatively small, but still important, Curie terms to be separated from other contributions to the susceptibility. Our data support a picture in which the Curie terms arise from oxygen disorder in the Cu-O chains. This agrees with published work on polycrystalline samples where the sample cooling rate was varied, but here we show that the Curie plots flatten out above 200 K. We identify small effects of charge density wave (CDW) instabilities in the temperature (T ) derivative of the in-plane susceptibility dab(T)/dT and discuss their x dependence. For x = 0.67 we make a detailed comparison with published high energy x-ray diffraction data using a minimal model involving Fermi arcs, thereby obtaining values for the CDW energy gap and the Helmholtz free energy in a coherence volume. At 80 and 100 K the latter is comparable with, or smaller than, kBT , respectively, highlighting the probable importance of thermal fluctuations. We note that the effect of the Lorentz force on charge carriers in the Fermi arcs could provide a simple mechanism for enhancing the CDWs in high magnetic fields, as suggested by recent experiments.

We report measurements of the magnetic susceptibility of twinned single crystals of YBa$_{2}$Cu$_{3}$O$_{6+x}$ from just above their superconducting transition temperatures to 300 K with magnetic fields of up to 5 T applied parallel and perpendicular to the CuO$_2$ planes at 7 values of $x$. Appropriate analysis allows the relatively small, but still important, Curie terms to be separated from other contributions to the susceptibility. Our data support a picture in which the Curie terms arise from oxygen disorder in the Cu-O chains. This agrees with published work on polycrystalline samples where the sample cooling rate was varied, but here we show that the Curie plots flatten out above 200 K. We identify small effects of charge density wave (CDW) instabilities in the temperature ($T$) derivative of the in-plane susceptibility $d\chi_{ab}(T)/dT$ and discuss their $x$-dependence. For $x=$0.67 we make a detailed comparison with published high energy X-ray diffraction data using a minimal model involving Fermi arcs, thereby obtaining values for the CDW energy gap and the Helmholtz free energy in a coherence volume. At 80 and 100 K the latter is comparable with, or smaller than $k_BT$ respectively, highlighting the probable importance of thermal fluctuations. We note that the effect of the Lorentz force on charge carriers in the Fermi arcs could provide a simple mechanism for enhancing the CDWs in high magnetic fields, as suggested by recent experiments., Comment: 11 pages, 10 Figures, accepted by Phys. Rev. B. References corrected

Torque magnetization measurements on YBa$_2$Cu$_3$O$_{y}$ (YBCO) at doping $y=6.67$($p=0.12$), in DC fields ($B$) up to 33 T and temperatures down to 4.5 K, show that weak diamagnetism persists above the extrapolated irreversibility field $H_{\rm irr} (T=0) \approx 24$ T. The differential susceptibility $dM/dB$, however, is more rapidly suppressed for $B\gtrsim 16$ T than expected from the properties of the low field superconducting state, and saturates at a low value for fields $B \gtrsim 24$ T. In addition, torque measurements on a $p=0.11$ YBCO crystal in pulsed field up to 65 T and temperatures down to 8 K show similar behaviour, with no additional features at higher fields. We discuss several candidate scenarios to explain these observations: (a) superconductivity survives but is heavily suppressed at high field by competition with CDW order; (b) static superconductivity disappears near 24 T and is followed by a region of fluctuating superconductivity, which causes $dM/dB$ to saturate at high field; (c) the stronger 3D ordered CDW that sets in above 15 T may suppress the normal state spin susceptibility sufficiently to give an apparent diamagnetism of the magnitude observed., 15 pages, 7 figures

We report intrinsic tunnelling data for mesa structures fabricated on three over- and optimally-doped $\rm{Bi_{2.15}Sr_{1.85}CaCu_{2}O_{8+\delta}}$ crystals with transition temperatures of 86-78~K and 0.16-0.19~holes per CuO$_2$ unit, for a wide range of temperature ($T$) and applied magnetic field ($H$), primarily focusing on one over-doped crystal(OD80). The differential conductance above the gap edge shows clear dip structure which is highly suggestive of strong coupling to a narrow boson mode. Data below the gap edge suggest that tunnelling is weaker near the nodes of the d-wave gap and give clear evidence for strong $T$-dependent pair breaking. These findings could help theorists make a detailed Eliashberg analysis and thereby contribute towards understanding the pairing mechanism. We show that for our OD80 crystal the gap above $T_c$ although large, is reasonably consistent with the theory of superconducting fluctuations., Comment: 15 pages, 15 figures plus supplemental material, 1 table and 47 ASCII files with raw data. Corrected files for Fig. 12a

We discuss a recent resonant ultrasound spectroscopy (RUS) study of YBa$_2$Cu$_3$O$_{6+\delta}$, which infers a line of phase transitions bounding the pseudogap phase and argue that this scenario is not supported by thermodynamic evidence. We show that the anomalies in RUS, heat capacity and thermal expansion at the superconducting transition temperatures agree well. But there are large discrepancies between RUS and thermodynamic measurements at $T^*$ where the pseudogap phase transitions are purported to occur. Moreover, the frequency and temperature dependence of the RUS data for the crystal with $\delta = 0.98$, interpreted in terms of critical slowing down near an electronic phase transition, is five orders of magnitude smaller than what is expected. For this crystal the RUS data near $T^*$ are more consistent with non-equilibrium effects such as oxygen relaxation., Comment: Published version

We discuss a recent resonant ultrasound spectroscopy (RUS) study of YBa_2Cu_3O_6+δ, which infers a line of phase transitions bounding the pseudogap phase and argue that this scenario is not supported by thermodynamic evidence. We show that the anomalies in RUS, heat capacity, and thermal expansion at the superconducting transition temperatures agree well, but there are large discrepancies between RUS and thermodynamic measurements at T∗ where the pseudogap phase transitions are purported to occur. Moreover, the frequency and temperature dependence of the RUS data for the crystal with δ=0.98, interpreted in terms of critical slowing down near an electronic phase transition, is five orders of magnitude smaller than what is expected. For this crystal the RUS data near T∗ are more consistent with nonequilibrium effects, such as oxygen relaxation.

Using a high-resolution differential technique we have determined the electronic specific heat coefficient gamma(T) of Ba1-xKxFe2As2 with x=0 to 1.0, at temperatures (T) from 2K to 380K and in magnetic fields H=0 to 13T. In the normal state gamma_n(x,T) increases strongly with x at low temperature, compatible with a mass renormalisation ~12 at x=1, and decreases weakly with x at high temperature. A superconducting transition is seen in all samples from x=0.2 to 1, with transition temperatures and condensation energies peaking sharply at x=0.4. Superconducting coherence lengths xi_{ab}~20{\AA} and xi_c~3{\AA} are estimated from an analysis of Gaussian fluctuations. For many dopings we see features in the H and T-dependences of gamma_s(T,H) in the superconducting state that suggest superconducting gaps in three distinct bands. A broad "knee" and a sharp mean-field-like peak are typical of two coupled gaps. However, several samples show a shoulder above the sharp peak with an abrupt onset at T_{c,s} and a T-dependence gamma_s(T)\propto\sqrt{1-T/T_{c,s}}. We provide strong evidence that the shoulder is not due to doping inhomogeneity and suggest it is a distinct gap with an unconventional T-dependence Delta_s(T)\propto(1-T/T_{c,s})^{0.75} near T_{c,s}. We estimate band fractions and T=0 gaps from 3-band alpha-model fits to our data and compare the x-dependences of the band fractions with spectroscopic studies of the Fermi surface., Comment: 20 pages, 23 figures, published in Physical Review B

International audience; On July 19 2011 UT, the (90) Antiope double system occulted a 6.7-mag star (LQ Aquarii) with a path predicted to pass over much of northern California. The shape and separation of the components were predicted based on Descamps et al. (2009) model, plus additional Keck AO observations (Merline, Neyman, Tamblyn, Owen) collected on July 13 and 15, 2011 UT. Through a large collaboration in cooperation with the IOTA we organized a campaign of bservations involving 42 observers and 92 stations spread along the path of the occultation in northern California, Nevada, and Idaho to sample both components. The stellar occultation was successfully recorded by 41 stations with a maximum duration of ~33 s. A preliminary analysis of the data that are being processed and analyzed shows that an improved shape model of both components could be derived based on this campaign. We will present the final analysis of this campaign, which allow us to derive a more accurate period and separation for the binary system and also an improved density. We will discuss the origin of (90) Antiope based on the detection of a large concavity, possibly interpreted as a large impact crater on one of the components, already suggested by Descamps et al (2009). This research is partially supported by the NSF grant AAG-0807468, NASA grant NNX11AD62G and CNRS. We thank the many other members of IOTA who took part in this campaign.

We present a detailed study of quantum oscillations in the antiferromagnetically ordered pnictide compound SrFe$_2$As$_2$ as the angle between the applied magnetic field and crystalline axes is varied. Our measurements were performed on high quality single crystals in a superconducting magnet, and in pulsed magnetic fields up to 60 T, allowing us to observe orbits from several small Fermi surface pockets. We extract the cyclotron effective mass $m^{\star}$ and frequency $F$ for these orbits and track their values as the field is rotated away from the c-axis. While a constant ratio of $m^{\star}/F$ is observed for one orbit as expected for a parabolic band, a clear deviation is observed for another. We conclude that this deviation points to an orbit derived from a band with Dirac dispersion near the Fermi level., 5 pages, 4 figures