Fermiology and electronic homogeneity of the superconducting overdoped cuprate Tl-2201 revealed by quantum oscillations

We report an angular quantum oscillation study of Tl_2Ba_2CuO_{6+delta} for two different doping levels (Tc = 10K and 26 K) and determine the Fermi surface size and topology in considerable detail. Our results show that Fermi liquid behavior is not confined to the edge of the superconducting dome and is robust up to at least T_c^{max}/3.5. Superconductivity is found to survive up to a larger doping p_c = 0.31 than in La_{2-x}Sr_xCuO_4. Our data imply that electronic inhomogeneity does not play a significant role in the loss of superconductivity and superfluid density in overdoped cuprates, and point towards a purely magnetic or electronic pairing mechanismComment: 4 page

Tunable terahertz emission from Bi2Sr2CaCu2O8+\delta\ mesa devices

We have measured coherent terahertz emission spectra from Bi2Sr2CaCu2O8+\delta\ mesa devices, as a function of temperature and mesa bias voltage. The emission frequency is found to be tunable by up to 12% by varying the temperature and bias voltage. We attribute the appearance of tunability to asymmetric boundaries at the top and bottom, and the non-rectangular cross-section of the mesas. This interpretation is consistent with numerical simulations of the dynamics of intrinsic Josephson junctions in the mesa. Easily tunable emission frequency may have important implications for the design of terahertz devices based on stacked intrinsic Josephson junctions.Comment: 24 pages, 6 figure

Evidence for Dirac nodes from quantum oscillations in SrFe2As2

We present a detailed study of quantum oscillations in the antiferromagnetically ordered pnictide compound SrFe2As2 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☆ 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☆/F is expected for a parabolic band, we observe deviations from this behavior. We conclude that this observation points to orbits derived from a band with Dirac dispersion near the Fermi level

In-plane oxygen diffusion in single crystals of Bi2Sr2CaCu2O8+delta

We have determined the in-plane diffusion coefficient for nonstoichiometric oxygen in single crystals of Bi2Sr2CaCu2O8+delta (Bi-2212). This was done by measuring the superconducting diamagnetic transition of the crystals by AC susceptometry, following repeated annealing of the crystals at a range of temperatures. We find that the chemical diffusion coefficient for oxygen in Bi-2212 is well described by D-ab* = (1.5(-0.7)(+1.4)) x 10(-3) exp [-(1.23 +/- 0.06) eV/k(B)T] m(2)/S. Crown Copyright (c) 2007 Published by Elsevier B.V. All rights reserved

The ac Josephson relation and inhomogeneous temperature distributions in large Bi2Sr2CaCu2O8+δmesas for THz emission

We have studied the terahertz emission from a 720 × 60 × 1.2 μm3 mesa patterned from under-doped Bi2Sr2CaCu2O8+δ. This device has an S-shaped current–voltage characteristic due to self-heating, allowing us to compare its THz emission behaviours at up to three different bias currents for the same voltage. The THz frequency generated along the lowest current branch follows the expected Josephson relation for a stack of intrinsic Josephson junctions connected in series. However, in the high current regimes, THz emission occurs at a significantly lower frequency than expected. We show that this behaviour is consistent with strongly non-uniform self-heating of the mesa at high bias currents