Dynamic charge inhomogenity in cuprate superconductors

The inelastic x-ray scattering spectrum for phonons of $\Delta_{1}$-symmetry including the CuO bond-stretching phonon dispersion is analyzed by a Lorentz fit in HgBa$_{2}$CuO$_{4}$ and Bi$_{2}$Sr$_{2}$CuO$_{6}$, respectively, using recently calculated phonon frequencies as input parameters. The resulting mode frequencies of the fit are almost all in good agreement with the calculated data. An exception is the second highest $\Delta_{1}$-branch compromising the bond-stretching modes which disagrees in both compounds with the calculations. This branch unlike the calculations shows an anomalous softening with a minimum around the wavevector \vc{q}=\frac{2\pi}{a}(0.25, 0, 0). Such a disparity with the calculated results, that are based on the assumption of an undisturbed translation- and point group invariant electronic structure of the CuO plane, indicates some {\it static} charge inhomogenities in the measured probes. Most likely these will be charge stripes along the CuO bonds which have the strongest coupling to certain longitudinal bond-stretching modes that in turn selfconsistently induce corresponding {\it dynamic} charge inhomogenities. The symmetry breaking by the mix of dynamic and static charge inhomogenities can lead to a reconstruction of the Fermi surface into small pockets.Comment: 7 pages, 4 figure

Heat Transport in a Strongly Overdoped Cuprate: Fermi Liquid and Pure d-wave BCS Superconductor

The transport of heat and charge in the overdoped cuprate superconductor Tl_2Ba_2CuO_(6+delta) was measured down to low temperature. In the normal state, obtained by applying a magnetic field greater than the upper critical field, the Wiedemann-Franz law is verified to hold perfectly. In the superconducting state, a large residual linear term is observed in the thermal conductivity, in quantitative agreement with BCS theory for a d-wave superconductor. This is compelling evidence that the electrons in overdoped cuprates form a Fermi liquid, with no indication of spin-charge separation.Comment: 4 pages, 2 figures, published version, title changed, Phys. Rev. Lett. 89, 147003 (2002

Influence of a magnetic field on the antiferromagnetic order in UPt_3

A neutron diffraction experiment was performed to investigate the effect of a magnetic field on the antiferromagnetic order in the heavy fermion superconductor UPt_3. Our results show that a field in the basal plane of up to 3.2 Tesla, higher than H_c2(0), has no effect: it can neither select a domain nor rotate the moment. This has a direct impact on current theories for the superconducting phase diagram based on a coupling to the magnetic order.Comment: 7 pages, RevTeX, 3 postscript figures, submitted to Phys. Rev.