188 research outputs found
Extent of Fermi-surface reconstruction in the high-temperature superconductor HgBaCuO
High magnetic fields have revealed a surprisingly small Fermi-surface in
underdoped cuprates, possibly resulting from Fermi-surface reconstruction due
to an order parameter that breaks translational symmetry of the crystal
lattice. A crucial issue concerns the doping extent of this state and its
relationship to the principal pseudogap and superconducting phases. We employ
pulsed magnetic field measurements on the cuprate HgBaCuO to
identify signatures of Fermi surface reconstruction from a sign change of the
Hall effect and a peak in the temperature-dependent planar resistivity. We
trace the termination of Fermi-surface reconstruction to two hole
concentrations where the superconducting upper critical fields are found to be
enhanced. One of these points is associated with the pseudogap end-point near
optimal doping. These results connect the Fermi-surface reconstruction to both
superconductivity and the pseudogap phenomena.Comment: 5 pages. 3 Figures. PNAS (2020
Vortex phases and glassy dynamics in the highly anisotropic superconductor HgBaCuO
We present an extensive study of vortex dynamics in a high-quality single crystal of HgBaCuO, a highly anisotropic superconductor that is a model system for studying the effects of anisotropy. From magnetization M measurements over a wide range of temperatures T and fields H, we construct a detailed vortex phase diagram. We find that the temperature-dependent vortex penetration field H(T), second magnetization peak H(T), and irreversibility field H(T) all decay exponentially at low temperatures and exhibit an abrupt change in behavior at high temperatures T/Tc >~ 0.5. By measuring the rates of thermally activated vortex motion (creep) S(T, H) = |dlnM(T, H)/dlnt|, we reveal glassy behavior involving collective creep of bundles of 2D pancake vortices as well as temperature- and time-tuned crossovers from elastic (collective) dynamics to plastic flow. Based on the creep results, we show that the second magnetization peak coincides with the elastic-to-plastic crossover at low T, yet the mechanism changes at higher temperatures
High-field and high-temperature magnetoresistance reveals the superconducting behaviour of the stacking faults in multilayer graphene
In spite of 40 years of experimental studies and several theoretical
proposals, an overall interpretation of the complex behavior of the
magnetoresistance (MR) of multilayer graphene, i.e. graphite, at high fields
(T) and in a broad temperature range is still lacking. Part of
the complexity is due to the contribution of stacking faults (SFs), which most
of thick enough multilayer graphene samples have. We propose a procedure that
allows us to extract the SF contribution to the MR we have measured at 0.48~K
250~K and 0~T 65~T. We found that the MR
behavior of part of the SFs is similar to that of granular superconductors with
a superconducting critical temperature 350~K, in agreement with
recent publications. The measurements were done on a multilayer graphene TEM
lamella, contacting the edges of the two-dimensional SFs.Comment: 8 pages, 5 figure
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Magnetoresistance Scaling Reveals Symmetries of the Strongly Correlated Dynamics in BaFe_{2}(As_{1-x}P_{x})_{2}.
The phenomenon of T-linear resistivity commonly observed in a number of strange metals has been widely seen as evidence for the breakdown of the quasiparticle picture of metals. This study shows that a recently discovered H/T scaling relationship in the magnetoresistance of the strange metal BaFe_{2}(As_{1-x}P_{x})_{2} is independent of the relative orientations of current and magnetic field. Rather, its magnitude and form depend only on the orientation of the magnetic field with respect to a single crystallographic axis: the direction perpendicular to the magnetic iron layers. This finding suggests that the magnetotransport scaling does not originate from the conventional averaging or orbital velocity of quasiparticles as they traverse a Fermi surface, but rather from dissipation arising from two-dimensional correlations
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