1,064 research outputs found
Collective Dynamics and Strong Pinning near the Onset of Charge Order in LaNdSrCuO
The dynamics of charge-ordered states is one of the key issues in underdoped
cuprate high-temperature superconductors, but static short-range charge-order
(CO) domains have been detected in almost all cuprates. We probe the dynamics
across the CO (and structural) transition in
LaNdSrCuO by measuring nonequilibrium charge
transport, or resistance as the system responds to a change in temperature
and to an applied magnetic field. We find evidence for metastable states,
collective behavior, and criticality. The collective dynamics in the critical
regime indicates strong pinning by disorder. Surprisingly, nonequilibrium
effects, such as avalanches in , are revealed only when the critical region
is approached from the charge-ordered phase. Our results on
LaNdSrCuO provide the long-sought evidence for
the fluctuating order across the CO transition, and also set important
constraints on theories of dynamic stripes.Comment: final version: 5 pages, 3 figures; includes Supplemental Material (3
pages, 7 figures
Current-voltage characteristics and vortex dynamics in highly underdoped LaSrCuO
The temperature dependence of the nonlinear current-voltage (-)
characteristics in highly underdoped LaSrCuO ( and
0.08) thick films has been studied in both zero and perpendicular magnetic
fields . Power-law behavior of is found for both and . The critical current was extracted, and its temperature and
magnetic field dependences were studied in detail. The
Berezinskii-Kosterlitz-Thouless physics dominates the nonlinear - near
the superconducting transition at , and it continues to contribute up to a
characteristic temperature . Nonlinear - persists up to an even
higher temperature due to the depinning of vortices.Comment: 4 pages, 4 figures; Superstripes 2015 conferenc
Effect of Local Magnetic Moments on the Metallic Behavior in Two Dimensions
The temperature dependence of conductivity in the metallic phase
of a two-dimensional electron system in silicon has been studied for different
concentrations of local magnetic moments. The local moments have been induced
by disorder, and their number was varied using substrate bias. The data suggest
that in the limit of the metallic behavior, as characterized by
, is suppressed by an arbitrarily small amount of scattering by
local magnetic moments.Comment: 4 pages, revtex, plus four encapsulated postscript figure
Mesoscopic Behavior Near a Two-Dimensional Metal-Insulator Transition
We study conductance fluctuations in a two-dimensional electron gas as a
function of chemical potential (or gate voltage) from the strongly insulating
to the metallic regime. Power spectra of the fluctuations decay with two
distinct exponents (1/v_l and 1/v_h). For conductivity , we find a third exponent (1/v_i) in the shortest samples, and
non-monotonic dependence of v_i and v_l on \sigma. We study the dependence of
v_i, v_l, v_h, and the variances of corresponding fluctuations on \sigma,
sample size, and temperature. The anomalies near
indicate that the dielectric response and screening length are critically
behaved, i.e. that Coulomb correlations dominate the physics.Comment: Revised according to referee remark
Tuning from failed superconductor to failed insulator with magnetic field
Do charge modulations compete with electron pairing in high-temperature
copper-oxide superconductors? We investigated this question by suppressing
superconductivity in a stripe-ordered cuprate compound at low temperature with
high magnetic fields. With increasing field, loss of three-dimensional
superconducting order is followed by reentrant two-dimensional
superconductivity and then an ultra-quantum metal phase. Circumstantial
evidence suggests that the latter state is bosonic and associated with the
charge stripes. These results provide experimental support to the theoretical
perspective that local segregation of doped holes and antiferromagnetic spin
correlations underlies the electron-pairing mechanism in cuprates.Comment: 20 pp, 4 figs.; accepted version; for open-access published version,
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Cantu syndrome–associated SUR2 (ABCC9) mutations in distinct structural domains result in KATP channel gain-of-function by differential mechanisms
The complex disorder Cantu syndrome (CS) arises from gainof-function mutations in either KCNJ8 or ABCC9, the genes encoding the Kir6.1 and SUR2 subunits of ATP-sensitive potassium (KATP) channels, respectively. Recent reports indicate that such mutations can increase channel activity by multiple molecular mechanisms. In this study, we determined the mechanism by which KATP function is altered by several substitutions in distinct structural domains of SUR2: D207E in the intracellular L0-linker and Y985S, G989E, M1060I, and R1154Q/R1154W in TMD2. We engineered substitutions at their equivalent positions in rat SUR2A (D207E, Y981S, G985E, M1056I, and R1150Q/R1150W) and investigated functional consequences using macroscopic rubidium (86Rb-) efflux assays and patchclamp electrophysiology. Our results indicate that D207E increases KATP channel activity by increasing intrinsic stability of the open state, whereas the cluster of Y981S/G985E/M1056I substitutions, as well as R1150Q/R1150W, augmented Mg-nucleotide activation. We also tested the responses of these channel variants to inhibition by the sulfonylurea drug glibenclamide, a potential pharmacotherapy for CS. None of the D207E, Y981S, G985E, or M1056I substitutions had a significant effect on glibenclamide sensitivity. However, Gln and Trp substitution at Arg-1150 significantly decreased glibenclamide potency. In summary, these results provide additional confirmation that mutations in CS-Associated SUR2 mutations result in KATP gain-of-function. They help link CS genotypes to phenotypes and shed light on the underlying molecular mechanisms, including consequences for inhibitory drug sensitivity, insights that may inform the development of therapeutic approaches to manage CS
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