5 research outputs found
Pseudogap phase of cuprate superconductors confined by Fermi surface topology
The properties of cuprate high-temperature superconductors are largely shaped
by competing phases whose nature is often a mystery. Chiefly among them is the
pseudogap phase, which sets in at a doping that is material-dependent.
What determines is currently an open question. Here we show that the
pseudogap cannot open on an electron-like Fermi surface, and can only exist
below the doping at which the large Fermi surface goes from hole-like
to electron-like, so that . We derive this result from
high-magnetic-field transport measurements in
LaNdSrCuO under pressure, which reveal a large and
unexpected shift of with pressure, driven by a corresponding shift in
. This necessary condition for pseudogap formation, imposed by details
of the Fermi surface, is a strong constraint for theories of the pseudogap
phase. Our finding that can be tuned with a modest pressure opens a new
route for experimental studies of the pseudogap.Comment: 15 pages, 5 figures, 7 supplemental figure
Integrin/Fak/Src-mediated regulation of cell survival and anoikis in human intestinal epithelial crypt cells: selective engagement and roles of PI3-K isoform complexes
In human intestinal epithelial crypt (HIEC) cells, the PI3-K/Akt-1 pathway is crucial for the promotion of cell survival and suppression of anoikis. Class I PI3-K consists of a complex formed by a catalytic (C) and regulatory (R) subunit. Three R (p85α, β, and p55γ) and four C (p110α, β, γ and δ) isoforms are known. Herein, we analyzed the expression of PI3-K isoforms in HIEC cells and determined their roles in cell survival, as well as in the β1 integrin/Fak/Src-mediated suppression of anoikis. We report that: (1) the predominant PI3-K complexes expressed by HIEC cells are p110α/p85β and p110α/p55γ; (2) the inhibition and/or siRNA-mediated expression silencing of p110α, but not that of p110β, γ or δ, results in Akt-1 down-activation and consequent apoptosis; (3) the expression silencing of p85β or p55γ, but not that of p85α, likewise induces Akt-1 down-activation and apoptosis; however, the impact of a loss of p55γ on both Akt-1 activation and cell survival is significantly greater than that from the loss of p85β; and (4) both the p110α/p85β and p110α/p55γ complexes are engaged by β1 integrin/Fak/Src signaling; however, the engagement of p110α/p85β is primarily Src-dependent, whereas that of p110α/p55γ is primarily Fak-dependent (but Src-independent). Hence, HIEC cells selectively express PI3-K isoform complexes, translating into distinct roles in Akt-1 activation and cell survival, as well as in a selective engagement by Fak and/or Src within the context of β1 integrin/Fak/Src-mediated suppression of anoikis
Sensitivity of T c to pressure and magnetic field in the cuprate superconductor YBa2Cu3 Oy:Evidence of charge-order suppression by pressure
Cuprate superconductors have a universal tendency to form charge density-wave
(CDW) order which competes with superconductivity and is strongest at a doping
. Here we show that in the archetypal cuprate
YBaCuO (YBCO) pressure suppresses charge order, but does not
affect the pseudogap phase. This is based on transport measurements under
pressure, which reveal that the onset of the pseudogap at is independent
of pressure, while the negative Hall effect, a clear signature of CDW order in
YBCO, is suppressed by pressure. We also find that pressure and magnetic field
shift the superconducting transition temperature of YBCO in the
same way as a function of doping - but in opposite directions - and most
effectively at . This shows that the competition between
superconductivity and CDW order can be tuned in two ways, either by suppressing
superconductivity with field or suppressing CDW order by pressure. Based on
existing high-pressure data and our own work, we observe that when CDW order is
fully suppressed at high pressure, the so-called "1/8 anomaly" in the
superconducting dome vanishes, revealing a smooth dome which now
peaks at . We propose that this dome is shaped by
the competing effects of the pseudogap phase below its critical point
and spin order at low doping.Comment: New Hall data added. 11 pages, 9 figures and 2 table
Wiedemann-Franz law in the underdoped cuprate superconductor YBa 2 Cu 3 O y
International audienceThe electrical and thermal Hall conductivities of the cuprate superconductor YBa2Cu3Oy, σxy and κxy, were measured in a magnetic field up to 35 T, at a hole concentration (doping) p=0.11. In the T=0 limit, we find that the Wiedemann-Franz law, κxy/T=(π2/3)(kB/e)2σxy, is satisfied for fields immediately above the vortex-melting field Hvs. This rules out the existence of a vortex liquid at T=0 and it puts a clear constraint on the nature of the normal state in underdoped cuprates, in a region of the doping phase diagram where charge-density-wave order is known to exist. As the temperature is raised, the Lorenz ratio, Lxy=κxy/(σxyT), decreases rapidly, indicating that strong small-q scattering processes are involved