140 research outputs found
Evidence for a small hole pocket in the Fermi surface of underdoped YBa2Cu3Oy
The Fermi surface of a metal is the fundamental basis from which its
properties can be understood. In underdoped cuprate superconductors, the Fermi
surface undergoes a reconstruction that produces a small electron pocket, but
whether there is another, as yet undetected portion to the Fermi surface is
unknown. Establishing the complete topology of the Fermi surface is key to
identifying the mechanism responsible for its reconstruction. Here we report
the discovery of a second Fermi pocket in underdoped YBa2Cu3Oy, detected as a
small quantum oscillation frequency in the thermoelectric response and in the
c-axis resistance. The field-angle dependence of the frequency demonstrates
that it is a distinct Fermi surface and the normal-state thermopower requires
it to be a hole pocket. A Fermi surface consisting of one electron pocket and
two hole pockets with the measured areas and masses is consistent with a
Fermi-surface reconstruction caused by the charge-density-wave order observed
in YBa2Cu3Oy, provided other parts of the reconstructed Fermi surface are
removed by a separate mechanism, possibly the pseudogap.Comment: 23 pages, 5 figure
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
Inverse correlation between quasiparticle mass and Tc in a cuprate high-Tc superconductor
Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature Tc is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-Tc superconductivity. We have tested the robustness of this correlation between m* and Tc by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as Tc increases under pressure. This inverse correlation between m* and Tc suggests that quantum fluctuations of the charge order enhance m* but do not enhance Tc
Dispersive charge density wave excitations and temperature dependent commensuration in Bi2Sr2CaCu2O8+{\delta}
Experimental evidence on high-Tc cuprates reveals ubiquitous charge density
wave (CDW) modulations, which coexist with superconductivity. Although the CDW
had been predicted by theory, important questions remain about the extent to
which the CDW influences lattice and charge degrees of freedom and its
characteristics as functions of doping and temperature. These questions are
intimately connected to the origin of the CDW and its relation to the
mysterious cuprate pseudogap. Here, we use ultrahigh resolution resonant
inelastic x-ray scattering (RIXS) to reveal new CDW character in underdoped
Bi2Sr2CaCu2O8+{\delta} (Bi2212). At low temperature, we observe dispersive
excitations from an incommensurate CDW that induces anomalously enhanced phonon
intensity, unseen using other techniques. Near the pseudogap temperature T*,
the CDW persists, but the associated excitations significantly weaken and the
CDW wavevector shifts, becoming nearly commensurate with a periodicity of four
lattice constants. The dispersive CDW excitations, phonon anomaly, and
temperature dependent commensuration provide a comprehensive momentum space
picture of complex CDW behavior and point to a closer relationship with the
pseudogap state
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Effect of pressure on the pseudogap and charge density wave phases of the cuprate Nd-LSCO probed by thermopower measurements
We report thermopower measurements under hydrostatic pressure on the cuprate superconductor
La1.6−xNd0.4SrxCuO4 (Nd-LSCO), at low temperature in the normal state accessed by suppressing superconduc-
tivity with a magnetic field up to H = 31 T. Using an ac thermopower measurement technique suitable for high
pressure and high field, we track the pressure evolution of the Seebeck coefficient S. At ambient pressure and
low temperature, S/T in Nd-LSCO was recently found to suddenly increase below the pseudogap critical doping
p
⋆ = 0.23, consistent with a drop in carrier density n from n = 1 + p above p⋆ to n = p below. Under a pressure
of 2.0 GPa, we observe that the large S/T value just below p
⋆ is suppressed. This confirms a previous pressure
study based on electrical resistivity and Hall effect, which found that pressure lowers p
⋆, thereby reinforcing
the interpretation that this effect is driven by the pressure-induced shift of the van Hove point. It implies that
the pseudogap only exists when the Fermi surface is hole-like, which puts strong constraints on theories of the
pseudogap phase. We also report thermopower measurements on Nd-LSCO and La1.8−xEu0.2SrxCuO4 in the
charge density wave phase near p ∼ 1/8, which reveals a weakening of this phase under pressure.L.T.
acknowledges support from the Canadian Institute for Ad-
vanced Research (CIFAR) as a CIFAR Fellow and funding
from the Institut Quantique, the Natural Sciences and Engi-
neering Research Council of Canada (PIN:123817), the Fonds
de Recherche du Québec–Nature et Technologies (FRQNT),
the Canada Foundation for Innovation (CFI), and a Canada
Research Chair. This research was undertaken thanks in part
to funding from the Canada First Research Excellence Fund
and the Gordon and Betty Moore Foundation’s EPiQS Ini-
tiative (Grant No. GBMF5306 to L.T.). The National High
Magnetic Field Laboratory is supported by the National Sci-
ence Foundation through Grant No. NSF/DMR-1644779 and
the State of Florida. J.-S.Z. was supported by NSF MRSEC
under Cooperative Agreement No. DMR-1720595.Center for Dynamics and Control of Material
Rituximab in B-Cell Hematologic Malignancies: A Review of 20 Years of Clinical Experience
Rituximab is a human/murine, chimeric anti-CD20 monoclonal antibody with established efficacy, and a favorable and well-defined safety profile in patients with various CD20-expressing lymphoid malignancies, including indolent and aggressive forms of B-cell non-Hodgkin lymphoma. Since its first approval 20 years ago, intravenously administered rituximab has revolutionized the treatment of B-cell malignancies and has become a standard component of care for follicular lymphoma, diffuse large B-cell lymphoma, chronic lymphocytic leukemia, and mantle cell lymphoma. For all of these diseases, clinical trials have demonstrated that rituximab not only prolongs the time to disease progression but also extends overall survival. Efficacy benefits have also been shown in patients with marginal zone lymphoma and in more aggressive diseases such as Burkitt lymphoma. Although the proven clinical efficacy and success of rituximab has led to the development of other anti-CD20 monoclonal antibodies in recent years (e.g., obinutuzumab, ofatumumab, veltuzumab, and ocrelizumab), rituximab is likely to maintain a position within the therapeutic armamentarium because it is well established with a long history of successful clinical use. Furthermore, a subcutaneous formulation of the drug has been approved both in the EU and in the USA for the treatment of B-cell malignancies. Using the wealth of data published on rituximab during the last two decades, we review the preclinical development of rituximab and the clinical experience gained in the treatment of hematologic B-cell malignancies, with a focus on the well-established intravenous route of administration. This article is a companion paper to A. Davies, et al., which is also published in this issue
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