76 research outputs found
Lifshitz critical point in the cuprate superconductor YBa2Cu3Oy from high-field Hall effect measurements
The Hall coefficient R_H of the cuprate superconductor YBa2Cu3Oy was measured
in magnetic fields up to 60 T for a hole concentration p from 0.078 to 0.152,
in the underdoped regime. In fields large enough to suppress superconductivity,
R_H(T) is seen to go from positive at high temperature to negative at low
temperature, for p > 0.08. This change of sign is attributed to the emergence
of an electron pocket in the Fermi surface at low temperature. At p < 0.08, the
normal-state R_H(T) remains positive at all temperatures, increasing
monotonically as T \to 0. We attribute the change of behaviour across p = 0.08
to a Lifshitz transition, namely a change in Fermi-surface topology occurring
at a critical concentration p_L = 0.08, where the electron pocket vanishes. The
loss of the high-mobility electron pocket across p_L coincides with a ten-fold
drop in the conductivity at low temperature, revealed in measurements of the
electrical resistivity at high fields, showing that the so-called
metal-insulator crossover of cuprates is in fact driven by a Lifshitz
transition. It also coincides with a jump in the in-plane anisotropy of ,
showing that without its electron pocket the Fermi surface must have strong
two-fold in-plane anisotropy. These findings are consistent with a
Fermi-surface reconstruction caused by a unidirectional spin-density wave or
stripe order.Comment: 16 pages, 13 figures, see associated Viewpoint: M. Vojta, Physics 4,
12 (2011
Broken rotational symmetry in the pseudogap phase of a high-Tc superconductor
The nature of the pseudogap phase is a central problem in the quest to
understand high-Tc cuprate superconductors. A fundamental question is what
symmetries are broken when that phase sets in below a temperature T*. There is
evidence from both polarized neutron diffraction and polar Kerr effect
measurements that time- reversal symmetry is broken, but at temperatures that
differ significantly. Broken rotational symmetry was detected by both
resistivity and inelastic neutron scattering at low doping and by scanning
tunnelling spectroscopy at low temperature, but with no clear connection to T*.
Here we report the observation of a large in-plane anisotropy of the Nernst
effect in YBa2Cu3Oy that sets in precisely at T*, throughout the doping phase
diagram. We show that the CuO chains of the orthorhombic lattice are not
responsible for this anisotropy, which is therefore an intrinsic property of
the CuO2 planes. We conclude that the pseudogap phase is an electronic state
which strongly breaks four-fold rotational symmetry. This narrows the range of
possible states considerably, pointing to stripe or nematic orders.Comment: Published version. Journal reference and DOI adde
Interactions of the Apolipoprotein A5 Gene Polymorphisms and Alcohol Consumption on Serum Lipid Levels
Little is known about the interactions of apolipoprotein (Apo) A5 gene polymorphisms and alcohol consumption on serum lipid profiles. The present study was undertaken to detect the interactions of ApoA5-1131T>C, c.553G>T and c.457G>A polymorphisms and alcohol consumption on serum lipid levels.A total of 516 nondrinkers and 514 drinkers were randomly selected from our previous stratified randomized cluster samples. Genotyping was performed by polymerase chain reaction and restriction fragment length polymorphism. The levels of serum total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), ApoA1 and ApoB were higher in drinkers than in nondrinkers (P<0.05-0.001). The genotypic and allelic frequencies of three loci were not different between the two groups. The interactions between -1131T>C genotypes and alcohol consumption on ApoB levels (P<0.05) and the ApoA1/ApoB ratio (P<0.01), between c.553G>T genotypes and alcohol consumption on low-density lipoprotein cholesterol (LDL-C) levels (P<0.05) and the ApoA1/ApoB ratio (P<0.05), and between c.457G>A genotypes and alcohol consumption on TG levels (P<0.001) were detected by factorial regression analysis after controlling for potential confounders. Four haplotypes (T-G-G, C-G-G, T-A-G and C-G-T) had frequencies ranging from 0.06 to 0.87. Three haplotypes (C-G-G, T-A-G, and C-G-T) were significantly associated with serum lipid parameters. The -1131T>C genotypes were correlated with TG, and c.553G>T and c.457G>A genotypes were associated with HDL-C levels in nondrinkers (P<0.05 for all). For drinkers, the -1131T>C genotypes were correlated with TC, TG, LDL-C, ApoB levels and the ApoA1/ApoB ratio (P<0.01 for all); c.553G>T genotypes were correlated with TC, TG, HDL-C and LDL-C levels (P<0.05-0.01); and c.457G>A genotypes were associated with TG, LDL-C, ApoA1 and ApoB levels (P<0.05-0.01).The differences in some serum lipid parameters between the drinkers and nondrinkers might partly result from different interactions of the ApoA5 gene polymorphisms and alcohol consumption
Observation of the Transverse Optical Plasmon in SmLa0.8Sr0.2CuO4-d
We present microwave and infrared measurements on SmLa0.8Sr0.2CuO4-d, which
are direct evidence for the existence of a transverse optical plasma mode,
observed as a peak in the c-axis optical conductivity. This mode appears as a
consequence of the existence of two different intrinsic Josephson couplings
between the CuO2 layers, one with a Sm2O2 block layer, and the other one with a
(La,Sr)O block layer. From the frequencies and the intensities of the
collective modes we determine the value of the compressibility of the two
dimensional electron fluid in the copper oxygen planes.Comment: REVTeX, 4 pages, 5 eps-figures, PRL, in pres
Universal scaling relation in high-temperature superconductors
Scaling laws express a systematic and universal simplicity among complex
systems in nature. For example, such laws are of enormous significance in
biology. Scaling relations are also important in the physical sciences. The
seminal 1986 discovery of high transition-temperature (high-T_c)
superconductivity in cuprate materials has sparked an intensive investigation
of these and related complex oxides, yet the mechanism for superconductivity is
still not agreed upon. In addition, no universal scaling law involving such
fundamental properties as T_c and the superfluid density \rho_s, a quantity
indicative of the number of charge carriers in the superconducting state, has
been discovered. Here we demonstrate that the scaling relation \rho_s \propto
\sigma_{dc} T_c, where the conductivity \sigma_{dc} characterizes the
unidirectional, constant flow of electric charge carriers just above T_c,
universally holds for a wide variety of materials and doping levels. This
surprising unifying observation is likely to have important consequences for
theories of high-T_c superconductivity.Comment: 11 pages, 2 figures, 2 table
Doping dependence of the superconducting gap in Tl_2Ba_2CuO_{6+delta} from heat transport
We present low-temperature thermal conductivity measurements on the cuprate
Tl_2Ba_2CuO_{6+delta} throughout the overdoped regime. In the T -> 0 limit, the
thermal conductivity due to d-wave nodal quasiparticles provides a bulk
measurement of the superconducting gap, Delta. We find Delta to decrease with
increasing doping, with a magnitude consistent with spectroscopic measurements
(photoemission and tunneling). This argues for a pure and simple d-wave
superconducting state in the overdoped region of the phase diagram, which
appears to extend into the underdoped regime down to a hole concentration of
0.1 hole/Cu. As hole concentration is decreased, the gap-to-Tc ratio increases,
showing that the suppression of the superconducting transition temperature Tc
(relative to the gap) begins in the overdoped regime.Comment: 7 pages, 4 figure
- …