334 research outputs found
In-beam gamma-ray spectroscopy of 35Mg and 33Na
Excited states in the very neutron-rich nuclei 35Mg and 33Na were populated
in the fragmentation of a 38Si projectile beam on a Be target at 83 MeV/u beam
energy. We report on the first observation of gamma-ray transitions in 35Mg,
the odd-N neighbor of 34Mg and 36Mg, which are known to be part of the "Island
of Inversion" around N = 20. The results are discussed in the framework of
large- scale shell-model calculations. For the A = 3Z nucleus 33Na, a new
gamma-ray transition was observed that is suggested to complete the gamma-ray
cascade 7/2+ --> 5/2+ --> 3/2+ gs connecting three neutron 2p-2h intruder
states that are predicted to form a close-to-ideal K = 3/2 rotational band in
the strong-coupling limit.Comment: Accepted for publication Phys. Rev. C. March 16, 2011: Replaced
figures 3 and 5. We thank Alfredo Poves for pointing out a problem with the
two figure
Effects of next-nearest-neighbor hopping on the electronic structure of cuprates
Photoemission spectra of underdoped and lightly-doped
BiPbSrCa{\it R}CuO ( Pr, Er)
(BSCCO) have been measured and compared with those of LaSrCuO
(LSCO). The lower-Hubbard band of the insulating BSCCO, like
CaCuOCl, shows a stronger dispersion than LaCuO from () to (). The flat band at () is found generally deeper in BSCCO. These observations
together with the Fermi-surface shapes and the chemical potential shifts
indicate that the next-nearest-neighbor hopping of the
single-band model is larger in BSCCO than in LSCO and that
rather than the super-exchange influences the pseudogap energy scale.Comment: 5 pages,4 figures, 1 tabl
Unusual T_c variation with hole concentration in Bi_2Sr_{2-x}La_xCuO_{6+\delta}
We have investigated the variation with the hole concentration in
the La-doped Bi 2201 system, BiSrLaCuO. It is
found that the Bi 2201 system does not follow the systematics in and
observed in other high- cuprate superconductors (HTSC's). The vs
characteristics are quite similar to what observed in Zn-doped HTSC's. An
exceptionally large residual resistivity component in the inplane resistivity
indicates that strong potential scatterers of charge carriers reside in CuO
planes and are responsible for the unusual variation with , as in the
Zn-doped systems. However, contrary to the Zn-doped HTSC's, the strong scatter
in the Bi 2201 system is possibly a vacancy in the Cu site.Comment: RevTeX, 3 figures, to be published in the Physical Review
A Universal Intrinsic Scale of Hole Concentration for High-Tc Cuprates
We have measured thermoelectric power (TEP) as a function of hole
concentration per CuO2 layer, Ppl, in Y1-xCaxBa2Cu3O6 (Ppl = x/2) with no
oxygen in the Cu-O chain layer. The room-temperature TEP as a function of Ppl,
S290(Ppl), of Y1-xCaxBa2Cu3O6 behaves identically to that of La2-zSrzCuO4 (Ppl
= z). We argue that S290(Ppl) represents a measure of the intrinsic equilibrium
electronic states of doped holes and, therefore, can be used as a common scale
for the carrier concentrations of layered cuprates. We shows that the Ppl
determined by this new universal scale is consistent with both hole
concentration microscopically determined by NQR and the hole concentration
macroscopically determined by the Cu valency. We find two characteristic
scaling temperatures, TS* and TS2*, in the TEP vs. temperature curves that
change systematically with doping. Based on the universal scale, we uncover a
universal phase diagram in which almost all the experimentally determined
pseudogap temperatures as a function of Ppl fall on two common curves; upper
pseudogap temperature defined by the TS* versus Ppl curve and lower pseudogap
temperature defined by the TS2* versus Ppl curve. We find that while pseudogaps
are intrinsic properties of doped holes of a single CuO2 layer for all high-Tc
cuprates, Tc depends on the number of layers, therefore the inter-layer
coupling, in each individual system.Comment: 11 pages, 9 figures, accepted for publication in Physical Review
Metal-to-Insulator Crossover in the Low-Temperature Normal State of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta}
We measure the normal-state in-plane resistivity of La-doped Bi-2201 single
crystals at low temperatures by suppressing superconductivity with 60-T pulsed
magnetic fields. With decreasing hole doping, we observe a crossover from a
metallic to insulating behavior in the low-temperature normal state. This
crossover is estimated to occur near 1/8 doping, well inside the underdoped
regime, and not at optimum doping as reported for other cuprates. The
insulating regime is marked by a logarithmic temperature dependence of the
resistivity over two decades of temperature, suggesting that a peculiar charge
localization is common to the cuprates.Comment: 4 pages, 5 figures, accepted for publication in PR
Effects of Electronic Correlations on the Thermoelectric Power of the Cuprates
We show that important anomalous features of the normal-state thermoelectric
power S of high-Tc materials can be understood as being caused by doping
dependent short-range antiferromagnetic correlations. The theory is based on
the fluctuation-exchange approximation applied to Hubbard model in the
framework of the Kubo formalism. Firstly, the characteristic maximum of S as
function of temperature can be explained by the anomalous momentum dependence
of the single-particle scattering rate. Secondly, we discuss the role of the
actual Fermi surface shape for the occurrence of a sign change of S as a
function of temperature and doping.Comment: 4 pages, with eps figure
Theory of Thermoelectric Power in High-Tc Superconductors
We present a microscopic theory for the thermoelectric power (TEP) in high-Tc
cuprates. Based on the general expression for the TEP, we perform the
calculation of the TEP for a square lattice Hubbard model including all the
vertex corrections necessary to satisfy the conservation laws. In the present
study, characteristic anomalous temperature and doping dependences of the TEP
in high-Tc cuprates, which have been a long-standing problem of high-Tc
cuprates, are well reproduced for both hole- and electron-doped systems, except
for the heavily under-doped case. According to the present analysis, the strong
momentum and energy dependences of the self-energy due to the strong
antiferromagnetic fluctuations play an essential role in reproducing
experimental anomalies of the TEP.Comment: 5 pages, 8 figures, to appear in J. Phys. Soc. Jpn. 70 (2001) No.10.
Figure 2 has been revise
Doping Dependence of Anisotropic Resistivities in Trilayered Superconductor Bi2Sr2Ca2Cu3O10+delta (Bi-2223)
The doping dependence of the themopower, in-plane resistivity rho_ab(T),
out-of-plane resistivity rho_c(T), and susceptibility has been systematically
measured for high-quality single crystal Bi2Sr2Ca2Cu3O10+delta. We found that
the transition temperature Tc and pseudogap formation temperature T_rho_c*,
below which rho_c shows a typical upturn, do not change from their optimum
values in the "overdoped" region, even though doping actually proceeds. This
suggests that, in overdoped region, the bulk is determined by the always
underdoped inner plane, which have a large superconducting gap, while the
carriers are mostly doped in the outer planes, which have a large phase
stiffness.Comment: 5 pages, 4 figures. to be published in PR
Thermopower in the strongly overdoped region of single-layer Bi2Sr2CuO6+d superconductor
The evolution of the thermoelectric power S(T) with doping, p, of
single-layer Bi2Sr2CuO6+d ceramics in the strongly overdoped region is studied
in detail. Analysis in term of drag and diffusion contributions indicates a
departure of the diffusion from the T-linear metallic behavior. This effect is
increased in the strongly overdoped range (p~0.2-0.28) and should reflect the
proximity of some topological change.Comment: 4 pages, 4 figure
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