549 research outputs found
Strong charge fluctuations manifested in the high-temperature Hall coefficient of high-T_c cuprates
By measuring the Hall coefficient R_H up to 1000 K in La_2CuO_4,
Pr_{1.3}La_{0.7}CuO_4, and La_{2-x}Sr_xCuO_4 (LSCO), we found that the
temperature (T) dependence of R_H in LSCO for x = 0 - 0.05 at high temperature
undoubtedly signifies a gap over which the charge carriers are thermally
activated, which in turn indicates that in lightly-doped cuprates strong charge
fluctuations are present at high temperature and the carrier number is not a
constant. At higher doping (x = 0.08 - 0.21), the high-temperature R_H(T)
behavior is found to be qualitatively the same, albeit with a weakened
temperature dependence, and we attempt to understand its behavior in terms of a
phenomenological two-carrier model where the thermal activation is considered
for one of the two species. Despite the crude nature of the model, our analysis
gives a reasonable account of R_H both at high temperature and at 0 K for a
wide range of doping, suggesting that charge fluctuations over a gap remain
important at high temperature in LSCO deep into the superconducting doping
regime. Moreover, our model gives a perspective to understand the seemingly
contradicting high-temperature behavior of R_H and the in-plane resistivity
near optimum doping in a consistent manner. Finally, we discuss possible
implications of our results on such issues as the scattering-time separation
and the large pseudogap.Comment: 9 pages, 8 figures; final version, to appear in Phys. Rev.
Zn-impurity effects on quasi-particle scattering in La2-xSrxCuO4 studied by angle-resolved photoemission spectroscopy
Angle-resolved photoemission measurements were performed on Zn-doped
La2-xSrxCuO4 (LSCO) to investigate the effects of Zn impurities on the low
energy electronic structure. The Zn-impurity-induced increase in the
quasi-particle (QP) width in momentum distribution curves (MDC) is
approximately isotropic on the entire Fermi surface and energy-independent near
the Fermi level (EF). The increase in the MDC width is consistent with the
increase in the residual resistivity due to the Zn impurities if we assume the
carrier number to be 1-x for x=0.17 and the Zn impurity to be a potential
scatterer close to the unitarity limit. For x=0.03, the residual resistivity is
found to be higher than that expected from the MDC width, and the effects of
antifferomagnetic fluctuations induced around the Zn impurities are discussed.
The leading edges of the spectra near (pi,0) for x=0.17 are shifted toward
higher energies relative to EF with Zn substitution, indicating a reduction of
the superconducting gap.Comment: 7 pages, 7 figure
Highly Invasive Intracranial Malignant Schwannoma in a Rat
A highly invasive intracranial malignant schwannoma containing several masses was detected in a 28-week-old male Crl:CD(SD) rat. Macroscopically, 3 masses were noted in the cranial cavity; one was present at the bottom of the cranial cavity and involved the trigeminal nerve, and the other two were in the parietal bone. Histologically, each mass consisted of fusiform cells with interlacing fascicular, wavy and nuclear pseudopalisading arrangements and round cells with cystic lesions. The tumor cells invaded not only the brain but also the parietal bone. In the brain, the tumor cells infiltrated diffusely into the leptomeningeal and perivascular spaces and parenchyma, in which the tumor cell morphology and invasive pattern closely resembled those of malignant astrocytoma and malignant reticulosis. Immunohistochemically, the tumor cells in the masses showed positive reactions for both S-100 protein and GFAP, while those in the cerebral invasion sites were negative for GFAP and less positive for S-100 protein. Electron microscopically, a single basal lamina layer and short intricate cell processes were confirmed in the tumor cells. From these results, the present tumor was diagnosed as a malignant schwannoma arising in the cranial cavity, probably originating from the trigeminal nerve. The present tumor is considered to be a relatively unique malignant schwannoma based on its growth and invasion patterns
Carrier concentrations in Bi_{2}Sr_{2-z}La_{z}CuO_{6+\delta} single crystals and their relation to Hall coefficient and thermopower
We measured the thermopower S and the Hall coefficients R_H of
Bi_{2}Sr_{2-z}La_{z}CuO_{6+\delta} (BSLCO) single crystals in a wide doping
range, in an effort to identify the actual hole concentrations per Cu, p, in
this system. It is found that the "universal" relation between the
room-temperature thermopower and T_c does not hold in the BSLCO system.
Instead, comparison of the temperature-dependent R_H data with other cuprate
systems is used as a tool to identify the actual p value. To justify this
approach, we compare normalized R_H(T) data of BSLCO, La_{2-x}Sr_{x}CuO_{4}
(LSCO), YBa_{2}Cu_{3}O_{y}, and Tl_{2}Ba_{2}CuO_{6+\delta}, and demonstrate
that the R_H(T) data of the LSCO system can be used as a template for the
estimation of p. The resulting phase diagram of p vs T_c for BSLCO suggests
that T_c is anomalously suppressed in the underdoped samples, becoming zero at
around p ~ 0.10, while the optimum T_c is achieved at p ~ 0.16 as expected.Comment: 4 pages including 5 figures, accepted for publication in Phys. Rev.
B, Rapid Communication
Electronic specific heat and low energy quasiparticle excitations in superconducting state of single crystals
Low temperature specific heat has been measured and extensively analyzed on a
series of single crystals from underdoped to overdoped
regime. From these data the quasiparticle density of states (DOS) in the mixed
state is derived and compared to the predicted scaling law
of d-wave superconductivity. It is found that
the scaling law can be nicely followed by the optimally doped sample (x=0.15)
in quite wide region of (). However, the region
for this scaling becomes smaller and smaller towards more underdoped region: a
clear trend can be seen for samples from x=0.15 to 0.069. Therefore, generally
speaking, the scaling quality becomes worse on the underdoped samples in terms
of scalable region of . This feature in the underdoped region is
explained as due to the low energy excitations from a second order (for
example, anti-ferromagnetic correlation, d-density wave, spin density wave or
charge density wave order) that may co-exist or compete with superconductivity.
Surprisingly, deviations from the d-wave scaling law have also been found for
the overdoped sample (x=0.22). While the scaling law is reconciled for the
overdoped sample when the core size effect is taken into account. An important
discovery of present work is that the zero-temperature data follow the
Volovik's relation quite well for all samples
investigated here although the applicability of the d-wave scaling law to the
data at finite temperatures varies with doped hole concentration. Finally we
present the doping dependence of some parameters, such as, the residual linear
term , the value, etc. ...Comment: 15 pages, 24 figure
Doping Evolution of the Underlying Fermi Surface in La2-xSrxCuO4
We have performed a systematic doping dependent study of
LaSrCuO (LSCO) (0.030.3) by angle-resolved
photoemission spectroscopy. In the entire doping range, the underlying ``Fermi
surface" determined from the low energy spectral weight approximately satisfies
Luttinger's theorem, even down to the lightly-doped region. This is in strong
contrast to the result on CaNaCuOCl (Na-CCOC), which shows
a strong deviation from Luttinger's theorem. The differences between LSCO and
Na-CCOC are correlated with the different behaviors of the chemical potential
shift and spectral weight transfer induced by hole doping.Comment: 4 pages, 4 figure
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