615 research outputs found
Doping evolution of the electronic specific heat coefficient in slightly-doped La2-xSrxCuO4 single crystals
Detailed doping dependence of the electronic specific heat coefficient gamma
is studied for La2-xSrxCuO4 (LSCO) single crystals in the slightly-doped
regime. We find that gamma systematically increases with doping, and
furthermore, even for the samples in the antiferromagnetic (AF) regime, gamma
already acquires finite value and grows with x. This suggests that finite
electronic density of states (DOS) is created in the AF regime where the
transport shows strong localization at low temperatures, and this means the
system is not a real insulator with a clear gap even though it still keeps long
range AF order.Comment: 4 pages, 4 figures, accepted for publication in Journal of Physics:
Conference Series (LT25 proceeding
Hall effect in superconducting Fe(Se0.5Te0.5) thin films
The Hall effect is investigated for eight superconducting Fe(Se_0.5_Te_0.5_)
thin films grown on MgO and LaSrAlO_4_ substrates with different transition
temperatures (T_c_). The normal Hall coefficients (R_H_) have positive values
with magnitude of 1 - 1.5 x 10^-3^ cm^3^/C at room temperature for the all
samples. With decreasing temperature, we find two characteristic types of
behavior in R_H_(T) depending on T_c_. For thin films with lower T_c_
(typically T_c_ < 5 K), R_H_ start decreasing approximately below T = 250 K
toward a negative side, some of which shows sign reversal at T = 50 - 60 K, but
turns positive toward T = 0 K. On the other hand for the films with higher T_c_
(typically T_c_ > 9 K), R_ H_ leaves almost unchanged down to T = 100 K, and
then starts decreasing toward a negative side. Around the temperatures when
R_H_ changes its sign from positive to negative, obvious nonlinearity is
observed in the field-dependence of Hall resistance as to keep the low-field
R_H_ positive while the high-field R_H_ negative. Thus the electronic state
just above T_c_ is characterized by n_e_ (electron density) > n_h_ (hole
density) with keeping \mu_e_ < \mu_h_. These results suggest the dominance of
electron density to the hole density is an essential factor for the occurence
of superconductivity in Fe-chalcogenide superconductors.Comment: 11 pages, 4 figures, revised version for Physical Review B. accepted
for publication in Physical Review
An Infrared study of the Josephson vortex state in high-Tc cuprates
We report the results of the c-axis infrared spectroscopy of La_{2-x} Sr_x
CuO_4 in high magnetic field oriented parallel to the CuO_2 planes. A
significant suppression of the superfluid density with magnetic field rho_s(H)
is observed for both underdoped (x=0.125) and overdoped (x=0.17) samples. We
show that the existing theoretical models of the Josephson vortex state fail to
consistently describe the observed effects and discuss possible reasons for the
discrepancies
Large magneto-thermal effect and the spin-phonon coupling in a parent insulating cuprate Pr_{1.3}La_{0.7}CuO_4
The magnetic-field (H) dependence of the thermal conductivity \kappa of
Pr_{1.3}La_{0.7}CuO_4 is found to show a pronounced minimum for in-plane fields
at low temperature, which is best attributed to the scattering of phonons by
free spins that are seen by a Schottky-type specific heat and a Curie-Weiss
susceptibility. Besides pointing to a strong spin-phonon coupling in cuprates,
the present result demonstrates that the H-dependence of the phonon heat
transport should not be naively neglected when discussing the \kappa(H)
behavior of cuprates, since the Schottky anomaly is ubiquitously found in
cuprates at any doping.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.
Microscopic analysis of the chemical reaction between Fe(Te,Se) thin films and underlying CaF
To understand the chemical reaction at the interface of materials, we
performed a transmission electron microscopy (TEM) observation in four types of
Fe(Te,Se) superconducting thin films prepared on different types of substrates:
CaF2 substrate, CaF2 substrate with a CaF2 buffer layer, CaF2 substrate with a
FeSe buffer layer, and a LaAlO3 substrate with a CaF2 buffer layer. Based on
the energy-dispersive X-ray spectrometer (EDX) analysis, we found possible
interdiffusion between fluorine and selenium that has a strong influence on the
superconductivity in Fe(Te,Se) films. The chemical interdiffusion also plays a
significant role in the variation of the lattice parameters. The lattice
parameters of the Fe(Te,Se) thin films are primarily determined by the chemical
substitution of anions, and the lattice mismatch only plays a secondary role.Comment: 30 pages, 9 figur
Magnetoresistive study of antiferromagnetic--weak ferromagnetic transition in single-crystal LaCuO
The resistive measurements were made to study the magnetic field-induced
antiferromagnetic (AF) - weak ferromagnetic (WF) transition in LaCuO
single-crystal. The magnetic field (DC or pulsed) was applied normally to the
CuO layers. The transition manifested itself in a drastic decrease of the
resistance in critical fields of ~5-7 T. The study is the first to display the
effect of the AF -WF transition on the conductivity of the LaCuO
single-crystal in the parallel - to - CuO layers direction. The results
provide support for the 3-dimensional nature of the hopping conduction of this
layered oxide.Comment: 8 pages, 7 figures, RevTe
Point-contact Andreev-reflection spectroscopy in Fe(Te,Se) films: multiband superconductivity and electron-boson coupling
We report on a study of the superconducting order parameter in
Fe(TeSe) thin films (with different Se contents: x=0.3, 0.4, 0.5)
by means of point-contact Andreev-reflection spectroscopy (PCARS). The PCARS
spectra show reproducible evidence of multiple structures, namely two clear
conductance maxima associated to a superconducting gap of amplitude and additional shoulders at higher energy that, as we
show, are the signature of the strong interaction of charge carriers with a
bosonic mode whose characteristic energy coincides with the spin-resonance
energy. The details of some PCARS spectra at low energy suggest the presence of
a smaller and not easily discernible gap of amplitude . The existence of this gap and its amplitude are confirmed by PCARS
measurements in Fe(TeSe) single crystals. The values of the two
gaps and , once plotted as a function of the local
critical temperature , turn out to be in perfect agreement with the
results obtained by various experimental techniques reported in literature.Comment: 8 pages, 6 figures. This is an author-created, un-copyedited version
of an article published in Supercond. Sci. Technol. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The Version of Record is available online at
10.1088/0953-2048/27/12/12401
2004-2005 International Whaling Commission-Southern Ocean Whale and Ecosystem Research (IWC-SOWER) Cruise, Area III
We conducted the 27th annual IWC-SOWER (formerly IDCR) Cruise in Area III (000°-070°E) aboard the Japanese Research Vessels Shonan Maru and Shonan Maru No.2. The 65-day cruise departed Cape Town, South Africa on 4 January 2005 and returned to Fremantle, Australia on 9 March 2005. After transiting to the study area, we carried out a minke whale survey and several research experiments from 12 January to 25 February. A systematic minke whale survey was conducted in Area IIIW (000°-035°E) from 12 January until 8 February. The survey design was intentionally similar to that used during the IWC/IDCR second circumpolar series of cruises (CPII) to provide information towards addressing the effect of changing cruise track design on Antarctic minke whale abundance estimates. 000°-020°E was surveyed in two contiguous strata (Northern and Southern), from 64°30'S to the ice edge. Poor weather limited the coverage 020°E-035°E to the Southern Stratum only. A total of 1788.2 nmiles was surveyed (000°-035°E) including 935.5 nmiles in closing mode and 930.3 nmiles in independent observer mode, and a total of 466 minke whales were sighted. Minke whale visual dive time experiments were conducted during the minke whale survey. 35 trials were completed, recording surfacing cues for a total of 45.81 hours. From 10-22 February the ships conducted collaborative studies with the Japanese icebreaker, Shirase to investigate the relationship between minke whale abundance and the sea ice. During this study the SOWER vessels surveyed for minke whales in the near-ice area from 035°-050°E. 575.3 nmiles were covered and a total of 22 minke whales were detected. The Shirase surveyed in the pack ice zone 040°-050°E from 12-15 February. Two methods-testing experiments were carried out during the cruise: Adaptive Line Transect Sampling and ‘BT Mode.’ Adaptive Line Transect Sampling was tested during survey in Area IIIW. BT Mode trials were conducted 22-25 February in the area between 050° and 065°E. A direct electronic data acquisition program was evaluated during the cruise on both ships. Sightings for the entire cruise included: minke whales (237 groups/515 animals); blue whales (13 groups/46 individuals) of which 6 groups (28 individuals) were identified as true blue whales and 3 groups (3 individuals) were identified as pygmy blue whales; fin whales (14/132); humpback whales (251/646); sperm whales (35/49); killer whales (23/217); southern bottlenose whales (32/60); Gray’s beaked whales (1/7); Layard’s beaked whales (2/3); pilot whales (4/265); hourglass dolphins (4/17); striped dolphins (3/435) and common bottlenose dolphins (1/20). Opportunistic research during the cruise included blue whale research on 8 groups/29 animals resulting in 5 biopsies and images of 23 individuals for photo-identification studies. Biopsy samples and photo-ID images were also obtained opportunistically from other species. Biopsies were collected from 6 humpback whales and 1 southern right whale. Photo-ID images were collected from 45 humpback whales, 1 southern right whale and 8 groups of killer whales. Estimated Angle and Distance Training Exercise and Experiment were each completed on both vessels
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