共查询到20条相似文献,搜索用时 15 毫秒
1.
Kyung-Hee Kim H.-G. Lee Sung-Ik Lee S.-W. Han 《Journal of Superconductivity and Novel Magnetism》2010,23(3):391-395
The local structural properties of Ca2?x Na x CuO2Cl2 (x=0.0 and 0.18) single crystals were investigated by using X-ray absorption fine structure (XAFS) measurements at the Cu K edge at the temperature range 10–300 K. XAFS showed that the chemical valence state of the Cu atoms was 2+ and that there are two different bonding lengths between the apical Cl atoms and Cu atoms. The long and short bonding lengths differed by approximately 0.25 Å and their ratio was 1:1 regardless of the temperature for both specimens. The two-site behavior of the apical Cl atoms of the CuO4Cl2 octahedra in the Ca2?x Na x CuO2Cl2 crystals resulted from the removal of degeneracy of the Cu 3d 9 electron ground state, and might be related to two-dimensional charge ordering in the Ca2?x Na x CuO2Cl2 crystals. 相似文献
2.
K.-H. Kim H.-G. Lee S.-W. Han 《Journal of Superconductivity and Novel Magnetism》2013,26(5):1795-1798
We examined the local structural properties of checkerboard phased Ca2?x Na x CuO2Cl2 (T c =0, 15, 21, 27 K) using extended X-ray absorption fine structure (EXAFS) measurements at the Cu K edge. EXAFS revealed anomalous disorders existing in the bond lengths of Cu–Cu and Cu-Ca/Na pairs for all crystals below 50 K. A static disorder was observed even at room temperature. The disorders of the Cu–Cu in the a- and b-axes were independent of the T c value whereas these of the Cu–Ca/Na pairs located about 30° off from the Cu–O, ab-plane decreased, as T c increased. 相似文献
3.
M. Sato T. Noji T. Adachi T. Kawamata H. Akagawa Y. Koike 《Journal of Low Temperature Physics》2003,131(3-4):293-297
For La2–x
Sr
x
CuO4 single-crystals in the underdoped and overdoped regimes, we have measured the electrical resistivity along the c-axis,
c
, under constant magnetic fields, changing the field direction in the ab-plane. At x=0.08, 0.12 and 0.16 in the underdoped and almost optimally-doped regimes, clear anisotropy of
c
with the fourfold symmetry in the ab-plane has been observed. This symmetry is regarded as the fourfold symmetry of the upper critical field, H
c2, and explained as being mainly due to the anisotropy of the superconducting energy gap owing to the dx
2-y
2 pairing. The magnitude of the fourfold component of H
c2, H
c2/H
c2, is largest in x=0.08 among the three crystals. At x=0.20 in the overdoped regime, no clear fourfold symmetry has been observed. It appears that the fourfold symmetry is easy to observe in the underdoped regime rather than in the overdoped regime. 相似文献
4.
Takami Tohyama Susumu Nagai Yasumasa Shibata Sadamichi Maekawa 《Journal of Low Temperature Physics》1999,117(3-4):211-215
We investigate the electronic states of underdoped La
2–x
Sr
x
CuO
4
(LSCO) by using a microscopic model, i.e., t-t-t-J model, containing charge stripes. The numerically exact diagonalization calculation is employed on small clusters. The physical properties observed in the angle-resolved photoemission and optical conductivity experiments are consistently explained in the model with vertical stripes, but not diagonal ones. These results demonstrate a crucial role of the vertical stripes in underdoped LSCO. 相似文献
5.
Teruhiko Akazawa Hiroshi Ikeda Norihiko Ozawa Hideki Kouno Ryozo Yoshizaki 《Journal of Low Temperature Physics》1999,117(5-6):1235-1239
In order to investigate a relationship between the carrier concentration and negative magnetoresistance in the underdoped region, we have performed out-of-plane electrical resistivity measurements for underdoped Bi
2
Sr
1.6
La
0.4
CuO
6+
single crystals. Giant negative magnetoresistance has been observed in the most abundant carrier sample with = 0.12 in our experiment. The negative magnetoresistance reduces with decreasing carrier concentration. 相似文献
6.
T. B. Charikova N. G. Shelushinina G. I. Harus A. A. Ivanov 《Journal of Superconductivity and Novel Magnetism》2009,22(1):21-24
Temperature dependences of the electrical resistivity measured in different magnetic fields (B
∥
c, J
∥
ab) of electron doped Nd2−x
Ce
x
CuO4+δ
single crystals with different cerium concentration (x=0.15, 0.17, and 0.20) and oxygen content (δ) were studied in a temperature range of 1.8–40 K. It was found that the slope of the upper critical field
decreases with the increase of the disorder in the system. So, we can distinguish experimentally d-wave and anisotropic s-wave
superconductors. Moreover, the slope of the upper critical field and critical temperature decrease with increase of the disorder
parameter like in d-wave superconductors with anisotropic scattering. 相似文献
7.
8.
John A. Skinta Mun-Seog Kim Thomas R. Lemberger T. Greibe M. Naito 《Journal of Low Temperature Physics》2003,131(3-4):359-368
From measurements of the magnetic penetration depth, (T), from 1.6 K to T
c in films of electron-doped cuprates La2–x
Ce
x
CuO4–y
and Pr2–x
Ce
x
CuO4–y
we obtain the normalized density of states, N
s(E) at T=0 by using a simple model. In this framework, the flat behavior of –2(T) at low T implies N
s(E) is small, possibly gapped, at low energies. The upward curvature in –2(T) near T
c seen in overdoped films implies that superfluid comes from an anomalously small energy band within about 3k
B
T
c of the Fermi surface. 相似文献
9.
S. Sugai T. Adachi K. Sugiura T. Takahashi K. Obara Y. Takayanagi Y. Koike 《Journal of Superconductivity and Novel Magnetism》2009,22(3):313-317
The superconductivity depression mechanisms at x≈1/8 in La2−x
Ba
x
CuO4 and Zn substitution in La2−x
Sr
x
CuO4 were investigated by Raman scattering. About 80% of low-energy electronic states are two-dimensional at x≈1/8 and form the Fermi arc around (π/2,π/2). The low-energy states are composed of the resonant peak relating to the insulator–metal transition and the polaron states
of the B
3u phonons. Zn substitution depresses the resonant peak, while the LTT structure depresses the polaron states. The superconductivity
is suppressed if one of them is reduced. 相似文献
10.
L. Stojchevska T. Mertelj Juin-Haw Chu Ian R. Fisher D. Mihailovic 《Journal of Superconductivity and Novel Magnetism》2013,26(8):2593-2596
We apply the femtosecond optical pump-probe spectroscopy to study the relaxation dynamics in photoexcited Co-doped Ba(Fe1?x Co x )2As2 single crystals in the underdoped spin-density wave (SDW) state region of the x?T phase diagram. Underdoped SDW samples with Co-0 % and Co-2.5 % show a bottleneck in the relaxation as a consequence of the partial charge gap opening in the orthorhombic SDW phase, similar to previous results in other SDW iron-pnictides. Moreover, the charge gap magnitude decreases with increasing doping. The sample with Co-5.1 % displays both a SDW ordering and superconductivity at low T. We were able to observe a 2-fold anisotropy in our samples, existing up to ~200 K, without any applied uniaxial stress. We associate the 2-fold symmetry breaking in nominally tetragonal phase with nematic ordering of the Fe d orbitals. 相似文献
11.
Michael R. Koblischka Masato Murakami Satoru Koishikawa Tom Henning Johansen Michael Baziljevich Thomas Frello Thomas Wolf 《Journal of Low Temperature Physics》1999,117(5-6):1483-1487
Instabilities of the critical state are observed in various NdBa
2
Cu
3
O
7–
single crystals by means of direct magneto-optic (MO) imaging while warming up flux states containing vortices of opposite polarity. Using the same samples as in the MO investigations, we observe for the first time characteristic steps in the integral magnetization measured by means of a SQUID system, which allows a constant temperature sweep. The integral measurement technique enables the study of the instability phenomenon (turbulence) in a much wider range of temperatures and fields than the MO investigations, and also in the orientations H
a
c and H
a
c. As a result, we find turbulence not only in a narrow window of temperatures (65 T 80 K), but also in a window of applied negative fields ranging between 30 and 80 mT. 相似文献
12.
13.
S. Kurogi K. Kudo T. Noji Y. Koike T. Nishizaki N. Kobayashi 《Journal of Low Temperature Physics》2003,131(3-4):353-357
We have investigated the spin state of the one-dimensional edge-sharing chain system Ca2+x
Y2–x
Cu5O10 with 0x1.667 by means of the magnetic susceptibility and specific heat measurements, using the large-size single-crystals. It has been found that the magnetic ground state is an antiferromagnetically ordered state for 0x1.0, while a spin-gap state seems to be formed for x1.5. Accordingly, it appears that the quantum critical point is located between x=1.0 and 1.5 in Ca2+x
Y2–x
Cu5O10. 相似文献
14.
W. P. Liu M. T. Li C. T. Lin 《Journal of Superconductivity and Novel Magnetism》2014,27(11):2419-2426
We report the structure, transport, and magnetic properties of K x Fe2?y Se2?z Te z single crystals grown by optical floating zone technique. The phase separation phenomena were observed in the Te-doped samples. With increasing Te doping level, the c-axis lattice parameter expands for both insulating/semiconducting and superconducting phases while the superconducting transition temperature (T c) decreases and eventually vanishes at z = 0.51. The critical current density was estimated to be 103–104 A/cm2 for the all doped samples. The upper critical field and anisotropic superconducting ratio increase with Te doping. We compared the results of critical current density J c, upper critical field μ 0 H c2 and apparent thermally activated energy U 0 for the samples with z = 0, 0.09, and 0.16. The influence of Te doping on the vortex pinning and the implication of U 0 versus μ 0 H is discussed. 相似文献
15.
J. Hofer J. Karpinski Guo-meng Zhao M. Willemin G. I. Meijer E. M. Kopnin R. Molinski H. Schwer C. Rosse H. Keller 《Journal of Superconductivity》1999,12(1):45-47
Torque magnetization measurements on HgBa2CuO4+ microcrystals withdifferent oxygen doping were performed in order to extract the dopingdependence of the effective mass anisotropy=m
*
c/m
*
ab, of the in-plane penetration depth
ab
, and of the in-plane coherencelength
ab
. The anisotropy increases monotonically withdecreasing , suggesting a smooth 3D–2D crossover in the superconductingproperties on reducing the oxygen content. Within the framework of abipolaronic model this increase can be explained by an increase of thepolaron binding energy with reduced doping. 相似文献
16.
Khadzhai G. Ya. Chroneos A. Goulatis Ι. L. Kamchatnaya S. N. Chikina A. L. Vovk N. R. Vovk R. V. 《Journal of Low Temperature Physics》2021,203(5-6):430-436
Journal of Low Temperature Physics - The effect of high pressure on the conductivity in the basal plane of HTSC single crystals of Y0.77Pr0.23Ba2Cu3O7?δ is investigated. It has been... 相似文献
17.
C. Rial E. Morán M. A. Alario-Franco 《Journal of Superconductivity and Novel Magnetism》1994,7(6):913-916
A series of oxidized La2?x Sr x CuO4+y $(0.05 \preccurlyeq x \preccurlyeq 0.3)$ compounds has been prepared by treating the starting materials with a solution of Br2 in NaOH at room temperature. The structural modifications due to the oxidation of the materials have been studied by X-ray diffraction. Some of the observed changes are: (i) a large increase in the long parameter of the unit cell for samples with Sr content $0.05 \preccurlyeq x \preccurlyeq 0.15$ and (ii) a slight decrease in a along the whole range ofx. Interesting features have been observed regarding the critical temperatures of these materials: transition temperatures are higher for those containing lower Sr amounts (some of them were even nonsuperconducting before the oxidation treatment) in contrast to materials with x?0.15, whoseT c's do not change very much. The influence of both oxygen and strontium contents on the structural modifications and the superconducting properties of the oxidized materials will be discussed. 相似文献
18.
George A. Kapustin 《Journal of Low Temperature Physics》1999,117(5-6):1489-1493
Magnetic properties of high-T
c
superconductor Yba
2
Cu
3
O
7–x
and their dependencies on the magnetic field variation rate (from 2·102
up to 3·104
T/s) have been investigated in pulsed magnetic fields up to 35 T, parallel to the ab plane of the crystals. A dependence of fast magnetization relaxation on the high electric field (from 10–1
to 10 V/m) has been revealed and studied for the case of electric current directed along the c axis and for a vortex movement parallel to the ab plane. A pronounced peak effect accompanying such movement has been observed over a wide range of magnetic and electric fields including the flux creep to flux flow transition region. The peak effect origin is discussed in connection with this observation. 相似文献
19.
S. Sugai Y. Takayanagi N. Hayamizu Y. Sone N. Nakagawa T. Muroi 《Journal of Superconductivity and Novel Magnetism》2013,26(8):2697-2701
The mechanism of the high temperature hole-doped superconductivity was investigated by Raman scattering. The Raman selection rule is unique, so that anisotropic magnetic excitations in a fluctuating spin-charge stripe can be detected as if it is static. We use different Raman selection rules for two kinds of magnetic Raman scattering processes, two-magnon scattering and high-energy electronic scattering. In order to confirm the stripe effect, the Raman spectra of striped La2?x Sr x CuO4 (LSCO) and nonstriped Nd2?x Ce x CuO4 (NCCO) were compared. The main results in LSCO are (1) magnetic excitations are presented by individual energy dispersions for the k∥ stripe and the k⊥ stripe, (2) the charge transfer is allowed only in the direction perpendicular to the stripe. The direction is the same as the Burgers vector of an edge dislocation. Hence, we assume that a charge moves together with the edge dislocation of the charge stripe. The superconducting coherence length is close to the intercharge stripe distance at x<0.2. Therefore, we propose a model that superconducting pairs are formed in the edge dislocations. The binding energy is related to the stripe formation energy. 相似文献
20.
D. Nicoletti P. Calvani P. Di Pietro O. Limaj U. Schade S. Ono Yoichi Ando S. Lupi 《Journal of Superconductivity and Novel Magnetism》2013,26(4):969-977
The ab-plane optical conductivity of seven single crystals, belonging to the family Bi2Sr2?x La x CuO6, has been measured for hole concentrations per Cu site 0.03≤p≤0.18, and for 6 K≤T≤300 K (500 K for p=0.16). At low doping, ten phonon lines are detected, which are due to the removal of the degeneracy of five E u modes (out of the predicted six). They are superimposed to a far-infrared band, which as doping increases, closes the insulating gap thus building up the Drude term. The insulator-to-metal transition occurs between p=0.7 and p=0.10 consistently with a Mott mechanism. In the metallic phase, a multiband analysis identifies a Drude term plus a mid-infrared band, which weakly depends on temperature and softens as p increases, like in other cuprates. The optical response of the crystal at optimum doping has been analyzed also in the superconducting phase. The Ferrel–Glover–Tinkham sum rule requires an integration up to Ω?6Δ and the penetration depth is 290 nm. The bosonic spectral function includes a strong peak around 50 meV, which survives up to 500 K and, therefore, might be assigned to an electron–phonon interaction. 相似文献