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1.
Magnetic properties of superconducting yttrium barium copper oxide (YBa2Cu3O7-δ) nanoparticles (31–43 nm) prepared by a chemical route have been studied. These nanoparticles have been found to clearly
exhibit ferromagnetism at room temperature while superconducting transition is observed at lower temperatures. The low temperature
hysteresis loops show evidence suggesting the presence of a large paramagnetic contribution in addition to the superconducting
contributions from the particles. Bulk YBCO obtained by pelletizing and heating the same nanoparticles at a high temperature,
displays the usual superconducting characteristics and gives no trace of ferromagnetism down to 10 K. The superconducting
transition temperature of the nanoparticles is lower than for the bulk YBCO and there is a trend of decreasing T
c with smaller size of the particles. In contrast the ferromagnetic moment increases with decreasing particle size. The development
of ferromagnetism is attributed to the presence of surface oxygen vacancies that lead to electron redistribution on the different
ions at the surface. The simultaneous decrease of superconducting T
c and the increase of ferromagnetism with decreasing size considered as being reflective of the increased role of finite size
and surface defects that weaken the superconductivity and enhance the ferromagnetism. Possible coexistence of surface ferromagnetism
and bulk superconductivity at lower temperatures is discussed. 相似文献
2.
Mei Yu Green S. M. Reynolds G. G. Wiczynski T. Luo H. L. Politis C. 《Zeitschrift für Physik B Condensed Matter》1987,67(3):303-305
The magnetic properties of superconducting GdBa2Cu3O7–x
withT
c95 K are measured. In the normal state, its susceptibility closely follows the Curie law with an effective moment of 7.77
B
.H
c1 is determined to be 650 Oe. No superconducting fluctuation can be delineated. Flux pinning indicated behavior of type II superconductors. A 25–405 diamagnetic state indicating bulk superconductivity in GdBa2Cu3O7–x
. 相似文献
3.
A system of self-consistent integral equations for the superconducting gap is formulated and solved taking account of the
instability of the normal phase of bilayer cuprates against charge-density waves. The critical parameters are calculated as
a function of the wave vector, temperature, and doping index. It is found that the region in which superconductivity coexists
with d-type charge-density waves depends strongly on the doping index. The effective energy-gap parameter, determined as the interval
between the peaks of the density of states, can have a local minimum at temperatures T<T
c
.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 583–587 (10 October 1998) 相似文献
4.
A generalized t-J-I-model is proposed for Sr2RuO4 that takes the strong intra-atomic correlations of the d electrons and the features of the electronic structure of Sr2RuO4 into account. It is shown that, in the limit of strong correlations, there are no singlet s-type solutions for the superconducting state, but triplet solutions exist because of ferromagnetic spin correlations. For
typical values of the model parameters, T
c
∼1 K, consistent with the value of T
c
for Sr2RuO4.
Fiz. Tverd. Tela (St. Petersburg) 41, 1936–1938 (November 1999) 相似文献
5.
S. A. Nemov M. K. Zhitinskaya R. V. Parfen’ev D. V. Shamshur 《Physics of the Solid State》1998,40(7):1096-1097
A study is reported of the effect of low-level germanium additions (∼0.01–0.1 at. %) on the parameters of the superconducting
transition, viz. the critical temperature T
c, the second critical magnetic field H
c2, and
in PbTe doped with 2 at. % Tl, which are derived from the dependence of the electrical resistivity of a sample on temperature
(0.4–4.2 K) and magnetic field (0–1.3 T). The discontinuity revealed by experimental data is related to the onset of a Ge-induced
structural phase transition.
Fiz. Tverd. Tela (St. Petersburg) 40, 1204–1205 (July 1998) 相似文献
6.
V. R. Shaginyan 《JETP Letters》1998,68(6):527-533
Fermion condensation (FC) is studied within the density functional theory. FC can fulfill the role of a boundary, separating
the region of strongly interacting electron liquid from the region of strongly correlated electron liquid. Consideration of
the superconductivity in the presence of FC shows that, under certain circumstances, at temperatures above T
c
the superconductivity vanishes and the superconducting gap smoothly transforms into a pseudogap. The pseudogap occupies only
a part of the Fermi surface, and one that shrinks with increasing temperature and vanishes at T=T*, and the single-particle excitations of the gapped area of the Fermi surface have a width γ ∼(T-T
c
).
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 491–496 (25 September 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
7.
I. N. Khlyustikov 《Journal of Experimental and Theoretical Physics》1997,85(3):609-615
Supercooling in the transition of a type I superconductor to the superconducting state in contact with another superconductor
whose critical temperature is higher has been measured. Using aluminum as a test material, it has been demonstrated that at
temperatures below the critical temperature T
c and magnetic fields below the critical field H
c(T), aluminum remains in a metastable normal state, in spite of its contact with another superconductor. This means that it
is not possible to generate a thermodynamic instability in a superconductor’s electronic system through the “proximity effect”
with another superconductor whose critical temperature is higher. This experimental observation demonstrates a radical difference
between surface superconductivity, which certainly generates instability in normal electronic states, and superconductivity
induced by the proximity effect near a junction with another superconductor.
Zh. éksp. Teor. Fiz. 112, 1119–1131 (September 1997) 相似文献
8.
A. V. Samokhvalov 《Physics of the Solid State》2017,59(11):2143-2149
Calculations of critical temperature T c of the phase transition to superconducting state of a superconductor/ ferromagnet/superconductor (SFS) hybrid structure with proximity effect is performed on the base of linearized Usadel equations. It is shown that the proximity effect between S and F metals and the exchange interaction can induce an inhomogeneous superconducting state with longitudinal to layers Δ ∝ exp(ipz) modulation of the superconductivity order parameter, which is characterized by nonzero value of the wave number p, describing the Larkin–Ovchinnikov–Fulde–Ferrell instability. Influence of this instability on transitions between 0- and π-states of the SFS structure is studied. It is shown that the 0–π transition is accompanied by a nonmonotonic dependence of both the critical temperature T c and the effective penetration depth Λ of the magnetic field into the hybrid structure on the characteristic size of the ferromagnetic region. 相似文献
9.
B. Dauth T. Kachel P. Sen K. Fischer M. Campagna 《Zeitschrift für Physik B Condensed Matter》1987,68(4):407-410
The high-temperature superconducting Cu oxides — which are intrinsically Mott insulators — are strongly correlated metals because of valence fluctuations involving Cud
9–d
10 configurations. Temperature-dependent X-ray photoemission spectroscopy of theO 1s and Cu 2p levels in the range 10–300 K provides evidence for O-dimerization, with corresponding increase of the Cud
10O 2p
5 well-screened XPS-final state belowT
c
. This supports the suggestion of dynamical mixed-valence and double-exchange antiferromagnetic interaction as an important mechanism for the origin of highT
c
superconductivity. 相似文献
10.
Summary It is shown that the behaviour of the temperature dependence of the critical current in polycrystalline thin films of high-T
c superconductors depends crucially on the assumption made concerning the nature of the intergranular material. The usual assumption
of a superconductor-insulator-superconductor (=SIS) ?sandwich? between each grain leads to a crossover fromI
c∼(1−T/T
c) toI
c∼(1−T/T
c)3/2, for temperatures nearT
c (whereI
c is the critical current,T the absolute temperature, andT
c the superconducting transition temperature). Instead, for a superconductor-normal metal-superconductor (=SNS) sandwich the
dependenceI
c∼(1−T/T
c)2 is found for all temperatures. Consideration is given to the effect of self-magnetic field on the analysis. The comparison
between expressions for continuous and granular systems is extended.
Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction. 相似文献
11.
A. A. Blinkin V. V. Derevyanko T. V. Sukhareva V. L. Uvarov V. A. Finkel Yu. N. Shakhov I. N. Shlyakhov 《Physics of the Solid State》2011,53(2):245-255
This paper reports on the results of investigations of the influence of irradiation of the two-band BCS superconductor MgB2 by electrons with an average energy $
\bar {\rm E}
$
\bar {\rm E}
∼ 10 MeV at high doses (0 ≤ ϕt ≤ ∼2.5 × 1018 cm−2) on the temperature and width of the transition to the superconducting state, the temperature dependence of the electrical
resistivity in the normal state, the crystal lattice parameters, and the diffraction line intensity. An increase in the electron
irradiation dose ϕt leads to the following effects: a decrease in the critical temperature T
c
; an increase in the width of the superconducting transition ΔT
c
; and a decrease in the “residual electrical resistivity” ρ273 K/ρ40 K, in the parameters a and c of the hexagonal crystal lattice, and in the ratio between the diffraction line intensities I
110/I
100. From analyzing the results obtained, it has been established that the main type of radiation damages under irradiation of
the BCS superconductor MgB2 by high-energy electrons is the formation of vacancies in the B sublattice, which leads to a narrowing of the large band
gap Δσ on the Fermi surface. 相似文献
12.
13.
We report synthesis and search for superconductivity of Ba, Sr, Ca and Mg-GIC. We adopted conventional vapor phase reaction in order to prepare high quality GICs. No superconducting transition was found for Ba and Mg-GIC. As for Sr, Sr-GIC showed a sharp superconducting transition at Tc=1.65 K. Sr graphite compound SrCx prepared from powder graphite by thermal treatment at higher temperature showed ferromagnetic character. 相似文献
14.
Pairing symmetry in oxypnictides, a new family of multiband high-T
c
superconductors, is partially imposed by the positions of multiple Fermi pockets, which itself can give rise to new order
parameters, such as s
+,− states or the state of the symmetry. Other pairing states may appear on small pockets for long-range interactions, but they are expected to be sensitive
to defects. We identify the competing antiferromagnetic order with the triplet exciton transition in the semimetallic background
and discuss whether its coexistence with superconductivity explains the doping dependence of T
c
.
The text was submitted by the authors in English. 相似文献
15.
Variations in the temperature behavior of resistivity, ρ(T), in the ab plane of the anisotropic single-crystal high-T
c
superconductor BiSrCuO (2201 phase) have been observed at the insulator-metal (IM) transition. At low temperatures, as one
approaches the transition, the Mott relation for two dimensions, ln ρ ∝ T
−1/3, changes to ln ρ ∝ T
−1/2, which corresponds to hopping conduction with a Coulomb gap in the density of states. Negative temperature slopes were revealed
in the samples near the transition. Estimates suggest that superconductivity in these samples sets in from the Anderson insulator
state. The behavior of the width of the superconducting transition and of the temperature of its onset, T
con, at the IM transition has been studied from measurements of the ac magnetic susceptibility. It is shown that in the vicinity
of the IM transition the superconducting transition becomes broader, and the onset of the transition T
con shifts toward higher temperatures. This behavior is attributed to nonuniform superconductivity resulting from formation in
the crystal of superconducting droplets with different values of T
c
, which is caused by fluctuations in the local density of states due to the inherent disorder in the crystal. In these conditions,
superconductivity has a percolation character.
Fiz. Tverd. Tela (St. Petersburg) 40, 1190–1194 (July 1998) 相似文献
16.
G. Kh. Panova A. A. Nikonov A. A. Naberezhnov A. V. Fokin 《Physics of the Solid State》2009,51(11):2225-2228
This paper reports on a study of the resistance and differential magnetic susceptibility χ
ac
of lead embedded in nanosized glass pores with a diameter of ∼7 mm, which was performed at temperatures of 6–300 K and magnetic
fields of up to 6 T. The field dependence of the resistance R(H) and the temperature dependences of the real, χ″(T), and imaginary, χ″(T), parts of magnetic susceptibility reveal indications of superconducting phase transitions associated with the volume and
surface superconductivity of Pb nanopar ticles. The measurements of the field dependence of resistance have been used to set
up the H
c
-T
c
phase diagram and to carry out a comparison with the study of the heat capacity performed on the same samples. 相似文献
17.
Li Fen Guo Tao Zhang Kai-cheng Chen Chin-ping Feng Qing-rong 《Frontiers of Physics in China》2006,1(4):446-448
Thick MgB2 (magnesium diborate) films, ∼10 μm, with T
c (onset) = 39.4 K and T
c (zero) = 39.2 K have been successfully grown on a stainless steel substrate using a technique called hybrid physical-chemical
deposition (HPCVD). The deposition rate is high, ∼6.7 nm/s. The X-ray diffraction (XRD) indicates that it is highly (101)
and c-axis oriented. The scanning electron microscope (SEM) images demonstrate that the film grown is in “island-mode”. The uniform
superconducting phase in the film is shown by the M-T measurement. 相似文献
18.
The question of the effect of the structure of the anisotropic quasi-two-dimensional electron spectrum of high-T
c
superconductors on the character of the screening of the Coulomb interaction and the symmetry of the superconducting order
parameter is studied. Calculations of the polarization operator of electrons are performed on the basis of the single-particle
band spectrum extracted from angle-resolved photoemission spectroscopy data. It is shown that the static screened Coulomb
repulsion has a minimum at small momentum transfers. This corresponds to an effective electron-electron attraction in the
-wave channel of Cooper pairing of the charge carriers on account of their interaction with the long-wavelength charge-density
fluctuations. This attraction together with the anisotropic electron-phonon interaction increase the critical superconducting
transition temperature T
c
with increasing hole density and can give quite high values of T
c
while at the same time suppressing the isotope effect, in qualitative agreement with the experimental data for underdoped
hole-type cuprate metal-oxide compounds.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 10, 703–710 (25 May 1999) 相似文献
19.
G. Hilscher N. Pillmayr R. Eibler E. Bauer K. Remschnig P. Rogl 《Zeitschrift für Physik B Condensed Matter》1988,72(4):461-470
Samples from the oxide series of solid solutions La1.85Sr0.15Cu1–xZn
x
O4, quenched from 1100°C, have been characterized by X-ray powder analysis. We report on the structural chemistry and on measurements of the electrical resistivity, magnetization, ac susceptibility and specific heat of these samples. Zinc was found to statistically replace the copper atoms in the body centered tetragonal K2NiF4-type of structure up to values ofx smaller than 0.15. At higher zinc-concentrations (0.15<x<0.45) the crystal structure transformes into the orthorhombically distorted K2NiF4-type, known for the low-temperature form of Sr-and Zn-free La2CuO4. Limited solid solutions are encountered when Cu is substituted by Cd and Hg. Whilst the Zn-free sample La1.85Sr0.15CuO4 was superconducting with a sharp onset at 35 K, substitution of Cu by Zn by as little as 6 mole percent was sufficient to suppress superconductivity belowT
c<4.5 K. Isoelectronic substitution of Cu by (Ni0.5Zn0.5) was found to cause an even larger degradation ofT
c than equivalent amounts of Zn. At the superconducting transition the discontinuity of the specific heat C
p is observed in agreement with recent publications, but is found to decrease with Zn substitution. A linear term inC
p(T) is resolved at low temperatures which significantly rises upon Cu/Zn substitution. 相似文献
20.
X-ray and resistivity measurements on YBa2Cu3O7−δ
(1-2-3) samples show that for the same but low oxygen concentration,δ⋍0·55, no superconducting transition down to 4·2 K is observed for the tetragonal phase samples while the orthorhombic phase
shows aT
c ∼ 31 K. The effect of oxygen concentration onT
c is isolated.T
c=91±1 K has, however, been observed continuously for the normal oxygen annealed samples,δ⋍0·07. The experimental results suggest strongly the necessity of the 1-2-3 compound to be in the orthorhombic phase for the
superconducting mechanism to be operative. 相似文献