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1.
This paper discusses the effect of magnetic translational symmetry on the vortex structure in superconducting crystals with
a large basis in artificial Josephson media (regular lattices of superconducting clusters) prepared with opal as the base
material. For external magnetic fields lower than the upper critical field, the lattice Ginzburg-Landau model reduces to the
two-dimensional Frenkel’-Kontorova model which in some cases is exactly solvable, in which the crystal lattice plays the role
of an “hard sublattice” while the deformable vortex lattice plays the role of a “soft sublattice.” It is shown that static
shear waves in the vortex lattice are solutions to the two-dimensional sine-Gordon equation with an additional condition of
incompressibility implied by flux quantization. The pinning energy is found as a function of the magnetic field, nearness
to the transition line, and the crystal lattice constant.
Fiz. Tverd. Tela (St. Petersburg) 39, 1158–1162 (July 1997) 相似文献
2.
The phase transition “triangular lattice-vortex liquid” in layered high-T
c
superconductors in the presence of pinning centers is studied. A two-dimensional system of vortices simulating the superconducting
layers in a high-T
c
Shubnikov phase is calculated by the Monte Carlo method. It was found that in the presence of defects the melting of the
vortex lattice proceeds in two stages: First, the ideal triangular lattice transforms at low temperature (≃3 K)into islands
which are pinned to the pinning centers and rotate around them and then, at a higher temperature (≃8 K for T
c
584 K), the boundaries of the “islands” become smeared and the system transforms into a vortex liquid. As the pinning force
increases, the temperatures of both phase transitions shift: The temperature of the point “triangular lattice-rotating lattice”
decreases slightly (to ≃2 K)and the temperature of the phase transition “rotating lattice-vortex liquid” increases substantially
(≃70 K).
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 269–274 (25 August 1997) 相似文献
3.
M. A. Zelikman 《Technical Physics》1997,42(9):1019-1026
The behavior of planar (laminar) vortices in a three-dimensional, ordered Josephson medium as a function of the parameter
I, which is proportional to the critical junction current and the cell size, is investigated with allowance for pinning due
to the cellular structure of the medium. The minimum possible distances between two isolated vortices are calculated. A system
of vortices formed in a sample in a monotonically increasing external magnetic field is analyzed. The minimum distance from
the outermost vortex to the nearest neighbor is proportional to I
−1.1. For I⩽1.3 each vortex contains a single flux quantum Φ0, and the distance between them does not decrease in closer proximity to the boundary but remains approximately constant,
implying that the magnetic field does not depend on the coordinate in the region penetrated by vortices. These facts contradict
the generally accepted Bean model. The sample magnetization curve has a form typical of type II superconductors. Allowance
for pinning raises the critical field H
c and induces a sudden jump in the curve at H=H
c.
Zh. Tekh. Fiz. 67, 38–46 (September 1997) 相似文献
4.
L. Ya. Vinnikov A. V. Radaev I. S. Veshchunov A. G. Troshina Y. Liu C. T. Lin A. V. Boris 《JETP Letters》2011,93(5):287-289
Vortex structure in FeTe0.66Se0.44 and FeTe0.6Se0.4 single crystals with T
c
∼ 11.7 and 14.5 K, respectively, has been studied using the decoration technique. It has been found that in single crystals
with the simplest crystalline structure of 11-family iron-containing superconductors (without interlayers), no regular vortex
lattice is observed, similar to the case of the previously studied 122 and 1111 families. Using transmission electron microscopy,
the dislocation structure with a density of ∼109 cm−2 has been observed. The problem of pinning in iron-containing superconductor single crystals is discussed. 相似文献
5.
The influence of surface-layer vortex pinning in a type-II superconductor on the propagation of surface magnetostatic waves
in a ferromagnet-superconductor structure is analyzed. The pinning is assumed to be strong enough to prevent vortex displacement
under the influence of the Lorentz force generated by the surface magnetostatic waves, so that the ground state of the superconductor
is determined by the elastic properties of the vortex lattice and by pinning. In the given model the problem reduces to the
analysis of the wave spectrum in the scattered field created by the disordered vortex surface layer. A calculation shows that
the influence of this field on the surface magnetostatic-wave spectrum is slight and, hence, degradation of the shielding
properties of the superconductor does not take place in the presence of strong vortex pinning (as opposed to the ferromagnet-ideal
superconductor structure).
Fiz. Tverd. Tela (St. Petersburg) 40, 32–35 (January 1998) 相似文献
6.
Yu. I. Golovin R. B. Morgunov M. B. Badylevich S. Z. Shmurak 《Physics of the Solid State》1997,39(8):1232-1234
Observations indicate that illuminating NaCl crystals by ultraviolet light (λ=350 nm) suppresses the magnetoplastic effect. The processes induced by illumination take place in a subsystem of point defects
and are related to a change in the state of magnetically sensitive dislocation pinning sites.
Fiz. Tverd. Tela (St. Petersburg) 39, 1389–1391 (1996) 相似文献
7.
I. F. Voloshin A. V. Kalinov L. M. Fisher K. I. Kugel’ A. L. Rakhmanov 《Journal of Experimental and Theoretical Physics》1997,84(6):1177-1185
Measurements of the imaginary part of the ac magnetic susceptibility of single crystals and melt-textured samples of YBa2Cu3Ox (YBCO) at T=77 K in a magnetic field ranging between 1 and 20 kOe are reported. If the dc magnetic field H
dc is rotated in the ab plane of the sample, the magnetic susceptibility and critical current density j
c have peaks corresponding to the magnetic field aligned with twin boundaries. Peaks in the curve of j
c versus magnetic field are observed at angles corresponding to these peaks, where
AH
dc in a wide range of magnetic fields. The results have been interpreted in terms of the theory describing twin boundaries as
a system of quasi-planar pinning sites. The pinning is strong if the elastic displacements of flux lines are of the order
of the vortex lattice constant d
f. These displacements decrease with the magnetic field because of the decrease in d
f, and the contribution of the elastic energy to the Gibbs potential is reduced accordingly, which is the cause of the peak
effect.
Zh. éksp. Teor. Fiz. 111, 2158–2174 (June 1997) 相似文献
8.
The present paper reports the dislocation unpinning model of acoustic emission (AE) from alkali halide crystals. Equations
are derived for the strain dependence of the transient AE pulse rate, peak value of the AE pulse rate and the total number
of AE pulse emitted. It is found that the AE pulse rate should be maximum for a particular strain of the crystals. The peak
value of the AE pulse rate should depend on the volume and strain rate of the crystals, and also on the pinning time of dislocations.
Since the pinning time of dislocations decreases with increasing strain rate, the AE pulse rate should be weakly dependent
on the strain rate of the crystals. The total number of AE should increase linearly with deformation and then it should attain
a saturation value for the large deformation. By measuring the strain dependence of the AE pulse rate at a fixed strain rate,
the time constantτ
s for surface annihilation of dislocations and the pinning timeτ
p of the dislocations can be determined. A good agreement is found between the theoretical and experimental results related
to the AE from alkali halide crystals. 相似文献
9.
A. A. Zhukov M. G. Mikheev V. I. Voronkova K. I. Kugel’ A. L. Rakhmanov H. Küpfer T. Wolf G. K. Perkins A. D. Caplin 《JETP Letters》1999,69(11):881-886
Magnetization oscillations due to the commensurability of the vortex and crystal lattice periods in YBa2Cu3Oy (y=6.97±0.02) single crystals are investigated using a high angular resolution magnetometer. A sharp peak in the temperature
dependence of the oscillation amplitude as well as other features in the behavior of the oscillation amplitude and of the
irreversible magnetization are observed at T
f
∼60 K. It is inferred that T
f
is the temperature of a transition of the solid vortex state to a smectic phase.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 832–837 (10 June 1999) 相似文献
10.
K. Yu. Terent’ev D. M. Gokhfel’d S. I. Popkov K. A. Shaikhutdinov M. I. Petrov 《Physics of the Solid State》2011,53(12):2409-2414
The current-voltage characteristics of a porous superconductor Bi2Sr2Ca2Cu3O
x
(Bi2223) have been measured at temperatures in the range from 10 to 90 K in magnetic fields of 0–80 kOe. The experimental
dependences have been analyzed within the model allowing for pinning by clusters of a normal phase with fractal boundaries,
as well as the model taking into account phase transformations of vortex matter. It has been found that the electrical resistance
of the superconductor material significantly increases at temperatures of 60–70 K over the entire range of magnetic fields
under consideration without changing in the sign of the curvature of the dependence R(I). It has been assumed that this behavior is associated with the specific feature of the pinning in a highly porous high-temperature
superconductor, which lies in the fractality of the distribution of pinning centers in a wide range of self-similarity scales.
The studied material at the aforementioned temperatures is characterized by the melting of the vortex structure. 相似文献
11.
V. A. Shklovskii A. K. Soroka A. A. Soroka 《Journal of Experimental and Theoretical Physics》1999,89(6):1138-1153
The nonlinear resistive properties of superconductors in the mixed state in the presence of a system of unidirectional planar
defects (twins) have been investigated theoretically within the framework of the two-dimensional stochastic model of anisotropic
pinning based on the Fokker-Planck equations with a concrete form of the pinning potential. These equations allow one to obtain
an exact analytical solution of the problem. Formulas are obtained for experimentally observable even and odd (relative to
reversal of the direction of the external magnetic field) nonlinear longitudinal and transverse magnetoresistivities ρ
‖,⊥
±
( j,t,α,ε) as functions of the transport current density j, temperature t, the angle α between the directions of the current and the twins, and the relative volume fraction ε occupied by the twins. In light of the great variety of types of nonlinear resistive dependences contained in these expressions
for ρ
‖,⊥
±
the most characteristic of them are presented in the form of graphs with commentary. The desired nonlinear dependences ρ
‖,⊥
±
are linear combinations of the even and odd parts of the function v(j,t, α,ε), which has the sense of the probability of overcoming the potential barrier of the twins; this makes it possible to give
a simple physical treatment of the nonlinear regimes. New scaling relations for the Hall conductivity are obtained and investigated
which differ from the previously known relations for isotropic pinning. The interaction of vortex motion directed along the
twins and the Hall effect is considered for Hall constants which are arbitrary in magnitude and sign, and it is shown that
in the case of small Hall viscosity vortex motion directed along the twins has an effect on the odd magnetoresistivities ρ
‖
−
and ρ
⊥
−
, whereas the reverse effect can be neglected. It is shown that pinning anisotropy is sufficient to manifest the new nonlinear
(in the current) magnetoresistivities ρ
⊥
+
and ρ
‖
−
.
Zh. éksp. Teor. Fiz. 116, 2103–2129 (December 1999) 相似文献
12.
R. F. Konopleva B. A. Borisov I. V. Nazarkin V. A. Chekanov 《Physics of the Solid State》1998,40(11):1777-1782
Changes in the temperature and dose dependences of I-V characteristics and of the critical current j
c of YBaCuO films on MgO and SrTiO3 substrates under neutron irradiation has been studied at 25–80 K. The transport properties of YBaCuO films on MgO (M1) and
SrTiO3 (S1) substrates were found to behave differently. It is shown that the M1 films have granular structure, and their transport
properties were considered within the concept of percolation over weak intergranular links. The S1 are single-crystal films,
and their properties are analyzed within a resistive-state theory associated with thermal activation of Abrikosov vortices.
It is shown that the degradation rate of the critical temperature T
c of S1 films is 3.5 times smaller than that of the M1 films. The dose dependence of j
c has an exponential character, j
c=j
c(0)exp(−kΦ), where k is related to the number of displaced atoms per neutron and is the same for the M1 and S1 films, irrespective of the irradiation
temperature. The pinning energy has been derived from the I-V characteristics and it has been found that the U/kT ratio lies within 20–25 and is independent of neutron flux. It is shown that the radiation-induced disorder changes the pinning
mechanism, from pinning at the boundaries of misoriented crystals to that at spatial inhomogeneities, apparently radiation
induced.
Fiz. Tverd. Tela (St. Petersburg) 40, 1961–1967 (November 1998) 相似文献
13.
M. A. Zelikman 《Physics of the Solid State》1997,39(11):1751-1755
A system of pancake vortices formed near the boundary of a sample in a monotonically increasing external magnetic field is
calculated with allowance for pinning due to the cellular structure of the medium for various values of the pinning parameter
I, which is proportional to the critical current of the junction and the cell diameter. The shortest distance from the outermost
vortex to the nearest neighbor is proportional to I
−11. It is shown that the pinning parameter has a critical value I
c separating two regimes with different types of critical states. For I<I
c the external magnetic field has a threshold value H
t(I), above which the field immediately penetrates the interior of the junction to an infinite distance. For I>I
c the magnetic field decays linearly from the boundary into the interior of the junction. The value obtained in the study,
I
c=3.369, differs from the value of 0.9716 postulated by other authors. The dependence of the slope of the magnetic field profile
near the boundary on I is determined. It is shown that the slope is independent of I in intervals 2πk<I<2πk+π.
Fiz. Tverd. Tela (St. Petersburg) 39, 1958–1963 (November 1997) 相似文献
14.
S. Okuma T. Ichimura H. Takeya K. Hirata 《Physica C: Superconductivity and its Applications》2009,469(15-20):1093-1095
We report on measurements of current–voltage (I–V) characteristics for YNi2B2C single crystals with weak pinning in various fields at 7.6 K. We find nonmonotonic, N-shaped I–V curves in a certain field region deep in the vortex solid phase. This behavior is anomalous, since there exists an intermediate I region where flow voltage V shows a decrease with increasing I (a driving force). While the exact nature remains unknown, this phenomenon suggests vortex motion (driving I) induced pinning. 相似文献
15.
Evidence that pinning on linear or planar defects dominates the vortex dynamics in YBa2Cu3O7−x (YBCO) films is provided by complex impedance measurements at temperature 8 K<T<T
c
and magnetic field 0<B<6 T. Below the vortex lattice melting transition Bg(T) but above a threshold field Bp≈8(1-T/T
c
) T, the inductance of vortices increases as B2, much less rapidly than predicted for collective pinning of vortices by point defects. Above the vortex melting line, critical
scaling persists over the region Bg(T<B<B*(T) where the vortex correlation length ξ exceeds a characteristic length scale ξ*≡ξ(B=B*)≈450?. The value of ξ* is not sensitive to Al-doping in the Cu sites in the lattice and is close to the size of twin domains in the film. The nature
of the observed crossovers is discussed in terms of available theoretical models for a glass-liquid transition at Bg. 相似文献
16.
We explore the effect of varying drive on metastability features exhibited by the vortex matter in single crystals of 2H-NbSe2 and CeRu2 with varying degree of random pinning. The metastable nature of vortex matter is reflected in the path dependence of the
critical current density, which in turn is probed in a contact-less way via AC-susceptibility measurements. The sinusoidal
AC magnetic field applied during AC susceptibility measurements appears to generate a driving force on the vortex matter.
In a nascent pinned single crystal of 2H-NbSe2, where the peak effect (PE) pertaining to the order—disorder phenomenon is a sharp first-order-like transition, the supercooling
feature below the peak temperature is easily wiped out by the reorganization caused by the AC driving force. In this paper,
we elucidate the interplay between the drive and the pinning which can conspire to make the path-dependent AC-susceptibility
response of different metastable vortex states appear identical. An optimal balance between the pinning and driving force
is needed to view the metastability effects in typically weakly pinned specimen of low temperature superconductors. As one
uses samples with larger pinning in order to differentiate the response of different metastable vortex states, one encounters
a new phenomenon, viz., the second magnetization peak (SMP) anomaly prior to the PE. Supercooling/superheating can occur across
both the PE and the SMP anomalies and both of these are known to display non-linear characteristics as well. Interplay between
the path dependence in the critical current density and the non-linearity in the electromagnetic response determine the metastability
effects seen in the first and the third harmonic response of the AC susceptibility across the temperature regions of the SMP
and the PE. The limiting temperature above which metastability effects cease can be conveniently located in the third harmonic
data, and the observed behavior can be rationalized within the Bean’s critical state model. A vortex phase diagram showing
different vortex phases for a typically weakly pinned specimen has been constructed via the AC susceptibility data in a crystal
of 2H-NbSe2 which shows the SMP and the PE anomalies. The phase space of coexisting weaker and stronger pinned regions has been identified.
It can be bifurcated into two parts, where the order and disorder dominate, respectively. The former part continuously connects
to the reentrant disordered vortex phase pertaining to the small bundle pinning regime, where the vortices are far apart,
interaction effects are weak and the polycrystalline form of flux line lattice prevails. 相似文献
17.
L. Ya. Vinnikov A. G. Troshina I. S. Veschunov D. Analytis I. R. Fisher Yu. Liu C. T. Lin L. Fang U. Welp W. K. Kwok 《JETP Letters》2013,96(10):655-658
Single crystals of iron-containing Ba(FeAs)2 superconductors doped with phosphorus have been studied. The vortex structure has been studied by means of the decoration method. Large domains of the triangular vortex structures have been observed in the phosphorus-doped single crystals of iron-containing superconductors. The effect of doping on pinning in iron-containing superconductors has been discussed. 相似文献
18.
The effect of γ irradiation on the mechanical characteristics and dislocation structure of slip bands in LiF crystals is studied at doses
D⩽7.3×108 R. Irradiation causes a substantial increase (up to a factor of 30) in the yield stress τ
y of the crystals, with τ
y ∝ D
0.4 in the first approximation. The deformation shear increases in the slip bands of irradiated crystals, as do the densities
of the screw and edge dislocation components, while the dislocation mean free paths decrease. Irradiation also raises the
probability of twinning cross slip for screw dislocations. The observed effects are assumed to be related to the formation
of a different kind of defects in the irradiated crystals, primarily clusters of implanted atoms.
Fiz. Tverd. Tela (St. Petersburg) 39, 1072–1075 (June 1997) 相似文献
19.
We examine theoretically the generation of electromagnetic radiation in the relative motion of vortex lattices in magnetically
coupled films in the dc transformer geometry. We establish the conditions under which the force of mutual pinning of the vortex
lattices varies according to a harmonic law as a function of the relative displacement of the vortices in the films within
a given range of magnetic field inductions. In this case the equation describing the viscous flow of vortex lattices in magnetically
coupled films is the same as the equation of the resistively shunted Josephson junction model. We show that magnetically coupled
superconductors exhibit the properties of a Josephson element without any restrictions on the geometrical size of such a system
imposed by the coherence length ξ. The frequency f of the electromagnetic radiation generated by the relative motion of vortex lattices in magnetically coupled superconductors
depends on the spatial period of the vortex lattices and the velocity of relative vortex motion, which means that the frequency
of the radiation can be tuned by applying a magnetic field or a current.
Zh. éksp. Teor. Fiz. 113, 1319–1338 (April 1998) 相似文献
20.
The vortex dynamics at microwave frequencies in YBa2Cu3O7-δ (YBCO) films have been studied. We observe a peak in the microwave (4.88 and 9.55 GHz) surface resistance in some films in
magnetic fields up to 0.8 T. This is associated with the ‘peak-effect’ phenomenon and reflects the order-disorder transformation
of the flux line lattice near the transition temperature. Introduction of artificial pinning centers like columnar defects
created as a result of irradiation with 200 MeV Ag ion (at a fluence of 4×1010 ions/cm2) leads to the suppression of the peak in films previously exhibiting ‘peak effect’. 相似文献