共查询到20条相似文献,搜索用时 31 毫秒
1.
The resultant Seebeck coefficient α of the touching p- and n-type Cu/Bi–Te/Cu composites with different thicknesses of t
Bi–Te and t
Cu was measured as a function of t, where t
Bi–Te was varied from 0.1 to 2.0 mm, t
Cu from 0.3 to 4.0 mm and t is the lapse time after imposing the voltage. The temperature difference ΔT is produced by imposing a constant voltage of 1.70 V on two Peltier modules connected in series. The resultant α of composites
was calculated from the relation α = ΔV/ΔT, where ΔV and ΔT were measured with two probes placed on both end coppers. ΔV decreases abruptly with an increase of t below t = 5 min, while above t = 7 min, it tends to saturate to a constant value. The resultant α and saturated ΔV vary significantly with changes in t
Cu and t
Bi–Te. When a composite has a combination of t
Cu = 1.0 mm and t
Bi–Te=0.1 mm, the generating powers ΔW (=(ΔV)2/4R) estimated using the saturated ΔV and calculated electrical resistance R for the p- and n-type composites have great local maximum values which are 4–5 times as large as those obtained for the conventional
combination of t
Bi-Te = 2.0 mm and t
Cu = 0.3 mm. It is surprising that the generating power ΔW is enhanced significantly by sandwiching a very thin Bi–Te material between two thick coppers, unlike the conventional composition
of thermoelectric modules. On the other hand, when a composite has a combination of t
Bi–Te = 0.1 mm and t
Cu = 0.3 mm, the resultant α of the p- and n-type composites exhibited great values of 711 and −755 μV/K, respectively, so that
the maximum resultant ZT of the p- and n-type composites reached extremely large values of 8.81 and 5.99 at 298 K. However, the resultant ZT decreases rapidly with an increase of t
Cu or t
Bi–Te. The resultant ZT is thus found to be enhanced significantly not only in superlattice systems but also in macroscopic composites. The present
enhancement in ZT is attributed to the large barrier thermo-emf generated in the Bi–Te region shallower than 50 μm from the boundary. 相似文献
2.
V. M. H. Ruutu Ü. Parts J. H. Koivuniemi N. B. Kopnin M. Krusius 《Journal of Low Temperature Physics》1997,107(1-2):93-164
We report on the first comprehensive measurements of critical superflow velocities in3He-B which allow different mechanisms of vortex formation to be identified. As a function of temperatureT and pressureP, we measure the critical angular velocity Ωc(T, P) at which vortices start to form in slowly accelerating rotation in a cylindrical container filled with3He-B. Owing to the long coherence length ξ(T, P)∼10–100 nm, either trapped remanent vorticity or intrinsic nucleation may dominate vortex formation, depending on the roughness
of the container wall and the presence of loaded traps.
NMR measurement with a resolution of one single vortex line allows us to distinguish between different processes: (1) Three
extrinsic mechanisms of vortex formation have been observed. One of them is the vortex mill, a continuous periodic source
which is activated in a rough-walled container well below the limit for intrinsic nucleation. (2) In a closed smooth-walled
container intrinsic nucleation is the only mechanism available, with a critical velocity vc(T, P)=Ωc(T, P), whereR is the radius of the container. We findv
c
(T, P) to be related to the calculated intrinsic stability limitv
ch
(T, P) of homogeneous superflow. The existence of this connection in the form of a scaling law implies that nucleation takes place
at an instability, rather than by thermal activation or quantum tunneling which become impossible because of an inaccessibly
high energy barrier. 相似文献
3.
R. de Graaf R. Hänninen T. V. Chagovets V. B. Eltsov M. Krusius R. E. Solntsev 《Journal of Low Temperature Physics》2008,153(5-6):197-227
A profound change occurs in the stability of quantized vortices in externally applied flow of superfluid 3He-B at temperatures ?0.6?T c, owing to the rapidly decreasing damping in vortex motion with decreasing temperature. At low damping an evolving vortex may become unstable and generate a new independent vortex loop. This single-vortex instability is the generic precursor of turbulence. We investigate the instability with non-invasive NMR measurements on a rotating cylindrical sample in the intermediate temperature regime (0.3–0.6)?T c. From comparisons with numerical calculations we interpret that the instability occurs at the container wall, when the vortex end moves along the wall in applied flow. 相似文献
4.
The thermo-emf ΔV of the touching p- and n-type Cu/Bi-Te/Cu composites with different thicknesses of t
Bi-Te and t
Cu was measured as a function of time by alternating the temperature difference ΔT at periods of T = 20, 60, 120, 240 and ∞ sec, where t
Bi-Te was varied from 0.1 to 2.0 mm and t
Cu from 0 to 4.0 mm. As a result, ΔV changes significantly with t
Bi-Te, t
Cu and T. The effective thermo-emf ΔV
eff increases significantly with an increase of 1/T and exhibited a local maximum at 1/T = 1/240 s−1. The resultant | α | and the effective temperature difference ΔT
eff were increased significantly by optimizing t
Bi-Te and t
Cu at 1/T = 1/240 s−1. The power generation ΔW
eff (= ΔV
eff2/4R
calc) estimated using the measured ΔV
eff and calculated R
calc also exhibited a local maximum at 1/240 s−1 for an optimum combination of t
Bi-Te = 0.1 mm and t
Cu = 2.0 mm, so that the maxima ΔW
eff at 1/T = 1/240 s−1 for the p- and n-type composites were 2.28 and 2.92 times higher than those obtained at 1/T = 0 s−1. This significant increase in ΔW
eff is owing to both the increase in ΔT
eff and the increase in ZT due to the increase in |α|. The power generation was thus found to be enhanced significantly by imposing the alternating
temperature gradients on touching Cu/Bi-Te/Cu composites. 相似文献
5.
The voltage ΔV and electric current ΔI of the p- and n-type Cu/Bi–Te/Cu composite thermoelectric devices were measured as a function of ΔT for four regions of the intrinsic Bi–Te compound, Cu/Bi–Te and Bi–Te/Cu interfaces and Cu/Bi–Te/Cu composite using thermocouples
set at intervals of s = 2 and 6 mm, where the lengths of Bi–Te compound and copper are 4 and 5 mm, respectively. ΔV and ΔI of all regions tended to increase linearly with an increase of ΔT. The resultant α was obtained from the relation ΔV/ΔT. The resultant α values of regions including the interface are much higher in absolute value than those of the intrinsic
Bi–Te compounds, so that the barrier thermo-emf is found to occur in the forward-bias direction. It indicates that the barrier
thermo-emf appears even in the semiconductor-metal junction, as in the case of the p–n junctions. The resultant α of Cu(T
H)/Bi–Te interface rich in the heat flow increases with an increase of ΔT, while that of Bi–Te/Cu(T
C
) interface poor in the heat flow decreases with an increase of ΔT. The ΔT-dependence of α of the interfaces is entirely opposite at the hot and cold sides. As a result, the resultant α of the p-
and n-type Cu/Bi–Te/Cu composites remained little varied with changes of ΔT, so that the present composites have a thermal stability superior to the intrinsic Bi–Te compounds.The generating powers
ΔW
Bi-Te and ΔW
Cu/Bi-Te/Cu for the p- and n-type intrinsic Bi–Te compounds and Cu/Bi–Te/Cu composites increased parabolalically with an increase of
ΔT, and the ratios of ΔW
Cu/Bi–Te/Cu to ΔW
Bi–Te reached great values of 1.41 and 1.45 for the p- and n-type composites, respectively. It was thus found that the enhancement
in the resultant α of the composite materials results in a significant improvement in the conversion efficiency for generators. 相似文献
6.
Changes in Curie temperature (ΔT
c, electrical resistivity (Δϱ/ϱ) and volume (ΔV/V) caused by isochronal annealing in as-quenched and pre-annealed Fe27Ni53P14B6 metallic glasses were compared. It was found that the ΔT
c against annealing temperature (T
a) curves in as-quenched and pre-annealed samples are very similar to the Δϱ/ϱ against T
a curves. Particularly, almost a linear relationship was observed between ΔT
c and Δϱ/ϱ in the pre-annealed sample. The results strongly suggest that the origins of both ΔT
c and Δϱ/ϱ during structural relaxation in the pre-annealed sample are attributed to identical, reversible, short-range ordering. 相似文献
7.
G. R. Somayajulu 《International Journal of Thermophysics》1988,9(4):567-575
Two new equations are proposed for the enthalpy of vaporization from the triple point to the critical point. One of these equations containing four parameters is exceptionally good for fitting the data. The other equation containing three parameters is quite adequate for fitting the data but it is exceptionally suited for interpolation when the data do not cover the entire range. These equations have been tested using the enthalpy of vaporization of water from the triple point to the critical point and are compared with other equations.Nomenclature
T
c
Critical temperature, K
-
T
t
Triple point, K
-
T
x
Any particular temperature, K
-
T
r
Reduced temperature
-
P
r
Reduced pressure
-
R
Gas constant
-
P
Vapor pressure
-
X
(T
c–T)/T
c
-
Y
(T
c–T)/T
-
X
x
(T
c–T)/(T
c–T
x)
-
X
t
(T
c–T)/(T
c–T
t)
-
H
vt
Enthalpy of vaporization at the triple point, kJ · mol–1
-
H
vx
Enthalpy of vaporization at any temperature x, kJ · mol–1
-
Z
v
Compressibilty factor of the saturated vapor
-
Z
1
Compressibilty factor of the saturated liquid Relative deviation = 100[Hv(obs)–Hv(cal)]/Hv(obsd) Standard deviation = { [H
v(obs)–H
v(cal)]2/(No. points — No. parameters)}0.5 相似文献
8.
Shubhra Kakani M. L. Kalra S. L. Kakani 《Journal of Superconductivity and Novel Magnetism》2008,21(3):177-185
A microscopic coexistence of itinerant ferromagnetism and superconductivity is studied in a single- band homogeneous system,
using an equation of motion method and Green’s function technique. Self-consistent equations for the superconducting order
parameter Δ and magnetization m are derived. It is shown that there generally exists coexistent (Δ≠0 and
m≠0) solutions to the coupled equations of the order parameters in the temperature range 0<T<min (T
c
,T
FM
), where T
c
and
T
FM
are respectively the superconducting and ferromagnetic transition temperatures. The expressions for specific heat, density
of states, free energy, and critical field are also derived. The theory is applied to explain the observations in ZrZn2. The agreement between the theory and experimental observations is quite satisfactory.
相似文献
9.
D. I. Bletskan I. I. Madyar S. V. Mikulaninets M. Yu. Sichka 《Inorganic Materials》2000,36(6):544-550
Thermally stimulated currents and anisotropic electrical conductivity are studied in GeS layered crystals prepared by the
Bridgman-Stockbarger, Pizzarello, and sublimation techniques. All the crystals arep-type, regardless of the growth technique, owing to the presence of Ge vacancies. The conductivity anisotropy in the melt-grown
crystals is high compared to the vapor-grown GeS. The anisotropy rises exponentially with temperature. The concentrations
and ionization energies of traps in GeS crystals are determined from thermally stimulated current curves. The spectral response
of the photocurrent through the crystals prepared by sublimation, whose structural perfection is higher than that of the melt-grown
crystals, is governed by the spectral dependence of the absorption coefficient forad ≪ 1 (near-edge region) and by the spectral dependence of reflectivity for αd > 1 (high-α region). Regardless of the growth technique, the 293-K photocurrent spectra of GeS crystals show strongly polarized
peaks at 1.65 (E ∥a) and 1.78 eV (E ∥b), which are due to the Λ
1
v
→ Λ
1
c
and Δ
2
v
→ Δ
2
c
optical transitions. The low-temperature photoresponse athv < 1.7 eV is due to absorption by Si impurity. 相似文献
10.
A procedure for estimating the critical temperature T
c
and width ΔT
c
for the superconducting transition of high-temperature superconductor materials based on plotting the first derivative of
the temperature correlation dependence of the electrical resistance of a sample is developed. The critical point of the derivative
corresponds to T
c
, and its width at half-height corresponds to ΔT
c
. The procedure provides a decrease in the relative error of estimation of T
c
and ΔT
c
for qualitative samples by a factor of 1.7–2. 相似文献
11.
The thermo-emf ΔV and temperature difference ΔT across the boundary were measured as functions of r and I for the touching p- and n-type Cu/Bi–Te/Cu composites composed of t
Bi–Te = 2.0 mm and t
Cu = 0.3 mm, where r is the distance from the boundary and I is a direct current producing ΔT which flows through two Peltier modules connected in series. The resultant Seebeck coefficient α across the boundary is obtained
from the relation α = ΔV/ΔT. As a result, the resultant |α| of the touching p- and n-type composites have a great local maximum value at r ≈ 0.03 mm and decrease rapidly with further increase of r to approach the intrinsic |αBi–Te|. The maximum resultant α of the p- and n-type composites reached great values of 1,043 and −1,187 μV/K at 303 K corresponding
to I = 0.8 A and of 1,477 and −725 μV/K at 360 K corresponding to I = 2.0 A. Reflecting the temperature dependence of the intrinsic αBi–Te, the maximum α of the p-type composite increases with an increase of T, while that of the n-type one decrease with an increase of T. Surprisingly, the maximum α of the p- and n-type composites have great gradients of 8.36 and −7.15 μV/K2 in the range from 303 to 366 K, respectively, which are 21.8 and 134 times larger in absolute value than 0.383 and −0.0535 μV/K2 of the intrinsic p- and n-type αBi–Te, so that the maximum resultant α was thus found to be much more sensitive to temperature than the intrinsic αBi–Te. Moreover, the local Seebeck coefficient α
l
(r) derived analytically from the resultant α(r) is enhanced significantly in the narrow region below r ≈ 0.05 mm and the maximum α
l
values of the p- and n-type composites were found to have extremely great values of approximately 1,800 μV/K at 360 K and
−1,400 μV/K at 303 K, respectively, which are approximately 7.3 and 6.5 times higher in absolute value than the intrinsic
p- and n-type αBi–Te at the corresponding temperatures. 相似文献
12.
D. L. Bashlakov Yu. G. Naidyuk I. K. Yanson G. Behr S. -L. Drechsler G. Fuchs L. Schultz D. Souptel 《Journal of Low Temperature Physics》2007,147(3-4):335-352
Point-contact (PC) spectroscopy measurements of YNi2B2C single crystals in the normal and superconducting (SC) state (T
c
≃ 15.4 K) for the main crystallographic directions are reported. The PC study reveals the electron–phonon interaction (EPI)
spectral function with dominant phonon maximum around 12 meV and further weak structures (hump or kink) at higher energy at
about 50 meV. No “soft” modes below 12 meV are resolved in the normal state. The PC EPI spectra are qualitatively similar
for the different directions. Contrary, directional study of the SC gap results in Δ{[100] ≈ 1.5 meV for the a direction and Δ{[001] ≈ 2.3 meV along the c axis; however the critical temperature T
c in PC in all cases is near to that in the bulk sample. The value 2Δ[001]/k
B
T
c ≈ 3.6 is close to the BCS value of 3.52, and the temperature dependence Δ[001](T) is BCS-like, while the for small gap Δ[100](T) is below BCS behavior at T > T
c
/2 similarly as in the two-gap superconductor MgB2. It is supposed that the directional variation Δ can be attributed to a multiband nature of the SC state in YNi2B2C. 相似文献
13.
Z. Ferhat-Hamida H. Phuong-Nguyen P. Bernazzani A. Haine G. Delmas 《Journal of Materials Science》2007,42(9):3138-3154
LLDPE samples synthesized with Ziegler–Natta (ZN) and Metallocene (MT) catalysts have been analyzed to investigate a potential
catalyst-dependent morphology and to find an explanation for the difficult processing of MT. Slow calorimetry at v = 0.02 K/min and IR at RT and in the melt are used. The differences between MT and ZN are assigned to their different composition,
MT not having the linear segments, which are present in ZN. Slow calorimetry is effectively a drawing process of the melt
with chain orientation followed by decay. The later event, characterized by an endotherm, ΔH
network, occurs at higher temperatures for MT, the presence of a regular distribution of methyl groups slowing down the process.
The rocking, gauche, bending and stretching regions of the IR spectra are analyzed. The nascent MT has more strained bands
in the rocking region. The wagging region reveals the more homogeneous environment of MT through the maximum absorbance at
1,368 cm−1. Decomposition of bands is made for the rocking and wagging regions. The orthorhombic crystallinity, αc (FTIR), measures the sum of long- and short-range orthorhombic order, the latter being obtained by αc (FTIR)-αc (X-rays). The values of αc (FTIR) for MT and ZN are very similar in conditions of equilibrium. The justifications for the molecular origin of ΔH
network are presented: (i) the slow relaxation of long chains strained and oriented in the melt measured by other techniques, (ii)
The correlation, for gels of a linear sample, made in different solvents, between the maximum drawability, λmax, and ΔH
network in a slow T-ramp. The range is 80–270 for λmax and 40–120 J/g for ΔH
network. (iii) The comparison of two traces of the same sample, between 140 °C and 270 °C, show that comparable events in the melt
appear in the integrated absorbance and in the slow calorimetry signal. Analysis on thin films of the little-studied CH2 stretching region reveals that their extinction coefficient, ε, and the shape of the bands are highly sensitive to the sample
history, ε diminishing by a large factor in slowly crystallized samples. Events in the slow T-ramp, followed by a fast crystallization, on the other hand, leads to materials with standard characteristics. Slow calorimetry
traces display more events (endothermic and exothermic) for MT than for ZN, a finding consistent with more flow irregularities
during processing. Equilibrium conditions and better processing could be reached for MT by extending time in the melt or using
higher temperatures. 相似文献
14.
Satoshi Sasaki Atsuyoshi Nakayama Yutaka Sasaki Takao Mizusaki 《Journal of Low Temperature Physics》2008,151(5-6):1113-1148
We have measured the temperature and magnetic-field dependences of the sound velocity for one longitudinal and two transverse
waves in the low field phase (LFP) and the high field phase (HFP) of nuclear spin ordered bcc solid 3He crystals with a single magnetic domain along the melting curve. From sound velocity measurements for various crystal orientations
as a function of the sound propagation direction, we determined the elastic stiffness constants, c
ij
(T,B). In the LFP with tetragonal symmetry for the nuclear spin structure, we extracted six nuclear spin elastic stiffness constants
Δc
ij
ℓ
(T,0.06 T) from the temperature dependence of the sound velocity at 0.06 T and Δc
ij
ℓ
(0.5 mK,B) from the magnetic-field dependence of sound velocity at 0.5 mK. In the HFP with cubic symmetry for the nuclear spin structure,
we extracted three Δc
ij
h
(T,0.50 T) at 0.50 T and Δc
ij
h
(0.5 mK,B) at 0.5 mK. At the first-order magnetic phase transition from the LFP to the HFP at the lower critical field B
c1, large jumps in sound velocities were observed for various crystal directions and we extracted three
. Using the thermodynamic relation between Δc
ij
and the change in the internal energy for the exchange interaction in this system, ΔU
ex(T,B), Δc
ij
are related to the generalized second-order Grüneisen constants Γ
ij
X
≡∂
2ln X/∂
ε
i
∂
ε
j
as Δc
ij
(T,B)=Γ
ij
X
ΔU
ex(T,B), where X represents some physical quantity which depends on the molar volume and ε
j
is the j-th component of a strain tensor. In the LFP, the Δc
ij
ℓ
(T,0.06 T) were proportional to T
4, and Δc
ij
ℓ
(0.5 mK,B) were proportional to B
2. We extracted
for the spin wave velocity in the LFP, s
ℓ
, from Δc
ij
ℓ
(T,0.06 T) and
for the inverse susceptibility, 1/χ
ℓ
from Δc
ij
ℓ
(0.5 mK,B). In the HFP, Δc
ij
h
(T,0.50 T) were proportional to T
4 and Δc
ij
h
(0.5 mK,ΔB) were proportional to ΔB(≡B−B
c1). We obtained
for the spin wave velocity in the HFP, s
h
, from Δc
ij
h
(T,0.50 T) and
for B
c1 from Δc
ij
h
(0.5 mK,ΔB). The values obtained for
and
were compared with the Multiple Spin Exchange model (MSE) with three parameters by using analytic expressions for s
ℓ
and χ
ℓ
. The three-parameter MSE does not agree with the observed Δc
ij
in the LFP.
相似文献
15.
H. Kubo Y. Nago A. Nishijima K. Obara H. Yano O. Ishikawa T. Hata 《Journal of Low Temperature Physics》2013,171(5-6):466-472
An oscillating obstacle generates quantum turbulence in superfluids, when vortices remained attached to obstacle surfaces or vortex rings collided with it during oscillation. Turbulence provides a source of vortices; however, the characteristics of these vortices are not clear. In the present work, we report the flight of vortices emitted from quantum turbulence in superfluid 4He at low temperatures, using vibrating wires as a generator and a detector of vortices. A vortex-free vibrating wire can detect only the first colliding vortex ring, though it will be refreshed after low vibration and be able to detect a vortex ring again. By measuring a period from the start of turbulence generation to the vortex detection repeatedly, we find an exponential distribution of time-of-flights with a non-detection period t 0 and a mean detection period t 1, suggesting a Poisson process. Both periods t 0 and t 1 increase with increasing distance between a generator and a detector. A vortex flight velocity estimated from period t 0 suggests that the sizes of the emitted vortex rings distribute to a range smaller than a generator thickness or a generator vibration amplitude. Vortices are emitted radially from a turbulence region, at least in the direction of oscillator vibration. 相似文献
16.
N.-C. Yeh A. D. Beyer M. L. Teague S.-P. Lee S. Tajima S. I. Lee 《Journal of Superconductivity and Novel Magnetism》2010,23(5):757-765
The low-energy excitations of cuprate superconductors exhibit various characteristics that differ from those of simple Bogoliubov
quasiparticles for pure
dx2-y2d_{x^{2}-y^{2}}
-wave superconductors. Here, we report experimental studies of spatially resolved quasiparticle tunneling spectra of hole-
and electron-type cuprate superconductors that manifest direct evidences for the presence of competing orders (COs) in the
cuprates. In contrast to conventional type-II superconductors that exhibit enhanced local density of states (LDOS) peaking
at zero energy near the center of field-induced vortices, the vortex-state LDOS of YBa2Cu3O7−δ
(Y-123) and La0.1Sr0.9CuO2 (La-112) remains suppressed inside the vortex core, with pseudogap (PG)-like features at an energy larger (smaller) than
the superconducting (SC) gap ΔSC in Y-123 (La-112). Energy histograms of the SC and PG features reveal steady spectral shifts from SC to PG with increasing
magnetic field H. These findings may be explained by coexisting COs and SC: For hole-type cuprates with PG above T
c, the primary CO gap (V
CO) is larger than ΔSC and the corresponding COs are charge/pair-density waves with wave-vectors parallel to (π,0)/(0,π). For electron-type cuprates without PG above T
c, V
CO is smaller than ΔSC and the CO wave-vector is along (π,π). This CO scenario may be extended to the ARPES data to consistently account for the presence (absence) of Fermi arcs in
hole- (electron)-type cuprates. Fourier transformation of the vortex-state LDOS in Y-123 further reveals multiple sets of
energy-independent wave-vectors due to field-enhanced pair- and spin-density waves. These results imply important interplay
of SC with low-energy collective excitations. 相似文献
17.
Following the equation of motion method and Green’s function technique, the coexistence of itinerant ferromagnetism (FM) and
superconductivity (SC) is investigated in a single band homogeneous system. Self-consistent equations for superconducting
order parameter (Δ) and magnetic order parameter (ΔFM) are derived. It is shown that there generally exists a coexistent (Δ≠0 and ΔFM≠0) solutions to the coupled equations of the order parameter in the temperature range 0<T<min (T
C,T
FM) where T
C and T
FM are respectively the superconducting and ferromagnetic transition temperatures. Expressions for the specific heat, density
of states and free energy are derived. The specific heat has a linear temperature dependence at low temperatures as opposed
to the exponential decrease in the BCS theory. The density of states for a finite ΔFM increases as opposed to that of a standard ferromagnetic metal. The free energy shows that the superconducting ferromagnetic
state has lower energy than the normal ferromagnetic state and therefore is realized at low enough temperature. The theory
is applied to explain the observations of URhGe. The agreement between theory and experimental results is quite satisfactory.
相似文献
18.
Topological defects such as vortices subsist for some time in a rapidly frozen superconducting film (W. H. Zurek, Phys. Rep.
276, 177, 1996). We propose to use as a probe of the vortex density the finite delay T
d, which, in narrow strips, exists between a current step and the voltage response. Technically, this amounts to driving a bridge into the localized hot-spot regime by means of a pump pulse (laser or electrical). Cooling of such films as epitaxial YBCO-on-MgO, or niobium-on-sapphire, requires only a few nanoseconds at low T. A time t later, a probe pulse is applied to measure T
d. The dependence t T
d is interpreted as a witness of the fossil vorticity, long after quenching into the zero-resistance regime. 相似文献
19.
We have simulated the decay of thermal counterflow quantum turbulence from a statistically steady state at T=1.9 K, with the assumption that the normal fluid is at rest during the decay. The results are consistent with the predictions of the Vinen equation (in essence the vortex line density decays as t ?1). For the statistically steady state, we determine the parameter c 2, which connects the curvature of the vortex lines and the mean separation of vortices. A formula connecting the parameter χ 2 of the Vinen equation with c 2 is shown to agree with the results of the simulations. Disagreement with experiment is discussed briefly. 相似文献
20.
A. E. Koshelev 《Journal of Low Temperature Physics》2005,139(1-2):111-125
In presence of the Josephson vortex lattice in layered superconductors, small c-axis magnetic field penetrates in the form
of vortex chains. In general, structure of a single chain is determined by the ratio of the London [λ] and Josephson [λ
J
] lengths, α=λ/λ
J
. The chain is composed of tilted vortices at large α's (tilted chain) and at small α's it consists of crossing array of Josephson
vortices and pancake-vortex stacks (crossing chain). We study chain structures at the intermediate α's and found two types
of phase transitions. For α≲0.6 the groud state is given by the crossing chain in a wide range of pancake separationsa≳[2−3]λ
J
. However, due to attractive coupling between deformed pancake stacks, the equilibrium separation can not exceed some maximum
value depending on the in-plane field and α. The first phase transition takes place with decreasing pancake-stack separation
a ata≳[1−2]λ
J
, and rather wide range of the ratio α, 0.4≲α≲0.65. With decreasing a, the crossing chain goes through intermediate strongly-deformed
configurations and smoothly transforms into the tilted chain via the second-order phase transition. Another phase transition
occurs at very small densities of pancake vortices,a ~ [20−30]λ
J
, and only when α exceeds a certain critical value ∼0.5. In this case small c-axis field penetrates in the form of kinks.
However, at very small concentration of kinks, the kinked chains are replaced with strongly deformed crossing chains via the
first-order phase transition. This transition is accompanied by a very large jump in the pancake density. 相似文献