共查询到20条相似文献,搜索用时 31 毫秒
1.
We have studied the peak effect (PE) phenomenon in single crystals of weakly pinned superconductors CeRu 2 and 2H-NbS 2. 2H-NbS 2 is iso-structural and iso-electronic to 2H-NbSe 2, whose similarity with CeRu 2 as regards the PE representing the order-to-disorder transformation of the flux line lattice was claimed some time ago. We
report on the step change in equilibrium magnetization across the peak effect in CeRu 2. We also present the vortex phase diagram of 2H-NbS 2 obtained from the magnetization data, and compare the PE phenomenon in 2H-NbS 2 and 2H-NbSe 2. 相似文献
2.
We explore the effect of varying drive on metastability features exhibited by the vortex matter in single crystals of 2H-NbSe 2 and CeRu 2 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-NbSe 2, 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-NbSe 2 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
3.
Low-temperature specific heat in a dichalcogenide superconductor 2H-NbSe2 is measured in various magnetic fields. It is found that the specific heat can be described very well by a simple model concerning two components corresponding to vortex normal core and ambient superconducting region, separately. For calculating the specific heat outside the vortex core region, we use the Bardeen-Cooper Schrieffer (BCS) formalism under the assumption of a narrow distribution of the superconducting gaps. The field-dependent vortex core size in the mixed state of 2H-NbSe2, determined by using this model, can explain the nonlinear field dependence of specific heat coefficient γ(H), which is in good agreement with the previous experimental results and more formal calculations. With the high-temperature specific heat data, we can find that, in the multi-band superconductor 2H-NbSe2, the recovered density of states (or Fermi surface) below Tc under a magnetic field seems not to be gapped again by the charge density wave (CDW) gap, which suggests that the superconducting gap and the CDW gap may open on different Fermi surface sheets. 相似文献
4.
We present a study of magnetization measurements performed on the single crystals of YNi 2B 2C and LuNi 2B 2C. For both the compounds, we find flux jumps in magnetisation values in the respective field regions, where the structural
transitions in the flux line lattice symmetry have been reported in these systems via the small angle neutron scattering experiments.
The magnetisation hysteresis loops and the AC susceptibility measurements show pronounced peak effect as well as second magnetisation
peak anomaly for both YNi 2B 2C and LuNi 2B 2C. Based on these results, a vortex phase diagram has been constructed for YNi 2B 2C for H∥c depicting different glassy phases of the vortex matter. 相似文献
5.
We have studied metastability effects pertaining to the peak effect (PE) in critical current density ( J
c) via isofield scans in AC susceptibility measurements in a weakly pinned single crystal of Yb 3Rh 4Sn 13 ( T
c(0) ≈ 7.6 K). The order-disorder transition in this specimen proceeds in a multi-step manner. The phase coexistence regime
between the onset temperature of the PE and the spinodal temperature (where metastability effects cease) seems to comprise
two parts, where ordered and disordered regions dominate the bulk behavior, respectively. The PE line in the vortex phase
diagram is argued to terminate at the low field end at a critical point in the elastic (Bragg) glass phase. 相似文献
6.
Resistance ratios of crystals of 2H-NbSe 2 grown with and without iodine were measured over the temperature range 6K–40K. Iodine-free crystals had higher ratios than any NbSe 2 previously reported and exhibited an abrupt anomaly at the onset of the charge density wave phase. All crystals displayed a cubic temperature dependence of their resistivities below 18K. 相似文献
7.
We have studied the order–disorder transition in high quality MgB 2 single crystals, using a torque magnetometry combined with a ‘vortex shaking’ technique. In the wide range of temperature T, field H and the H direction, we succeed in obtaining reversible magnetization curves Mrev( T, H) by shaking the pinned vortices. Especially at low temperatures below 25 K and high fields, where the irreversible magnetization curve exhibits the peak effect due to the order–disorder transition, it is found that the peak is transformed into the clear step in Mrev( H). Similar step-like behavior is also observed in the temperature dependence of magnetization Mrev( T). These results give direct evidence that the order–disorder transition, which is hidden by the large hysteresis of magnetization, has the nature of first-order transition. 相似文献
8.
New experimental data are presented on the scan rate dependence of the magnetization hysteresis width ΔM( H) (∞ critical current density J
c( H)) in isothermal MH scans in a weakly pinned single crystal of Ca 3Rh 4Sn 13, which displays second magnetization peak (SMP) anomaly as distinct from the peak effect (PE). We observe an interesting
modulation in the field dependence of a parameter which purports to measure the dynamical annealing of the disordered bundles
of vortices injected through the sample edges towards the destined equilibrium vortex state at a given H. These data, in conjunction with the earlier observations made while studying the thermomagnetic history dependence in J
c( H) in the tracing of the minor hysteresis loops, imply that the partially disordered state heals towards the more ordered state
between the peak field of the SMP anomaly and the onset field of the PE. The vortex phase diagram in the given crystal of
Ca 3Rh 4Sn 13 has been updated in the context of the notion of the phase coexistence of the ordered and disordered regions between the
onset field of the SMP anomaly and the spinodal line located just prior to the irreversibility line. A multi-critical point
and a critical point in the ( H,T) region of the Bragg glass phase have been marked in this phase diagram and the observed behavior is discussed in the light
of recent data on multi-critical point in the vortex phase diagram in a single crystal of Nb. 相似文献
9.
We have performed extensive small-angle neutron scattering (SANS) diffraction studies of the vortex lattice in single crystal
YNi 2B 2C for B‖ c. High-resolution SANS, combined with a field-oscillation vortex lattice preparation technique, allows us to separate Bragg
scattered intensities from two orthogonal domains and accurately determine the unit cell angle, β. The data suggest that upon increasing field there is a finite transition width where both low- and high-field distorted
hexagonal vortex lattice phases, mutually rotated by 45°, coexist. The smooth variation of diffracted intensity from each
phase through the transition corresponds to a redistribution of populations between the two types of domains. 相似文献
10.
使用牛津震动样品磁强计(VSM)研究了Bi 2Sr 2CaCu 2O 8单晶的磁滞回线.在20到40K温度之间发现了反常的尖锋效应,随样品O含量的增加,发生尖锋效应的外场也相应提高.可以认为在尖峰效应处发生了由涡漩物质的有序固态到无序固态的相变,在有少量点缺陷存在的BSCCO单晶相图上,B sp线终止于20K温度处,在20K以下温区没有发生准格子到涡漩玻璃的相变,涡漩固相始终以准格子形式存在;可以认为尖峰效
关键词:
2Sr 2CaCu 2O 8单晶')" href="#">Bi 2Sr 2CaCu 2O 8单晶
磁滞回线
尖锋效应
相变 相似文献
11.
The dynamical phase transitions in two-dimensional fully frustrated Josephson junction arrays at zero temperature are investigated numerically with the resistively shunted junction model through the fluctuating twist boundary condition. The model is subjected to a driving current with nonzero orthogonal components i
x
, i
y
parallel to both axes of the square lattice. We find a roughly lattice size independent phase diagram with three dynamical phases: a pinned vortex lattice phase, a moving vortex lattice phase and a moving plastic phase. The phase diagram shows a direct transition from the pinned vortex to the moving vortex phase and the separation of the pinned vortex and the moving plastic phases. The time-dependent voltages v
x
and v
y
are periodic in the moving vortex lattice phase. But they are aperiodic in the moving plastic phase, resulting in non-monotonic characteristics and hysteresis in the current-voltage curves. It is found that the characteristic frequency is twice the time-averaged voltage in the moving vortex phase and around the time-averaged voltage in the plastic flow regime.Received: 29 May 2003, Published online: 2 October 2003PACS:
64.60.Ht Dynamic critical phenomena - 74.25.Sv Critical currents - 74.25.Fy Transport properties 相似文献
12.
测量了Bi 2Sr 2CaCu 2O 8单晶的ab面和c轴方 向电阻,在其超导转变温度附近发现了反常的电阻峰出现.其随外磁场(>100Gs)和电流的增 加而逐渐消失.文章认为这个反常的电阻峰是由于单晶中超导相的不均匀分布而导致的准再 进入行为.
关键词:
2Sr 2CaCu 2O 8单晶')" href="#">Bi 2Sr 2CaCu 2O 8单晶
反常电阻峰
准再入行为 相似文献
13.
Previous work on Ba 2TiGe 2O 8 crystals has shown an unusual low-temperature (~ 223 K on cooling, ~ 273 K on heating) phase transition. Precession x-ray photographs on Ba 2TiGe 2O 8 single crystals show an incommensurate modulation along b*, and, for the first time, also along a*. Single crystal intensity data confirm the average structure in space group Cmm2. There is positional disorder in the pyrogermanate groups, and this is the probable cause for the modulated structure. The low-temperature phase transition is proposed to be a lock-in transition, with the modulation along a* locking in at a value of 1/3. Several properties, as well as other unusual features of the low-temperature phase transition, are discussed in light of the proposed lock-in transition. Domain studies show that the ferroelastic domains are unstable in the low-temperature phase. 相似文献
14.
A glass model of vortex pinning in highly disordered thin superconducting films in magnetic fields B ≪ Hc2 at low temperatures is proposed. Strong collective pinning of a vortex system realized in disordered superconductors that are close to the quantum phase transition to the insulating phase, such as InOx, NbN, TiN, MoGe, and nanogranular aluminum, is considered theoretically for the first time. Utilizing the replica trick developed for the spin glass theory, we demonstrate that such vortex system is in non-ergodic state of glass type with a large kinetic inductance per square LK. The distribution function of local pinning energies is calculated, and it is shown that it possesses a wide gap; i.e., the probability to find a weakly pinned vortex is extremely low. 相似文献
15.
We present the results for thermal expansion coefficients of Sn 2P 2S 6 crystals determined both in the crystallographic system and the system based on eigenvectors of thermal expansion tensor. Peculiarities of temperature evolution of the indicative surface of thermal expansion tensor for Sn 2P 2S 6 are discussed, including the region of their ferroelectric phase transition. 相似文献
16.
Good-quality hexagonal NbSe 2 single crystals were prepared. In 2H-NbSe 2, superconducting and charge density wave (CDW) transitions were found at T
s = 7.4 K and T
c = 35 K respectively as reported previously. We have noticed that these two transitions are changed to T
c = 42 K and T
s = 6.5 K, in 4H-NbSe 2. Thermopower has shown clear anomaly at CDW transitions. The anisotropic upper critical field was calculated as ~3 and 6.3
for 2H- and 4H-single crystals around t = 0.81, where t = T/ T
s, from resistivity and explained in terms of coherence length. From the relation, Hc2 ( T)= Hc2 (0)[1- t2]H_{\rm c2} (T)=H_{\rm c2} (0)[1-t^2], Hc2l (0)H_{\rm c2}^l (0) was calculated as ~8.15 T and 16.98 T at t = 0.84 in 2H-NbSe 2 and 4H-NbSe 2 respectively. However, Hc2t (0) = 2.68H_{\rm c2}^t (0) = 2.68T for both single crystals. 相似文献
17.
We have performed a series of neutron diffraction experiments from the magnetic order and the vortex lattice in single crystal
ErNi 2B 2C. The incommensurate magnetic structure develops additional even harmonics below the ‘ferromagnetic’ ordering temperature,
T
F of 2.3 K. This feature and the existence of rods of diffuse scattering suggest the development of ferromagnetic microdomain
walls. The magnetic structure is very sensitive to the application of a magnetic field with changes in modulation vector and
harmonic content. Studies of the vortex lattice show the presence of a 45° reorientation transition and a distorted hexagonal
to square transition as a function of applied field. Further distortions of the vortex lattice occur at T
N, but no changes are seen at T
F. 相似文献
18.
A comparative study of the thermomagnetic memory effects of J
c in two weakly pinned low T
c superconductors, Ca 3Rh 4Sn 13 (CaRhSn) and Yb 3Rh 4Sn 13 (YbRhSn), is presented. In both the systems, the peak effect (PE) phenomenon appears as an order-disorder transformation
through stepwise amorphization of the flux line lattice (FLL). However, in CaRhSn. we can witness another disorder-driven
transition (Bragg glass (BG) to a vortex glass (VG) in a distinct manner as in a single crystal of high T
c YBa 2Cu 3O 7-δ for H‖ c. 相似文献
19.
Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization
in very pure twinned and twin-free NdBa 2 Cu 3 O y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half
the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within
the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure. 相似文献
20.
We observed an unconventional parity-violating vortex in single domain Sr 2RuO 4 single crystals using a transport measurement. The current–voltage characteristics of submicron Sr 2RuO 4 show that the induced voltage has anomalous components which are even functions of the bias current. The results may suggest that the vortex itself has a helical internal structure characterized by a Hopf invariant (a topological invariant). We also discuss that the hydrodynamics of such a helical vortex causes the parity violation to retain the topological invariant. 相似文献
|