共查询到20条相似文献,搜索用时 15 毫秒
1.
K. Behnia L. Taillefer J. Flouquet D. Jaccard K. Maki Z. Fisk 《Journal of Low Temperature Physics》1991,84(3-4):261-278
The thermal conductivity of the heavy-fermion superconductor UPt3 has been measured on two single crystals of different quality as a function of temperature and applied magnetic field for different orientations of the heat current relative to both the field and the crystalline axes. The temperature dependence of is far from exponential and nearly the same for both crystals, in which the heat current is, respectively, parallel and perpendicular to the hexagonalc axis, suggesting a gap structure with nodes in the basal plane and normal to it. The field dependence of is strongly anisotropic. In the best sample at low fields, where the scattering of heat carriers by vortices is thought to be important, (H) depends on the relative orientation of field and current. On the other hand, at high fields nearH
c2 (in both samples), (H) depends on the relative orientation of field and crystalline axes, reflecting an anisotropy in the gap structure and in the Fermi velocities. 相似文献
2.
K. Hasselbach A. Lacerda K. Behnia L. Taillefer J. Flouquet A. de Visser 《Journal of Low Temperature Physics》1990,81(5-6):299-315
The specific heat and thermal expansion of UPt3 were measured in the vicinity of the superconducting transition for magnetic fields up to 10 kOe, applied along the hexagonalc axis. Both thermodynamic techniques show clear evidence of two transitions in zero field, which merge at a critical field of approximately 8 kOe. The upper critical field curve determined by the resistivity for the upper transition exhibits a small but abrupt change of slope at a comparable value of the field. The phase diagram that emerges forHc is therefore qualitatively similar to that previously found forHc, this time with a critical point (or region) aroundH*=8 kOe,T*=0.36 K. The implications of a nearly isotropic phase diagram are discussed in connection with recent theories. 相似文献
3.
采用QM-1SP4-CL行星式球磨机将Mo、Cu粉简单混合和机械合金化后进行压片,在1250℃液相烧结1.5h后获得致密的Mo-30Cu合金;添加1.5%硬脂酸作造孔剂的Mo、Cu混合粉压片在1050℃固相烧结1.5h后获得孔隙率为33.186%的Mo-30Cu合金。利用激光热导仪测定所制备的Mo-30Cu合金的热导率。采用Maxwell模型、Hasselman and Johnson模型、单元结构模型和多相系统的传导性计算Mo-30Cu合金的理论热导率值。通过Mo-30Cu合金的热导率实测值与理论值的比较,得出适用于不同工艺状态的Mo-30Cu合金的热导率模型。 相似文献
4.
用于材料导热系数瞬态测量的数学模型 总被引:2,自引:0,他引:2
本文介绍了用于材料导热系数瞬态测量的两种数学模型。它们考虑到在实验过程中材料膨胀的影响。两个微分方程均适用于由大脉冲电流直接加热的细长型管状样品的瞬态实验。在第二个方程中 ,时空变量完全保持独立。它对于进行计算机模拟特别有效。 相似文献
5.
H. Suderow J. P. Brison A. Huxley J. Flouquet 《Journal of Low Temperature Physics》1997,108(1-2):11-30
We present new measurements of the thermal conductivity (κ) of UPt3 down to very low temperatures (16 mK) and under magnetic fields (up to 4 T) which cover all the superconducting phases of
UPt3. The measurements in zero field are compared with recent theoretical predictions for the thermal conductivity, which is dominated
by impurity states at the lowest temperatures studied. The measurements under magnetic field at low temperatures are surprising
since they don’t show the expected low field square root dependence,
. The discontinuity ofdκ/dT atT
c
changes drastically when passing from the high field low temperatureC phase to the low field high temperatureA phase: this is related to the change of the symmetry of the superconducting order parameter when crossing theA→C phase transition. 相似文献
6.
7.
We study the thermal conductivity within the E1g and E2u models for superconductivity in UPt3 and compare the theoretical results for electronic heat transport with recently measured results reported by Lussier, Ellman and Taillefer. The existing data down to T/Tc 0.1 provides convincing evidence for the presence of both line and point nodes in the gap, but the data can be accounted for either by an E1g or E2u order parameter. We discuss the features of the pairing symmetry, Fermi surface, and excitation spectrum that are reflected in the thermal conductivity at very low temperatures. Significant differences between the E1g and E2u models are predicted to develop at excitation energies below the bandwidth of the impurity-induced Andreev bound states. The zero-temperature limit of the axis thermal conductivity, limT0 kc/T, isuniversal for the E2u model, but non-universal for the E1g model. Thus, impurity concentration studies at very low temperatures should differentiate between the nodal structures of the E2u and E1g models. 相似文献
8.
P. Rodière S. Kambe A. D. Huxley J. Flouquet 《Journal of Low Temperature Physics》2002,128(5-6):251-261
The superconducting critical current along the c-axis of the unconventional superconductor UPt3 has been determined as a function of magnetic field direction in the basal (a-a*) plane in the three (A, B and C) phases of the mixed state. The critical current has maxima for field directions parallel to both the a- and a*-axis in the superconducting C phase, but has maxima only parallel to the a-axis in the A and B phases. Our experiments thus show that the anisotropy of the superconducting critical current in UPt3 changes at the same field at which the symmetry of the order parameter changes. This demonstrates for the first time that the critical current is sensitive to the symmetry of the superconducting order parameter. 相似文献
9.
10.
Thermal conductivity (k) of 0, 5, 10, and 15 wt.% aluminium nitride (n-AlN)-added polycrystalline MgB 2 superconductors, synthesized by solid reaction is discussed both in the normal and superconducting states between 20 and 300 K. The prepared samples are characterized using X-ray diffraction (XRD) and field electron gun scanning electron microscope (FEG–SEM). Resistivity measurement confirms a decrease in superconducting transition temperature of MgB 2 (T c=38.5 K) with n-AlN addition and decreases to ~35 K in case of 15 wt.% n-AlN-added MgB 2 sample. Thermal conductivity of both MgB 2 and n-AlN-added MgB 2 pellets does not show any hump around T c, and the absolute values of k decrease with increasing n-AlN in MgB 2. Temperature dependence of the thermal conductivity of MgB 2 and n-AlN-added MgB 2 has been analyzed, assuming the role of both electrons and phonons. The Wiedemann–Franz law does not work well for the present samples, which indicates inelastic scattering (L eff < L 0). Thermal conductivity of MgB 2 and n-AlN-added MgB 2 pellets is explained by assuming effective Lorentz number, L eff= 0.1 L 0. Electronic thermal conductivity in superconducting state ( \(k_{\text {el}}^{\mathrm {s}} )\) follows “two-gap model” and has been used to estimate the values of band gaps, relative contribution of each band in thermal transport, and intraband scattering relaxation time. The estimated values are fairly consistent with the previously reported results for MgB 2. We further confirm that n-AlN addition in MgB 2 introduces disorders in π bands, which reduce the π band gapsand intraband relaxation time ( \(\tau _{\pi }^{\text {im}})\) . The lattice contribution of thermal conductivity in both normal and superconducting states is analyzed in the terms of Callaway’s model, assuming various phonon scatterings. Our analysis indicates that the lattice thermal conductivity of MgB 2 is dominated by phonon-sheet-like fault scattering. Addition of n-AlN in MgB 2 enhances the phonon scattering from sheet-like faults, and dislocations induced strain field scattering by >7 times compared to that for pure MgB 2 pellets. 相似文献
11.
12.
H. Suderow S. Kambe J. P. Brison A. Huxley J. Flouquet F. Rullier-Albenque 《Journal of Low Temperature Physics》1999,116(5-6):393-405
The superconducting properties of the heavy fermion UPt
3
have been changed by irradiation with high energy electrons which creates point defects in a reproducible and controled way. Measurements of the residual resistivity, critical temperature, upper critical field and thermal conductivity have been realized on these irradiated samples. The strong suppresion of superconductivity with increasing defect concentration is in agreement with the theory of unconventional superconductivity. However, our thermal conductivity data contradicts the simple predictions derived from the most popular modelsE
1g
and E
2u) of the superconducting order parameter in UPt
3
. 相似文献
13.
K. Kamata K. Izawa Y. Nakajima Y. Matsuda T. Watanabe M. Nohara H. Takagi H. Takeya K. Hirata P. Thalmeier K. Maki 《Journal of Low Temperature Physics》2003,131(5-6):1095-1099
In order to determine the superconducting gap structure of the borocarbide superconductor YNi2B2C, we have measured the angular variation of the c-axis thermal conductivity
zz
in magnetic field rotated within the ab-planes. A clear fourfold symmetry with narrow cusps was observed in the angular variation of
zz
. These results provide a strong evidence that the gap function has point nodes which are located along the a- and b-axes of the crystal. 相似文献
14.
Fan Yu Gaosheng Wei Xinxin Zhang Kui Chen 《International Journal of Thermophysics》2006,27(1):293-303
Based on the microstructure features of xonotlite-type micro-pore calcium silicate, two unit cell models, the point-contact hollow spherical model and the surface-contact hollow cubic model, are developed. As one of several excellent insulation materials, xonotlite is represented as porous media with hollow spherical agglomerates. By one-dimensional heat conduction analysis using theunit cell, the effective thermal conductivity of xonotlite is determined. The results show that both of the models are in agreement with experimental data. The algebraic expressions based on the unit cell models can be used to calculate the effective thermal conductivity of porous media that have similar structure features as xonotlite.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China 相似文献
15.
H. Kitano R. Matsuo K. Miwa A. Maeda T. Takenobu Y. Iwasa 《Journal of Low Temperature Physics》2003,131(5-6):1251-1258
Superconductivity of A3C60 (A=K and Rb) is destroyed by the intercalation of neutral ammonia molecules, and is replaced by the antiferromagnetic ground state. These properties suggest the importance of the electronic correlation in fullerides, which have been believed to be simple BCS superconductors. By using a microwave cavity perturbation technique, we confirmed that the conductivity of the antiferromagnet (NH3)K3–x
Rb
x
C60 at 200 K is already 3–4 orders of magnitude smaller than those of superconductors, K3C60 and (NR3)
x
NaRb2C60, and that the antiferromagnetic compounds are insulators without metal-insulator transition at the Néel temperature. These results indicate that the Mott–Hubbard transition in the A3C60 systems is driven by a reduction of lattice symmetry from face-centered-cubic (fcc) to face-centered-orthorhombic (fco), rather than by the magnetic ordering. 相似文献
16.
J. A. Sauls 《Journal of Low Temperature Physics》1994,95(1-2):153-168
I discuss a phenomenological theory for the multiple superconducting phases of UPt3 that is based on an order parameter belonging to an orbital 2D representation of the hexagonal point group which is coupled to a weak symmetry breaking field. I show that (1) the existing H-T and P-T phase diagrams (including an apparent tetracritical point in the H-T plane for all field orientations), (2) the anisotropy of the upper critical field over the full temperature range, (3) the correlation between superconductivity and basal plane antiferromagnetism and (4) low-temperature power laws in the transport and thermodynamic properties can be explained qualitatively, and in many respects quantitatively, by an odd-parity, E2u order parameter with a pair spin projection of zero along the -axis. AFM ordering in the basal plane, which couples to the superconducting order parameter, acts as the symmetry breaking field that is responsible for both the apparent tetracritical point and the zero-field double transition. 相似文献
17.
A. Sulpice P. Gandit J. Chaussy J. Flouquet D. Jaccard P. Lejay J. L. Tholence 《Journal of Low Temperature Physics》1986,62(1-2):39-54
In the normal phase of UPt3, the magnetoresistivity is large and positive with the striking feature of a quasi-independence of the temperature and magnetic field terms; the thermoelectric power has aT
2 dependence and the susceptibility is almost constant up to 4 K. The superconducting transition is broadened and the specific heat jump is weak due to the strong anisotropy of its normal phase. FromT
c to 146 mK (the lowest experimental temperature), a largeT
2 contribution is observed in the specific heat, but the thermal conductivity has the same dependence only below 150 mK. These results are compared with the predictions given for polar odd-pairing superconductivity. 相似文献
18.
P. A. Reeves G. Tvalashvili S. N. Fisher A. M. Guénault G. R. Pickett 《Journal of Low Temperature Physics》2002,129(3-4):185-193
We report thermal conductivity measurements for normal phase liquid 3He inside 98 and 95% aerogels at dilution refrigerator temperatures (5 to 50 mK). In our measurements we use cylindrical samples of aerogel which have been fabricated inside quartz tubes. Each tube is enclosed at one end by a small chamber to which a known heat input is applied at a measured temperature. The other end is in an open volume of helium which is heat sunk to the refrigerator. Vibrating wire thermometry is used to measure the helium temperatures. The thermal conductivity measurements show clearly the effects of quasiparticle-impurity scattering, from which values of the mean free path are derived. These are 92 nm for the 98% aerogel and 56 nm for the 95% sample. 相似文献
19.
Hyejin Jang Christopher R. Ryder Joshua D. Wood Mark C. Hersam David G. Cahill 《Advanced materials (Deerfield Beach, Fla.)》2017,29(35)
ReS2 represents a different class of 2D materials, which is characterized by low symmetry having 1D metallic chains within the planes and extremely weak interlayer bonding. Here, the thermal conductivity of single‐crystalline ReS2 in a distorted 1T phase is determined at room temperature for the in‐plane directions parallel and perpendicular to the Re‐chains, and the through‐plane direction using time‐domain thermoreflectance. ReS2 is prepared in the form of flakes having thicknesses of 60–450 nm by micromechanical exfoliation, and their crystalline orientations are identified by polarized Raman spectroscopy. The in‐plane thermal conductivity is higher along the Re‐chains, (70 ± 18) W m?1 K?1, as compared to transverse to the chains, (50 ± 13) W m?1 K?1. As expected from the weak interlayer bonding, the through‐plane thermal conductivity is the lowest observed to date for 2D materials, (0.55 ± 0.07) W m?1 K?1, resulting in a remarkably high anisotropy of (130 ± 40) and (90 ± 30) for the two in‐plane directions. The thermal conductivity and interface thermal conductance of ReS2 are discussed relative to the other 2D materials. 相似文献
20.
Khem B. Thapa Sanjay Srivastava Sarika Tiwari 《Journal of Superconductivity and Novel Magnetism》2010,23(4):517-525
We show theoretically that the frequency range of photonic band gap of a hetero-structure which is made of a metallic photonic
and superconducting photonic crystal can be enlarged due to the combination of the reflection band properties of the superconductor–dielectric
(PC1) and metallic–dielectric (PC2) periodic structures. The transmittance and band structure of the considered structures
are calculated using simple transfer matrix method and the Bloch theorem. Beside this, we have also calculated the transmittance
of the superconducting photonic structure (PC1), metallic photonic structure (PC2) and heterostructure of metallic photonic
and superconductor photonic crystals (PC1/PC2) for TE and TM-mode at the different angles of incidence. 相似文献