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1.
Mg10±δIr19B16δ是具有非中心对称性的超导材料. 通过对两种组分的样品Mg9.3Ir19B16.7和Mg11Ir19B15的比热测量, 得到了这类超导体的超导态和正常态的特征参数:包括转变温度TC, 正常态态密度N(EF), 德拜温度ΘD, 上临界场HC2等. 并由此求出Ginzburg-London相干长度ξGL, 穿透深度λGL, 下临界场HC1和热力学临界场HC. 这些参数因化学组分不同而变化. 高的N(EF)和ΘD对应高的TC, 因此也具有较高的HC2. 另外比热跃变ΔC/γnTC=1.66 和电声子耦合常数λ=0.58不随化学组分变化, 表明此超导体是中等强度耦合的第二类超导体.
关键词:
非中心对称超导体
比热 相似文献
2.
利用格林函数方法,通过Klemm-Clem变换,计算具有正交晶格结构椭球形费米面的手性ABM态p波超导体上临界磁场的角依赖关系.超导序参量选取具有手性ABM对称性的等自旋配对单分量形式.当椭球形费米面满足一定条件时,上临界磁场随角度呈现非单调变化,表明除配对电子有效质量的各向异性外,手性ABM态p波超导体也具有超导序参量的各向异性.计算结果可用于判断重费米子超导体Sr2RuO4的配对电子空间结构. 相似文献
3.
采用密度泛函理论中的赝势平面波方法研究了高压下超导材料 ErNi2B2C 的弹性性质、电子结构和热力学性质.分析表明, 弹性常数、体弹模量、剪切模量、杨氏模量和弹性各向异性因子的外压力效应明显. 电子态密度(DOS)的计算结果显示, 在费米能级(EF)处的 DOS 峰随外界压强的增大显著降低, 由于 ErNi2B2C 相对较高的超导温度(Tc)起因于EF处的 DOS 峰, 因此推测压强增大可能会降低 ErNi2B2C 的 Tc.类似的现象在超导材料 MgB2和 SrAlSi 中已被发现.此外, 基于准谐德拜模型, 对 ErNi2B2C 在高温高压下的热力学性质的研究表明, 在一定范围内, 温度和压强将对其热膨胀系数和热容产生明显的影响.
关键词:
高压
弹性性质
电子结构
热力学性质 相似文献
4.
在强关联电子体系中,轨道、自旋和晶格等自由度之间的相互作用一直是研究的热点.这些自由度之间的竞争和共存产生了复杂新奇的物理现象,如超导现象、量子相变、自旋有序、拓扑相变、金属绝缘转变等,这些丰富的物理现象来源于不同的有序态或量子涨落之间的竞争和耦合.自旋轨道耦合作用是指粒子的自旋角动量和轨道角动量之间的相互作用,在4d/5d基化合物中,由于电子的运动速度较快,自旋轨道耦合的效应不可忽视,可能表现出与3d基化合物不同的物性.例如,在含4d/5d过渡族金属元素的超导体中,其电子配对的机制可能不同于常规的s波Bardeen-Cooper-Schrieffer超导体.本文以几种典型的4d/5d基超导体为例,对其晶体结构和超导物性及其内在联系进行了详细论述,重点探讨了阴离子共价键强弱对晶体结构、相变和超导物性的影响,希望引起相关研究者对该类超导体的重视. 相似文献
5.
6.
通过混合物理化学气相沉积法 (hybrid physical-chemical vapor deposition, HPCVD), 在(000l) SiC 衬底上制得一系列从10 nm到8 μm的MgB2超导膜样品, 并对它们的形貌、超导转变温度Tc 和临界电流密度Jc与膜厚度的关系进行了研究. 观察到Tc随膜厚度增加上升到最大值后, 尽管膜继续增厚, 但Tc值保持近乎平稳, 而Jc则先随膜厚度增加上升到最高值后, 继而则随膜的厚度的增加而下降. MgB2膜的Tc(0)和Tc(onset)值与膜厚的关系基本一致, Tc(0)在膜厚为230 nm处达到最大值Tc(0)=41.4 K, 而Jc(5K,0T)在膜厚为100 nm时达到最大值, Jc (5 K, 0 T)=2.3×108A·cm-2, 这也说明了我们能用HPCVD方法制备出高质量干净MgB2超导膜. 本文研究的超导膜厚度变化跨度非常大, 从10 nm级的超薄膜到100 nm级的薄膜, 再到几微米的厚膜, 如此Tc和Jc对膜厚度变化的依赖就有了较完整、成体系的研究. 并且本文的工作对MgB2超导薄膜制备的厚度选取具有实际应用意义.
关键词:
2超导膜')" href="#">MgB2超导膜
混合物理化学气相沉积法
厚度
临界电流密度 相似文献
7.
8.
用Mg/B多层膜退火的方法制备了一系列MgB2超导薄膜,研究了退火温度、退火时间和薄膜厚度对于MgB2薄膜性质的影响.厚度为250 nm的Mg/B多层膜经400 ℃低温退火后已经生成超导相,此厚度薄膜750 ℃下退火20—30 min实现最佳超导转变温度(Tc).前驱膜分层厚度相同时,随着薄膜厚度减小MgB2薄膜Tc明显降低,而且较薄的膜Tc
关键词:
2超导薄膜')" href="#">MgB2超导薄膜
电子束蒸发
超导成相 相似文献
9.
应用不可约张量理论构造了三角对称晶场中3d2/3d8态离子的45阶可完全对角化的微扰哈密顿矩阵,研究了CsNiCl3晶体的光谱精细结构、晶体结构、零场分裂参量、Jahn-Telller效应以及自旋单重态对Ni2+离子基态能级的影响,理论与实验相符合.在此基础上,进一步研究了以前工作中被忽略的自旋-自旋耦合作用和Trees修正对CsNiCl3晶体的光谱精细结构和零场分裂参量的影响,发现有四种机理会影响零场分裂参量:1)自旋-轨道耦合机理,2)自旋-自旋耦合机理;3)自旋-轨道与自旋-自旋联合耦合机理;4)自旋-轨道与Trees修正联合耦合机理,其中自旋-轨道耦合机理是最主要的,其他三种机理也是不可忽略的.
关键词:
基态能级
精细结构
零场分裂
自旋-自旋耦合 相似文献
10.
11.
K. Yada S. Onari Y. Tanaka 《Physica C: Superconductivity and its Applications》2009,469(15-20):991-994
We study possible pairing symmetries of non-centrosymmetric superconductors in the Hubbard model with the Rashba-type spin–orbit interaction (RSOI). Because of the breakdown of space inversion symmetry due to RSOI, a mixture of pairing states with different symmetries can emerge. We find that the RSOI mixes not only the spin-singlet even-parity pairing and spin-triplet odd-parity pairings with even-frequency symmetry, but it also mixes the spin-singlet odd-parity pairing and spin-triplet even-parity pairings with odd-frequency symmetry. 相似文献
12.
Yuichiro Shimokaji Seiichiro Onari Kazumasa Miyake 《Journal of Physics and Chemistry of Solids》2008,69(12):3280-3282
It is an important issue to clarify whether the odd-frequency superconducting state can be derived from microscopic Hamiltonian or not, where gap function has an odd-parity in frequency. We study the instability of following four superconducting states: (1) even-frequency spin-singlet, (2) even-frequency spin-triplet, (3) odd-frequency spin-singlet and (4) odd-frequency spin-triplet. By using the fluctuation exchange (FLEX) approximation on a triangular and square lattice, we find that the odd-frequency spin-triplet pairing can become dominant at a certain region where the suppression of the antiferromagnetic fluctuation due to a geometric frustration becomes prominent. 相似文献
13.
We present a general theory of the proximity effect in junctions between diffusive normal metals (DN) and superconductors. Various possible symmetry classes in a superconductor are considered: even-frequency spin-singlet even-parity (ESE) state, even-frequency spin-triplet odd-parity state, odd-frequency spin-triplet even-parity (OTE) state and odd-frequency spin-singlet odd-parity state. It is shown that the pair amplitude in a DN belongs, respectively, to an ESE, OTE, OTE, and ESE pairing state since only the even-parity s-wave pairing is possible due to the impurity scattering. 相似文献
14.
P. A. Frigeri D. F. Agterberg I. Milat M. Sigrist 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):435-448
In materials without an inversion center of symmetry the spin
degeneracy of the conducting band is lifted by an antisymmetric
spin orbit coupling (ASOC). Under such circumstances, spin and
parity cannot be separately used to classify the Cooper pairing
states. Consequently, the superconducting order parameter is
generally a mixture of spin singlet and triplet pairing states. In
this paper we investigate the structure of the order parameter and
its response to disorder for the most symmetric pairing state
(A1). Using the example of the heavy Fermion superconductor
CePt3Si, we determine characteristic properties of the
superconducting instability. Depending on the type of the
pairing interaction, the gap function is characterized
by the presence of line nodes. We show that this line nodes move in general
upon temperature.
Such nodes would be essential to explain recent low-temperature
data of thermodynamic quantities such as the NMR-T1
-1,
London penetration depth, and heat conductance.
Moreover, we study the effect of (non-magnetic) impurity on the superconducting state. 相似文献
15.
R. Gonczarek L. Jacak M. Krzyzosiak A. Gonczarek 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(2):171-186
Based upon the tight-binding formalism a model of a
high-Tc superconductor with isotropic and anisotropic
attractive interactions is considered analytically. Symmetry
facets of the group C4v are included within a method of
successive transformations of the reciprocal space. Complete sets
of basis functions of C4v irreducible representations are
given. Plausible spin-singlet and spin-triplet superconducting
states are classified with regard to the chosen basis functions. It
is displayed that pairing interaction coefficients and the
dispersion relation, which can be characterized by the parameter
η= 2t1/t0, have a diverse and mutually competing
influence on the value of the transition temperature. It is also
shown that
in the case of a nearly half-filled conduction band
and an anisotropic pairing interaction the spin-singlet
d-wave symmetry superconducting state is realized for
small values of the parameter η, whereas in the opposite
limit, for sufficiently large values, the spin-triplet
p-wave symmetry superconducting state has to be formed.
This result cannot be obtained within the Van Hove scenario or
BCS-type approaches, where the p-wave symmetry
superconducting state absolutely dominates. The specific heat jump
and the isotope shift as functions of the parameter η are
assessed and discussed for the d-wave symmetry singlet and
the p-wave symmetry triplet states. 相似文献
16.
Superconductivity in materials without spatial inversion symmetry is studied. We show that in contrast to common belief, spin-triplet pairing is not entirely excluded in such systems. Moreover, paramagnetic limiting is analyzed for both spin-singlet and -triplet pairing. The lack of inversion symmetry reduces the effect of the paramagnetic limiting for spin-singlet pairing. These results are applied to MnSi and CePt3Si. 相似文献
17.
Yuan HQ Agterberg DF Hayashi N Badica P Vandervelde D Togano K Sigrist M Salamon MB 《Physical review letters》2006,97(1):017006
We investigate the order parameter of noncentrosymmetric superconductors Li2Pd3B and Li2Pt3B via the behavior of the penetration depth lambda(T). The low-temperature penetration depth shows BCS-like behavior in Li2Pd3B, while in Li2Pt3B it follows a linear temperature dependence. We propose that broken inversion symmetry and the accompanying antisymmetric spin-orbit coupling, which admix spin-singlet and spin-triplet pairing, are responsible for this behavior. The triplet contribution is weak in Li2Pd3B, leading to a wholly open but anisotropic gap. The significantly larger spin-orbit coupling in Li2Pt3B allows the spin-triplet component to be larger in Li2Pt3B, producing line nodes in the energy gap as evidenced by the linear temperature dependence of lambda(T). The experimental data are in quantitative agreement with theory. 相似文献
18.
We show that finite angular momentum pairing chiral superconductors on the triangular lattice have point zeroes in the complex gap function. A topological quantum phase transition takes place through a nodal superconducting state at a specific carrier density x(c) where the normal state Fermi surface crosses the isolated zeros. For spin-singlet pairing, we show that the second-nearest-neighbor (d+id)-wave pairing can be the dominant pairing channel. The gapless critical state at x (c) approximately 0.25 has six Dirac points and is topologically nontrivial with a T3 spin relaxation rate below T(c). This picture provides a possible explanation for the unconventional superconducting state of Na(x)Co O(2). yH(2)O. Analyzing a pairing model with strong correlation using the Gutzwiller projection and symmetry arguments, we study these topological phases and phase transitions as a function of Na doping. 相似文献
19.
Exotic superconducting properties of have provided strong support for an unconventional pairing symmetry. However, the extensive efforts over the past decade have not yet unambiguously resolved the controversy about the pairing symmetry in this material. While recent phase-sensitive experiments using flux modulation in Josephson junctions consisting of and a conventional superconductor have been interpreted as conclusive evidence for a chiral spin-triplet pairing, we propose here an alternative interpretation. We show that an overlooked chiral spin-singlet pairing is also compatible with the observed phase shifts in Josephson junctions and propose further experiments which would distinguish it from its spin-triplet counterpart. 相似文献
20.
We report (11)B and (195)Pt NMR measurements in noncentrosymmetric superconductor Li(2)Pt(3)B. We find that the spin susceptibility measured by the Knight shift remains unchanged across the superconducting transition temperature T(c). With decreasing temperature (T) below T(c), the spin-lattice relaxation rate 1/T(1) decreases with no coherence peak and is in proportion to T3. These results indicate that the Cooper pair is in the spin-triplet state and that there exist line nodes in the superconducting gap function. They are in sharp contrast to those in the isostructural Li(2)Pd(3)B which is a spin-singlet, s-wave superconductor, and are ascribed to the enhanced spin-orbit coupling due to the lack of spatial inversion symmetry. Our finding points to a new paradigm where exotic superconductivity arises in the absence of electron-electron correlations. 相似文献