Synthesis and Physical Properties of Li_2Pd_3B and Li_2Pt_3B Superconductors

最近在两种含锂化合物Li_2Pd_3B和Li_2Pt_3B中发现了超导电性。在7.2K和2.6K的温度下，它们都表现出超导转变。它们的超导电性是由Li加成引起的。在电弧炉熔炼过程中，由于Li在高温下易挥发，控制Li化学计量比是合成高质量样品的关键。这些材料具有相同的立方结构(P4332)，在任何方向上都不具有镜像或反转对称性。这是这些材料的一个非常有趣的特征，与超导电性的对称性有关。测量了这些化合物的比热，以研究其超导性质。Li_2Pd_3B的索末菲系数(γ_n)和德拜温度(θ_D)分别为9.8mJmo1~(-1)和202K。ΔαγNTC，估值为1.6%。同样，Li_2Pt3B的这些参数被描述为9.6mJmol^&lt；01&gt；K^&lt；-2&gt；，240K和0.74。由于Δαγ理论的弱耦合极限的Ntc为1.43，因此Li_2Pd_3B的值稍高，而Li_2Pt_3B的值较低。电子比热(CES)是从整个比热中减去晶格比热得到的。得到的CES、Te以下的数据。在Li_2Pd_3B中，超导电性与BCS理论预测的指数(-1/7)有明显的相关性，而Li_2Pd-3B的CEs似乎不是指数行为，而是二次行为。这种二次行为表明在超导带隙中存在线节。这一结果支持点接触[1]和核磁共振[2]的测量结果。首页--期刊主要分类--期刊细介绍--期刊题录与文摘--期刊详细文摘内容97(2006年)017006.[2]M.西山，Y.稻田，G.郑，物理牧师莱特。98(2007年)047002.

Superconductivity has been recently found in two Li containing compounds, Li_2Pd_3B, and Li_2Pt_3B. They show superconducting transition at the temperatures, 7.2 K and 2.6 K, respectively. Their superconductivity is induced by Li addition. Controlling the Li stoichiometry is a key to synthesize high quality samples in the preparation process of arc-melting because Li is volatile at high temperatures. Those materials have the same cubic structure (P4332) which does not have mirror or inversion symmetry along any directions. It is a very interesting feature of those materials in relation to the symmetry of superconductivity. Specific heat of these compounds was measured for investigating superconducting properties. The Sommerfeld coefficient (γn) and Debye temperature (θD) of Li_2Pd_3B were given as 9.8 mJmo1^<-1>K^<-2> and 202 K respectively. The value of Δα γnTc, was estimated to be 1.6. In the same manner, those parameters were described for Li_2Pt_3B as 9.6 mJmol^<01>K^<-2>, 240 K, and 0.74. Since Δα γnTc in the weak-coupling limit by the BCS theory is 1.43, the value of 1.6 for Li_2Pd_3B is slightly higher, while the value for Li_2Pt_3B is lower. The electronic specific heat (Ces) was estimated by subtracting the lattice one from the entire specific heat. The obtained Ces, data below Te. in Li_2Pd_3B gives clearly exp (-1/7) dependence as predicted by the BCS theory for the superconductivity, while the Ces of Li_2Pt-3B seems not to reflect an exponential behavior but to reflect a quadratic behavior. The quadratic behavior suggests the existence of line nodes in the superconducting gap. This result supports the results of point contact [1] and NMR[2] measurements. [1]H.Q.Yuan D. F. Agterberg, N. Hayashi, P. Badica, D. Vandervelde, K. Togano, M. Sigrist, M. B. Salamon, Phys.Rev.Lett. 97 (2006)017006.[2] M. Nishiyama, Y. Inada, G.-q. Zheng, Phys.Rev.Lett. 98 (2007)047002.