Abstract

Characteristics of the Josephson effect in Pb_0.6In_0.4/FeSe_0.4Te_0.6 point contacts with the current flowing parallel to ab plane of the iron chalcogenide crystal (with critical temperature T_c ≈ 15 K) have been studied. Dependences of the critical current I_c and amplitudes I_n of the first steps of current (Shapiro steps) in the current–voltage (I–V) characteristics (n = 0, 1, 2; I₀ = I_c) on the microwave power P (at frequency f = 7.6 GHz) and dependences of the characteristic voltage V_c(T) = I_cR_N (R_N being the normal state resistance) on the temperature T have been measured. It is found that the characteristics of contacts (I_c, R_N, V_c) obtained for initial parts of the I–V curves do not adequately describe the oscillations of current steps in the microwave radiation field. A method is proposed for determining the normalized microwave frequency Ω = 2πf(2eV_c/\(\hbar \))^–1 that provides quantitative description of the current oscillation steps in the framework of a resistive contact model and allows one to check that the Josephson superconducting current I_s is proportional to sin(aφ) (a = 1, 2), where φ is the phase difference of the order parameters. Comparison of the measured I_n(\(\sqrt P \)) curves to those calculated using the resistive model showed that I_s = I_csinφ, in agreement with the conventional s and s⁺⁺ symmetry of the order parameter in FeSe_0.4Te_0.6. It is established that V_c of the contacts studied is proportional to T in a wide temperature interval.

中文翻译：

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PbIn / Fe 1 – y Se 1 – x Te x点接触中的约瑟夫森效应：探测阶次参数对称性

摘要

在铅的约瑟夫逊效应特性_0.6在_0.4 / FESE _0.4碲_0.6与电流流动平行于点接触AB的铁硫族化物晶体的平面（与临界温度Ť _Ç ≈15 K）进行了研究。的临界电流的依赖性我_Ç和振幅我_Ñ的在电流-电压的电流（夏皮罗步骤）第一步骤（我- V）特性（Ñ ; = 0，1，2余₀ =我_Ç对微波）功率P（在频率f＝ 7.6GHz下）和特征电压V _c（T）＝I _c R _N（R _N为常态电阻）对温度T的依赖性已被测量。结果发现接触的特性（我_Ç，- [R _Ñ，V _Ç为的初始部分而获得）我- V曲线不充分地描述的在微波辐射场电流的步骤的振荡。提出了确定归一化微波频率Ω=2π的方法f（2 eV _c / \（\ hbar \））– ¹提供电阻性接触模型框架中电流振荡步骤的定量描述，并允许人们检查约瑟夫森超导电流I _s与sin（a φ）（a  = 1，2），其中φ是阶数参数的相位差。所测量的比较我_Ñ（\（\ SQRT P \） ）曲线的那些使用计算出的电阻模型表明，我_小号=我_Ç sinφ，与传统协议小号和小号FeSe _0.4 Te _0.6中有序参数的⁺⁺对称性。已经确定，V _Ç研究的触点的正比于Ť在较宽的温度间隔。