FeSeTe单晶中出现起始转变温度为146K的超导电性.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,Fe(SeTe),单晶中出现起始转变温度为,14.6K,的超导电性和过量,Fe,发挥的的作用40961056,赵旭鹏,Superconductivity at 14.6 K in Fe(SeTe)single crystal and the roleof excess Fe,JOURNAL OF APPLIED PHYSICS 110,033914(2011),直至今日，对于铜基超导材料的高温超导机制，物理学界仍未形成一致看法，这也使得高温超导成为当今凝聚态物理学中最大的谜团之一。

因此很多科学家都希望在铜基超导材料以外再找到新的高温超导材料，从而能够使高温超导机制更加明朗2008,年,Hosono,等发现,LaFeAsO,1-x,F,x,具有,26K,的超导转变之后，全世界掀起了一股铁基超导热Fe,1+y,Se,x,Te,1-x,体系具有结构简单、不含,As,、容易生长较高质量的单晶的优点研究背景,Single crystal was successfully grown by self-ux method,and effect of post-annealing technique on structure and superconelfductivity was also systemically studied.The results show the as-grown sample has an excellent superconductivity with an onset transition temperature Tc,onset,14.6 K and a zero resistivity temperature Tc,zero,13.4 K.After annealing at 400 C for 48 h,excess Fe in the post-annealing sample appears with Fe1.06Se0.34Te0.66 formula,and superconductivity was strongly suppressed with Tc,zero,8.0 K.The experiments found that excess Fe is located at Fe(2)site with local magnetic moment.,ABSTRACT,According to the Werthamer-Helfand-Hohenberg(WHH)theory,the upper critical elds H,c2,at zero temperature were estimated to be 54.2T for as-grown sample and 28.2 T for post-annealing sample.Two abnormal drops in DC magnetization are found near 40 K and 125 K for all samples,the one near 40K may be related to a spin freezing of excess Fe and that near 120K should be corresponding to the structural transition from tetragonal to monoclinic.This is conrmed by the strain measurement.On the other hand,a kink change of specic heat was also found around 10K for a post-annealed sample.,我们对采用自助溶剂法生长得到的,Fe,1.01,Se,0.38,Te,0.62,单晶和退火技术对于材料结构和超导电性的影响进行了系统的研究。

研究结果表明制备出的生成态晶体样品有着优良的超导特性，起始转变温度为,14.6 K,，零电阻率温度为,13.4 K.,在,400,下退火,48,小时,退火后样品中过量的,Fe,的比例为,Fe,1.06,Se,0.34,Te,0.66,，超导电性将明显出现在零电阻率温度,Tc,zero,=8.0 K,实验发现过量的,Fe,处于,Fe(2),位并造成局域磁矩根据,WHH,理论，在零电阻处的生成态样品上临界磁场估计达到了,54.2T,，退火后达到了,28.2 T,在所有样品的直流磁化曲线中发现了两个异常的下降，分别在,40K,到,125 K,40 K,附近的下降可能与过量的,Fe,的自旋冻结有关,而,117K,附近的下降应该对应于从正方到单斜的结构性转变这点通过应变测量得到了确认另一方面,在退火后的样品中，比热的扭结改变温度大约为,10k,左右摘要,The discovery of iron-based oxypnictide superconductor LaFeAsO,1-x,F,x,with Tc,=,26 K arouses a widespread interest of research.The transition,temperature has been raised up to 55 K in RE,FeAsO,1-x,F,x,(RE=Sm,Nd,Pr,Ce,and La,1111-family),followed by Tc=38 K in Ba,1-x,K,x,Fe,2,As,2,(122-family),Tc=18 K in LiFeAs(111-family),andTc=8.0 K in Fe1xSe,(11-family).,All iron-based superconductors share a common feature of,FeAs/(Se,Te)layers,which is similar to that of CuO2 in high temperature,cupratesuperconductors.,In general,there are several ways to grow single crystal samples,such as,Bridgman method,self-ux technique,and optical zone-melting technique.,INTRODUCTION,在,REFeAsO,1-x,F,x,(RE=Sm,Nd,Pr,Ce,La)(1111-,体系,),中，最,高超导转变温度达到,55K,，在,Ba,1-x,K,x,Fe,2,As,2,(122-,体系,),中超导温,度也达到了,38K,，同时在,LiFeAs(111-,体系,),以及,Fe,1+x,Se(11-,体系,),中也分别出现了,18K,以及,8 K,的超导现象。

与铜氧化物高温超导体相比，铁基超导体也具有类似于,CuO,2,的,FeAs/(Se,Te),层状结构，其作用是作为载流子的传导层不过与铜,氧化物母体从反铁磁型的,Mott,绝缘体中通过掺杂来产生超导电性不,同，铁基超导体更像是在抑制金属性基态后产生超导电性单晶生长的方法，包括,Bridgeman,方法、自助溶剂法和光学浮区,炉法等其中,Bridgeman,方法和光学浮区炉法生长得到样品的超导,体积分数比较小，而采用自助溶剂法可以较好地解决这个问题A single crystal of Fe1.01Se0.4Te0.6 with approximately 8 mm in diameter and 18 mm in length has been grown by self-ux method.The sample was prepared from stoichiometric quantities of iron powder(99.9 wt.%),selenium powder(99.99 wt.%),and tellurium powder(99.999 wt.%)with the nominal proportion of 1.01:0.4:0.6.The mixed powder wasn rst pressed into arod by using anisostatic press up to 60MPa,then sealed in double-walled evacuated quartz ampoules and sintered at 950 C for 48 h followed by cooling down to 600 C at a rate of 1 C per hour,and nally annealed at 400 C for 24 h.For comparison,a plate cleaved from the asgrown single crystal was annealed again at 400 C for 48 hrs.,EXPERIMENT,本实验所用单晶样品采用自助溶剂法生长，直径大约为,8mm,长度约为,18mm,。

将铁粉,(99%),、硒粉,(99.99%),和碲粉,(99.999%),按照,1.01:0.4:0.6,的配比在手套箱里混合研磨均匀；其次将研磨后的粉末在,60MPa,的等静压力下把粉末压成棒状，并将压成的棒封装到双层石英管里面，石英管内保护气体压强小于,5Pa,；随后将封装在双层石英管的样品在,950,保温,48,小时，然后以,1/,小时的速率降温至,600,，最后在,400,保温,24,小时取一小块剥离下来的样品在,400,进行,48,小时的退火后作为对比样品样品制备,点火损失测量 称重 混合 干燥 装料 空气驱除 压制 钻孔,绑丝 烘结 晶体生长 方向测定 切割抛光,光学浮区法流程：,The compositions were analyzed using energy dispersive x ray spectroscopy(EDX)attaching to eld emission scanning electron microscopy(FESEM,JEOLJSM-6700).Resistivity measurements were performed using a standard four-probe method on Physical Property Measurement System(PPMS-9 T,Quantum Design)from 3 K to 300 K and a magnetic eld up to 90 000 Oe.DC magnetization and specic heat measurements were carried out on PPMS-9 T.Strain measurement was 。