文章信息/Info

Title:

Research Progress of Iron-Based Superconductors KxFe2-ySe2

文章編號:

1674—3962 (2013)09-0513-09

作者:

丁夏欣; 聞�；�

(南京大學(xué)物理學(xué)院 固體微結(jié)構(gòu)國家重點(diǎn)實(shí)驗(yàn)室 超導(dǎo)物理與材料研究中心,江蘇 南京 210093)

Author(s):

DING Xiaxin;  WEN Hai-Hu

(Center for Superconducting Physics and Materials, National Laboratory for Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093, China)

關(guān)鍵詞:

鐵基超導(dǎo); 高溫超導(dǎo)體; 相分離; 超導(dǎo)母體; KxFe2-ySe2

分類號:

TH142.8

DOI:

10.7502/j.issn.1674-3962.2013.09.01

文獻(xiàn)標(biāo)志碼:

A

摘要:

自2008年在F摻雜的LaOFeAs化合物中發(fā)現(xiàn)高達(dá)26 K的超導(dǎo)電性后，高溫超導(dǎo)研究迎來了新一輪熱潮。隨后一系列不同結(jié)構(gòu)的鐵基超導(dǎo)材料被發(fā)現(xiàn)，到目前為止，鐵基超導(dǎo)體的最高臨界溫度記錄為56 K。在2010年末，臨界溫度高達(dá)32 K的KxFe2-ySe2這一新的鐵硫族超導(dǎo)體被發(fā)現(xiàn)。與其他鐵磷族超導(dǎo)體相比，這個(gè)系統(tǒng)有著許多不同尋常的性質(zhì)。角分辨光電子譜實(shí)驗(yàn)與能帶結(jié)構(gòu)計(jì)算都表明此材料在費(fèi)米能附近沒有空穴型費(fèi)米面。這一性質(zhì)強(qiáng)烈地挑戰(zhàn)了被廣為接受的S( 超導(dǎo)配對圖像：理論物理學(xué)家提出在鐵基超導(dǎo)體中，電子在空穴型費(fèi)米面與電子型費(fèi)米面之間散射，通過交換反鐵磁自旋漲落來達(dá)到超導(dǎo)配對。不久之后，在此材料中又確定了相分離的性質(zhì)。其中一個(gè)主要的相是具有K2Fe4Se5結(jié)構(gòu)的反鐵磁絕緣相，另一個(gè)是少量的超導(dǎo)相。聞�；⑿〗M最近的一篇論文認(rèn)定了此材料的超導(dǎo)相以三維網(wǎng)絡(luò)狀的細(xì)絲形態(tài)存在，相關(guān)實(shí)驗(yàn)數(shù)據(jù)表明每8個(gè)Fe原子位置中存在1個(gè)空位，并由此提出超導(dǎo)的母體相是由Fe空位形成的這種有序平行四邊形結(jié)構(gòu)組成。本文比較全面的介紹了這一快速發(fā)展領(lǐng)域的研究進(jìn)展，包括晶體生長與淬火處理，F(xiàn)e空位有序與塊反鐵磁相，相分離與超導(dǎo)相的探索，配對對稱性與能隙結(jié)構(gòu)。本文的最后列舉了一些重要的問題，并且展望了將來的研究內(nèi)容。

Abstract:

Since the discovery in 2008 of superconductivity at 26K in fluorine-doped LaFeAsO, the research has been tuned to a new direction on high temperature superconductivity. So far, several types of iron-based superconductors with different structures have been discovered, with the highest transition temperature to date being 56K. By the end of 2010, the iron-chalcogenide superconductor KxFe2-ySe2 with Tc ~ 32K was discovered. This system shows a set of distinctive properties as compared with other iron-pnictide compounds. Both angle resolved photoemission spectroscopy experiments and band structure calculations indicate that the hole pockets are missing at the Fermi energy. This greatly challenges the widely perceived picture that the superconducting pairing is established by exchanging antiferromagnetic (AF) spin fluctuations and the electrons are scattered between the electron and hole pockets. Later, it was found that this material separates into two phases-a dominant AF insulating phase with a K2Fe4Se5 structure, and a minority superconducting phase. A recent paper of Hai-Hu Wen抯 group identifies a three-dimensional network of superconducting filaments within this material and present evidence for the existence of K2Fe7Se8 which may be the possible parent phase for superconductivity. This 278 phase has a Fe structure of a single Fe vacancy out of every eight Fe-sites arranged in a parallelogram structure. In this paper, we review the status of research in this rapidly growing field. Crystal growth and quenching technique, Fe-vacancy orders and the block-AF state, phase separation and the hunt for the superconducting phase, pairing symmetry and the gap structure are introduced and discussed. In the end, important issues are listed as perspective for future research