1Institute of Physics, Chinese Academy of Sciences, Beijing 100190 2Department of Physics and Texas Center for Superconductivity, University of Houston, Houston 77004, USA 3Collaborative Innovation Center of Quantum Matter, Beijing 100190 4Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050
Abstract：In CaFe$_{2}$As$_{2}$, superconductivity can be achieved by applying a modest $c$-axis pressure of several kbar. Here we use scanning tunneling microscopy/spectroscopy (STM/S) to explore the STM tip pressure effect on single crystals of CaFe$_{2}$As$_{2}$. When performing STM/S measurements, the tip-sample interaction can be controlled to act repulsive with reduction of the junction resistance, thus to apply a tip pressure on the sample. We find that an incoherent energy gap emerges at the Fermi level in the differential conductance spectrum when the tip pressure is increased. This energy gap is of the similar order of magnitude as the superconducting gap in the chemical doped compound Ca$_{0.4}$Na$_{0.6}$Fe$_{2}$As$_{2}$ and disappears at the temperature well below that of the bulk magnetic ordering. Moreover, we also observe the rhombic distortion of the As lattice, which agrees with the orthorhombic distortion of the underlying Fe lattice. These findings suggest that the STM tip pressure can induce the local Cooper pairing in the orthorhombic phase of CaFe$_{2}$As$_{2}$.
Kreyssig A, Greeen M A, Lee Y, Samolyuk G D, Zajdel P, Lynn J W, Bud'ko S L, Torikachvili M S, Ni N, Nandi S, Leao J, Poulton S J, Argyriou D N, Harmon B N, McQueeney R J, Canfield P C and Goldman A I 2008 Phys. Rev. B 78 184517
[8]
Proke? K, Kreyssig A, Ouladdiaf B, Pratt D K, Ni N, Bud'ko S L, Canfield P C, McQueeney R J, Argyriou D N and Goldman A I 2010 Phys. Rev. B 81 180506(R)
Goko T, Aczel A A, Baggio-Saitovitch E, Bud'ko S L, Canfield P C, Carlo J P, Chen G F, Dai P C, Hamann A C, Hu W Z, Kageyama H, Luke G M, Luo J L, Nachumi B, Ni N, Reznik D, Sanchez-Candela D R, Savici A T, Sikes K J, Wang N L, Wiebe C R, Williams T J, Yamamoto T, Yu W and Uemura Y J 2009 Phys. Rev. B 80 024508
Huang Y B, Richard P, Wang J H, Wang X P, Shi X, Xu N, Wu Z, Li A, Yin J X, Qian T, Lv B, Chu C W, Pan S H, Shi M and Ding H 2013 Chin. Phys. Lett.30 017402
[13]
Li A, Yin J X, Wang J H, Wu Z, Ma J H, Sefat A S, Sales B C, Mandrus D G, Jin R Y, Zhang C L, Dai P C, Lv B, Liang X J, Hor P H, Ting C S and Pan S H 2016 arXiv:1602.04937 [cond-mat.supr-con]
Evtushinsky D V, Zabolotnyy V B, Harnagea L, Yaresko A N, Thirupathaiah S, Kordyuk A A, Maletz J, Aswartham S, Wurmehl S, Rienks E, Follath R, Büchner B and Borisenko S V 2013 Phys. Rev. B 87 094501
[16]
Chuang T M, Allan M P, Lee J, Xie Y, Ni N, Bud'ko S L, Boebinger G S, Canfield P C and Davis J C 2010 Science327 181
WANG Qing-Yan1,2, LI Zhi2, ZHANG Wen-Hao1, ZHANG Zuo-Cheng1, ZHANG Jin-Song1, LI Wei1, DING Hao1, OU Yun-Bo2, DENG Peng1, CHANG Kai1, WEN Jing1, SONG Can-Li1, HE Ke2, JIA Jin-Feng1, JI Shuai-Hua1, WANG Ya-Yu1, WANG Li-Li2, CHEN Xi1, MA Xu-Cun2**, XUE Qi-Kun1**. Interface-Induced High-Temperature Superconductivity in Single Unit-Cell FeSe Films on SrTiO3[J]. 中国物理快报, 2012, 29(3): 37402-037402.
2016, Vol. 33 
