Chin. Phys. Lett.  2016, Vol. 33 Issue (06): 067401    DOI: 10.1088/0256-307X/33/6/067401
Tip-Pressure-Induced Incoherent Energy Gap in CaFe$_{2}$As$_{2}$
Jia-Xin Yin1,2, Ji-Hui Wang2, Zheng Wu2, Ang Li2,4, Xue-Jin Liang1, Han-Qing Mao1, Gen-Fu Chen1, Bing Lv2, Ching-Wu Chu2, Hong Ding1,3, Shu-Heng Pan1,2,3**
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
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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$_{2}$.
Received: 07 April 2016      Published: 30 June 2016
PACS:  74.55.+v (Tunneling phenomena: single particle tunneling and STM)  
  74 (Superconductivity)  
  74.62.Fj (Effects of pressure)  
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Jia-Xin Yin, Ji-Hui Wang, Zheng Wu et al  2016 Chin. Phys. Lett. 33 067401
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Jia-Xin Yin
Ji-Hui Wang
Zheng Wu
Ang Li
Xue-Jin Liang
Han-Qing Mao
Gen-Fu Chen
Bing Lv
Ching-Wu Chu
Hong Ding
Shu-Heng Pan
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