Volume 84, Number 6, December 2008
Article Number 67009
Number of page(s) 4
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 12 January 2009
EPL, 84 (2008) 67009
DOI: 10.1209/0295-5075/84/67009

High-pressure study on LaFeAs(O1 - xFx) and LaFeAsO$_\delta$ with different Tc

Wei Yi, Chao Zhang, Liling Sun, Zhi-an Ren, Wei Lu, Xiaoli Dong, Zhengcai Li, Guangcan Che, Jie Yang, Xiaoli Shen, Xi Dai, Zhong Fang, Fang Zhou and Zhongxian Zhao

Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences - Beijing 100190, PRC

received 28 September 2008; accepted in final form 19 November 2008; published December 2008
published online 12 January 2009

We report studies on pressure dependence of superconducting transition temperature (Tc of ${\rm LaFeAsO}_{\delta}\,(\delta < 0.3)$, ${\rm LaFeAs(O}_{0.5}{\rm F}_{0.5})$ and ${\rm LaFeAs}({\rm O}_{0.89}{\rm F}_{0.11})$ samples. In situ resistance measurements under high pressure showed that the Tc of these three compounds increases with pressure initially, reaches a maximum value and then decreases with further increasing pressure, although Tc's at ambient pressure are different. The onset Tc of LaFeAsO$_\delta$ is ~ 50  K at 1.5 GPa, which is the highest record in La-based oxypnictide system. The significant change in Tc induced by pressure is attributed to the orbital degeneracy and the electron density of state at the Fermi level.

74.70.-b - Superconducting materials.
62.50.-p - High-pressure effects in solids and liquids.

© EPLA 2008