Competition between superconductivity and magnetic/nematic order as a source of anisotropic superconducting gap in underdopedBa1−xKxFe2As2
| Autor: | Rafael M. Fernandes, J.-Ph. Reid, Hai-Hu Wen, N. Spyrison, Makariy A. Tanatar, Bing Shen, Kyuil Cho, H. Kim, J. Murphy, W. E. Straszheim, Ruslan Prozorov |
|---|---|
| Rok vydání: | 2014 |
| Předmět: | |
| Zdroj: | Physical Review B. 90 |
| ISSN: | 1550-235X 1098-0121 |
| DOI: | 10.1103/physrevb.90.014517 |
| Popis: | The in-plane London penetration depth $\ensuremath{\Delta}\ensuremath{\lambda}(T)$ was measured using a tunnel diode resonator technique in single crystals of ${\mathrm{Ba}}_{1\ensuremath{-}x}$${\mathrm{K}}_{x}$${\mathrm{Fe}}_{2}$${\mathrm{As}}_{2}$ with doping levels $x$ ranging from heavily underdoped, $x=0.16$ $({T}_{c}=7\text{K})$, to nearly optimally doped, $x=0.34$ $({T}_{c}=39\text{K})$. Exponential saturation of $\ensuremath{\Delta}\ensuremath{\lambda}(T)$ in the $T\ensuremath{\rightarrow}0$ limit is found in optimally doped samples, with the superfluid density ${\ensuremath{\rho}}_{s}(T)\ensuremath{\equiv}{[\ensuremath{\lambda}(0)/\ensuremath{\lambda}(T)]}^{2}$ quantitatively described by a self-consistent $\ensuremath{\gamma}$ model with two nodeless isotropic superconducting gaps. As the doping level is decreased towards the extreme end of the superconducting dome at $x=0.16$, the low-temperature behavior of $\ensuremath{\Delta}\ensuremath{\lambda}(T)$ becomes nonexponential and is best described by the power law $\ensuremath{\Delta}\ensuremath{\lambda}(T)\ensuremath{\propto}{T}^{2}$, characteristic of strongly anisotropic gaps. The change between the two regimes happens within the range of coexisting magnetic/nematic order and superconductivity, $xl0.25$, and is accompanied by a rapid rise in the absolute value of $\ensuremath{\Delta}\ensuremath{\lambda}(T)$ with underdoping. This effect, characteristic of the competition between superconductivity and other ordered states, is very similar to but of significantly smaller magnitude than what is observed in the electron-doped Ba$({\mathrm{Fe}}_{1\ensuremath{-}x}$${\mathrm{Co}}_{x})$${}_{2}$${\mathrm{As}}_{2}$ compounds. Our study suggests that the competition between superconductivity and magnetic/nematic order in hole-doped compounds is weaker than in electron-doped compounds, and that the anisotropy of the superconducting state in the underdoped iron pnictides is a consequence of the anisotropic changes in the pairing interaction and in the gap function promoted by both magnetic and nematic long-range orders. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|