Multiband, paramagnetic effects and vortices in KFe$_2$As$_2$
ORAL
Abstract
We study the normal- and superconducting-state properties of the iron pnictide superconductor KFe$_{2}$As$_{2}$ using heat-capacity, thermal-expansion and magnetization measurements. In the normal state, our data show strong evidence of the existence of strong local fluctuations and of the coherence-incoherence crossover predicted by theory. In zero field, for T \textless\ T$_{\mathrm{c}}$, the temperature dependence of the heat capacity provides evidence for the existence of extremely small energy gaps. The (H,T) phase diagram is also determined down to 80 mK using calorimetric measurements. We reveal the existence of strong paramagnetic effects for field parallel to the Fe$_{\mathrm{2}}$As$_{2}$ planes. We discuss the symmetry of the order parameter and the interplay between multiband, paramagnetic and orbital effects.
*Supported by the Deutsche Forschungsgemeinschaft through SPP1458.
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