Regensburg 2016 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 79: Superconductivity: Fe-based Superconductors - 122

TT 79.5: Vortrag

Donnerstag, 10. März 2016, 16:30–16:45, H21

Reversible tuning of the collapsed tetragonal phase transition in CaFe₂As₂ by separate control of chemical pressure and electron doping — •kan zhao and philipp gegenwart — Experimentalphysik VI, Center for Electronic Correlations and Magnetism, Augsburg University, 86159 Augsburg, Germany

Single crystals of Ca(Fe_1−xRu_x)₂As₂ (0≤ x ≤ 0.065) and Ca_1−yLa_y(Fe_0.973Ru_0.027)₂As₂ (0≤ y≤ 0.2) have been synthesized and studied with respect to their structural, electronic and magnetic properties. The partial substitution of Fe by Ru induces a decrease of the c-axis constant leading for x ∼ 0.023 to the suppression of the coupled magnetic and structural (tetragonal to orthorhombic) transitions. At x_cr = 0.023 a first order transition to a collapsed tetragonal (CT) phase is found, which behaves like a Fermi liquid and which is stabilized by further increase of x. The absence of superconductivity near xcr is consistent with truly hydrostatic pressure experiments on undoped CaFe₂As₂. Starting in the CT regime at x=0.027 we investigate the additional effect of electron doping by partial replacement of Ca by La. Most remarkably, with increasing y the CT phase transition is destabilized and the system is tuned back into a tetragonal ground state at y ∼ 0.08. This effect is ascribed to a weakening of interlayer As-As bonds by electron doping. Upon further electron doping filamentary superconductivity with T_c of 41 K at y=0.2 is observed.