Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 36: Focussed Session: Superconductivity and Magnetism in Ferropnictides and Related Materials

TT 36.3: Topical Talk

Thursday, March 26, 2009, 10:30–11:00, HSZ 03

Structural and magnetic transitions of underdoped (Ba_1−xK_x)Fe₂As₂ — •Dirk Johrendt¹, Marianne Rotter¹, Marcus Tegel¹, Inga Schellenberg², Falko M. Schappacher², and Rainer Poettgen² — ¹LMU München, Department Chemie, Butenandtstr. 5-13 (Haus D), 81377 München, Germany — ²WWU Münster, Institut für Anorganische und Analytische Chemie, Corrensstr. 30, 48149 Münster. Germany

BaFe₂As₂ is the parent compound of the 122-type family of iron arsenide superconductors. Superconductivity up to T_c = 38 K is induced by doping the barium site by potassium or the iron site by cobalt or even without chemical doping under high pressure. The structural and magnetic phase transition of the parent compound is completely suppressed at the optimal doping level in (Ba_1−xK_x)Fe₂As₂ around x = 0.4. But In the underdoped regime, superconductivity co-exists with the orthorhombically distorted lattice and it is debatable at the moment, to what extent the superconducting state may also co-exist with the antiferromagnetic order.

The talk will first briefly review the properties of BaFe₂As₂ and the doped Ba122-superconductors. Then recent results of studies in the underdoped regime will be reported. (Ba_1−xK_x)Fe₂As₂ (x < 0.4) has been studied in detail by low-temperature x-ray powder diffraction and ⁵⁷Fe-Mössbauer spectroscopy. Relationships between the evolution of magnetic ordering and the onset of the orthorhombic lattice distortion are discussed in connection with possible inhomogeneities of the potassium distribution in underdoped superconducting Ba122-materials.