Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 2: SC: Properties, Electronic Structure, Mechanisms 1

TT 2.7: Talk

Monday, March 14, 2011, 12:15–12:30, HSZ 301

Electronic structure of striped phase of Ca_1.875Na_0.125CuO₂Cl₂ — •Charles Patterson — Trinity College Dublin, Ireland

We present hybrid DFT calculations on stripe formation in hole doped Ca₂CuO₂Cl₂ (CCOC) [1]. Stripes have been extensively studied by STM in sodium-doped CCOC with hole concentrations, x, in the range x = 0.05 to x = 0.15 per Cu ion [2]. Around x = 0.125, 1-D stripes are observed with a spacing of four lattice constants. STM imaging in topographic mode allows positions of Cl ions and Cu ions directly beneath to be observed. Stripes imaged in conductance mode are centred on O ions in rows running perpendicular to the stripe direction, i.e. they are bond centred stripes on O ions.

O ions between transition metal ions with a magnetic moment induce anti-ferromagnetic coupling between the metal ion magnetic moments via super-exchange. However, when a hole is localized on the O ion between two transition metal magnetic moments, it induces ferromagnetic coupling between the metal ion magnetic moments by double-exchange. We propose a magnetic order for Cu ion spins and hole localisation on O ions in the CuO₂ layers of CCOC with x = 0.125. Holes are localised in rows on O ions, separated by four lattice constants; each pair of Cu magnetic moments on either side of an O ion with a localized hole are parallel and each pair of Cu magnetic moments on either side of an ordinary O ion are anti-parallel, satisfying the rules for super- and double-exchange.

[1] C. H. Patterson, Phys. Rev. B 77, 094523 (2008).

[2] Y. Kohsaka et al, Science 315, 1380 (2007).