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Calendar of Physics Talks Vienna
| Designing nickelate heterostructures with Fermi surfaces like those of high‐temperature superconducting cuprates |
| Speaker: | Ole K. Andersen (Max-Planck Institute Stuttgart ) |
| Abstract: | To my knowledge, no new class of superconductors has been discovered by design, but by chance
or by following empirical rules, which the next discovery then showed to be of limited validity. The
discoveries of the A15 compounds in the seventies, the cuprates in the eighties, MgB2 in 2001, and
the iron pnictides and chalcogenides in 2008, are all examples of this. High‐temperature superconductivity
in the cuprates has not been understood, despite 25 years’ intensive research, and no
superconductor with Tc higher than 150 K has been found since 1993. Even in cases where the mechanism
behind the superconductivity has been understood, as for MgB2, this has not helped in
designing any better superconductor, so far.
With the new possibilities for building oxide heterostructures, it has been speculated that d7 = eg
1=
(3z2‐1, x2‐y2)1 nickelates might be used instead of d9 = eg
3= (3z2‐1)2 (x2‐y2)1 cuprates to obtain even
higher Tc by confining a single layer of LaNiO3 between layers of an insulating oxide. By using densityfunctional
calculations followed by downfolding to a correlated, low‐energy Hubbard Hamiltonian,
and solving the latter in the dynamical mean‐field approximation (DMFT), we have shown that it
might be possible to empty the (3z2‐1)‐like band and enforce a single (x2‐y2)‐like conduction band
with a Fermi‐surface whose shape is like that of the cuprates with the highest Tc [1]. The electronic
correlations help to achieve this, but it is even more important to limit the nickelate to a single layer
and to choose the confining material properly, i.e. by cation control. Competing phase instabilities,
such as charge disproportionation (2d7 → d6+d8) and magnetism should be simultaneously suppressed,
as LDA+U calculations show. Experimental studies are under way.2
I start by mentioning the empirical correlation found for the cuprates between Tc max and the Fermi‐
surface shape. Understanding the chemical origin of the trends in the shapes of the cuprate
Fermi‐surfaces, then leads me to the nickelates.
[1] P. Hansmann, Xiaoping Yang, A. Toschi, G. Khaliullin, O. K. Andersen, K. Held; Phys. Rev. Lett. 103,
016401 (2009).
[2] J. Chakalian et al. (private communication), B. Keimer et al. (private communication), Y. Tokura et al. (private communication), S. Stemmer et al. (private communication). |
| Date: | Mon, 26.04.2010 |
| Time: | 16:00 |
| Duration: | 45 min |
| Location: | Josef-Stefan-Hoersaal Boltzmanngasse 5, 3rd floor, 1090 Wien |
| Contact: | Karsten Held |
| Thermalization in quasi-1D ultracold atomic gases |
| Speaker: | Igor Mazets (TU Wien) (Fakultät für Physik) |
| Abstract: | im Rahmen des Seminars für Mathematische Physik |
| Date: | Tue, 27.04.2010 |
| Time: | 14:15 |
| Duration: | 60 min |
| Location: | Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock |
| Contact: | J. Yngvason |
| Gravity on Conformal Superspace |
| Speaker: | Prof. Niall O`Murchadha (Univ. College Cork, Irland) (Fakultät für Physik) |
| Abstract: | im Rahmen des Literaturseminars |
| Date: | Thu, 29.04.2010 |
| Time: | 13:30 |
| Duration: | 60 min |
| Location: | Währinger Straße 17, 1. Stock, Zimmer 118 |
| Contact: | R. Beig |
| Schwarzschild Geometry emerging from Matrix Models |
| Speaker: | Daniel Blaschke (Univ.Wien) (Fakultät für Physik) |
| Abstract: | im Rahmen des Seminars für Mathematische Physik |
| Date: | Thu, 29.04.2010 |
| Time: | 14:15 |
| Duration: | 60 min |
| Location: | Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock |
| Contact: | H. Steinacker |
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