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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 |
| Quantum fluid properties of light and cavity quantum electrodynamics in solids |
| Speaker: | Cristiano Ciuti (Université Paris Diderot) |
| Abstract: | In this lecture, I will discuss theoretically some interesting physical properties of strongly interacting photons in nonlinear microcavities. In particular, I will discuss the superfluidity of light in semiconductor microcavities, predicted theoretically in 2004 and recently observed experimentally. Moreover, I will present some recent advances on the cavity quantum electrodynamics of solid-state systems (semiconductors and superconductors) in the unconventional ultrastrong coupling limit, showing how the quantum vacuum can be manipulated. |
| Date: | Mon, 26.04.2010 |
| Time: | 17:30 |
| Duration: | 60 min |
| Location: | Schütte-Lihotzky Hörsaal, Karlsplatz 13, HS 7, Hof 2, 1040 Wien |
| Contact: | Prof. Karl Unterrainer |
| 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 |
| Structural and magnetic properties of Fe and Co clusters on Alumina on Ni3Al(111) |
| Speaker: | Dipl.-Ing. Andreas Buchsbaum (TU Wien, Institut für Angewandte Physik) |
| Abstract: | Growing nanoparticles with well-defined size, shape and structure is an essential prerequisite to understand their magnetic properties. Templates are not only a means to grow regularly arranged clusters but also provide the opportunity to grow well-defined clusters with a narrow size distribution by simple evaporation, taking advantage of the fact that the capture zones of equidistant clusters have equal area.
In particular, I will demonstrate the applicability of an ultrathin alumina film on Ni3Al(111) as a template for growing Pd, Fe and Co clusters with a 4.1-nm lattice and a tuneable size between 1 and ≈1000 atoms. The structure of the ≈5 Å thick oxide film exhibits holes at the corner of the ( )R12.2° unit cell reaching down to the metal substrate. Pd atoms trapped in these corner holes create metallic nucleation sites where the clusters can nucleate and form a well-ordered hexagonal arrangement on the oxide nanomesh. We have applied different methods like scanning tunneling microscopy (STM), surface x-ray diffraction (SXRD), grazing-incidence small-angle x-ray scattering (GISAXS) and x-ray magnetic circular dichroism (XMCD) to determine the morphology, crystallographic and magnetic properties of the clusters.
|
| Date: | Tue, 27.04.2010 |
| Time: | 16:00 |
| Location: | Technische Universität Wien, Institut für Angewandte Physik, Seminarraum 134A, Turm B (gelbe Leitfarbe), 5. OG, 1040 Wien, Wiedner Hauptstraße 8-10 |
| Contact: | Ao.Univ.Prof. Dr. Peter Varga |
| New tools for quantum field theory |
| Speaker: | Prof. Vincent Rivasseau (Universite Paris Sud) |
| Date: | Wed, 28.04.2010 |
| Time: | 11:00 |
| Location: | ESI Schrödinger Lecture Hall |
| Contact: | secr@esi.ac.at |
| Holographic Entanglement Entropy |
| Speaker: | Prof. Tadashi Takayanagi (IPMU, Tokyo) |
| Date: | Thu, 29.04.2010 |
| Time: | 11:00 |
| Location: | ESI Schrödinger Lecture Hall |
| Contact: | ESI Secretary |
| 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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