Psi-k - Ab initio (from electronic structure) calculation of complex processes in materials


Ab-initio understanding of superconducting and normal state properties of MgB2

1. Title: Ab-initio understanding of superconducting and normal state properties of MgB2

Purpose: MgB2, a recently discovered superconductor with a critical temperature of 40K, has attracted enormous attention since January 2001. It was one of the hottest research topics in 2001. The main understanding of the unexpected superconductivity came from electronic band structure calculations. Nearly all key ideas in that field have been suggested by our community and were then experimentally confirmed. The aim of this workshop is to give an overview about the results from ab-initio simulation in MgB2. The idea is to demonstrate by example of a scientifically highly important material the power of these methods so that the materials research community is able to understand the predictive capabilities of electronic structure calculation in their daily work.

Organizer:
Prof. Dr. Ole K. Andersen
Max-Planck-Institute for Solid State Research
Heisenbersgstr. 1, D-70569 Stuttgart, Germany
Phone: +49 (0)711 - 689-1630
Fax: +49 (0)711 - 689-1632
E-Mail:

Dr. Jens Kortus
Max-Planck-Institute for Solid State Research
Heisenbersgstr. 1, D-70569 Stuttgart, Germany
Phone: +49 (0)711 - 689-1664
Fax: +49 (0)711 - 689-1632
E-Mail:

Prof. Dr. Giovanni B. Bachelet
Department of Physics and INFM-SMC
University Rome, La Sapienza, Italy
Phone: +39 06 4991-3474
FAX: +39 06 446-3158
E-mail:

Prof. Dr. Luciano Pietronero
Department of Physics, CNR and INFM-SMC
University Rome, La Sapienza, Italy
Phone: +39 06 4991-3488
FAX: +39 06 446-3158
E-mail:

Scientific co-organizer:
Dr. Igor I. Mazin
Center for Computational Materials Science
Naval Research Laboratory
4555 Overlook Ave, Washington, DC 20375, USA
Phone: +1 (202) 767-6990
Fax: +1 (202) 404-7546;
E-mail

2. Scientific content:
The announcement by Akimitsu at a conference in Japan in January 2001 of the discovery of superconductivity in MgB2 with a critical temperature of 39K was a great surprise for the scientific community. Several hundreds papers on that single material appeared in only two years, nearly all possible experimental methods have been applied, which makes MgB2 to one of the best characterized materials. Many of its physical properties showed surprising features which called for theoretical investigation. Now, only two years later many of the unexpected physical properties, in particular the relatively high critical temperature, are well understood. This is quite different to the case of high temperature superconductors where more than one decade after their discovery no consensus on the mechanism exists. The key for our understanding was given by the calculation of the electronic structure, which is in excellent agreement with experimental data obtained from de-Haas-van-Alphen or ARPES measurements. The simple hexagonal unit cell with only one Mg- and two B-atoms allows for first-principles calculations without any limiting assumptions. Nearly all key ideas in that field have been suggested from this kind of simulations and were then experimentally confirmed. The aim of this workshop is twofold, first it should give an overview of the current status of the field, which still is a very active research area with 20-30 new papers appearing every month on cond-mat. Due to a mix of invited speakers from theory and experiment it will be shown which information can be obtained from first-principles calculations and how this information can be experimentally proven. Because we reached a high level of understanding of this material it seems very appropriate to look forward and define future directions of research in this field. The proposed workshop in 2003 would be a very timely opportunity to fulfill that goal. Second, MgB2 can be seen as a great success of the standard theory of electron-phonon mediated superconductivity. Based on the example of MgB2 young researchers will be able to get a complete description of superconducting and normal state properties from an ab-initio point of view. This will demonstrate the usefulness of first-principles methods and should also show which information can be obtained and where possible limitations will be. Possible limitations will be for example in the Born-Oppenheimer approximation. This should also help researchers to understand electronic structure calculations better and enable them to use these methods in future work.

3. Tentative list of speakers:

  1. A.A. Golubov (Twente, The Netherlands) | T-Eliashberg theory
  2. E. Pavarini (Pavia, Italy) | T-NMR
  3. O.K. Andersen (Stuttgart, Germany) | T-electronic structure
  4. I.I. Mazin (Washington, USA) | overview
  5. E. Cappelluti (Rome, Italy) | T-anharmonicity
  6. S. Massidda (Cagliari, Italy) | T-structural properties
  7. K.P. Bohnen/R. Heid (Karlsruhe, Germany) | T-linear response
  8. S. Savrasov (Newark, USA) | T-linear response
  9. S.L. Drechsler (Dresden, Germany) | T-dHvA, Eliashberg
  10. J.R. Cooper/E.A. Yelland (Cambridge, UK) | E-dHvA
  11. A.G.M. Jansen (Grenoble, France) | E-Andreev
  12. A. Junod/Y. Wang (Geneva, Switzerland) | E-specific heat
  13. R.S. Gonnelli (Torino, Italy) | E-tunnel
  14. A.D. Caplin (London, UK) | E-critical fields
  15. M.R. Eskildsen (Geneva, Switzerland) | E-vortex state
  16. S. Tajima/H. Uchiyama (Tokyo, Japan) | E-ARPES
  17. H. Rosner/W. Pickett (Davis, USA) | T-LiBC
  18. A.Congeduti/P.Postorino (Rome, Italy) | E-phonons, Raman
  19. M. D'Astuto (Grenoble, France) | E-phonons, inelastic X
  20. A. V. Sologubenko (Zurich, Switzerland) | E-transport

4. Number of participants:
20 invited speakers with a mix of theory and related experiment
30 young scientists
total 50 participants

5. Tutorial element
There are several codes available for electronic structure calculations together with linear response method in order to calculate the electron-phonon interaction from first-principles. Currently not so common are codes for the solution of the Eliashberg equations using as input the Eliashberg spectral functions calculated by the above mentioned codes. Many important physical properties like tunnel spectra or specific heat in the superconducting state can be calculated directly. The tutorial will give an introduction to the Eliashberg theory of electron-phonon coupling and demonstrate numerical solution of multigap Eliashberg equations (Golubov).

6. Budget
There will be no registration fee in order to attract younger researcher. The living expenses and depending on funding also part of the travel costs of the invited speakers will be covered.

Hotel: 3 nights*20 speakers * 100 EUR = 6000 EUR
Travel: 15000 EUR
Social dinner: 3000 EUR
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estimated Total cost 24000 EUR
We would like to ask ESF Ψk to cover 9000 EURO.

7. Statement of co-sponsorship of other organizations and additional funding
INFM Center for Statistical Mechanics and Complexity, Italy
(10K EURO)

Department of Physics of La Sapienza and CNR, Italy
(meeting place and local organization)

NSF International Materials Science program
(5K EURO)

8. Place of workshop
University Rome, La Sapienza, Italy
DATE: 02 July 2003 - 04 July 2003

9. Support for American participants
Some American participants will be supported by the co-sponsorship of the INFM Center for Statistical Mechanics and Complexity and NSF.