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


Diluted Magnetic Semiconductors


Workshop Proposal


Title: Diluted Magnetic Semiconductors

Aim: to strengthen the understanding of diluted magnetic semiconductors and bring together theorists from the ab-initio and model hamiltonian field and some leading experimentalists.

Organisers:

Peter H. Dederichs Tel: +49 2461 61 4351
Institut für Festkoerperforschung Fax: +49 2461 61 2620
Research Center Juelich e-mail:
D-52425  
Germany  

Josef Kudrnovsky Tel: +420-2-6605-2905
Institute of Physics Fax: +420-2-86890527
Academy of Sciences e-mail:
CZ-18040 Praha 8  
Czech Republik  

Allan H. MacDonald Tel: 001-512-232-9113
Department of Physics Fax: 001-512-471-9637
University of Texas at Austin e-mail:
Austin, TX 78712  
USA  


Scientific Content

Diluted magnetic semiconductors like Ga(1-x)Mn(x)As are at present intensively studied in spin electronics because they are ferromagnetic at very low magnetic impurity concentrations (1-5% Mn). Because of their structural similarities with standard semiconductors and their large spin-polarisation at the Fermi energy they are considered as ideal materials for spin injection into semiconductors and for collective magnetoresistance effects. Up to now the only practical bottleneck to useful applications for these materials seems to be the relatively low Curie temperatures of these materials. The current record is in GaMnAs and is around 140 K. Recent calculations as well as the latest experimental results indicate that Curie temperatures above room temperature might be realizable however.

Our present understanding of these material is very limited and controversial. On one hand, a widely accepted model hamiltonian considers the impurity states bound to Mn ions to be shollow acceptors formed from the valence band of the host material, and the interaction between the Mn impurity spin orientations to be induced by these valence band holes (Zener's p-d exchange model). One the other hand ab-initio calculations give more localized impurity states that in the concentration range considered overlap more weakly leading to narrow impurity bands and a short-range double-exchange interaction between impurity spins. This type of interaction is well-known from the ferromagnetism of the transition metal oxides. Despite their fundamental differences, the two models make similar predictions for some properties, making it difficult to determine which picture is correct.

The workshop aims at a more fundamental understanding of diluted magnetic semiconductors (DMS). It should bring together the leading experts from model hamiltonian calculations, such as Allan MacDonald and Thomasz Dietl, with the ab-initio community to discuss the advantages and limitations of both approaches. Leading experimentalists will be invited to present recent experimental results and to draw attention to new challenging systems and problems.

The scope of the workshop should also include: effects of dopants, antiferromagnetic and non-collinear phases, calculations of Curie temperatures by the mean field approximation and beyond, DMS in layered structures, transport in DMS and the problem of spin-injection into semiconductors.


Tentative List of Speakers

A.H. MacDonald, University of Texas at Austin, USA
"Theory of Magnetic Semiconductors"

T. Dietl, Polish Academy of Sciences, Warsaw, Poland
"Manipulation of Spin Order in Ferromagnetic Semiconductors"

L. Molenkamp, University of W"urzburg, Germany
"Spin injection and Transport in II-VI Semiconductors"

H. Ohno, Tohoku University, Sendai, Japan
"Transport in Semiconductors"

K. Sato, Osaka University/Research Center J"ulich, Germany
"Double Exchange versus Zener Exchange in Magnetic Semiconductors"

B.T. Jonker, Naval Research Laboratory, USA
"Ferromagnetic Semiconductors: New and Old"l

O. Eriksson, Uppsala University, Sweeden

K. Ando, Nanoelectronics Research Institute, Tsukuba, Japan

W.M. Butler, University of Tulane, USA

B. Gallagher, University of Nottingham, UK

Participants

Participants of the RT Network "Computational Magnetoelectronics" and of the Working Group 9 of the ESF Ψk Programme:

Other invited participants:

In total we expect about 40 participants.


The workshop will include

about 10 review talks of 50 min each
about 15 contributed papers of 30 min each
a poster session with about 10 posters (2 hours)

There will be ample time for discussion.

Budget and Co-sponsors

The workshop will be co-sponsored by:

-RT-Network "Computational Magnetoelectronics"
-ESF Ψk Programme
-CECAM

The participants of the RT Network "Computational Magnetoelectronics" will be financed by this Network.

We need support for about 20 additional participants

Travel + local expenses (3 days)
about 10 from Europe: 300 Euro + 240 Euro = 5.400 Euro
and 5 from USA: 500 Euro + 240 Euro = 3.700 Euro
and 5 from Japan: 700 Euro + 240 Euro = 4.700 Euro
Total: 13,800 Euro

We apply for funding to both CECAM and the Ψk Programme of the ESF. Therefore we ask both sponsors for a 50% contribution, i.e.

6.900 Euro.

Location and Date

CECAM, Lyon, June 12-14, 2003

We would like to organise the workshop at CECAM, in order to profit from the CECAM infrastructure and the central location of Lyon.

American Participants

With Allan MacDonald, Austin, we have an american coorganiser. However, since the general policy of the NSF has been changed, it is not clear, if we can get additional support from the NSF. Nevertheless we will try.