Research Topics - Forschung

Activities of the group: (Kurzzusammenfassung) (Short Summary)

 

Complex and nanostructured materials

 

Topics:

bullet

light - matter interaction and electronic reconstruction in nanoscale systems and metamaterials

bullet

large cross susceptibilities in inhomogeneous matter

bullet

novel sensor applications and information storage concepts: bistable molecules in templates

In detail:

bullet

Tip-enhanced scattering on templated molecules
A novel light scattering technique based on the combination of Raman scattering and an atomic force microscope is implemented and used on single molecular magnets and buried molecules in nanoporous templates. -> TERS LAB

bullet

Elastic and magnetic properties of nanocomposites
Nanocomposites have an exceptional large internal surface that supports the coupling of different order parameters. Plasma sparc sintering allows the preparation of uniform bulk materials with a well defined length scales in the nm range, complex nanostructures and exceptional mechanical and electronic properties. Investigations are performed together with groups from the Inst. of Inorganic Chemistry, Univ. Stockholm and the MPI-FKF Stuttgart. -> US LAB

bullet

Coupling of FM and FE order parameters
Mutual exclusive order parameters can be coupled leading to new functionalities as observed in multiferroics. Such a behavior is presently studied in nanoscale composites (meta materials), incommensurate antiferromagnets and lone pair compounds. Work is performed in collaboration with groups from the Univ. of Augsburg, Chisinau and the TU Braunschweig.

bullet

Doping of correlated oxides and molecular systems
Phase diagrams with competing states, phase separation or unusual criticality are observed. The resulting soft electronic modes lead to colossal response to external magnetic or electric fields. Low energy intermolecular modes critically affect the spin state of the molecular systems. Work is performed in collaboration with groups from the university of Frankfurt, Erlangen and Bielefeld.

Examples:

bullet

colossal magnetoresistance, magnetocapacitace, thermopower in manganites, thiospinels and cobaltates

bullet

Interdisciplinary material research:
Physics/chemistry data base search for novel functional material

bullet

Interdisciplinary approach to characterize and develop novel preparation concepts:

- electrochemical preparation of nanoporous systems
- plasma sparc sintering of nanoscale composites
- magnetic host-guest compounds

We acknowledge financial support by DFG (projects and topical centers), ESF, Vinnova, and the NMWK.

 

 

 

 

Magnetism, electronic correlations and competing interactions

Interrelation of spin, orbit and topology

on small length scales

--

 

Unusual criticality in low dimensions and due to competing interactions

--

Bose-Einstein transition of diluted magnons
(Ultrasonic spectroscopy)

--

Giant response of the lattice system

--

Geometrically frustrated systems and competing interactions

 

 

 

 

 

Introduction to magnetism and correlated electron systems

bullet

magnetism & electronic correlations in systems with restricted or confined geometries

bullet

structural principles of transition metal oxides:
1D
spin chains, spin ladders, 2D topologies und tetrahedra 

bullet

some interesting transition metal oxides 

bullet

collective magnetic excitations and  bound states

bullet

spin defects and doping of quantum spin systems

bullet

spin frustration and competing interactions  

bullet

stripe phases und orbital degrees of freedom

bullet

quantum critical behavior 

 

Experimental Techniques:  

- optical spectroscopies and apertureless Raman scattering

- preparation and search for NEW MATERIALS (Database mining)

- ultrasonic spectroscopy

 

Recent Seminars:  

- "Quantum Magnetism in Novel Materials and Geometries", (1999)

- IGSM Lecture on Superconductivity

- Magnetismus und Datenspeicherung (populärwiss. VL, "Physik am Samstag")

- Habilitation colloquium "Sonolumineszenz - Aus Schall wird Licht" (1999)

- Übersicht zum DFG-Schwerpunkt SPP 1073, "Kollektive Quantenzustände in
  elektronisch 1D Übergangsmetall-Verbindungen
" (2000) 

- Frühjahrstagung der DPG in Hamburg (2001)

- Frühjahrstagung der DPG in Regensburg (2002)

- Frühjahrstagung der DPG in Dresden (2003)

- Frühjahrstagung der DPG in Regensburg (2004)

- Frühjahrstagung der DPG in Berlin (2005)

- Frühjahrstagung der DPG und der EPS in Dresden (2006)

- Frühjahrstagung der DPG in Dresden (2007)

- Frühjahrstagung der DPG in Berlin (2008)

- lectures and seminars

- recent lecture materials

 

Further Contributions:

- publications

- running projects and proposals

- important links

 


Webpages of Peter Lemmens

Diese Web-Seite stellt keine Meinungsäußerung der TU Braunschweig dar.

p.lemmens at tu-bs.de, letzte Änderung: 24.04.2009