Local Spectroscopy and molecular Systems - P. Lemmens








  Peter Lemmens

Institute for Condensed Matter Physics
Institut für Physik der Kondensierten Materie

TU Braunschweig, Mendelssohnsstr. 3,
Braunschweig, Germany

Tel:  +49 (0)531 391 5130
Fax: +49 (0)531 391 5155

p.lemmens at tu-bs.de

ORCID and Scopus ID


     Welcome! Herzlich Willkommen!

Our work relates to the interplay of photons with electronic correlations, topological effects, and metrology of nanosystems. 

News/Neuigkeiten: (older news)


  • Summertime means cryostat leak testing together with Arno Ellermann, head of the machinery shop, 1.8.2016

  • Teilnahme am Workshop "MitarbeiterInnengespräche in der Wissenschaft" beim Teach4TU, 29.6.2016

  • Grundsteinlegung (und hier) von Lena, ein Zuhause für Nanomesstechnik, "Emergent Nanometrology", 18.4.2016

  • Berufsinfotag am Gymnasium Julianeum in Helmstedt mit dem Vortrag: Physik - wiss. Grundlagen für die Welt von Morgen, 20.1.2016

  • Misael Chavarria's farewell, Nov. 27, 2015

  • with 4 presentations, coffee, cake, sweets, wine, and best wishes.

  • Our visitor from Taipei (National University and Academica Sinica) explains us the properties of Weyl semimetals (from left to right: Liu Bio, Azat Sharafeev, Silvia Müllner, Raman Sankar, Robert Bohle, Peter Lemmens) 


Published results:


Fractionalized modes: The Kiteav model with anisotropic exchange on a honeycomb-like lattice predicts the existence of topological excitations with fractionalized quantum statistics. Such modes have recently been predicted and now observed experimentally in quasi-3D coordinated Iridium oxides, see Nature Commun., in print (2016).


Mercury a serious health thread ... can be detected using Ag nanoparticles with a turn on ultrasensitive fluorescence sensor and a linear regime from 0 to 1 ppb, P. K. Sarkar, et al., ACS Sensors (2016). 


Plexcitons in a periodic structure... periodic arrays of plasmonic Au wires in proximity to a dye shows strong coupling to molecular excitons. Such plexcitons can be modelled in some microscopic approach using a Zubarev Green's function method following the work of Manjavacas et al.., preprint by Liu Bo, et al. (2016). 


The Dance of DNA... Although many forms of dynamical behaviour of proteins under allosteric interactions with effectors are predicted, little evidence of dynamics in the interaction has been reported. Here, we demonstrate the ultrafast dynamics of the allosteric interaction of the Gal repressor (GalR) protein dimer with DNA operator sequences using time resolved optics , see S. Choudhury, et al. ChemBioChem (2016)

Editors Choice... Evidence for a Z2 quantum phase transition from a dimer to a resonating valence bond state driven by singlet fluctuations. The rich spectrum of singlet bound modes is attributed to a melting of a dimer crystal, see Phys. Rev. Lett. 110 (2013).

Surface engineering of various nanoparticles (NPs) is of growing interest and an important step to induce/control optical and/or catalytic activities. Here we report a top-down fabrication methodology to modify a model ferrofluid with parent NPs sizes of about 23 nm. The surface engineering involves ligand exchange and simultaneous phase transfer, and core etching, resulting in a reduction of particle diameter to about 5 nm. We have used the functionalized NPs for the photodegradation of biomedically important jaundice marker bilirubin in aqueous solution. Overall, the results represent a promising route for the fabrication of NPs adaptable to diverse applications, see Journ. of Phys. Chem. C (2014).

Charge migration along DNA molecules is a key factor for DNA-based devices in optoelectronics and biotechnology. We have investigated the role of water molecules in DNA-based materials for the intactness of the DNA structure and their dynamic role in the charge-transfer (CT) dynamics. This study uses time resolved optical spectroscopy and is based on a collaboration between groups from Kolkata, Idia and the TU-Braunschweig, see Chemistry, An Asian Journal (2014).

Figure 5

In the giant Rashba system BiTeI as well as in topological insulator there exist an enhanced quasiparticle dynamics of quantum well states. This is due to a time dependent band beneding leading to a surface confined quantum well state. Topological insulators and Giant Rashba system share a very similar surface chemistry and strong spin orbit coupling of bulk and surface states. However, they have a different symmetry in the bulk. This leads to a different symmetry of electronic Raman scattering, see PRB.

A novel solid solution (Co1-xNix)3Sb4O6F6 with a pseudo kagome structure can be taylored with respect to its physical properties by changing its composition. This systems can be used to better understand the interplay of dimensionality, anisotroy and magnetism within one crystallographic structure. This is a collaboration between groups from Stockholm, Houston and Braunschweig, see Chem. of Mat., (2014).

The novel oxofluoride Cu7(TeO3)6F2 shows features of both zero and one dimensional magnetism. This is due to an interplay of composition that contains fluorine ions as well as the lone pair element Te with the electronic configuration of the Cu 3d orbitals. In contrast to many other compounds the fluorine terminates the magnetic exchange path. Te with its lone pair electrons opens up the structure like a scissor. The alternation of different Cu orbitals (see right figure) has a further important consequence for the exchange from one Cu2 sites (brown plaquette) to the other. As a result low energy fluctuations exist in a broad temperature range. This is a collaboration between groups from Stockholm, Houston and Braunschweig, see Inorganic Chemistry, (2014).
Dynamic lattice distortion and spin fluctuation cooperate in the spin liquid phase of a low-dimensional compound nitrosonium nitratocuprate. This system has been proposed to be a model compound for the resonanting valence bond ground state (RVB). Our data, however, point towards a structural instability at low temperatures that freezes out spin correlations by an excitation gap (Phys. Rev. B 85, (2012) and cond-mat).

The magnetoelectric compound Cu2OSeO3 shows a state with an inhomogenous spin polarization called SKYRMION phase. These objects are topologically protected and form a superstructure that can be investigated by small angle neutron scattering. The skyrmion phase in an insulator with coupled dielectric-spin degrees of freedom allows new applications in the field of spintronics (Phys. Rev. Lett).
Frustrated quantum spins realized by transition metal ions in solids form states of matter with novel properties. We show how a modification of the chemical composition in zinc paratacamite can be used to tailor its magnetic properties from a spin liquid to a spin glas (Phys. Rev. B and cond-mat).
Molecules that consist of three Cu ions and are arranged in a lattice (freestanding porous silicon) realize a novel hybrid material. It provides a promising scheme for implementing spin-based quantum gates. By measuring the spin relaxation times of samples with different symmetries and environments we give evidence that a spin chirality is the main decoherence source of spin triangle molecules (Phys. Rev. Lett.).
Topological insulators allow collision dominated scattering with spin-helical symmetry. This scattering is due to fluctuations from Dirac to bulk states of the compound despite topological protection. The scattering rate is determined from the position of a maximum in the RL scattering component as G=40cm-1 (Phys. Rev. B).

Magnetic molecules can be tuned by a confinement in the nanocage of a Protein, (Chem Phys Chem).




  Group members:   (former members) 

 Group members: Room / Tel. - Lab. / Tel. - Email:

Prof. Dr. Peter Lemmens
204 / (0531) 391-5130
(0531) 391-5110
p.lemmens - at - tu-bs.de

Principal Investigator 


Dr. Vladimir Gnezdilov
113 / (0531) 391-5108
(0531) 391-7969
v.gnezdilov - at - tu-bs.de


Inelastic Light Scattering
Quantum Spin Systems and Molecular Magnets

Project: DFG


Azat Sharafeev
113 / (0531) 391-5131
(0531) 391-5110

sharafeev - at - tu-bs.de

Inelastic Light Scattering
Project: GIF


Bo Liu
113 / (0531) 391-5131
(0531) 391-5110

- at - tu-bs.de

Nano- and Mesoporous Templates
Plasmonic Arrays


Silvia Müllner
113 / (0531) 391-5131
(0531) 391-5110

Weyl and Dirac metals


Savutjan Sidik
114 / (0531) 391-5133
(0531) 391-5110

Correlated Electron Systems
Project: NTH nano, Contacts in Nanosystems


Andreas Reutter
115 / (0531) 391-5133
(0531) 391-7986
- at - tu-bs.de

Nano- and Mesoporous Templates
Functionalization of Anodized Alumina (AAO)
Electrochemical Growth of Nano Wires/Dots
Project: IGSM and NTH

Long term and frequent visitors:

Prof. Dr. Kwang-Yong Choi
115 / (0531) 391-5108
(0531) 391-5110
kchoi - at - cau.ac.kr

Prof. at Chung-Ang University, Seoul, Korea

Correlated Electron Systems and Multiferroics 

Project: AvH and DFG


Dr. Hongdan Yan
115 / (0531) 391-5133
(0531) 391-7986
- at - tu-bs.de

Nano- and Mesoporous Templates
Functionalization of Anodized Alumina (AAO)
Electrochemical Growth of Nano Wires/Dots
Project: IGSM and NTH


Dr. Oleksandr Glamazda
Chung-Ang University, Seoul, Korea
115 / (0531) 391-5108
(0531) 391-5110

Correlated Electron Systems
Project: DFG, Humboldt


Prof. Dr. Samir Kumar Pal
115 / 391-5117
skpal at bose.res.in

S.N. Bose Nat. Center for Basic Science, Kolkata, India

Macromolecular, Nanoscience
and time resolved spectroscopies


Prof. Dr. Yurii Pashkevich
/ (0531) 391-5121

Prof. at O.O. Galkin, DIPE, NAS Ukraine

, Band structure calculations


Prof. Dr. Zhenya Sherman
/ (0531) 391-5117
evgeny_sherman - at - ehu.es

Ikerbasque Research Professor
Dpto. de Química-Física
Univ. del País Vasco, UPV/EHU
48080 Bilbao, Spain
Spin-Orbit coupling, Dissipation in CES



  Research Projects:

   Research Topics - complete funding list, CV


Metrology for Complex Nanosystems - NANOMET
DFG-RTG 1952, Graduate School, Speaker: M. Schilling, TU-BS

Part of the Metrology Initiative Braunschweig

(b) Interactions, Control and Quantum Dynamics (NMWK-supported, Graduate school, 2014-2018)
(c) German-Israel Research Foundation (GIF)
Magnetic Equivalence of the Isotope Effect in Cuprates
together with A. Keren, Technion, Haifa, Israel
Laboratory for Emerging Nanometrology Braunschweig
Principal Applicant, Speaker: A. Waag (2014-2017)

Part of the Metrology Initiative Braunschweig

(e) Intern. Graduate School on Metrology

Member of the Management Board and Principal Applicant
(NMWK-supported, inaugurated Oct. 2007)
Part of the Metrology Initiative Braunschweig

(f) Plasma-enhanced ALD of Nanocontact and Energy Conversion Systems (HBFG funding, 2013-2014)
(g) Ferrum - Functional Iron (NTH, 2013-2014) and LU Hannover (2015)

NTH-Project and Preproposal for a DFG Graduation School,
Associated Member. Contact: F. Renz



Webpages of Peter Lemmens

Impressum: Diese Web-Seite stellt keine Meinungsäußerung der TU Braunschweig dar. Verantwortlich ist P. Lemmens, Adresse: siehe oben. Die Inhalte auf den folgenden Seiten dienen allein der Förderung von Wissenschaft und Forschung und sind nicht kommerziell. Vorlesungsmaterialien werden hier nur für Studenten der TU Braunschweig zur Verfügung gestellt und unterliegen zum Teil einem Copyright der Autoren/Verlage. Die Quellen sind angegeben. Bei Unstimmigkeiten bitte ich um umgehende Information. 

p.lemmens at tu-bs.de, letzte Änderung: 22.05.2016