# Highlights

Awards and Honors

### Hertha-Sponer-Preis 2011 der DPG

Martina Hentschel vom Dresdner Max-Planck-Institut für Physik komplexer Systeme erhält den mit 3.000 Euro dotierten „Hertha-Sponer-Preis“ der Deutschen Physikalischen Gesellschaft. Forschungsschwerpunkt der 39-jährigen Wissenschaftlerin ist die theoretische Beschreibung mesoskopischer elektronischer und optischer Systeme. Ihre Arbeiten sind für die Entwicklung miniaturisierter Laser von praktischer Bedeutung.
Publication Highlights

### A Homonuclear Molecule with a Permanent Electric Dipole Moment

Permanent electric dipole moments in molecules require a breaking of parity symmetry. Conventionally, this symmetry breaking relies on the presence of heteronuclear constituents. We report the observation of a permanent electric dipole moment in a homonuclear molecule in which the binding is based on asymmetric electronic excitation between the atoms. These exotic molecules consist of a ground-state rubidium (Rb) atom bound inside a second Rb atom electronically excited to a high-lying Rydberg state. Detailed calculations predict appreciable dipole moments on the order of 1 Debye, in excellent agreement with the observations. Weibin Li, Thomas Pohl, Jan-Michael Rost, Seth T. Rittenhouse, Hossein R. Sadeghpour, Johannes Nipper, Bjoern Butscher, Jonathan Balweski, Vera Bendowsky, Robert Löw, Tilman Pfau Science 334, 1110 (2011)
Awards and Honors

### Paul Ehrlich- und Ludwig Darmstädter-Nachwuchspreis 2011 der Paul Ehrlich-Stiftung

Wie differenzieren sich Zellen in die verschiedenen Zelltypen, die einen lebenden Organismus ausmachen? Neben molekularen Mechanismen spielen dabei mechanische Prozesse eine wesentliche Rolle. Wie diese Parameter miteinander interagieren, steht im Zentrum der Forschungsaktivitäten von Dr. Stephan Grill. Der Biophysiker hat dazu eine Methode entwickelt, mit der die mechanischen Kräfte in lebenden Zellen gemessen werden können. Mit Hilfe eines Lasers kann er bestimmte Zellstrukturen minimal-invasiv zerstören. Deren Fragmente bewegen sich danach voneinander weg, falls die Struktur unter mechanischer Spannung stand. Auf diese Weise erhält der Wissenschaftler einen Überblick darüber, wo in der Zelle mechanische Kräfte walten.
Publication Highlights

### Polarization of PAR Proteins by Advective Triggering of a Pattern-Forming System

In the Caenorhabditis elegans zygote, a conserved network of partitioning defective 4 (PAR) polarity proteins segregate into an anterior and a posterior domain, facilitated by flows of the cortical actomyosin meshwork. The physical mechanisms by which stable asymmetric PAR distributions arise from transient cortical flows remain unclear. We present evidence that PAR polarity arises from coupling of advective transport by the flowing cell cortex to a multistable PAR reaction-diffusion system. By inducing transient PAR segregation, advection serves as a mechanical trigger for the formation of a PAR pattern within an otherwise stably unpolarized system. We suggest that passive advective transport in an active and flowing material may be a general mechanism for mechanochemical pattern formation in developmental systems. W. Goehring, Philipp Khuc Trong, Justin S. Bois, Debanjan Chowdhury, Ernesto M. Nicola, Anthony A. Hyman, Stephan W. Grill Science 334, 1137 (2011)
Awards and Honors

### Marian-Smoluchowski-Emil-Warburg-Preis 2011 der DPG

Der Dresdner Physiker Peter Fulde, emeritierte Direktor des Max-Planck-Instituts für Physik komplexer Systeme, erhält den deutsch-polnischen „Marian-Smoluchowski-Emil-Warburg-Preis“, der mit 3.000 Euro dotiert ist. Der 74-Jährige wird für seine Beiträge zur Theorie der Festkörperphysik ausgezeichnet. Peter Fulde hat insbesondere zur Erforschung der Supraleitung, des Magnetismus und zum Verständnis „elektronischer Korrelationen“ maßgeblich beigetragen.
Institute's News

### New research group 'Computational Biology and Evolutionary Genomics'

The joint junior research group between our institute and the MPI of Molecular Cellbiology and Genetics is headed by Dr. Michael Hiller and uses computational approaches to link phenotypic differences between species to differences in their genomes, which is key to understand how nature’s phenotypic diversity evolved.
Institute's News

### New research group 'Collective Dynamics of Cells'

The research group headed by Dr. Vasily Zaburdaev develops and applies methods of statistical physics helping to understand complex biological phenomena.
Publication Highlights

Vulnerabilities related to weak passwords are a pressing global economic and security issue. We report a novel, simple, and effective approach to address the weak password problem. Building upon chaotic dynamics, criticality at phase transitions, CAPTCHA recognition, and computational round-off errors we design an algorithm that strengthens security of passwords. The core idea of our method is to split a long and secure password into two components. The first component is memorized by the user. The second component is transformed into a CAPTCHA image and then protected using evolution of a two-dimensional dynamical system close to a phase transition, in such a way that standard brute-force attacks become ineffective. We expect our approach to have wide applications for authentication and encryption technologies. T.V.Laptyeva, S. Flach, K. Kladko arXiv:1103.6219v1 (2011)
### Emerging local Kondo screening and spatial coherence in the heavy-fermion metal YbRh$_2$Si$_2$
The entanglement of quantum states is both a central concept in fundamental physics and a potential tool for realizing advanced materials and applications. The quantum superpositions underlying entanglement are at the heart of the intricate interplay of localized spin states and itinerant electronic states that gives rise to the Kondo effect in certain dilute magnetic alloys. In systems where the density of localized spin states is sufficiently high, they can no longer be treated as non-interacting; if they form a dense periodic array, a Kondo lattice may be established1. Such a Kondo lattice gives rise to the emergence of charge carriers with enhanced effective masses, but the precise nature of the coherent Kondo state responsible for the generation of these heavy fermions remains highly debated. Here we use atomic-resolution tunnelling spectroscopy to investigate the low-energy excitations of a generic Kondo lattice system, YbRh$_2$Si$_2$. We find that the hybridization of the conduction electrons with the localized 4f electrons results in a decrease in the tunnelling conductance at the Fermi energy. In addition, we observe unambiguously the crystal-field excitations of the Yb$^{3+}$ ions. A strongly temperature-dependent peak in the tunnelling conductance is attributed to the Fano resonance resulting from tunnelling into the coherent heavy-fermion states that emerge at low temperature. Taken together, these features reveal how quantum coherence develops in heavy 4f-electron Kondo lattices. Our results demonstrate the efficiency of real-space electronic structure imaging for the investigation of strong electronic correlations, specifically with respect to coherence phenomena, phase coexistence and quantum criticality. S. Ernst, S. Kirchner, C. Krellner, C. Geibel, G. Zwicknagel, F. Steglich & S. Wirth Nature 474, 362 (2011)