ERC FUNDED PROJECTS

"One of the greatest challenges these days in condensed matter physics is the fundamental understanding of the mechanisms leading to high-Tc superconductivity and ultimately, as a result of that, the discovery of a material system exhibiting a superconducting state with a transition temperature Tc above room temperature. While several different classes of high-Tc materials have been discovered in the past decades, including the well-known CuO-based superconductors (cuprates) or the more recently discovered class of Fe-based superconductors (pnictides), the mechanisms behind high-Tc superconductivity remain controversial. Up to date, no theory exists which would allow for a rational design of a superconducting material with a transition temperature above room temperature. On the other hand, experiments on rather complex material systems often suffer from material imperfections or from a lack of tunability of materials’ properties within a wide range. Our experimental studies within this project therefore will focus on model-type systems which can be prepared and thoroughly characterized with atomic level precision. The growth of the model-type samples will be controlled vertically one atomic layer at a time and laterally by making use of single-atom manipulation techniques. Atomic-scale characterization at low energy-scales will be performed by low-temperature spin-resolved elastic and inelastic scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by non-contact atomic force microscopy and spectroscopy based techniques. Transport experiments will be conducted by a four-probe STM setup under well-defined ultra-high vacuum conditions. By having access to the electronic and spin, as well as to the vibrational degrees of freedom down to the atomic level, we hope to be able to identify the nature of and the conditions for inducing superconductivity at high temperatures, which could ultimately lead a knowledge-based design of high-Tc superconductors."

2 170 696 €

Start date: 2014-01-01, End date: 2018-12-31

Biological cells possess a chemical “sense of smell” and a physical “sense of touch”. Structure, dynamics, development, differentiation and even apoptosis of cells are guided by physical stimuli feeding into a regulatory network integrating biochemical and mechanical signals. Cells are equipped with both, force-generating structures, and stress sensors including force-sensitive structural proteins or mechanosensitive ion channels. Pathways from force sensing to structural and transcriptional controls are not yet understood. The goal of the proposed interdisciplinary project is to quantitatively establish such pathways, connecting the statistical physics and the mechanics to the biochemistry. We will measure and model the complex non-equilibrium mechanical structures in cells, and we will study how external and cell-generated forces activate sensory processes that (i) act (back) on the morphology of the cell structures, and (ii) lead to cell-fate decisions, such as differentiation. The most prominent stress-bearing and -generating structures in cells are actin/myosin based, and the most prominent mechanoactive and -sensitive cell types are fibroblasts in connective tissue and myocytes in muscle. We will first focus on actin/myosin bundles in fibroblasts and in sarcomeres in developing heart muscle cells. We will observe cells under the influence of exactly controlled external stresses. Forces on suspended single cells or cell clusters will be exerted by laser trapping and sensitively detected by laser interferometry. We furthermore will monitor mechanically triggered transcriptional regulation by detecting mRNA in the nucleus of mouse stem cells differentiating to cardiomyocytes. We will develop fluorescent mRNA sensors that can be imaged in cells, based on near-IR fluorescent single-walled carbon nanotubes. Understanding mechanical cell regulation has far-ranging relevance for fundamental cell biophysics, developmental biology and for human health.

2 425 200 €

Start date: 2014-06-01, End date: 2019-05-31

The world of quantum physics is usually associated with the microscopic cosmos of atoms and photons. In principle, but so far without any demonstration, even heavy objects can exhibit the distinguished properties of quantum world particles. In 1935, Einstein, Podolsky and Rosen (EPR) challenged a particular prediction of quantum theory saying that two particles can exist in a so-called entangled state in which the two particles do not have individually defined (‘local’) positions and momenta. Most interestingly, the existence of entangled states was subsequently fully confirmed in experiments with photons and atoms. The new project MassQ aims to test and to confirm quantum theory in the macroscopic world of massive, human-world sized objects by realizing an EPR entanglement experiment with heavy mirrors. Two kg-sized mirrors will be cooled to low temperature and their centre of mass motion driven by radiation pressure of intense laser light in such a way that the mirrors will lose their individually defined positions and momenta. As a result, their joint motion will form a unified massive quantum object. This project will realize a fundamental test of quantum theory in the so far unexplored regime of human-world sized objects. Recent advances in gravitational wave detector research and in opto-mechanics make this project feasible. The vision of this project points even further into the future. This project aims to lay the basis for a completely new class of physics experiments. Mirrors with kilogram masses have a proper gravitational field and cause a space-time curvature in their vicinity. This way, in principle, the dynamics of two heavy entangled mirrors need to be described not only by quantum theory but also by general relativity. Today it is completely unclear what the results of such a new class of physics experiments will be. Undoubtedly, they are important to illuminate the deep connection between the two most successful theories in physics.

1 566 210 €

Start date: 2014-02-01, End date: 2019-01-31

This proposal brings together the fields of ultracold Fermi gases and of mesoscopic systems. Starting with a two-dimensional (2D) Fermi gas, we will imprint small-scale potential structures onto the atoms. Thus, a mesoscopic system embedded in a 2D reservoir is produced. Specifically, we will imprint optical dipole potentials varying on a micrometre scale onto a 2D gas of 6Li atoms. Due to the widely different energy scales, the entropy of the atoms in the mesoscopic structures will be massively reduced as compared to the reservoir atoms. The atoms in the mesoscopic structures will be characterised by an innovative detection scheme with single atom sensitivity. The combination of mesoscopic potentials, single atom detection and entropy reduction will put us in a unique position to access new regimes of many-body physics. First, we will investigate a mesoscopic realisation of the 2D Hubbard model. Beyond the study of the fermionic Mott insulating phase and its excitations, the possibility to study staggered Hubbard models and create domain structures is a very attractive prospect. Most importantly, the massive entropy reduction inherent to the mesoscopic approach will enable us to observe antiferromagnetic ordering, the major milestone central to further progress in the field. Going beyond periodic structures, we will focus on the direct creation of mesoscopic model systems. In a bottom-up approach, we will realise a plaquette consisting of 2x2 sites, the essential building block for models of d-wave superconductivity. The creation of 1D structures with local defects will open the possibility to study phenomena such as spin-charge separation, Friedel oscillations and the rectification of atomic transport. Finally, the physics of open quantum systems will become accessible when studying the interaction between mesoscopic system and reservoir. In conclusion, I believe that the proposed research programme will bring a new level of functionality to the field.

1 236 060 €

Start date: 2013-10-01, End date: 2018-09-30