Highlights of Max Planck Institute for the Physics of Complex Systems https://www.pks.mpg.de/ here are the highlights of Max Planck Institute for the Physics of Complex Systems en_GB Max Planck Institute for the Physics of Complex Systems Fri, 03 Feb 2023 01:37:08 +0100 Fri, 03 Feb 2023 01:37:08 +0100 TYPO3 EXT:news news-726 Thu, 02 Feb 2023 10:00:00 +0100 New Research Group: Superconductivity and Magnetic Correlations https://www.pks.mpg.de/de/smc We cordially welcome the arrival of our new group at the institute, headed by Alexander Wietek, who joins us from the Flatiron Institute. Alex's group is interested in the way quantum particles, like electrons or atoms, organize themselves while interacting with one another. This way, Alex and his colleagues aim at understanding how the macroscopic behavior of materials, like various forms of magnetism or superconductivity, emerges. Besides trying to explain existing experimental phenomena in solid-state physics, they investigate under which circumstances entirely new states of matter, like quantum spin liquids, can occur. To solve these questions, the new group is developing numerical technology to simulate quantum many-body systems. The quantum many-body problem is considered to be exponentially hard in the number of particles. One approach Alex is pursuing is to push the limits of exact simulations by developing high-performance computing software and distributed parallel algorithms for quantum many-body systems. Furthermore, the team is also embracing tensor network methods to reduce computational complexity by representing data efficiently. Welcome at MPI-PKS!! Institute's News news-725 Sat, 14 Jan 2023 22:00:00 +0100 Discrete time crystal created by two-frequency external driving https://www.nature.com/articles/s41567-022-01891-7 Time crystals are a freshly discovered nonequilibrium phase of matter without an equilibrium counterpart, stabilized by external periodic drives and characterized by broken spatiotemporal symmetry. Scientists from the Nonequilibrium quantum dynamics group at the Max Planck Institute for the Physics of Complex Systems, together with collaborators at the KTH Royal Institute of Technology and at UC Berkeley, created a critical time crystal in a system of long-range interacting nuclear spins. Designing a novel two-frequency external driving protocol allowed the scientists to monitor the time-crystalline behavior continuously (avoiding the wave function collapse), and take real-time movies displaying the formation, lifetime, and meltdown of this exotic phase of matter. The experimental platform used offers unprecedented clarity and measurement throughput, which turned out fundamental for determining the boundaries of the time-crystalline phase, and investigating in detail the melting dynamics of the time crystal as it gradually heats up. W. Beatrez et al., Nat. Phys. (2023) Publication Highlights news-723 Mon, 19 Dec 2022 22:00:00 +0100 Dynamical fractal discovered in clean magnetic crystal https://www.science.org/doi/10.1126/science.add1644 A new type of fractal has been discovered in a class of materials called spin ices—famous, among other reasons, for their emergent magnetic monopole excitations. Spin ice materials are some of the most researched and best understood topological magnets. Nevertheless, the unusual dynamical properties of spin ice have been puzzling scientists for almost two decades. An international research team, including Jonathan N. Hallén and Roderich Moessner of the Max Planck Institute for the Physics of Complex Systems, has now shown that the dynamical rules governing the motion of the magnetic monopoles constrain these to move on fractal structures. By hosting the monopole motion, the fractals cause the peculiar dynamical behaviours observed in spin ice materials. The discovery was surprising because the fractals were seen in a clean three-dimensional crystal, where they would not be expected conventionally. Even more remarkably, the fractals are visible in dynamical properties of the crystal, and hidden in static ones. The capacity of spin ice to exhibit such striking phenomena makes the team hopeful that spin ice will allow further surprising discoveries in the cooperative dynamics of even simple topological many-body systems. More details can be found in a press release (PDF). J. N. Hallén et al., Science 378, 1218 (2022) See also the related Science Perspective article by F. Flicker. Publication Highlights news-720 Mon, 12 Dec 2022 22:00:00 +0100 Recipe for a spin-orbital liquid https://www.nature.com/articles/s41567-022-01816-4 An international team of scientists including Roderich Moessner of the Max Planck Institute for the Physics of Complex Systems has observed an exotic quantum state of matter: a spin-orbital liquid formed on the pyrochlore oxide Pr2Zr2O7. Here, both spin and orbital degrees of freedom remain dynamic down to extremely low temperature. It is known from the long history of condensed matter physics that suppressing orbital order down to low temperatures is extremely difficult, a precondition for the next tricky step of obtaining a spin-orbital liquid state. Pr2Zr2O7 serves as a rare counterexample in which spins and orbitals are interlocked, so that fluctuation of one necessitates fluctuation of the other. More details can be found in a press release (PDF). N. Tang, Y. Grisenko, K. Kimura et al., Nat. Phys. (2022) See also the related Nat. Phys. News & Views article by V. S. Zapf, M. Lee, and P. F. S. Rosa. Publication Highlights news-718 Mon, 28 Nov 2022 22:00:00 +0100 Scaling Description of Creep Flow in Amorphous Solids https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.208001 Amorphous solids, which include colloidal glasses, dense emulsions, foams, and granular materials, are ubiquitous and important in both engineering and industry. When subjected to a suddenly imposed stress, they can exhibit a transient flow known as creep during which the flow rate decays as a power law over time. This power law is characterized by a quantity called the creep exponent. If the stress inducing the creep flow is low, the material eventually stops moving. But if this stress is sufficiently high, the power-law decay can be followed by sudden fluidization. Together with colleagues from École polytechnique fédérale de Lausanne (EPFL) and Université Paris-Saclay, Marko Popović of the Max Planck Institute for Physics of Complex Systems developed a theory of creep flow that can predict both the creep exponent and the time at which sudden fluidization occurs, as well as the temperature dependence of these two quantities. These predictions have been tested in numerical simulations and are consistent with previously published experimental observations. The key ingredient of the proposed theory is the new concept of a transient yield stress, which reflects the dynamics of the maximal stress that the material could sustain without flowing while it undergoes creep flow. Remarkably, the scaling of the creep exponent and the time of fluidization then follow from generic properties of the transient yield stress for both athermal and thermal systems. The success of the transient yield stress concept opens new exciting questions: What is the origin of the transient yield stress and what controls its dynamics? Can the concept of a transient yield stress be employed to describe other characteristic behaviours associated with the yielding of amorphous solids, such as shear banding instabilities? Marko Popović, et al., Phys. Rev. Lett. 129, 208001 (2022), Editors' Suggestion Selected for a Synopsis in Physics Publication Highlights news-715 Tue, 18 Oct 2022 22:00:00 +0200 Fragmented Cooper Pair Condensation in Striped Superconductors https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.177001 The mechanism behind high-temperature superconductors has long been a great mystery to physicists. Even though the fundamental physical equations of interacting electrons in these materials are well-known, their solution has proved challenging. Whether or not superconductivity or the so-called "stripe order", where the density of electrons forms regular waves called "stripes", is realized has been an open question and these two states of matter have been considered in competition to one another. This study now shows that stripe order and superconductivity can, in fact, get along with one another quite well. By performing exact numerical simulations on a minimal model for cuprate superconductors, the author demonstrates that there exist states of matter with exactly one superconducting condensate per stripe. Since there are multiple stripes in the systems, there are also multiple condensates, a phenomenon called "fragmentation". The physical picture proposed in this study agrees well with experimental observations and demonstrates the predictive power of modern numerical techniques to study quantum many-body systems. A. Wietek, Phys. Rev. Lett. 129, 177001 (2022) Publication Highlights news-713 Thu, 29 Sep 2022 11:04:00 +0200 Call for Distinguished PKS Postdoctoral Fellowship 2023 now open! https://www.pks.mpg.de/fileadmin/user_upload/MPIPKS/Contact/Work_with_us/BMO-28026090-MPI-Physik-komplexer-Systeme_3_.pdf Application deadline: 17 November 2022. Distinguished PKS postdoctoral fellows appear personally along with the departments and groups on the main research page of the institute and are expected to have at least one year of postdoctoral experience at an institution other than the one at which their PhD was awarded. Applications for this fellowship directly after completion of the PhD might be considered in exceptional cases. Please click on the link- button to see the full advertisement!  

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Institute's News
news-712 Tue, 20 Sep 2022 22:00:00 +0200 Responsive switching between subpopulations can stabilise microbial communities https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.4.033224 The different microbial species in complex ecological communities like the human microbiome often have different subpopulations called phenotypes, between which they can switch stochastically or in response to environmental cues, such as toxins released by competitors or antibiotics. Pierre Haas of the Max Planck Institute for the Physics of Complex Systems and the Max Planck Institute of Molecular Cell Biology and Genetics and collaborators at the University of Cambridge have analysed the ecological implications of such responsive switching. They combined a statistical analysis of many-species systems, a numerical study of a minimal two-species model, and analytical results for still simpler mathematical models. While responsive switching to a rare phenotype is destabilising on average, they could show that responsive switching to a rare "attack" phenotype is stabilising on average. A similar "attack" subpopulation was recently observed experimentally, which underlines the importance of responsive switching for ecological stability. P. A. Haas, M. A. Gutierrez, N. M. Oliveira, and R. E. Goldstein, Phys. Rev. Research 4, 033224 (2022) Publication Highlights news-710 Fri, 02 Sep 2022 22:00:00 +0200 The rise to royalty; how paper wasps balance specialization and plasticity https://doi.org/10.1016/j.cels.2022.08.002 Biological systems fascinate scientists across disciplines because of the highly complex structures that emerge from these systems, from cells to organisms and societies. While biological systems fulfil highly specialised tasks despite noisy signals, they can also rapidly break up these structures and perform entirely different tasks when the right signals are present. A new study in Cell Systems published by Adolfo Alsina and Steffen Rulands from MPI-PKS, Wolf Reik from the Babraham Institute in Cambridge and Solenn Patalano from the BBSRC Alexander Fleming in Athens used paper wasps as a paradigmatic example. Paper wasps are social insects that display societal division of labor between workers and a queen. While this division of labor remains stable for the entire lifetime of the queen, when the queen is removed from the nest or dies the remaining workers can rapidly change their behavior and establish a new queen. Due to this behavior the paper wasps serve an experimental testing ground to study biological plasticity. Rulands and colleagues carried out a unique set of experiments in Panama where they removed the queen from paper wasp nests and then followed the reorganization process back to the intact society simultaneously on different scales of biological organization: from time-resolved profiling of brains using multi-omics of the brains to colony-level video recordings. Using theory, they showed that by balancing antagonistic molecular and colony-level processes these societies are able to distinguish between different kinds of perturbations affecting the nest: intrinsic perturbations, such as molecular noise, affect insects independently of each other and these perturbations are actively suppressed by the society. By contrast, extrinsic perturbations affect the entire society and the society reacts plasticly. Given the above, the authors conclude that by employing a self-organised multi-scale mechanism Polistes manages to overcome the seeming paradox between specialisation and plasticity. S. Patalano et al., Cell Systems 13, 1–12 (2022) Publication Highlights news-709 Thu, 01 Sep 2022 14:00:00 +0200 New Research Group: Nonequilibrium Quantum Dynamics https://www.pks.mpg.de/nqd The research in our new group "Nonequlibrium Quantum Dynamics" lies at the intersection of many-body dynamics, quantum simulation, quantum control, and applications of machine learning in physics. It is headed by Marin Bukov, who joins MPI-PKS from the University of Sofia. Marin and his coworkers are interested in problems of both fundamental nature and immediate applications. They develop approximate analytical methods, and design numerical techniques in order to investigate different problems in quantum dynamics, and collaborate with theory groups and experimental labs to test the theoretical predictions against experiment. Welcome to the institute, Marin!  

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Institute's News
news-708 Tue, 02 Aug 2022 22:00:00 +0200 The full spectrum of a quantum many-body system in one shot https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.066401 Quantum excited states underpin new states of matter, support biological processes such as vision, and determine opto-electronic properties of photovoltaic devices. Yet, while ground-state properties can be determined by rather accurate computational methods, there remains a need for theoretical and computational developments to target excited states efficiently. Inspired by the duplication of the Hilbert space used to study black-hole entanglement and the electronic pairing of conventional superconductivity, researchers from the Max Planck Institute for the Physics of Complex Systems and their collaborators from Munich and Modena have developed a new scheme to compute the full spectrum of a quantum many-body Hamiltonian, rather than only its ground or lowest-excited states. An important feature of their proposed scheme is that these spectra can be computed in a one-shot calculation. The scheme thus provides a novel variational platform to excited-state physics. It is also suitable for efficient implementation on quantum computers, so has the potential to enable unprecedented calculations of excited-state processes of quantum many-body systems. C. L. Benavides-Riveros et al., Phys. Rev. Lett. 129, 066401 (2022), Editors' Suggestion Publication Highlights news-707 Mon, 04 Jul 2022 22:00:00 +0200 Cells sense their way together https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.148101 Much like animals can trace odors, cells also move toward certain chemicals. In fact, cells often do this in groups, which can be up to millions of individuals strong. But how do these cell populations manage to move together as a cohesive unit while following chemical cues? New work by Ricard Alert of the Max Planck Institute for the Physics of Complex Systems and collaborators shows that the answer lies in limitations in the ability of cells to sense chemicals at high concentrations. Thus, the work bridges scales by connecting the sensing of tiny molecules by individual cells to the shape and motion of an entire cell population, which can be centimeters or even larger in size. The work is important because it reveals a potentially general principle: Sensing—a distinguishing feature of living systems—governs the ability of cells to migrate in groups. This principle could operate in many other examples of collective migration, as cells and other living creatures can sense and follow a variety of stimuli, such as electric fields, temperature, and light intensity. Finally, the new results open a tantalizing question for future work: Has evolution pushed the sensing limitations of cells to ensure that they can follow chemical cues as a cohesive group? (Image credit: Mariona Esquerda Ciutat.) R. Alert, A. Martínez-Calvo, and S. S. Datta, Phys. Rev. Lett. 128, 148101 (2022) Publication Highlights news-705 Wed, 22 Jun 2022 22:00:00 +0200 Anomalous dynamics and equilibration in the classical Heisenberg chain https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.L100403 The search for departures from standard hydrodynamics in many-body systems has yielded a number of promising leads, especially in low dimension. Researchers at the Max Planck Institute for the Physics of Complex Systems studied one of the simplest classical interacting lattice models, the nearest-neighbour Heisenberg chain, with temperature as tuning parameter. Their numerics expose strikingly different spin dynamics between the antiferromagnet, where it is largely diffusive, and the ferromagnet, where they observe strong evidence either of spin superdiffusion or an extremely slow crossover to diffusion. At low temperatures in the ferromagnet, they observe an extremely long-lived regime of remarkably clean Kardar-Parisi-Zhang (KPZ) scaling (see figure). The anomalous behaviour also governs the equilibration after a quench, and, remarkably, is apparent even at very high temperatures. A. J. McRoberts, T. Bilitewski, M. Haque, and R. Moessner, Phys. Rev. B 105, L100403 (2022) Publication Highlights news-704 Tue, 14 Jun 2022 22:00:00 +0200 Non-Markovian Quantum State Diffusion: Matrix-product-state approach to the hierarchy of pure states https://journals.aps.org/pra/abstract/10.1103/PhysRevA.105.L030202 An important but challenging task is to treat mesoscopic systems that are coupled to a complex environment at finite temperature. Alexander Eisfeld of the Max Planck Institute for the Physics of Complex Systems and his collaborators have derived a stochastic hierarchy of matrix product states (HOMPS) for non-Markovian dynamics, which is numerically exact and efficient. In this way the exponential complexity of the problem can be reduced to scale polynomially with the number of particles and modes of the environment. An additional feature caused by the stochastic noise is that individual trajectories stay well localized. The validity and efficiency of HOMPS is demonstrated for the spin-boson model and long chains where each site is coupled to a structured, strongly non-Markovian environment. X. Gao, J. Ren, A. Eisfeld, and Z. Shuai, Phys. Rev. A 105, L030202 (2022) Publication Highlights news-703 Mon, 13 Jun 2022 18:00:00 +0200 New Research Group: Dynamics of quantum information https://www.pks.mpg.de/de/forschung/abteilungen-und-gruppen A warm welcome to Pieter Claeys! Coming to our institute from the University of Cambridge, Pieter establishes the research group "Dynamics of quantum information". The group’s research lies at the interface of condensed matter physics and quantum information, using a variety of theoretical and numerical approaches to study the dynamics of quantum many-body systems. Research topics include the dynamics of entanglement, quantum chaos and thermalization, unitary circuit models, and general aspects of non-equilibrium quantum dynamics. The group will also focus on bridging recent advances in the dynamics of quantum systems and quantum computation.  

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Institute's News
news-702 Tue, 07 Jun 2022 11:49:47 +0200 "Physik-Preis Dresden 2022" awarded to Professor Tomaž Prosen On May 24, 2022, Prof. Tomaž Prosen from the University of Ljubljana in Slovenia received the "Physik-Preis Dresden" (Dresden Physics Prize), jointly awarded by the TU Dresden and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS). The theoretical physicist receives the award for his outstanding work on quantum mechanical many-body systems, nonequilibrium statistical physics, quantum information, classical chaos and quantum chaos. Tomaž Prosen has authored over 200 publications on this broad range of topics, which have over 7000 citations and are recognized in expert circles worldwide. In 2016, he received a prestigious ERC Advanced Grant. The award ceremony took place at a festive colloquium in the Recknagel Building of the TU Dresden, preceded by a reception. Prof. Carsten Timm, Dean of the Faculty of Physics, gave the welcome address, and Prof. Roderich Moessner of MPI-PKS delivered the laudation. The Physik-Preis Dresden was endowed in 2015 by Dresden physicist Prof. Peter Fulde, the founding director of the MPI-PKS. The prize winners are determined by a joint commission of the TU Dresden and the MPI-PKS. In addition to the central criterion of scientific excellence, it is particularly important for the decision that the work of the award winners is of special significance for the cooperation between the two DRESDEN-concept partners MPI-PKS and TU Dresden and that their connection has been further strengthened in the long term. The 2022 awardee, Prof. Tomaž Prosen, has a wide range of connections to the professorships at the Institute for Theoretical Physics at TU Dresden and at MPI-PKS due to his broad scientific orientation. On May 24, 2022, Prof. Tomaž Prosen from the University of Ljubljana in Slovenia received the "Physik-Preis Dresden" (Dresden Physics Prize), jointly awarded by the TU Dresden and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS). The theoretical physicist receives the award for his outstanding work on quantum mechanical many-body systems, nonequilibrium statistical physics, quantum information, classical chaos and quantum chaos.

Tomaž Prosen has authored over 200 publications on this broad range of topics, which have over 7000 citations and are recognized in expert circles worldwide. In 2016, he received a prestigious ERC Advanced Grant. The award ceremony took place at a festive colloquium in the Recknagel Building of the TU Dresden, preceded by a reception. Prof. Carsten Timm, Dean of the Faculty of Physics, gave the welcome address, and Prof. Roderich Moessner of MPI-PKS delivered the laudation.

The Physik-Preis Dresden was endowed in 2015 by Dresden physicist Prof. Peter Fulde, the founding director of the MPI-PKS. The prize winners are determined by a joint commission of the TU Dresden and the MPI-PKS. In addition to the central criterion of scientific excellence, it is particularly important for the decision that the work of the award winners is of special significance for the cooperation between the two DRESDEN-concept partners MPI-PKS and TU Dresden and that their connection has been further strengthened in the long term. The 2022 awardee, Prof. Tomaž Prosen, has a wide range of connections to the professorships at the Institute for Theoretical Physics at TU Dresden and at MPI-PKS due to his broad scientific orientation.

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Awards and Honors
news-700 Wed, 25 May 2022 11:00:00 +0200 Left-right symmetry of zebrafish embryos requires surface tension https://www.nature.com/articles/s41586-022-04646-9 Bilateral symmetry of the vertebrate musculoskeletal system is necessary for proper function and its defects are associated with debilitating conditions, such as scoliosis. In a collaboration with biologists from the École polytechnique fédérale de Lausanne (EPFL) in Switzerland, Marko Popović of the Max Planck Institute for Physics of Complex Systems has studied the early stage of body segmentation using zebrafish as a model organism. They discovered that biochemical signalling and transcriptional processes that drive segmentation are not sufficient to explain the precision and symmetry of tissue shapes and sizes. However, they found that surface tension forces of the newly formed segments are a crucial component of the mechanism that is responsible for recovery and maintenance of the symmetric body plan. This discovery highlights the importance of physical interactions for precise and robust development of living beings. S. R. Naganthan, M. Popovic, and A. C. Oates, Nature 605, 516-521 (2022) Publication Highlights news-698 Thu, 05 May 2022 18:00:00 +0200 New Research Group: Transport and flows in complex environments https://www.pks.mpg.de/de/tfce We cordially welcome Christina Kurzthaler at the institute! Christina joins MPI-PKS from Princeton University and establishes the research group "Transport and flows in complex environments“. The group aims to unravel physical phenomena arising in soft and active matter, with emphasis on the role of transport and flows for biological systems and microfluidics. Its research topics range from the hydrodynamics of swimming bacteria and their interactions with their environments to the statistical physics of active transport in porous materials to the motion of colloidal suspensions in microfluidic settings. While the group's work is theoretical, it seeks to establish collaborations with experimentalists of the Dresden research community.  

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Institute's News
news-697 Mon, 18 Apr 2022 11:00:00 +0200 Novel quantum phases of droplets https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.103201 Attractive forces are ubiquitous in nature: they glue very different objects ranging from atomic nuclei, droplets of water, to stars, galaxies, and black holes. Peter Karpov and Francesco Piazza of the Max Planck Institute for the Physics of Complex Systems have now demonstrated that highly tuneable attractive interactions can be engineered artificially using optical cavities, leading to various novel phases of quantum droplets of ultracold atoms. Upon tuning the cavity-mediated interactions it is possible to switch between superfluid droplets and incompressible water-like droplets, as well as to realise crystalline and even more exotic supersolid droplets combining superfluid and solid properties. P. Karpov and F. Piazza, Phys. Rev. Lett. 128, 103201 (2022) Publication Highlights news-696 Wed, 30 Mar 2022 11:00:00 +0200 Molecular Assembly Lines in Active Droplets https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.108102 A fundamental question in biology is how complexes of several molecules can assemble reliably. Tyler Harmon and Frank Jülicher of the Max Planck Institute for the Physics of Complex Systems have now shown that a molecular assembly line can be self-organized by active droplets where it can form spontaneously. This assembly line arranges different assembly steps spatially so that a specific order of assembly is achieved and incorrect assembly is suppressed. They have shown how assembly bands are positioned and controlled and discuss the rate and fidelity of assembly as compared to other assembly scenarios. T. S. Harmon and F. Jülicher, Phys. Rev. Lett. 128, 108102 (2022) Publication Highlights