Background and rationale: Quantum spin liquids (QSLs) represent an intriguing state of matter, where quantum entanglement plays a decisive role. These states that are typically born out of geometrical frustration, remain magnetically disordered even at zero temperatures. In the majority of cases, the stabilization and destabilization mechanisms of QSLs remain vague. According to theory, perturbations to the simplest nearest-neighbor isotropic (Heisenberg) exchange Hamiltonian, like structural disorder, interactions with further neighbors, and magnetic anisotropy, are of key importance. As these effects are usually intertwined in real materials and since QSL realizations are scarce, the experimental confirmation of these predictions is eagerly anticipated.
Objectives and specific aims: The main objective of the proposed project is to provide a new experimental insight into the problem of perturbation by studying several novel representatives of the two most common frustrated spin lattices in two dimensions, the triangular lattice (TL) and the kagome lattice (KL). In the TL case we will focus on the predicted randomness-induced QSL-like states in the newly synthesized family of materials Ba2MnTe1-xWxO6, for which preliminary bulk characterizations hint at this intriguing effect. The same effect will be systematically investigated also in two representatives of KL, Zn-brochantite and Zn-barlowite, which feature different QSL ground states. Our specific aim is to find how impurities interact with various QSL states in a Kondo-like effect, which has been very recently observed for the first time in a magnetic insulator. Secondly, we will thoroughly investigate the influence of further-neighbor couplings and magnetic anisotropy on the ground state in the above-mentioned materials and in another KL representative YCu3(OH)6Cl3, where impurities are absent.
Methods to be used: To reach the goals of the project, complementary expertise is necessary, which is provided by our bilateral approach. We will employ a combination of highly sensitive local-probe techniques, each providing indispensable insight. The Swiss team are experts in muon spin relaxation (μSR), with the leader Dr. Hubertus Luetkens being the head of the Bulk μSR Group at the Paul Scherrer Institute (PSI) and in charge of the new μSR instrument FLAME that will start operation in 2020. The high magnetic fields and low temperatures that this instrument can reach perfectly fit the needs of this project. The Slovenian team lead by Prof. Dr. Andrej Zorko are experts in magnetic resonance techniques, including nuclear magnetic resonance (NMR) and electron spin resonance (ESR). The instruments at the Jožef Stefan Institute (JSI) cover a broad range of magnetic fields, while experiments under extreme conditions will be performed in specialized facilities. To complement the experiments numerical calculations will also be performed at JSI.
Expected results and impact for the field: Our holistic approach will provide missing information about the effects of various perturbations on the ground states of the TL and the KL models. The results will allow us to assess the theories of the randomness-induced QSL-like states and the predicted perturbation-dependent phase diagrams of both lattices. This is an important step towards understanding these enigmatic ground states. Moreover, the QSL concept may be related to other intriguing quantum phenomena, such as high-Tc superconductivity, and possesses a high application potential in quantum technologies. We plan to employ a PhD student on the Swiss side and to co-finance several researchers on the Slovenian side, including PhD students and postdocs. Young scientists involved in the project will thus have access to top-level facilities, expertise, and knowledge, as the project will foster frequent exchange of researchers between two leading laboratories in their respective fields.
Project phases and their realization:
Characterization of the ground states and randomness induced QSL state in TL Ba2MnTe1-xWxO6
Determination of the spin Hamiltonian and defect interactions in Zn-brochantite
Determination of the doping effect on the magnetic ground state of kagome antiferromagnets
Characterization of the magnetic ground states of YCu3(OH)6Cl3 and Y3Cu9(OH)19Cl8
Inhalation of fine particulate matter (PM ) and ultrafine nanoparticles in polluted air is knowingly associated with neurodegenerative and other chronic diseases, which are one of the major contributors to the global death burden. Even though increasing amounts of engineered nanoparticles enter the environment, our limited understanding of the mechanisms of their action hinders efficient prevention and treatment of associated health conditions.
To understand the causal relationship between exposure to nanoparticles and disease progression, it is crucial to discern Adverse Outcome Pathways (AOPs), which connect initiating events on the molecular level to the adverse outcome at the level of an organism via a complete sequence of causally linked key events. We have recently visualised such early supramolecular rearrangements at the NP-cell contact by advanced live-cell superresolution microscopy and spectroscopy techniques.
However, their slow acquisition process has precluded adequate sampling of such rare events to complete the AOPs.
We aim to improve the statistics of the captured rare events by developing the Intelligent Content-Aware Nanospectroscopy (iCAN). We will employ intelligent state-of-the-art computer-vision algorithms to automatically identify the content of interest for targeted nanospectroscopic measurements, which will allow us to identify and quantify early events following NP exposure. By additional evaluation of the response of individual cells to their local dose, we aim to causally connect the early events leading towards neurodegenerative effects of exposure to nanoparticles.
Project phases and their realization:
Automated recognition of events in images
Automated characterisation of events by advanced microscopic modalities
Correlation of the event rates and local dose with the cellular response
The aim of this project is to explore active turbulence of chiral orientational fields confined to spherical droplets, using combination of experiments and numerical modelling. The project addresses the four main research objectives: Research Objective 1: Realize Janus micro-spheres and micro-rods with surface functionalisation that will be propelled in the nematic liquid crystal (NLC), when an external electric field be applied. Research Objective 2: To propel Janus particles in NLCs by external electric field and determine the nature of their pair interaction in 2D. Research objective 3: To explore and understand the collective behaviour of electrically propelled Janus particles in 2D. Research Objective 4: To explore and understand collective behaviour of electrically propelled Janus particles –active turbulence- in chiral nematic droplets.
This is a very high risk project, which aims at studying active topology of electrically driven soft matter in 3D microscale confinement that has never been studied before. This will be possible by using state-of-the-art 3D imaging STED technique that allows for real-time imaging of topological defects formation and their identification. Given the tremendous complexity of orientationally ordered liquid crystals compared to isotropic fluids, the success of this project is likely to open the door to entirely new topological phenomena in self-organized active soft matter.
Project phases and their realization:
Materials and methods.
Single Janus particle in the nematic LC driven by the external electric field.
Pair interaction of Janus particles in a nematic LC propelled by the electric field.
Collective motion of electrically propelled Janus particles in a 2D nematic.
Collective motion of micro-rods in chiral nematic droplets.
Numerical simulations of active Janus particles in nematic.
Background and rationale: Quantum spin liquids (QSLs) represent an intriguing state of matter, where quantum entanglement plays a decisive role. These states are endorsed by geometrical frustration and remain magnetically disordered even at zero temperature. They feature unconventional magnetic excitations known as spinons, which behave as quasiparticles with complex interactions and statistics, making QSLs potentially useful for quantum computation. A number of QSL states, which differ by spinon dispersion, can be stabilized by different perturbations to the nearest-neighbor Heisenberg exchange Hamiltonian. The relevant perturbations include structural disorder, interactions with further neighbors and magnetic anisotropy. However, due to their complexity and difficult experimental determination, these states are very poorly understood.
Objectives and specific aims: The main objective of the proposed project is to provide the first experimental approach for microscopic determination of QSLs that will allow clear distinction between various possible states. We suggest a novel method, which uses impurities as in-situ probes of the host QSL state, an approach that is well-established in superconductors. We will exploit a spinon Kondo effect, which we have recently discovered and can be effectively detected by muon spectroscopy (SR). The focus will be on the quantum kagome antiferromagnetic model (KAFM), being a promising platform of the QSL states. Indeed, a theoretical consensus about the QSL ground state of this model has already been reached, yet, its true nature remains controversial. Both, states with zero or finite gap to the lowest-lying excitation have been theoretically proposed, but never conclusively confirmed by experiment. A specific aim of our study is to determine how different perturbations affect the selection of the QSL ground state of three most promising KAFM materials with seemingly fundamentally different spinon properties.
Methods to be used: To reach the project goals, various complementary expertise in experimental and theoretical physics and in chemistry are essential. Our team, therefore, consists of experts in sensitive localprobe magnetic techniques, state-of-the-art numerical calculations and advanced sample synthesis routes. The project leader has had a long record in the field of frustrated magnetism. Since 2008, he has published several top-level papers (4 Nat. Phys, 2 Nat. Commun., 10 PRL), the majority of them (1 Nat. Phys, 1 Nat. Commun., 7 PRL) as the corresponding author. This experience will provide the backbone for the planned activities, which include SR, nuclear magnetic resonance (NMR) and electron spin resonance (ESR) experiments, numerical renormalization group, finite temperature Lanczos and density-functional theory calculations, and hydrothermal sample syntheses. These will be performed at the Jožef Stefan Institute (IJS), with the exception of more specific experiments, like SR and experiments under extreme conditions (NMR and ESR at high fields and low temperatures) which will be performed in specialized partner laboratories at the Paul Scherrer Institute, Université Paris-Sud 11 and the National High Magnetic Field Laboratory.
Expected results and impact for the field: Our systematic study will overcome the pending issue of reliable QSL determination by providing a new local-probe-based approach. Furthermore, it will address the most fundamental questions related to various perturbations that are intrinsically present in KAFM materials. Our project will thus provide the foundations for understanding the enigmatic QSLs. The developed methodology will allow characterization of QSLs beyond the KAFM model. The knowledge about QSLs may also help explaining other intriguing quantum phenomena, like high-Tc superconductivity. Moreover, understanding the stability of QSLs and ways of their manipulation could be highly relevant for development of new quantum technologies.
Project phases and their realization:
Kondo response of herbertsmithite and the nature of its ground state
Spinon-spinon interactions in the Kondo response and the spin Hamiltonian of Zn-brochantite
Magnetic ground state of barlowite, its spin Hamiltonian and doping effects
The project aims to develop advanced soft materials with a giant mechanocaloric effect based on liquid crystal elastomers and to build a first prototype of mechanocaloric device. Specifically, we propose research on soft liquid-crystal-elastomer (LCE) based mechanocaloric materials, to initiate the development of novel mechanocaloric cooling elements for environmentally friendlier cooling technologies with superior energy efficiency. We will synthesize liquid crystal elastomers with optimized elastocaloric and barocaloric effect. These materials will be used as cooling elements in a prototype of mechanocaloric cooling device that will be developed and tested within the proposed project.
Description of the work programme:
The project will start with the search for physical and structural parameters such as the elastomer network architecture (main/side chain architecture, degree of mechanical anisotropy imprinted upon synthesis, crosslinker density), mesogenic unit properties (length, nematic-isotropic transition temperature), and the degree of sample swelling that can have significant impact on the magnitude of the elastocaloric and barocaloric response in different groups of the LCE materials. The LCE materials will be chosen to serve as cooling material in the prototype of the elastocaloric cooling device.
In this step the most optimal mechanocaloric materials chosen in the first step will be synthesized and characterized. These materials will be used later in the third step for the building of the prototype of the elastocaloric cooling device. In addition, in this step the planning of the technical implementation of the prototype elastocaloric device supported by modelling will be carried out.
In this final step the technical realization of the elastocaloric cooling device prototype based on the LCE together with characterization and optimization of its operation will be done. This step also includes the dissemination of the final results.
This project will form the basis for a completely new branch of scientific research and development, applying innovative AI methods to newly developed 64-channel sensor array for detection of trace vapors of dangerous molecules in the atmosphere. Lately, there has been a lot of activities the field of development of new e-nose methods and platforms for the obvious reason of terrorist attack prevention. Many different sensors and concepts were developed in the last decade with the aim of detecting very low concentrations of trace vapors of explosives such as TNT, PETN and RDX in the atmosphere in order to protect urban areas from terrorist threats. The current sensitivity of the state-of-the-art sensor systems allows us to detect very low concentrations of target molecules, of the order of 1 target molecule in 1012 to 1014 molecules of atmosphere. The successful realisation of numerous research projects (Strle et al., IEEE Sens. J., 2012) showed that micro-capacitive sensor arrays based on COMS micro-capacitors and low-noise detection chips are able to detect such low concentrations of dangerous vapors. The sensitivity we have achieved has pushed the boundaries of the existing sensor technology. Its greatest limitation is the chemical selectivity of the sensor array which, up until now, has consisted of at most 16 chemically selective functionalised micro-capacitors. The aim of this project is to improve signal processing and pattern recognition methods by developing a new, 64-channel senor system. This will be a small yet important step towards the realisation of an e-nose with a high density of sensors, which we expect to be made from thousands of olfactory cells, mimicking the efficiency of a dog’s nose. Based on the proposed research actvities, we want to introduce the concept of application of AI methods to improve the chemical selectivity of the 64-sensor array. As the first of its kind, this project will bring together an interdisciplinary team of physicists, chemists specialised in organic chemistry, microelectronic engineers, mathematicians and AI specialists.