Topological magnons in quantum materials
Topology has become an essential paradigm in condensed matter, making it possible to classify phases of matter according to properties that are invariant under continuous deformations. Early research has mainly focused on electronic band structures, leading to the discovery of “topological insulators” for example. However, there is growing interest in applying topological concepts to bosons, in particular magnons. Magnons, which are collective excitations in magnetic materials, illustrate how topology influences magnetic dynamics and affects heat and spin transport. Analogues of topological insulators and semi-metals appear in their band structures. Magnons thus offer a platform for studying the interplay between magnetic symmetries and topology, examining the effect of interactions on topological bands, and generating protected spin currents at interfaces. The search for materials containing topological magnons is therefore crucial, especially for applications in magnonics, which exploit spin waves for fast data storage and processing.
This thesis project is dedicated to exploring these topological aspects in candidate quantum materials using neutron and X-ray scattering techniques in large scale facilities (ILL, ESRF, SOLEIL) to probe the magnon band structure in search of topological features such as Dirac or Weyl points. Experimental results will be supported by numerical and theoretical calculations of magnonic bands incorporating topological concepts.
Development of a microfluidic bioanalytical platform to quantify the cellular bio-distribution of a drug
A drug's mode of action and efficacy are correlated not only with its ability to accumulate in the targeted pathological tissues, i.e. its tissue bio-distribution, but also with its ability to specifically reach its molecular target within cells. Non-specific accumulation of a drug in these cells can be the cause of undesired effects, such as side effects during chemotherapy. In other words, assessing a drug's efficacy, specificity and absence of toxicity requires precise, quantitative determination of its cellular bio-distribution. Antibody-drug conjugates (ADCs) have become an indispensable tool in oncology, enabling vectorized therapy to preferentially target a subset of tumor cells expressing the antigen recognized by the antibody.
These ADCs target specific tumor cells expressing a particular antigen, thus limiting toxicity to healthy tissue. Radioactive labeling of drugs (3H, 14C) is a key method for quantifying their accumulation in tumor and non-tumor cells, in order to assess targeting accuracy and avoid undesirable side effects. However, the detection of low-level tritium emissions requires new technological solutions. The project proposes the development of an innovative microfluidic platform to detect and quantify these isotopes in single cells. This approach will enable us to better document ADC distribution in heterogeneous tissues and refine therapeutic strategies.
High Harmonic Generation in cavity for an attosecond quantum source
Attophysics is at the forefront of time-resolved spectroscopy. Indeed, it harnesses the shortest light pulse probe that can be produced experimentally, thanks to the high harmonic generation (HHG) process. A standard way to trigger HHG is to submit an atomic system to an oscillating electromagnetic field whose strength compares with the Coulomb potential bounding electrons with their nuclei. This non-linear, non-perturbative optical effect produces a broadband coherent radiation in the extreme ultraviolet (XUV) frequency range, which forms attosecond pulses (1e-18 s). Since its discovery in the late 1980s, continuous experimental and theoretical efforts have been dedicated to get a complete understanding of this complex phenomenon. Despite the tremendous success of attosecond science, there is still no consensus about a quantum description of the process. We foresee that such a description of HHG would push forward our understanding of non-linear optics and open up new perspectives for attosecond science.
Theoretical study of the physical and optical properties of some titanium oxide surfaces for greenhouse gas sensing applications
The international community is engaged in developing the policy to reduce greenhouse gases (GHGs) emission, in particular carbon dioxide (CO2), in order to reduce the risks associated to the global warming. Consequently, it is very important to find low-cost processes to dissociate and then capture carbon dioxide (CO2), as well as to develop low power, high performance sensors suitable to monitor GHGs reductions.A common and existing method for sensing the concentration of gases is achieved by using semiconducting metal oxides surfaces (MOS) like SnO2, ZnO, and TiO2. Moreover, one route to achieve CO2 dissociation is plasma assisted catalytic decomposition. However, surface defects, and in particular oxygen vacancies and charged trapped therein, play an important role in the (photo)reactivity of MOS. The way optical properties of surfaces are modified by such defects is not completely understood, nor is the additional effect of the presence of the gas. In some models, the importance of charge transfer is also emphasized.
In this Ph.D. work, theoretical methods will be used to model the surface with defects and predict the optical properties. The objective is threefold: To apply the theoretical frameworks developed at LSI for the study of defects to predict the defect charge states in bulk; To study the effect of the surface on the defect stability; to study bulk and surface optical properties, and find out spectroscopic fingerprints of the molecular absorption and dissociation near to the surface. Materials/gas under considerations are oxides like titanium oxide, eventually deposited on a layer on gold, and carbon dioxide. The theoretical method will be the time dependent density functional perturbation theory method (TDDFPT) developed at LSI in collaboration with SISSA, Trieste (Italy).
Ref.: I. Timrov, N. Vast, R. Gebauer, S. Baroni, Computer Physics Communications 196, 460 (2015).