Machine Learning-Accelerated Electron Density Calculations
Density Functional Theory (DFT) in the Kohn-Sham formalism is one of the most widespread methods for simulating microscopic properties in solid-state physics and chemistry. Its main advantage lies in its ability to strike a favorable balance between accuracy and computational cost. The continuous evolution of increasingly efficient numerical techniques has constantly broadened the scope of its applicability.
Among these techniques that can be associated with DFT, machine learning is being used more and more. Today, a very common application consists in producing potentials capable of predicting interactions between atoms using supervised learning models, relying on properties computed by DFT.
The objective of the project proposed as part of this thesis is to use machine learning techniques at a deeper level, notably to predict the electronic density in crystals or molecules. Compared to predicting properties such as forces between atoms, calculating the electronic density presents certain challenges: the electronic density is high-dimensional since it must be calculated throughout all space; its characteristics vary strongly from one material to another (metals, insulators, charge transfer, etc.). Ultimately, this can represent a significant computational cost. There are several options to reduce the dimensionality of the electronic density, such as computing projections or using localization functions.
The final goal of this project is to be able to predict, with the highest possible accuracy, the electronic density, in order to use it as a prediction or as a starting point for calculations of electron-specific properties (magnetism, band structure, for example).
In a first stage, the candidate will be able to implement methods recently proposed in the literature; in a second part of the thesis, it will then be necessary to propose new ideas. Finally, the implemented method will be used to accelerate the prediction of properties of large systems involving charge transfers, such as defect migration in crystals.
Turbulent geophysical flows above topography
The project is focused on the large-scale organization and the energy budget of idealized oceanic flows above random topography. We will first characterize the enhanced energy dissipation due to the topography and its impact on the transport properties of an idealized parcelle of Ocean. To wit, we will consider models of increasing complexity, from quasi-two-dimensional to fully three-dimensional. We will then turn to the large-scale spatial organization of the flow, building on recent progress regarding the application of statistical mechanics to such flows. A special effort will be devoted to adapting these tools to forced-dissipative flows.
Interface physics of ferroelectric AlBN/Ga2O3 and AlBN/GaN stacks for power electronics
Commercial aviation accounts for about 2.5% total world CO2 emissions (1bT). A true, long-term, clean perspective eliminating a significant part of CO2 emissions is electric. One viable solution could be the hybrid airplane in which gas turbines are used for take-off and landing and in-flight cruising is electrically powered. Such a solution requires high voltage components. Fundamental research is required to optimize materials for integration into electronic components, capable of sustaining these power ratings.
The original idea of the Ferro4Power proposal is to increase the range of applications of Ga2O3 and GaN based devices by introducing a high breakdown, power electronics compatible, ferroelectric layer into the device stack. The up or down polarization state of the ferroelectric layer will provide an electric field capable of modulating the Ga2O3 and GaN valence and conduction bands, and hence the properties of possible devices, such as Schottky diodes (SBD), hybrid depletion mode transistors for Ga2O3 and high frequency HEMTs for GaN. Our hypothesis is to control the electronic bands of Ga2O3 and GaN using an adjacent AlBN.
We will explore the chemistry and electronic structure of AlBN/Ga2O3 and AlBN/GaN interfaces, focusing on the key phenomena of polarization screening, charge trapping/dissipation, internal fields. The project will use advanced photoelectron spectroscopy techniques including synchrotron radiation induced Hard X-ray photoelectron spectroscopy and Photoemission electron microscopy as well as complementary structural analysis including high-resolution electron microscopy, X-ray diffraction and near field microscopy.
The results should therefore be of interest to both physicists studying fundamental aspects of functionality in artificial heterostructures and engineers working in R & D applications of power electronics.
Merging Optomechanics and Photonics: A New Frontier in Multi-Physics Sensing
Optomechanical sensors are a groundbreaking class of MEMS devices, offering ultra-high sensitivity, wide bandwidth, and seamless integration with silicon photonics. These sensors enable diverse applications, including accelerometry, mass spectrometry, and gas detection. Optical sensors, leveraging photonic integrated circuits (PICs), have also shown great potential for gas sensing.
This PhD focuses on developing a hybrid multi-physics sensor, integrating optomechanical and optical components to enhance sensing capabilities. By combining these technologies, the sensor will provide unprecedented multi-dimensional insights, pushing MEMS-enabled silicon photonic devices to new limits.
At CEA-Leti, you will access world-class facilities and expertise in MEMS fabrication, photonics, and sensor integration. Your work will involve:
-Sensor Design – Using analytical Tools and simulation software for numerical analysis to optimize device architecture.
-Cleanroom Fabrication – Collaborating with CEA’s expert teams to develop the sensor.
-Experimental Characterization – Conducting optomechanical and optical evaluations.
-Benchmarking & Integration – Assessing performance with optics, electronics, and fluidics.
This PhD offers a unique chance to merge MEMS and silicon photonics in a cutting-edge research environment. Work at CEA-Leti to pioneer next-generation sensor technology with applications in healthcare, environmental monitoring, and beyond. Passionate about MEMS, photonics, and sensors? Join us and help shape the future of optomechanical sensing!
Electronic effects dans les cascades de collisions dans le GaN
In radiation environments like space and nuclear plants, microelectronic devices are subject to intense flux of particles degrading the devices by damaging the materials they are made of. Particles collide with atoms of the semi-conducting materials, ejecting them for their lattice site. Those displaced atoms also collide and set in motion a new generation of atoms, and so on, leading to a cascade of collisions which creates defects in the material. Moreover, primary or secondary particles (created following interaction with a neutron for example) also specifically interact with electrons of the target material, and lose kinetic energy in doing so by promoting electrons to higher energy bands. This aspect is called electronic stopping. Simulations of collision cascades must therefore describe both nuclei-nuclei collisions and electronic stopping effects.
The preferred method for collision cascades simulations at the atomic scale is Molecular Dynamics (MD). However, electronic effects are not included in this method as electrons are not taken into account explicitly. To circumvent this issue, additional modules have to be employed on top of MD to model electronic effects in a collision cascade. The state-of-the-art regarding electronic stopping simulation of a projectile in a target material is the real time - time dependent density functional theory (RT-TDDFT). The purpose of this thesis is to combine MD and RT-TDDFT to perform collision cascades simulations in GaN and study the influence of electronic effects. In addition to skills common to all thesis, the candidate will develop very specific skills in different atomic scale simulation methods, solid state physics, particle-matter interactions, linux environment and programming.
Measurement of the speed of sound in H2 and He, key components of gas giant interiors.
The goal of this thesis is to study hydrogen-helium mixtures in the fluid phase under high pressure and high temperature using Raman and Brillouin spectroscopy. The experiments will be conducted in a diamond anvil cell with laser heating, allowing exploration of a wide range of pressure and temperature conditions representative of the interiors of gas giant planets (1-300 GPa, 300-4000 K). Raman spectroscopy will be used to probe possible chemical changes occurring under extreme conditions, while Brillouin spectroscopy will provide access to the adiabatic sound velocity and the equations of state of these fluid mixtures. These data will be particularly useful for improving the modeling of Jupiter and Saturn’s interiors.
The solid-state systems, presently considered for quantum computation, are built from localized two-level systems, prime examples are superconducting qubits or semiconducting
quantum dots. Due to the fact that they are localized, they require a fixed amount of hardware per qubit.
Propagating or “flying” qubits have distinct advantages with respect to localised ones: the hardware footprint depends only on the gates and the qubits themselves (photons) can be created on demand making these systems easily scalable. A qubit that would combine the advantages of localised two-level systems and flying qubits would provide a paradigm shift in quantum technology. In the long term, the availability of these objects would unlock the possibility to build a universal quantum computer that combines a small, fixed hardware footprint and an arbitrarily large number of qubits with long-range interactions. A promising approach in this direction is to use electrons rather than
photons to realise such flying qubits. The advantage of electronic excitations is the Coulomb interaction, which allows the implementation of a two-qubit gate.
The aim of the present Phd will be the development of the first quantum-nanoelectronic platform for the creation, manipulation and detection of flying electrons on time scales down to the picosecond and to exploit them for quantum technologies.
Relationship between the nature of hard carbons and the properties of electrodes for Na-ion batteries
Hard carbons are the most commonly used negative electrode materials in Na-ion batteries. Their capacity exceeding 300 mAh/g, low operating voltage, long lifespan, and power performance make them the best option for commercializing Na-ion batteries. However, several challenges remain to approach the performance of low-impact Li-ion technologies like LF(M)P/graphite. One major limitation is their low volumetric density. Their disordered nature and resulting microporosity lead to a lower skeletal density compared to graphite. This significantly affects both the volumetric and gravimetric energy densities due to the difficulty of compressing the electrodes.
The main objective of this thesis is to establish a link between the material's skeletal density and the electrode's calendering capability to reduce its porosity. First, we will evaluate the relationship between the structure, morphology, and surface state of hard carbon and the electrode's density. We will attempt to understand the impact of calendering on the material’s properties. Then, we will assess the tortuosity and conductivity of hard carbon electrodes to predict their performance. Finally, we will work on improving and optimizing the electrodes in terms of energy densities, focusing particularly on electrode formulations.
Measuring quantum decoherence and entanglement in attosecond photoemission
The PhD project is centered on the advanced study of attosecond photoemission dynamics. The objective is to access in real time decoherence processes induced, e.g., by electron-ion quantum entanglement. To that aim, the young researcher will develop attosecond spectroscopy techniques making use of a new high repetition rate Ytterbium laser.
Detailed summary :
In recent years, there has been spectacular progress in the generation of attosecond (1 as=10-18 s) pulses, awarded the 2023 Nobel Prize [1]. These ultrashort pulses are generated from the strong nonlinear interaction of short intense laser pulses with gas jets [2]. They have opened new prospects for the exploration of matter at the electron intrinsic timescale. Attosecond spectroscopy allows studying in real time the quantum process of photoemission and shooting the 3D movie of the electron wavepacket ejection [3, 4]. However, these studies were confined to fully coherent dynamics by the lack of experimental and theoretical tools to deal with decoherence and quantum entanglement. Recently, two techniques have been proposed to perform a quantum tomography of the photoelectron in its final asymptotic state [5, 6].
The objective of the PhD project is to develop attosecond spectroscopy to access the full time evolution of decoherence and entanglement during the photoemission process. Quantum tomographic techniques will be implemented on the ATTOLab laser platform (https://iramis.cea.fr/en/lidyl/atto/attolab-platform/) using a new Ytterbium laser source. This novel laser technology is emerging, with stability 5 times higher and repetition rate 10 times higher than the current Titanium:Sapphire technology. These new capabilities represent a breakthrough for the field and allow, e.g., charged particle coincidence techniques, to study the dynamics of photoemission and quantum entanglement with unprecedented precision.
This PhD project is performed in the frame of a recently funded European Network QU-ATTO (https://quatto.eu/), providing an advanced training to 15 young researchers, and opening many opportunities of joint work with European laboratories. In particular, strong collaborations are already ongoing with the groups of Prof. Anne L’Huillier in Lund, and Prof. Giuseppe Sansone in Freiburg. Due to the Mobility Rule, candidates must not have resided (work, studies) in France for more than 12 months since August 2022.
The student will receive solid training in ultrafast optics, atomic and molecular physics, attosecond science, quantum optics, and will acquire a broad mastery of XUV and charged-particle spectroscopy techniques.
References :
[1] https://www.nobelprize.org/prizes/physics/2023/summary/
[2] Y. Mairesse, et al., Science 302, 1540 (2003)
[3] V. Gruson, et al., Science 354, 734 (2016)
[4] A. Autuori, et al., Science Advances 8, eabl7594 (2022)
[5] C. Bourassin-Bouchet, et al., Phys. Rev. X 10, 031048 (2020)
[6] H. Laurell, et al., Nature Photonics, https://doi.org/10.1038/s41566-024-01607-8 (2025)
Development and study of laminated composite material with carbon nanotubes functionalisation dedicated to launcher linerless cryogenic tank
The use of composite materials in the space field has led to great weight improvements. To continue to achieve significant weight gain, composite cryogenic tank is the next technological application to reach by replacing the current metal alloy cryogenic propellant tanks. Lighter reinforced organic matrix composite materials (that are at least as efficient from a mechanical, thermal, chemical and ignition resistance point of view) are a realistic target to be reached that has been explored in recent years. Many research approaches tend to answer to this technological lock, but the potentialities of Carbon NanoTubes (CNTs) in terms of mechanical and physical properties, need to be explored deeper.
A first phase to assess the interest of CNTs for space applications (collaboration CNES/CEA/I2M/CMP Composite) was carried out to associate CNTs with a cyanate ester matrix in layered composite materials through three processes: (i) transfer of aligned CNTs mats by hot pressing (ii) dispersion of entangled CNTs mixed with resin, or (iii) growth of nanotubes aligned directly on the dry ply. Knowing mechanical and thermal loads, the aim is to demonstrate the efficiency of CNTs and influence of their characteristics with regard to damage tolerance of the material and consist in delaying the cracking process of the composite nearby the CNT layer and thus blocking the percolation of the cracking network which leads to the loss of tightness. For the preferred development process identified, the aim of this doctoral work is now to consolidate the material functionalisation with CNTs (shape, density, etc.) and the understanding of the mechanical behaviour (at room temperature and at low temperature) for the development of the layered material integrating CNTs.
Knowing the potential final application as cryogenic tank or for the improvement of structural materials sustainability in dual application, relevant tests will be performed to demonstrate the impact in terms of damage development and tightness in comparison with the same material without CNTs.