Description du sujet de thèse

TITLE: FERROELECTRIC TOPOLOGICAL INSULATORS FOR THE STUDY OF WEYL FERMIONS

SUMMARY OF THESIS PROJECT:
In recent years, merging of topology with other physical phenomena such as superconductivity, ferromagnetism or ferroelectricity as attracted tremendous interest. The resulting reduction of symmetry has led to outstanding breakthroughs and the discovery of novel exotic phases of matter, such as the quantum anomalous Hall phase in the presence of magnetic interactions and Majorana fermions at the interface of a quantum anomalous Hall insulator and a superconductor. These are considered to be highly promising roads towards quantum computing because of the robustness of Majorana fermions against decoherence and in addition, numerous other applications have been envisioned.
In the present work, we will focus on the intriguing interplay between topology and ferroelectricity. From a fundamental point of view, combining ferroelectricity with topology is predicted to host Weyl fermions. These relativistic fermions can be mimicked by massless electrons that possess a definite chirality, meaning that their spins are parallel or antiparallel to their momenta. They are at the heart of a large number of outstanding properties that are just starting to be addressed, such as dissipationless chiral currents driven by the chiral magnetic effect, efficient spin-charge conversion due to the large anomalous Hall effect or efficient higher harmonic generation due to ultrafast dynamics. Weyl fermions are also promising particles to form qubits based on chirality. Therefore, it is of great interest to establish a platform capable of control and manipulation of Weyl fermions.
The objective of the proposal is to develop ferroelectric topological insulators as a new class of quantum materials and to employ them for the control and manipulation of chiral Weyl fermions. The three goals of the study will be to
• Design and synthesize novel ferroelectric topological materials,
• Demonstrate the interplay between the ferroelectric distortions and fundamental electronic properties to induce and tailor Weyl Fermions,
• Unravel novel transport and optical phenomena specific to the Weyl phase in order to open up new routes towards Weyl physics applications.
The high quality studied heterostructures will be grown by molecular beam epitaxy and characterized using XRD, STM and ARPES by our collaborators at the Johannes Kepler University in Linz (Austria).

Contexte de travail

LPENS is a laboratory located in the heart of the 5th arrondissement of Paris. It is part of the ENS physics department, and interacts closely with other ENS scientific departments. The host team is part of the Quantum Materials and Devices axis. It specialises in the optical and electronic properties of novel quantum materials in the terahertz (THz) and mid-infrared spectral range. It specializes in ultra-fast THz spectroscopy and magneto-spectroscopy of nanostructures such as quantum cascade lasers and detectors, new 2D materials, spintronics materials and devices, and topological insulators.