Description of the thesis topic

BiSb, a Topological Insulator for Spintronics
Topological insulators (TI) belong to a new class of materials which are insulating in the bulk, while having, intrinsically, protected metallic surface states. Bi1-xSbx is one of them and belongs to the 3D Z_2 topological family.
The PhD thesis will focus on two topics
- spin to charge current conversion. The TI surface states present this unique property where the spin of the carriers is locked to the carrier momentum. Hence a spin current flowing into these states is converted into a charge current. To produce a spin current, we deposit a ferromagnetic layer on the top of a thin BiSb layer. Conversely, a charge current in the TI will generate a spin current which exerts a torque on the magnetization. The TI conversion efficiency is very high compared to other materials, and is therefore a very appealing material for spintronic applications. BiSb is a model TI system to investigate spin to charge current conversion in topological surface states.
- magnetic TI. When doped with magnetic impurities, TI can become ferromagnetic. This time-reversal symmetry breaking opens a gap on both top and bottom surface states. Because of their distinct topological character, a chiral metallic 2D edge state occurs, with quantized conductance: this is the Quantum Anomalous Hall Effect. Ferromagnetic BiSb has not yet be demonstrated, and will be investigated.
The first topic is already well advanced in our teams, with key publications. The other subject is at its infancy in our group.

Work Context

BiSb, a Topological Insulator for Spintronics
Topological insulators (TI) belong to a new class of materials which are insulating in the bulk, while having, intrinsically, protected metallic surface states. Bi1-xSbx is one of them and belongs to the 3D Z_2 topological family.
The PhD thesis will focus on two topics
- spin to charge current conversion. The TI surface states present this unique property where the spin of the carriers is locked to the carrier momentum. Hence a spin current flowing into these states is converted into a charge current. To produce a spin current, we deposit a ferromagnetic layer on the top of a thin BiSb layer. Conversely, a charge current in the TI will generate a spin current which exerts a torque on the magnetization. The TI conversion efficiency is very high compared to other materials, and is therefore a very appealing material for spintronic applications. BiSb is a model TI system to investigate spin to charge current conversion in topological surface states.
- magnetic TI. When doped with magnetic impurities, TI can become ferromagnetic. This time-reversal symmetry breaking opens a gap on both top and bottom surface states. Because of their distinct topological character, a chiral metallic 2D edge state occurs, with quantized conductance: this is the Quantum Anomalous Hall Effect. Ferromagnetic BiSb has not yet be demonstrated, and will be investigated.
The first topic is already well advanced in our teams, with key publications. The other subject is at its infancy in our group.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Constraints and risks

The thesis will take place at the C2N, a joint CNRS-Université Paris Saclay lab, and at the Laboratoire Albert Fert, both on the Palaiseau plateau. The C2N (400 people) is organized in four departments, Material, Photonics, Nanoelectronics and Microsystems and Nanobiofluidics. It hosts the largest academic clean-room facilities in France. The PhD student will work in the ELPHYSE team, in the Material Department.

Additional Information

Work will be performed partly in a clean-room environment. Chemicals (mostly acids) will be used on a weekly basis. Manipulation of arsenic contaminated pieces will also be needed. However strict safety rules are communicated and enforced to minimize risk.