Subventions et des contributions :

Subvention ou bourse octroyée s'appliquant à plus d'un exercice financier. (2017-2018 à 2022-2023)

The technological revolution we have seen unfolding over the last 40 years was fueled by quantum mechanics, which was developed in the early 20 th century. Quantum mechanics was first based on the properties of individual atoms, and non-interacting particles, such as free electrons. A firm understanding of its principles gave us semiconductors for transistors, and ferromagnets for storage. However, we came to realize that strong interactions between many particles lead to new emergent phenomena, as well as novel phases.

The search for such phases is what is driving the interest in frustrated magnetism. It goes back to the geometric problem of placing three spins with antiferromagnetic interactions on a triangle. The interaction between nearest neighbors favors an anti-parallel alignment between any of two neighboring spins, which is a condition that is impossible to fulfill simultaneously for the three spins.

Systems where quantum mechanical fluctuations, and geometrical constraints prevent order, are called quantum spin liquids (QSL). These ground states have truly exotic excitations, which cannot be studied in any other systems. For example, excitations in a QSL can be fermionic, which makes them completely different from the excitations in an ordered magnetic state, which are always bosonic. Furthermore, the spins in a QSL are quantum mechanically entangled over long distances leading to topological wave functions which gives them properties which are desired for applications in quantum computing.

While in the past it has only been possible to study QSL in theoretical models, we are currently at the cusp of a breakthrough due to the discovery of a number of candidate materials. This grant will allow us to use multiple crystal chemistry methods to synthesize new classes of frustrated magnets. The materials we are planning to study are based on strongly interacting spins on a triangular motif which repeats itself in three dimensions (Ce 2 Zr 2 O 7 ), or one dimension (BaRE 2 O 4 ), and in 3D for the rare case of spin 1/2 (PbCuTe 2 O 6 ). Once synthesized, we will first characterize the thermodynamic properties of these materials by specific heat and magnetization measurements to test for the absence of order. This will be followed by detailed neutron diffraction experiments on single crystals. Neutron scattering will not only allow us to show the absence of order, but it is the direct way to probe a QSL, as it measures the magnetic structure factor.

Finding a QSL ground state in one of the proposed materials would have a truly transformative impact on the field of frustrated magnetism. It would give us a laboratory in which we can probe novel physics of fascinating quasiparticles, which is the first step to a detailed understanding. We believe that such an understanding is critical for the path to develop applications based on QSL’s in quantum computing, where QSL’s could be used for robust error corrections schemes.