Engineering Topological and Interaction-Driven Quantum Phases in HfTe5

Quantum materials can host electronic states that do not exist in ordinary solids, many of which are topological and protected by symmetry. In this seminar, I will present HfTe₅, a layered van der Waals material whose electronic structure can be tuned in situ to access multiple topological and interaction-driven phases. 

By applying uniaxial strain, we drive a transition between weak and strong topological insulating states, producing a nearly three-order-of-magnitude increase in resistance and a crossover to surface-state-dominated transport. In the weak topological phase, a magnetic field generates a sequence of Landau levels and one-dimensional Weyl-like modes. At low carrier density, strong Coulomb interactions stabilize a spin-triplet excitonic insulator that we recently discovered. In the strong topological phase, this condensate appears at lower fields and can be tuned through isotope-controlled electron–phonon coupling. 

When thinned below ~100 nm, HfTe₅ becomes increasingly surface dominated and exhibits new correlated behavior, providing a clean platform to study the interplay of topology, dimensionality, and interactions. 

In summary, HfTe₅ offers an exceptional opportunity to control topological phase transitions, interaction-driven condensates, and symmetry-protected boundary transport within a single material system. Its tunability and rich phase diagram make it a promising platform for spin- based electronics and topologically robust quantum devices.

Séminaire organisé dans le cadre du programme interdisciplinaire MAT-PULSE