Last 5 December 2024, Josu Diego successfully defended his thesis entitled “Anharmonic Effects in Two-Dimensional Systems: Charge Density Wave Transitions and Their Mechanical Stability”
In his PhD thesis, Josu explored the impact of non-perturbative anharmonic effects on ionic dynamics in low-dimensional systems, employing the self-consistent harmonic approximation as his main theoretical tool. His work focused on two-dimensional and quasi-two-dimensional materials, offering new insights into their structural and dynamical properties.
The first part of the thesis investigated charge density wave (CDW) instabilities in transition metal dichalcogenides, with a particular emphasis on 1T-VSe₂. Josu’s analysis combined first-principles calculations with experimental data from inelastic x-ray scattering (IXS), successfully describing the transition to the charge-modulated state in the bulk. In the monolayer, his theoretical study resolved a longstanding experimental controversy regarding the nature of CDW orders, clarifying previously conflicting observations.
In the second part, Josu examined the mechanical stability of strictly two-dimensional materials, highlighting the role of thermal fluctuations and anharmonic effects. His findings challenge conventional theories of 2D rigidity, demonstrating that a non-perturbative approach is essential for understanding the true mechanical behavior of these systems.
Josu presented his results in a well-attended and engaging defense, showcasing a deep understanding of the field and a strong command of both theory and experiment. His thesis was supervised by Ion Errea and Raffaello Bianco, and the committee was formed by Massimiliano Stengel, Maria Blanco, and Matteo Calandra. The discussion was lively and insightful.
To celebrate, Josu gathered with family, colleagues, and committee members for a meal following the defense. He now continues his academic journey as a postdoctoral researcher at the University of Trento in Italy, working with Matteo Calandra.
You can read Josu’s thesis here.