ABSTRACT

Phase transitions are fundamental phenomena in condensed matter physics accompanied by a spontaneous symmetry breaking at a critical point. In the framework of Landau theory [1], these transitions occur when an order parameter changes discontinuously (first-order transition) or continuously (second-order transition) as external conditions, such as temperature or magnetic field, are varied. Structural phase transitions, for instance, involve a lattice symmetry breaking and are typically first order, while second-order transitions, such as superconductivity breaks the unitary gauge symmetry. These thermodynamic phase transitions are driven by thermal fluctuations at finite temperature.

In contrast, quantum phase transitions occur at absolute zero temperature, driven not by thermal but by quantum fluctuations [2]. These transitions happen at a quantum critical point (QCP), where the system undergoes a fundamental change in its ground state as a function of a non-thermal control parameter, such as pressure, doping, or magnetic field. Near the QCP, exotic phenomena such as non-Fermi liquid behavior [3][4], strange metallicity [5][6] and unconventional superconductivity [4][7] often emerge, making the study of quantum criticality central to understanding strongly correlated systems.

Traditionally, phase transitions are explored by varying thermodynamic parameters like temperature or magnetic field. In this presentation, I will expose an alternative approach: driving symmetry breaking through uniaxial pressure. I will describe our efforts to adapt uniaxial pressure environments to several experimental probes such as transport, infrared spectroscopy and ARPES. Uniaxial pressure allows precise control of structural distortions, directly tuning crystallographic symmetries. This environment enables a deeper investigation into the interplay between structure and electronic properties, particularly in systems where strong electron-phonon interactions mediate phase transitions and lead to the emergence of exotic electronic states.

[1] L. Landau, Zh. Eksp. Teor. Fiz. 7, 19-32 (1937).
[2] H. v. L?hneysen, Rev. of Mod. Phys. 79, 1015 (2007).
[3] P. Coleman, Phys. B: Cond. Matt. 259-261, 353-358 (1999).
[4] T. Shibauchi et al., Ann. Rev. Cond. Matt. Phys. 5, 113-135 (2014).
[5] B. Keimer et al., Nature 518, 179-186 (2015).
[6] B. Michon et al., Nat. Comm. 14, 3033 (2023).
[7] J.G. Bednorz and K.A. Müller, Z. Phys. B Cond. Matt. 64, 189-193 (1986).

BIOGRAPHY

Former colleague in the Physics Department at CityU, Dr. Bastien Michon has developed strong expertise in experimental physics, particularly in transport measurements, specific heat, and infrared spectroscopy under extreme conditions—including high magnetic fields (up to 35 T) and ultra-low temperatures (down to 400 mK)—to investigate quantum materials like unconventional superconductors and Weyl semimetals. Currently a postdoctoral fellow at the Laboratoire de Physique des Solides (LPS) on the University Paris-Saclay campus, he is adapting uniaxial pressure environments for various experimental techniques, including transport, infrared spectroscopy, and ARPES, in close collaboration with LPS, SOLEIL synchrotron, and international collaborators.