Quantum materials host fascinating properties. Understanding their origins, the interaction between coexisting quantum phases and their tuning parameters is central for the future uses of such properties. Collective modes, that emerge when a phase transition to a quantum order sets, are witnesses of their underlying quantum order. Studying such collective modes is then crucial for a global understanding of the phenomena.
The HiggS² project particularly focus on the quest and the study of one type of collective mode of the superconducting state, the Higgs mode. A mode of Higgs type, of crucial importance in the standard model of elementary particle physics, is also a fundamental collective mode in quantum many-body systems. It is remarkable that such collective Higgs modes predicted by theory many years ago, and lying at the core of the electronic properties of several classes of materials (cold atoms, superconductors, magnetic materials ...) still remain elusive to experimental validation. Besides, many crucial questions remain open, like the mechanism of its observability, its mere existence in two-dimensional or unconventional superconductors, to name a few. Similarly to the Higgs boson, its detection remains a challenge for physicists. Our interest is then double: we aim at finding new example of Higgs mode in superconductors and at establishing a platform to use the Higgs mode as a probe of the superconducting state it-self. In a larger perspective, we expect cross-fertilization with High Energy Physics.
The project will use a potential mechanism of observability making the Higgs mode detectable by Raman spectroscopy, based on the interplay between an adjacent quantum order and superconductivity. The overall objective of the project is to contribute to the quest of new observations of Higgs mode in superconductors, to study them in a large variety of situations, by changing the type of adjacent quantum orders, by changing the type of superconducting orders or by changing the dimensionality. For this, we will use advanced Raman spectroscopy, notably under extreme conditions, beyond the state-of-the-art experiments. This project will establish definitive examples of the observation and mechanism of observability of the Higgs mode in superconductors, while developing its phenomenology to address major problems at the frontier of quantum materials research, with impact beyond mere superconductivity and even condensed matter.
