Quantum Matter Seminar by Yuji Hirono on December 22, 2023

On December 22nd, Professor Yuji Hirono from Kyoto University gave an online seminar talk in Quantum Matter Study Group, exploring the intricate world of fractonic phases. His talk, titled "A symmetry principle for gauge theories with fractons," ran from 5pm to 6:15pm JST.

Taking center stage were fractons, unusual quasiparticles with a surprising quirk – they are practically immobile when alone. A key feature of the fractons, making them distinct from typical topological objects, is that their stability is not protected by an energy gap. Instead, it is the underlying symmetries that guarantee their properties. Professor Hirono used simple examples, like the conservation laws of dipoles and the connection to the immobility, to illuminate this unique property. This immobility sets fractons apart from the more conventional particles that we are familiar with, sparking fascination and curiosity about their underlying mechanisms.

Central to his discussion was the formulation of effective theories based on the spontaneous breaking of these nonuniform symmetries. At low energies, these theories simplify into known higher-rank gauge theories, such as scalar/vector charge gauge theories. The gapless excitations in these theories are interpreted as Nambu–Goldstone modes for higher-form symmetries. A novel aspect highlighted was the acquisition of a gap by some modes due to the nonuniformity of the symmetry, analogous to the inverse Higgs mechanism in spacetime symmetries. This framework elucidates the mobility restrictions of fractons as determined by the commutation relations of charges with translations. This illuminating seminar offered a glimpse into the remarkable world of fractonic phases and the power of novel symmetry principles.

Reported by Ching-Kai Chiu