Alladi Ramakrishnan Hall

Symmetry routes to novel phases of matter

Abhishodh Prakash

Oxford University

This talk, split into two parts, will be on how symmetry principles can help us identify new phases of matter.

In the first part (based on [1,2]), I will introduce a novel system of classical 'fractons' which exhibit a remarkable set of features defying conventional expectations from almost all known classical mechanical systems. This includes the disassociation of velocity and momenta, the appearance of attractors seemingly in violation of Liouville's theorem, the formation of crystalline structures, evading the famous theorem by Hohenberg, Mermin, Wagner and Coleman and the failure of statistical mechanics. I will show that all this is a robust feature of underlying symmetries which enforces 'Machian' dynamics wherein isolated particles are immobile, and motion requires the assistance of proximate particles.

In the second part of my talk (based on [3,4]), I will discuss how new gapless phases emerge when unbroken microscopic symmetries manifest themselves in distinct ways on infrared fields. I will demonstrate the existence of several `symmetry-enriched' critical phases in the phase diagram of well-known coupled spin ladders which have been missed in all previous study. One of these is also a gapless topological phase and hosts protected edge modes of a distinct nature compared to their gapped counterparts.

[1] Phys. Rev. B 109, 054313 (2024)
[2] arXiv:2312.02271
[3] Phys. Rev. Lett. 130, 256401 (2023)
[4] Phys. Rev. B 108, 245135 (2023)