Spectroscopic fingerprints of gapless type-II fracton phases

TL;DR

This paper proposes experimental signatures, such as exotic pinch points in neutron scattering and specific heat features, to identify gapless type-II fracton phases like the U(1) Haah code, which previously lacked diagnostics.

Contribution

It introduces spectroscopic fingerprints based on UV-IR mixing effects for detecting gapless type-II fracton phases experimentally.

Findings

Neutron scattering should reveal exotic pinch points with anisotropic contours.

Distinctive low-temperature specific heat signatures of the U(1) Haah code.

UV-IR mixing causes characteristic structure factor features.

Abstract

Fracton phases feature elementary excitations with fractionalized mobility and are exciting interest from multiple areas of theoretical physics. However, the most exotic 'type-II' fracton phases, like the Haah codes, currently have no known experimental diagnostics. Here, we explain how type-II fracton phases with gapless gauge modes, such as the $\mathrm{U}(1)$ Haah code, may be identified experimentally. Our analysis makes use of the 'multipole gauge theory' description of type-II fracton phases, which exhibits ultraviolet-infrared (UV-IR) mixing. We show that neutron scattering experiments on gapless type-II fracton phases should generically exhibit exotic pinch points in the structure factor, with distinctive anisotropic contours as a direct consequence of UV-IR mixing. This characteristic pinch point structure provides a clean diagnostic of type-II fracton phases. We also identify distinctive signatures of the (3+1)-D $\mathrm{U}(1)$ Haah code in the low-temperature specific heat.