Localization of helical edge states in the absence of external magnetic field

Theoretically, the helical edge states of two-dimensional topological insulators are protected from coherent backscattering due to nonmagnetic disorder provided electron interactions not too strong. Experimentally, edges typically do demonstrate systematic and robust quantization, at same time little is known about sub-Kelvin temperature behavior. Here, we report surprising localization in an 8 nm HgTe quantum well zero magnetic field millikelvin temperatures. Additionally, magnetoresistance data 0.5 K for few micrometers long suggests field-dependent length $l_B\propto B^{-\alpha}$, with $\alpha$ ranging approximately $1.6$ $2.8$ fields $B\lesssim0.1\,\text{T}$ $\alpha\approx1.1$ higher up $0.5\,\text{T}$. In frame disordered interacting edge, these values correspond Luttinger liquid parameters $K\approx 0.9-1.1$ 0.6$, respectively. We discuss possible scenarios which could result localization.