Symmetry differences between high- and low-temperature nematic phases in Fe-doped CoSn

Establish the precise symmetry-breaking differences between the high-temperature nematic phase (T ≥ 16 K) and the low-temperature nematic phase (T < 8 K) in Fe-doped CoSn (Co_{1−x}Fe_xSn, 0 < x < 0.2), including determining whether the low-temperature phase breaks time-reversal symmetry and quantifying how its rotational symmetry breaking differs from that of the high-temperature phase.

Background

The paper reports a cascade of correlated phases in the kagome flat bands of Fe-doped CoSn, including a high-temperature nematic phase observed for T ≥ 16 K and a distinct low-temperature phase below T < 8 K. The high-temperature phase exhibits C6z-to-C2z rotational symmetry breaking without evidence of translation symmetry breaking and is suggested to preserve time-reversal symmetry (TRS).

In contrast, the low-temperature nematic phase shows stronger rotational symmetry breaking with a non-monotonic doping dependence. Magnetometry in related work indicates antiferromagnetic interactions and a magnetic transition below 10 K across a similar doping range, suggesting possible TRS breaking. However, TRS cannot be directly inferred from the STM measurements used here, leaving unresolved the exact differences in symmetry breaking between the two nematic regimes.