Chiral to Nematic Crossover in the Superconducting State of 4Hb-TaS$_2$

Abstract: Most superconductors have an isotropic, single component order parameter, and are well described by the BCS theory for superconductivity. Unconventional, multiple components superconductors are exceptionally rare and are much less understood. Here, we combine scanning tunneling microscopy and angle-resolved macroscopic transport to study the candidate chiral superconductor, 4Hb-TaS$_2$. We reveal quasi-periodic one-dimensional modulations in the tunneling conductance accompanied by two-fold symmetric superconducting critical field. The strong modulation of the in-plane critical field, points to a nematic, unconventional order parameter. However, the imaged vortex core is nearly circular symmetric, suggesting an isotropic order parameter. We reconcile this apparent discrepancy by modeling a competition between a dominating chiral superconducting order parameter and a nematic one, the latter emerges close to the normal phase. Our results strongly support the existence of two-component superconductivity in 4Hb-TaS$_2$ and can provide useful insights to other systems with coexistent charge order and superconductivity.