Vortex Penetration Into the Putative Chiral Superconductor 4Hb TaS2 by Local Magnetization Measurements

Date

Dec 13, 2024

Time

11:00 AM - 12:00 PM

Speaker

Tomasz Cichorek

Affiliation

Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-422 Wrocła

Language

en

Main Topic

Materialien

Host

Rita Taubert

Description

Heterostructures formed by alternating magnetic and superconducting layers are predicted systems for the realization of exotic topological quantum phases and resultant Majorana bound states. A promising route to realize topological superconductivity is related to a van der Waals material 4Hb-TaS2 (a critical temperature Tc ≃ 2.7 K). This naturally occurring heterostructure is composed of strongly correlated phases with drastically different ground states [1]. In bulk form, 2H-TaS2 is a conventional superconductor (Tc = 0.7 K), while 1T TaS2 is a Mott insulator and can host a quantum spin liquid. Chiral superconductivity in 4Hb-TaS2 is suggested from, e.g., muon spin relaxation experiments that revealed a spontaneous appearance of magnetic moments at T ≤ Tc [1]. Furthermore, an intriguing vortex memory effect [2], which has been observed slightly above Tc, is a topic of present debate whether topological order is involved in vortex nucleation in the thermal cycling process. Here we investigate vortex penetration into 4Hb Ta1.000(8)S1.97(4)Se0.017(2) samples for a magnetic field H parallel to the layers stacking direction. Using micro-Hall-probe magnetometry, we focus on the field of first flux penetration and the resultant temperature dependence of the lower critical field Hc1(T) as a function of sample thickness d. For thick samples (d ≃ 180 mm), we observe an anomalous enhancement of Hc1 at 0.5Tc that consists of a non-saturating T-dependence down to 0.007 K being preceded by a concave curvature below 0.5 K. Above 1.5 K, the Hc1(T) data show a single-band isotropic s-wave behavior. A sharp anomaly in Hc1(T) far below Tc and no sign of saturation in the limit T = 0 suggest that the superconducting state of 4Hb-TaS2 is both multiband and multisymmetric. This scenario is similar to that realized in the other putative chiral superconductor PrOs4Sb12 (Tc ≃ 1.85 K) where multiband order parameters are composed of a sign-changing smaller gap and a large isotropic s-wave gap [3]. However, when the thickness is reduced, the anomaly in Hc1(T) of 4Hb-TaS2 is shifted toward lower temperatures and its magnitude substantially diminishes. For a thin sample (d ≃ 4 mm), the lack of saturation is absent and the entire Hc1(T) dependence is well described by the conventional relation derived from the Bardeen-Cooper-Schrieffer theory. We emphasize that Tc does not depend on d. Our findings are at odds with the effect produced by the Bean-Livingston and geometric barriers, and thus point at the presence of unknown yet factor determining a vortex penetration into the putative chiral superconductor 4Hb-TaS2. References 1. A. Ribak et al., Sci. Adv. 6 eaax9480 (2020). 2. B. Persky, et al., Nature 607, 692 (2022). 3. J. Juraszek et al., Phys. Rev. Lett. 124, 027001 (2020).

Links

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Last modified: Dec 13, 2024, 7:44:14 AM