Novel spin dynamics in the superconducting CsV3Sb5

Crystal structure is known to have a significant effect on the properties of materials. Especially, crystals with partial lattice structures called sublattices have been attracting much attention because such structures can host fascinating phenomena including topological states, extended multipolar order, and unconventional superconductivity. One typical example of those structures is the kagomé lattice, which is a 2-dimensional pattern consisting of corner sharing triangles. In CsV₃Sb₅, V ions form perfect kagomé lattices and novel electronic states, charge order, and superconductivity emerge. Therefore, it has been the subject of intensive research.

Despite a large number of studies performed to investigate the superconducting properties of CsV₃Sb₅, a unified interpretation of its superconducting symmetry has not yet been reached. A previous study using nuclear magnetic/quadrupole resonance (NMR/NQR) concluded that conventional s-wave superconductivity is realized based on the observation of a coherence peak just below the transition temperature in nuclear spin-lattice relaxation rate 1/T₁. However, this is not conclusive because the observed peak was so small, and the lowest temperature of the measurements was not sufficiently low for the precise discussion on the superconducting gap structure. This situation drove us to perform NMR/NQR measurements using single crystals of CsV₃Sb₅ down to extremely low temperature.

We observed a large coherence peak just below the transition temperature and exponential decay in very low temperatures in 1/T₁ under zero magnetic field. This is a characteristic of full-gap spin singlet superconductivity. When considered in conjunction with the sublattice properties of the kagomé lattice, the superconducting symmetry can be narrowed down to s-wave or chiral d-wave. In contrast, the coherence peak was suppressed and the upturn of 1/T₁T was observed in extremely low temperature region under magnetic field. This upturn cannot be explained solely by the existence of a superconducting gap, suggesting the presence of some kind of dynamics that develops at low temperatures. This result indicates that the superconducting state of CsV₃Sb₅ has a special property originating from the kagomé lattice. Our work is expected to advance the search for novel superconductivity appearing in the kagomé lattice.

Reference

@article{M.Shibta_commphys_2025,

title = {Novel spin dynamics in the superconducting state of kagomé superconductor},

author = {M Shibata and H Takahashi and S Oguchi and S Kitagawa and K Ishida and S Yamane and S Yonezawa and Y Li and Y Yao and Z Wang },

doi = {https://doi.org/10.1038/s42005-025-02210-1},

year  = {2025},

date = {2025-07-16},

journal = {Communications Physics},

volume = {8},

pages = {298},

abstract = {The kagomé lattice, characterized by its unique geometry, hosts exotic electronic structures such as Dirac points, flat bands, and van Hove singularities, which are closely linked to electronic instabilities. Recently, the AV3Sb5 family (A = K, Rb, Cs) has emerged as a prime platform for exploring these intriguing phenomena, exhibiting both charge-density wave (CDW) and superconductivity. The coexistence of two phenomena suggests the possibility of unconventional superconducting mechanisms. Here, we report a detailed investigation of two phenomena in CsV3Sb5 using high-quality single crystals. For zero-field 121Sb-nuclear quadrupole resonance, a Hebel-Slichter peak suggesting the realization of conventional superconductivity is observed just below the superconducting transition temperature. In contrast, 51V-nuclear magnetic resonance shows an anomalous increase in spin fluctuations deep inside the superconducting phase, suggesting the unconventional properties in CsV3Sb5 superconductivity. Our work enhances the understanding of unconventional superconducting properties in kagomé lattice systems by revealing the relationship between two phenomena.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}