Superconductivity in V-based kagome metals has recently raised great interest
as they exhibit the competing ground states associated with the flat bands and
topological electronic structures. Here we report the discovery of
superconductivity in Ta2V3.1Si0.9 with a superconducting transition temperature
Tc of 7.5 K, much higher than those in previously reported kagome metals at
ambient pressure. While the V ions form a two-dimensional breathing kagome
structure, the length difference between two different V-V bonds is just 0.04,
making it very close to the perfect kagome structure. Our results show that
Ta2V3.1Si0.9 is a moderate-coupled superconductor with a large upper critical
field that is close to the Pauli limit. DFT calculations give a
van-Hove-singularity band located at Fermi energy, which may explain the
relatively high Tc observed in this material.Comment: 19 pages, 5 figure