Kagome superconductors

The newly discovered Kagome superconductors provide a platform to investigate theinterplay of the topological property, superconductivity and geometrical frustration. Since their discovery, manyresearch groups, especially many groups in China, have made tremendous progress in this field, including time-reversal-symmetry-breaking (TRSB), charge density wave (CDW), electronic nematicity, superconductivityproperties and pair density wave (PDW). In this paper, we introduce the properties, discuss the recentresearch progress and highlight the future focus of this Kagome superconductor. The paper is organized as follows. We start from the exotic normal states of , AV(3)sb(5)where a CDWemerges at the temperature around 70-100 K depending on . This CDW enlarges the unit cell size to 2x2with additional c-direction modulation as observed by scanning tunneling microscope (STM) and X-rayscattering experiments. Interestingly, this CDW behaves differently under opposite magnetic fields. Namely, thisCDW may break the time reversal symmetry. To confirm this property, the zero field muon spin relaxation(ZF mu SR) experiment is performed with increasing relaxation rates after the CDW transition. Additionally, theintrinsic anomalous Hall effect is also observed, which may relate to this time reversal symmetry breaking(TRSB). Since there are no long-range magnetic orders observed in the elastic neutron scattering experimentand mu SR, the TRSB is not related to the electron spin degree of freedom. To explain the TRSB, the chiral fluxphase (CFP) with orbital magnetism is theoretically proposed. Moreover, the electronic nematicity is alsoobserved at about 30 -50 K below the CDW transition temperature. This phase breaks the rotationsymmetry of the Kagome lattice as confirmed by STM and nuclear magnetic resonance (NMR). What is themicroscopic origin of this nematicity is still under investigation. Then, we move to the superconducting properties ofAV(3)Sb(5) . Combining the inversion symmetry propertyfound in optical measurement and decreasing of the spin susceptibility found in NMR, the supercon-ductor is proven to be a spin-singlet superconductor. Experiments in NMR, angle-resolved photoemission,superfluid density and specific heat further confirm the superconductivity in Kagome superconductors is aconventional s-wave superconductor. Although this superconductor is conventional, also contains theunconventional property. Importantly, a PDW is observed in by high-resolution STM. What is thePDW origin or microscopic mechanism is still an open question. These new progress reveal the intriguingphysical properties behind the Kagome superconductors and also bring many unsolved questions, which calls forfurther investigations