Unconventional Planar Hall Effect in Kagome Metal KV$_3$Sb$_5$

Exploration of novel transport behavior in correlated topological materials is of great importance and interest for revealing exotic orders and states. Recently, a new family of kagome materials AV$_3$Sb$_5$(A=K, Rb, Cs) was discovered which hosts chiral charge density wave (CDW), superconductivity, and topological nontrivial states, etc, providing a new platform to study the correlated and topological physics. In this letter, we report the observation of unconventional planar Hall effect (PHE) and anisotropic magnetoresistivity (PAMR) in KV$_3$Sb$_5$. At low temperatures, with increasing the applied field, PHE and PAMR exhibit more and more prominent high-fold symmetrical oscillations with the rotating angle instead of only regular two-fold symmetrical oscillation which violates the conventional empirical law. These high-fold such as four-fold or six-fold symmetrical oscillations exhibit strong temperature and field dependence and varnish at high temperatures or low fields. In addition, the anisotropic in-plane magnetoresistivity is revealed to exhibit non-monotonous behavior and strong angular-dependent evolution. The abnormal in-plane transport properties suggest a significant interplay among the anisotropic magnetic correlation, lattice, and electronic structure in KV$_3$Sb$_5$.