We report the physical properties of ThRu$_3$Si$_2$ featured with distorted Ru kagome lattice. The combined experiments of resistivity, magnetization and specific heat reveal bulk superconductivity with $T_{\rm{c}}= 3.8$ K. The specific heat jump and calculated electron-phonon coupling indicate a moderate coupled BCS superconductor. In comparison with LaRu$_3$Si$_2$, the calculated electronic structure in ThRu$_3$Si$_2$ shows an electron-doping effect with electron filling lifted from 100 meV below flat bands to 300 meV above it. This explains the lower superconducting transition temperature and weaker electron correlations observed in ThRu$_3$Si$_2$. Our work suggests the $T_{\rm{c}}$ and electronic correlations in the kagome superconductor could have an intimate connection with the flat bands.

We report on the magnetization and anomalous Hall effect (AHE) in the high-quality single crystals of the kagome magnet YbMn$_{6}$Sn$_{6}$, where the spins of the Mn atoms in the kagome lattice order ferromagnetically and the intermediate-valence Yb atoms are nonmagnetic. The intrinsic mechanism plays a crucial role in the AHE, leading to an enhanced anomalous Hall conductivity (AHC) compared with the other rare-earth $R$Mn$_{6}$Sn$_{6}$ compounds. Our band structure calculation reveals a strong hybridization between the 4f electrons of Yb and conduction electrons.

The kagome superconductor CsV$_{3}$Sb$_{5}$ has attracted widespread attention due to its rich correlated electron states including superconductivity, charge density wave (CDW), nematicity, and pair density wave. Notably, the modulation of the intertwined electronic orders by the chemical doping is significant to illuminate the cooperation/competition between multiple phases in kagome superconductors. In this study, we have synthesized a series of tantalum-substituted Cs(V$_{1-x}$Ta$_{x}$)$_{3}$Sb$_{5}$ by a modified self-flux method. Electrical transport measurements reveal that CDW is suppressed gradually and becomes undetectable as the doping content of $ x$ is over 0.07. Concurrently, the superconductivity is enhanced monotonically from $T_{\rm c} \sim 2.8 $ K at $x =0$ to 5.2 K at $x = 0.12$. Intriguingly, in the absence of CDW, Cs(V$_{1-x}$Ta$_{x}$)$_{3}$Sb$_{5}$ ($x = 0.12$) crystals exhibit a pronounced two-fold symmetry of the in-plane angular-dependent magnetoresistance (AMR) in the superconducting state, indicating the anisotropic superconducting properties in the Cs(V$_{1-x}$Ta$_{x}$)$_{3}$Sb$_{5}$. Our findings demonstrate that Cs(V$_{1-x}$Ta$_{x}$)$_{3}$Sb$_{5}$ with the non-trivial band topology is an excellent platform to explore the superconductivity mechanism and intertwined electronic orders in quantum materials.

A recently discovered family of kagome lattice materials, ${A}\mathrm{V}_{3}\mathrm{Sb}_{5}$ (${A}=\mathrm{K,Rb,Cs}$), has attracted great interest, especially in the debate over their dominant superconducting pairing symmetry. To explore this issue, we study the superconducting pairing behavior within the kagome-lattice Hubbard model through the constrained path Monte Carlo method. It is found that doping around the Dirac point generates a dominant next-nearest-neighbor-d pairing symmetry driven by on-site Coulomb interaction $U$. However, when considering the nearest-neighbor interaction $V$, it may induce nearest-neighbor-p pairing to become the preferred pairing symmetry. Our results provide useful information to identify the dominant superconducting pairing symmetry in the ${A}\mathrm{V}_{3}\mathrm{Sb}_{5}$ family.

The hysteresis of magnetoresistance observed in superconductors is of great interest due to its potential connection with unconventional superconductivity. In this study, we perform electrical transport measurements on kagome superconductor CsV$_3$Sb$_5$ nanoflakes and uncover unusual hysteretic behavior of magnetoresistance in the superconducting state. This hysteresis can be induced by applying either a large DC or AC current at temperatures ($T$) well below the superconducting transition temperature ($T_{\rm c}$). As $T$ approaches $T_{\rm c}$, similar weak hysteresis is also detected by applying a small current. Various scenarios are discussed, with particular focus on the effects of vortex pinning and the presence of time-reversal-symmtery-breaking superconducting domains. Our findings support the latter, hinting at chiral superconductivity in kagome superconductors.

We systematically study the electronic structure of a kagome superconductor ${\rm Cs}{\rm V}_{{\rm 3}}{{\rm Sb}}_{{\rm 5}}$ at different temperatures covering both its charge density wave state and normal state with angle-resolved photoemission spectroscopy. We observe that the V-shaped band around $\bar{\varGamma }$ shows three different behaviors, referred to as $\alpha /\alpha '$, $\beta $ and $\gamma $, mainly at different temperatures. Detailed investigations confirm that these bands are all from the same bulk Sb-p$_{z}$ origin, but they are quite sensitive to the sample surface conditions mainly modulated by temperature. Thus, the intriguing temperature dependent electronic behavior of the band near $\bar{\varGamma }$ is affected by the sample surface condition, rather than intrinsic electronic behavior originating from the phase transition. Our result systematically reveals the confusing electronic structure behavior of the energy bands around $\bar{\varGamma }$, facilitating further exploration of the novel properties in this material.

The kagome lattice system has been identified as a fertile ground for the emergence of a number of new quantum states, including superconductivity, quantum spin liquids, and topological electronic states. This has attracted significant interest within the field of condensed matter physics. Here, we present the observation of an anomalous Hall effect in an iron-based kagome antiferromagnet LuFe$_{6}$Sn$_{6}$, which implies a non-zero Berry curvature in this compound. By means of extensive magnetic measurements, a high Neel temperature, $T_{\rm N} = 552 $ K, and a spin reorientation behavior were identified and a simple temperature-field phase diagram was constructed. Furthermore, this compound was found to exhibit a large Sommerfeld coefficient of $\gamma = 87 $ mJ$\cdot $mol$^{-1}\cdot$K$^{-2}$, suggesting the presence of a strong electronic correlation effect. Our research indicates that LuFe$_{6}$Sn$_{6}$ is an intriguing compound that may exhibit magnetism, strong correlation, and topological states.

The alkali adatoms with controlled coverage on the surface have been demonstrated to effectively tune the surface band of quantum materials through in situ electron doping. However, the interplay of orderly arranged alkali adatoms with the surface states of quantum materials remains unexplored. Here, by using low-temperature scanning tunneling microscopy/spectroscopy (STM/S), we observed the emergent 3$\times$3 super modulation of electronic states on the $\sqrt 3\times\sqrt 3R30^\circ$ (R3) Cs ordered surface of kagome superconductor CsV$_{3}$Sb$_{5}$. The nondispersive 3$\times$3 superlattice at R3 ordered surface shows contrast inversion in positive and negative differential conductance maps, indicating a charge order origin. The 3$\times$3 charge order is suppressed with increasing temperature and undetectable at a critical temperature of $\sim 62$ K. Furthermore, in the Ta substituted sample CsV$_{2.6}$Ta$_{0.4}$Sb$_{5}$, where long-range 2$\times$2$\times$2 charge density wave is significantly suppressed, the 3$\times$3 charge order on the R3 ordered surface becomes blurred and much weaker than that in the undoped sample. It indicates that the 3$\times$3 charge order on the R3 ordered surface is directly correlated to the bulk charge density waves in CsV$_{3}$Sb$_{5}$. Our work provides a new platform for understanding and manipulating the cascade of charge orders in kagome superconductors.

The kagome lattice has garnered significant attention due to its ability to host quantum spin Fermi liquid states. Recently, the combination of unique lattice geometry, electron-electron correlations, and adjustable magnetism in solid kagome materials has led to the discovery of numerous fascinating quantum properties. These include unconventional superconductivity, charge and spin density waves (CDW/SDW), pair density waves (PDW), and Chern insulator phases. These emergent states are closely associated with the distinctive characteristics of the kagome lattice's electronic structure, such as van Hove singularities, Dirac fermions, and flat bands, which can exhibit exotic quasi-particle excitations under different symmetries and magnetic conditions. Recently, various quantum kagome materials have been developed, typically consisting of kagome layers stacked along the $z$-axis with atoms either filling the geometric centers of the kagome lattice or embedded between the layers. In this topical review, we begin by introducing the fundamental properties of several kagome materials. To gain an in-depth understanding of the relationship between topology and correlation, we then discuss the complex phenomena observed in these systems. These include the simplest kagome metal $T_3X$, kagome intercalation metal $TX$, and the ternary compounds $AT_6X_6$ and $RT_3X_5$ ($A = {\rm Li}$, Mg, Ca, or rare earth; $T = {\rm V}$, Cr, Mn, Fe, Co, Ni; $X = {\rm Sn}$, Ge; $R = {\rm K}$, Rb, Cs). Finally, we provide a perspective on future experimental work in this field.

Kagome materials are known for hosting exotic quantum states, including quantum spin liquids, charge density waves, and unconventional superconductivity. The search for kagome monolayers is driven by their ability to exhibit neat and well-defined kagome bands near the Fermi level, which are more easily realized in the absence of interlayer interactions. However, this absence also destabilizes the monolayer forms of many bulk kagome materials, posing significant challenges to their discovery. In this work, we propose a strategy to address this challenge by utilizing oxygen vacancies in transition metal oxides within a "1$+$3" design framework. Through high-throughput computational screening of 349 candidate materials, we identified 12 thermodynamically stable kagome monolayers with diverse electronic and magnetic properties. These materials were classified into three categories based on their lattice geometry, symmetry, band gaps, and magnetic configurations. Detailed analysis of three representative monolayers revealed kagome band features near their Fermi levels, with orbital contributions varying between oxygen 2p and transition metal d states. This study demonstrates the feasibility of the "1$+$3" strategy, offering a promising approach to uncovering low-dimensional kagome materials and advancing the exploration of their quantum phenomena.

The complex symmetry breaking states in $A$V$_{3}$Sb$_{5}$ family have attracted extreme research attention, but controversy still exists, especially in the question of time reversal symmetry breaking of the charge density wave (CDW). Most recently, a chiral CDW has been suggested in kagome magnet FeGe, but the related study is very rare. Here, we use a scanning tunneling microscope to study the symmetry breaking behavior of both the short- and long-range CDWs in FeGe. Different from previous studies, our study reveals an isotropic long-range CDW without obvious symmetry breaking, while local rotational symmetry breaking appears in the short-range CDW, which may be related to the existence of strong structural disorders. Moreover, the charge distribution of the short-range CDW is inert to the applied external magnetic fields and the detailed spin arrangements of FeGe, inconsistent with the expectation of a chiral CDW associated with chiral flux. Our results rule out the existence of spontaneous chiral and rotational symmetry breaking in the CDW state of FeGe, putting strong constraints on the further understanding of CDW mechanism.

Angle-resolved photoemission spectroscopy (ARPES) has become a cornerstone technique for elucidating the electronic structures of emergent quantum materials. Among these, kagome materials - distinguished by their two-dimensional lattice of corner-sharing triangles - provide a fertile ground for investigating exotic quantum phenomena, driven by geometric frustration, electronic correlation, and topology. In this review, we present an overview of recent ARPES studies on transition-metal kagome materials. We first outline the fundamental features of their electronic structures, including van Hove singularities, Dirac points, and flat bands, and discuss the novel quantum states that arise from many-body interactions within the kagome lattice. We then highlight key ARPES investigations into these unique electronic structures, detailing their manifestation and associated quantum states in representative kagome materials. Finally, we offer a forward-looking perspective on the potential of ARPES to uncover new quantum phenomena and its broader implications for the study of underlying physics in kagome materials.