Kagome lattice materials have attracted considerable attention due to their intriguing topological properties and potential applications in next-generation quantum and spintronic technologies. In particular, rare-earth permanent magnets with Kagome structure provide an ideal platform that combines robust magnetism with nontrivial quantum phenomena. However, their anomalous transport properties, particularly thermoelectric responses, remain insufficiently explored. In this work, we perform systematic first-principles calculations on the anomalous Hall and anomalous Nernst effects in Kagome permanent magnets RCo5 (R = Ce, La, Sm, Gd). We find that CeCo5 exhibits a pronounced anomalous Hall conductivity of about 1500 Omega^-1 cm^-1 while GdCo5 displays a substantial anomalous Nernst conductivity of 11 A m^-1 K^-1 within +/- 0.1 eV of the Fermi energy, both comparable to or surpassing the measured intrinsic values reported in many typical Weyl and Heusler magnets. These exceptional anomalous transport properties originate from Berry curvature hotspots near spin-orbit coupling induced band gaps. If validated, these theoretical predictions would be important for Berry-curvature-driven transport in magnetic intermetallics. Our results establish RCo5 compounds as versatile platforms for exploring Berry curvature-driven transport in tunable magnetic topological materials.

The anomalous Nernst effect (ANE), generating a voltage perpendicular to a temperature gradient due to magnetization, is closely linked to the Berry curvature (BC) near the Fermi energy in topological magnets. We report an enhanced spontaneous ANE in the ferromagnetic Kondo lattice CeCo_{2}As_{2}, which features Kondo-screened cerium-based 4f moments embedded in a ferromagnetic d-electron framework. The observed large anomalous Nernst coefficient, greater than the Seebeck coefficient, is attributed to the strong BC present in the f-orbital-dominated flat bands. The enhanced ANE in CeCo_{2}As_{2} serves as a signature of the Fermi energy pinning within the topological flat band, highlighting the correlation-driven topology in the Kondo lattice.

The kagome ferrimagnet TbMn6Sn6, featuring a pristine Mn kagome lattice, emerges as a candidate Chern magnet with a large intrinsic anomalous Hall effect (AHE). While chemical substitution can modulate its properties, hydrostatic pressure provides a disorder-free route to manipulate electronic and magnetic interactions. Here, we investigate the effect of hydrostatic pressure on electrical- and magneto-transport in TbMn 6 Sn 6 up to 18.3 GPa. Pressure significantly enhances hysteresis in the magnetoresistance and Hall responses, concurrent with a monotonic increase in coercive field, suggesting the enhancement of interlayer magnetic couplings in a robust c -axis ferrimagnetic order. The intrinsic anomalous Hall conductivity dramatically rises from 129.5 S·cm -1 at ambient pressure to 448.7 S·cm -1 at 14.0 GPa-a 247 % enhancement that is unprecedented among pressure-tuned kagome magnets. Bolstered with density functional theory calculations, we reveal that pressure induces multiple gap openings near the Fermi level, giving rise to pronounced Berry curvature hotspots that may contribute to the AHE. Our results establish pressure as a powerful tool for enhancing intrinsic topological responses in such kagome magnet.

Electrons on Fermi arcs (FAs), a hallmark of Weyl semimetals, exhibit chiral transport harboring chiral anomaly, negative magnetoresistance, and Majorana zero modes. While FAs were observed in exemplary Weyl semimetal TaAs and Co3Sn2S2, the manipulation of FAs has been rarely explored. Here we take Co3Sn2S2 as an example and demonstrate that tuning the electronic correlation strength is an effective way to control the topology and connectivity of FAs. After achieving a good agreement with experimentally measured band structure by employing combined density functional theory and dynamical mean field theory (DFT+DMFT) calculations, we show that the experimental charge dynamics are well reproduced by DFT+DMFT calculations but not DFT calculations. Electronic correlation renormalizes the bands around the Fermi level and modifies the energy and location of Weyl points, and the resulting FAs. In particular, on the Co-terminated surface, the FAs are formed by connecting Weyl points located in adjacent Brillouin zones in DFT+DMFT calculations and experiments, in strong contrast to the FAs connecting Weyl points within the same Brillouin zone in DFT calculations. We further show the evolution of FAs with correlation and reveal a topological change of the FAs on the Sn-terminated surface at stronger correlation strength. Our study sheds new light on experimental manipulation of FAs to improve the electronic properties of correlated Weyl semimetals.

The kagome ferrimagnet TbMn6Sn6, featuring a pristine Mn kagome lattice, has emerged as a candidate Chern magnet with a large intrinsic anomalous Hall effect (AHE). While chemical substitution can modulate its properties, hydrostatic pressure provides a disorder-free route to manipulate electronic and magnetic interactions. Herein, we investigate the effects of hydrostatic pressure on electrical and magneto-transport in TbMn6Sn6 up to 18.3 GPa. Pressure significantly enhances hysteresis in the magnetoresistance and Hall responses, causing a concurrent monotonic coercive field increase, suggesting the enhancement of interlayer magnetic couplings in a robust c-axis ferrimagnetic order. The intrinsic anomalous Hall conductivity increases considerably from 129.5 S & sdot;cm-1 at ambient pressure conditions to 448.7 S & sdot;cm-1 at 14.0 GPa-an enhancement of 247% that is unprecedented among pressure-tuned kagome magnets. Based on density functional theory calculations, we reveal that pressure induces multiple gap openings near the Fermi level, giving rise to pronounced Berry curvature hotspots that may contribute to the AHE. Our results show that pressure can be used to enhance the intrinsic topological responses of this kagome magnet.

Using first-principles calculations, we predict a new perovskite compound SrAsO_3 . The undoped cubic phase has pronounced soft-phonon instabilities, which are gradually suppressed upon K doping the Sr site. The cubic phase becomes dynamically stable for K-doping levels above approximately 60

The coexistence of unconventional high-temperature superconductivity, topological surface states, and strong electronic correlations makes iron-based superconductors a prominent platform for exploring topological superconductivity and Majorana zero modes. Here, we design a novel intergrowth-structured compound, LaNa2Fe4As4 (1244-type), by combining uncollapsed tetragonal LaFe2As2 and NaFeAs. This unique inter-growth structure provides a new route to engineer topological states in iron-based superconductors. Using density functional theory combined with dynamical mean-field theory calculations, we reveal nontrivial band topologies near the Fermi level (EF) in LaNa2Fe4As4, hosting both topological insulator (TI) and topological Dirac semimetal states, and giving rise to two sets of Dirac-cone-type surface states on the (001) surface. Strong electronic correlations renormalize the band structure, bringing the topological surface states closer to EF. Moreover, slight electron doping at the Fe sites can further tune the TI surface states to EF, enhancing their experimental accessibility. The intrinsic self-doping and multiband Fermi surface of LaNa2Fe4As4 also suggest potential superconductivity. These findings establish LaNa2Fe4As4 as a promising candidate for studying topological superconductivity and Majorana zero modes, calling for experimental validation and further exploration of its potential in quantum applications. They also underscore the effectiveness of the intergrowth strategy in optimizing the topological properties of iron-based superconductors.

Recently, it was proposed that a nontrivial Z8 topological index could induce double topological insulator (TI) surface states on the (001) surface of LaBaFe4As4 (LBFA). Here, we carry out a comprehensive investigation of the electronic structure, topological index, and topological surface states of other 1144-type iron-based compounds. We find that the coexistence of double band inversions in LaSrFe4As4 leads to a nontrivial Z8 topological index and two sets of TI surface states on the (001) surface, similar to LBFA. On the other hand, when Ba is substituted by Ca, K, Rb, or Cs, the system is characterized by a nontrivial Z2 topological index and exhibits only one set of TI surface states on the (001) surface. Further analysis shows that both the lattice parameter c and the nominal valence of the alkali or alkaline earth metal atom are crucial in determining the bandwidth of La 5dx2-y2, topological index, and topological surface states. Moreover, we substitute La with Lu and Hf in LBFA and find that they also have a nontrivial Z8 topological index. However, only one set of the double TI surface states is clearly visible on the (001) surface, whereas the other set is difficult to identify due to a different mechanism of the band inversion between As 4pz and Fe 3dz2 bands. Our findings extend previous studies on LaBaFe4As4 and provide insights for manipulating the topological index Z8 or Z2 and topological surface states in iron-based compounds.

The spontaneous rotational symmetry breaking (RSB), a hallmark phenomenon in cuprates and iron-based high-temperature superconductors, originates from intricate interactions between superconducting order and competing quantum states. Understanding this mechanism is pivotal for unraveling the microscopic origin of unconventional superconductivity. Although infinite-layer nickelates (ILNs) share similar crystalline structure and the same nominal 3d-electron configurations with cuprates, they have significant differences in Fermi surface topology, electronic band characteristics, and charge order. These distinctions make ILNs an ideal platform for studying RSB in unconventional superconductors. Through angular-resolved resistivity measurements within a large temperature and doping range, we identify pronounced RSB signatures near doping concentrations x=0.05 and 0.25. Based on the strongly correlated electronic structures from combined density functional theory and dynamical mean field theory calculations, we find that the calculated electronic susceptibility has a peak structure at the corresponding doping concentration, indicating pronounced electronic instabilities which drive RSB. Our findings reveal the important role of electronic correlation and Fermi surface nesting in the emergence of RSB. Our work not only deepens the understanding of electronic behavior in ILNs, but also provides new ideas and methods for exploring RSB in other unconventional superconductors.

The spontaneous rotational symmetry breaking (RSB), a hallmark phenomenon in cuprates and iron-based high-temperature superconductors, originates from intricate interactions between superconducting order and competing quantum states. Understanding this mechanism is pivotal for unraveling the microscopic origin of unconventional superconductivity. Although infinite-layer nickelates (ILNs) share similar crystalline structure and the same nominal 3d-electron configurations with cuprates, they have significant differences in Fermi surface topology, electronic band characteristics, and charge order. These distinctions make ILNs an ideal platform for studying RSB in unconventional superconductors. Through angular-resolved resistivity measurements within a large temperature and doping range, we identify pronounced RSB signatures near doping concentrations x=0.05 and 0.25. Based on the strongly correlated electronic structures from combined density functional theory and dynamical mean field theory calculations, we find that the calculated electronic susceptibility has a peak structure at the corresponding doping concentration, indicating pronounced electronic instabilities which drive RSB. Our findings reveal the important role of electronic correlation and Fermi surface nesting in the emergence of RSB. Our work not only deepens the understanding of electronic behavior in ILNs, but also provides new ideas and methods for exploring RSB in other unconventional superconductors.

Flat bands with small energy dispersion can give rise to strongly correlated electronic and topological phases, especially when located at the Fermi level. Whilst flat bands have been experimentally realized in two-dimensional (2D) twisted van der Waals heterostructures, they are highly sensitive to twist angle, necessitating complex fabrication techniques. Geometrically frustrated kagome lattices have emerged as an attractive platform as they natively host flat bands that have been observed experimentally in quasi-2D bulk-crystal kagome metals. An outstanding experimental question is whether flat bands can be realized in atomically thin metals, with opportunities for stronger electron-electron interactions through tuning of the surrounding dielectric environment. Here we use angle-resolved photoelectron spectroscopy, scanning tunnelling microscopy and band structure calculations to show that ultra-thin films of the kagome metal Mn3Sn host a robust dispersionless flat band with a bandwidth of 50 meV. Furthermore, we demonstrate chemical tuning of the flat band to near the Fermi level via manganese defect engineering. The realization of tunable kagome-derived flat bands in an ultra-thin kagome metal, represents a promising platform to study strongly correlated and topological phenomena, with applications in quantum computing, spintronics and low-energy electronics.

Flat bands with narrow energy dispersion can give rise to strongly correlated electronic and topological phases, especially when located at the Fermi level. Whilst flat bands are experimentally realized in 2D twisted van der Waals heterostructures, they are highly sensitive to twist angle, necessitating complex fabrication techniques. Geometrically frustrated kagome lattices have emerged as an attractive alternative platform as they can natively host flat bands that are observed experimentally in quasi-2D bulk-crystal kagome metals. An outstanding experimental question is whether flat bands can be realized in ultra-thin metals, with opportunities for stronger electron-electron interactions through tuning of the surrounding dielectric environment. Here, angle-resolved photoelectron spectroscopy, scanning tunnelling microscopy, and band structure calculations are used to show that ultra-thin films of the kagome metal Mn3Sn host a robust dispersionless flat band with a bandwidth of 50 meV. Furthermore, chemical tuning of the flat band to near the Fermi level via manganese defect engineering is demonstrated. The realization of tunable kagome-derived flat bands in an ultra-thin kagome metal represents a promising platform to study strongly correlated and topological phenomena, with applications in quantum computing, spintronics and low-energy electronics.

Paramagnetic LaCoSi, a ternary intermetallic electride, consists of CoSi blocks separated by two layers of La atoms. Its structure is similar to that of the widely studied 111 system of iron-based superconductors. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, we demonstrate the existence of linear bands and flat bands mainly originating from the eg orbitals of Co 3d states near the Fermi energy. The anomalous scattering rate of the linear bands varies linearly with the binding energy. The flat band above the Fermi energy indicated by the calculations could be modulated by substitutions and pressure to induce new ordered quantum phases, such as magnetism and superconductivity. Our findings reveal flat-band physics in electrides.

With extensive structure searches for XB2 (X = Sc, Ti, V, Cr, and Tc) under pressures up to 100 GPa, we uncovered that the crystal structures of these compounds with the lowest enthalpy have the same space group (P6/mmm) as MgB2 at ambient pressure. Among them, ScB2, TiB2 and VB2 are dynamically stable at ambient pressure, but they do not superconduct. CrB2 becomes dynamically stable at 108 GPa and shows superconductivity with a transition temperature (Tc) of 26.0 K. TcB2 is not dynamically stable until 9 GPa. At 20 GPa, it has a Tc of 23.5 K. Further calculations indicate that CrB2 and TcB2 are also thermodynamically stable, suggesting that it is highly likely that they can be synthesized successfully in the laboratory. We found that transition metal atoms (Cr/Tc) dominate soft phonon vibrations and make significant contributions to the electron-phonon coupling (EPC) and superconductivity in CrB2/TcB2, which is in strong contrast to the case of MgB2, where high-frequency B vibrations dominate the EPC and superconductivity. Our work enriches the understanding of superconductivity in transition metal borides.

We design two new layered indium halide compounds LaOInF2 and LaOInCl2 by means of first-principles calculations and evolutionary crystal structure prediction. We find both compounds crystallize in a tetragonal structure with P4/nmm space group and have indirect band gaps of 2.58 eV and 3.21 eV, respectively. By substituting O with F, both of them become metallic and superconducting at low temperature. The F-doping leads to strong electron-phonon coupling in the low-energy acoustic phonon modes which is mainly responsible for the induced superconductivity. The total electron-phonon coupling strength are 1.86 and 1.48, while the superconducting transition temperature (T-c) are about 7.2 K and 6.5 K with 10% and 5% F doping for LaOInF2 and LaOInCl2, respectively.

In this work, we investigate the electronic structures, spin Hall effects, and topological properties of the superconductor YIr2, 2 , which crystallizes in the cubic Laves phase and contains two-dimensional (2D) kagomelattice planes. We find it has an intrinsic 3D flat band originated from two intersecting kagome-lattice planes. This 3D flat band gives rise to large intrinsic spin Hall conductivity, which suggests YIr2 2 can be used for charge-spin conversion devices. On the (111) surface, it has Dirac-cone type topological surface states in close vicinity of the Fermi level. More importantly, they are distinct from the bulk states, indicating that YIr2 2 is a promising candidate topological superconductor to host Majorana zero modes. Our work provides an encouraging platform on which to study flat band physics, spin Hall effects, and topological superconductivity.

We design a kagome compound Pt3P2Te8 and find it is a topological semimetal with a symmetry-protected three-dimensional (3D) bulk Dirac point along the P-A path. This Dirac point is not intrinsic to kagome lattice and brings a parity inversion, leading to topological surface states and fragile Fermi arcs on the (100) surface. These features are very close to the Fermi level and distinct from the bulk states, which suggests they can be observed in experiments. We further characterize the 3D bulk Dirac point and compute a high-order topological invariant, i.e., the change of the filling anomaly, whose value of 4 indicates the high-order bulk-hinge correspondence and the existence of high-order Fermi arcs. Moreover, Pt3P2Te8 exhibits rich topological phase transitions under hydrostatic pressure. Our results provide a potential platform to study topological properties related to 3D bulk Dirac points and pressure-induced topological phase transitions in the kagome lattice.

We investigate the electronic structure and topological properties of iron-based superconductors LaFe2As2 using density functional theory plus dynamical mean-field theory. We find that the uncollapsed tetragonal LaFe2As2 is in a nontrivial Z2 topological phase and has topological Dirac surface states near the Fermi energy which suggests there could be Majorana zero modes in the superconducting LaFe2As2. In light of the nontrivial topological properties and superconductivity of LaFe2As2 and CaKFe4As4, we predict a new iron-based compound LaBaFe4As4 and find it possesses two sets of topological Dirac surface states near the Fermi energy despite of a trivial Z2 topological index. These topological surface states are induced by a nontrivial high-order topological index Z8, a new mechanism that is distinct from all-known iron-based superconductors. Our study not only demonstrates that both LaBaFe4As4 and uncollapsed tetragonal LaFe2As2 can be good platforms for exploring topological superconductivity but also paves a new way to realize it with a nontrivial high-order topological index.

Utilizing ultrafast light-matter interaction to manipulate electronic states of quantum materials is an emerging area of research in condensed matter physics. It has significant implications for the development of future ultrafast electronic devices. However, the ability to induce long-lasting metastable electronic states in a fully reversible manner is a long-standing challenge. Here, by using ultrafast laser excitations, we demonstrate the capability to manipulate the electronic polar states in the charge-density-wave material EuTe4 in a non-volatile manner. The process is completely reversible and is achieved at room temperature with an all-optical approach. Each induced non-volatile state brings about modifications to the electrical resistance and second harmonic generation intensity. The results point to layer-specific phase inversion dynamics by which photoexcitation mediates the stacking polar order of the system. Our findings extend the scope of non-volatile all-optical control of electronic states to ambient conditions, and highlight a distinct role of layer-dependent phase manipulation in quasi-two-dimensional systems with inherent sublayer stacking orders.