Nodal Lines Research Articles

Unconventional magnons in collinear magnets dictated by spin space groups.

Magnonic systems provide a fertile playground for bosonic topology1, for example, Dirac2-6 and Weyl7,8 magnons, leading to a variety of exotic phenomena such as charge-free topologically protected boundary modes6,7, the magnon thermal Hall effect9 and the magnon spin Nernst effect10. However, their understanding has been hindered by the absence of fundamental symmetry descriptions of magnetic geometries and spin Hamiltonians primarily governed by isotropic Heisenberg interactions. The ensuing magnon dispersions enable gapless magnon band nodes that go beyond the scenario of representation theory of the magnetic space groups11,12, thus referred to as unconventional magnons. Here we developed spin space group13-17 theory to elucidate collinear magnetic configurations, classifying the 1,421 collinear spin space groups into 4 types, constructing their band representations and providing a comprehensive tabulation of unconventional magnons, such as duodecuple points, octuple nodal lines and charge-4 octuple points. On the basis of the MAGNDATA database18, we identified 498 collinear magnets with unconventional magnons, among which more than 200 magnon band structures were obtained by using first-principles calculations and linear spin wave theory. In addition, we evaluated the influence of the spin-orbit-coupling-induced exchange interaction in these magnets and found that more than 80 per cent are predominantly governed by the Heisenberg interactions, indicating that the spin space group serves as an ideal framework for describing magnon band nodes in most 3d, 4d and half-filled 4f collinear magnets.

Magneto-optical properties of three-dimensional nodal semimetals

ABSTRACT The magneto-optical response of the heterostructure of a topological insulator with an ordinary insulator was studied theoretically. More specifically, ferromagnetic impurities added in the heterostructure along a certain direction lead to nodal semimetals, which are point and line node semimetals. It was found that topological phase transition occurs by tuning various parameters. In addition to this, LL transitions for n = 0 were observed, witnessing semimetals. For magneto-optical properties, conductivities have been plotted and discussed. It is seen that the absorptive part of conductivity was ascribed to allowed transitions between LLs. In Hall conductivity, LLs overlapping occurs in the form of plateaus.

Research on autonomous control strategy for low-voltage station area considering new energy sources and loads uncertainty

ABSTRACT To improve the autonomous level of low-voltage station areas under the uncertainty of new energy resource generation and load electricity consumption, a novel autonomous control model of low-voltage station areas is established. Firstly, the characteristic of this model is the integration of the maximum deficit and maximum surplus generated by the uncertainty of new energy resources and load. Then, the impact of uncertainty is analyzed and an uncertain operation model is proposed by integrating two extreme scenarios. Finally, in a low-voltage station area, the control effects of the proposed method and the determined optimisation model are compared in two extreme scenarios. The results indicate that the proposed method effectively mitigates the impact of uncertainty on line loss, node voltage, and power interaction between low-voltage station area and medium-voltage distribution network. It has a positive promoting effect on the autonomous operation of low-voltage station areas.

Coexistence of topological nodal lines and Weyl nodes in a room-temperature half-metallic ferromagnet Cr3Si2Te6

Topological half-metallic ferromagnets, featured by topologically nontrivial states and fully spin-polarized electronic carriers at the Fermi level, are fertile playgrounds for exploring topo-spintronic applications. However, such exotic compounds are still limited. Here, we systematically study a self-intercalated van der Waals magnet Cr3Si2Te6 by combining first-principles calculations and Monte Carlo simulations. We demonstrate that Cr3Si2Te6 is thermodynamically stable and a half-metallic ferromagnet with a Curie temperature up to 485 K, much above room temperature. Excitingly, we find that topological nodal lines and Weyl nodes coexist in the Cr3Si2Te6 bulk. Correspondingly, the Cr3Si2Te6 bulk exhibits a large anomalous Hall conductivity of 160 and 427 Ω−1 cm−1 when its magnetization is along its magnetic easy and hard axes, respectively. Moreover, its anomalous Hall conductivity can be increased to 374 (882) Ω−1 cm−1 by doping electrons (holes). Finally, we disclose that the 7-layer Cr3Si2Te6 thin film possesses half-metallic ferromagnetism with a high TC of 425 K, strong out-of-plane magnetic anisotropy energy, and large anomalous Hall conductivity. Our findings suggest that Cr3Si2Te6 is a room-temperature topological half-metallic ferromagnet, which could have promising prospects for practical applications in next-generation topo-spintronic and nanoscale electronic devices.

Behavior of water at lipid/water interfaces upon phase transition of the lipid bilayer: Insights from 1D- and 2D-vibrational sum frequency generation spectral calculations from molecular dynamics simulations.

We have investigated the structural and dynamical changes of the interfacial water near [1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine] (DMPC) lipid bilayer across various temperatures, ranging from 285K (gel phase of lipid) to 320K (liquid phase of lipid), through calculations of one-dimensional (1D) and two-dimensional (2D) vibrational sum frequency generation (VSFG) spectra from molecular dynamics simulations. The 1D-VSFG spectra show a broad positive peak in the hydrogen-bonded region, which means that water molecules are oriented upward toward the lipid bilayer. Although DMPC is a zwitterionic lipid, the negatively charged phosphate group primarily influences the orientation of the water molecules. The absence of a dangling peak in the 1D- and 2D-VSFG spectra shows that the water molecules form hydrogen bonds with the lipid headgroup atoms. The spectral diffusion timescales obtained from the 2D-VSFG metrics of the slope of the nodal line clearly reveal a dynamical crossover and exhibit Arrhenius behavior with different activation energies before and after the melting of the lipid bilayer. Apart from 2D-VSFG, the frequency fluctuation time correlation function also exhibits a dynamical crossover upon melting of the lipid bilayer.

Fluid–structure boundary-driven simultaneous standard-inverse Chladni patterns for selective particles manipulation

In fluid, particles patterning and selective manipulation are essential for material, biomedical, and robotic handling. The German physicist Chladni has investigated the particles manipulation on a flat vibrating plate. Generally, particles bounce with the vibrating plate, gradually accumulate to nodal lines or anti-nodes, forming either standard or inverse Chladni patterns. The Chladni patterns show great potential for particles assembly in different environments. The mechanisms for simultaneous manipulation by multiple kinds of forces are still unclear. Here, the Chladni plate with a vertical boundary is used for selective particles manipulation. The simultaneous standard-inverse Chladni patterns are realized on the vibrating plate by modulating the frequency. First, the particles patterning mechanisms on the Chladni plate with vertical boundary are investigated for the acoustic radiation force and the acoustic streaming. The simultaneous standard-inverse Chladni patterns are realized due to the driving of vertical boundary. Then, through switching the excitation frequencies, the tunable particles patterns are realized. Finally, the selective separation of particles with different sizes and densities is investigated using the standard-inverse Chladni patterns. This work investigates the particles manipulation mechanisms on vibrating plate by the fluid–structure boundary-driven acoustic field, thereby potentially providing a platform for selective patterning and separation of particles.

Fermi-liquid behavior of nonaltermagnetic RuO2

The presence of magnetism in potentially altermagnetic RuO2 has been a subject of intense debate. Using broadband infrared spectroscopy combined with density-functional band-structure calculations, we show that the optical conductivity of RuO2, the bulk probe of its electronic structure, is best described by a nonmagnetic model. The sharp Pauli edge demonstrates the presence of a Dirac nodal line lying 45 meV below the Fermi level. An excellent match between the experimental and plasma frequencies underpins the weakness of electronic correlations. The intraband part of the optical conductivity indicates Fermi-liquid behavior with two distinct scattering rates below 150 K. Fermi-liquid theory also accounts for the temperature-dependent magnetic susceptibility of RuO2 and allows a consistent description of this material as a paramagnetic metal. Published by the American Physical Society 2025

Evolution of nodal line induced out-of-plane anomalous Hall effect in Co3Sn2S2

Weyl semimetals have attracted considerable research interest over the past decade, with a number of intriguing transport phenomena reported. Magnetic Weyl semimetals, which break time reversal symmetry, have been predicted and recently discovered. Co3Sn2S2 is a magnetic Weyl semimetal that exhibit a giant anomalous Hall effect (AHE) when the magnetic moments are aligned along the c axis. In this paper, we report the evolution of the AHE with an external magnetic field applied in the ab plane and current along the c axis, namely, the out-of-plane AHE of Co3Sn2S2. Density functional theory calculations predict a finite out-of-plane AHE when the spins are fully aligned in the ab plane. The evolution of the magnetic structure modifies the nodal line distribution and the Berry curvature, resulting in a weaker AHE with an amplitude of 200Scm−1 at the saturation field. To ensure the alignment of the magnetic field in the ab plane, a two-round scanning process was performed experimentally. After this, the out-of-plane AHE was measured at multiple temperatures. The observed AHE signals with applied fields of 1 and 2 T were in good agreement with theoretical predictions. These results suggest that engineering the anomalous Hall effect may be possible by designing the symmetry relation of the local Berry curvature. Published by the American Physical Society 2025

Infrared surface plasmon and hot carrier properties of topological nodal line semimetal ZrSiS.

Recently, a new plasmon mode, the nodal-line plasmon, was discovered in ZrSiS, which provides promising possibilities for plasmonics or optics. However, there remains a lack of research on the surface plasmon (SP) properties and carrier transport characteristics of ZrSiS. In this paper, we conduct an in-depth study of these properties and compare them with the traditional SP material Au. The interband contribution of the dielectric function of ZrSiS is much greater than the intraband contribution, which is opposite to the properties of traditional SP materials such as Au. In addition, it's found that ZrSiS can generate SP in the infrared range, with the imaginary part of the dispersion relation larger than that of Au and a much shorter propagation length. This implies that ZrSiS has significant potential for generating hot carriers in the infrared range. Notably, the initial energy distribution and hot carrier transport properties indicate that the hot carriers generated by ZrSiS are concentrated in the high-energy region and exhibit good separation. Furthermore, ZrSiS can simultaneously produce long-lived hot electrons and holes with lifetimes comparable to those of Au, which is crucial for the collection and application of hot carriers. Our results not only provide theoretical analysis for understanding the surface plasmonic properties of ZrSiS but also offer important guidance for the collection and application of the carriers in ZrSiS.

Correspondence between Euler charges and nodal-line topology in Euler semimetals.

Real multi-bandgap systems have non-abelian topological charges, with Euler semimetals being a prominent example characterized by real triple degeneracies (RTDs) in momentum space. These RTDs serve as "Weyl points" for real topological phases. Despite theoretical interest, experimental observations of RTDs have been lacking, and studies mainly focus on individual RTDs. Here, we experimentally demonstrate physical systems with multiple RTDs in crystals, analyzing the distribution of Euler charges and their global connectivity. Through Euler curvature fields, we reveal that type I RTDs have quantized point Euler charges, while type II RTDs show continuously distributed Euler charges along nodal lines. We discover a correspondence between the Euler number of RTDs and the abelian/non-abelian topological charges of nodal lines, extending the Poincaré-Hopf index theorem to Bloch fiber bundles and ensuring nodal line connectivity. In addition, we propose a "no-go" theorem for RTD systems, mandating the balance of positive and negative Euler charges within the Brillouin zone.

Direct Observation of Anisotropic Coulomb Interaction in a Topological Nodal Line Semimetal.

The fundamental characteristics of collective interactions in topological band structures can be revealed by the exploration of charge screening in topological materials. In particular, distinct anisotropic screening behaviors are predicted to occur in Dirac nodal line semimetals (DNLSMs) due to their peculiar anisotropic low-energy dispersion. Despite the recent extensive theoretical research, experimental observations of exotic charge screening in DNLSMs remain elusive, which is partly attributed to the coexisting trivial bands near the Fermi energy. This study reports the first direct observation of highly anisotropic charge-screening behavior in the DNLSM SrAs3. Through atomically resolved conductance measurements, a highly anisotropic charge-screening pattern around charged impurities on a surface is demonstrated. Moreover, the combination of model studies and first-principles calculations reveals the unique nature of the screening anisotropy in DNLSMs. The results of this study are expected to pave the way for understanding the profound collective behavior of interacting low-energy fermions in topological materials.

Coexistence of multiple electronic and phononic nodal lines in a two-dimensional macroporous carbon material

Coexistence of multiple electronic and phononic nodal lines in a two-dimensional macroporous carbon material

Topological electronic structure and transport properties of the distorted rutile-type WO2

We elucidate the transport properties and electronic structures of distorted rutile-type WO2. Electrical resistivity and Hall effect measurements of high-quality single crystals revealed the transport property characteristics of topological materials; these characteristics included an extremely large magnetoresistance of 13 200% (2 K and 9 T) and a very high carrier mobility of 25 700 cm2 V−1 s−1 (5 K). First-principles calculations revealed Dirac nodal lines (DNLs) near the Fermi energy in the electronic structure when spin–orbit interactions (SOIs) were absent. Although these DNLs mostly disappeared in the presence of SOIs, band crossings at high-symmetry points in the reciprocal space existed as Dirac points. Furthermore, DNLs protected by nonsymmorphic symmetry persisted on the ky = π/b plane. The unique transport properties originating from the topological electronic structure of chemically and thermally stable WO2 could represent an opportunity to investigate the potential electronic applications of the material.

Multi-fold fermionic and bosonic states in topologically non-trivial Ti3Pd.

The topological properties of the A15-type compound Ti3Pd reveal a complex landscape of multi-fold fermionic and bosonic states, as uncovered through ab initio calculations within the framework of density functional theory (DFT). The electronic band structure shows multi-fold degenerate crossings at the high-symmetry point R near the Fermi level, which evolves into 4-fold and 8-fold degenerate fermionic states upon the introduction of spin-orbit coupling (SOC). Likewise, the phononic band structure features multi-fold degenerate bosonic crossings at the same R point. Topological analysis, including the calculation of 2 invariant and surface states, confirms the non-trivial nature of Ti3Pd. Moreover, both fermionic and bosonic quasiparticles exhibit nodal line features, whose topological non-triviality is further substantiated by Berry phase calculation. This research illuminates the intricate topological framework of Ti3Pd, opening avenues for experimental exploration in the field of topological quantum materials.

Essentially degenerate hidden nodal lines in two-dimensional magnetic layer groups

Essentially degenerate hidden nodal lines in two-dimensional magnetic layer groups

Two-dimensional cooling without repump laser beams through ion motional heating

Laser cooling typically requires one or more repump lasers to clear dark states, which complicates experimental setups, especially for systems with multiple repumping frequencies. Here, we demonstrate cooling of Be+ ions using a single laser beam, enabled by micromotion-induced one-dimensional heating. By manipulating the displacement of Be+ ions from the trap’s nodal line, we precisely control the ion micromotion velocity, eliminating the necessity of a 1.25 GHz offset repump laser while keeping ions cold in the direction perpendicular to the micromotion. We use two equivalent schemes, cooling laser detuning and ion trajectory imaging to measure the speed of the Be+ ions, with results accurately reproduced by molecular dynamics simulations based on a machine learned time-dependent electric field inside the trap. This work provides a robust method to control micromotion velocity of ions and demonstrates the potential of micromotion-assisted laser cooling to simplify setups for systems requiring multiple repumping frequencies.

Thermoelectric properties of type-I and type-II nodal line semimetals: a comparative study

Abstract We investigate the thermoelectric (TE) properties of nodal line semimetals (NLSs) using a combination of semi-analytical calculations within Boltzmann's linear transport theory and the relaxation time approximation, along with first-principles calculations for the so-called type-I and type-II NLSs. We consider the conduction and valence bands that cross near the Fermi level of these materials through first-principles calculations of typical type-I (TiS) and type-II (Mg$_3$Bi$_2$) NLSs and use the two-band model fit to find the Fermi velocity $v_{F}$ and effective mass $m$ that will be employed as the initial energy dispersion parameters. The optimum curvature value for each energy band is searched by tuning both $v_{F}$ and $m$ to improve the TE properties of the NLSs. By systematically comparing all of our calculation results, we observe that tuning $v_{F}$ significantly improves TE properties in both types of NLS compared to tuning $m$. We also find that in all TE metrics, the type-I NLS surprisingly can surpass the type-II NLS, which seems counter-intuitive to the fact that within the two-band model, the type-I NLS contains a parabolic band while the type-II NLS possesses a higher-order, Mexican-hat band. Our study demonstrates that optimizing the curvature of energy bands by tuning $v_F$ can significantly improve the TE performance of NLSs. This approach could guide future efforts in exploring other semimetals as potential TE materials by manipulating their band structures.

Impurity bands, line nodes, and anomalous thermal Hall effect in Weyl superconductors

Impurity bands, line nodes, and anomalous thermal Hall effect in Weyl superconductors

Anomalous Crystalline-Electromagnetic Responses in Semimetals

We present a unifying framework that allows us to study the mixed crystalline-electromagnetic responses of topological semimetals in spatial dimensions up to D=3 through dimensional augmentation and reduction procedures. We show how this framework illuminates relations between the previously known topological semimetals and use it to identify a new class of quadrupolar nodal line semimetals for which we construct a lattice tight-binding Hamiltonian. We further utilize this framework to quantify a variety of mixed crystalline-electromagnetic responses, including several that have not previously been explored in existing literature, and show that the corresponding coefficients are universally proportional to weighted momentum-energy multipole moments of the nodal points (or lines) of the semimetal. We introduce lattice gauge fields that couple to the crystal momentum and describe how tools including the gradient expansion procedure, dimensional reduction, compactification, and the Kubo formula can be used to systematically derive these responses and their coefficients. We further substantiate these findings through analytical physical arguments, microscopic calculations, and explicit numerical simulations employing tight-binding models. Published by the American Physical Society 2024

Topological nodal line features in NiSe semimetal: Insights from electronic transport and density functional theory studies

Topological nodal line features in NiSe semimetal: Insights from electronic transport and density functional theory studies