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Guodong Liu - One of the best experts on this subject based on the ideXlab platform.
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Two-dimensional Weyl Nodal-Line semimetal in a d 0 ferromagnetic K 2 N monolayer with a high Curie temperature
Physical Review B, 2020Co-Authors: Lei Jin, Xiaoming Zhang, Xuefang Dai, Ying Liu, Xunan Shen, Liying Wang, Guodong LiuAbstract:Nodal-Line semimetals in two-dimensional (2D) materials have attracted intense attention recently. From fundamental physics and spintronic application points of view, high Curie temperature ferromagnetic (FM) ones with Nodal Lines robust against spin-orbit coupling (SOC) are extremely desirable. Here, we propose that the FM ${\mathrm{K}}_{2}\mathrm{N}$ monolayer is such a Weyl Nodal-Line semimetal. We show that the ${\mathrm{K}}_{2}\mathrm{N}$ monolayer is dynamically stable and has a FM ground magnetic state with out-of-plane [001] magnetization. It shows two Nodal Lines in the low-energy band structures. Both Nodal Lines are robust against SOC, under the protection of mirror symmetry. We construct an effective Hamiltonian, which can well characterize the Nodal Lines in the system. Remarkably, the Nodal-Line semimetal proposed here is distinct from the previously studied ones in that the ${\mathrm{K}}_{2}\mathrm{N}$ monolayer is a 2D ${d}^{0}$-type ferromagnet with the magnetism arising from the partially filled the $p$ orbitals of the N atom, which can bring special advantages in spintronic applications. In addition, the Curie temperature in the ${\mathrm{K}}_{2}\mathrm{N}$ monolayer is estimated to be 942 K, which is significantly higher than previous FM Nodal-Line materials. We also find that specific tensile strains can transform the Nodal Line from type-I to type-II, making its Nodal-Line characteristics even more interesting.
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Topological Nodal Line Electrides: Realization of an Ideal Nodal Line State Nearly Immune from Spin–Orbit Coupling
The Journal of Physical Chemistry C, 2019Co-Authors: Xiaoming Zhang, Lei Jin, Xuefang Dai, Guodong Liu, Yugui YaoAbstract:Nodal Line semimetals (NLSs) have attracted broad interest in current research. In most of the existing NLSs, the intrinsic properties of Nodal Lines are greatly destroyed because Nodal Lines usual...
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Topological Nodal Line state in superconducting NaAlSi compound
Journal of Materials Chemistry C, 2019Co-Authors: Lei Jin, Xiaoming Zhang, Xuefang Dai, Weizhen Meng, Guodong LiuAbstract:Superconductors with a nontrivial band structure are promising to realize a topological superconducting state. Herein, we report the presence of a topological phase in a well-known superconductor, NaAlSi. Our first-principles computations show that NaAlSi naturally possesses four Nodal Lines in the kz = 0 and kz = π planes and hosts clear drumhead surface states. Comparing with those identified in other superconductors, the Nodal Line band structure of NaAlSi can more favor experimental detection on considering that: (1) it possesses four Nodal Lines in total in the system; (2) all the Nodal Lines appear slightly below the Fermi level; (3) the Nodal Lines do not coexist with other fermions or extraneous bands. Our findings indicate that NaAlSi is an excellent material platform to investigate the entanglement of superconducting and topological Nodal Line states.
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Topological phase with a critical-type Nodal Line state in intermetallic CaPd
Physical Review B, 2018Co-Authors: Guodong Liu, Xuefang Dai, Lei Jin, Guifeng Chen, Xiaoming ZhangAbstract:In recent years, realizing new topological phases of matter has been a hot topic in the fields of physics and materials science. Topological semimetals and metals can conventionally be classified into two types: type-I and type-II, according to the tilting degree of the fermion cone. Here we report an unexplored topological metal phase with the critical-type Nodal Line between type-I and type-II Nodal Lines. The critical-type Nodal Line shows a unique nontrivial band crossing, which is composed of a flat band and a dispersive band and leads to an unexplored fermionic state. We propose intermetallic CaPd can be an existing topological metal for the fermionic state, characterized with critical-type Nodal Line in the bulk and drumhead band structure on the surface. Our work not only promotes the concept of a critical-type Nodal Line, but also provides the material realization to study its exotic properties in future experiments.
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Highly anisotropic type-II Nodal Line state in pure titanium metal
Applied Physics Letters, 2018Co-Authors: Xiaoming Zhang, Lei Jin, Xuefang Dai, Guodong LiuAbstract:A type-II Nodal Line state, along with its unique optical, magnetic, and transport properties, was theoretically proposed and experimentally evidenced quite recently. Here, based on first-principles calculations, we report that a pure Ti metal can serve as an excellent type-II Nodal Line material for experimental detection. In the Ti metal, the type-II Nodal Line situates in a quite large momenta region with a Linear energy range larger than 1.5 eV. Its surface band is quite dispersive and thus is promising to be detected in a wide energy range. The position of the Nodal Line in the Ti metal can be flexibly tuned by applying uniaxial strain and elemental doping. Most interestingly, the band dispersions along the Nodal Line are highly anisotropic in three typical directions, and therefore, strong direction-dependent transport behavior can be expected. Our findings in the Ti metal are the first proposal of a highly anisotropic type-II Nodal Line state in elemental materials.A type-II Nodal Line state, along with its unique optical, magnetic, and transport properties, was theoretically proposed and experimentally evidenced quite recently. Here, based on first-principles calculations, we report that a pure Ti metal can serve as an excellent type-II Nodal Line material for experimental detection. In the Ti metal, the type-II Nodal Line situates in a quite large momenta region with a Linear energy range larger than 1.5 eV. Its surface band is quite dispersive and thus is promising to be detected in a wide energy range. The position of the Nodal Line in the Ti metal can be flexibly tuned by applying uniaxial strain and elemental doping. Most interestingly, the band dispersions along the Nodal Line are highly anisotropic in three typical directions, and therefore, strong direction-dependent transport behavior can be expected. Our findings in the Ti metal are the first proposal of a highly anisotropic type-II Nodal Line state in elemental materials.
Zhong Wang - One of the best experts on this subject based on the ideXlab platform.
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Floquet multi-Weyl points in crossing-Nodal-Line semimetals
Physical Review B, 2017Co-Authors: Zhongbo Yan, Zhong WangAbstract:Weyl points with monopole charge $\ifmmode\pm\else\textpm\fi{}1$ have been extensively studied; however, real materials of multi-Weyl points, whose monopole charges are higher than 1, have yet to be found. In this Rapid Communication, we show that Nodal-Line semimetals with nontrivial Line connectivity provide natural platforms for realizing Floquet multi-Weyl points. In particular, we show that driving crossing Nodal Lines by circularly polarized light generates double-Weyl points. Furthermore, we show that monopole combination and annihilation can be observed in crossing-Nodal-Line semimetals and Nodal-chain semimetals. These proposals can be experimentally verified in pump-probe angle-resolved photoemission spectroscopy.
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Tunable Weyl Points in Periodically Driven Nodal Line Semimetals
Physical review letters, 2016Co-Authors: Zhongbo Yan, Zhong WangAbstract:Weyl semimetals and Nodal Line semimetals are characterized by Linear band touching at zero-dimensional points and one-dimensional Lines, respectively. We predict that a circularly polarized light drives Nodal Line semimetals into Weyl semimetals. The Floquet Weyl points thus obtained are tunable by the incident light, which enables investigations of them in a highly controllable manner. The transition from Nodal Line semimetals to Weyl semimetals is accompanied by the emergence of a large and tunable anomalous Hall conductivity. Our predictions are experimentally testable by transport measurement in film samples or by pump-probe angle-resolved photoemission spectroscopy.
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Tunable Weyl Semimetals in Periodically Driven Nodal Line Semimetals
arXiv: Strongly Correlated Electrons, 2016Co-Authors: Zhongbo Yan, Zhong WangAbstract:Weyl semimetals and Nodal Line semimetals are characterized by Linear band-touching at Nodal points and Lines, respectively. We predict that a circularly polarized light drives Nodal Line semimetals into Weyl semimetals. The Weyl points of the Floquet Weyl semimetal thus obtained are tunable by the incident light, which enables investigations of them in a highly controllable manner. The transition from Nodal Line semimetals to Weyl semimetals is accompanied by the emergence of a large and tunable anomalous Hall conductivity. Our predictions are experimentally testable in thin films of topological semimetals by either pump-probe ARPES or transport measurement.
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Collective modes in Nodal Line semimetals
Physical Review B, 2016Co-Authors: Zhongbo Yan, Peng-wei Huang, Zhong WangAbstract:Recently, the Nodal Line semimetals have attracted considerable interest in condensed matter physics. We show that their distinct band structure can be detected by measuring the collective modes. In particular, we find that the dependence of the plasmon frequency ${\ensuremath{\omega}}_{p}$ on the electron density $n$ follows a ${\ensuremath{\omega}}_{p}\ensuremath{\sim}{n}^{1/4}$ law in the long wavelength limit. Our results will be useful in the ongoing search for new candidates of Nodal Line semimetals.
Shuichi Murakami - One of the best experts on this subject based on the ideXlab platform.
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Nodal-Line semimetal superlattices.
Journal of Physics: Condensed Matter, 2018Co-Authors: Kazuki Yokomizo, Hiroaki Yamada, Shuichi MurakamiAbstract:Spatial modulations, such as superlattices, to realize topological materials have recently been studied in theoretical and experimental works. In this paper, we investigate properties of the superlattices of the Nodal-Line semimetal and the normal insulator. We consider two types of superlattices, with the stacking direction being perpendicular or parallel to the plane where the Nodal Line lies. In particular, we show that when the stacking direction is parallel to the plane, the Nodal Lines remain but they change their shapes because of the folding of the Brillouin zone. We also study the superlattices with magnetization. One can expect that the quantum anomalous Hall (QAH) phase emerges in some cases, depending on the direction of the magnetization. If the magnetization is along the C 2-invariant axis, the superlattice becomes the Weyl semimetal phase if the C 2-invariant axis intersects the Nodal Lines, and otherwise it becomes the QAH phase.
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Nodal-Line semimetal multilayers
arXiv: Mesoscale and Nanoscale Physics, 2018Co-Authors: Kazuki Yokomizo, Hiroaki Yamada, Shuichi MurakamiAbstract:Spatial modulations, such as multilayers, to realize topological materials have recently been studied in theoretical and experimental works. In this paper, we investigate properties of the multilayers of the Nodal-Line semimetal (NLS) and the normal insulator. We consider two types of multilayers, with the stacking direction being perpendicular or parallel to the plane where the Nodal Line lies. In particular, we show that when the stacking direction is parallel to the plane, the Nodal Lines remain but they change their shapes because of the folding of the Brillouin zone. We also consider the multilayers with magnetization. One can expect that the quantum anomalous Hall (QAH) phase emerges in some cases, depending on the direction of the magnetization. If the magnetization is along the $C_2$-invariant axis, the multilayer becomes the Weyl semimetal phase if the $C_2$-invariant axis intersects the Nodal Lines, and otherwise it becomes the QAH phases.
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Spinless hourglass Nodal-Line semimetals
Physical Review B, 2017Co-Authors: Ryo Takahashi, Motoaki Hirayama, Shuichi MurakamiAbstract:Nodal-Line semimetals, one of the topological semimetals, have degeneracy along Nodal Lines where the band gap is closed. In many cases, the Nodal Lines appear accidentally, and in such cases it is impossible to determine whether the Nodal Lines appear or not, only from the crystal symmetry and the electron filling. In this paper, for spinless systems, we show that in specific space groups at $4N+2$ fillings ($8N+4$ fillings including the spin degree of freedom), presence of the Nodal Lines is required regardless of the details of the systems. Here, the spinless systems refer to crystals where the spin-orbit coupling is negligible and the spin degree of freedom can be omitted because of the SU(2) spin degeneracy. In this case the shape of the band structure around these Nodal Lines is like an hourglass, and we call this a spinless hourglass Nodal-Line semimetal. We construct a model Hamiltonian as an example and we show that it is always in the spinless hourglass Nodal-Line semimetal phase even when the model parameters are changed without changing the symmetries of the system. We also establish a list of all the centrosymmetric space groups, under which spinless systems always have hourglass Nodal Lines, and illustrate where the Nodal Lines are located. We propose that ${\mathrm{Al}}_{3}{\mathrm{FeSi}}_{2}$, whose space-group symmetry is Pbcn (No. 60), is one of the Nodal-Line semimetals arising from this mechanism.
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Universal phase transition and band structures for spinless Nodal-Line and Weyl semimetals
Physical Review B, 2017Co-Authors: Ryo Okugawa, Shuichi MurakamiAbstract:We study a general phase transition between spinless topological Nodal-Line semimetal and Weyl semimetal phases. We classify topological Nodal Lines into two types based on their positions and shapes, and their phase transitions depend on their types. We show that a topological Nodal-Line semimetal becomes a Weyl semimetal by breaking time-reversal symmetry when the Nodal Lines enclose time-reversal-invariant momenta (type-A Nodal Lines). We also discuss an effect of crystallographic symmetries determining the band structure of the topological Nodal-Line semimetals. Thanks to protection by the symmetries, the topological Nodal-Line semimetals can transition into spinless Weyl semimetals or maintain the Nodal Lines in many crystals after inversion symmetry is broken.
Lei Jin - One of the best experts on this subject based on the ideXlab platform.
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Two-dimensional Weyl Nodal-Line semimetal in a d 0 ferromagnetic K 2 N monolayer with a high Curie temperature
Physical Review B, 2020Co-Authors: Lei Jin, Xiaoming Zhang, Xuefang Dai, Ying Liu, Xunan Shen, Liying Wang, Guodong LiuAbstract:Nodal-Line semimetals in two-dimensional (2D) materials have attracted intense attention recently. From fundamental physics and spintronic application points of view, high Curie temperature ferromagnetic (FM) ones with Nodal Lines robust against spin-orbit coupling (SOC) are extremely desirable. Here, we propose that the FM ${\mathrm{K}}_{2}\mathrm{N}$ monolayer is such a Weyl Nodal-Line semimetal. We show that the ${\mathrm{K}}_{2}\mathrm{N}$ monolayer is dynamically stable and has a FM ground magnetic state with out-of-plane [001] magnetization. It shows two Nodal Lines in the low-energy band structures. Both Nodal Lines are robust against SOC, under the protection of mirror symmetry. We construct an effective Hamiltonian, which can well characterize the Nodal Lines in the system. Remarkably, the Nodal-Line semimetal proposed here is distinct from the previously studied ones in that the ${\mathrm{K}}_{2}\mathrm{N}$ monolayer is a 2D ${d}^{0}$-type ferromagnet with the magnetism arising from the partially filled the $p$ orbitals of the N atom, which can bring special advantages in spintronic applications. In addition, the Curie temperature in the ${\mathrm{K}}_{2}\mathrm{N}$ monolayer is estimated to be 942 K, which is significantly higher than previous FM Nodal-Line materials. We also find that specific tensile strains can transform the Nodal Line from type-I to type-II, making its Nodal-Line characteristics even more interesting.
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Topological Nodal Line Electrides: Realization of an Ideal Nodal Line State Nearly Immune from Spin–Orbit Coupling
The Journal of Physical Chemistry C, 2019Co-Authors: Xiaoming Zhang, Lei Jin, Xuefang Dai, Guodong Liu, Yugui YaoAbstract:Nodal Line semimetals (NLSs) have attracted broad interest in current research. In most of the existing NLSs, the intrinsic properties of Nodal Lines are greatly destroyed because Nodal Lines usual...
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Topological Nodal Line state in superconducting NaAlSi compound
Journal of Materials Chemistry C, 2019Co-Authors: Lei Jin, Xiaoming Zhang, Xuefang Dai, Weizhen Meng, Guodong LiuAbstract:Superconductors with a nontrivial band structure are promising to realize a topological superconducting state. Herein, we report the presence of a topological phase in a well-known superconductor, NaAlSi. Our first-principles computations show that NaAlSi naturally possesses four Nodal Lines in the kz = 0 and kz = π planes and hosts clear drumhead surface states. Comparing with those identified in other superconductors, the Nodal Line band structure of NaAlSi can more favor experimental detection on considering that: (1) it possesses four Nodal Lines in total in the system; (2) all the Nodal Lines appear slightly below the Fermi level; (3) the Nodal Lines do not coexist with other fermions or extraneous bands. Our findings indicate that NaAlSi is an excellent material platform to investigate the entanglement of superconducting and topological Nodal Line states.
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Topological phase with a critical-type Nodal Line state in intermetallic CaPd
Physical Review B, 2018Co-Authors: Guodong Liu, Xuefang Dai, Lei Jin, Guifeng Chen, Xiaoming ZhangAbstract:In recent years, realizing new topological phases of matter has been a hot topic in the fields of physics and materials science. Topological semimetals and metals can conventionally be classified into two types: type-I and type-II, according to the tilting degree of the fermion cone. Here we report an unexplored topological metal phase with the critical-type Nodal Line between type-I and type-II Nodal Lines. The critical-type Nodal Line shows a unique nontrivial band crossing, which is composed of a flat band and a dispersive band and leads to an unexplored fermionic state. We propose intermetallic CaPd can be an existing topological metal for the fermionic state, characterized with critical-type Nodal Line in the bulk and drumhead band structure on the surface. Our work not only promotes the concept of a critical-type Nodal Line, but also provides the material realization to study its exotic properties in future experiments.
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Highly anisotropic type-II Nodal Line state in pure titanium metal
Applied Physics Letters, 2018Co-Authors: Xiaoming Zhang, Lei Jin, Xuefang Dai, Guodong LiuAbstract:A type-II Nodal Line state, along with its unique optical, magnetic, and transport properties, was theoretically proposed and experimentally evidenced quite recently. Here, based on first-principles calculations, we report that a pure Ti metal can serve as an excellent type-II Nodal Line material for experimental detection. In the Ti metal, the type-II Nodal Line situates in a quite large momenta region with a Linear energy range larger than 1.5 eV. Its surface band is quite dispersive and thus is promising to be detected in a wide energy range. The position of the Nodal Line in the Ti metal can be flexibly tuned by applying uniaxial strain and elemental doping. Most interestingly, the band dispersions along the Nodal Line are highly anisotropic in three typical directions, and therefore, strong direction-dependent transport behavior can be expected. Our findings in the Ti metal are the first proposal of a highly anisotropic type-II Nodal Line state in elemental materials.A type-II Nodal Line state, along with its unique optical, magnetic, and transport properties, was theoretically proposed and experimentally evidenced quite recently. Here, based on first-principles calculations, we report that a pure Ti metal can serve as an excellent type-II Nodal Line material for experimental detection. In the Ti metal, the type-II Nodal Line situates in a quite large momenta region with a Linear energy range larger than 1.5 eV. Its surface band is quite dispersive and thus is promising to be detected in a wide energy range. The position of the Nodal Line in the Ti metal can be flexibly tuned by applying uniaxial strain and elemental doping. Most interestingly, the band dispersions along the Nodal Line are highly anisotropic in three typical directions, and therefore, strong direction-dependent transport behavior can be expected. Our findings in the Ti metal are the first proposal of a highly anisotropic type-II Nodal Line state in elemental materials.
Yugui Yao - One of the best experts on this subject based on the ideXlab platform.
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Weyl Nodal Line-Surface Half-metal in CaFeO$_3$
arXiv: Materials Science, 2021Co-Authors: Run-wu Zhang, Jian-min Zhang, Yugui YaoAbstract:Manipulating the spin degrees of freedom of electrons affords an excellent platform for exploring novel quantum states in condensed-matter physics and material science. Based on first-principles calculations and analysis of crystal symmetries, we propose a fully spin-polarized composite semimetal state, which is combined with the one-dimensional Nodal Lines and two-dimensional Nodal surfaces, in the half-metal material CaFeO$_3$. In the Nodal Line-surface states, the Baguenaudier-like Nodal Lines feature six rings linked together, which are protected by the three independent symmetry operations:$\mathcal{PT}$, $\mathcal{M}_{y}$, and $\mathcal{\widetilde{M}}_{z}$. Near the Fermi level, the spin-polarized Nodal surface states are guaranteed by the joint operation $\mathcal{T}\mathcal{S}_{2i}$ in the $k_{i(i=x,y,z)}=\pi$ plane. Furthermore, high-quality CaFeO$_3$ harbors ultra-clean energy dispersion, which is rather robust against strong triaxial compressional strain and correlation effect. The realization of the Weyl Nodal Line-surface half-metal presents great potential for spintronics applications with high speed and low power consumption.
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Double Dirac Nodal Line Semimetal with Torus Surface State.
arXiv: Mesoscale and Nanoscale Physics, 2021Co-Authors: Chaoxi Cui, Yugui YaoAbstract:We propose a class of Nodal Line semimetals that host an eight-fold degenerate double Dirac Nodal Line (DDNL) with negligible spin-orbit coupling. We find only 5 of the 230 space groups host the DDNL. The DDNL can be considered as a combination of two Dirac Nodal Lines, and has a trivial Berry phase. This leads to two possible but completely different surface states, namely, a torus surface state covering the whole surface Brillouin zone and no surface state at all. Based on first-principles calculations, we predict that the hydrogen storage material LiBH is an ideal DDNL semimetal, where the Line resides at Fermi level, is relatively flat in energy, and exhibits a large Linear energy range. Interestingly, both the two novel surface states of DDNL can be realized in LiBH. Further, we predict that with a magnetic field parallel to DDNL, the Landau levels of DDNL are doubly degenerate due to Kramers-like degeneracy and have a doubly degenerate zero-mode.
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Topological Nodal Line Electrides: Realization of an Ideal Nodal Line State Nearly Immune from Spin–Orbit Coupling
The Journal of Physical Chemistry C, 2019Co-Authors: Xiaoming Zhang, Lei Jin, Xuefang Dai, Guodong Liu, Yugui YaoAbstract:Nodal Line semimetals (NLSs) have attracted broad interest in current research. In most of the existing NLSs, the intrinsic properties of Nodal Lines are greatly destroyed because Nodal Lines usual...
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Mirror protected multiple Nodal Line semimetals and material realization
Physical Review B, 2018Co-Authors: Jianhui Zhou, Cheng-cheng Liu, Yugui YaoAbstract:The conventional $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ method fails to capture the full and essential physics of many symmetry enriched multiple Nodal Line structures in the three-dimensional Brillouin zone. Here, we present a systematical method to construct the effective lattice model of mirror symmetry protected three-dimensional multiple Nodal Line semimetals, when the spin-orbit interaction is ignored. For systems with a given pair of perpendicular Nodal rings, we obtain all the effective lattice models and 11 inequivalent Nodal Line Fermi surfaces together with their related constraints. By means of first-principles calculations, we first propose a family of real materials, the $\ensuremath{\beta}$ phase of ternary nitrides ${X}_{2}{\mathrm{GeN}}_{2}$ ($X=\mathrm{Ca},\mathrm{Sr},\mathrm{Ba}$), that support one kind of these Fermi surfaces. Therefore, our work deepens the understanding of the Nodal Line structures and promotes the experimental progress of topological Nodal Line semimetals.