Pub Date : 2024-05-21DOI: 10.1088/2053-1583/ad4b38
Jithin T Surendran, Yunus Waheed, Sumitra Shit, Indrajeet D Prasad, Kenji Watanabe, Takashi Taniguchi and Santosh Kumar
A van der Waals heterostructure containing an atomically thin monolayer (ML) transition-metal dichalcogenide as a single-photon emitting layer is emerging as an intriguing solid-state quantum-photonic platform. Here, we report the utilization of spin-coating of silica nanoparticles for semi-deterministically creating the spectrally isolated, energetically stable, and narrow-linewidth single-photon emitters in ML-WS2. We also demonstrate that long-duration low-temperature annealing of the photonic heterostructure in the vacuum removes the energetically unstable emitters that are present due to fabrication-associated residue and lead to the emission of single-photons in a 25 nm narrowband visible spectral range centered at ~620 nm. This work may pave the way toward realizing a hybrid-quantum-photonic platform containing a van der Waals heterostructure/device and an atomic-vapor system emitting/absorbing in the same visible spectral range.
{"title":"Nanoparticle stressor-induced single-photon sources in monolayer WS2 emitting into a narrowband visible spectral range","authors":"Jithin T Surendran, Yunus Waheed, Sumitra Shit, Indrajeet D Prasad, Kenji Watanabe, Takashi Taniguchi and Santosh Kumar","doi":"10.1088/2053-1583/ad4b38","DOIUrl":"https://doi.org/10.1088/2053-1583/ad4b38","url":null,"abstract":"A van der Waals heterostructure containing an atomically thin monolayer (ML) transition-metal dichalcogenide as a single-photon emitting layer is emerging as an intriguing solid-state quantum-photonic platform. Here, we report the utilization of spin-coating of silica nanoparticles for semi-deterministically creating the spectrally isolated, energetically stable, and narrow-linewidth single-photon emitters in ML-WS2. We also demonstrate that long-duration low-temperature annealing of the photonic heterostructure in the vacuum removes the energetically unstable emitters that are present due to fabrication-associated residue and lead to the emission of single-photons in a 25 nm narrowband visible spectral range centered at ~620 nm. This work may pave the way toward realizing a hybrid-quantum-photonic platform containing a van der Waals heterostructure/device and an atomic-vapor system emitting/absorbing in the same visible spectral range.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"35 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141147606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-10DOI: 10.1088/2053-1583/ad4611
Nicholas G Richardson, Andrew O’Hara, Sokrates T Pantelides
Ferroelectricity with out-of-plane polarization has so far been found in several two-dimensional (2D) materials, including monolayers comprising three to five planes of atoms, e.g. α-In2Se3 and MoTe2. Here, we explore the generation of out-of-plane polarization within a one-atom-thick monolayer material, namely hexagonal boron nitride. We performed density-functional-theory calculations to explore inducing ferroelectric-like distortions through incorporation of isovalent substitutional impurities that are larger than the host atoms. This disparity in bond lengths causes a buckling of the h-BN, either up or down, which amounts to a dipole with two equivalent energies and opposing orientations. We tested several impurities to explore the magnitude of the induced dipole and the switching energy barrier for dipole inversion. The effects of strain, dipole–dipole interactions, and vertical heterostructures with graphene are further explored. Our results suggest a highly-tunable system with ground state antiferroelectricity and metastable ferroelectricity. We expect that this work will help foster new ways to include functionality in layered 2D-material-based applications.
{"title":"Generation of out-of-plane ferroelectric behavior in a one-atom-thick monolayer","authors":"Nicholas G Richardson, Andrew O’Hara, Sokrates T Pantelides","doi":"10.1088/2053-1583/ad4611","DOIUrl":"https://doi.org/10.1088/2053-1583/ad4611","url":null,"abstract":"Ferroelectricity with out-of-plane polarization has so far been found in several two-dimensional (2D) materials, including monolayers comprising three to five planes of atoms, e.g. <italic toggle=\"yes\">α</italic>-In<sub>2</sub>Se<sub>3</sub> and MoTe<sub>2</sub>. Here, we explore the generation of out-of-plane polarization within a one-atom-thick monolayer material, namely hexagonal boron nitride. We performed density-functional-theory calculations to explore inducing ferroelectric-like distortions through incorporation of isovalent substitutional impurities that are larger than the host atoms. This disparity in bond lengths causes a buckling of the h-BN, either up or down, which amounts to a dipole with two equivalent energies and opposing orientations. We tested several impurities to explore the magnitude of the induced dipole and the switching energy barrier for dipole inversion. The effects of strain, dipole–dipole interactions, and vertical heterostructures with graphene are further explored. Our results suggest a highly-tunable system with ground state antiferroelectricity and metastable ferroelectricity. We expect that this work will help foster new ways to include functionality in layered 2D-material-based applications.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"28 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140926931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-09DOI: 10.1088/2053-1583/ad3e0a
N Khan, D Kumar, V Kumar, Y Shemerliuk, S Selter, B Büchner, K Pal, S Aswartham, Pradeep Kumar
The Mermin–Wagner theorem forbids spontaneous symmetry breaking of spins in one/two-dimensional (2D) systems at a finite temperature and rules out the stabilization of this ordered state. However, it does not apply to all types of phase transitions in low dimensions, such as the topologically ordered phase rigorously shown by Berezinskii–Kosterlitz–Thouless (BKT) and experimentally realized in very limited systems such as superfluids and superconducting thin films. Quasi-2D van der Waals magnets provide an ideal platform to investigate the fundamentals of low-dimensional magnetism. We explored the quasi-2D honeycomb antiferromagnetic single crystals of (NixFe1−x)2P2S6 (x = 1, 0.7, 0.5, 0.3, and 0) using in-depth temperature-dependent Raman measurements supported by first-principles calculations of the phonon frequencies. Quite surprisingly, we observed renormalization of the phonon modes much below the long-range magnetic ordered temperature attributed to the topological ordered state, namely the BKT phase, which is also found to change as a function of doping. The extracted critical exponent of the order-parameter (spin–spin correlation length, ξ(T)) evinces the signature of a topologically active state driven by vortex–antivortex excitations. As a function of doping, a tunable transition from paramagnetic to antiferromagnetic ordering is shown via phonons reflected in the strong renormalization of the self-energy parameters of the Raman active phonon modes. The extracted exchange parameter (J) is found to vary by ∼100% by increasing the value of doping, ranging from ∼6 meV (for x = 0.3) to 13 meV (for x = 1).
{"title":"The interplay of topology and antiferromagnetic order in two-dimensional van der Waals crystals of (Ni x Fe1−x )2P2S6","authors":"N Khan, D Kumar, V Kumar, Y Shemerliuk, S Selter, B Büchner, K Pal, S Aswartham, Pradeep Kumar","doi":"10.1088/2053-1583/ad3e0a","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3e0a","url":null,"abstract":"The Mermin–Wagner theorem forbids spontaneous symmetry breaking of spins in one/two-dimensional (2D) systems at a finite temperature and rules out the stabilization of this ordered state. However, it does not apply to all types of phase transitions in low dimensions, such as the topologically ordered phase rigorously shown by Berezinskii–Kosterlitz–Thouless (BKT) and experimentally realized in very limited systems such as superfluids and superconducting thin films. Quasi-2D van der Waals magnets provide an ideal platform to investigate the fundamentals of low-dimensional magnetism. We explored the quasi-2D honeycomb antiferromagnetic single crystals of (Ni<italic toggle=\"yes\">\u0000<sub>x</sub>\u0000</italic>Fe<sub>1−<italic toggle=\"yes\">x</italic>\u0000</sub>)<sub>2</sub>P<sub>2</sub>S<sub>6</sub> (<italic toggle=\"yes\">x</italic> = 1, 0.7, 0.5, 0.3, and 0) using in-depth temperature-dependent Raman measurements supported by first-principles calculations of the phonon frequencies. Quite surprisingly, we observed renormalization of the phonon modes much below the long-range magnetic ordered temperature attributed to the topological ordered state, namely the BKT phase, which is also found to change as a function of doping. The extracted critical exponent of the order-parameter (spin–spin correlation length, <inline-formula>\u0000<tex-math><?CDATA $xi (T)$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>ξ</mml:mi><mml:mo stretchy=\"false\">(</mml:mo><mml:mi>T</mml:mi><mml:mo stretchy=\"false\">)</mml:mo></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3e0aieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>) evinces the signature of a topologically active state driven by vortex–antivortex excitations. As a function of doping, a tunable transition from paramagnetic to antiferromagnetic ordering is shown via phonons reflected in the strong renormalization of the self-energy parameters of the Raman active phonon modes. The extracted exchange parameter (<italic toggle=\"yes\">J</italic>) is found to vary by ∼100% by increasing the value of doping, ranging from ∼6 meV (for <italic toggle=\"yes\">x</italic> = 0.3) to 13 meV (for <italic toggle=\"yes\">x</italic> = 1).","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"87 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140927078","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-08DOI: 10.1088/2053-1583/ad3cea
Árpád Pásztor, Ishita Pushkarna, Christoph Renner
Geometric phase analysis (GPA) is a widely used technique for extracting displacement and strain fields from scanning probe images. Here, we demonstrate that GPA should be implemented with caution when several fundamental lattices contribute to the image, in particular in twisted heterostructures featuring moiré patterns. We find that in this case, GPA is likely to suggest the presence of chiral displacement and periodic strain fields, even if the structure is completely relaxed and without distortions. These delusive fields are subject to change with varying twist angles, which could mislead the interpretation of twist angle-dependent properties.
{"title":"Delusive chirality and periodic strain pattern in moiré systems","authors":"Árpád Pásztor, Ishita Pushkarna, Christoph Renner","doi":"10.1088/2053-1583/ad3cea","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3cea","url":null,"abstract":"Geometric phase analysis (GPA) is a widely used technique for extracting displacement and strain fields from scanning probe images. Here, we demonstrate that GPA should be implemented with caution when several fundamental lattices contribute to the image, in particular in twisted heterostructures featuring moiré patterns. We find that in this case, GPA is likely to suggest the presence of chiral displacement and periodic strain fields, even if the structure is completely relaxed and without distortions. These delusive fields are subject to change with varying twist angles, which could mislead the interpretation of twist angle-dependent properties.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"40 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140926930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-01DOI: 10.1088/2053-1583/ad4166
Pantelis Bampoulis, Carolien Castenmiller, Dennis J Klaassen, Jelle V Mil, Paul L de Boeij, Motohiko Ezawa and Harold J W Zandvliet
Twisting bilayers of two-dimensional topological insulators has the potential to create unique quantum states of matter. Here, we successfully synthesized a twisted bilayer of germanene on Ge2Pt(101) with a 21.8° twist angle, corresponding to a commensurate (√7×√7) structure. Using scanning tunneling microscopy and spectroscopy, we unraveled the structural and electronic properties of this configuration, revealing a moiré-modulated band gap and a well-defined edge state. This band gap opens at AB/BA stacked sites and closes at AA stacked sites, a phenomenon attributed to the electric field induced by the scanning tunneling microscopy tip. Our study further revealed two van Hove singularities at −0.8 eV and +1.04 eV, resulting in a Fermi velocity of (8 ± 1) × 105 m s−1. Our tight-binding results uncover a unique quantum state, where the topological properties could be regulated through an electric field, potentially triggering two topological phase transitions.
扭转二维拓扑绝缘体的双层膜有可能创造出独特的物质量子态。在这里，我们成功地在 Ge2Pt(101) 上合成了锗烯扭转双层膜，其扭转角为 21.8°，对应于同位（√7×√7）结构。利用扫描隧道显微镜和光谱学，我们揭示了这种构型的结构和电子特性，发现了一个摩尔调制带隙和一个定义明确的边缘态。这种带隙在 AB/BA 叠层位点处打开，在 AA 叠层位点处关闭，这种现象归因于扫描隧道显微镜尖端诱导的电场。我们的研究进一步揭示了在 -0.8 eV 和 +1.04 eV 处的两个范霍夫奇点，从而得出费米速度为 (8 ± 1) × 105 m s-1。我们的紧密结合结果揭示了一种独特的量子态，在这种态中，拓扑特性可以通过电场进行调节，并有可能引发两种拓扑相变。
{"title":"Moiré-modulated band gap and van Hove singularities in twisted bilayer germanene","authors":"Pantelis Bampoulis, Carolien Castenmiller, Dennis J Klaassen, Jelle V Mil, Paul L de Boeij, Motohiko Ezawa and Harold J W Zandvliet","doi":"10.1088/2053-1583/ad4166","DOIUrl":"https://doi.org/10.1088/2053-1583/ad4166","url":null,"abstract":"Twisting bilayers of two-dimensional topological insulators has the potential to create unique quantum states of matter. Here, we successfully synthesized a twisted bilayer of germanene on Ge2Pt(101) with a 21.8° twist angle, corresponding to a commensurate (√7×√7) structure. Using scanning tunneling microscopy and spectroscopy, we unraveled the structural and electronic properties of this configuration, revealing a moiré-modulated band gap and a well-defined edge state. This band gap opens at AB/BA stacked sites and closes at AA stacked sites, a phenomenon attributed to the electric field induced by the scanning tunneling microscopy tip. Our study further revealed two van Hove singularities at −0.8 eV and +1.04 eV, resulting in a Fermi velocity of (8 ± 1) × 105 m s−1. Our tight-binding results uncover a unique quantum state, where the topological properties could be regulated through an electric field, potentially triggering two topological phase transitions.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"45 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140834663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-30DOI: 10.1088/2053-1583/ad3b0e
A Ceferino, F Guinea
We present simple models to describe the in-plane and the out-of-plane lattice relaxation in twisted bilayer and symmetrically twisted trilayer graphene. Analytical results and series expansions show that for twist angles θ>1.4∘, the in-plane atomic displacements lead to pseudomagnetic fields weakly dependent on θ. In symmetrically twisted trilayer graphene, the central layer in-plane relaxation is greatly enhanced. The joint effect of the relaxation-induced pseudoscalar potentials and the associated energy difference between interlayer dimer and non-dimer pairs resulted in a significant electron–hole asymmetry both in twisted bilayer and trilayer graphene.
{"title":"Pseudomagnetic fields in fully relaxed twisted bilayer and trilayer graphene","authors":"A Ceferino, F Guinea","doi":"10.1088/2053-1583/ad3b0e","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3b0e","url":null,"abstract":"We present simple models to describe the in-plane and the out-of-plane lattice relaxation in twisted bilayer and symmetrically twisted trilayer graphene. Analytical results and series expansions show that for twist angles <inline-formula>\u0000<tex-math><?CDATA $thetagt 1.4^{circ}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>θ</mml:mi><mml:mo>></mml:mo><mml:msup><mml:mn>1.4</mml:mn><mml:mrow><mml:mo>∘</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3b0eieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>, the in-plane atomic displacements lead to pseudomagnetic fields weakly dependent on <italic toggle=\"yes\">θ</italic>. In symmetrically twisted trilayer graphene, the central layer in-plane relaxation is greatly enhanced. The joint effect of the relaxation-induced pseudoscalar potentials and the associated energy difference between interlayer dimer and non-dimer pairs resulted in a significant electron–hole asymmetry both in twisted bilayer and trilayer graphene.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"10 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140834682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-25DOI: 10.1088/2053-1583/ad3b13
V V Enaldiev
Long-period moiré superlattices at the twisted interface of van der Waals heterostructures relax into preferential stacking domains separated by dislocation networks. Here, we develop a mesoscale theory for dislocations in networks formed in twistronic bilayers with parallel (P) and antiparallel (AP) alignment of unit cells across the twisted interface. For P bilayers we find an exact analytical displacement field across partial dislocations and determine analytic dependences of energy per unit length and width on the orientation and microscopic model parameters. For AP bilayers we formulate a semi-analytical approximation for displacement fields across perfect dislocations, establishing parametric dependences for their widths and energies per unit length. In addition, we find regions in the parametric space of crystal thicknesses and Moiré periods for strong and weak relaxation of the Moiré pattern in multilayered twistronic heterostructures.
范德瓦尔斯异质结构扭曲界面上的长周期摩尔超晶格会松弛成由位错网络分隔的优先堆叠域。在此，我们开发了一种介尺度理论，用于研究在扭曲界面上单位晶胞平行（P）和反平行（AP）排列的双晶双层中形成的网络中的位错。对于 P 双层膜，我们找到了跨部分位错的精确分析位移场，并确定了单位长度和宽度的能量与取向和微观模型参数的分析依赖关系。对于 AP 双层膜，我们提出了完美位错位移场的半解析近似值，并确定了位错宽度和单位长度能量的参数依赖关系。此外，我们还在晶体厚度和莫伊里周期的参数空间中找到了多层双晶异质结构中莫伊里图案强弛豫和弱弛豫的区域。
{"title":"Dislocations in twistronic heterostructures","authors":"V V Enaldiev","doi":"10.1088/2053-1583/ad3b13","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3b13","url":null,"abstract":"Long-period moiré superlattices at the twisted interface of van der Waals heterostructures relax into preferential stacking domains separated by dislocation networks. Here, we develop a mesoscale theory for dislocations in networks formed in twistronic bilayers with parallel (P) and antiparallel (AP) alignment of unit cells across the twisted interface. For P bilayers we find an exact analytical displacement field across partial dislocations and determine analytic dependences of energy per unit length and width on the orientation and microscopic model parameters. For AP bilayers we formulate a semi-analytical approximation for displacement fields across perfect dislocations, establishing parametric dependences for their widths and energies per unit length. In addition, we find regions in the parametric space of crystal thicknesses and Moiré periods for strong and weak relaxation of the Moiré pattern in multilayered twistronic heterostructures.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"6 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140798318","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-24DOI: 10.1088/2053-1583/ad3e08
U Yorulmaz, D Šabani, C Sevik and M V Milošević
Seminal Goodenough–Kanamori–Anderson (GKA) rules provide an inceptive understanding of the superexchange interaction of two magnetic metal ions bridged with an anion, and suggest fostered ferromagnetic interaction for orthogonal bridging bonds. However, there are no examples of two-dimensional (2D) materials with structure that optimizes the GKA arguments towards enhanced ferromagnetism and its critical temperature. Here we reveal that an ideally planar GKA ferromagnetism is indeed stable in selected tetragonal transition-metal xenes (tTMXs), with Curie temperature above 300 K found in CrC and MnC. We provide the general orbitally-resolved analysis of magnetic interactions that supports the claims and sheds light at the mechanisms dominating the magnetic exchange process in these structures. Furthermore, we propose the set of three GKA-like rules that will guarantee room temperature ferromagetnism. With recent advent of epitaxially-grown tetragonal 2D materials, our findings earmark tTMXs for facilitated spintronic and magnonic applications, or as a desirable magnetic constituent of functional 2D heterostructures.
{"title":"Goodenough–Kanamori–Anderson high-temperature ferromagnetism in tetragonal transition-metal xenes","authors":"U Yorulmaz, D Šabani, C Sevik and M V Milošević","doi":"10.1088/2053-1583/ad3e08","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3e08","url":null,"abstract":"Seminal Goodenough–Kanamori–Anderson (GKA) rules provide an inceptive understanding of the superexchange interaction of two magnetic metal ions bridged with an anion, and suggest fostered ferromagnetic interaction for orthogonal bridging bonds. However, there are no examples of two-dimensional (2D) materials with structure that optimizes the GKA arguments towards enhanced ferromagnetism and its critical temperature. Here we reveal that an ideally planar GKA ferromagnetism is indeed stable in selected tetragonal transition-metal xenes (tTMXs), with Curie temperature above 300 K found in CrC and MnC. We provide the general orbitally-resolved analysis of magnetic interactions that supports the claims and sheds light at the mechanisms dominating the magnetic exchange process in these structures. Furthermore, we propose the set of three GKA-like rules that will guarantee room temperature ferromagetnism. With recent advent of epitaxially-grown tetragonal 2D materials, our findings earmark tTMXs for facilitated spintronic and magnonic applications, or as a desirable magnetic constituent of functional 2D heterostructures.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"18 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140798322","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-22DOI: 10.1088/2053-1583/ad3b11
Hao-Chien Wang and Chen-Hsuan Hsu
We investigate the domain wall network in twisted bilayer graphene (TBG) under the influence of interlayer bias and screening effect from the layered structure. Starting from the continuum model, we analyze the low-energy domain wall modes within the moiré bilayer structure and obtain an analytic form representing charge density distributions of the two-dimensional structure. By computing the screened electron–electron interaction strengths both within and between the domain walls, we develop a bosonized model that describes the correlated domain wall network. We demonstrate that these interaction strengths can be modified through an applied interlayer bias, screening length and dielectric materials, and show how the model can be employed to investigate various properties of the domain wall network and its stability. We compute correlation functions both without and with phonons. Including electron–phonon coupling in the network, we establish phase diagrams from these correlation functions. These diagrams illustrate electrical tunability of the network between various phases, such as density wave states and superconductivity. Our findings reveal the domain wall network as a promising platform for the experimental manipulation of electron–electron interactions in low dimensions and the study of strongly correlated matter. We point out that our investigation not only enhances the understanding of domain wall modes in TBG but also has broader implications for the development of moiré devices.
{"title":"Electrically tunable correlated domain wall network in twisted bilayer graphene","authors":"Hao-Chien Wang and Chen-Hsuan Hsu","doi":"10.1088/2053-1583/ad3b11","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3b11","url":null,"abstract":"We investigate the domain wall network in twisted bilayer graphene (TBG) under the influence of interlayer bias and screening effect from the layered structure. Starting from the continuum model, we analyze the low-energy domain wall modes within the moiré bilayer structure and obtain an analytic form representing charge density distributions of the two-dimensional structure. By computing the screened electron–electron interaction strengths both within and between the domain walls, we develop a bosonized model that describes the correlated domain wall network. We demonstrate that these interaction strengths can be modified through an applied interlayer bias, screening length and dielectric materials, and show how the model can be employed to investigate various properties of the domain wall network and its stability. We compute correlation functions both without and with phonons. Including electron–phonon coupling in the network, we establish phase diagrams from these correlation functions. These diagrams illustrate electrical tunability of the network between various phases, such as density wave states and superconductivity. Our findings reveal the domain wall network as a promising platform for the experimental manipulation of electron–electron interactions in low dimensions and the study of strongly correlated matter. We point out that our investigation not only enhances the understanding of domain wall modes in TBG but also has broader implications for the development of moiré devices.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"4 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140798251","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-21DOI: 10.1088/2053-1583/ad3e0c
Jingheng Fu, Mikael Kuisma, Ask Hjorth Larsen, Kohei Shinohara, Atsushi Togo and Kristian S Thygesen
The symmetry of a crystal structure with a three-dimensional (3D) lattice can be classified by one of the 230 space group types. For some types of crystals, e.g. crystalline films, surfaces, or planar interfaces, it is more appropriate to assume a two-dimensional (2D) lattice. With this assumption the structure can be classified by one of the 80 layer group types. We have implemented an algorithm to determine the layer group type of a 3D structure with a 2D lattice, and applied it to more than 15 000 monolayer structures in the Computational 2D Materials Database (C2DB). We compare the classification of monolayers by layer groups and space groups, respectively. The latter is defined as the space group of the 3D bulk structure obtained by repeating the monolayer periodically in the direction perpendicular to the 2D lattice (AA-stacking). By this correspondence, nine pairs of layer group types are mapped to the same space group type due to the inability of the space group to distinguish the in-plane and out-of-plane axes. In total 18% of the monolayers in the C2DB belong to one of these layer group pairs and are thus not properly classified by the space group type. Our results show that symmetry classification of 2D materials should be based on layer groups rather than the commonly used space groups.
{"title":"Symmetry classification of 2D materials: layer groups versus space groups","authors":"Jingheng Fu, Mikael Kuisma, Ask Hjorth Larsen, Kohei Shinohara, Atsushi Togo and Kristian S Thygesen","doi":"10.1088/2053-1583/ad3e0c","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3e0c","url":null,"abstract":"The symmetry of a crystal structure with a three-dimensional (3D) lattice can be classified by one of the 230 space group types. For some types of crystals, e.g. crystalline films, surfaces, or planar interfaces, it is more appropriate to assume a two-dimensional (2D) lattice. With this assumption the structure can be classified by one of the 80 layer group types. We have implemented an algorithm to determine the layer group type of a 3D structure with a 2D lattice, and applied it to more than 15 000 monolayer structures in the Computational 2D Materials Database (C2DB). We compare the classification of monolayers by layer groups and space groups, respectively. The latter is defined as the space group of the 3D bulk structure obtained by repeating the monolayer periodically in the direction perpendicular to the 2D lattice (AA-stacking). By this correspondence, nine pairs of layer group types are mapped to the same space group type due to the inability of the space group to distinguish the in-plane and out-of-plane axes. In total 18% of the monolayers in the C2DB belong to one of these layer group pairs and are thus not properly classified by the space group type. Our results show that symmetry classification of 2D materials should be based on layer groups rather than the commonly used space groups.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"28 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140798478","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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