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}
Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe2 as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe2 across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.
{"title":"Effect of niobium doping on excitonic dynamics in MoSe2","authors":"Wenjie Wang, Yongsheng Wang, Jiaqi He, Zhiying Bai, Guili Li, Xiaoxian Zhang, Dawei He, Hui Zhao","doi":"10.1088/2053-1583/ad3b0d","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3b0d","url":null,"abstract":"Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe<sub>2</sub> as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe<sub>2</sub> across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"96 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140612816","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 : 2024-04-15DOI: 10.1088/2053-1583/ad3b10
Sukanya Ghosh, Soheil Ershadrad, Biplab Sanyal
Achieving beyond room-temperature ferromagnetism in two-dimensional (2D) magnets is immensely desirable for spintronic applications. Fe5GeTe2 is an exceptional van der Waals metallic ferromagnet due to its tunable physical properties and relatively higher Curie temperature (TC) than other 2D magnets. Using density functional theory combined with dynamical electron correlation and Monte Carlo simulations, we find the TC of (Fe1−δNiδ)5GeTe2 monolayer can increase up to ∼400 K at δ∼0.20 (δ: fractional occupation). Two specific Fe sublattices are identified to be the most energetically preferred sites to host Ni. Exchange interactions between particular Fe pairs play a dominating role in controlling TC, influenced by the dopant-induced structural distortions. Dynamical electron correlation induces site- and orbital-specific quasi-particle mass of Fe-d states with varying Ni concentrations. This work provides fundamen
{"title":"Structural distortion and dynamical electron correlation driven enhanced ferromagnetism in Ni-doped two-dimensional Fe5GeTe2 beyond room temperature","authors":"Sukanya Ghosh, Soheil Ershadrad, Biplab Sanyal","doi":"10.1088/2053-1583/ad3b10","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3b10","url":null,"abstract":"Achieving beyond room-temperature ferromagnetism in two-dimensional (2D) magnets is immensely desirable for spintronic applications. Fe<sub>5</sub>GeTe<sub>2</sub> is an exceptional van der Waals metallic ferromagnet due to its tunable physical properties and relatively higher Curie temperature (<inline-formula>\u0000<tex-math><?CDATA $T_mathrm{C}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3b10ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>) than other 2D magnets. Using density functional theory combined with dynamical electron correlation and Monte Carlo simulations, we find the <inline-formula>\u0000<tex-math><?CDATA $T_mathrm{C}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3b10ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> of (Fe<inline-formula>\u0000<tex-math><?CDATA $_{1-delta}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mi></mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3b10ieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>Ni<inline-formula>\u0000<tex-math><?CDATA $_{delta})_{5}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mi></mml:mi><mml:mrow><mml:mi>δ</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mo stretchy=\"false\">)</mml:mo><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3b10ieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>GeTe<sub>2</sub> monolayer can increase up to ∼400 K at <inline-formula>\u0000<tex-math><?CDATA $delta sim 0.20$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>δ</mml:mi><mml:mo>∼</mml:mo><mml:mn>0.20</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3b10ieqn5.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> (<italic toggle=\"yes\">δ</italic>: fractional occupation). Two specific Fe sublattices are identified to be the most energetically preferred sites to host Ni. Exchange interactions between particular Fe pairs play a dominating role in controlling <inline-formula>\u0000<tex-math><?CDATA $T_mathrm{C}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3b10ieqn6.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>, influenced by the dopant-induced structural distortions. Dynamical electron correlation induces site- and orbital-specific quasi-particle mass of Fe-<italic toggle=\"yes\">d</italic> states with varying Ni concentrations. This work provides fundamen","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"63 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140612680","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}
For a time-reversal symmetric system, the quantum spin Hall phase is assumed to be the same as the <inline-formula> <tex-math><?CDATA $mathbb{Z}_2$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="double-struck">Z</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="tdmad3136ieqn1.gif" xlink:type="simple"></inline-graphic> </inline-formula> topological insulator phase in the existing literature. The spin Chern number <inline-formula> <tex-math><?CDATA $mathcal{C}_s$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mi>s</mml:mi></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="tdmad3136ieqn2.gif" xlink:type="simple"></inline-graphic> </inline-formula> is presumed to yield the same topological classification as the <inline-formula> <tex-math><?CDATA $mathbb{Z}_2$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="double-struck">Z</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="tdmad3136ieqn3.gif" xlink:type="simple"></inline-graphic> </inline-formula> invariant. Here, by investigating the electronic structures of monolayer <italic toggle="yes">α</italic>-phase group V elements, we uncover the presence of a topological phase in <italic toggle="yes">α</italic>-Sb, which can be characterized by a spin Chern number <inline-formula> <tex-math><?CDATA $mathcal{C}_s$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mi>s</mml:mi></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="tdmad3136ieqn4.gif" xlink:type="simple"></inline-graphic> </inline-formula> = 2, even though it is <inline-formula> <tex-math><?CDATA $mathbb{Z}_2$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="double-struck">Z</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="tdmad3136ieqn5.gif" xlink:type="simple"></inline-graphic> </inline-formula> trivial. Although <italic toggle="yes">α</italic>-As and Sb would thus be classified as trivial insulators within the classification schemes, we demonstrate the existence of a phase transition between <italic toggle="yes">α</italic>-As and Sb, which is induced by band inversions at two generic <italic toggle="yes">k</italic> points. Without spin–orbit coupling (SOC), <italic toggle="yes">α</italic>-As is a trivial insulator, while <italic toggle="yes">α</italic>-Sb is a Dirac semimetal with four Dirac points (DPs) located away from the high-symmetry lines. Inclusion of the SOC gaps out the DPs and induces a nontrivial Berry curvature, endowing <italic toggle="yes">α</italic>-Sb with a high spin Chern number of <inline-formula> <tex-math><?CDATA $mathcal{C}_s$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:msub><mml:mrow><mml:mi>C</mml:mi><
{"title":"High spin-Chern-number insulator in α-antimonene with a hidden topological phase","authors":"Baokai Wang, Xiaoting Zhou, Yi-Chun Hung, Yen-Chuan Lin, Hsin Lin, Arun Bansil","doi":"10.1088/2053-1583/ad3136","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3136","url":null,"abstract":"For a time-reversal symmetric system, the quantum spin Hall phase is assumed to be the same as the <inline-formula>\u0000<tex-math><?CDATA $mathbb{Z}_2$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant=\"double-struck\">Z</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3136ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> topological insulator phase in the existing literature. The spin Chern number <inline-formula>\u0000<tex-math><?CDATA $mathcal{C}_s$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mi>s</mml:mi></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3136ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> is presumed to yield the same topological classification as the <inline-formula>\u0000<tex-math><?CDATA $mathbb{Z}_2$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant=\"double-struck\">Z</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3136ieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> invariant. Here, by investigating the electronic structures of monolayer <italic toggle=\"yes\">α</italic>-phase group V elements, we uncover the presence of a topological phase in <italic toggle=\"yes\">α</italic>-Sb, which can be characterized by a spin Chern number <inline-formula>\u0000<tex-math><?CDATA $mathcal{C}_s$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mi>s</mml:mi></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3136ieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> = 2, even though it is <inline-formula>\u0000<tex-math><?CDATA $mathbb{Z}_2$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant=\"double-struck\">Z</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3136ieqn5.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> trivial. Although <italic toggle=\"yes\">α</italic>-As and Sb would thus be classified as trivial insulators within the classification schemes, we demonstrate the existence of a phase transition between <italic toggle=\"yes\">α</italic>-As and Sb, which is induced by band inversions at two generic <italic toggle=\"yes\">k</italic> points. Without spin–orbit coupling (SOC), <italic toggle=\"yes\">α</italic>-As is a trivial insulator, while <italic toggle=\"yes\">α</italic>-Sb is a Dirac semimetal with four Dirac points (DPs) located away from the high-symmetry lines. Inclusion of the SOC gaps out the DPs and induces a nontrivial Berry curvature, endowing <italic toggle=\"yes\">α</italic>-Sb with a high spin Chern number of <inline-formula>\u0000<tex-math><?CDATA $mathcal{C}_s$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mrow><mml:mi>C</mml:mi><","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"5 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313720","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 : 2024-03-15DOI: 10.1088/2053-1583/ad3137
Luigi Camerano, Gianni Profeta
In the light of new experimental evidence we study the insulating ground state of the 3d2-transition metal trihalides VX3 (X = Cl, I). Based on density functional theory with the Hubbard correction we systematically show how these systems host multiple metastable states characterised by different orbital ordering and electronic behaviour. Our calculations reveal the importance of imposing a precondition in the on site d density matrix and of considering a symmetry broken unit cell to correctly take into account the correlation effects in a mean field framework. Furthermore we ultimately found a ground state with the a1g orbital occupied in a distorted VX6 octahedra driven by an optical phonon mode.
{"title":"Symmetry breaking in vanadium trihalides","authors":"Luigi Camerano, Gianni Profeta","doi":"10.1088/2053-1583/ad3137","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3137","url":null,"abstract":"In the light of new experimental evidence we study the insulating ground state of the <inline-formula>\u0000<tex-math><?CDATA $3d^2$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mn>3</mml:mn><mml:msup><mml:mi>d</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3137ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>-transition metal trihalides V<italic toggle=\"yes\">X</italic>\u0000<sub>3</sub> (<italic toggle=\"yes\">X</italic> = Cl, I). Based on density functional theory with the Hubbard correction we systematically show how these systems host multiple metastable states characterised by different orbital ordering and electronic behaviour. Our calculations reveal the importance of imposing a precondition in the on site <italic toggle=\"yes\">d</italic> density matrix and of considering a symmetry broken unit cell to correctly take into account the correlation effects in a mean field framework. Furthermore we ultimately found a ground state with the <inline-formula>\u0000<tex-math><?CDATA $a_{1g}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mi>a</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mi>g</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3137ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> orbital occupied in a distorted V<italic toggle=\"yes\">X</italic>\u0000<sub>6</sub> octahedra driven by an optical phonon mode.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"2022 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313534","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 : 2024-03-15DOI: 10.1088/2053-1583/ad3133
Hanqing Liu, Gabriele Baglioni, Carla Boix-Constant, Herre S J van der Zant, Peter G Steeneken, Gerard J Verbiest
The high susceptibility of ultrathin two-dimensional (2D) material resonators to force and temperature makes them ideal systems for sensing applications and exploring thermomechanical coupling. Although the dynamics of these systems at high stress has been thoroughly investigated, their behavior near the buckling transition has received less attention. Here, we demonstrate that the force sensitivity and frequency tunability of 2D material resonators are significantly enhanced near the buckling bifurcation. This bifurcation is triggered by compressive displacement that we induce via thermal expansion of the devices, while measuring their dynamics via an optomechanical technique. We understand the frequency tuning of the devices through a mechanical buckling model, which allows to extract the central deflection and boundary compressive displacement of the membrane. Surprisingly, we obtain a remarkable enhancement of up to 14× the vibration amplitude attributed to a very low stiffness of the membrane at the buckling transition, as well as a high frequency tunability by temperature of more than 4.02% K−1. The presented results provide insights into the effects of buckling on the dynamics of free-standing 2D materials and thereby open up opportunities for the realization of 2D resonant sensors with buckling-enhanced sensitivity.
{"title":"Enhanced sensitivity and tunability of thermomechanical resonance near the buckling bifurcation","authors":"Hanqing Liu, Gabriele Baglioni, Carla Boix-Constant, Herre S J van der Zant, Peter G Steeneken, Gerard J Verbiest","doi":"10.1088/2053-1583/ad3133","DOIUrl":"https://doi.org/10.1088/2053-1583/ad3133","url":null,"abstract":"The high susceptibility of ultrathin two-dimensional (2D) material resonators to force and temperature makes them ideal systems for sensing applications and exploring thermomechanical coupling. Although the dynamics of these systems at high stress has been thoroughly investigated, their behavior near the buckling transition has received less attention. Here, we demonstrate that the force sensitivity and frequency tunability of 2D material resonators are significantly enhanced near the buckling bifurcation. This bifurcation is triggered by compressive displacement that we induce via thermal expansion of the devices, while measuring their dynamics via an optomechanical technique. We understand the frequency tuning of the devices through a mechanical buckling model, which allows to extract the central deflection and boundary compressive displacement of the membrane. Surprisingly, we obtain a remarkable enhancement of up to 14× the vibration amplitude attributed to a very low stiffness of the membrane at the buckling transition, as well as a high frequency tunability by temperature of more than 4.02<inline-formula>\u0000<tex-math><?CDATA $%$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">%</mml:mi></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad3133ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> K<sup>−1</sup>. The presented results provide insights into the effects of buckling on the dynamics of free-standing 2D materials and thereby open up opportunities for the realization of 2D resonant sensors with buckling-enhanced sensitivity.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"47 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313536","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 : 2024-03-06DOI: 10.1088/2053-1583/ad2caa
Baojuan Xin, Boyan Li, Wen Yang, Luyan Li, Hong Dong, Yahui Cheng, Hui Liu, Wei-Hua Wang, Feng Lu
Constructing twisted mixed dimensional graphene-based van der Waals heterostructure (vdWH) is an effective strategy to manipulate the electronic structures and improve the quantum capacitance (Cq) of graphene. In this work, mixed dimensional vdWH of graphene/C2H has been proposed owing to similar Dirac semimetal character of one-dimensional C2H with that of graphene. Meanwhile, the influence of twisting angle (θ) and interlayer interaction strength on the electronic structures and the Cq of the MD vdWH are systemically explored based on tight binding model. With the fitted hopping integral parameters, it is found that the linear dispersion of the graphene is basically preserved but the bandwidth is decreased with modulating twisting angle and interlayer interaction, and the Cq of mixed dimensional vdWH is improved 5–19 times compared with graphene at zero bias. Moreover, the compressed strain could enhance the Cq of mixed dimensional vdWH to 74.57 μF cm−2 at zero bias and broaden the low working voltage window of mixed-dimensional vdWH with considerable Cq. Our results provide suitable tight-binding model parameters and theoretical guidance for exploring the twisted MD vdWH of graphene/C2H and offer an effective strategy to modulate the electronic structures and the Cq of graphene through constructing the MD vdWH.
{"title":"Electronic structures and quantum capacitance of twisted mixed-dimensional van der Waals heterostructures of graphene/C2H based on tight-binding model","authors":"Baojuan Xin, Boyan Li, Wen Yang, Luyan Li, Hong Dong, Yahui Cheng, Hui Liu, Wei-Hua Wang, Feng Lu","doi":"10.1088/2053-1583/ad2caa","DOIUrl":"https://doi.org/10.1088/2053-1583/ad2caa","url":null,"abstract":"Constructing twisted mixed dimensional graphene-based van der Waals heterostructure (vdWH) is an effective strategy to manipulate the electronic structures and improve the quantum capacitance (<italic toggle=\"yes\">C</italic>\u0000<sub>q</sub>) of graphene. In this work, mixed dimensional vdWH of graphene/C<sub>2</sub>H has been proposed owing to similar Dirac semimetal character of one-dimensional C<sub>2</sub>H with that of graphene. Meanwhile, the influence of twisting angle (<italic toggle=\"yes\">θ</italic>) and interlayer interaction strength on the electronic structures and the <italic toggle=\"yes\">C</italic>\u0000<sub>q</sub> of the MD vdWH are systemically explored based on tight binding model. With the fitted hopping integral parameters, it is found that the linear dispersion of the graphene is basically preserved but the bandwidth is decreased with modulating twisting angle and interlayer interaction, and the <italic toggle=\"yes\">C</italic>\u0000<sub>q</sub> of mixed dimensional vdWH is improved 5–19 times compared with graphene at zero bias. Moreover, the compressed strain could enhance the <italic toggle=\"yes\">C</italic>\u0000<sub>q</sub> of mixed dimensional vdWH to 74.57 <italic toggle=\"yes\">μ</italic>F cm<sup>−2</sup> at zero bias and broaden the low working voltage window of mixed-dimensional vdWH with considerable <italic toggle=\"yes\">C</italic>\u0000<sub>q</sub>. Our results provide suitable tight-binding model parameters and theoretical guidance for exploring the twisted MD vdWH of graphene/C<sub>2</sub>H and offer an effective strategy to modulate the electronic structures and the <italic toggle=\"yes\">C</italic>\u0000<sub>q</sub> of graphene through constructing the MD vdWH.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"68 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313532","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}
Due to its large absorption coefficient and high carrier mobility, SnS exhibits strong promise in the area of optoelectronic devices. Nevertheless, the fabrication of large-area, high-quality films for SnS photodetectors (PDs) with superior photoresponse remains a formidable task, seriously limiting its further practical application. In the present study, we report a superior-performance broadband PD founded on the epitaxial SnS film. Large-area uniform SnS films were grown epitaxially on (100)-oriented KBr using magnetron sputtering technique, further exfoliated, and transferred in a wafer size to fabricated two-ends PD devices. Benefitting from high crystallization and unique photoconductive-bolometric coupling effect, the two modes of operation exhibit a wide range of spectral responses from the visible to near-infrared wavelength (405–1920 nm). Particularly noteworthy is the SnS device fabricated, which demonstrates an impressive responsivity of 95.5 A W−1 and a detectivity of 7.8 × 1011 Jones, outperforming other devices by 1–2 orders of magnitude. In addition, SnS PD shows excellent environmental durability. This work provides a robust approach to develop high-performance broadband SnS PDs, while simultaneously offering deep insight into the light–matter interactions.
{"title":"High-performance broadband SnS photodetector based on photoconductive-bolometric coupling effect","authors":"Bo Zhang, Yunjie Liu, Bing Hu, Fuhai Guo, Mingcong Zhang, Siqi Li, Weizhuo Yu, Lanzhong Hao","doi":"10.1088/2053-1583/ad2c11","DOIUrl":"https://doi.org/10.1088/2053-1583/ad2c11","url":null,"abstract":"Due to its large absorption coefficient and high carrier mobility, SnS exhibits strong promise in the area of optoelectronic devices. Nevertheless, the fabrication of large-area, high-quality films for SnS photodetectors (PDs) with superior photoresponse remains a formidable task, seriously limiting its further practical application. In the present study, we report a superior-performance broadband PD founded on the epitaxial SnS film. Large-area uniform SnS films were grown epitaxially on (100)-oriented KBr using magnetron sputtering technique, further exfoliated, and transferred in a wafer size to fabricated two-ends PD devices. Benefitting from high crystallization and unique photoconductive-bolometric coupling effect, the two modes of operation exhibit a wide range of spectral responses from the visible to near-infrared wavelength (405–1920 nm). Particularly noteworthy is the SnS device fabricated, which demonstrates an impressive responsivity of 95.5 A W<sup>−1</sup> and a detectivity of 7.8 × 10<sup>11</sup> Jones, outperforming other devices by 1–2 orders of magnitude. In addition, SnS PD shows excellent environmental durability. This work provides a robust approach to develop high-performance broadband SnS PDs, while simultaneously offering deep insight into the light–matter interactions.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"48 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313510","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 : 2024-02-22DOI: 10.1088/2053-1583/ad27e7
A Mehrnejat, M Ciomaga Hatnean, M C Rosamond, N Banerjee, G Balakrishnan, S E Savel’ev, F K Dejene
In ferromagnet/superconductor bilayer systems, dipolar fields from the ferromagnet can create asymmetric energy barriers for the formation and dynamics of vortices through flux pinning. Conversely, the flux emanating from vortices can pin the domain walls of the ferromagnet, thereby creating asymmetric critical currents. Here, we report the observation of a superconducting diode effect (SDE) in a NbSe2/CrGeTe3 van der Waals heterostructure in which the magnetic domains of CrGeTe3 control the Abrikosov vortex dynamics in NbSe2. In addition to extrinsic vortex pinning mechanisms at the edges of NbSe2, flux-pinning-induced bulk pinning of vortices can alter the critical current. This asymmetry can thus be explained by considering the combined effect of this bulk pinning mechanism along with the vortex tilting induced by the Lorentz force from the transport current in the NbSe2/CrGeTe3 heterostructure. We also provide evidence of critical current modulation by flux pinning depending on the history of the field setting procedure. Our results suggest a method of controlling the efficiency of the SDE in magnetically coupled van der Waals superconductors, where dipolar fields generated by the magnetic layer can be used to modulate the dynamics of the superconducting vortices in the superconductors.
{"title":"Flux-pinning mediated superconducting diode effect in NbSe2/CrGeTe3 heterostructure","authors":"A Mehrnejat, M Ciomaga Hatnean, M C Rosamond, N Banerjee, G Balakrishnan, S E Savel’ev, F K Dejene","doi":"10.1088/2053-1583/ad27e7","DOIUrl":"https://doi.org/10.1088/2053-1583/ad27e7","url":null,"abstract":"In ferromagnet/superconductor bilayer systems, dipolar fields from the ferromagnet can create asymmetric energy barriers for the formation and dynamics of vortices through flux pinning. Conversely, the flux emanating from vortices can pin the domain walls of the ferromagnet, thereby creating asymmetric critical currents. Here, we report the observation of a superconducting diode effect (SDE) in a NbSe<sub>2</sub>/CrGeTe<sub>3</sub> van der Waals heterostructure in which the magnetic domains of CrGeTe<sub>3</sub> control the Abrikosov vortex dynamics in NbSe<sub>2</sub>. In addition to extrinsic vortex pinning mechanisms at the edges of NbSe<sub>2</sub>, flux-pinning-induced bulk pinning of vortices can alter the critical current. This asymmetry can thus be explained by considering the combined effect of this bulk pinning mechanism along with the vortex tilting induced by the Lorentz force from the transport current in the NbSe<sub>2</sub>/CrGeTe<sub>3</sub> heterostructure. We also provide evidence of critical current modulation by flux pinning depending on the history of the field setting procedure. Our results suggest a method of controlling the efficiency of the SDE in magnetically coupled van der Waals superconductors, where dipolar fields generated by the magnetic layer can be used to modulate the dynamics of the superconducting vortices in the superconductors.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"12 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010520","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}
Hexagonal boron-nitride (h-BN) provides an ideal substrate for supporting graphene devices to achieve fascinating transport properties, such as Klein tunneling, electron optics and other novel quantum transport phenomena. However, depositing graphene on h-BN creates moiré superlattices, whose electronic properties can be significantly manipulated by controlling the lattice alignment between layers. In this work, the effects of these moiré structures on the transport properties of graphene are investigated using atomistic simulations. At large misalignment angles (leading to small moiré cells), the transport properties (most remarkably, Klein tunneling) of pristine graphene devices are conserved. On the other hand, in the nearly aligned cases, the moiré interaction induces stronger effects, significantly affecting electron transport in graphene. In particular, Klein tunneling is significantly degraded. In contrast, strong Fabry-Pérot interference (accordingly, strong quantum confinement) effects and non-linear I-V characteristics are observed. P-N interface smoothness engineering is also considered, suggesting as a potential way to improve these transport features in graphene/h-BN devices.
{"title":"Klein tunneling degradation and enhanced Fabry-Pérot interference in graphene/h-BN moiré-superlattice devices","authors":"Viet-Anh Tran, Viet-Hung Nguyen, Jean-Christophe Charlier","doi":"10.1088/2053-1583/ad27e8","DOIUrl":"https://doi.org/10.1088/2053-1583/ad27e8","url":null,"abstract":"Hexagonal boron-nitride (<italic toggle=\"yes\">h</italic>-BN) provides an ideal substrate for supporting graphene devices to achieve fascinating transport properties, such as Klein tunneling, electron optics and other novel quantum transport phenomena. However, depositing graphene on <italic toggle=\"yes\">h</italic>-BN creates moiré superlattices, whose electronic properties can be significantly manipulated by controlling the lattice alignment between layers. In this work, the effects of these moiré structures on the transport properties of graphene are investigated using atomistic simulations. At large misalignment angles (leading to small moiré cells), the transport properties (most remarkably, Klein tunneling) of pristine graphene devices are conserved. On the other hand, in the nearly aligned cases, the moiré interaction induces stronger effects, significantly affecting electron transport in graphene. In particular, Klein tunneling is significantly degraded. In contrast, strong Fabry-Pérot interference (accordingly, strong quantum confinement) effects and non-linear I-V characteristics are observed. P-N interface smoothness engineering is also considered, suggesting as a potential way to improve these transport features in graphene/<italic toggle=\"yes\">h</italic>-BN devices.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"31 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010512","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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