Piezoelectricity of organic polymers has attracted increasing interest because of several advantages they exhibit over traditional inorganic ceramics.While most organic piezoelectrics rely on the presence of intrinsic...Piezoelectricity of organic polymers has attracted increasing interest because of several advantages they exhibit over traditional inorganic ceramics.While most organic piezoelectrics rely on the presence of intrinsic local dipoles,a highly nonlocal electronic polarisation can be foreseen in conjugated polymers,characterised by delocalised and highly responsiveπ-electrons.These 1D systems represent a physical realisation of a Thouless pump,a mechanism of adiabatic charge transport of a topological nature which results,as shown in this work,in anomalously large dynamical effective charges,inversely proportional to the bandgap energy.展开更多
We develop a multiscale approach to magnetoelectric effects,bridging atomistic and continuum models,with all parameters determined from ab initio electronic structure calculations.We show that the parameters of the mo...We develop a multiscale approach to magnetoelectric effects,bridging atomistic and continuum models,with all parameters determined from ab initio electronic structure calculations.We show that the parameters of the model are equivalent to the electric field-induced Dzyaloshinski-Moriya interactions.After careful validation,we apply the models to study electric polarization and dipole moments carried by spin spirals and topological solitons,in the form of magnetic domain walls and Skyrmions,in the prototypical 2D magnet CrI3.We show that the reduced symmetry of the material leads to additional magnetoelectric coupling terms,dominating over those expected in high symmetry(cubic)materials.An interesting consequence is that Skyrmions carry an out-of-plane electric dipole moment,while that of anti-Skyrmions is an order of magnitude larger and in-plane.Finally,we discuss the possibility to stabilize non-collinear spin states using electric fields.展开更多
Using first principles techniques,we show that infrared optical response allows us to discriminate between the topological and the trivial phases of 2D quantum spin Hall insulators(QSHI).We showcase germanene and jacu...Using first principles techniques,we show that infrared optical response allows us to discriminate between the topological and the trivial phases of 2D quantum spin Hall insulators(QSHI).We showcase germanene and jacutingaite,of recent experimental realization,as prototypical systems where the infrared spectrum is discontinuous across the transition,due to sudden and large discretized jumps of the Born effective charges(up to~2).Our results,rationalized thanks to the lowenergy Kane–Mele model,are robust with respect to dynamical effects,relevant when the electronic energy gap is comparable with the phonon frequency.In the small gap QSHI germanene,due to dynamical effects,the in-plane phonon resonance in the optical conductivity shows a Fano profile with remarkable differences in the intensity and the shape between different phases.Instead,the large-gap QSHI jacutingaite presents several IR-active phonon modes whose spectral intensities drastically change between different phases.展开更多
基金The authors acknowledge financial support from the European Union under ERC-SYN MORE-TEM,No.951215from the Italian MIUR through the PRIN-2017 project,Grant No.2017Z8TS5BCINECA awards under ISCRA initiative Grant No.HP10CCJFWR and HP10C7XPLJ for the availability of high-performance computing resources and support.
文摘Piezoelectricity of organic polymers has attracted increasing interest because of several advantages they exhibit over traditional inorganic ceramics.While most organic piezoelectrics rely on the presence of intrinsic local dipoles,a highly nonlocal electronic polarisation can be foreseen in conjugated polymers,characterised by delocalised and highly responsiveπ-electrons.These 1D systems represent a physical realisation of a Thouless pump,a mechanism of adiabatic charge transport of a topological nature which results,as shown in this work,in anomalously large dynamical effective charges,inversely proportional to the bandgap energy.
基金support from the Swedish Research Council(VR-2018-06807 and 2022-04720),ÅForsk(22-441),the Göran Gustafsson Foundation,and the Swedish e-Science Research Center(SeRC)M.S.acknowledges the support of the State Investigation Agency through the Severo Ochoa Program for Centres of Excellence in R&D(CEX2023-001263-S),of the Ministry of Science,Innovation and Universities(Grant No.PID2023-152710NB-I00)+1 种基金of Generalitat de Catalunya(Grant No.2021 SGR 01519)This work has been funded by the European Union-NextGenerationEU,under the Italian Ministry of University and Research(MUR)PRIN-2022 project"SORBET:Spin-ORBit Effects in Two-dimensional magnets"(IT-MIUR Grant No.2022ZY8HJY)and National Innovation Ecosystem grant ECS00000041-VITALITY-CUP B43C22000470005.Computational work was done on resources at PDC,Stockholm,and NSC,Linköping,via the National Academic Infrastructure for Supercomputing in Sweden(NAISS),as well as the Galileo system of Cineca through HPC-Europa3(HPC17A3WLE),which also supported the collaborative effort by funding an international research visit.
文摘We develop a multiscale approach to magnetoelectric effects,bridging atomistic and continuum models,with all parameters determined from ab initio electronic structure calculations.We show that the parameters of the model are equivalent to the electric field-induced Dzyaloshinski-Moriya interactions.After careful validation,we apply the models to study electric polarization and dipole moments carried by spin spirals and topological solitons,in the form of magnetic domain walls and Skyrmions,in the prototypical 2D magnet CrI3.We show that the reduced symmetry of the material leads to additional magnetoelectric coupling terms,dominating over those expected in high symmetry(cubic)materials.An interesting consequence is that Skyrmions carry an out-of-plane electric dipole moment,while that of anti-Skyrmions is an order of magnitude larger and in-plane.Finally,we discuss the possibility to stabilize non-collinear spin states using electric fields.
文摘Using first principles techniques,we show that infrared optical response allows us to discriminate between the topological and the trivial phases of 2D quantum spin Hall insulators(QSHI).We showcase germanene and jacutingaite,of recent experimental realization,as prototypical systems where the infrared spectrum is discontinuous across the transition,due to sudden and large discretized jumps of the Born effective charges(up to~2).Our results,rationalized thanks to the lowenergy Kane–Mele model,are robust with respect to dynamical effects,relevant when the electronic energy gap is comparable with the phonon frequency.In the small gap QSHI germanene,due to dynamical effects,the in-plane phonon resonance in the optical conductivity shows a Fano profile with remarkable differences in the intensity and the shape between different phases.Instead,the large-gap QSHI jacutingaite presents several IR-active phonon modes whose spectral intensities drastically change between different phases.
