Topological insulating states in 2-dimensional(2D)materials are ideal systems to study different types of quantized response signals due to their in gap metallic states.Very recently,the quantum spin Hall effect was d...Topological insulating states in 2-dimensional(2D)materials are ideal systems to study different types of quantized response signals due to their in gap metallic states.Very recently,the quantum spin Hall effect was discovered in monolayer TalrTe Via the observation of quantized longitudinal conductance that rarely exists in other 2D topological insulators.The nontrivial Z_(2)topological charges can exist at both charge neutrality point and the van Hove singularity point with correlation-effect-induced bandgap.On the basis of this model 2D material,we studied the switch of quantized signals between longitudinal conductance and transversal Hall conductance via tuning external magnetic field.In Z_(2)topological phase of monolayer TalrTe_(4),the zero Chern number can be understood as 1-1=O from the double band inversion from spinup and spin-down channels.After applying a magnetic field perpendicular to the plane,the Zeeman split changes the band order for one branch of the band inversion from spin-up and spin-down channels,along with a sign charge of the Berry phase.Then,the net Chern number of 1-1=0 is tuned to 1+1=2 or-1-1=-2 depending on the orientation of the magnetic field.The quantized signal not only provides another effective method for the verification of topological state in monolayer TalrTe_(4)but also offers a strategy for the utilization of the new quantum topological states based on switchable quantized responses.展开更多
In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By emp...In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.展开更多
A quantized Hall conductance(not conductivity)in three dimensions has been searched for more than 30 years.Here we explore it in 3D topological nodal-ring semimetals,by employing a minimal model describing the essenti...A quantized Hall conductance(not conductivity)in three dimensions has been searched for more than 30 years.Here we explore it in 3D topological nodal-ring semimetals,by employing a minimal model describing the essential physics.In particular,the bulk topology can be captured by a momentum-dependent winding number,which confines the drumhead surface states in a specific momentum region.This confinement leads to a surface quantum Hall conductance in a specific energy window in this 3D system.The winding number for the drumhead surface states and Chern number for their quantum Hall effect form a two-fold topological hierarchy.We demonstrate the one-to-one correspondence between the momentum-dependent winding number and wavefunction of the drumhead surface states.More importantly,we stress that breaking chiral symmetry is necessary for the quantum Hall effect of the drumhead surface states.The analytic theory can be verified numerically by the Kubo formula for the Hall conductance.We propose an experimental setup to distinguish the surface and bulk quantum Hall effects.The theory will be useful for ongoing explorations on nodal-ring semimetals.展开更多
基金supported by the Foundation from Liaoning Province(grant no.XLYC2203080)the National Natural Science Foundation of China(grant nos.52271016 and 52188101)the National Key R&D Program of China(grant no.2021YFB3501503)。
文摘Topological insulating states in 2-dimensional(2D)materials are ideal systems to study different types of quantized response signals due to their in gap metallic states.Very recently,the quantum spin Hall effect was discovered in monolayer TalrTe Via the observation of quantized longitudinal conductance that rarely exists in other 2D topological insulators.The nontrivial Z_(2)topological charges can exist at both charge neutrality point and the van Hove singularity point with correlation-effect-induced bandgap.On the basis of this model 2D material,we studied the switch of quantized signals between longitudinal conductance and transversal Hall conductance via tuning external magnetic field.In Z_(2)topological phase of monolayer TalrTe_(4),the zero Chern number can be understood as 1-1=O from the double band inversion from spinup and spin-down channels.After applying a magnetic field perpendicular to the plane,the Zeeman split changes the band order for one branch of the band inversion from spin-up and spin-down channels,along with a sign charge of the Berry phase.Then,the net Chern number of 1-1=0 is tuned to 1+1=2 or-1-1=-2 depending on the orientation of the magnetic field.The quantized signal not only provides another effective method for the verification of topological state in monolayer TalrTe_(4)but also offers a strategy for the utilization of the new quantum topological states based on switchable quantized responses.
基金Acknowledgements This work was supported by the National Natural Science Foundation of China （Nos. 21503179, 21403181, 61573295, 21522508, 21673195, 21533006, and 61071010）, the National Basic Research Program of China （No. 2015CB932300）, the Natural Science Foundation of Fujian Province （No. 2016J05162）, the Fundamental Research Funds for the Central Universities in China （Xiamen University, Nos. 20720170035 and 20720160092）, and the Young Thousand Talent Project of China.
文摘In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction （EC-MCBJ） method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.
基金supported by the National Key R&D Program of China(2022YFA1403700)the Innovation Program for Quantum Science and Technology(2021ZD0302400)+3 种基金the National Natural Science Foundation of China(11925402,11534001,and 11974249)Guangdong province(2020KCXTD001 and 2016ZT06D348)the Natural Science Foundation of Shanghai(19ZR1437300)supported by Center for Computational Science and Engineering of SUSTech.
文摘A quantized Hall conductance(not conductivity)in three dimensions has been searched for more than 30 years.Here we explore it in 3D topological nodal-ring semimetals,by employing a minimal model describing the essential physics.In particular,the bulk topology can be captured by a momentum-dependent winding number,which confines the drumhead surface states in a specific momentum region.This confinement leads to a surface quantum Hall conductance in a specific energy window in this 3D system.The winding number for the drumhead surface states and Chern number for their quantum Hall effect form a two-fold topological hierarchy.We demonstrate the one-to-one correspondence between the momentum-dependent winding number and wavefunction of the drumhead surface states.More importantly,we stress that breaking chiral symmetry is necessary for the quantum Hall effect of the drumhead surface states.The analytic theory can be verified numerically by the Kubo formula for the Hall conductance.We propose an experimental setup to distinguish the surface and bulk quantum Hall effects.The theory will be useful for ongoing explorations on nodal-ring semimetals.
