Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of ...Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of n-type Si C/graphene,while a comprehensive understanding of the quantum resistance metrology behavior of graphene with different doping types is lacking.Here,we fabricated both n-and p-type Si C/graphene devices via polymer-assisted molecular adsorption and conducted systematic magneto-transport measurements in a wide parameter space of carrier density and temperature.It is demonstrated that n-type devices show greater potential for development of quantum resistance metrology compared with p-type devices,as evidenced by their higher carrier mobility,lower critical magnetic field for entering quantized Hall plateaus,and higher robustness of the quantum Hall effect against thermal degeneration.These discrepancies can be reasonably attributed to the weaker scattering from molecular dopants for n-type devices,which is further supported by the analyses on the quantum interference effect in multiple devices.These results enrich our understanding of the charged impurity on electronic transport performance of graphene and,more importantly,provide a useful reference for future development of graphene-based quantum resistance metrology.展开更多
MICAtronics, based on the functional oxide/mica heterostructures, has recently attracted much attention due to its potential applications in transparent, flexible electronics and devices. However, the weak van der Waa...MICAtronics, based on the functional oxide/mica heterostructures, has recently attracted much attention due to its potential applications in transparent, flexible electronics and devices. However, the weak van der Waals interaction decreases the tolerable lattice mismatch and thus limits the species of function oxides that are able to be epitaxially grown on mica. We successfully fabricate relatively high-quality epitaxial anatase TiO2 thin films on mica substrates. Structural analyses reveal that the carefully chosen growth temperature(650℃) and suitable crystalline phase(anatase phase) of TiO2 are the key issues for this van der Waals epitaxy. Moreover, as a buffer layer, the TiO2 layer successfully suppresses the decomposition of BiFeO3 and the difficulty of epitaxial growth of BiFeO3 is decreased. Therefore, relatively high-quality anatase TiO2 is proved to be an effective buffer layer for fabricating more functional oxides on mica.展开更多
As an elemental semiconductor,tellurium has recently attracted intense interest due to its non-trivial band topology,and the resulted intriguing topological transport phenomena.In this study we report systematic elect...As an elemental semiconductor,tellurium has recently attracted intense interest due to its non-trivial band topology,and the resulted intriguing topological transport phenomena.In this study we report systematic electronic transport studies on tellurium flakes grown via a simple vapor deposition process.The sample is self-hole-doped,and exhibits typical weak localization behavior at low temperatures.Substantial negative longitudinal magnetoresistance under parallel magnetic field is observed over a wide temperature region,which is considered to share the same origin with that in tellurium bulk crystals,i.e.,the Weyl points near the top of valence band.However,with lowering temperature the longitudinal magnetoconductivity experiences a transition from parabolic to linear field dependency,differing distinctly from the bulk counterparts.Further analysis reveals that such a modulation of Weyl behaviors in this low-dimensional tellurium structure can be attributed to the enhanced inter-valley scattering at low temperatures.Our results further extend Weyl physics into a low-dimensional semiconductor system,which may find its potential application in designing topological semiconductor devices.展开更多
For conductors in the ballistic regime, electron-boundary scattering at the sample edge plays a dominant role in determining the transport performance, giving rise to many intriguing phenomena like low-field negative ...For conductors in the ballistic regime, electron-boundary scattering at the sample edge plays a dominant role in determining the transport performance, giving rise to many intriguing phenomena like low-field negative magnetoresistance effect. We systematically investigate the magneto-transport behaviors of BN-encapsulated graphene devices with narrow channel width W, wherein the bulk mean free path Lmfp can be very large and highly tunable. By comparing the magnetoresistance features and the amplitude of Lmfp in a large parameter space of temperature and carrier density, we reveal that the boundary-scattering-dominated negative magnetoresistance effect can still survive even when the ballistic ratio(Lmfp/W) is as low as 0.15. This striking value is much smaller than the expected value for achieving(quasi-) ballistic transport regime(Lmfp/W ≥ 1), and can be attributed to the ultra-low specularity of the sample edge of our graphene devices. These findings enrich our understanding of the effects of boundary scattering on channel transport, which is of vital importance for future designs of two-dimensional electronic devices with limited lateral sizes.展开更多
The reconstruction process of the Si(111)√3 ×√3 R30°-Ag surface is studied by using a scanning tunnelling microscope at 78K.By applying a strong interaction between the tip and the surface,a tip-induced re...The reconstruction process of the Si(111)√3 ×√3 R30°-Ag surface is studied by using a scanning tunnelling microscope at 78K.By applying a strong interaction between the tip and the surface,a tip-induced reconstruction corresponding to the mergence of two Si(111)√3 ×√3 R30°-Ag domains is observed.Based on the inequivalent trimers(IET)model,this reconstruction process is attributed to a transition between the clockwise and counterclockwise IET domains.With this transition,the honeycomb-chained-trimer Si(111)√3 ×√3 R30°-Ag anti-phase boundary disappears and changes to the IET structure.展开更多
The Weyl semimetal has emerged as a new topologically nontrivial phase of matter,hosting low-energy excitations of massless Weyl fermions.Here,we present a comprehensive study of a type-ⅡWeyl semimetal WP2.Transport ...The Weyl semimetal has emerged as a new topologically nontrivial phase of matter,hosting low-energy excitations of massless Weyl fermions.Here,we present a comprehensive study of a type-ⅡWeyl semimetal WP2.Transport studies show a butterfly-like magnetoresistance at low temperature,reflecting the anisotropy of the electron Fermi surfaces.This four-lobed feature gradually evolves into a two-lobed variant with an increase in temperature,mainly due to the reduced relative contribution of electron Fermi surfaces compared to hole Fermi surfaces for magnetoresistance.Moreover,an angle-dependent Berry phase is also discovered,based on quantum oscillations,which is ascribed to the effective manipulation of extremal Fermi orbits by the magnetic field to feel nearby topological singularities in the momentum space.The revealed topological character and anisotropic Fermi surfaces of the WP2 substantially enrich the physical properties of Weyl semimetals,and show great promises in terms of potential topological electronic and Fermitronic device applications.展开更多
Hybrid structures of two distinct materials provide an excellent opportunity to optimize functionalities.We report the realization of wide quantum Hall plateaus in graphene field-effect devices on the LaAlO3/SrTiO3 he...Hybrid structures of two distinct materials provide an excellent opportunity to optimize functionalities.We report the realization of wide quantum Hall plateaus in graphene field-effect devices on the LaAlO3/SrTiO3 heterostructures.Well-defined quantized Hall resistance plateaus at filling factors ν=±2 can be obtained over wide ranges of the magnetic field and gate voltage,e.g.,extending from 2 T to a maximum available magnetic field of 9 T.By using a simple band diagram model,it is revealed that these wide plateaus arise from the ultralarge capacitance of the ultra-thin LAO layer acting as the dielectric layer.This is distinctly different from the case of epitaxial graphene on Si C substrates,where the realization of giant Hall plateaus relies on the charge transfer between the graphene layer and interface states in SiC.Our results offer an alternative route towards optimizing the quantum Hall performance of graphene,which may find its applications in the further development of quantum resistance metrology.展开更多
基金V. ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China （No.11374279 and No.11034006）, the National Basic Research Program of China （No.2014CB921102）, the Strategic Priority Research Program of the Chinese Academy of Sciences （No.XDB01020000）, the Specialized Research Fund for the Doctoral Program of Higher Education （No.20113402110046）, and the Fundamental Research Funds for the Central Universities （No.WK2340000035）.
基金supported by the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-046)the National Natural Science Foundation of China(Grant Nos.92165201,11974324,12104435)+4 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)Hefei Science Center CAS(Grant No.2020HSC-UE014)the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000013 and WK2310000104)supported by USTC Tang Scholar。
文摘Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of n-type Si C/graphene,while a comprehensive understanding of the quantum resistance metrology behavior of graphene with different doping types is lacking.Here,we fabricated both n-and p-type Si C/graphene devices via polymer-assisted molecular adsorption and conducted systematic magneto-transport measurements in a wide parameter space of carrier density and temperature.It is demonstrated that n-type devices show greater potential for development of quantum resistance metrology compared with p-type devices,as evidenced by their higher carrier mobility,lower critical magnetic field for entering quantized Hall plateaus,and higher robustness of the quantum Hall effect against thermal degeneration.These discrepancies can be reasonably attributed to the weaker scattering from molecular dopants for n-type devices,which is further supported by the analyses on the quantum interference effect in multiple devices.These results enrich our understanding of the charged impurity on electronic transport performance of graphene and,more importantly,provide a useful reference for future development of graphene-based quantum resistance metrology.
基金Supported by National Basic Research Program of China(2014CB 921102)National Natural Science Foundation of China(11434009,11374279,11461161009)+1 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB01020000)the Fundamental Research Funds for the Central Universities(WK2030020027)
基金Supported by the National Key Research and Development Program of China under Grant No 2016YFA0300102the National Natural Science Foundation of China under Grant Nos 11675179,11434009 and 11374010the Fundamental Research Funds for the Central Universities under Grant No WK2340000065
文摘MICAtronics, based on the functional oxide/mica heterostructures, has recently attracted much attention due to its potential applications in transparent, flexible electronics and devices. However, the weak van der Waals interaction decreases the tolerable lattice mismatch and thus limits the species of function oxides that are able to be epitaxially grown on mica. We successfully fabricate relatively high-quality epitaxial anatase TiO2 thin films on mica substrates. Structural analyses reveal that the carefully chosen growth temperature(650℃) and suitable crystalline phase(anatase phase) of TiO2 are the key issues for this van der Waals epitaxy. Moreover, as a buffer layer, the TiO2 layer successfully suppresses the decomposition of BiFeO3 and the difficulty of epitaxial growth of BiFeO3 is decreased. Therefore, relatively high-quality anatase TiO2 is proved to be an effective buffer layer for fabricating more functional oxides on mica.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDC07010000)the National Natural Science Foundation of China(Grant Nos.11974324,U1832151,11804326,and 11904001)+2 种基金the National Key Research and Development Program of China(Grant No.2017YFA0403600)the Anhui Initiative Fund in Quantum Information Technologies(Grant No.AHY170000)the Fund from the Hefei Science Center,Chinese Academy of Sciences(Grant No.2020HSC-UE014).
文摘As an elemental semiconductor,tellurium has recently attracted intense interest due to its non-trivial band topology,and the resulted intriguing topological transport phenomena.In this study we report systematic electronic transport studies on tellurium flakes grown via a simple vapor deposition process.The sample is self-hole-doped,and exhibits typical weak localization behavior at low temperatures.Substantial negative longitudinal magnetoresistance under parallel magnetic field is observed over a wide temperature region,which is considered to share the same origin with that in tellurium bulk crystals,i.e.,the Weyl points near the top of valence band.However,with lowering temperature the longitudinal magnetoconductivity experiences a transition from parabolic to linear field dependency,differing distinctly from the bulk counterparts.Further analysis reveals that such a modulation of Weyl behaviors in this low-dimensional tellurium structure can be attributed to the enhanced inter-valley scattering at low temperatures.Our results further extend Weyl physics into a low-dimensional semiconductor system,which may find its potential application in designing topological semiconductor devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.92165201 and 11974324)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDC07010000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)the Hefei Science Center CAS(Grant No.2020HSC-UE014)the Fundamental Research Funds for the Central Universities(Grant No.WK3510000013)。
文摘For conductors in the ballistic regime, electron-boundary scattering at the sample edge plays a dominant role in determining the transport performance, giving rise to many intriguing phenomena like low-field negative magnetoresistance effect. We systematically investigate the magneto-transport behaviors of BN-encapsulated graphene devices with narrow channel width W, wherein the bulk mean free path Lmfp can be very large and highly tunable. By comparing the magnetoresistance features and the amplitude of Lmfp in a large parameter space of temperature and carrier density, we reveal that the boundary-scattering-dominated negative magnetoresistance effect can still survive even when the ballistic ratio(Lmfp/W) is as low as 0.15. This striking value is much smaller than the expected value for achieving(quasi-) ballistic transport regime(Lmfp/W ≥ 1), and can be attributed to the ultra-low specularity of the sample edge of our graphene devices. These findings enrich our understanding of the effects of boundary scattering on channel transport, which is of vital importance for future designs of two-dimensional electronic devices with limited lateral sizes.
基金Supported by the National Natural Science Foundation of China under Grant Nos.5997203 and G1999075305the Hong Kong'Qiu Shi'Foundation.
文摘The reconstruction process of the Si(111)√3 ×√3 R30°-Ag surface is studied by using a scanning tunnelling microscope at 78K.By applying a strong interaction between the tip and the surface,a tip-induced reconstruction corresponding to the mergence of two Si(111)√3 ×√3 R30°-Ag domains is observed.Based on the inequivalent trimers(IET)model,this reconstruction process is attributed to a transition between the clockwise and counterclockwise IET domains.With this transition,the honeycomb-chained-trimer Si(111)√3 ×√3 R30°-Ag anti-phase boundary disappears and changes to the IET structure.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11974324,11804326,U1832151,and 11674296),the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDC07010000)the National Key Research and Development Program of China(Grant No.2017YFA0403600)+4 种基金the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)the Hefei Science Center CAS(Grant No.2018HSC-UE014)the Jiangsu Provincial Science Foundation for Youth(Grant No.BK20170821)the National Natural Science Foundation of China for Youth(Grant No.11804160)the Anhui Provincial Natural Science Foundation(Grant No.1708085MF136)。
文摘The Weyl semimetal has emerged as a new topologically nontrivial phase of matter,hosting low-energy excitations of massless Weyl fermions.Here,we present a comprehensive study of a type-ⅡWeyl semimetal WP2.Transport studies show a butterfly-like magnetoresistance at low temperature,reflecting the anisotropy of the electron Fermi surfaces.This four-lobed feature gradually evolves into a two-lobed variant with an increase in temperature,mainly due to the reduced relative contribution of electron Fermi surfaces compared to hole Fermi surfaces for magnetoresistance.Moreover,an angle-dependent Berry phase is also discovered,based on quantum oscillations,which is ascribed to the effective manipulation of extremal Fermi orbits by the magnetic field to feel nearby topological singularities in the momentum space.The revealed topological character and anisotropic Fermi surfaces of the WP2 substantially enrich the physical properties of Weyl semimetals,and show great promises in terms of potential topological electronic and Fermitronic device applications.
基金Supported by the National Natural Science Foundation of China (Grant Nos.11974324,11804326 and U1832151)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDC07010000)+2 种基金the National Key Research and Development Program of China (Grant No.2017YFA0403600)Anhui Initiative in Quantum Information Technologies (Grant No.AHY170000)Hefei Science Center CAS (Grant No.2018HSC-UE014)。
文摘Hybrid structures of two distinct materials provide an excellent opportunity to optimize functionalities.We report the realization of wide quantum Hall plateaus in graphene field-effect devices on the LaAlO3/SrTiO3 heterostructures.Well-defined quantized Hall resistance plateaus at filling factors ν=±2 can be obtained over wide ranges of the magnetic field and gate voltage,e.g.,extending from 2 T to a maximum available magnetic field of 9 T.By using a simple band diagram model,it is revealed that these wide plateaus arise from the ultralarge capacitance of the ultra-thin LAO layer acting as the dielectric layer.This is distinctly different from the case of epitaxial graphene on Si C substrates,where the realization of giant Hall plateaus relies on the charge transfer between the graphene layer and interface states in SiC.Our results offer an alternative route towards optimizing the quantum Hall performance of graphene,which may find its applications in the further development of quantum resistance metrology.
