We report a systematic study on the transport properties of(Bi_(0.2)Sb_(0.8))_(2)Te_(3)and(Bi_(0.4)Sb_(0.6))_(2)Te_(3)nanoplates with a thickness of about 6 nm grown by chemical vapor deposition(CVD)on Si/SiO_(2)subst...We report a systematic study on the transport properties of(Bi_(0.2)Sb_(0.8))_(2)Te_(3)and(Bi_(0.4)Sb_(0.6))_(2)Te_(3)nanoplates with a thickness of about 6 nm grown by chemical vapor deposition(CVD)on Si/SiO_(2)substrate.We achieve a significant ambipolar field effect in the two samples with different compositions by applying back-gate voltage,successfully tuning the Fermi level across the Dirac point of surface states.It is found that the Hall resistance exhibits strong non-linear behavior and magnetic field induced sign change of the slope when the Fermi level is near the Dirac point,indicating the coexistence of n-type and p-type carriers.Moreover,this coincides with the striking crossover from weak antilocalization(WAL)to linear magnetoresistance(LMR).These gate and temperature dependent magneto-transport studies provide a deeper insight into the nature of LMR and WAL in topological materials.展开更多
Electron-electron interactions(EEIs),quantum interference,and the effects of disorder on transport properties are essential topics in condensed matter physics.A series of our characterization work demonstrates that th...Electron-electron interactions(EEIs),quantum interference,and the effects of disorder on transport properties are essential topics in condensed matter physics.A series of our characterization work demonstrates that the morphology of Bi_(2)Te_(3)/MnTe bilayer film mainly depends on the magnetic substrate's growth mode and thickness.We propose that the temperature-dependent quantum interference of the electron wave function caused by disorder drives the transition from weak antilocalization(WAL) to weak localization(WL).Due to spin regulation,WL under low fields originates from the ferromagnetism in MnTe.The quantum interference effect(QIE) model analysis gives the degree of impurity scattering of the electron wave function.The electron wave is scattered by impurities,which causes the Berry phase to change from π to 0,producing a complete WL behavior.The stacked structure provides tunable degrees of freedom,allowing for independent optimization of topological properties and magnetic order through preferential growth orientation of topological insulator(TI) and magnetic layers,respectively.展开更多
In chalcogenide topological insulator materials, two types of magnetoresistance （MR） effects are widely discussed： a sharp MR dip around zero magnetic field, associated with the weak antilocalization （WAL） effect...In chalcogenide topological insulator materials, two types of magnetoresistance （MR） effects are widely discussed： a sharp MR dip around zero magnetic field, associated with the weak antilocalization （WAL） effect, and a linear MR （LMR） effect that generally persists to high fields and high temperatures. We have studied the MR of thin films of the topological insulator Bi2Te3 from the metallic to semiconducting transport regime. In the metallic samples, the WAL is difficult to identify owing to the low magnitude of the WAL compared to the samples＇ conductivity. Furthermore, the sharp WAL dip in the MR is dearly present in samples with a higher resistivity. To correctly account for the low-field MR with the quantitative theory of the WAL according to the Hikami-Larkin-Nagaoka （HLN） model, we find that the classical （linear） MR effect should be taken into account in combination with the WAL quantum correction. Otherwise, the WAL fitting alone yields an unrealistically large coefficient in the HLN analysis. This work clarifies the WAL and LMR as two distinct effects and offers an explanation for the overly large a in the WAL analysis of topological insulators in some studies.展开更多
Weak antilocalization(WAL)effect is commonly observed in low-dimensional systems,three-dimensional(3D)topological insulators and semimetals.Here,we report the growth of high-quality Ta_(0.7)Nb_(0.3)Sb_(2)single crysta...Weak antilocalization(WAL)effect is commonly observed in low-dimensional systems,three-dimensional(3D)topological insulators and semimetals.Here,we report the growth of high-quality Ta_(0.7)Nb_(0.3)Sb_(2)single crystals via the chemical vapor transport(CVT).Clear sign of the WAL effect is observed below 50 K,probably due to the strong spin–orbital coupling in 3D bulk.In addition,it is worth noting that a relatively large MR of 120%appears under 1 T magnetic field at T=2 K.Hall measurements and two-band model fitting results reveal high carrier mobility(>1000 cm^(2)·V^(–1)·s^(–1)in 2–300 K region),and off-compensation electron/hole ratio of~8:1.Due to the angular dependence of the WAL effect and the fermiology of the Ta_(0.7)Nb_(0.3)Sb_(2)crystals,interesting magnetic-field-induced changes of the symmetry of the anisotropic magnetoresistance(MR)from two-fold(≤0.6 T)to four-fold(0.8–1.5 T)and finally to two-fold(≥2 T)are observed.This phenomenon is attributed to the mechanism shift from the low-field WAL dominated MR to WAL and fermiology co-dominated MR and finally to high-field fermiology dominated MR.All these signs indicate that Ta_(0.7)Nb_(0.3)Sb_(2)may be a topological semimetal candidate,and these magnetotransport properties may attract more theoretical and experimental exploration of the(Ta,Nb)Sb_(2)family.展开更多
A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to o...A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to obtain high-quality Bi_(2) Te_(3) films with the carrier density down to 4.0 × 10^(13) cm^(-2). In contrast to the most-used method of high substrate temperature growth, we firstly sputtered Bi_(2) Te_(3) thin films at room temperature and then applied post-annealing. It enables the growth of highly-oriented Bi_(2) Te_(3) thin films with larger grain size and smoother interface. The results of electrical transport show that it has a lower carrier density as well as a larger coherent length(~ 228 nm, 2 K). Our studies pave the way toward large-scale, cost-effective production of Bi_(2) Te_(3) thin films to be integrated with other materials in wafer-level scale for electronic and spintronic applications.展开更多
The surface impurity effect on the surface-state conductivity and weak antilocalization（WAL） effect has been investigated in epitaxial Bi（111） films by magnetotransport measurements at low temperatures. The surfac...The surface impurity effect on the surface-state conductivity and weak antilocalization（WAL） effect has been investigated in epitaxial Bi（111） films by magnetotransport measurements at low temperatures. The surface-state conductivity is significantly reduced by the surface impurities of Cu, Fe, and Co. The magnetotransport data demonstrate that the observed WAL is robust against deposition of nonmagnetic impurities, but it is quenched by the deposition of magnetic impurities which break the time reversal symmetry. Our results help to shed light on the effect of surface impurities on the electron and spin transport properties of a 2D surface electron systems.展开更多
The magneto-transport properties of （111）-oriented single-crystal thin films of SnTe were investigated. SnTe （111） thin films were epitaxially grown on a BaF2 substrate by molecular beam epitaxy. By optimizing the...The magneto-transport properties of （111）-oriented single-crystal thin films of SnTe were investigated. SnTe （111） thin films were epitaxially grown on a BaF2 substrate by molecular beam epitaxy. By optimizing the growth conditions and the thickness of the films, the bulk carrier density could be reduced, making it possible to detect the surface transport. Magneto-conductance （MC） measurements show a cusp-like feature around zero magnetic field, which is attributed to the weak-antilocalization effect of the transport in the topological surface state. Detailed analysis of this negative MC reveals a reduced number of transport channels contributing to the surface transport, suggesting strong coupling between Dirac valleys on the SnTe （111） surface, as a characteristic feature of the transport in the multivalley structure of topological crystalline insulators.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52201233,52371204,and 52031014).
文摘We report a systematic study on the transport properties of(Bi_(0.2)Sb_(0.8))_(2)Te_(3)and(Bi_(0.4)Sb_(0.6))_(2)Te_(3)nanoplates with a thickness of about 6 nm grown by chemical vapor deposition(CVD)on Si/SiO_(2)substrate.We achieve a significant ambipolar field effect in the two samples with different compositions by applying back-gate voltage,successfully tuning the Fermi level across the Dirac point of surface states.It is found that the Hall resistance exhibits strong non-linear behavior and magnetic field induced sign change of the slope when the Fermi level is near the Dirac point,indicating the coexistence of n-type and p-type carriers.Moreover,this coincides with the striking crossover from weak antilocalization(WAL)to linear magnetoresistance(LMR).These gate and temperature dependent magneto-transport studies provide a deeper insight into the nature of LMR and WAL in topological materials.
基金financially supported by the National Natural Science Foundation of China (Nos.52371204, 52201233,and 52031014)
文摘Electron-electron interactions(EEIs),quantum interference,and the effects of disorder on transport properties are essential topics in condensed matter physics.A series of our characterization work demonstrates that the morphology of Bi_(2)Te_(3)/MnTe bilayer film mainly depends on the magnetic substrate's growth mode and thickness.We propose that the temperature-dependent quantum interference of the electron wave function caused by disorder drives the transition from weak antilocalization(WAL) to weak localization(WL).Due to spin regulation,WL under low fields originates from the ferromagnetism in MnTe.The quantum interference effect(QIE) model analysis gives the degree of impurity scattering of the electron wave function.The electron wave is scattered by impurities,which causes the Berry phase to change from π to 0,producing a complete WL behavior.The stacked structure provides tunable degrees of freedom,allowing for independent optimization of topological properties and magnetic order through preferential growth orientation of topological insulator(TI) and magnetic layers,respectively.
文摘In chalcogenide topological insulator materials, two types of magnetoresistance （MR） effects are widely discussed： a sharp MR dip around zero magnetic field, associated with the weak antilocalization （WAL） effect, and a linear MR （LMR） effect that generally persists to high fields and high temperatures. We have studied the MR of thin films of the topological insulator Bi2Te3 from the metallic to semiconducting transport regime. In the metallic samples, the WAL is difficult to identify owing to the low magnitude of the WAL compared to the samples＇ conductivity. Furthermore, the sharp WAL dip in the MR is dearly present in samples with a higher resistivity. To correctly account for the low-field MR with the quantitative theory of the WAL according to the Hikami-Larkin-Nagaoka （HLN） model, we find that the classical （linear） MR effect should be taken into account in combination with the WAL quantum correction. Otherwise, the WAL fitting alone yields an unrealistically large coefficient in the HLN analysis. This work clarifies the WAL and LMR as two distinct effects and offers an explanation for the overly large a in the WAL analysis of topological insulators in some studies.
基金the National Natural Science Foundation of China(Grant Nos.11974155 and 12104128)the Natural Science Foundation of Jiangsu Province(Grant No.BK20210360)+2 种基金the Postdoctoral Research Program of Jiangsu Province(Grant No.2021K581C)the Fundamental Research Funds for the Central Universities(Grant No.B210201026)W.Z.and X.W.acknowledge the support from ARC Centre of Excellence in Future Low-Energy Electronic Technologies(No.CE170100039).
文摘Weak antilocalization(WAL)effect is commonly observed in low-dimensional systems,three-dimensional(3D)topological insulators and semimetals.Here,we report the growth of high-quality Ta_(0.7)Nb_(0.3)Sb_(2)single crystals via the chemical vapor transport(CVT).Clear sign of the WAL effect is observed below 50 K,probably due to the strong spin–orbital coupling in 3D bulk.In addition,it is worth noting that a relatively large MR of 120%appears under 1 T magnetic field at T=2 K.Hall measurements and two-band model fitting results reveal high carrier mobility(>1000 cm^(2)·V^(–1)·s^(–1)in 2–300 K region),and off-compensation electron/hole ratio of~8:1.Due to the angular dependence of the WAL effect and the fermiology of the Ta_(0.7)Nb_(0.3)Sb_(2)crystals,interesting magnetic-field-induced changes of the symmetry of the anisotropic magnetoresistance(MR)from two-fold(≤0.6 T)to four-fold(0.8–1.5 T)and finally to two-fold(≥2 T)are observed.This phenomenon is attributed to the mechanism shift from the low-field WAL dominated MR to WAL and fermiology co-dominated MR and finally to high-field fermiology dominated MR.All these signs indicate that Ta_(0.7)Nb_(0.3)Sb_(2)may be a topological semimetal candidate,and these magnetotransport properties may attract more theoretical and experimental exploration of the(Ta,Nb)Sb_(2)family.
基金supported by the National Natural Science Foundation of China (Grant Nos. 52072030, 52071025, and 51871018)the Beijing Outstanding Young Scientists Projects (Grant No. BJJWZYJH01201910005018)+2 种基金Beijing Natural Science Foundation,China (Grant No. Z180014)the Science and Technology Innovation Team Program of Foshan (Grant No. FSOAA-KJ919-4402-0087)Beijing Laboratory of Metallic Materials and Processing for Modern Transportation。
文摘A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to obtain high-quality Bi_(2) Te_(3) films with the carrier density down to 4.0 × 10^(13) cm^(-2). In contrast to the most-used method of high substrate temperature growth, we firstly sputtered Bi_(2) Te_(3) thin films at room temperature and then applied post-annealing. It enables the growth of highly-oriented Bi_(2) Te_(3) thin films with larger grain size and smoother interface. The results of electrical transport show that it has a lower carrier density as well as a larger coherent length(~ 228 nm, 2 K). Our studies pave the way toward large-scale, cost-effective production of Bi_(2) Te_(3) thin films to be integrated with other materials in wafer-level scale for electronic and spintronic applications.
基金supported by the National Basic Research Program of China(Grants Nos.2015CB921400 and 2011CB921802)the National Natural Science Foundation of China(Grants Nos.11374057,11434003,and 11421404)
文摘The surface impurity effect on the surface-state conductivity and weak antilocalization（WAL） effect has been investigated in epitaxial Bi（111） films by magnetotransport measurements at low temperatures. The surface-state conductivity is significantly reduced by the surface impurities of Cu, Fe, and Co. The magnetotransport data demonstrate that the observed WAL is robust against deposition of nonmagnetic impurities, but it is quenched by the deposition of magnetic impurities which break the time reversal symmetry. Our results help to shed light on the effect of surface impurities on the electron and spin transport properties of a 2D surface electron systems.
文摘The magneto-transport properties of （111）-oriented single-crystal thin films of SnTe were investigated. SnTe （111） thin films were epitaxially grown on a BaF2 substrate by molecular beam epitaxy. By optimizing the growth conditions and the thickness of the films, the bulk carrier density could be reduced, making it possible to detect the surface transport. Magneto-conductance （MC） measurements show a cusp-like feature around zero magnetic field, which is attributed to the weak-antilocalization effect of the transport in the topological surface state. Detailed analysis of this negative MC reveals a reduced number of transport channels contributing to the surface transport, suggesting strong coupling between Dirac valleys on the SnTe （111） surface, as a characteristic feature of the transport in the multivalley structure of topological crystalline insulators.
