Near the metal-insulator transition, the Hall coefficient R of metal-insulator composites (M-I composite) can be up to 104 times larger than that in the pure metal called Giant Hall effect. Applying the physical model...Near the metal-insulator transition, the Hall coefficient R of metal-insulator composites (M-I composite) can be up to 104 times larger than that in the pure metal called Giant Hall effect. Applying the physical model for alloys with phase separation developed in [1] [2], we conclude that the Giant Hall effect is caused by an electron transfer away from the metallic phase to the insulating phase occupying surface states. These surface states are the reason for the granular structure typical for M-I composites. This electron transfer can be described by [1] [2], provided that long-range diffusion does not happen during film production (n is the electron density in the phase A. u<sub>A </sub>and u<sub>B</sub> are the volume fractions of the phase A (metallic phase) and phase B (insulator phase). β is a measure for the average potential difference between the phases A and B). A formula for calculation of R of composites is derived and applied to experimental data of granular Cu<sub>1-y</sub>(SiO<sub>2</sub>)<sub>y</sub> and Ni<sub>1-y</sub>(SiO<sub>2</sub>)<sub>y</sub> films.展开更多
The strategy of a reliable transition temperature control of vanadium dioxide(VO2)is reported.Rectangular VO2 nanobeams were synthesized by a thermal chemical vapor deposition(TCVD)system.The metal-insulator transitio...The strategy of a reliable transition temperature control of vanadium dioxide(VO2)is reported.Rectangular VO2 nanobeams were synthesized by a thermal chemical vapor deposition(TCVD)system.The metal-insulator transition(MIT)temperature increases to above 380K when the TiO2 ratio of the source is 5 at.%,although the Ti source is not physically doped into VO2 nanobeams.The XPS spectra of the V 2p orbital reveal the excessive oxidation of V after the TCVD processes with a higher TiO2 ratio,indicating that the TiO2 precursor is important in the O-doping of the surface V O bonds when forming volatile Ti-O gas species.Thus,TiO2 reactants can be used as a VO2 surface chemical modifier to manipulate the MIT transition temperature and maintain a homogenous VO2 phase,which is useful for a Mott device application with a record on/off switching ratio>104 and Mott transition temperature>380 K.展开更多
Manipulating metal-insulator transitions in strongly correlated materials is of great importance in condensed matter physics,with implications for both fundamental science and technology.Vanadium dioxide(VO_(2)),as an...Manipulating metal-insulator transitions in strongly correlated materials is of great importance in condensed matter physics,with implications for both fundamental science and technology.Vanadium dioxide(VO_(2)),as an ideal model system,is metallic at high temperatures and shown a typical metal-insulator structural phase transition at 341 K from rutile structure to monoclinic structure.This behavior has been absorbed tons of attention for years.However,how to control this phase transition is still challenging and little studied.Here we demonstrated that to control the Ag nanonet arrays(NAs)in monoclinic VO_(2)(M)could be effective to adjust this metal-insulator transition.With the increase of Ag NAs volume fraction by reducing the template spheres size,the transition temperature(Tc)decreased from 68°C to 51°C.The mechanism of Tc decrease was revealed as:the carrier density increases through the increase of Ag NAs volume fraction,and more free electrons injected into the VO_(2)films induced greater absorption energy at the internal nanometal-semiconductor junction.These results supply a new strategy to control the metal-insulator transitions in VO_(2),which must be instructive for the other strongly correlated materials and important for applications.展开更多
Tin dioxide (SnO2) has attracted broad interest due to its particular gas-sensor property. Nano- or atom-scale SnO2 material has always been the aim in order to ultimately improve the sensitivity. However, until now, ...Tin dioxide (SnO2) has attracted broad interest due to its particular gas-sensor property. Nano- or atom-scale SnO2 material has always been the aim in order to ultimately improve the sensitivity. However, until now, it remains difficult to synthesize SnO2 nanoclusters by using traditional methods. In the present work, we have achieved the preparation of SnO2 nanoclusters by using the cluster beam deposition technique. The obtained nanoclusters were well characterized by high resolution transmission electron microscope HR-TEM. Results indicated the formation of the well-dispersed SnO2 nanoclusters with uniform size distribution (5-7 nm). Furthermore, an obvious metal insulator transition was observed by gating with ionic liquid. Combined with theory calculation, the corresponding mechanism was systematically analyzed from oxygen vacancy induced electron doping.展开更多
In this paper, we present a monolithic integration of a self-protected AlGaN/GaN metal-insulator field-effect transistor （MISFET）. An integrated field-controlled diode on the drain side of the AlGaN/GaN MISFET featu...In this paper, we present a monolithic integration of a self-protected AlGaN/GaN metal-insulator field-effect transistor （MISFET）. An integrated field-controlled diode on the drain side of the AlGaN/GaN MISFET features a self- protected function for a reverse bias. This diode takes advantage of the recessed-barrier enhancement-mode technique to realize an ultra-low voltage drop and a low turn-ON voltage. In the smart monolithic integration, this integrated diode can block a reverse bias （〉 70 V/μm） and suppress the leakage current （〈 5 × 10-11 A/mm）. Compared with conventional monolithic integration, the numerical results show that the MISET integrated with a field-controlled diode leads to a good performance for smart power integration. And the power loss is lower than 50% in conduction without forward current degeneration.展开更多
As one of intriguing physical results of electronic reconstruction,the metal-insulator transition plays an important role in exploring new electronic devices.In this study,the density functional theory is employed to ...As one of intriguing physical results of electronic reconstruction,the metal-insulator transition plays an important role in exploring new electronic devices.In this study,the density functional theory is employed to investigate the metal-insulator transition in(LaTiO3)m/(CaVO3)n superlattices.Herein,three kinds of physical avenues,i.e.,stacking orientation,epitaxial strain,and thickness periods,are used to tune the metal-insulator transition.Our calculations find that the[001]-and[110]-oriented(LaTiO3)1/(CaVO3)1 superlattices on SrTiO3 substrate are insulating,while[111]-oriented case is metallic.Such metallic behavior in[111]orientation can also be modulated by epitaxial strain.Besides the structural orientation and strain effect,the highly probable metal-insulator transition is presented in(LaTiO3)m/(CaVO3)n superlattices with increasing thickness.In addition,several interesting physical phenomena have also been revealed,such as selective charge transfer,charge ordering,and orbital ordering.展开更多
We investigate the metal-insulator transition in quasi-one-dimensional organic crystals of tetrathiotetracene-iodide, TTT2I3, in the 2D model. A crystal physical model is applied which takes into account two the most ...We investigate the metal-insulator transition in quasi-one-dimensional organic crystals of tetrathiotetracene-iodide, TTT2I3, in the 2D model. A crystal physical model is applied which takes into account two the most important hole-phonon interaction mechanisms. One is similar to that of deformation potential and the other is of polaron type. The scattering on defects is also considered and it is crucial for the explanation of the transition. The phonon polarization operator and the renormalized phonon spectrum are calculated in the random phase approximation for different temperatures applying the method of Green functions. We show that the transition is of Peierls type. The effect of lattice distortion on the dispersion of renormalized acoustic phonons is analyzed.展开更多
We discuss hole-induced magnetic solitons and metal-insulator transition of transport properties in diluted magnetic semiconductors Ga1-xMnxAs from the standpoint of a field theoretical formulation, and analyze experi...We discuss hole-induced magnetic solitons and metal-insulator transition of transport properties in diluted magnetic semiconductors Ga1-xMnxAs from the standpoint of a field theoretical formulation, and analyze experimental data of transport properties, using the supersymmetry sigma formula and the effective Lagrangian of diffusion model.展开更多
Due to the limitations of traditional silicon-based semiconductors at the nanoscale,such as short-channel effects and quantum effects,two-dimensional(2D)transition metal dichalcogenides(TMDs)like MoS_(2) and MoTe_(2) ...Due to the limitations of traditional silicon-based semiconductors at the nanoscale,such as short-channel effects and quantum effects,two-dimensional(2D)transition metal dichalcogenides(TMDs)like MoS_(2) and MoTe_(2) are increasingly recognized for their remarkable characteristics.These materials exhibit unique properties,including tunable bandgaps and the ability to mitigate electron scattering.The metal-insulator transition(MIT),a special electrical property found in some 2D materials,holds great potential for various applications.The MIT in TMDs can be induced through external parameters,but challenges like charge inhomogeneity and the detrimental effects of ionic liquid gating complicate device fabrication and measurement.In this work,we report the MIT behavior in an isoelectronic doped transition metal dichalcogenide MoS_(2(1-x))Se2_(x).By studying the dependence of conductivity on temperature in MoS_(2(1-x))Se_(2)x field-effect transistors employing a single back-gate device structure,we observe clear evidence of the metal-insulator transition in the electron carriers.More importantly,we demonstrate that this MIT behavior can be replicated in other 2D material systems that lack such properties by heterostructure engineering.Our research lays the foundation for further enhancing the performance of 2D materials and may lead to broader applications in functional electronic devices.展开更多
Two-dimensional transition metal dichalcogenides(2D TMDs)with metal-insulator transition(MIT)have garnered significant attention for their potential in elucidating electronic state regulation mechanisms and advancing ...Two-dimensional transition metal dichalcogenides(2D TMDs)with metal-insulator transition(MIT)have garnered significant attention for their potential in elucidating electronic state regulation mechanisms and advancing novel electronic devices,ultra-low power switches,and memory technologies.Generally,MIT behavior is often obscured by Schottky barrier(SB).Previous approaches,such as using four-probe methods or barrier-free van der Waals(vdW)semimetal electrodes,have aimed to eliminate the influence of SB on MIT.However,these methods are either complicated by intricate fabrication and testing processes or limited by the availability of suitable semimetal electrodes.Here,we demonstrated a bias voltage(Vds)-switchable MIT in pure vdW TMDs field-effect transistors(FETs)for the first time,driven by Vds-tunable effective SB and charge injection mechanisms.We identified a conversion voltage(V_(conversion)),which can be reduced by eliminating extra tunneling barriers introduced by vdW gaps before the inherent SB.This work offers comprehensive perspective on how tunneling barriers influence MIT and introduces a straightforward approach to fabricating MIT-based electronic devices.展开更多
Oxygen usually plays crucial roles in tuning the phase structures and functionalities of complex oxides such as high temperature superconductivity, colossal magnetoresistance, catalysis, etc. Effective and considerabl...Oxygen usually plays crucial roles in tuning the phase structures and functionalities of complex oxides such as high temperature superconductivity, colossal magnetoresistance, catalysis, etc. Effective and considerable control of the oxygen content in those functional oxides could be highly desired. Here, using perovskite manganite(La0.5Sr0.5)MnO3 as a paradigm, we develop a new pathway to synthesize the epitaxial thin films assisted by an in-situ chemical process, where the oxygen content can be precisely controlled by varying oxidative activity tuned by the atmospheric temperature(Tatm)during the growth. A hidden metal-insulator transition(MIT)emerges due to the phase competition, which is never shown in the phase diagram of this classic manganite. The oxygenmediated interaction between Mn ions together with the change of carrier density might be responsible for this emerging phase, which is compatible with the results of firstprinciple calculations. This work demonstrates that, apart from traditional cation doping, a precise modulation of anion(O2-, S2-, etc.) may provide a new strategy to control phase structures and functionalities of epitaxial compound thin films.展开更多
The quantum limit, where only the lowest Landau level is occupied by electrons, can be achieved under a high magnetic field when the Landau level splitting is comparable with the Fermi energy. The rather small Fermi p...The quantum limit, where only the lowest Landau level is occupied by electrons, can be achieved under a high magnetic field when the Landau level splitting is comparable with the Fermi energy. The rather small Fermi pockets and Fermi energy in CaFeAsF reported recently make this compound a good candidate for investigating the electrical transport near the quantum limit.Here, we report high-field experiments up to 65 T on a single-crystalline CaFeAsF, which shows a metal-insulator quantum phase transition tuned by the out-of-plane magnetic field. The obtained critical exponent zν through the finite-size scaling analysis is very close to 4/3. This transition is closely associated with the evolution of electronic states approaching the quantum limit.The resistivity behaviors as a function of field and temperature were evaluated based on Adams-Holstein theory(A-H theory).Moreover, the in-plane component of the field, which does not affect the transport behavior in the classical region, suppressed the magnetoresistance near the quantum limit.展开更多
Optical control of exotic properties in strongly correlated electron materials is very attractive owing to their potential applications in optical and electronic devices.Herein,we demonstrate a vertical heterojunction...Optical control of exotic properties in strongly correlated electron materials is very attractive owing to their potential applications in optical and electronic devices.Herein,we demonstrate a vertical heterojunction made of a correlated electron oxide thin film VO_(2) and a conductive 0.05 wt% Nb-doped TiO_(2) single crystal,whose metal-insulator transition(MIT)across the nanoscale heterointerface can be efficiently modulated by visible light irradiation.The magnitude of the MIT decreases from ~350 in the dark state to ~7 in the illuminated state,obeying a power law with respect to the light power density.The junction resistance is switched in a reversible and synchronous manner by turning light on and off.The optical tunability of it is also exponentially proportional to the light power density,and a 320-fold on/off ratio is achieved with an irradiance of 65.6 mW cm^(-2) below the MIT temperature.While the VO_(2) thin film is metallic above the MIT temperature,the optical tunability is remarkably weakened,with a one-fold change remaining under light illumination.These results are co-attributed to a net reduction(~15 meV)in the apparent barrier height and the photocarrier-injection-induced metallization of the VO_(2) heterointerface through a photovoltaic effect,which is induced by deep defect level transition upon the visible light irradiance at low temperature.Additionally,the optical tunability is minimal,resulting from the quite weak modulation of the already metallic band structure in the Schottky-type junction above the MIT temperature.This work enables a remotely optical scheme to manipulate the MIT,implying potential uncooled photodetection and photoswitch applications.展开更多
Using the extensively studied V_(2)O_(3) as a prototype system, we investigate the role of percolation in metal-insulator transition(MIT). We apply scanning microwave impedance microscopy to directly determine the met...Using the extensively studied V_(2)O_(3) as a prototype system, we investigate the role of percolation in metal-insulator transition(MIT). We apply scanning microwave impedance microscopy to directly determine the metallic phase fraction p and relate it to the macroscopic conductance G, which shows a sudden jump when p reaches the percolation threshold. Interestingly, the conductance G exhibits a hysteretic behavior against p, suggesting two different percolating processes upon cooling and warming. Based on our image analysis and model simulation, we ascribe such hysteretic behavior to different domain nucleation and growth processes between cooling and warming, which is likely caused by the decoupled structural and electronic transitions in V_(2)O_(3) during MIT. Our work provides a microscopic view of how the interplay of structural and electronic degrees of freedom affects MIT in strongly correlated systems.展开更多
To interpret the metal-insulator transition and depression of Tc induced by Pr-and Ce-doping in YBa_2Cu_3O_7, we propose a model of mixed local hole states which describe a strong admixture of 4f^1 state with states o...To interpret the metal-insulator transition and depression of Tc induced by Pr-and Ce-doping in YBa_2Cu_3O_7, we propose a model of mixed local hole states which describe a strong admixture of 4f^1 state with states of 4f^2 plus a hole in the CuO_2 planes for Y_(1-x)-Pr_x-0_7 and 4f^0 state with states of 4f^1 plus a hole in Y_(1-x)Ce_x-O_7. Our model resolves the controversy between the magnetic and spectroscopic measurements. As a natural consequence, most of the experimental results on Y_(1-x)Pr_x-O_7 can be explained and certain properties of Y_(1-x)Ce_x-O_7 are predicted. The critical doping density of Pr will take the value of x_c ≈0.5.展开更多
Using the determinant quantum Monte Carlo method,we explore a rich phase diagram featuring strain-induced metal-insulator and magnetic phase transitions in an interacting two-dimensional Dirac fermion system.Asymmetri...Using the determinant quantum Monte Carlo method,we explore a rich phase diagram featuring strain-induced metal-insulator and magnetic phase transitions in an interacting two-dimensional Dirac fermion system.Asymmetric strain applied along the zigzag crystal direction drives the semimetallic regime into a band-insulating phase,or it breaks the antiferromagnetic order of the Mott insulator,inducing a nonmagnetic insulating phase under strong correlations.The critical strain required for band gap opening or for a transport phase transition is significantly reduced in the presence of Coulomb repulsion,while increasing interaction strength makes it more difficult for strain to induce a nonmagnetic phase transition.In addition,we measure in detail the band gap modulation by strain and identify a doping effect whereby doping inhibits band gap opening.Our results provide an effective way to tune the transport gap,which could help extend the applications of graphene,whose zero band gap currently limits its use.展开更多
The transport properties of two-dimensional(2D)molybdenum diselenide(MoSe_(2))were comprehensively investigated.To understand experimental data,a detailed transport theory was developed by considering charged impurity...The transport properties of two-dimensional(2D)molybdenum diselenide(MoSe_(2))were comprehensively investigated.To understand experimental data,a detailed transport theory was developed by considering charged impurity,acoustic phonon,and optical phonon scatterings,and excellent quantitative agreements were obtained between theory and experiment.The observed metal-insulator transition(MIT)in MoSe_(2)is attributed to the screened Coulombic disorder arising from the random distribution of charged impurities in the semiconductor structures,indicating that MoSe_(2)2D MIT is a finite-temperature density-inhomogeneity-driven effective transition.We argue that the critical carrier density(nc)is sensitive to impurity density(ni)as a result of the competition with intrinsic phonons.Due to low impurity density,our devices show linear ohmic contact between the channel and electrodes.Furthermore,high performance MoSe_(2)all-2D photodetectors are fabricated by using a transparent electrode on a hexagonal boron nitride(hBN)substrate.The fabricated all-2D MoSe_(2)photodetectors demonstrate a substantial enhancement of photocurrent due to multiple reflections at the hBN and MoSe_(2)interface.Additionally,they exhibit a high photo-to-dark current ratio(1.1×10^(4)),high responsivity(3500 A/W),and high detectivity(5.8×10^(10)Jones).展开更多
Metal-insulator transition(MIT)in perovskite iridium oxides Sr_(n+1)IrnO_(3n+1)represents one of the most attractive phenomena exemplifying the cooperation of Coulomb interaction and spin-orbit coupling(SOC).MIT takes...Metal-insulator transition(MIT)in perovskite iridium oxides Sr_(n+1)IrnO_(3n+1)represents one of the most attractive phenomena exemplifying the cooperation of Coulomb interaction and spin-orbit coupling(SOC).MIT takes place when Sr_(n+1)IrnO_(3n+1)(n=1,2)is doped with carriers.While electron-doped Sr_(n+1)IrnO_(3n+1)(n=1,2)systems have been extensively investigated,hole-doped samples are still limited.Here,we report the first growth of Fe-doped(hole-doped)Sr_(3)Ir_(2)O_(7)single crystals[Sr_3(Ir_(1-x)Fe_x)_(2)O_(7)]with the doping level 0.1≤x≤0.28.An MIT behavior is observed at the doping level of x~0.16 from resistivity measurements.Electronic structures of Fe-doped Sr_(3)Ir_(2)O_(7)have been revealed by angle-resolved photoemission spectroscopy(ARPES)measurements.The evident energy shift of the band structure indicates higher hole-doping level as compared with Rh-doped Sr_(3)Ir_(2)O_(7).Our results demonstrate that Fe doping serves as an effective approach for heavily hole doping in Sr_(3)Ir_(2)O_(7),thereby offering a powerful strategy to modulate MIT in this material system.展开更多
The metal-insulator transition （MIT） of VO2 （M） nanorods was studied. It was found that there were two MITs in the differential scanning calorimetry （DSC） curves of the VO2（M） nanorods, one situated at low tem...The metal-insulator transition （MIT） of VO2 （M） nanorods was studied. It was found that there were two MITs in the differential scanning calorimetry （DSC） curves of the VO2（M） nanorods, one situated at low temperature from -3 ℃ to 19 ℃ and the other was at high temperature of 65-74℃. The low temperature MIT was always accompanied with VO2（B） nanorods, and the high temperature MIT existed singly only in pure VO2（M） nanorods. The mechanisms of these two MITs were analyzed and discussed.展开更多
The influence of aluminum doping at Mn-site in nanograin compound La0.8Sr0.2MnO3 was investigated based on X-ray diffraction, scanning electron microscope and resistivity measurement, in the light of structure and tra...The influence of aluminum doping at Mn-site in nanograin compound La0.8Sr0.2MnO3 was investigated based on X-ray diffraction, scanning electron microscope and resistivity measurement, in the light of structure and transport properties. The results showed that Al doping was favorable to the globurizing of powders and grain size uniformity, however, depressed the particles growth. The resistivity of system increased rapidly and the metal-insulator transition temperature (TIM) and room temperature magnetoresistance decreased as the aluminum concentration increased. In the T>TIM region, the current carriers were moving in variable range transition mode. The resistivity of La0.8Sr0.2Mn1-xAlxO3 for x=0.05 and 0.1 satisfied metal model in the T<TIM region. The characteristics of the transport behavior for aluminum doping were analyzed in terms of destroying the double exchange channel of Mn3+-O-Mn4+, distortion of the cell lattice and change of powder particles size and shape.展开更多
文摘Near the metal-insulator transition, the Hall coefficient R of metal-insulator composites (M-I composite) can be up to 104 times larger than that in the pure metal called Giant Hall effect. Applying the physical model for alloys with phase separation developed in [1] [2], we conclude that the Giant Hall effect is caused by an electron transfer away from the metallic phase to the insulating phase occupying surface states. These surface states are the reason for the granular structure typical for M-I composites. This electron transfer can be described by [1] [2], provided that long-range diffusion does not happen during film production (n is the electron density in the phase A. u<sub>A </sub>and u<sub>B</sub> are the volume fractions of the phase A (metallic phase) and phase B (insulator phase). β is a measure for the average potential difference between the phases A and B). A formula for calculation of R of composites is derived and applied to experimental data of granular Cu<sub>1-y</sub>(SiO<sub>2</sub>)<sub>y</sub> and Ni<sub>1-y</sub>(SiO<sub>2</sub>)<sub>y</sub> films.
基金This study was supported through the National Research Foundation of Korea[NRF-2019M3F3A1A03079739 and NRF-2019R1A2C2003804]of the Ministry of Science and ICT,Republic of Korea.This study was partially supported by Leaders in Industryuniversity Cooperation+Project,supported by the Ministry of Education,Republic of Korea and by Ajou University.Minhwan Ko and Sang Yeon Lee contributed equally to this study.
文摘The strategy of a reliable transition temperature control of vanadium dioxide(VO2)is reported.Rectangular VO2 nanobeams were synthesized by a thermal chemical vapor deposition(TCVD)system.The metal-insulator transition(MIT)temperature increases to above 380K when the TiO2 ratio of the source is 5 at.%,although the Ti source is not physically doped into VO2 nanobeams.The XPS spectra of the V 2p orbital reveal the excessive oxidation of V after the TCVD processes with a higher TiO2 ratio,indicating that the TiO2 precursor is important in the O-doping of the surface V O bonds when forming volatile Ti-O gas species.Thus,TiO2 reactants can be used as a VO2 surface chemical modifier to manipulate the MIT transition temperature and maintain a homogenous VO2 phase,which is useful for a Mott device application with a record on/off switching ratio>104 and Mott transition temperature>380 K.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11904299 and U1930124)the Foundation of China Academy of Engineering Physics(Grant No.2018AB02)。
文摘Manipulating metal-insulator transitions in strongly correlated materials is of great importance in condensed matter physics,with implications for both fundamental science and technology.Vanadium dioxide(VO_(2)),as an ideal model system,is metallic at high temperatures and shown a typical metal-insulator structural phase transition at 341 K from rutile structure to monoclinic structure.This behavior has been absorbed tons of attention for years.However,how to control this phase transition is still challenging and little studied.Here we demonstrated that to control the Ag nanonet arrays(NAs)in monoclinic VO_(2)(M)could be effective to adjust this metal-insulator transition.With the increase of Ag NAs volume fraction by reducing the template spheres size,the transition temperature(Tc)decreased from 68°C to 51°C.The mechanism of Tc decrease was revealed as:the carrier density increases through the increase of Ag NAs volume fraction,and more free electrons injected into the VO_(2)films induced greater absorption energy at the internal nanometal-semiconductor junction.These results supply a new strategy to control the metal-insulator transitions in VO_(2),which must be instructive for the other strongly correlated materials and important for applications.
基金supported by the National Natural Science Foundation of China(No.11704325,No.11604288,and No.11774178)the Natural Science Foundation of Jiangsu Province(BK20170473,BK20160061)the Joint Open Fund of Jiangsu Collaborative Innovation Center for Ecological Building Material and Environmental Protection Equipment and Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province(JH201843)
文摘Tin dioxide (SnO2) has attracted broad interest due to its particular gas-sensor property. Nano- or atom-scale SnO2 material has always been the aim in order to ultimately improve the sensitivity. However, until now, it remains difficult to synthesize SnO2 nanoclusters by using traditional methods. In the present work, we have achieved the preparation of SnO2 nanoclusters by using the cluster beam deposition technique. The obtained nanoclusters were well characterized by high resolution transmission electron microscope HR-TEM. Results indicated the formation of the well-dispersed SnO2 nanoclusters with uniform size distribution (5-7 nm). Furthermore, an obvious metal insulator transition was observed by gating with ionic liquid. Combined with theory calculation, the corresponding mechanism was systematically analyzed from oxygen vacancy induced electron doping.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60906037)the Fundamental Research Funds for the Central Universities,China (Grant No. ZYGX2009J027)the Foundation of State Key Laboratory of Electronic Thin Films and Integrated Devices
文摘In this paper, we present a monolithic integration of a self-protected AlGaN/GaN metal-insulator field-effect transistor （MISFET）. An integrated field-controlled diode on the drain side of the AlGaN/GaN MISFET features a self- protected function for a reverse bias. This diode takes advantage of the recessed-barrier enhancement-mode technique to realize an ultra-low voltage drop and a low turn-ON voltage. In the smart monolithic integration, this integrated diode can block a reverse bias （〉 70 V/μm） and suppress the leakage current （〈 5 × 10-11 A/mm）. Compared with conventional monolithic integration, the numerical results show that the MISET integrated with a field-controlled diode leads to a good performance for smart power integration. And the power loss is lower than 50% in conduction without forward current degeneration.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11804168 and 51872145)the Natural Science Foundation of Jiangsu Province,China(Grant Nos.BK20180736 and BK20190726)+1 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.18KJB140009)the Science Foundation from Nanjing University of Posts and Telecommunications,China(Grant No.NY219026).
文摘As one of intriguing physical results of electronic reconstruction,the metal-insulator transition plays an important role in exploring new electronic devices.In this study,the density functional theory is employed to investigate the metal-insulator transition in(LaTiO3)m/(CaVO3)n superlattices.Herein,three kinds of physical avenues,i.e.,stacking orientation,epitaxial strain,and thickness periods,are used to tune the metal-insulator transition.Our calculations find that the[001]-and[110]-oriented(LaTiO3)1/(CaVO3)1 superlattices on SrTiO3 substrate are insulating,while[111]-oriented case is metallic.Such metallic behavior in[111]orientation can also be modulated by epitaxial strain.Besides the structural orientation and strain effect,the highly probable metal-insulator transition is presented in(LaTiO3)m/(CaVO3)n superlattices with increasing thickness.In addition,several interesting physical phenomena have also been revealed,such as selective charge transfer,charge ordering,and orbital ordering.
文摘We investigate the metal-insulator transition in quasi-one-dimensional organic crystals of tetrathiotetracene-iodide, TTT2I3, in the 2D model. A crystal physical model is applied which takes into account two the most important hole-phonon interaction mechanisms. One is similar to that of deformation potential and the other is of polaron type. The scattering on defects is also considered and it is crucial for the explanation of the transition. The phonon polarization operator and the renormalized phonon spectrum are calculated in the random phase approximation for different temperatures applying the method of Green functions. We show that the transition is of Peierls type. The effect of lattice distortion on the dispersion of renormalized acoustic phonons is analyzed.
文摘We discuss hole-induced magnetic solitons and metal-insulator transition of transport properties in diluted magnetic semiconductors Ga1-xMnxAs from the standpoint of a field theoretical formulation, and analyze experimental data of transport properties, using the supersymmetry sigma formula and the effective Lagrangian of diffusion model.
基金supported by the National Natural Science Foundation of China(Nos.92464303,U23A20364,and 62274121)the Open Research Fund of Suzhou Laboratory(No.SZLAB-1508-2024-ZD014)the Wuhan Industrial Innovation Joint Laboratory(No.2024050902040443).
文摘Due to the limitations of traditional silicon-based semiconductors at the nanoscale,such as short-channel effects and quantum effects,two-dimensional(2D)transition metal dichalcogenides(TMDs)like MoS_(2) and MoTe_(2) are increasingly recognized for their remarkable characteristics.These materials exhibit unique properties,including tunable bandgaps and the ability to mitigate electron scattering.The metal-insulator transition(MIT),a special electrical property found in some 2D materials,holds great potential for various applications.The MIT in TMDs can be induced through external parameters,but challenges like charge inhomogeneity and the detrimental effects of ionic liquid gating complicate device fabrication and measurement.In this work,we report the MIT behavior in an isoelectronic doped transition metal dichalcogenide MoS_(2(1-x))Se2_(x).By studying the dependence of conductivity on temperature in MoS_(2(1-x))Se_(2)x field-effect transistors employing a single back-gate device structure,we observe clear evidence of the metal-insulator transition in the electron carriers.More importantly,we demonstrate that this MIT behavior can be replicated in other 2D material systems that lack such properties by heterostructure engineering.Our research lays the foundation for further enhancing the performance of 2D materials and may lead to broader applications in functional electronic devices.
基金supported by the open research of Songshan Lake Materials Laboratory(No.2023SLABFK07)the National Science Foundation of China(Nos.62304151,62204170,and 62474124)+2 种基金the Natural Science Foundation of Tianjin(No.24JCQNJC00520)the China Postdoctoral Science Foundation(No.2023M742585)the State Key Laboratory of Fluid Power and Mechatronic Systems under Grant(No.GZKF-202327).
文摘Two-dimensional transition metal dichalcogenides(2D TMDs)with metal-insulator transition(MIT)have garnered significant attention for their potential in elucidating electronic state regulation mechanisms and advancing novel electronic devices,ultra-low power switches,and memory technologies.Generally,MIT behavior is often obscured by Schottky barrier(SB).Previous approaches,such as using four-probe methods or barrier-free van der Waals(vdW)semimetal electrodes,have aimed to eliminate the influence of SB on MIT.However,these methods are either complicated by intricate fabrication and testing processes or limited by the availability of suitable semimetal electrodes.Here,we demonstrated a bias voltage(Vds)-switchable MIT in pure vdW TMDs field-effect transistors(FETs)for the first time,driven by Vds-tunable effective SB and charge injection mechanisms.We identified a conversion voltage(V_(conversion)),which can be reduced by eliminating extra tunneling barriers introduced by vdW gaps before the inherent SB.This work offers comprehensive perspective on how tunneling barriers influence MIT and introduces a straightforward approach to fabricating MIT-based electronic devices.
基金financially supported by the National Key Research and Development Program of China (2016YFA0302300)the support from the National Natural Science Foundation of China (51332001)the Fundamental Research Funds for the Central Universities (2017EYT26)
文摘Oxygen usually plays crucial roles in tuning the phase structures and functionalities of complex oxides such as high temperature superconductivity, colossal magnetoresistance, catalysis, etc. Effective and considerable control of the oxygen content in those functional oxides could be highly desired. Here, using perovskite manganite(La0.5Sr0.5)MnO3 as a paradigm, we develop a new pathway to synthesize the epitaxial thin films assisted by an in-situ chemical process, where the oxygen content can be precisely controlled by varying oxidative activity tuned by the atmospheric temperature(Tatm)during the growth. A hidden metal-insulator transition(MIT)emerges due to the phase competition, which is never shown in the phase diagram of this classic manganite. The oxygenmediated interaction between Mn ions together with the change of carrier density might be responsible for this emerging phase, which is compatible with the results of firstprinciple calculations. This work demonstrates that, apart from traditional cation doping, a precise modulation of anion(O2-, S2-, etc.) may provide a new strategy to control phase structures and functionalities of epitaxial compound thin films.
基金supported by the Youth Innovation Promotion Association of the Chinese Academy of Sciences (Grant Nos. 2015187, and 2016215)National Natural Science Foundation of China (Grant Nos. 11574338, 11204338, and 11404359)and the ”Strategic Priority Research Program (B)” of the Chinese Academy of Sciences (Grant No. XDB04040300)
文摘The quantum limit, where only the lowest Landau level is occupied by electrons, can be achieved under a high magnetic field when the Landau level splitting is comparable with the Fermi energy. The rather small Fermi pockets and Fermi energy in CaFeAsF reported recently make this compound a good candidate for investigating the electrical transport near the quantum limit.Here, we report high-field experiments up to 65 T on a single-crystalline CaFeAsF, which shows a metal-insulator quantum phase transition tuned by the out-of-plane magnetic field. The obtained critical exponent zν through the finite-size scaling analysis is very close to 4/3. This transition is closely associated with the evolution of electronic states approaching the quantum limit.The resistivity behaviors as a function of field and temperature were evaluated based on Adams-Holstein theory(A-H theory).Moreover, the in-plane component of the field, which does not affect the transport behavior in the classical region, suppressed the magnetoresistance near the quantum limit.
基金supported by the Fundamental Research Funds for the Central Universities(108-4115100092)the National Key Research and Development Program of China(2016YFA0300102 and 2017YFA0205004)+2 种基金the National Natural Science Foundation of China(11775224,11504358,11804324 and 52072102)the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology(2018CXFX001)the Natural Science Research Projects for the Colleges and Universities of Anhui Province(KJ2018A0660)。
文摘Optical control of exotic properties in strongly correlated electron materials is very attractive owing to their potential applications in optical and electronic devices.Herein,we demonstrate a vertical heterojunction made of a correlated electron oxide thin film VO_(2) and a conductive 0.05 wt% Nb-doped TiO_(2) single crystal,whose metal-insulator transition(MIT)across the nanoscale heterointerface can be efficiently modulated by visible light irradiation.The magnitude of the MIT decreases from ~350 in the dark state to ~7 in the illuminated state,obeying a power law with respect to the light power density.The junction resistance is switched in a reversible and synchronous manner by turning light on and off.The optical tunability of it is also exponentially proportional to the light power density,and a 320-fold on/off ratio is achieved with an irradiance of 65.6 mW cm^(-2) below the MIT temperature.While the VO_(2) thin film is metallic above the MIT temperature,the optical tunability is remarkably weakened,with a one-fold change remaining under light illumination.These results are co-attributed to a net reduction(~15 meV)in the apparent barrier height and the photocarrier-injection-induced metallization of the VO_(2) heterointerface through a photovoltaic effect,which is induced by deep defect level transition upon the visible light irradiance at low temperature.Additionally,the optical tunability is minimal,resulting from the quite weak modulation of the already metallic band structure in the Schottky-type junction above the MIT temperature.This work enables a remotely optical scheme to manipulate the MIT,implying potential uncooled photodetection and photoswitch applications.
基金Fudan University was supported by the National Natural Science Foundation of China (Grant Nos. 12074080, 11804052, 11827805,11725521, and 12035004)the National Postdoctoral Program for Innovative Talents (Grant No. BX20180079)+5 种基金the Shanghai Science and Technology Committee Rising-Star Program (Grant No. 19QA1401000)the Science and Technology Commission of Shanghai Municipality (Grant No.20JC1414700)the Major Project (Grant No. 2019SHZDZX01)the Ministry of Science and Technology of China (Grant Nos. 2017YFA03030002021YFA1400100)(synthesis, structural characterization and global transport of V2O3) at University of California San Diego was supported by the US Air Force Office of Scientific Research (Grant No.FA9550-20-1-0242)。
文摘Using the extensively studied V_(2)O_(3) as a prototype system, we investigate the role of percolation in metal-insulator transition(MIT). We apply scanning microwave impedance microscopy to directly determine the metallic phase fraction p and relate it to the macroscopic conductance G, which shows a sudden jump when p reaches the percolation threshold. Interestingly, the conductance G exhibits a hysteretic behavior against p, suggesting two different percolating processes upon cooling and warming. Based on our image analysis and model simulation, we ascribe such hysteretic behavior to different domain nucleation and growth processes between cooling and warming, which is likely caused by the decoupled structural and electronic transitions in V_(2)O_(3) during MIT. Our work provides a microscopic view of how the interplay of structural and electronic degrees of freedom affects MIT in strongly correlated systems.
文摘To interpret the metal-insulator transition and depression of Tc induced by Pr-and Ce-doping in YBa_2Cu_3O_7, we propose a model of mixed local hole states which describe a strong admixture of 4f^1 state with states of 4f^2 plus a hole in the CuO_2 planes for Y_(1-x)-Pr_x-0_7 and 4f^0 state with states of 4f^1 plus a hole in Y_(1-x)Ce_x-O_7. Our model resolves the controversy between the magnetic and spectroscopic measurements. As a natural consequence, most of the experimental results on Y_(1-x)Pr_x-O_7 can be explained and certain properties of Y_(1-x)Ce_x-O_7 are predicted. The critical doping density of Pr will take the value of x_c ≈0.5.
基金supported by the National Natural Science Foundation of China(Grant No.12474218)the Beijing Natural Science Foundation(Grant No.1242022)the Guangxi Key Laboratory of Precision Navigation Technology and Application,Guilin University of Electronic Technology(Grant No.DH202322)。
文摘Using the determinant quantum Monte Carlo method,we explore a rich phase diagram featuring strain-induced metal-insulator and magnetic phase transitions in an interacting two-dimensional Dirac fermion system.Asymmetric strain applied along the zigzag crystal direction drives the semimetallic regime into a band-insulating phase,or it breaks the antiferromagnetic order of the Mott insulator,inducing a nonmagnetic insulating phase under strong correlations.The critical strain required for band gap opening or for a transport phase transition is significantly reduced in the presence of Coulomb repulsion,while increasing interaction strength makes it more difficult for strain to induce a nonmagnetic phase transition.In addition,we measure in detail the band gap modulation by strain and identify a doping effect whereby doping inhibits band gap opening.Our results provide an effective way to tune the transport gap,which could help extend the applications of graphene,whose zero band gap currently limits its use.
基金supported by the National Research Foundation of Korea(NRF)(No.2021R1A2C1012176)support from the National Natural Science Foundation of China(No.62105018 and 61975007)+1 种基金the Fundamental Research Funds for the Central Universities 2021RC212Beijing Natural Science Foundation of China(Nos.Z190006 and 4222073).
文摘The transport properties of two-dimensional(2D)molybdenum diselenide(MoSe_(2))were comprehensively investigated.To understand experimental data,a detailed transport theory was developed by considering charged impurity,acoustic phonon,and optical phonon scatterings,and excellent quantitative agreements were obtained between theory and experiment.The observed metal-insulator transition(MIT)in MoSe_(2)is attributed to the screened Coulombic disorder arising from the random distribution of charged impurities in the semiconductor structures,indicating that MoSe_(2)2D MIT is a finite-temperature density-inhomogeneity-driven effective transition.We argue that the critical carrier density(nc)is sensitive to impurity density(ni)as a result of the competition with intrinsic phonons.Due to low impurity density,our devices show linear ohmic contact between the channel and electrodes.Furthermore,high performance MoSe_(2)all-2D photodetectors are fabricated by using a transparent electrode on a hexagonal boron nitride(hBN)substrate.The fabricated all-2D MoSe_(2)photodetectors demonstrate a substantial enhancement of photocurrent due to multiple reflections at the hBN and MoSe_(2)interface.Additionally,they exhibit a high photo-to-dark current ratio(1.1×10^(4)),high responsivity(3500 A/W),and high detectivity(5.8×10^(10)Jones).
基金supported by the National Natural Science Foundation of China(Grant No.12074358)the National Key Research and Development Program of China(Grant No.2024YFA1408103)+2 种基金the International Partnership Program of the Chinese Academy of Sciences(Grant No.123GJHZ2022035MI)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302802)the Fundamental Research Funds for the Central Universities(Grant No.WK3510000015)。
文摘Metal-insulator transition(MIT)in perovskite iridium oxides Sr_(n+1)IrnO_(3n+1)represents one of the most attractive phenomena exemplifying the cooperation of Coulomb interaction and spin-orbit coupling(SOC).MIT takes place when Sr_(n+1)IrnO_(3n+1)(n=1,2)is doped with carriers.While electron-doped Sr_(n+1)IrnO_(3n+1)(n=1,2)systems have been extensively investigated,hole-doped samples are still limited.Here,we report the first growth of Fe-doped(hole-doped)Sr_(3)Ir_(2)O_(7)single crystals[Sr_3(Ir_(1-x)Fe_x)_(2)O_(7)]with the doping level 0.1≤x≤0.28.An MIT behavior is observed at the doping level of x~0.16 from resistivity measurements.Electronic structures of Fe-doped Sr_(3)Ir_(2)O_(7)have been revealed by angle-resolved photoemission spectroscopy(ARPES)measurements.The evident energy shift of the band structure indicates higher hole-doping level as compared with Rh-doped Sr_(3)Ir_(2)O_(7).Our results demonstrate that Fe doping serves as an effective approach for heavily hole doping in Sr_(3)Ir_(2)O_(7),thereby offering a powerful strategy to modulate MIT in this material system.
基金V. ACKNOWLEDGMENTS This work was financially Natural Science Foundation supported by the National of China （No.51372250）.
文摘The metal-insulator transition （MIT） of VO2 （M） nanorods was studied. It was found that there were two MITs in the differential scanning calorimetry （DSC） curves of the VO2（M） nanorods, one situated at low temperature from -3 ℃ to 19 ℃ and the other was at high temperature of 65-74℃. The low temperature MIT was always accompanied with VO2（B） nanorods, and the high temperature MIT existed singly only in pure VO2（M） nanorods. The mechanisms of these two MITs were analyzed and discussed.
基金Project supported bythe Programfor New Century Excellent Talents in University
文摘The influence of aluminum doping at Mn-site in nanograin compound La0.8Sr0.2MnO3 was investigated based on X-ray diffraction, scanning electron microscope and resistivity measurement, in the light of structure and transport properties. The results showed that Al doping was favorable to the globurizing of powders and grain size uniformity, however, depressed the particles growth. The resistivity of system increased rapidly and the metal-insulator transition temperature (TIM) and room temperature magnetoresistance decreased as the aluminum concentration increased. In the T>TIM region, the current carriers were moving in variable range transition mode. The resistivity of La0.8Sr0.2Mn1-xAlxO3 for x=0.05 and 0.1 satisfied metal model in the T<TIM region. The characteristics of the transport behavior for aluminum doping were analyzed in terms of destroying the double exchange channel of Mn3+-O-Mn4+, distortion of the cell lattice and change of powder particles size and shape.
