Science.gov

Sample records for induced metal-insulator transition

  1. Metal-insulator-transition in SrTiO3 induced by argon bombardment combined with field effect

    SciTech Connect

    Xu, Jie; Zhu, Zhengyong; Zhao, Hengliang; Luo, Zhijiong

    2014-12-15

    By fabricating the Field-Effect-Transistors on argon bombardment SrTiO3 substrates, not only we have achieved one of the best mobility for Field-Effect-Transistors fabricated on SrTiO3, but also realized strong field induced Metal-Insulator-Transition. The critical sheet resistance for the Metal-Insulator-Transition is only 1/7 of the value obtained in the former experiments, indicating a different mechanism. Further study shows that the Metal-Insulator-Transition can be attributed to the oxygen vacancies formed after the bombardment becoming the electron donor under the electric field modulation, increasing SrTiO3 surface electron density and transforming the substrate into metallic state.

  2. Disorder-induced metal-insulator transition in cooled silver and copper nanoparticles: A statistical study

    NASA Astrophysics Data System (ADS)

    Medrano Sandonas, Leonardo; Landauro, Carlos V.

    2017-08-01

    The existence of a disorder-induced metal-insulator transition (MIT) has been proved in cooled silver and copper nanoparticles by using level spacing statistics. Nanoparticles are obtained by employing molecular dynamics simulations. Results show that structural disorder is not strong enough to affect their electronic character, and it remains in the metallic regime. Whereas, electronic properties cross to the insulating regime after increasing the chemical disorder strength, W / t . Then, based on scaling theory, we have found that the critical chemical disorder WC / t in which MIT happens for silver and copper nanoparticles are 24.0 ± 1.1 and 22.3 ± 0.9 , respectively. Its universality has also been studied.

  3. Field-Induced Reversible Phase Manipulation in Metal-Insulator Transition using Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Park, Se Jun

    2005-03-01

    Reversible electronic switching between insulating and metallic phases is a novel idea that may allow new types of field effect devices feasible.^1 Here we demonstrate the reversible manipulation between metallic and insulating phases in two-dimensional In nanowire arrays on Si(111) surface near the metal-insulator transition temperature (Tc). The electronic switching of phases was induced by local electric field applied by the probe tip of a scanning tunneling microscope. The field-dependent hysteresis behavior was also observed in tip height measurements as a function of the sample bias, under the constraint of constant tunneling current. A model including the intrinsic bi-stability of the nanometer-scale domains of In nanowire arrays will be discussed. ^1C. Ahn, J. Triscone, J. Mannhart, Nature 6952, 1015 (2003)

  4. Magnetic field induced metal-insulator transition in a kagome nanoribbon

    NASA Astrophysics Data System (ADS)

    Dey, Moumita; Maiti, Santanu K.; Karmakar, S. N.

    2011-11-01

    In the present work, we investigate two-terminal electron transport through a finite width kagome lattice nanoribbon in presence of a perpendicular magnetic field. We employ a simple tight-binding (T-B) Hamiltonian to describe the system and obtain the transmission properties by using Green's function technique within the framework of Landauer-Büttiker formalism. After presenting an analytical description of energy dispersion relation of a kagome nanoribbon in presence of the magnetic field, we investigate numerically the transmittance spectra together with the density of states and current-voltage characteristics. It is shown that for a specific value of the Fermi energy, the kagome network can exhibit a magnetic field induced metal-insulator transition, which is the central investigation of this communication. Our analysis may be inspiring in designing low-dimensional switching devices.

  5. Local Peltier-effect-induced reversible metal-insulator transition in VO2 nanowires

    NASA Astrophysics Data System (ADS)

    Takami, Hidefumi; Kanki, Teruo; Tanaka, Hidekazu

    2016-06-01

    We report anomalous resistance leaps and drops in VO2 nanowires with operating current density and direction, showing reversible and nonvolatile switching. This event is associated with the metal-insulator phase transition (MIT) of local nanodomains with coexistence states of metallic and insulating phases induced by thermoelectric cooling and heating effects. Because the interface of metal and insulator domains has much different Peltier coefficient, it is possible that a significant Peltier effect would be a source of the local MIT. This operation can be realized by one-dimensional domain configuration in VO2 nanowires because one straight current path through the electronic domain-interface enables theoretical control of thermoelectric effects. This result will open a new method of reversible control of electronic states in correlated electron materials.

  6. Metal-insulator transition at lanthanum aluminate-strontium titanate interface induced by oxygen plasma treatment

    NASA Astrophysics Data System (ADS)

    Dai, Weitao; Cen, Cheng

    The formation of two-dimensional electron gas (2DEG) at lanthanum aluminate (LAO)-strontium titanate (STO) interface, as well as the 2DEG's unique characters in metal-insulator transition, have evoked widespread interest. Highly insulating interfaces are obtained for the structures with LAO thickness below 3 unit cell (uc) and abrupt transition from an insulating to conducting interface was observed for samples with thicker LAO layers. For 3uc LAO/STO samples, reversible nanoscale control of the metal-insulator transition was implemented by a conductive AFM writing. Our research furtherly discovered a very stable metal-insulator transition can be achieved by oxygen plasma (OP) treatment for samples with thicker LAO layers. AFM imaging and XPS measurement demonstrated the low energy OP treatment altered only the surface bonds, which confirmed the importance of surface properties in the heterostructures. Then microscale Hall bars were patterned at the interface and imaged by electrostatic force microscope. Their transport and magnetic properties were measured. This research will promote deeper understanding about the interfacial metal-insulator transition mechanism and open new device opportunities. This work is supported by the Department of Energy Grant No. DE-SC-0010399 and National Science Foundation Grant No. NSF-1454950.

  7. Holographic lattices and metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Ling, Yi

    2015-10-01

    This paper is an extension of the talk given at the conference on Gravitation and Cosmology/The Fourth Galileo-Xu Guangqi Meeting. We intend to present a short review on recent progress on the construction of holographic lattices and its application to metal-insulator transition (MIT), which is a fundamentally important phenomenon in condensed matter physics. We will firstly implement the Peierls phase transition by constructing holographic charge density waves which are induced by the spontaneous breaking of translational symmetry. Then we turn to the holographic realization of metal-insulator transition as a quantum critical phenomenon with many strongly correlated electrons involved. The holographic entanglement entropy as a diagnostic for such quantum phase transitions will be briefly mentioned.

  8. Metal insulator transition induced by the magnetic field in n-type GaSb

    NASA Astrophysics Data System (ADS)

    Ghezzi, C.; Magnanini, R.; Parisini, A.

    2005-10-01

    The metal-insulator (MI) transition induced by a magnetic field was evidenced for the first time in compensated n-type GaSb layers grown by molecular beam epitaxy. The free electron densities were in the low 10 16 cm -3 range or even slightly lower, so that the zero-field 3D electron gas was degenerate and, at the BMI magnetic field of the MI transition, it populates only the spin-split 0 (+) Landau level (extreme quantum limit). On the metallic side of the MI transition a T1/3 dependence of the conductivity was assumed to fit the low- T data and to estimate the BMI value, which resulted of 9.1 T in the purest sample. The MI transition manifests in a strong increase of the diagonal resistivity with the magnetic field, but not of the Hall coefficient, suggesting that the apparent electron density is practically constant, whereas the mobility varies strongly. The evidence of a maximum in the temperature dependence of the Hall coefficient has been explained through a two channels transport mechanism involving localized and extended states.

  9. Approximating metal-insulator transitions

    NASA Astrophysics Data System (ADS)

    Danieli, Carlo; Rayanov, Kristian; Pavlov, Boris; Martin, Gaven; Flach, Sergej

    2015-12-01

    We consider quantum wave propagation in one-dimensional quasiperiodic lattices. We propose an iterative construction of quasiperiodic potentials from sequences of potentials with increasing spatial period. At each finite iteration step, the eigenstates reflect the properties of the limiting quasiperiodic potential properties up to a controlled maximum system size. We then observe approximate Metal-Insulator Transitions (MIT) at the finite iteration steps. We also report evidence on mobility edges, which are at variance to the celebrated Aubry-André model. The dynamics near the MIT shows a critical slowing down of the ballistic group velocity in the metallic phase, similar to the divergence of the localization length in the insulating phase.

  10. Magnetic field induced metal insulator transitions in p-SiGe

    NASA Astrophysics Data System (ADS)

    Coleridge, P. T.

    2003-09-01

    Low density modulation doped p-SiGe, where the holes lie in a strained SiGe quantum well, frequently exhibits anomalous insulating behaviour between filling factors ν=2 and 1. There is also anomalous metallic behavior with a metal-insulator transition between the two. It is shown that in these samples exchange effects are sufficiently large to induce the paramagnetic-ferromagnetic phase transition predicted by Giuliani and Quinn in 1985, also that the metallic and insulating behavior is associated with the coincidence of two Landau levels of opposite spin. A model calculation shows that while a ferromagnetic polarization may occur at integer filling factors screening suppresses it for non-integer filling factors. It is argued the Landau levels then stick-together and allow a spin-density instability to form. Because of the strong spin-orbit coupling in p-SiGe the transport properties of this state differ from those of other systems where a similar quantum Hall ferromagnet probably forms.

  11. Two-dimensional metal-insulator transition as a strong localization induced crossover phenomenon

    NASA Astrophysics Data System (ADS)

    Das Sarma, S.; Hwang, E. H.

    2014-06-01

    Low-disorder and high-mobility two-dimensional (2D) electron (or hole) systems confined in semiconductor heterostructures undergo an apparent metal-insulator transition (MIT) at low temperatures as the carrier density (n) is varied. In some situations, the 2D MIT can be caused at a fixed low carrier density by changing an externally applied in-plane magnetic field parallel to the 2D layer. The goal of the current work is to obtain the critical density (nc) for the 2D MIT with the system being an effective metal (Anderson insulator) for density n above (below) nc. We study the 2D MIT phenomenon theoretically as a possible strong localization induced crossover process controlled by the Ioffe-Regel criterion, kFl=1, where kF(n) is the 2D Fermi wave vector and l (n) is the disorder-limited quantum mean free path on the metallic side. Calculating the quantum mean free path in the effective metallic phase from a realistic Boltzmann transport theory including disorder scattering effects, we solve the integral equation (with l depending on n through multidimensional integrals) defined by the Ioffe-Regel criterion to obtain the nonuniversal critical density nc as a function of the applicable physical experimental parameters including disorder strength, in-plane magnetic field, spin and valley degeneracy, background dielectric constant and carrier effective mass, and temperature. The key physics underlying the nonuniversal parameter dependence of the critical density is the density dependence of the screened Coulomb disorder. Our calculated results for the crossover critical density nc appear to be in qualitative and semiquantitative agreement with the available experimental data in different 2D semiconductor systems lending credence to the possibility that the apparent 2D MIT signals the onset of the strong localization crossover in disordered 2D systems. We also compare the calculated critical density obtained from the Ioffe-Regel criterion with that obtained from a

  12. Oxygen Vacancy Induced Room-Temperature Metal-Insulator Transition in Nickelate Films and Its Potential Application in Photovoltaics.

    PubMed

    Wang, Le; Dash, Sibashisa; Chang, Lei; You, Lu; Feng, Yaqing; He, Xu; Jin, Kui-juan; Zhou, Yang; Ong, Hock Guan; Ren, Peng; Wang, Shiwei; Chen, Lang; Wang, Junling

    2016-04-20

    Oxygen vacancy is intrinsically coupled with magnetic, electronic, and transport properties of transition-metal oxide materials and directly determines their multifunctionality. Here, we demonstrate reversible control of oxygen content by postannealing at temperature lower than 300 °C and realize the reversible metal-insulator transition in epitaxial NdNiO₃ films. Importantly, over 6 orders of magnitude in the resistance modulation and a large change in optical bandgap are demonstrated at room temperature without destroying the parent framework and changing the p-type conductive mechanism. Further study revealed that oxygen vacancies stabilized the insulating phase at room temperature is universal for perovskite nickelate films. Acting as electron donors, oxygen vacancies not only stabilize the insulating phase at room temperature, but also induce a large magnetization of ∼50 emu/cm³ due to the formation of strongly correlated Ni²⁺ t(2g)⁶e(g)² states. The bandgap opening is an order of magnitude larger than that of the thermally driven metal-insulator transition and continuously tunable. Potential application of the newly found insulating phase in photovoltaics has been demonstrated in the nickelate-based heterojunctions. Our discovery opens up new possibilities for strongly correlated perovskite nickelates.

  13. Composition induced metal-insulator quantum phase transition in the Heusler type Fe2VAl

    NASA Astrophysics Data System (ADS)

    Naka, Takashi; Nikitin, Artem M.; Pan, Yu; de Visser, Anne; Nakane, Takayuki; Ishikawa, Fumihiro; Yamada, Yuh; Imai, Motoharu; Matsushita, Akiyuki

    2016-07-01

    We report the magnetism and transport properties of the Heusler compound Fe2+x V1-x Al at  -0.10  ⩽  x  ⩽  0.20 under pressure and a magnetic field. A metal-insulator quantum phase transition occurred at x  ≈  -0.05. Application of pressure or a magnetic field facilitated the emergence of finite zero-temperature conductivity σ 0 around the critical point, which scaled approximately according to the power law (P  -  P c ) γ . At x  ⩽  -0.05, a localized paramagnetic spin appeared, whereas above the ferromagnetic quantum critical point at x  ≈  0.05, itinerant ferromagnetism was established. At the quantum critical points at x  =  -0.05 and 0.05, the resistivity and specific heat exhibited singularities characteristic of a Griffiths phase appearing as an inhomogeneous electronic state.

  14. Carbon kagome lattice and orbital-frustration-induced metal-insulator transition for optoelectronics.

    PubMed

    Chen, Yuanping; Sun, Y Y; Wang, H; West, D; Xie, Yuee; Zhong, J; Meunier, V; Cohen, Marvin L; Zhang, S B

    2014-08-22

    A three-dimensional elemental carbon kagome lattice, made of only fourfold-coordinated carbon atoms, is proposed based on first-principles calculations. Despite the existence of 60° bond angles in the triangle rings, widely perceived to be energetically unfavorable, the carbon kagome lattice is found to display exceptional stability comparable to that of C(60). The system allows us to study the effects of triangular frustration on the electronic properties of realistic solids, and it demonstrates a metal-insulator transition from that of graphene to a direct gap semiconductor in the visible blue region. By minimizing s-p orbital hybridization, which is an intrinsic property of carbon, not only the band edge states become nearly purely frustrated p states, but also the band structure is qualitatively different from any known bulk elemental semiconductors. For example, the optical properties are similar to those of direct-gap semiconductors GaN and ZnO, whereas the effective masses are comparable to or smaller than those of Si.

  15. Switchable Metal-Insulator Phase Transition Metamaterials.

    PubMed

    Hajisalem, Ghazal; Nezami, Mohammadreza S; Gordon, Reuven

    2017-05-10

    We investigate the switching of a gap plasmon tunnel junction between conducting and insulating states. Hysteresis is observed in the second and the third harmonic generation power dependence, which arises by thermally induced disorder ("melting") of a two-carbon self-assembled monolayer between an ultraflat gold surface and metal nanoparticles. The hysteresis is observed for a variety of nanoparticle sizes, but not for larger tunnel junctions where there is no appreciable tunneling. By combining quantum corrected finite-difference time-domain simulations with nonlinear scattering theory, we calculate the changes in the harmonic generation between the tunneling and the insulating states, and good agreement is found with the experiments. This paves the way to a new class of metal-insulator phase transition switchable metamaterials, which may provide next-generation information processing technologies.

  16. Mott metal-insulator transition induced by utilizing a glasslike structural ordering in low-dimensional molecular conductors

    NASA Astrophysics Data System (ADS)

    Hartmann, Benedikt; Müller, Jens; Sasaki, Takahiko

    2014-11-01

    We utilize a glasslike structural transition in order to induce a Mott metal-insulator transition in the quasi-two-dimensional organic charge-transfer salt κ -(BEDT-TTF)2Cu [N (CN)2Br ]. In this material, the terminal ethylene groups of the BEDT-TTF molecules can adopt two different structural orientations within the crystal structure, namely eclipsed (E) and staggered (S) with the relative orientation of the outer C-C bonds being parallel and canted, respectively. These two conformations are thermally disordered at room temperature and undergo a glasslike ordering transition at Tg˜75 K. When cooling through Tg, a small fraction that depends on the cooling rate remains frozen in the S configuration, which is of slightly higher energy, corresponding to a controllable degree of structural disorder. We demonstrate that, when thermally coupled to a low-temperature heat bath, a pulsed heating current through the sample causes a very fast relaxation with cooling rates at Tg of the order of several 1000 K /min . The freezing of the structural degrees of freedom causes a decrease of the electronic bandwidth W with increasing cooling rate, and hence a Mott metal-insulator transition as the system crosses the critical ratio (W/U ) c of bandwidth to on-site Coulomb repulsion U . Due to the glassy character of the transition, the effect is persistent below Tg and can be reversibly repeated by melting the frozen configuration upon warming above Tg. Both by exploiting the characteristics of slowly changing relaxation times close to this temperature and by controlling the heating power, the materials can be fine-tuned across the Mott transition. A simple model allows for an estimate of the energy difference between the E and S state as well as the accompanying degree of frozen disorder in the population of the two orientations.

  17. Dynamically tracking the joule heating effect on the voltage induced metal-insulator transition in VO2 crystal film

    NASA Astrophysics Data System (ADS)

    Liao, G. M.; Chen, S.; Fan, L. L.; Chen, Y. L.; Wang, X. Q.; Ren, H.; Zhang, Z. M.; Zou, C. W.

    2016-04-01

    Insulator to metal phase transitions driven by external electric field are one of the hottest topics in correlated oxide study. While this electric triggered phenomena always mixes the electric field switching effect and joule thermal effect together, which are difficult to clarify the intrinsic mechanism. In this paper, we investigate the dynamical process of voltage-triggered metal-insulator transition (MIT) in a VO2 crystal film and observe the temperature dependence of the threshold voltages and switching delay times, which can be explained quite well based on a straightforward joule thermal model. By conducting the voltage controlled infrared transmittance measurement, the delayed infrared transmission change is also observed, further confirming the homogeneous switching process for a large-size film. All of these results show strong evidences that joule thermal effect plays a dominated role in electric-field-induced switching of VO2 crystal.

  18. Joule Heating-Induced Metal-Insulator Transition in Epitaxial VO2/TiO2 Devices.

    PubMed

    Li, Dasheng; Sharma, Abhishek A; Gala, Darshil K; Shukla, Nikhil; Paik, Hanjong; Datta, Suman; Schlom, Darrell G; Bain, James A; Skowronski, Marek

    2016-05-25

    DC and pulse voltage-induced metal-insulator transition (MIT) in epitaxial VO2 two terminal devices were measured at various stage temperatures. The power needed to switch the device to the ON-state decrease linearly with increasing stage temperature, which can be explained by the Joule heating effect. During transient voltage induced MIT measurement, the incubation time varied across 6 orders of magnitude. Both DC I-V characteristic and incubation times calculated from the electrothermal simulations show good agreement with measured values, indicating Joule heating effect is the cause of MIT with no evidence of electronic effects. The width of the metallic filament in the ON-state of the device was extracted and simulated within the thermal model.

  19. Voltage-induced Metal-Insulator Transitions in Perovskite Oxide Thin Films Doped with Strongly Correlelated Electrons

    NASA Astrophysics Data System (ADS)

    Wang, Yudi; Gil Kim, Soo; Chen, I.-Wei

    2007-03-01

    We have observed a reversible metal-insulator transition in perovskite oxide thin films that can be controlled by charge trapping pumped by a bipolar voltage bias. In the as-fabricated state, the thin film is metallic with a very low resistance comparable to that of the metallic bottom electrode, showing decreasing resistance with decreasing temperature. This metallic state switches to a high-resistance state after applying a voltage bias: such state is non-ohmic showing a negative temperature dependence of resistance. Switching at essentially the same voltage bias was observed down to 2K. The metal-insulator transition is attributed to charge trapping that disorders the energy of correlated electron states in the conduction band. By increasing the amount of charge trapped, which increases the disorder relative to the band width, increasingly more insulating states with a stronger temperature dependence of resistivity are accessed. This metal-insulator transition provides a platform to engineer new nonvolatile memory that does not require heat (as in phase transition) or dielectric breakdown (as in most other oxide resistance devices).

  20. Ferroelectric control of metal-insulator transition

    NASA Astrophysics Data System (ADS)

    He, Xu; Jin, Kui-juan; Ge, Chen; Ma, Zhong-shui; Yang, Guo-zhen

    2016-03-01

    We propose a method of controlling the metal-insulator transition of one perovskite material at its interface with another ferroelectric material based on first principle calculations. The operating principle is that the rotation of oxygen octahedra tuned by the ferroelectric polarization can modulate the superexchange interaction in this perovskite. We designed a tri-color superlattice of (BiFeO3)N/LaNiO3/LaTiO3, in which the BiFeO3 layers are ferroelectric, the LaNiO3 layer is the layer of which the electronic structure is to be tuned, and LaTiO3 layer is inserted to enhance the inversion asymmetry. By reversing the ferroelectric polarization in this structure, there is a metal-insulator transition of the LaNiO3 layer because of the changes of crystal field splitting of the Ni eg orbitals and the bandwidth of the Ni in-plane eg orbital. It is highly expected that a metal-transition can be realized by designing the structures at the interfaces for more materials.

  1. Metal Insulator transition in Vanadium Dioxide

    NASA Astrophysics Data System (ADS)

    Jovaini, Azita; Fujita, Shigeji; Suzuki, Akira; Godoy, Salvador

    2012-02-01

    MAR12-2011-000262 Abstract Submitted for the MAR12 Meeting of The American Physical Society Sorting Category: 03.9 (T) On the metal-insulator-transition in vanadium dioxide AZITA JOVAINI, SHIGEJI FUJITA, University at Buffalo, SALVADOR GODOY, UNAM, AKIRA SUZUKI, Tokyo University of Science --- Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 340 K with the structural change from tetragonal to monoclinic crystal. The conductivity _/ drops at MIT by four orders of magnitude. The low temperature monoclinic phase is known to have a lower ground-state energy. The existence of the k-vector k is prerequisite for the conduction since the k appears in the semiclassical equation of motion for the conduction electron (wave packet). The tetragonal (VO2)3 unit is periodic along the crystal's x-, y-, and z-axes, and hence there is a three-dimensional k-vector. There is a one-dimensional k for a monoclinic crystal. We believe this difference in the dimensionality of the k-vector is the cause of the conductivity drop. Prefer Oral Session X Prefer .

  2. Metal-insulator transition in Pt-C nanowires grown by focused-ion-beam-induced deposition

    SciTech Connect

    Fernandez-Pacheco, A.; Ibarra, M. R.; De Teresa, J. M.; Cordoba, R.

    2009-05-01

    We present a study of the transport properties of Pt-C nanowires created by focused-ion-beam (FIB)-induced deposition. By means of the measurement of the resistance while the deposit is being performed, we observe a progressive decrease in the nanowire resistivity with thickness, changing from 10{sup 8} {mu}{omega} cm for thickness {approx}20 nm to a lowest saturated value of 700 {mu}{omega} cm for thickness >150 nm. Spectroscopy analysis indicates that this dependence on thickness is caused by a gradient in the metal-carbon ratio as the deposit is grown. We have fabricated nanowires in different ranges of resistivity and studied their conduction mechanism as a function of temperature. A metal-insulator transition as a function of the nanowire thickness is observed. The results will be discussed in terms of the Mott-Anderson theory for noncrystalline materials. An exponential decrease in the conductance with the electric field is found for the most resistive samples, a phenomenon understood by the theory of hopping in lightly doped semiconductors under strong electric fields. This work explains the important discrepancies found in the literature for Pt-C nanostructures grown by FIB and opens the possibility to tune the transport properties of this material by an appropriate selection of the growth parameters.

  3. Electric field induced metal-insulator transition and colossal magnetoresistance in CdCr2S4

    NASA Astrophysics Data System (ADS)

    Sun, C. P.; Lin, C. C.; Her, J. L.; Taran, S.; Chou, C. C.; Chan, C. L.; Huang, C. L.; Berger, H.; Yang, H. D.

    2008-03-01

    Multiferroic ordering existing in a single material is a recent hot topic in the field of condensed matter physics due to its potential application in device control. The chromium chalcogenide spinel CdCr2S4 is one of the attractive materials investigated by Hemberger et al. recently.[1] Based on the electrical measurement, there is no discontinuity through the ferromagnetic ordering at TC ˜ 85K.[2] We measure the temperature dependent resistance under various electric fields to investigate the electrical properties of the present material. To our knowledge, we first observe the electric field induced metal-insulator transition in this material around TC. Moreover, a colossal magnetoresistance (CMR), which is comparable to that of manganese-based CMR material, is also observed near TC. The origin for these properties is discussed. [1] J. Hemberger, P. Lunkenheimer, R. Fichtl, H.-A. Krug von Nidda, V. Tsurkan, A. Loidl, Nature 434, 364 (2006). [2] P. K. Baltzer, H. W. Lehmann, and M. Robbins, Phys. Rev. Lett. 15, 493 (1965).

  4. Investigation on onset voltage and conduction channel temperature in voltage-induced metal-insulator transition of vanadium dioxide

    SciTech Connect

    Yoon, Joonseok; Kim, Howon; Ju, Honglyoul; Mun, Bongjin Simon; Park, Changwoo

    2016-03-28

    The characteristics of onset voltages and conduction channel temperatures in the metal-insulator transition (MIT) of vanadium dioxide (VO{sub 2}) devices are investigated as a function of dimensions and ambient temperature. The MIT onset voltage varies from 18 V to 199 V as the device length increases from 5 to 80 μm at a fixed width of 100 μm. The estimated temperature at local conduction channel increases from 110 to 370 °C, which is higher than the MIT temperature (67 °C) of VO{sub 2}. A simple Joule-heating model is employed to explain voltage-induced MIT as well as to estimate temperatures of conduction channel appearing after MIT in various-sized devices. Our findings on VO{sub 2} can be applied to micro- to nano-size tunable heating devices, e.g., microscale scanning thermal cantilevers and gas sensors.

  5. Giant positive magnetoresistance and field-induced metal insulator transition in Cr2NiGa

    NASA Astrophysics Data System (ADS)

    Pramanick, S.; Dutta, P.; Chatterjee, S.; Giri, S.; Majumdar, S.

    2017-01-01

    We report the magneto-transport properties of the newly synthesized Heusler compound Cr2NiGa which crystallizes in a disordered cubic B2 structure belonging to the Pm\\bar{3} m space group. The sample is found to be paramagnetic down to 2 K with metallic characteristics. On application of a magnetic field, a significantly large increase in resistivity is observed which corresponds to magnetoresistance as high as 112% at 150 kOe of field at the lowest temperature. Most remarkably, the sample shows a negative temperature coefficient of resistivity below about 50 K under the application of field  ⩾80 kOe, signifying a field-induced metal to ‘insulating’ transition. The observed magnetoresistance follows Kohler’s rule below 20 K indicating the validity of the semiclassical model of electronic transport in metals with a single relaxation time. A multi-band model for electronic transport, originally proposed for semimetals, is found to be appropriate to describe the magneto-transport behavior of the sample.

  6. Disorder-Driven Metal-Insulator Transitions in Deformable Lattices

    NASA Astrophysics Data System (ADS)

    Di Sante, Domenico; Fratini, Simone; Dobrosavljević, Vladimir; Ciuchi, Sergio

    2017-01-01

    We show that, in the presence of a deformable lattice potential, the nature of the disorder-driven metal-insulator transition is fundamentally changed with respect to the noninteracting (Anderson) scenario. For strong disorder, even a modest electron-phonon interaction is found to dramatically renormalize the random potential, opening a mobility gap at the Fermi energy. This process, which reflects disorder-enhanced polaron formation, is here given a microscopic basis by treating the lattice deformations and Anderson localization effects on the same footing. We identify an intermediate "bad insulator" transport regime which displays resistivity values exceeding the Mott-Ioffe-Regel limit and with a negative temperature coefficient, as often observed in strongly disordered metals. Our calculations reveal that this behavior originates from significant temperature-induced rearrangements of electronic states due to enhanced interaction effects close to the disorder-driven metal-insulator transition.

  7. Thickness-Induced Metal-Insulator Transition in Sb-doped SnO2 Ultrathin Films: The Role of Quantum Confinement

    PubMed Central

    Ke, Chang; Zhu, Weiguang; Zhang, Zheng; Soon Tok, Eng; Ling, Bo; Pan, Jisheng

    2015-01-01

    A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition. Both electrical and spectroscopic studies provide clear evidence of a critical thickness for the metallic conductivity in SnO2:Sb thin films and the oxidation state transition of the impurity element Sb. With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect. Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system. PMID:26616286

  8. Thermodynamic behavior near a metal-insulator transition

    NASA Technical Reports Server (NTRS)

    Paalanen, M. A.; Graebner, J. E.; Bhatt, R. N.; Sachdev, S.

    1988-01-01

    Measurements of the low-temperature specific heat of phosphorus-doped silicon for densities near the metal-insulator transition show an enhancement over the conduction-band itinerant-electron value. The enhancement increases toward lower temperatures but is less than that found for the spin susceptibility. The data are compared with various theoretical models; the large ratio of the spin susceptibility to specific heat indicates the presence of localized spin excitations in the metallic phase as the metal-insulator transition is approached.

  9. Thermodynamic behavior near a metal-insulator transition

    NASA Technical Reports Server (NTRS)

    Paalanen, M. A.; Graebner, J. E.; Bhatt, R. N.; Sachdev, S.

    1988-01-01

    Measurements of the low-temperature specific heat of phosphorus-doped silicon for densities near the metal-insulator transition show an enhancement over the conduction-band itinerant-electron value. The enhancement increases toward lower temperatures but is less than that found for the spin susceptibility. The data are compared with various theoretical models; the large ratio of the spin susceptibility to specific heat indicates the presence of localized spin excitations in the metallic phase as the metal-insulator transition is approached.

  10. Terahertz spectroscopy of the metal insulator transition in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Hilton, David; Prasankumar, Rohit; Cavalleri, Andrea; Fourmaux, Sylvain; Kieffer, Jean-Claude; Taylor, Antoinette; Averitt, Richard

    2006-03-01

    We employ terahertz spectroscopy to study the metal-insulator phase transition in vanadium dioxide (VO2 ). We measure the terahertz frequency conductivity in the metallic phase that has a real conductivity of 1000 &-1circ; cm-1 and a negligible imaginary conductivity. The observed conductivity dynamics are consistent with a photoinduced transition in spatially inhomogeneous regions of the film, followed by a thermally driven transition to the maximum conductivity.

  11. Materials Characterization and Microelectronic Implementation of Metal-insulator Transition Materials and Phase Change Materials

    DTIC Science & Technology

    2015-03-26

    MATERIALS CHARACTERIZATION AND MICROELECTRONIC IMPLEMENTATION OF METAL -INSULATOR TRANSITION MATERIALS...MATERIALS CHARACTERIZATION AND MICROELECTRONIC IMPLEMENTATION OF METAL -INSULATOR TRANSITION MATERIALS AND PHASE CHANGE MATERIALS THESIS...DISTRIBUTION UNLIMITED AFIT-ENG-MS-15-M-016 MATERIALS CHARACTERIZATION AND MICROELECTRONIC IMPLEMENTATION OF METAL -INSULATOR TRANSITION

  12. Terahertz transport dynamics in the metal-insulator transition of V2O3 thin film

    NASA Astrophysics Data System (ADS)

    Luo, Y. Y.; Su, F. H.; Zhang, C.; Zhong, L.; Pan, S. S.; Xu, S. C.; Wang, H.; Dai, J. M.; Li, G. H.

    2017-03-01

    The dynamic behavior of thermally-induced metal-insulator transition of V2O3 thin film on Si substrate grown by reactive magnetron sputtering was investigated by the terahertz time-domain spectroscopy. It was found that the THz absorption and optical conductivity of the thin films are temperature-dependent, and the THz amplitude modulation can reach as high as 74.7%. The complex THz optical conductivity in the metallic state of the V2O3 thin films can be well-fitted by the Drude-Smith model, which offer the insight into the electron transport dynamic during the metal-insulator transition of the thin film.

  13. Metal-Insulator Transition and Topological Properties of Pyrochlore Iridates

    NASA Astrophysics Data System (ADS)

    Zhang, Hongbin; Haule, Kristjan; Vanderbilt, David

    2017-01-01

    Combining density functional theory (DFT) and embedded dynamical mean-field theory (DMFT) methods, we study the metal-insulator transition in R2Ir2 O7 (R =Y , Eu, Sm, Nd, Pr, and Bi) and the topological nature of the insulating compounds. Accurate free energies evaluated using the charge self-consistent DFT +DMFT method reveal that the metal-insulator transition occurs for an A -cation radius between that of Nd and Pr, in agreement with experiments. The all-in-all-out magnetic phase, which is stable in the Nd compound but not the Pr one, gives rise to a small Ir4 + magnetic moment of ≈0.4 μB and opens a sizable correlated gap. We demonstrate that within this state-of-the-art theoretical method, the insulating bulk pyrochlore iridates are topologically trivial.

  14. Metal-insulator transition in films of doped semiconductor nanocrystals.

    PubMed

    Chen, Ting; Reich, K V; Kramer, Nicolaas J; Fu, Han; Kortshagen, Uwe R; Shklovskii, B I

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.

  15. Metal-insulator transition near a superconducting state

    NASA Astrophysics Data System (ADS)

    Kaveh, M.; Mott, N. F.

    1992-03-01

    We show that when the metal-insulation transition occurs near a superconducting state it results in a different critical behavior from that of amorphous metals or uncompensated doped semiconductors. This difference results from the enhancement of the effective electron-electron interaction caused by fluctuations to the superconducting state. This explains the recent experiments of Micklitz and co-workers on amorphous superconducting mixtures Ga-Ar and Bi-Kr.

  16. The metal-insulator transition in magnetite.

    NASA Technical Reports Server (NTRS)

    Cullen, J. R.; Callen, E.

    1972-01-01

    We describe an electronic model for the low temperature transition in magnetite, in which the average number of electrons on a site is non-integral. The solution of the one-dimensional problem is reviewed, and the connection of the model with the Verwey ordering is discussed. Some of the implication of the three dimensional problem are discussed.

  17. The metal-insulator transition in magnetite.

    NASA Technical Reports Server (NTRS)

    Cullen, J. R.; Callen, E.

    1972-01-01

    We describe an electronic model for the low temperature transition in magnetite, in which the average number of electrons on a site is non-integral. The solution of the one-dimensional problem is reviewed, and the connection of the model with the Verwey ordering is discussed. Some of the implication of the three dimensional problem are discussed.

  18. Temperature and electric field induced metal-insulator transition in atomic layer deposited VO2 thin films

    NASA Astrophysics Data System (ADS)

    Tadjer, Marko J.; Wheeler, Virginia D.; Downey, Brian P.; Robinson, Zachary R.; Meyer, David J.; Eddy, Charles R.; Kub, Fritz J.

    2017-10-01

    Amorphous vanadium oxide (VO2) films deposited by atomic layer deposition (ALD) were crystallized with an ex situ anneal at 660-670 °C for 1-2 h under a low oxygen pressure (10-4 to 10-5 Torr). Under these conditions the crystalline VO2 phase was maintained, while formation of the V2O5 phase was suppressed. Electrical transition from the insulator to the metallic phase was observed in the 37-60 °C range, with an ROFF/RON ratio of up to about 750 and ΔTC ≅ 7-10 °C. Lateral electric field applied across two-terminal device structures induced a reversible phase change, with a room temperature transition field of about 25 kV/cm in the VO2 sample processed with the 2 h long O2 anneal. Both the width and slope of the field induced MIT I-V hysteresis were dependent upon the VO2 crystalline quality.

  19. Dielectric breakdown and avalanches at nonequilibrium metal-insulator transitions.

    PubMed

    Shekhawat, Ashivni; Papanikolaou, Stefanos; Zapperi, Stefano; Sethna, James P

    2011-12-30

    Motivated by recent experiments on the finite temperature Mott transition in VO(2) films, we propose a classical coarse-grained dielectric breakdown model where each degree of freedom represents a nanograin which transitions from insulator to metal with increasing temperature and voltage at random thresholds due to quenched disorder. We describe the properties of the resulting nonequilibrium metal-insulator transition and explain the universal characteristics of the resistance jump distribution. We predict that by tuning voltage, another critical point is approached, which separates a phase of boltlike avalanches from percolationlike ones.

  20. Critical metal-insulator transition and divergence in a two-particle irreducible vertex in disordered and interacting electron systems

    NASA Astrophysics Data System (ADS)

    Janiš, V.; Pokorný, V.

    2014-07-01

    We use the dynamical mean-field approximation to study singularities in the self-energy and a two-particle irreducible vertex induced by the metal-insulator transition of the disordered Falicov-Kimball model. We set general conditions for the existence of a critical metal-insulator transition caused by a divergence of the imaginary part of the self-energy. We calculate explicitly the critical behavior of the self-energy for the symmetric and asymmetric disorder distributions. We demonstrate that the metal-insulator transition is preceded by a pole in a two-particle irreducible vertex. We show that unlike the singularity in the self-energy the divergence in the irreducible vertex does not lead to nonanalyticities in measurable physical quantities. We reveal universal features of the critical metal-insulator transition that are transferable also to the Mott-Hubbard transition in the models of the local Fermi liquid.

  1. Metal-insulator transition in oriented poly(p-phenylenevinylene)

    NASA Astrophysics Data System (ADS)

    Ahlskog, M.; Menon, Reghu; Heeger, A. J.; Noguchi, T.; Ohnishi, T.

    1997-03-01

    The transport properties of H2 SO4 -doped, tensile drawn, and oriented poly(phenylenevinylene) have been studied in the metallic, critical, and insulating regimes of the disorder-induced metal-insulator transition (M-I) transition. The temperature dependence of the conductivity, σ(T) and the magnetoconductance (MC) were investigated between room temperature and 1.3 K and in magnetic fields up to 8 T, in freshly doped samples and in samples during controlled dedoping (aging). A complete set of measurements were carried out on a single, fully doped sample that was followed during ageing from the metallic state through the critical regime into the insulting state. The transport properties are characterized as a function of the resistivity ratio (ρr), where ρr=[ρ(1.3 K)/ρ(200 K)]. In the metallic regime (ρr<2), σ∥ (300 K)≅10 000 S/cm and σ⊥ (300 K)≅100 S/cm; for T<4 K, a T1/2 dependence is observed for σ(T), and the MC shows positive and negative contributions at low and high fields, respectively. The positive contribution to the MC vanishes at the M-I transition boundary (ρr≅2). The behaviors of σ(T)and the MC are consistent with the weak localization plus electron-electron interaction model. Very near the M-I transition, a field-induced transition from the metallic to the critical regime was observed \\{σ(T)~T0.1 at 8 T\\}. For samples in the critical regime with 4<ρr<30, σ(T)~TΒ at low temperatures. In the insulating state (ρr>50), ρ(T)~exp(T0/T)x indicating variable-range-hopping transport. Although anisotropic, the field and temperature dependences of the transport are similar both parallel and perpendicular to the chain axis, implying that oriented conducting polymers are anisotropic three-dimensional conductors.

  2. Role of phonons in the metal-insulator phase transition.

    NASA Technical Reports Server (NTRS)

    Langer, W. D.

    1972-01-01

    Review, for the transition series oxides, of the Mattis and Lander model, which is one of electrons interacting with lattice vibrations (electron and phonon interaction). The model displays superconducting, insulating, and metallic phases. Its basic properties evolve from a finite crystallographic distortion associated with a dominant phonon mode and the splitting of the Brillouin zone into two subzones, a property of simple cubic and body centered cubic lattices. The order of the metal-insulator phase transition is examined. The basic model has a second-order phase transition and the effects of additional mechanisms on the model are calculated. The way in which these mechanisms affect the magnetically ordered transition series oxides as described by the Hubbard model is discussed.

  3. Phonons and the metal-insulator transition in VO2

    NASA Astrophysics Data System (ADS)

    Chang, Sung; Alatas, A.

    2005-03-01

    VO2 undergoes a metal-insulator transition (MIT) at TC= 340 K, which is accompanied by a structural phase transition from a high temperature rutile phase to a low temperature monoclinic phase. Although VO2 has been studied extensively for over 40 years, a clear understanding of the origin of the phase transition has not been forthcoming. Still at issue is the relative importance of electron-lattice and electron-electron interactions as driving mechanisms for the MIT. Here, we report the phonon dispersion of VO2, measured along the rutile γ-R direction using high resolution inelastic X-ray scattering. Unusual phonon behavior at the R point, as the MIT is approached, suggests significant electron-phonon coupling.

  4. Electrocaloric effect of metal-insulator transition in VO{sub 2}

    SciTech Connect

    Matsunami, Daichi; Fujita, Asaya

    2015-01-26

    The electrocaloric effect was observed in association with an electric-field induced metal-insulator transition in VO{sub 2} using a calorimetric measurement under an applied voltage. For a VO{sub 2} plate with a 0.4 mm thickness located in the center of a capacitor-like structure, the metal-insulator transition was manipulated by applying a few volts. The occurrence of a transition in such a thick sample with relatively low voltage indicates that a surface charge accumulation mechanism is effective. The isothermal entropy change reached 94 J kg{sup −1} K{sup −1}, while the adiabatic temperature change was calculated as −3.8 K under a voltage change of 0–3 V. The large entropy change is attributed to correlation of the complex freedom among spin, charge, and lattice.

  5. Metal-insulator and charge ordering transitions in oxide nanostructures

    NASA Astrophysics Data System (ADS)

    Singh, Sujay Kumar

    Strongly correlated oxides are a class of materials wherein interplay of various degrees of freedom results in novel electronic and magnetic phenomena. Vanadium oxides are widely studied correlated materials that exhibit metal-insulator transitions (MIT) in a wide temperature range from 70 K to 380 K. In this Thesis, results from electrical transport measurements on vanadium dioxide (VO2) and vanadium oxide bronze (MxV 2O5) (where M: alkali, alkaline earth, and transition metal cations) are presented and discussed. Although the MIT in VO2 has been studied for more than 50 years, the microscopic origin of the transition is still debated since a slew of external parameters such as light, voltage, and strain are found to significantly alter the transition. Furthermore, recent works on electrically driven switching in VO2 have shown that the role of Joule heating to be a major cause as opposed to electric field. We explore the mechanisms behind the electrically driven switching in single crystalline nanobeams of VO2 through DC and AC transport measurements. The harmonic analysis of the AC measurement data shows that non-uniform Joule heating causes electronic inhomogeneities to develop within the nanobeam and is responsible for driving the transition in VO2. Surprisingly, field assisted emission mechanisms such as Poole-Frenkel effect is found to be absent and the role of percolation is also identified in the electrically driven transition. This Thesis also provides a new insight into the mechanisms behind the electrolyte gating induced resistance modulation and the suppression of MIT in VO2. We show that the metallic phase of VO2 induced by electrolyte gating is due to an electrochemical process and can be both reversible and irreversible under different conditions. The kinetics of the redox processes increase with temperature; a complete suppression of the transition and the stabilization of the metallic phase are achievable by gating in the rutile metallic phase

  6. Holographic metal-insulator transition in higher derivative gravity

    NASA Astrophysics Data System (ADS)

    Ling, Yi; Liu, Peng; Wu, Jian-Pin; Zhou, Zhenhua

    2017-03-01

    We introduce a Weyl term into the Einstein-Maxwell-Axion theory in four dimensional spacetime. Up to the first order of the Weyl coupling parameter γ, we construct charged black brane solutions without translational invariance in a perturbative manner. Among all the holographic frameworks involving higher derivative gravity, we are the first to obtain metal-insulator transitions (MIT) when varying the system parameters at zero temperature. Furthermore, we study the holographic entanglement entropy (HEE) of strip geometry in this model and find that the second order derivative of HEE with respect to the axion parameter exhibits maximization behavior near quantum critical points (QCPs) of MIT. It testifies the conjecture in [1,2] that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT).

  7. Quantum critical transport at a continuous metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2016-08-01

    In contrast to the first-order correlation-driven Mott metal-insulator transition, continuous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the strong disorder category. Employing cluster-dynamical mean-field theory, we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on both sides of the MIT. Surprisingly, we find that the beta function β (g ) scales as log(g ) deep into the bad-metallic phase as well, providing a sound unified basis for these findings. We argue that such strong localization quantum criticality may manifest in real three-dimensional systems where disorder effects are more important than electron-electron interactions.

  8. Metal-insulator transition above room temperature in maximum colossal magnetoresistance manganite thin films

    NASA Astrophysics Data System (ADS)

    Chen, X. J.; Habermeier, H.-U.; Zhang, H.; Gu, G.; Varela, M.; Santamaria, J.; Almasan, C. C.

    2005-09-01

    It has been suggested that the maximum magnitude of colossal magnetoresistance occurs in mixed-valent manganites with a tolerance factor t=0.96 [Zhou, Archibald, and Goodenough, Nature (London) 381, 770 (1996)]. However, at t≈0.96 most manganites have relatively low values of the metal-insulator transition temperature TMI(˜60-150K) . Here, we report that a 50 Å La0.9Sr0.1MnO3 thin film with t=0.96 grown on a (100) SrTiO3 substrate has a metal-insulator transition above room temperature, which represents a doubling of TMI compared with its value in the bulk material. We show that this spectacular increase of TMI is a result of the epitaxially compressive strain-induced reduction of the Jahn-Teller distortion.

  9. Thermal transport across a continuous metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2017-09-01

    The celebrated Wiedemann-Franz (WF) law is believed to be robust in metals as long as interactions between electrons preserve their fermion-quasiparticle character. We study thermal transport and the fate of the WF law close to a continuous metal-insulator transition (MIT) in the Falicov-Kimball model (FKM) using cluster-dynamical mean-field theory (CDMFT). Surprisingly, as for electrical transport, we find robust and novel quantum critical scaling in thermal transport across the MIT. We unearth the deeper reasons for these novel findings in terms of (i) the specific structure of energy-current correlations for the FKM and (ii) the microscopic electronic processes which facilitate energy transport while simultaneously blocking charge transport close to the MIT. However, within (C)DMFT, we also find that the WF law survives at T ⟶0 in the incoherent metal right up to the MIT, even in absence of Landau quasiparticles.

  10. On holographic disorder-driven metal-insulator transitions

    NASA Astrophysics Data System (ADS)

    Baggioli, Matteo; Pujolàs, Oriol

    2017-01-01

    We give a minimal holographic model of a disorder-driven metal-insulator transition. It consists in a CFT with a charge sector and a translation-breaking sector that interact in the most generic way allowed by the symmetries and by dynamical consistency. In the gravity dual, it reduces to a Massive Gravity-Maxwell model with a new direct coupling between the gauge field and the metric that is allowed when gravity is massive. We show that the effect of this coupling is to decrease the DC electrical conductivity generically. This gives a nontrivial check that holographic massive gravity can be consistently interpreted as disorder from the CFT perspective. The suppression of the conductivity happens to such an extent that it does not obey any lower bound and it can be very small in the insulating phase. In some cases, the large disorder limit produces gradient instabilities that hint at the formation of modulated phases.

  11. Capacitive network near the metal insulator transition in Vanadium Dioxide

    NASA Astrophysics Data System (ADS)

    Ramirez, J. G.; Patino, E. J.; Schmidt, R.; Sharoni, A.; Gomez, M. E.; Schuller, I. K.

    2011-03-01

    Recent infrared spectroscopy and transport measurements in nano-scaled junction of VO2 have revealed the existence of phase separation into metallic and insulating phases. Here we present Impedance spectroscopy measurements performed in high quality Vanadium dioxide (VO2) thin films for the first time. This technique allows distinguishing between the resistive and capacitive response of the VO2 films and provides the dielectric properties across the metal-insulator transition (MIT). The film capacitance exhibits an unusual increase close to the MIT which implies the formation of a capacitor network produced by the nanoscale phase separation of metallic and insulating phases. This work has been supported by AFOSR, COLCIENCIAS, CENM and Ramon y Cajal Fellowship.

  12. Metal insulator transitions in perovskite SrIrO{sub 3} thin films

    SciTech Connect

    Biswas, Abhijit; Jeong, Yoon Hee; Kim, Ki-Seok

    2014-12-07

    Understanding of metal insulator transitions in a strongly correlated system, driven by Anderson localization (disorder) and/or Mott localization (correlation), is a long standing problem in condensed matter physics. The prevailing fundamental question would be how these two mechanisms contrive to accomplish emergent anomalous behaviors. Here, we have grown high quality perovskite SrIrO{sub 3} thin films, containing a strong spin orbit coupled 5d element Ir, on various substrates such as GdScO{sub 3} (110), DyScO{sub 3} (110), SrTiO{sub 3} (001), and NdGaO{sub 3} (110) with increasing lattice mismatch, in order to carry out a systematic study on the transport properties. We found that metal insulator transitions can be induced in this system; by either reducing thickness (on best lattice matched substrate) or changing degree of lattice strain (by lattice mismatch between film and substrates) of films. Surprisingly these two pathways seek two distinct types of metal insulator transitions; the former falls into disorder driven Anderson type whereas the latter turns out to be of unconventional Mott-Anderson type with the interplay of disorder and correlation. More interestingly, in the metallic phases of SrIrO{sub 3}, unusual non-Fermi liquid characteristics emerge in resistivity as Δρ ∝ T{sup ε} with ε evolving from 4/5 to 1 to 3/2 with increasing lattice strain. We discuss theoretical implications of these phenomena to shed light on the metal insulator transitions.

  13. Chiral phase transition in lattice QCD as a metal-insulator transition

    SciTech Connect

    Garcia-Garcia, Antonio M.; Osborn, James C.

    2007-02-01

    We investigate the lattice QCD Dirac operator with staggered fermions at temperatures around the chiral phase transition. We present evidence of a metal-insulator transition in the low lying modes of the Dirac operator around the same temperature as the chiral phase transition. This strongly suggests the phenomenon of Anderson localization drives the QCD vacuum to the chirally symmetric phase in a way similar to a metal-insulator transition in a disordered conductor. We also discuss how Anderson localization affects the usual phenomenological treatment of phase transitions a la Ginzburg-Landau.

  14. Metal-insulator transition in low dimensional La{sub 0.75}Sr{sub 0.25}VO{sub 3} thin films

    SciTech Connect

    Dao, Tran M.; Mondal, Partha S.; Takamura, Y.; Arenholz, E.; Lee, Jaichan

    2011-06-15

    We report on the metal-insulator transition that occurs as a function of film thickness in ultrathin La{sub 0.75}Sr{sub 0.25}VO{sub 3} films. The metal-insulator transition displays a critical thickness of 5 unit cell. Above the critical thickness, metallic films exhibit a temperature driven metal-insulator transition with weak localization behavior. With decreasing film thickness, oxygen octahedron rotation in the films increases, causing enhanced electron-electron correlation. The electronelectron correlations in ultrathin films induce the transition from metal to insulator in addition to Anderson localization.

  15. Identifying the Collective Length in VO2 Metal-Insulator Transitions.

    PubMed

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2017-03-01

    The "collective length" in VO2 metal-insulator transitions is identified by controlling nanoscale dopant distribution in thin films. The crossover from the local transition to the collective transition is observed, which originates from the increased instability of the metal-insulator domain boundary. This instability renders the transition collective within the "collective length", which will enable the design of collective electronic devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Anderson metal-insulator transitions with classical magnetic impurities

    SciTech Connect

    Jung, Daniel; Kettemann, Stefan

    2014-08-20

    We study the effects of classical magnetic impurities on the Anderson metal-insulator transition (AMIT) numerically. In particular we find that while a finite concentration of Ising impurities lowers the critical value of the site-diagonal disorder amplitude W{sub c}, in the presence of Heisenberg impurities, W{sub c} is first increased with increasing exchange coupling strength J due to time-reversal symmetry breaking. The resulting scaling with J is compared to analytical predictions by Wegner [1]. The results are obtained numerically, based on a finite-size scaling procedure for the typical density of states [2], which is the geometric average of the local density of states. The latter can efficiently be calculated using the kernel polynomial method [3]. Although still suffering from methodical shortcomings, our method proves to deliver results close to established results for the orthogonal symmetry class [4]. We extend previous approaches [5] by combining the KPM with a finite-size scaling analysis. We also discuss the relevance of our findings for systems like phosphor-doped silicon (Si:P), which are known to exhibit a quantum phase transition from metal to insulator driven by the interplay of both interaction and disorder, accompanied by the presence of a finite concentration of magnetic moments [6].

  17. Correlation-induced metal-insulator transitions in d0 magnetic superlattices based on alkaline-earth monoxides: Insights from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Lu, Yi-Lin; Dong, Shengjie; Zhou, Baozeng; Zhao, Hui; Wu, Ping

    2015-06-01

    Using first-principles density functional theory calculations, we have investigated the electronic structure and magnetic properties of four superlattices (MO)1/(MX)1 (001) (M=Ca and Sr; X=N and C). Our results show that compared with standard GGA approach, the GGA plus effective Ueff scheme can correct electronic structure and magnetic properties in some extent. With enhancing electronic correlation, for (CaO)1/(CaN)1, (SrO)1/(SrN)1, and (SrO)1/(SrC)1, the bands across Fermi level are divided into two parts and the shape of isotropic spherical spin atmosphere becomes anisotropic dumbbell-like with specific orientation, accompanying metal-insulator transitions. For (CaO)1/(CaC)1, the states just smearing with the Fermi level shift to lower energy region below Fermi level, indicating the transformation from a nearly half metal to an actual half metal occurs. The different behavior of (CaO)1/(CaC)1 compared with three other compounds may be caused by the larger ionization energy of calcium than that of strontium and the smaller electronegativity of carbon than that of nitrogen.

  18. Metal-insulator transition in a switchable mirror

    NASA Astrophysics Data System (ADS)

    Roy, Arunabha Shasanka

    2001-11-01

    Rare earth hydride films can be converted reversibly from metallic mirrors to insulating windows simply by changing the surrounding hydrogen gas pressure at room temperature. At low temperatures, in situ doping is not possible in this way as hydrogen cannot diffuse. However, our finding of persistent photoconductivity under ultraviolet illumination enables us to tune yttrium hydride through the T = 0 metal-insulator transition. Conductivity and Hall measurements are used to determine the critical exponents in this system: mu = 1.0 +/- 0.1 and zv = 6.0 +/- 0.5. The simultaneous validity of finite-size scaling in the metal and its failure in the insulator motivates a study of the insulating phase of YHx in greater detail. A new transport regime is discovered which is consistent with our earlier determined values for the critical exponents but entails a new scaling dependence of the conductivity on the carrier density n and temperature T. The unusually large value for the product of the static and dynamic critical exponents appears to signify the important role played by electron-electron interactions in this system. Finally, possible schemes for the mechanism underlying the unusual photoconductivity are discussed.

  19. Metal Insulator Transition in p-SiGe

    NASA Astrophysics Data System (ADS)

    Coleridge, Peter

    2001-03-01

    The strained p-SiGe system exhibits many of the characteristics of the Metal Insulator transition first seen in Si-MOSFETs. Magnetoresistance and Hall data is presented for a series of samples with rs between about 4 and 8. Results are analysed using the Renormalisation Group theories of Finkel'stein[1] and Castellani et al.[2]. For samples well into the metallic regime the Hall effect data is generally consistent with this picture with a cross-over from low field to high field behaviour when the Zeeman splitting gμ_BB = 2kT and a spin triplet interaction parameter γ2 close to one. There is, however, a large and unexpected additional ln(B) dependence tentatively attributed to an anomalous Hall effect which is likely to be large here because of the strong spin-orbit coupling. If this is the case it provides a powerful way of probing the magnetisation or spin-texture in the system. Although weak localisation effects appear in the magnetoresistance there is no sign of their expected temperature dependence. The results generally support the view that the interactions are strong and play an important role in the MIT. The relationship to the insulating phase seen in some p-SiGe samples around filling factor 3/2 will also be commented on. [1] A.M. Finkel'stein, Z. Phys. B56, 189 (1984) [2] C. Castellaniet al. Phys. Rev B 30,1596 (1984)

  20. Metal-insulator transitions and magnetic susceptibility in doped cuprate compounds

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Kurbanov, U. T.; Khudayberdiev, Z. S.; Hafizov, A. R.

    2016-11-01

    Results are presented from a theoretical study of the possibility of hole carrier localization and metal-insulator transitions which show up in the temperature dependences of the magnetic susceptibility χ(T) of doped copper-oxide (cuprate) compounds. The criteria for metal-insulator transitions owing to strong hole-lattice interactions and the formation of very narrow polaron bands in these materials with reduced doping level x are analyzed. It is shown that these kinds of metal-insulator transitions occur in underdoped La2-xSrxCuO4 and YBa2Cu3O6+x cuprates (i.e., for x ranging from 0.04 to 0.12). The characteristic temperature dependences χ(T) of the HTSC cuprates are found for different doping levels. These results are in good agreement with experimental data on metal-insulator transitions and the magnetic susceptibility of the HTSC cuprates.

  1. Controlling the metal insulator transition using the ferroelectric field effect in rare earth nickelates

    NASA Astrophysics Data System (ADS)

    Marshall, Matthew; Disa, Ankit; Kumah, Divine; Chen, Hanghui; Ismail-Beigi, Sohrab; Walker, Fred; Ahn, Charles

    2013-03-01

    A ferroelectric field effect transistor (FE-FET) modulates conductivity in a non-volatile manner by electrostatically accumulating and depleting charge carriers at the interface between a conducting channel and ferroelectric gate. The rare earth nickelate LaNiO3 is metallic in bulk, while other rare earth nickelates, such as NdNiO3, exhibit metal-insulator transitions and anti-ferromagnetic behavior in the bulk. Here, we show that by coupling the ferroelectric polarization of Pb0.8Zr0.2TiO3 (PZT) to the carriers in a nickelate, we can dynamically induce a metal- insulator transition in ultra-thin films of LaNiO3, and induce large changes in the MIT transition temperature in NdNiO3. Density functional theory is used to determine changes in the physical and electronic Ni-O-Ni bond angle of the nickelate at the interface between PZT and LaNiO3. The effect of the ferroelectric polarization is to decrease the Ni-O-Ni bond angle from 180 degrees and increase the carrier effective mass. Related to this change in electronic structure, we observe a change in resistivity of approximately 80% at room temperature for an ultra-thin 3 unit cell thick film of LaNiO3. Work supported by FENA and the NSF under MRSEC DMR 1119826.

  2. Percolation metal-insullator transition in BiSrCaCuO films

    NASA Astrophysics Data System (ADS)

    Okunev, V. D.; Pafomov, N. N.; Svistunov, V. M.; Lewandowski, S. J.; Gierlowski, P.; Kula, W.

    1996-02-01

    An experimental investigation of the metal-insulator trnasition in BiSrCaCuO (BSCCO) films is reported. We performed resistivity, optical-absorption and critical-temperature measurements on several samples obtained by different technological methods. The results agree well with the percolation mechanism of the metal-insulator transition and show interesting correlations between room-temperature conductivity and superconducting properties of the investigated films.

  3. Striped nanoscale phase separation at the metal-insulator transition of heteroepitaxial nickelates.

    PubMed

    Mattoni, G; Zubko, P; Maccherozzi, F; van der Torren, A J H; Boltje, D B; Hadjimichael, M; Manca, N; Catalano, S; Gibert, M; Liu, Y; Aarts, J; Triscone, J-M; Dhesi, S S; Caviglia, A D

    2016-11-02

    Nucleation processes of mixed-phase states are an intrinsic characteristic of first-order phase transitions, typically related to local symmetry breaking. Direct observation of emerging mixed-phase regions in materials showing a first-order metal-insulator transition (MIT) offers unique opportunities to uncover their driving mechanism. Using photoemission electron microscopy, we image the nanoscale formation and growth of insulating domains across the temperature-driven MIT in NdNiO3 epitaxial thin films. Heteroepitaxy is found to strongly determine the nanoscale nature of the phase transition, inducing preferential formation of striped domains along the terraces of atomically flat stepped surfaces. We show that the distribution of transition temperatures is a local property, set by surface morphology and stable across multiple temperature cycles. Our data provide new insights into the MIT of heteroepitaxial nickelates and point to a rich, nanoscale phenomenology in this strongly correlated material.

  4. Striped nanoscale phase separation at the metal-insulator transition of heteroepitaxial nickelates

    NASA Astrophysics Data System (ADS)

    Mattoni, G.; Zubko, P.; Maccherozzi, F.; van der Torren, A. J. H.; Boltje, D. B.; Hadjimichael, M.; Manca, N.; Catalano, S.; Gibert, M.; Liu, Y.; Aarts, J.; Triscone, J.-M.; Dhesi, S. S.; Caviglia, A. D.

    2016-11-01

    Nucleation processes of mixed-phase states are an intrinsic characteristic of first-order phase transitions, typically related to local symmetry breaking. Direct observation of emerging mixed-phase regions in materials showing a first-order metal-insulator transition (MIT) offers unique opportunities to uncover their driving mechanism. Using photoemission electron microscopy, we image the nanoscale formation and growth of insulating domains across the temperature-driven MIT in NdNiO3 epitaxial thin films. Heteroepitaxy is found to strongly determine the nanoscale nature of the phase transition, inducing preferential formation of striped domains along the terraces of atomically flat stepped surfaces. We show that the distribution of transition temperatures is a local property, set by surface morphology and stable across multiple temperature cycles. Our data provide new insights into the MIT of heteroepitaxial nickelates and point to a rich, nanoscale phenomenology in this strongly correlated material.

  5. Reconfigurable van der Waals Heterostructured Devices with Metal-Insulator Transition.

    PubMed

    Heo, Jinseong; Jeong, Heejeong; Cho, Yeonchoo; Lee, Jaeho; Lee, Kiyoung; Nam, Seunggeol; Lee, Eun-Kyu; Lee, Sangyeob; Lee, Hyangsook; Hwang, Sungwoo; Park, Seongjun

    2016-11-09

    Atomically thin two-dimensional (2D) materials range from semimetallic graphene to insulating hexagonal boron nitride to semiconducting transition-metal dichalcogenides. Recently, metal-insulator-semiconductor field effect transistors built from these 2D elements were studied for flexible and transparent electronics. However, to induce ambipolar characteristics for alternative power-efficient circuitry, ion-gel gating is often employed for high capacitive coupling, limiting stable operation at ambient conditions. Here, we report reconfigurable MoTe2 optoelectronic transistors with all 2D components, where the device can be reconfigured by both drain and gate voltages. Eight different configurations for each fixed voltage are spatially resolved by scanning photocurrent microscopy. In addition, metal-insulator transitions are observed in both electron and hole carriers under 2 V due to strong Coulomb interaction in the system. Furthermore, the vertical tunneling photocurrent through multiple van der Waals layers between the gate and source contacts is measured. Our reconfigurable devices offer potential building blocks for system-on-a-chip optoelectronics.

  6. Density inhomogeneity driven percolation metal-insulator transition and dimensional crossover in graphene nanoribbons.

    PubMed

    Adam, S; Cho, S; Fuhrer, M S; Das Sarma, S

    2008-07-25

    Transport in graphene nanoribbons with an energy gap in the spectrum is considered in the presence of random charged impurity centers. At low carrier density, we predict and establish that the system exhibits a density inhomogeneity driven two dimensional metal-insulator transition that is in the percolation universality class. For very narrow graphene nanoribbons (with widths smaller than the disorder induced length scale), we predict that there should be a dimensional crossover to the 1D percolation universality class with observable signatures in the transport gap. In addition, there should be a crossover to the Boltzmann transport regime at high carrier densities. The measured conductivity exponent and the critical density are consistent with this percolation transition scenario.

  7. Photocurrent Switching of Monolayer MoS2 Using a Metal-Insulator Transition.

    PubMed

    Lee, Jin Hee; Gul, Hamza Zad; Kim, Hyun; Moon, Byoung Hee; Adhikari, Subash; Kim, Jung Ho; Choi, Homin; Lee, Young Hee; Lim, Seong Chu

    2017-02-08

    We achieve switching on/off the photocurrent of monolayer molybdenum disulfide (MoS2) by controlling the metal-insulator transition (MIT). N-type semiconducting MoS2 under a large negative gate bias generates a photocurrent attributed to the increase of excess carriers in the conduction band by optical excitation. However, under a large positive gate bias, a phase shift from semiconducting to metallic MoS2 is caused, and the photocurrent by excess carriers in the conduction band induced by the laser disappears due to enhanced electron-electron scattering. Thus, no photocurrent is detected in metallic MoS2. Our results indicate that the photocurrent of MoS2 can be switched on/off by appropriately controlling the MIT transition by means of gate bias.

  8. Metal-insulator transition in two-dimensional random fermion systems of chiral symmetry classes

    NASA Astrophysics Data System (ADS)

    König, E. J.; Ostrovsky, P. M.; Protopopov, I. V.; Mirlin, A. D.

    2012-05-01

    Field-theoretical approach to Anderson localization in 2D disordered fermionic systems of chiral symmetry classes (BDI, AIII, CII) is developed. Important representatives of these symmetry classes are random hopping models on bipartite lattices at the band center. As was found by Gade and Wegner two decades ago within the sigma-model formalism, quantum interference effects in these classes are absent to all orders of perturbation theory. We demonstrate that the quantum localization effects emerge when the theory is treated nonperturbatively. Specifically, they are controlled by topological vortexlike excitations of the sigma models. We derive renormalization-group equations including these nonperturbative contributions. Analyzing them, we find that the 2D disordered systems of chiral classes undergo a metal-insulator transition driven by topologically induced Anderson localization. We also show that the Wess-Zumino and Z2 θ terms on surfaces of 3D topological insulators (in classes AIII and CII, respectively) overpower the vortex-induced localization.

  9. Metal-insulator transition and local moment formation: A spin-density functional approach

    NASA Astrophysics Data System (ADS)

    Ghazali, A.; Leroux-Hugon, P.

    1980-01-01

    A more thorough description of the metal-insulator transition in correlated systems including local moment formation may be achieved through the spin-density functional method when compared to the Hubbard model. We have applied this method to doped semiconductors and found a transition between an insulating phase with local moments and a metallic one without moments.

  10. Metal-insulator transition in NaxWO3: Photoemission spectromicroscopy study

    NASA Astrophysics Data System (ADS)

    Paul, Sanhita; Ghosh, Anirudha; Raj, Satyabrata

    2014-04-01

    We have investigated the validity of percolation model, which is quite often invoked to explain the metal-insulator transition in sodium tungsten bronzes, NaxWO3 by photoelectron spectromicroscopy. The spatially resolved direct spectromicroscopic probing on both the insulating and metallic phases of high quality single crystals of NaxWO3 reveals the absence of any microscopic inhomogeneities embedded in the system within the experimental limit. Neither any metallic domains in the insulating host nor any insulating domains in the metallic host have been found to support the validity of percolation model to explain the metal-insulator transition in NaxWO3.

  11. Metal-insulator transitions of bulk and domain-wall states in pyrochlore iridates

    NASA Astrophysics Data System (ADS)

    Ueda, Kentaro

    A family of pyrochlore iridates R2Ir2O7 offers an ideal platform to explore intriguing phases such as topological Mott insulator and Weyl semimetal. Here we report transport and spectroscopic studies on the metal-insulator transition (MIT) induced by the modulations of effective electron correlation and magnetic structures, which is finely tuned by external pressure, chemical substitutions (R = Nd1-x Prx and SmyNd1-y) , and magnetic field. A reentrant insulator-metal-insulator transition is observed near the paramagnetic insulator-metal phase boundary reminiscent of a first-order Mott transition for R = SmyNd1-y compounds (y~0.8). The metallic states on the magnetic domain walls (DWs), which are observed for R = Nd in real space as well as in transport properties, is simultaneously turned into the insulating one. These findings imply that the DW electronic state is intimately linked to the bulk states. For the mixed R = Nd1-x Prx compounds, the divergent behavior of resistivity with antiferromagnetic order is significantly suppressed by applying a magnetic field along [001] direction. It is attributed to the phase transition from the antiferromagnetic insulating state to the novel Weyl (semi-)metal state accompanied by the change of magnetic structure. The present study combined with experiment and theory suggests that there are abundant exotic phases with physical parameters such as electron correlation and Ir-5 d magnetic order pattern. Work performed in collaboration with J. Fujioka, B.-J. Yang, C. Terakura, N. Nagaosa, Y. Tokura (University of Tokyo, RIKEN CEMS), J. Shiogai, A. Tsukazaki, S. Nakamura, S. Awaji (Tohoku University). 1This work was supported by JSPS FIRST Program and Grant-in-Aid for Scientific Research (Grants No. 80609488 and No. 24224009).

  12. Enhanced ferromagnetic and metal insulator transition in Sm0.55Sr0.45MnO3 thin films: Role of oxygen vacancy induced quenched disorder

    NASA Astrophysics Data System (ADS)

    Srivastava, M. K.; Siwach, P. K.; Kaur, A.; Singh, H. K.

    2010-11-01

    Effect of quenched disorder (QD) caused by oxygen vacancy (OV) and substrate induced inhomogeneous compressive strain, on the magnetic and transport properties of oriented polycrystalline Sm0.55Sr0.45MnO3 thin films is investigated. QD is related intimately to the ordering/disordering of the OVs and controls the paramagnetic-ferromagnetic/insulator-metal transition. OV ordered films show enhanced TC/TIM˜165 K, which is depressed by oxygen annealing. OV disordering realized by quenching reduces TC/TIM. The first order IM transition observed in SSMO single crystals is transformed into nonhysteretic and continuous one in the OV ordered films. QD appears to be diluted by OV disorder/annihilation and results in stronger carrier localization.

  13. Pure electronic metal-insulator transition at the interface of complex oxides

    PubMed Central

    Meyers, D.; Liu, Jian; Freeland, J. W.; Middey, S.; Kareev, M.; Kwon, Jihwan; Zuo, J. M.; Chuang, Yi-De; Kim, J. W.; Ryan, P. J.; Chakhalian, J.

    2016-01-01

    In complex materials observed electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. Here, we demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. These findings illustrate the utility of heterointerfaces as a powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change. PMID:27324948

  14. Pure electronic metal-insulator transition at the interface of complex oxides

    SciTech Connect

    Meyers, D.; Liu, Jian; Freeland, J. W.; Middey, S.; Kareev, M.; Kwon, Jihwan; Zuo, J. M.; Chuang, Yi-De; Kim, J. W.; Ryan, P. J.; Chakhalian, J.

    2016-06-21

    We observed complex materials in electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. We demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. Furthermore, these findings illustrate the utility of heterointerfaces as a powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change.

  15. Gas sensor based on metal-insulator transition in VO2 nanowire thermistor.

    PubMed

    Strelcov, Evgheni; Lilach, Yigal; Kolmakov, Andrei

    2009-06-01

    Using temperature driven sharp metal-insulator phase transition in single crystal VO(2) nanowires, the realization of a novel gas sensing concept has been tested. Varying the temperature of the nanowire close to the transition edge, the conductance of the nanowire becomes extremely responsive to the tiny changes in molecular composition, pressure, and temperature of the ambient gas environment. This gas sensing analog of the transition edge sensor radiometry used in astrophysics opens new opportunities in gas sensorics.

  16. Effects of Thickness on the Metal-Insulator Transition in Free-Standing Vanadium Dioxide Nanocrystals.

    PubMed

    Fadlelmula, Mustafa M; Sürmeli, Engin C; Ramezani, Mehdi; Kasırga, T Serkan

    2017-03-08

    Controlling solid state phase transitions via external stimuli offers rich physics along with possibilities of unparalleled applications in electronics and optics. The well-known metal-insulator transition (MIT) in vanadium dioxide (VO2) is one instance of such phase transitions emerging from strong electronic correlations. Inducing the MIT using electric field has been investigated extensively for the applications in electrical and ultrafast optical switching. However, as the Thomas-Fermi screening length is very short, for considerable alteration in the material's properties with electric field induced MIT, crystals below 10 nm are needed. So far, the only way to achieve thin crystals of VO2 has been via epitaxial growth techniques. Yet, stress due to lattice mismatch as well as interdiffusion with the substrate complicate the studies. Here, we show that free-standing vapor-phase grown crystals of VO2 can be milled down to the desired thickness using argon ion-beam milling without compromising their electronic and structural properties. Among our results, we show that even below 4 nm thickness the MIT persists and the transition temperature is lowered in two-terminal devices as the crystal gets thinner. The findings in this Letter can be applied to similar strongly correlated materials to study quantum confinement effects.

  17. Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r3(Ru1-xM nx) 2O7

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Ye, Feng; Tian, Wei; Cao, Huibo; Chi, Songxue; Hu, Biao; Diao, Zhenyu; Tennant, David A.; Jin, Rongying; Zhang, Jiandi; Plummer, Ward

    2017-06-01

    Bilayered S r3R u2O7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in S r3(Ru1-xM nx) 2O7 . Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in S r3(Ru1-xM nx) 2O7 (x =0.06 and 0.12). With the increase of Mn doping (x ) from 0.06 to 0.12 or the decrease of temperatures for x =0.12 , an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C4 v crystal lattice to a C2 v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.

  18. Computation of the correlated metal-insulator transition in vanadium dioxide from first principles.

    PubMed

    Zheng, Huihuo; Wagner, Lucas K

    2015-05-01

    Vanadium dioxide (VO2) is a paradigmatic example of a strongly correlated system that undergoes a metal-insulator transition at a structural phase transition. To date, this transition has necessitated significant post hoc adjustments to theory in order to be described properly. Here we report standard state-of-the-art first principles quantum Monte Carlo (QMC) calculations of the structural dependence of the properties of VO2. Using this technique, we simulate the interactions between electrons explicitly, which allows for the metal-insulator transition to naturally emerge, importantly without ad hoc adjustments. The QMC calculations show that the structural transition directly causes the metal-insulator transition and a change in the coupling of vanadium spins. This change in the spin coupling results in a prediction of a momentum-independent magnetic excitation in the insulating state. While two-body correlations are important to set the stage for this transition, they do not change significantly when VO2 becomes an insulator. These results show that it is now possible to account for electron correlations in a quantitatively accurate way that is also specific to materials.

  19. Functionalized graphene as a model system for the two-dimensional metal-insulator transition

    PubMed Central

    Osofsky, M. S.; Hernández, S. C.; Nath, A.; Wheeler, V. D.; Walton, S. G.; Krowne, C. M.; Gaskill, D. K.

    2016-01-01

    Reports of metallic behavior in two-dimensional (2D) systems such as high mobility metal-oxide field effect transistors, insulating oxide interfaces, graphene, and MoS2 have challenged the well-known prediction of Abrahams, et al. that all 2D systems must be insulating. The existence of a metallic state for such a wide range of 2D systems thus reveals a wide gap in our understanding of 2D transport that has become more important as research in 2D systems expands. A key to understanding the 2D metallic state is the metal-insulator transition (MIT). In this report, we explore the nature of a disorder induced MIT in functionalized graphene, a model 2D system. Magneto-transport measurements show that weak-localization overwhelmingly drives the transition, in contradiction to theoretical assumptions that enhanced electron-electron interactions dominate. These results provide the first detailed picture of the nature of the transition from the metallic to insulating states of a 2D system. PMID:26860789

  20. Change of universality class of metal-insulator transition due to magnetic ordering

    NASA Astrophysics Data System (ADS)

    de Oliveira, N. A.; Tovar Costa, M. V.; Troper, A.; Japiassú, Gloria M.; Continentino, M. A.

    1999-04-01

    Using a two-band model we report a theory to describe the metal-insulator (MI) transition as a function of an external applied magnetic field in Kondo insulators. To deal with electronic correlations we use a functional integral approach in the static approximation. We show the existence of a critical value of the Coulomb correlation Uc, such that for Utransition is continuous and occurs from a paramagnetic insulator to a paramagnetic metal. In this case this transition is in the universality class of density-driven transitions. For U>Uc, the transition is to a ferromagnetic metal and it is described by different critical exponents.

  1. Separation observation of metal-insulator transition and structural phase transition in VO2

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Tak; Kim, Bong-Jun; Lee, Yong Wook; Chae, Byung Gyu; Yun, Sun Jin; Oh, Soo-Young; Lim, Yong-Sik

    2007-03-01

    An intermediate monoclinic metal phase between the metal-insulator transition (MIT) and the structural phase transition (SPT) is observed with VO2-based two-terminal devices and can be explained in terms of the Mott MIT. The conductivity of this phase linearly increases with increasing temperature up to TSPT 68^oC and becomes maximum at TSPT. The SPT is confirmed by micro-Raman spectroscopy. Optical microscopic observation reveals the absence of a local current path in the metal phase. The current uniformly flows throughout the surface of the VO2 film when the MIT occurs. This device can be used as a programmable critical temperature sensor. (References: New J. Phys. 6 (1994) 52 (http://www.njp.org); Appl. Phys. Lett. 86 (2005) 24210); Physica B 369 (2005) 76; cond-mat/0607577; cond-mat/0608085; cond-mat/0609033).

  2. Metal-insulator transition in Na{sub x}WO{sub 3}: Photoemission spectromicroscopy study

    SciTech Connect

    Paul, Sanhita Ghosh, Anirudha Raj, Satyabrata

    2014-04-24

    We have investigated the validity of percolation model, which is quite often invoked to explain the metal-insulator transition in sodium tungsten bronzes, Na{sub x}WO{sub 3} by photoelectron spectromicroscopy. The spatially resolved direct spectromicroscopic probing on both the insulating and metallic phases of high quality single crystals of Na{sub x}WO{sub 3} reveals the absence of any microscopic inhomogeneities embedded in the system within the experimental limit. Neither any metallic domains in the insulating host nor any insulating domains in the metallic host have been found to support the validity of percolation model to explain the metal-insulator transition in Na{sub x}WO{sub 3}.

  3. GW study of the metal-insulator transition of bcc hydrogen

    SciTech Connect

    Li, Je-luen; Rignanese, G.-M.; Chang, Eric K.; Blase, Xavier; Louie, Steven G.

    2002-01-31

    We study the metal-insulator transition in a model Mott system, a bcc hydrogen solid, by performing ab initio quasiparticle band-structure calculations within the GW approximation for a wide range of lattice constants. The value of the critical electron density n-sub c is consistent with Mott's original criterion. For smaller lattice constants, our spin-polarized GW results agree well with previous variational quantum Monte Carlo calculations. For large lattice constants, the computed quasiparticle band gap corresponds to the difference between the ionization energy and electron affinity of an isolated hydrogen atom. Near the metal-insulator transition, we investigate the quality of the quasiparticle wave functions obtained from different starting approximations in density-functional theory. Finally, we gain new insight into the GW method and its applicability to spin-polarized systems, for which several refinements are introduced.

  4. Nanostructural model of metal-insulator transition in layered LixZrNCl superconductors

    NASA Astrophysics Data System (ADS)

    Phillips, J. C.

    2008-03-01

    The self-organized dopant percolative filamentary model, entirely orbital in character (no fictive spins), has recently quantitatively and specifically explained chemical trends in ceramic layered cuprate superconductors. Here, this model explains the observation of an abrupt jump ΔTc(x) in LixZrNCl powders over a wide composition range Δx , as well as many other features in the resistivity, lattice constants, Raman spectra, upper critical field, and Meissner volume factor. The ceramic data confirm one-dimensional features in realistic structural models of three-dimensional metal-insulator transitions that had been previously only hypothetical. These data provide a “missing link” between the metal-insulator transition in semiconductor impurity bands and cuprate superconductors. They show that all three material families are united by exhibiting an intermediate phase, absent from crystals, but seen in many properties of network glasses.

  5. Photoelectron spectromicroscopy study of metal-insulator transition in NaxWO3

    NASA Astrophysics Data System (ADS)

    Paul, Sanhita; Ghosh, Anirudha; Dudin, Pavel; Barinov, Alexei; Chakraborty, Anirban; Ray, Sugata; Sarma, D. D.; Oishi, Shuji; Raj, Satyabrata

    2013-07-01

    We have investigated the validity of percolation model, which is quite often invoked to explain the metal-insulator transition in sodium tungsten bronzes, NaxWO3 by photoelectron spectromicroscopy. The spatially resolved direct spectromicroscopic probing on both the insulating and metallic phases of high quality single crystals of NaxWO3 reveals the absence of any microscopic inhomogeneities embedded in the system within the experimental limit. Neither any metallic domains in the insulating host nor any insulating domains in the metallic host have been found to support the validity of percolation model to explain the metal-insulator transition in NaxWO3. The possible origin of insulating phase in NaxWO3 is due to the Anderson localization of all the states near EF. The localization occurs because of the strong disorder arising from random distribution of Na+ ions in the WO3 lattice.

  6. Verwey Metal-Insulator Transition in Magnetite from the Slave-Boson Approach

    NASA Astrophysics Data System (ADS)

    Sherafati, Mohammad; Satpathy, Sashi; Pettey, Dix

    2013-03-01

    We study the Verwey metal-insulator transition in magnetite (Ref.1) by solving a three-band extended Hubbard Hamiltonian for spinless fermions using the slave-boson approach, which also includes coupling to the local phonon modes. This model is suggested from the earlier density-functional studies of magnetite.(Ref.2) We first solve the 1D Hubbard model for the spinless fermions with nearest-neighbor interaction by both Gutzwiller variational and slave-boson methods and show that these two approaches yield different results unlike in the case of the standard Hubbard model, thereby clarifying some of the discrepancies in the literature (Ref.3), then we extend the formalism to three-band Hamiltonian for magnetite. The results suggest a metal-insulator transition at a critical value for the intersite interaction.

  7. Magnetic states, correlation effects and metal-insulator transition in FCC lattice

    NASA Astrophysics Data System (ADS)

    Timirgazin, M. A.; Igoshev, P. A.; Arzhnikov, A. K.; Irkhin, V. Yu

    2016-12-01

    The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals {{t}\\prime}/t . In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most {{t}\\prime}/t . The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on {{t}\\prime}/t . The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

  8. Magnetic states, correlation effects and metal-insulator transition in FCC lattice.

    PubMed

    Timirgazin, M A; Igoshev, P A; Arzhnikov, A K; Yu Irkhin, V

    2016-12-21

    The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals [Formula: see text]. In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most [Formula: see text]. The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on [Formula: see text]. The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

  9. Absence of a magnetic field driven metal-insulator transition in WTe{sub 2}.

    SciTech Connect

    Wang, Y. L.; Thoutam, L. R.; Xiao, Z. L.; Hu, J.; Das, S.; Mao, Z. Q.; Wei, J.; Divan, R.; Luican-Mayer, A.; Crabtree, G. W.; Kwok, W. K.

    2015-11-03

    A hallmark of materials with extremely large magnetoresistance (XMR) is the transformative ‘turn-on’ temperature behavior: when the applied magnetic field H is above certain value, the resistivity versus temperature ρ(T) curve shows a minimum at a field dependent temperature T*, which was seemingly interpreted as a magnetic field driven metal-insulator transition. Here, we demonstrate that ρ(T) curves with ubiquitous turn-on behavior in the newly discovered XMR material WTe2 can be scaled as MR ~ (H/ρ0)m with m ≈ 2 and ρ0 being the resistivity at zero-field. We obtained experimentally and also derived from the observed scaling the magnetic field dependence of the turn-on temperature T* ~ (H-Hc)ν with ν ≈ 1/2, which was earlier used as evidence for a predicted metal-insulator transition. The scaling also leads to a simple quantitative expression for the resistivity ρ* ≈ 2ρ0 at the onset of the XMR behavior, which fits the data remarkably well. These results evidently exclude the possible existence of a magnetic field driven metal-insulator transition in WTe2. This work resolves the origin of the turn-on behavior observed in several XMR materials and also provides a general route for a quantitative understanding of the temperature dependence of MR in both XMR and non-XMR materials.

  10. Disorder and metal-insulator transitions in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Jiang, Hua; Chen, Chui-Zhen; Song, Juntao; Sun, Qing-Feng; Wang, Ziqiang; Xie, X. C.

    The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has Weyl nodes in bulk excitations and Fermi arcs surface states. We study the effects of disorder and localization in WSMs and find three novel phase transitions.(I) Two Weyl nodes near the Brillouin zone boundary can be annihilated pairwise by disorder scattering, resulting in the opening of a topologically nontrivial gap and a transition from a WSM to a three-dimensional (3D) quantum anomalous Hall state. (II) When the two Weyl nodes are well separated in momentum space, the emergent bulk extended states can give rise to a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (III) Two Weyl nodes can emerge near the zone center when an insulating gap closes with increasing disorder, enabling a direct transition from a normal band insulator to a WSM. We determine the phase diagram by numerically computing the localization length and the Hall conductivity, and propose that the novel phase transitions can be realized on a photonic lattice.

  11. Disorder and Metal-Insulator Transitions in Weyl Semimetals

    NASA Astrophysics Data System (ADS)

    Chen, Chui-Zhen; Song, Juntao; Jiang, Hua; Sun, Qing-feng; Wang, Ziqiang; Xie, X. C.

    2015-12-01

    The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has Weyl nodes in bulk excitations and Fermi arc surface states. We study the effects of disorder and localization in WSMs and find three novel phase transitions. (i) Two Weyl nodes near the Brillouin zone boundary can be annihilated pairwise by disorder scattering, resulting in the opening of a topologically nontrivial gap and a transition from a WSM to a three-dimensional quantum anomalous Hall state. (ii) When the two Weyl nodes are well separated in momentum space, the emergent bulk extended states can give rise to a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (iii) Two Weyl nodes can emerge near the zone center when an insulating gap closes with increasing disorder, enabling a direct transition from a normal band insulator to a WSM. We determine the phase diagram by numerically computing the localization length and the Hall conductivity, and propose that the novel phase transitions can be realized on a photonic lattice.

  12. Interaction-Driven Metal-Insulator Transition in Strained Graphene.

    PubMed

    Tang, Ho-Kin; Laksono, E; Rodrigues, J N B; Sengupta, P; Assaad, F F; Adam, S

    2015-10-30

    The question of whether electron-electron interactions can drive a metal to insulator transition in graphene under realistic experimental conditions is addressed. Using three representative methods to calculate the effective long-range Coulomb interaction between π electrons in graphene and solving for the ground state using quantum Monte Carlo methods, we argue that, without strain, graphene remains metallic and changing the substrate from SiO_{2} to suspended samples hardly makes any difference. In contrast, applying a rather large-but experimentally realistic-uniform and isotropic strain of about 15% seems to be a promising route to making graphene an antiferromagnetic Mott insulator.

  13. Metal-insulator transition in random superconducting networks

    SciTech Connect

    Soukoulis, C.M.; Grest, G.S.; Li, Q.

    1988-12-01

    The nature of the eigenstates and the effects on the superconducting-to-normal phase boundary in a two-dimensional random superconducting network are examined by finite-size scaling transfer-matrix calculations within the mean-field Ginzburg-Landau theory of second-order phase transitions. Results for a site-diluted square lattice are presented and a rich structure in the mobility-edge trajectory is obtained. The critical exponent for the slope of the critical field on (p-p/sub c/) is calculated and compared with previous estimates.

  14. Metal-insulator transition in 1 T-TaS 2- xSe x

    NASA Astrophysics Data System (ADS)

    Shiino, O.; Watanabe, T.; Endo, T.; Hanaguri, T.; Kitazawa, K.; Nohara, M.; Takagi, H.; Murayama, C.; Takeshita, N.; Môri, N.; Hasegawa, T.; Yamaguchi, W.

    2000-07-01

    The transition metal dichalcogenide, 1 T-TaS 2, shows metal-insulator transition (MIT) accompanying the nearly commensurate (NC)-commensurate (C) charge density wave (CDW) phase transition at 180 K. It has been proposed that the low-temperature C-CDW phase is a Mott insulator. However, our specific heat and magnetic susceptibility measurements in the 1 T-TaS 2- xSe x system revealed no indications of effective mass enhancement or intrinsic localized spins in the insulating phase. So we propose a new model for the MIT in which the interlayer coupling of the CDW superstructure plays an important role.

  15. Control of plasmonic nanoantennas by reversible metal-insulator transition

    SciTech Connect

    Abate, Yohannes; Marvel, Robert E.; Ziegler, Jed I.; Gamage, Sampath; Javani, Mohammad H.; Stockman, Mark I.; Haglund, Richard F.

    2015-09-11

    We demonstrate dynamic reversible switching of VO2 insulator-to-metal transition (IMT) locally on the scale of 15 nm or less and control of nanoantennas, observed for the first time in the near-field. Using polarization-selective near-field imaging techniques, we simultaneously monitor the IMT in VO2 and the change of plasmons on gold infrared nanoantennas. Structured nanodomains of the metallic VO2 locally and reversibly transform infrared plasmonic dipole nanoantennas to monopole nanoantennas. Fundamentally, the IMT in VO2 can be triggered on femtosecond timescale to allow ultrafast nanoscale control of optical phenomena. In conclusion, these unique features open up promising novel applications in active nanophotonics.

  16. Control of plasmonic nanoantennas by reversible metal-insulator transition

    DOE PAGES

    Abate, Yohannes; Marvel, Robert E.; Ziegler, Jed I.; ...

    2015-09-11

    We demonstrate dynamic reversible switching of VO2 insulator-to-metal transition (IMT) locally on the scale of 15 nm or less and control of nanoantennas, observed for the first time in the near-field. Using polarization-selective near-field imaging techniques, we simultaneously monitor the IMT in VO2 and the change of plasmons on gold infrared nanoantennas. Structured nanodomains of the metallic VO2 locally and reversibly transform infrared plasmonic dipole nanoantennas to monopole nanoantennas. Fundamentally, the IMT in VO2 can be triggered on femtosecond timescale to allow ultrafast nanoscale control of optical phenomena. In conclusion, these unique features open up promising novel applications in activemore » nanophotonics.« less

  17. Control of plasmonic nanoantennas by reversible metal-insulator transition

    PubMed Central

    Abate, Yohannes; Marvel, Robert E.; Ziegler, Jed I.; Gamage, Sampath; Javani, Mohammad H.; Stockman, Mark I.; Haglund, Richard F.

    2015-01-01

    We demonstrate dynamic reversible switching of VO2 insulator-to-metal transition (IMT) locally on the scale of 15 nm or less and control of nanoantennas, observed for the first time in the near-field. Using polarization-selective near-field imaging techniques, we simultaneously monitor the IMT in VO2 and the change of plasmons on gold infrared nanoantennas. Structured nanodomains of the metallic VO2 locally and reversibly transform infrared plasmonic dipole nanoantennas to monopole nanoantennas. Fundamentally, the IMT in VO2 can be triggered on femtosecond timescale to allow ultrafast nanoscale control of optical phenomena. These unique features open up promising novel applications in active nanophotonics. PMID:26358623

  18. Phonon Anomalies and Metal Insulator Transition in Fe(1-x)Co(x)Si

    NASA Astrophysics Data System (ADS)

    Delaire, Olivier; Lucas, Matthew; Stone, Matthew; Abernathy, Douglas; Marty, Karol; Kent, Paul; Sales, Brian; Mandrus, David

    2010-03-01

    The Fe(1-x)Co(x)-Si ordered compound (B20 structure) undergoes a metal-insulator transition upon doping with Co or heating. FeSi is a narrow band-gap semiconductor, whereas CoSi is a metal. Phonons were measured on both single crystals and powders as function of composition and temperature, using inelastic neutron scattering. A reciprocal-space time-of-flight tomography technique, as well as conventional triple-axis spectrometry, were used to map extensive regions of the FeSi dispersions. The phonon branches in FeSi exhibit an excess softening compared to those of CoSi, which appears in better agreement with a pure volume effect. Using first-principles electronic structure calculations and ab-initio molecular dynamics, the anomalies are explained in terms of a metallization induced by thermal disorder. This effect is also related to other cases where the electronic structure leads to anomalous temperature dependencies of the phonons.

  19. Excitonic metal-insulator phase transition of the Mott type in compressed calcium

    NASA Astrophysics Data System (ADS)

    Voronkova, T. O.; Sarry, A. M.; Sarry, M. F.; Skidan, S. G.

    2017-05-01

    It has been experimentally found that, under the static compression of a calcium crystal at room temperature, it undergoes a series of structural phase transitions: face-centered cubic lattice → body-centered cubic lattice → simple cubic lattice. It has been decided to investigate precisely the simple cubic lattice (because it is an alternative lattice) with the aim of elucidating the possibility of the existence of other (nonstructural) phase transitions in it by using for this purpose the Hubbard model for electrons with half-filled ns-bands and preliminarily transforming the initial electronic system into an electron-hole system by means of the known Shiba operators (applicable only to alternative lattices). This transformation leads to the fact that, in the new system of fermions, instead of the former repulsion, there is an attraction between electrons and holes. Elementary excitations of this new system are bound boson pairs—excitons. This system of fermions has been quantitatively analyzed by jointly using the equation-of-motion method and the direct algebraic method. The numerical integration of the analytically exact transcendental equations derived from the first principles for alternative (one-, two-, and three-dimensional) lattices has demonstrated that, in systems of two-species (electrons + hole) fermions, temperature-induced metal-insulator phase transitions of the Mott type are actually possible. Moreover, all these crystals are in fact excitonic insulators. This conclusion is in complete agreement with the analytically exact calculations of the ground state of a one-dimensional crystal (with half-filled bands), which were performed by Lieb and Wu with the aim to find out the Mott insulator-metal transition of another type.

  20. Electron-Phonon Interactions, Metal-Insulator Transitions, and Holographic Massive Gravity

    NASA Astrophysics Data System (ADS)

    Baggioli, Matteo; Pujolàs, Oriol

    2015-06-01

    Massive gravity is holographically dual to "realistic" materials with momentum relaxation. The dual graviton potential encodes the phonon dynamics, and it allows for a much broader diversity than considered so far. We construct a simple family of isotropic and homogeneous materials that exhibit an interaction-driven metal-insulator transition. The transition relates to the formation of polarons—phonon-electron quasibound states that dominate the conductivities, shifting the spectral weight above a mass gap. We characterize the polaron gap, width, and dispersion.

  1. Tuning the metal-insulator transition temperature of Sm0.5Nd0.5NiO3 thin films via strain

    NASA Astrophysics Data System (ADS)

    Gardner, H. Jeffrey; Singh, Vijay; Zhang, Le; Hong, Xia

    2014-03-01

    We have investigated the effect of substrate induced strain and film thickness on the metal-insulator transition of the correlated oxide Sm0.5Nd0.5NiO3 (SNNO). We have fabricated epitaxial 3 - 40 nm thick SNNO films on (001) LaAlO3 (LAO), (001) SrTiO3 (STO), and (110) NdGaO3 (NGO) via off-axis RF magnetron sputtering. The SNNO films are atomically smooth with (001) orientation as determined by atomic force microscopy and x-ray diffraction. SNNO films grown on LAO, subject to compressive strain, exhibit a sharp metal-insulator transition at lower temperatures. Conversely, films grown on STO and NGO, subject to tensile strain, exhibit a smeared albeit above room temperature metal-insulator transition. For all substrates, we have observed that the metal-insulator transition temperature (TMI) increases monotonically with decreasing film thickness until the electrically dead layer is reached (below 4 nm). We discuss the effect of strain and oxygen deficiencies on the TMI of SNNO thin films.

  2. Novel Electronic Behavior Driving NdNiO3 Metal-Insulator Transition.

    PubMed

    Upton, M H; Choi, Yongseong; Park, Hyowon; Liu, Jian; Meyers, D; Chakhalian, J; Middey, S; Kim, Jong-Woo; Ryan, Philip J

    2015-07-17

    We present evidence that the metal-insulator transition (MIT) in a tensile-strained NdNiO3 (NNO) film is facilitated by a redistribution of electronic density and that it neither requires Ni charge disproportionation nor a symmetry change [U. Staub et al., Phys. Rev. Lett. 88, 126402 (2002); R. Jaramillo et al., Nat. Phys. 10, 304 (2014)]. Given that epitaxial tensile strain in thin NNO films induces preferential occupancy of the e(g) d(x(2)-y(2)) orbital we propose that the larger transfer integral of this orbital state with the O 2p orbital state mediates a redistribution of electronic density from the Ni atom. A decrease in the Ni d(x(2)-y(2)) orbital occupation is directly observed by resonant inelastic x-ray scattering below the MIT temperature. Furthermore, an increase in the Nd charge occupancy is measured by x-ray absorption at the Nd L(3) edge. Both spin-orbit coupling and crystal field effects combine to break the degeneracy of the Nd 5d states, shifting the energy of the Nd e(g) d(x(2)-y(2)) orbit towards the Fermi level, allowing the A site to become an active acceptor during the MIT. This work identifies the relocation of electrons from the Ni 3d to the Nd 5d orbitals across the MIT. We propose that the insulating gap opens between the Ni 3d and O 2p states, resulting from Ni 3d electron localization. The transition seems to be neither a purely Mott-Hubbard transition nor a simple charge transfer.

  3. Novel Electronic Behavior Driving NdNiO3 Metal-Insulator Transition

    NASA Astrophysics Data System (ADS)

    Upton, M. H.; Choi, Yongseong; Park, Hyowon; Liu, Jian; Meyers, D.; Chakhalian, J.; Middey, S.; Kim, Jong-Woo; Ryan, Philip J.

    2015-07-01

    We present evidence that the metal-insulator transition (MIT) in a tensile-strained NdNiO3 (NNO) film is facilitated by a redistribution of electronic density and that it neither requires Ni charge disproportionation nor a symmetry change [U. Staub et al., Phys. Rev. Lett. 88, 126402 (2002); R. Jaramillo et al., Nat. Phys. 10, 304 (2014)]. Given that epitaxial tensile strain in thin NNO films induces preferential occupancy of the eg dx2-y2 orbital we propose that the larger transfer integral of this orbital state with the O 2 p orbital state mediates a redistribution of electronic density from the Ni atom. A decrease in the Ni dx2-y2 orbital occupation is directly observed by resonant inelastic x-ray scattering below the MIT temperature. Furthermore, an increase in the Nd charge occupancy is measured by x-ray absorption at the Nd L3 edge. Both spin-orbit coupling and crystal field effects combine to break the degeneracy of the Nd 5 d states, shifting the energy of the Nd eg dx2-y2 orbit towards the Fermi level, allowing the A site to become an active acceptor during the MIT. This work identifies the relocation of electrons from the Ni 3 d to the Nd 5 d orbitals across the MIT. We propose that the insulating gap opens between the Ni 3 d and O 2 p states, resulting from Ni 3 d electron localization. The transition seems to be neither a purely Mott-Hubbard transition nor a simple charge transfer.

  4. Pure electronic metal-insulator transition at the interface of complex oxides

    DOE PAGES

    Meyers, D.; Liu, Jian; Freeland, J. W.; ...

    2016-06-21

    We observed complex materials in electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. We demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. Furthermore, these findings illustrate the utility of heterointerfaces as amore » powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change.« less

  5. Voltage- and current-activated metal-insulator transition in VO2-based electrical switches: a lifetime operation analysis

    NASA Astrophysics Data System (ADS)

    Crunteanu, Aurelian; Givernaud, Julien; Leroy, Jonathan; Mardivirin, David; Champeaux, Corinne; Orlianges, Jean-Christophe; Catherinot, Alain; Blondy, Pierre

    2010-12-01

    Vanadium dioxide is an intensively studied material that undergoes a temperature-induced metal-insulator phase transition accompanied by a large change in electrical resistivity. Electrical switches based on this material show promising properties in terms of speed and broadband operation. The exploration of the failure behavior and reliability of such devices is very important in view of their integration in practical electronic circuits. We performed systematic lifetime investigations of two-terminal switches based on the electrical activation of the metal-insulator transition in VO2 thin films. The devices were integrated in coplanar microwave waveguides (CPWs) in series configuration. We detected the evolution of a 10 GHz microwave signal transmitted through the CPW, modulated by the activation of the VO2 switches in both voltage- and current-controlled modes. We demonstrated enhanced lifetime operation of current-controlled VO2-based switching (more than 260 million cycles without failure) compared with the voltage-activated mode (breakdown at around 16 million activation cycles). The evolution of the electrical self-oscillations of a VO2-based switch induced in the current-operated mode is a subtle indicator of the material properties modification and can be used to monitor its behavior under various external stresses in sensor applications.

  6. Metal-insulator transition in epitaxial NdNiO3 thin film: A structural, electrical and optical study

    NASA Astrophysics Data System (ADS)

    Shao, Tao; Qi, Zeming; Wang, Yuyin; Li, Yuanyuan; Yang, Mei; Hu, Chuansheng

    2017-03-01

    NdNiO3 thin film has been prepared by pulsed laser deposition on LaAlO3 (001) single crystalline substrate. Temperature-dependent resistivity measurement shows a sharp metal-insulator transition in such thin film. The phase transition temperature can be tuned from 90 K to 121 K by changing the thickness of thin film. The structure evolution during phase transition is studied by Raman spectroscopy. Optical conductivity reveals that the variation carrier density in the process of phase transition. The results of structural, electrical and optical studies provide useful insights to understand the mechanism of metal-insulator transition of NdNiO3 thin film.

  7. Origin of the metal-insulator transition of indium atom wires on Si(111)

    NASA Astrophysics Data System (ADS)

    Kim, Sun-Woo; Cho, Jun-Hyung

    2016-06-01

    As a prototypical one-dimensional electron system, self-assembled indium (In) nanowires on the Si(111) surface have been believed to drive a metal-insulator transition by a charge-density-wave (CDW) formation due to Fermi surface nesting. Here, our first-principles calculations demonstrate that the structural phase transition from the high-temperature 4 ×1 phase to the low-temperature 8 ×2 phase occurs through an exothermic reaction with the consecutive bond-breaking and bond-making processes, giving rise to an energy barrier between the two phases as well as a gap opening. This atomistic picture for the phase transition not only identifies its first-order nature but also solves a long-standing puzzle of the origin of the metal-insulator transition in terms of the ×2 periodic lattice reconstruction of In hexagons via bond breakage and new bond formation, not by the Peierls-instability-driven CDW formation.

  8. Multilevel radiative thermal memory realized by the hysteretic metal-insulator transition of vanadium dioxide

    SciTech Connect

    Ito, Kota Nishikawa, Kazutaka; Iizuka, Hideo

    2016-02-01

    Thermal information processing is attracting much interest as an analog of electronic computing. We experimentally demonstrated a radiative thermal memory utilizing a phase change material. The hysteretic metal-insulator transition of vanadium dioxide (VO{sub 2}) allows us to obtain a multilevel memory. We developed a Preisach model to explain the hysteretic radiative heat transfer between a VO{sub 2} film and a fused quartz substrate. The transient response of our memory predicted by the Preisach model agrees well with the measured response. Our multilevel thermal memory paves the way for thermal information processing as well as contactless thermal management.

  9. The electrochemical impact on electrostatic modulation of the metal-insulator transition in nickelates

    SciTech Connect

    Bubel, Simon; Glaudell, Anne M.; Mates, Thomas E.; Chabinyc, Michael L.; Hauser, Adam J.; Stemmer, Susanne

    2015-03-23

    For physical studies of correlated electron systems and for realizing novel device concepts, electrostatic modulation of metal-insulator transitions (MITs) is desired. The inherently high charge densities needed to modulate MITs make this difficult to achieve. The high capacitance of ionic liquids are attractive but, voltages are needed that can be in excess of the electrochemical stability of the system. Here, we show temperature/resistivity data that suggest electrostatic modulation of the MIT temperature of NdNiO{sub 3} in a wide regime. However, additional voltammetric and x-ray photoelectron spectroscopy measurements demonstrate the electrochemical impact of the electrostatic doping approach with ionic liquids.

  10. Multilevel radiative thermal memory realized by the hysteretic metal-insulator transition of vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Ito, Kota; Nishikawa, Kazutaka; Iizuka, Hideo

    2016-02-01

    Thermal information processing is attracting much interest as an analog of electronic computing. We experimentally demonstrated a radiative thermal memory utilizing a phase change material. The hysteretic metal-insulator transition of vanadium dioxide (VO2) allows us to obtain a multilevel memory. We developed a Preisach model to explain the hysteretic radiative heat transfer between a VO2 film and a fused quartz substrate. The transient response of our memory predicted by the Preisach model agrees well with the measured response. Our multilevel thermal memory paves the way for thermal information processing as well as contactless thermal management.

  11. Metal-Insulator Transition in the Hubbard Model: Correlations and Spiral Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Timirgazin, Marat A.; Igoshev, Petr A.; Arzhnikov, Anatoly K.; Irkhin, Valentin Yu.

    2016-12-01

    The metal-insulator transition (MIT) for the square, simple cubic, and body-centered cubic lattices is investigated within the t-t^' Hubbard model at half-filling by using both the generalized for the case of spiral order Hartree-Fock approximation (HFA) and Kotliar-Ruckenstein slave-boson approach. It turns out that the magnetic scenario of MIT becomes superior over the non-magnetic one. The electron correlations lead to some suppression of the spiral phases in comparison with HFA. We found the presence of a metallic antiferromagnetic (spiral) phase in the case of three-dimensional lattices.

  12. Metal-insulator transition in NiS2-x Se x : chemical vs external pressure effects

    NASA Astrophysics Data System (ADS)

    Marini, C.; Valentini, M.; Perucchi, A.; Dore, P.; Sarma, D. D.; Lupi, S.; Postorino, P.

    2011-03-01

    The Se alloying (x)- and the pressure (P)-induced metal-insulator transitions on the strongly correlated NiS2-x Se x system have been investigated through Raman and infrared (IR) spectroscopies. Raman and IR responses of NiS2 to lattice compression are correlated to a metallization transition, occurring at ∼4 GPa. This result suggests a strong interaction between lattice and electronic degrees of freedom. In particular, IR measurements carried out by applying P on NiS2 (i.e. lattice contraction) and on Se alloying (i.e. lattice expansion) reveal that in both cases a metallic state is obtained. Our optical spectroscopy results deviate from the idea of a simple scaling factor between P and x previously claimed by transport measurements, but, on the contrary, point out the substantially different microscopic origin of the two transitions.

  13. Sequential insulator-metal-insulator phase transitions of V O2 triggered by hydrogen doping

    NASA Astrophysics Data System (ADS)

    Chen, Shi; Wang, Zhaowu; Fan, Lele; Chen, Yuliang; Ren, Hui; Ji, Heng; Natelson, Douglas; Huang, Yingying; Jiang, Jun; Zou, Chongwen

    2017-09-01

    As a typical correlated oxide, V O2 has attracted significant attentions due to its pronounced thermal-driven metal-insulator transition. Regulating electronic density through electron doping is an effective way to modulate the balance between competing phases in strongly correlated materials. However, the electron-doping triggered phase transitions in V O2 as well as the intermediate states are not fully explored. Here, we report a controlled and reversible phase transition in V O2 films by continuous hydrogen doping. Metallic and insulating phases are successively observed at room temperature as the doping concentration increases. The doped electrons linearly occupy V 3 d -O 2 p hybridized orbitals and consequently modulate the filling of the V O2 conduction band edge states, resulting in the electron-doping driven continuous phase transitions. These results suggest the exceptional sensitivity of V O2 electronic properties to electron concentration and orbital occupancy, providing key information for the phase transition mechanism.

  14. Ultrathin and Atomically Flat Transition-Metal Oxide: Promising Building Blocks for Metal-Insulator Electronics.

    PubMed

    Cui, Qingsong; Sakhdari, Maryam; Chamlagain, Bhim; Chuang, Hsun-Jen; Liu, Yi; Cheng, Mark Ming-Cheng; Zhou, Zhixian; Chen, Pai-Yen

    2016-12-21

    We present a new and viable template-assisted thermal synthesis method for preparing amorphous ultrathin transition-metal oxides (TMOs) such as TiO2 and Ta2O5, which are converted from crystalline two-dimensional (2D) transition-metal dichalcogenides (TMDs) down to a few atomic layers. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the chemical composition and bonding, surface morphology, and atomic structure of these ultrathin amorphous materials to validate the effectiveness of our synthesis approach. Furthermore, we have fabricated metal-insulator-metal (MIM) diodes using the TiO2 and Ta2O5 as ultrathin insulating layers with low potential barrier heights. Our MIM diodes show a clear transition from direct tunneling to Fowler-Nordheim tunneling, which was not observed in previously reported MIM diodes with TiO2 or Ta2O5 as the insulating layer. We attribute the improved performance of our MIM diodes to the excellent flatness and low pinhole/defect densities in our TMO insulting layers converted from 2D TMDs, which enable the low-threshold and controllable electron tunneling transport. We envision that it is possible to use the ultrathin TMOs converted from 2D TMDs as the insulating layer of a wide variety of metal-insulator and field-effect electronic devices for various applications ranging from microwave mixing, parametric conversion, infrared photodetection, emissive energy harvesting, to ultrafast electronic switching.

  15. Moderate pressure synthesis of rare earth nickelate with metal-insulator transition using polymeric precursors

    SciTech Connect

    Napierala, C.; Lepoittevin, C.; Edely, M.; Sauques, L.; Giovanelli, F.; Laffez, P.; VanTedeloo, G.

    2010-07-15

    Rare earth nickelates exhibit a reversible metal-semiconductor phase transition that is, in the infrared range, responsible for a thermo-optical contrast. The state of the art synthesis of these compounds usually requires high oxygen pressure to stabilize Ni in the oxidation state 3{sup +}. In this work, using polymeric precursor associated with moderate pressure annealing, we show that it is possible to obtain fully oxidized rare earth nickelate with metal-insulator transition. Using thermogravimetric analysis, X-ray diffraction and transmission electronic microscopy we compare different samples synthesized at different oxygen pressures and demonstrate their structural similarity. Thermo-optical properties were measured, in the infrared range, using reflectance measurements and confirmed the metal-insulator transition at 60 {sup o}C in both samples.TEM observations lead to the conclusion that the structure commonly obtained at 175 bar is perfectly observed in the 20 bar sample without major structural defects. The two samples exhibit a thermochromic behavior and thermo-optical properties of the two samples are equivalent. - Graphical Abstract: Thermochromic behavior of Nd{sub 0.3}Sm{sub 0.7}NiO{sub 3} samples annealed under 20 and 175 bar at 278 and 373 K.

  16. Metal-insulator transition in disordered systems from the one-body density matrix

    NASA Astrophysics Data System (ADS)

    Olsen, Thomas; Resta, Raffaele; Souza, Ivo

    2017-01-01

    The insulating state of matter can be probed by means of a ground state geometrical marker, which is closely related to the modern theory of polarization (based on a Berry phase). In the present work we show that this marker can be applied to determine the metal-insulator transition in disordered systems. In particular, for noninteracting systems the geometrical marker can be obtained from the configurational average of the norm-squared one-body density matrix, which can be calculated within open as well as periodic boundary conditions. This is in sharp contrast to a classification based on the static conductivity, which is only sensible within periodic boundary conditions. We exemplify the method by considering a simple lattice model, known to have a metal-insulator transition as a function of the disorder strength, and demonstrate that the transition point can be obtained accurately from the one-body density matrix. The approach has a general ab initio formulation and could in principle be applied to realistic disordered materials by standard electronic structure methods.

  17. Interplay between Ferroelastic and Metal-Insulator Phase Transitions in Strained Quasi-2D VO[subscript 2] Nanoplatelets

    SciTech Connect

    Tselev, Alexander; Strelcov, Evgheni; Luk’yanchuk, Igor A.; Budai, John D.; Tischler, Jonathan Z.; Ivanov, Ilia N.; Jones, Keith; Proksch, Roger; Kalinin, Sergei V.; Kolmakov, Aandrei

    2010-07-06

    Formation of ferroelastic twin domains in vanadium dioxide (VO{sub 2}) nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline VO{sub 2} quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the 2D geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate the possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and nontrivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that a complete picture of the phase transitions in single-crystalline and disordered VO{sub 2} structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

  18. Interplay between Ferroelastic and Metal-Insulator Phase Transitions in Strained Quasi-2D VO[subscript 2] Nanoplatelets

    SciTech Connect

    Tselev, Alexander; Strelcov, Evgheni; Luk’yanchuk, Igor A.; Budai, John D.; Tischler, Jonathan Z.; Ivanov, Ilia N.; Jones, Keith; Proksch, Roger; Kalinin, Sergei V.; Kolmakov, Andrei

    2011-08-09

    Formation of ferroelastic twin domains in vanadium dioxide (VO{sub 2}) nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline VO{sub 2} quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the 2D geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate the possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and nontrivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that a complete picture of the phase transitions in single-crystalline and disordered VO{sub 2} structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

  19. Dynamics of the metal-insulator transition of donor-doped SrTi O3

    NASA Astrophysics Data System (ADS)

    Meyer, René; Zurhelle, Alexander F.; De Souza, Roger A.; Waser, Rainer; Gunkel, Felix

    2016-09-01

    The electrical properties of donor-doped SrTi O3 (n -STO) are profoundly affected by an oxidation-induced metal-insulator transition (MIT). Here we employ dynamical numerical simulations to examine the high-temperature MIT of n -STO over a large range of time and length scales. The simulations are based on the Nernst-Planck equations, the continuity equations, and the Poisson equation, in combination with surface lattice disorder equilibria serving as time-dependent boundary conditions. The simulations reveal that n -STO, upon oxidation, develops a kinetic space charge region (SCR) in the near-surface region. The surface concentrations of the variously mobile defects (electrons, Sr vacancies, and O vacancies) are found to vary over time and to differ considerably from the values of the new equilibrium. The formation of the SCR in which electrons are strongly depleted occurs within nanoseconds, i.e., it yields a fast MIT in the near-surface region during the oxidation process. As a result of charge (over-)compensation by Sr vacancies incorporated at the surface of n -STO, this SCR is much more pronounced than conventionally expected. In addition, we find an anomalous increase of O vacancy concentration at the surface upon oxidation caused by the SCR. Our simulations show that the SCR fades in the long term as a result of the slow in-diffusion of Sr vacancies. We discuss implications for the electrical conductivity of n -STO crystals used as substrates for epitaxial oxide thin films, of n -STO thin films and interfaces, and of polycrystalline n -STO with various functionalities.

  20. Thermally driven analog of the Barkhausen effect at the metal-insulator transition in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Huber-Rodriguez, Benjamin; Kwang, Siu Yi; Hardy, Will J.; Ji, Heng; Chen, Chih-Wei; Morosan, Emilia; Natelson, Douglas

    2014-09-01

    The physics of the metal-insulator transition (MIT) in vanadium dioxide remains a subject of intense interest. Because of the complicating effects of elastic strain on the phase transition, there is interest in comparatively strain-free means of examining VO2 material properties. We report contact-free, low-strain studies of the MIT through an inductive bridge approach sensitive to the magnetic response of VO2 powder. Rather than observing the expected step-like change in susceptibility at the transition, we argue that the measured response is dominated by an analog of the Barkhausen effect, due to the extremely sharp jump in the magnetic response of each grain as a function of time as the material is cycled across the phase boundary. This effect suggests that future measurements could access the dynamics of this and similar phase transitions.

  1. Thermal Conductivity and Thermopower near the 2D Metal-Insulator transition, Final Technical Report

    SciTech Connect

    Sarachik, Myriam P.

    2015-02-20

    STUDIES OF STRONGLY-INTERACTING 2D ELECTRON SYSTEMS – There is a great deal of current interest in the properties of systems in which the interaction between electrons (their potential energy) is large compared to their kinetic energy. We have investigated an apparent, unexpected metal-insulator transition inferred from the behavior of the temperature-dependence of the resistivity; moreover, detailed analysis of the behavior of the magnetoresistance suggests that the electrons’ effective mass diverges, supporting this scenario. Whether this is a true phase transition or crossover behavior has been strenuously debated over the past 20 years. Our measurements have now shown that the thermoelectric power of these 2D materials diverges at a finite density, providing clear evidence that this is, in fact, a phase transition to a new low-density phase which may be a precursor or a direct transition to the long sought-after electronic crystal predicted by Eugene Wigner in 1934.

  2. Thermally driven analog of the Barkhausen effect at the metal-insulator transition in vanadium dioxide

    SciTech Connect

    Huber-Rodriguez, Benjamin; Ji, Heng; Chen, Chih-Wei; Kwang, Siu Yi; Hardy, Will J.; Morosan, Emilia; Natelson, Douglas

    2014-09-29

    The physics of the metal-insulator transition (MIT) in vanadium dioxide remains a subject of intense interest. Because of the complicating effects of elastic strain on the phase transition, there is interest in comparatively strain-free means of examining VO{sub 2} material properties. We report contact-free, low-strain studies of the MIT through an inductive bridge approach sensitive to the magnetic response of VO{sub 2} powder. Rather than observing the expected step-like change in susceptibility at the transition, we argue that the measured response is dominated by an analog of the Barkhausen effect, due to the extremely sharp jump in the magnetic response of each grain as a function of time as the material is cycled across the phase boundary. This effect suggests that future measurements could access the dynamics of this and similar phase transitions.

  3. Metal-insulator transition in the one-dimensional organic conductor (TSM-TTP)(I 3) 5/3

    NASA Astrophysics Data System (ADS)

    Kawamoto, T.; Mori, T.; Misaki, Y.; Tanaka, K.; Mori, H.; Tanaka, S.

    1998-04-01

    (TSM-TTP)(I 3) 5/3 (TSM-TTP: 2,5-bis[4,5-bis(methylseleno)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene) is a one-dimensional organic conductor which undergoes a metal-insulator transition at TMI≈20 K. High pressure resistivity, ESR, and static magnetic susceptibility measurements have been carried out to clarify the origin of the metal-insulator transition. The metal-insulator transition temperature is not completely suppressed even under a pressure of 11.8 kbar. The ESR line shape shows no anomaly and the magnetic susceptibility shows a slight increase below 70 K, and remains paramagnetic down to 1.75 K; no evidence of spin-Peierls or antiferromagnetic transition is obtained.

  4. Thermal radiative near field transport between vanadium dioxide and silicon oxide across the metal insulator transition

    SciTech Connect

    Menges, F.; Spieser, M.; Riel, H.; Gotsmann, B.; Dittberner, M.; Novotny, L.; Passarello, D.; Parkin, S. S. P.

    2016-04-25

    The thermal radiative near field transport between vanadium dioxide and silicon oxide at submicron distances is expected to exhibit a strong dependence on the state of vanadium dioxide which undergoes a metal-insulator transition near room temperature. We report the measurement of near field thermal transport between a heated silicon oxide micro-sphere and a vanadium dioxide thin film on a titanium oxide (rutile) substrate. The temperatures of the 15 nm vanadium dioxide thin film varied to be below and above the metal-insulator-transition, and the sphere temperatures were varied in a range between 100 and 200 °C. The measurements were performed using a vacuum-based scanning thermal microscope with a cantilevered resistive thermal sensor. We observe a thermal conductivity per unit area between the sphere and the film with a distance dependence following a power law trend and a conductance contrast larger than 2 for the two different phase states of the film.

  5. Mott metal-insulator transition in the doped Hubbard-Holstein model

    NASA Astrophysics Data System (ADS)

    Kurdestany, Jamshid Moradi; Satpathy, S.

    2017-08-01

    Motivated by the current interest in the understanding of the Mott insulators away from half-filling, observed in many perovskite oxides, we study the Mott metal-insulator transition in the doped Hubbard-Holstein model using the Hartree-Fock mean field theory. The Hubbard-Holstein model is the simplest model containing both the Coulomb and the electron-lattice interactions, which are important ingredients in the physics of the perovskite oxides. In contrast to the half-filled Hubbard model, which always results in a single phase (either metallic or insulating), our results show that away from half-filling, a mixed phase of metallic and insulating regions occurs. As the dopant concentration is increased, the metallic part progressively grows in volume, until it exceeds the percolation threshold, leading to percolative conduction. This happens above a critical dopant concentration δc, which, depending on the strength of the electron-lattice interaction, can be a significant fraction of unity. This means that the material could be insulating even for a substantial amount of doping, in contrast to the expectation that doped holes would destroy the insulating behavior of the half-filled Hubbard model. While effects of fluctuation beyond the mean field remain an open question, our results provide a starting point for the understanding of the density-driven metal-insulator transition observed in many complex oxides.

  6. Superconductivity and bandwidth-controlled Mott metal-insulator transition in 1T-TaS2-xSex

    NASA Astrophysics Data System (ADS)

    Ang, R.; Miyata, Y.; Ieki, E.; Nakayama, K.; Sato, T.; Liu, Y.; Lu, W. J.; Sun, Y. P.; Takahashi, T.

    2013-09-01

    We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) of layered chalcogenide 1T-TaS2-xSex to elucidate the electronic states especially relevant to the occurrence of superconductivity. We found a direct evidence for a Ta-5d-derived electron pocket associated with the superconductivity, which is fragile against a Mott-gap opening observed in the insulating ground state for S-rich samples. In particular, a strong electron-electron interaction-induced Mott gap driven by a Ta 5d orbital also exists in the metallic ground state for Se-rich samples, while finite ARPES intensity near the Fermi level likely originating from a Se 4p orbital survives, indicative of the orbital-selective nature of the Mott transition. Present results suggest that effective electron correlation and p-d hybridization play a crucial role to tune the superconductivity and Mott metal-insulator transition.

  7. Light scattering by epitaxial VO{sub 2} films near the metal-insulator transition point

    SciTech Connect

    Lysenko, Sergiy Fernández, Felix; Rúa, Armando; Figueroa, Jose; Vargas, Kevin; Cordero, Joseph; Aparicio, Joaquin; Sepúlveda, Nelson

    2015-05-14

    Experimental observation of metal-insulator transition in epitaxial films of vanadium dioxide is reported. Hemispherical angle-resolved light scattering technique is applied for statistical analysis of the phase transition processes on mesoscale. It is shown that the thermal hysteresis strongly depends on spatial frequency of surface irregularities. The transformation of scattering indicatrix depends on sample morphology and is principally different for the thin films with higher internal elastic strain and for the thicker films where this strain is suppressed by introduction of misfit dislocations. The evolution of scattering indicatrix, fractal dimension, surface power spectral density, and surface autocorrelation function demonstrates distinctive behavior which elucidates the influence of structural defects and strain on thermal hysteresis, twinning of microcrystallites, and domain formation during the phase transition.

  8. Diffusion Monte Carlo study of the metal-insulator transition in stretched graphene

    NASA Astrophysics Data System (ADS)

    Chen, Li; Wagner, Lucas K.

    At low energies and equilibrium geometries, graphene is well-described by a single-band Hubbard model, with U/t 1.4, which is well within the semimetal regime. One would expect that under tensile stress, U/t should increase and a transition from semimetal to Mott insulator should occur. However, the bonding σ electrons are also affected by the stretching and may affect the applicability of the single-band model. At the same time, the critical region near the metal-insulator transition is a highly multi-determinantal ground state which is a challenging case for fixed node diffusion Monte Carlo simulations. We address progress on both these points by assessing a number of wave functions for the critical region around the transition and assessing the validity of the single-band Hubbard model using the method of Ref 1. This work was supported by NSF DMR 1206242.

  9. Electronic Excitations and Metal-Insulator Transition inPoly(3-hexylthiophene) Organic Field-Effect Transistors

    SciTech Connect

    Sai, N.; Li, Z.Q.; Martin, M.C.; Basov, D.N.; Di Ventra, M.

    2006-11-07

    We carry out a comprehensive theoretical and experimentalstudy of charge injection in poly(3-hexylthiophene) (P3HT) to determinethe most likely scenario for metal-insulator transition in this system.Wecalculate the optical-absorption frequencies corresponding to a polaronand a bipolaron lattice in P3HT. We also analyze the electronicexcitations for three possible scenarios under which a first- or asecond-order metal-insulator transition can occur in doped P3HT. Thesetheoretical scenarios are compared with data from infrared absorptionspectroscopy on P3HT thin-film field-effect transistors (FETs). Ourmeasurements and theoretical predictions suggest that charge-inducedlocalized states in P3HT FETs are bipolarons and that the highest dopinglevel achieved in our experiments approaches that required for afirst-order metal-insulator transition.

  10. Role of magnetic and orbital ordering at the metal-insulator transition in NdNiO{sub 3}

    SciTech Connect

    Scagnoli, V.; Staub, U.; Mulders, A. M.; Janousch, M.; Meijer, G. I.; Hammerl, G.; Tonnerre, J. M.; Stojic, N.

    2006-03-01

    Soft x-ray resonant scattering at the Ni L{sub 2,3} edges is used to test models of magnetic- and orbital-ordering below the metal-insulator transition in NdNiO{sub 3}. The large branching ratio of the L{sub 3} to L{sub 2} intensities of the (1/2 0 1/2) reflection and the observed azimuthal angle and polarization dependence originates from a noncollinear magnetic structure. The absence of an orbital signal and the noncollinear magnetic structure show that the nickelates are materials for which orbital ordering is absent at the metal-insulator transition.

  11. Stable metal-insulator transition in epitaxial SmNiO{sub 3} thin films

    SciTech Connect

    Ha, Sieu D.; Otaki, Miho; Jaramillo, R.; Podpirka, Adrian; Ramanathan, Shriram

    2012-06-15

    Samarium nickelate (SmNiO{sub 3}) is a correlated oxide that exhibits a metal-insulator transition (MIT) above room temperature and is of interest for advanced electronics and optoelectronics. However, studies on SmNiO{sub 3} thin films have been limited to date, in part due to well-known difficulties in stabilizing the Ni{sup 3+} valence state during growth, which are manifested in non-reproducible electrical characteristics. In this work, we show that stable epitaxial SmNiO{sub 3} thin films can be grown by rf magnetron sputtering without extreme post-deposition annealing conditions using relatively high growth pressure (>200 mTorr). At low growth pressure, SmNiO{sub 3} is insulating and undergoes an irreversible MIT at {approx}430 K. As pressure is increased, films become metallic across a large temperature range from 100 to 420 K. At high pressure, films are insulating again but with a reversible and stable MIT at {approx}400 K. Phase transition properties can be continuously tuned by control of the sputtering pressure. - Graphical Abstract: X-ray diffraction (left) and resistivity-temperature characteristics (right) of sputtered SmNiO{sub 3} thin films as a function of sputtering pressure. As sputtering pressure increases, the out-of-plane lattice constant of SmNiO{sub 3} decreases, consistent with enhanced oxygen concentration. Concordantly, the electrical properties are strongly modified, and a reversible metal-insulator phase transition is observed at {approx}400 K in the film grown at high pressure. Highlights: Black-Right-Pointing-Pointer Stable SmNiO{sub 3} films grown by rf sputtering without extreme annealing conditions. Black-Right-Pointing-Pointer High sputtering pressures needed to fully stabilize SmNiO{sub 3}. Black-Right-Pointing-Pointer Reversible metal-insulator transition observed at {approx}400 K, similar to bulk. Black-Right-Pointing-Pointer Electrical properties strongly modifiable by varying sputtering pressure.

  12. Electrodynamics of the conducting polymer polyaniline on the insulating side of the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Helgren, Erik; Penney, Keith; Diefenbach, Matt; Longnickel, Maryna; Wainwright, Mark; Walker, Eldridge; Al-Azzawi, Sarah; Erhahon, Hendrix; Singley, Jason

    2017-03-01

    Conducting polymer samples of polyaniline (PANI) exhibit a dramatic change in their conductivity as a function of protonation level, analogous with the changes in the transport properties of semiconductors upon doping. In this paper, PANI samples were prepared by protonating with varying concentrations of hydrochloric acid. The complex terahertz frequency-dependent conductivity and the dc conductivity of these samples were measured and analyzed in the framework of the disorder-driven, metal-insulator quantum phase transition. The samples were determined to all fall in the insulating phase of this phase transition. The frequency dependence of both the real and imaginary terahertz conductivity are found to be consistent with theories that include electronic correlation effects.

  13. Metal - Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials

    PubMed Central

    Bragaglia, Valeria; Arciprete, Fabrizio; Zhang, Wei; Mio, Antonio Massimiliano; Zallo, Eugenio; Perumal, Karthick; Giussani, Alessandro; Cecchi, Stefano; Boschker, Jos Emiel; Riechert, Henning; Privitera, Stefania; Rimini, Emanuele; Mazzarello, Riccardo; Calarco, Raffaella

    2016-01-01

    Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows. PMID:27033314

  14. Suppression of the weak localization near the metal-insulator transition in two dimensions

    NASA Astrophysics Data System (ADS)

    Rahimi, Maryam; Anissimova, S.; Sakr, M. R.; Kravchenko, S. V.; Klapwijk, T. M.

    2003-03-01

    We have studied the suppression of weak localization by perpendicular magnetic field in low-disordered two-dimensional electron systems in silicon for a range of electron densities. We show that the negative corrections to the resistance, found in the metallic phase, disappear in the vicinity of the metal-insulator transition. Our data suggest that localization is fully suppressed near and at the transition even in zero field, confirming similar results in ultra-clean p-GaAs/AlGaAs heterostructures [1] and verifying their universality. [1] A. P. Mills, A. P. Ramirez, X. P. A. Gao, L. N. Pfeiffer, K. W. West, and S. H. Simon, preprint cond-mat/0101020.

  15. Low-energy description of the metal-insulator transition in the rare-earth nickelates

    NASA Astrophysics Data System (ADS)

    Subedi, Alaska; Peil, Oleg E.; Georges, Antoine

    2015-02-01

    We propose a simple theoretical description of the metal-insulator transition of rare-earth nickelates. The theory involves only two orbitals per nickel site, corresponding to the low-energy antibonding eg states. In the monoclinic insulating state, bond-length disproportionation splits the manifold of eg bands, corresponding to a modulation of the effective on-site energy. We show that, when subject to a local Coulomb repulsion U and Hund's coupling J , the resulting bond-disproportionated state is a paramagnetic insulator for a wide range of interaction parameters. Furthermore, we find that when U -3 J is small or negative, a spontaneous instability to bond disproportionation takes place for large enough J . This minimal theory emphasizes that a small or negative charge-transfer energy, a large Hund's coupling, and a strong coupling to bond disproportionation are the key factors underlying the transition. Experimental consequences of this theoretical picture are discussed.

  16. Hund's coupling and the metal-insulator transition in the two-band Hubbard model

    NASA Astrophysics Data System (ADS)

    Pruschke, Th.; Bulla, R.

    2005-03-01

    The Mott-Hubbard metal-insulator transition is investigated in a two-band Hubbard model within dynamical mean-field theory. To this end, we use a suitable extension of Wilson’s numerical renormalization group for the solution of the effective two-band single-impurity Anderson model. This method is non-perturbative and, in particular, allows to take into account the full exchange part of the Hund’s rule coupling between the two orbitals. We discuss in detail the influence of the various Coulomb interactions on thermodynamic and dynamic properties, for both the impurity and the lattice model. The exchange part of the Hund’s rule coupling turns out to play an important role for the physics of the two-band Hubbard model and for the nature of the Mott-transition.

  17. Metal - Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials

    NASA Astrophysics Data System (ADS)

    Bragaglia, Valeria; Arciprete, Fabrizio; Zhang, Wei; Mio, Antonio Massimiliano; Zallo, Eugenio; Perumal, Karthick; Giussani, Alessandro; Cecchi, Stefano; Boschker, Jos Emiel; Riechert, Henning; Privitera, Stefania; Rimini, Emanuele; Mazzarello, Riccardo; Calarco, Raffaella

    2016-04-01

    Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows.

  18. Metal-insulator-metal transition in NdNiO3 films capped by CoFe2O4

    NASA Astrophysics Data System (ADS)

    Saleem, M. S.; Song, C.; Peng, J. J.; Cui, B.; Li, F.; Gu, Y. D.; Pan, F.

    2017-02-01

    Metal-insulator transition features as a transformation from a highly charge conductive state to another state where the charge conductivity is greatly suppressed when decreasing the temperature. Here, we demonstrate two consecutive transitions in NdNiO3 films with CoFe2O4 capping, in which the metal-insulator transition occurs at ˜85 K, followed by an unprecedented insulator-metal transition below 40 K. The emerging insulator-metal transition associated with a weak antiferromagnetic behavior is observed in 20 unit cell-thick NdNiO3 with more than 5 unit cell CoFe2O4 capping. Differently, the NdNiO3 films with thinner CoFe2O4 capping only exhibit metal-insulator transition at ˜85 K, accompanied by a strong antiferromagnetic state below 40 K. Charge transfer from Co to Ni, instead of from Fe to Ni, formulates the ferromagnetic interaction between Ni-Ni and Ni-Co atoms, thus suppressing the antiferromagnetic feature and producing a metallic conductive behavior. Furthermore, a phase diagram for the metal-insulator-metal transition in this system is drawn.

  19. Tuning directional dependent metal-insulator transitions in quasi-1D quantum wires with spin-orbit density wave instability

    NASA Astrophysics Data System (ADS)

    Das, Tanmoy

    2016-07-01

    We study directional dependent band gap evolutions and metal-insulator transitions (MITs) in model quantum wire systems within the spin-orbit density wave (SODW) model. The evolution of MIT is studied as a function of varying anisotropy between the intra-wire hopping ({{t}\\parallel} ) and inter-wire hopping ({{t}\\bot} ) with Rashba spin-orbit coupling. We find that as long as the anisotropy ratio (β ={{t}\\bot}/{{t}\\parallel} ) remains below 0.5, and the Fermi surface nesting is tuned to {{\\mathbf{Q}}1}=≤ft(π,0\\right) , an exotic SODW induced MIT easily develops, with its critical interaction strength increasing with increasing anisotropy. As β \\to 1 (2D system), the nesting vector switches to {{\\mathbf{Q}}2}=≤ft(π,π \\right) , making this state again suitable for an isotropic MIT. Finally, we discuss various physical consequences and possible applications of the directional dependent MIT.

  20. Metal-insulator transition by isovalent anion substitution in Ga1-xMnxAs: Implications to ferromagnetism

    SciTech Connect

    Stone, P.R.; Alberi, K.; Tardif, S.K.Z.; Beeman, J.W.; Yu, K.M.; Walukiewicz, W.; Dubon, O.D.

    2008-02-07

    We have investigated the effect of partial isovalent anion substitution in Ga1-xMnxAs on electrical transport and ferromagnetism. Substitution of only 2.4percent of As by P induces a metal-insulator transition at a constant Mn doping of x=0.046 while the replacement of 0.4 percent As with N results in the crossover from metal to insulator for x=0.037. This remarkable behavior is consistent with a scenario in which holes located within an impurity band are scattered by alloy disorder in the anion sublattice. The shorter mean free path of holes, which mediate ferromagnetism, reduces the Curie temperature TC from 113 K to 60 K (100 K to 65 K) upon the introduction of 3.1 percent P (1percent N) into the As sublattice.

  1. Magnetic Field Induced Metal-Insulator Transition in Pr_1-x(La_1-ySr_y)_xMnO3 (x=0.45, y=0.15)

    NASA Astrophysics Data System (ADS)

    Ye, F.; Fernandez-Baca, J. A.; Dai, P.; Tomioka, Y.; Tokura, Y.

    2004-03-01

    Recently, the electronic phase diagram of Pr_1-x(Ca_1-ySr_y)_xMnO3 (x=0.45)has been studied in the vicinity of the metal-insulator transition boundary. By controlling the eg electron bandwidth W, the ground state can be tuned to change from a charged-ordered (CO) and orbitally-ordered (OO) state (y<=0.2) to a ferromagnetic metallic state (y>0.25). This system has been reported to exhibit bicritical features near y =0.25. We have used elastic and inelastic neutron scattering to study the magnetic correlations and spin dynamics of the sample near the insulator-metal boundary. The insulating CO/OO ground state of y=0.15 can be melted by the application of external field. The evolution of the CO/OO when a magnetic field is applied will be discussed in the context of the competing interactions that may be responsible for the CMR effect. This work was supported by the U.S. DOE under Contract No. DE-AC05-00OR22725 with UT-Batelle, LLC; and by NSF grant DMR-0139882.

  2. Enhanced conductivity and metal-insulator transition of ultrathin CaRuO3 in superlattices

    NASA Astrophysics Data System (ADS)

    Xu, Haoran; Chen, Binbin; Jin, Feng; Guo, Zhuang; Gao, Guanyin; Chen, Feng; Wu, Wenbin

    2016-12-01

    Transport characteristics of CaRuO3(CRO)/SmFeO3(SFO) superlattices are studied as a function of the thickness of CRO (0.8 nm ≤ t CRO ≤ 3.2 nm). An abrupt enhancement of the conductivity is observed on superlattices, although ultrathin CRO film show a very high resistance and SFO single layer is insulating. The superlattices with t CRO between 2.0 and 3.2 nm retain a metallic state. As t CRO decreases to 1.6 nm or even thinner in superlattices, the metallic state turns to insulating state. The metal-insulator transition could be attributed to the comparable scale for the disorder length and the electron travel distance at small t CRO value, which causes a change from weak localization to strong localization.

  3. Magnetically driven metal-insulator transition in NaOsO3.

    PubMed

    Calder, S; Garlea, V O; McMorrow, D F; Lumsden, M D; Stone, M B; Lang, J C; Kim, J-W; Schlueter, J A; Shi, Y G; Yamaura, K; Sun, Y S; Tsujimoto, Y; Christianson, A D

    2012-06-22

    The metal-insulator transition (MIT) is one of the most dramatic manifestations of electron correlations in materials. Various mechanisms producing MITs have been extensively considered, including the Mott (electron localization via Coulomb repulsion), Anderson (localization via disorder), and Peierls (localization via distortion of a periodic one-dimensional lattice) mechanisms. One additional route to a MIT proposed by Slater, in which long-range magnetic order in a three dimensional system drives the MIT, has received relatively little attention. Using neutron and x-ray scattering we show that the MIT in NaOsO(3) is coincident with the onset of long-range commensurate three dimensional magnetic order. While candidate materials have been suggested, our experimental methodology allows the first definitive demonstration of the long predicted Slater MIT.

  4. Magnetically Driven Metal-Insulator Transition in NaOsO3

    SciTech Connect

    Calder, Stuart A; Christianson, Andrew D; Lumsden, Mark D; Lang, Jonathan; Stone, Matthew B; McMorrow, D. F.; Garlea, Vasile O; Kim, Jong-Woo; Schlueter, J. A.; Shi, Y. G.; Yamaura, K.; Sun, Y. S.; Tsujimoto, Y.

    2012-01-01

    The metal-insulator transition (MIT) is one of the most dramatic manifestations of electron correlations in materials. Various mechanisms producing MITs have been extensively considered, including the Mott (electron localization via Coulomb repulsion), Anderson (localization via disorder), and Peierls (local- ization via distortion of a periodic one-dimensional lattice) mechanisms. One additional route to a MIT proposed by Slater, in which long-range magnetic order in a three dimensional system drives the MIT, has received relatively little attention. Using neutron and x-ray scattering we show that the MIT in NaOsO3 is coincident with the onset of long-range commensurate three dimensional magnetic order. While candidate materials have been suggested, our experimental methodology allows the first definitive demonstration of the long predicted Slater MIT.

  5. Metal-insulator transition in nanocomposite VO{sub x} films formed by anodic electrodeposition

    SciTech Connect

    Tsui, Lok-kun; Lu, Jiwei; Zangari, Giovanni; Hildebrand, Helga; Schmuki, Patrik

    2013-11-11

    The ability to grow VO{sub 2} films by electrochemical methods would open a low-cost, easily scalable production route to a number of electronic devices. We have synthesized VO{sub x} films by anodic electrodeposition of V{sub 2}O{sub 5}, followed by partial reduction by annealing in Ar. The resulting films are heterogeneous, consisting of various metallic/oxide phases and including regions with VO{sub 2} stoichiometry. A gradual metal insulator transition with a nearly two order of magnitude change in film resistance is observed between room temperature and 140 °C. In addition, the films exhibit a temperature coefficient of resistance of ∼ −2.4%/ °C from 20 to 140 °C.

  6. Surface states, surface metal-insulator, and surface insulator-metal transitions

    NASA Astrophysics Data System (ADS)

    Tosatti, E.

    1995-05-01

    An informal discussion of various cases where two-dimensional surface metal-insulator structural and charge-density-wave instabilities driven by partly filled surface states have been advocated is presented. These include reconstructions of clean semiconductor surfaces and of W(100) and Mo(100), as well as anomalies on the hydrogen-covered surfaces H/W(110) and H/Mo(110), and possibly alkali-covered surfaces such as K/Cu(111). In addition, there is a discussion of the opposite type of phenomena, namely surface insulator-metal transitions, which can be argued to occur on (alpha)-Ga(001), high-temperature Ge(111), and probably Be(0001).

  7. Mechanism of the metal-insulator transition of hollandite vanadate K2V8O16

    NASA Astrophysics Data System (ADS)

    Toriyama, T.; Konishi, T.; Ohta, Y.

    2012-12-01

    We make the electronic structure calculations of hollandite vanadate K2V8O16 using the generalized gradient approximation (GGA) in the density functional theory, where the Hubbard-type repulsive interaction U is taken into account (GGA+U). We in particular calculate the electronic structure of the low-temperature phase of this material using the crystal structure reported by Komarek et al. We find that the electronic wave functions near the Fermi level are predominantly of the dxy character and form the quasi-one-dimensional energy bands. The energy bands are made of the single chains of the VO6 octahedra rather than the double chains. The effects of strong electron correlations play an essential role here. Based on these results, we discuss possible mechanisms of the observed metal-insulator transition of this material.

  8. Hallmarks of Metal Insulator transition in Doped Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Cao, Yue; Wang, Qiang; Dhaka, Rajendra; Waugh, Justin; Reber, Theodore; Li, Haoxiang; Parham, Stephen; Zhou, Xiaoqing; Park, Seung Ryong; Qi, Tongfei; Korneta, Oleksandr; Plumb, Nicholas; Bostwick, Aaron; Rotenberg, Eli; Denlinger, Jonathan; Hermele, Michael; Cao, Gang; Dessau, Daniel

    2014-03-01

    How Mott insulators acquire metallicity upon the introduction of extra carriers lies at the heart of correlated electron physics. The evolution of the electronic structure and low energy dynamics in the ultra-low doped region where the Mottness begins to break down is a critical place to study this physics. We report ARPES studies of the Rh and La doped Sr2IrO4 and show the appearance and evolution of a pseudogap and Fermi arcs. Further more we present evidence how the Mott gap breaks down with a profound change in the band structure. The experimental results in the doped iridates resemble those observed in the cuprate systems, which are prototype Mott insulators, and suggest we could establish a series of signatures that occur in the metal insulator transition. Now at Los Alamos National Lab.

  9. Metal-insulator transition in nanocomposite VOx films formed by anodic electrodeposition

    NASA Astrophysics Data System (ADS)

    Tsui, Lok-kun; Hildebrand, Helga; Lu, Jiwei; Schmuki, Patrik; Zangari, Giovanni

    2013-11-01

    The ability to grow VO2 films by electrochemical methods would open a low-cost, easily scalable production route to a number of electronic devices. We have synthesized VOx films by anodic electrodeposition of V2O5, followed by partial reduction by annealing in Ar. The resulting films are heterogeneous, consisting of various metallic/oxide phases and including regions with VO2 stoichiometry. A gradual metal insulator transition with a nearly two order of magnitude change in film resistance is observed between room temperature and 140 °C. In addition, the films exhibit a temperature coefficient of resistance of ˜ -2.4%/ °C from 20 to 140 °C.

  10. Mott metal-insulator transition in a metallic liquid - Gutzwiller molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Barros, Kipton; Chern, Gia-Wei; Batista, Cristian D.; Kress, Joel D.; Kotliar, Gabriel

    2015-03-01

    Molecular dynamics (MD) simulations are crucial to modern computational physics, chemistry, and materials science, especially when combined with potentials derived from density-functional theory. However, even in state of the art MD codes, the on-site Coulomb repulsion is only treated at the self-consistent Hartree-Fock level. This standard approximation may miss important effects due to electron correlations. The Gutzwiller variational method captures essential correlated-electron physics yet is much faster than, e.g., the dynamical-mean field theory approach. We present our efficient Gutzwiller-MD implementation. With it, we investigate the Mott metal-insulator transition in a metallic fluid and uncover several surprising static and dynamic properties of this system.

  11. Electrical conduction and metal-insulator transition of indium nanowires on Si(111)

    NASA Astrophysics Data System (ADS)

    Hatta, Shinichiro; Noma, Takashi; Okuyama, Hiroshi; Aruga, Tetsuya

    2017-05-01

    We have studied the metal-insulator (MI) transition of indium nanowires on the Si(111) surface by electrical conductivity measurements with a four-point probe. Upon cooling, the sheet conductivity of the high-temperature (4 ×1 ) phase, which is known to have metallic electron bands, exhibited a gradual decrease in quantitative agreement with the Mott's variable range hopping conduction. Upon further cooling, the conductivity exhibited a sharp drop at 120 K, indicating the transition into the insulating (8 ×2 ) phase. The conductivity upon heating from 65 K did not trace the curve during cooling but showed a thermal hysteresis with a width of 8 K. The observation of the hysteresis agrees with the previous electron diffraction experiments, showing that the MI transition is first order. It was further found that, instead of the superheating behavior usually observed in first-order transitions, the transition upon heating starts below Tc, while the supercooling is always observed. This indicates a specific heterogeneous nucleation process only during heating. It is suggested that this is due to the destabilization of the nanowires near the domain boundaries. This is corroborated by the significant decrease of the transition temperature observed on a substrate with a high step density.

  12. Experimental Observation of a Metal-insulator Transition in 2D at Zero Magnetic Field

    NASA Astrophysics Data System (ADS)

    Kravchenko, S. V.

    1996-03-01

    The scaling theory of Abrahams et al. ^1 has had considerable success in describing many features of metal-insulator transitions. Within this theory, which was developed for non-interacting electrons, no such transition is possible in two-dimensional electron systems (2DES) in the absence of a magnetic field. However, we show experimentally that an ultra-high-mobility 2DES on the surface of silicon does exhibit the signature of a true metal-insulator phase transition at zero magnetic field at a critical electron density n_c ~10^11 cm-2. The energy of electron-electron interactions, ignored in the scaling theory,^1 is the dominant parameter in this 2DES. The resistivity, ρ, is empirically found to scale near the critical point both with temperature T and electric field E so that it can be represented by the form ρ(T,n_s)=ρ(T/T_0(n_s)) as Earrow0 or ρ(E,n_s)=ρ(E/E_0(n_s)) as Tarrow0. At the transition, the resistivity is close to 3h/e^2. Both scaling parameters, T0 and E_0, show power law behavior at the critical point. This is characteristic of a true phase transition and strongly resembles, in particular, the superconductor-insulator transition in disordered thin films,^2 as well as the transition between quantum Hall liquid and insulator.^3 Many high-mobility samples from two different sources (Institute for Metrological Service, Russia, and Siemens AG, Germany) with different oxide thicknesses and gate materials have been studied and similar results were found. Work done in collaboration with J. E. Furneaux, Whitney Mason, V. M. Pudalov, and M. D'Iorio, supported by NSF. ^1 E. Abrahams, P. W. Anderson, D. C. Licciardello, and T. V. Ramakrishnan, Phys. Rev. Lett. 42, 673 (1979). ^2 Y. Liu, K. A. McGreer, B. Nease, D. B. Haviland, G. Martinez, J. W. Halley, and A. M. Goldman, Phys. Rev. Lett. 67, 2068 (1991). ^3 T. Wang, K. P. Clark, G. F. Spencer, A. M. Mack, and W. P. Kirk, Phys. Rev. Lett. 72, 709 (1994).

  13. Metal-Insulator Transition in Nanoparticle Solids: Insights from Kinetic Monte Carlo Simulations

    DOE PAGES

    Qu, Luman; Vörös, Márton; Zimanyi, Gergely T.

    2017-08-01

    Progress has been rapid in increasing the efficiency of energy conversion in nanoparticles. However, extraction of the photo-generated charge carriers remains challenging. Encouragingly, the charge mobility has been improved recently by driving nanoparticle (NP) films across the metal-insulator transition (MIT). To simulate MIT in NP films, we developed a hierarchical Kinetic Monte Carlo transport model. Electrons transfer between neighboring NPs via activated hopping when the NP energies differ by more than an overlap energy, but transfer by a non-activated quantum delocalization, if the NP energies are closer than the overlap energy. As the overlap energy increases, emerging percolating clusters supportmore » a metallic transport across the entire film. We simulated the evolution of the temperature-dependent electron mobility. We analyzed our data in terms of two candidate models of the MIT: (a) as a Quantum Critical Transition, signaled by an effective gap going to zero; and (b) as a Quantum Percolation Transition, where a sample-spanning metallic percolation path is formed as the fraction of the hopping bonds in the transport paths is going to zero. We found that the Quantum Percolation Transition theory provides a better description of the MIT. We also observed an anomalously low gap region next to the MIT. We discuss the relevance of our results in the light of recent experimental measurements.« less

  14. Drastic change of the Casimir force at the metal-insulator transition

    SciTech Connect

    Galkina, E. G.; Ivanov, B. A.; Savel'ev, Sergey; Yampol'skii, V. A.; Nori, Franco

    2009-09-15

    The dependence of the Casimir force on material properties is important for both future applications and to gain further insight on its fundamental aspects. Here we apply the general Lifshitz theory of the Casimir force to low-conducting compounds, or poor metals. For distances in the micrometer range, the Casimir force for a large variety of such materials is described by universal equations containing a few parameters: the effective plasma frequency {omega}{sub p}, dissipation rate {gamma} of the free carriers, and electric permittivity {epsilon}{sub {infinity}} for {omega}{>=}{omega}{sub p} (in the infrared range). This theory of the Casimir force for poor metals can also describe inhomogeneous composite materials containing small regions with different conductivity. The Casimir force for systems involving samples made with compounds that have a metal-insulator transition shows a drastic change of the Casimir force within the transition region, where the metallic and dielectric phases coexist. Indeed, the Casimir force can increase by a factor of 2 near this transition.

  15. Critical behavior of ultrasonic attenuation near interaction-driven metal-insulator transitions

    NASA Astrophysics Data System (ADS)

    Dobrosavljević, V.; Kirkpatrick, T. R.; Chen, Changfeng; Belitz, D.

    1991-09-01

    We consider the critical behavior of the ultrasonic attenuation (UA) near interaction-driven metal-insulator transitions. To first order in the disorder no localization corrections are found. Using a field-theoretical nonlinear σ-model representation, and performing a renormalization-group analysis, we show that the absence of first-order corrections follows from the presence of two scaling parts for the UA. The critical exponents for the UA are shown to be sensitive to both the symmetry class and the interaction range, in contrast to the behavior of the conductivity. We have examined the cases of strong magnetic fields and of magnetic impurities where the critical exponents prove to be universal for Coulomb interactions, but are found to be nonuniversal for short-ranged interactions. The UA was further examined near the pseudomagnetic transition that occurs in the absence of magnetic perturbations. In that case, the UA critical exponents were found to vanish, indicating that the UA stays uncritical at this transition.

  16. New aspects of the metal-insulator transition in vanadium dioxide nanobeams

    NASA Astrophysics Data System (ADS)

    Cobden, David

    2010-03-01

    The fundamental properties of the famous metal-insulator phase transition in vanadium dioxide are obscured in traditional samples by domain structure. In contrast, single-crystal nanobeams of the material can be prepared in such a way that the frustration is absent, and the stress is zero or almost uniform, even while the transition is taking place. Studying nanobeams using a combination of transport and optical methods has allowed us to obtain a number of new results, including the following. First, the uniform metallic phase can be dramatically supercooled. Second, the so-called M2 insulating phase shows a temperature-independent resistivity at the transition, implicating electron-electron interactions in the controlling mechanism. Third, the M1 and M2 insulating phases have the same thermal electronic gap. Fourth, we establish a new phase diagram of the material as a function of stress along the rutile c-axis which helps to explain a number of recent experiments and some anomalies in the older literature. Work done in collaboration with Jiang Wei, Jae Park, Vinny Roma, Andrew Jones, Sam Berweger, and Markus Raschke.

  17. Three-terminal field effect switches probing the electrically triggered Metal-Insulator Transition in Vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Gopalakrishnan, Gokul; Ko, Changhyun; Ruzmetov, Dmitry; Narayanamurti, Venkatesh; Ramanathan, Shriram

    2010-03-01

    Electrostatic control of the Metal-Insulator Transition (MIT) in correlated oxides is valuable, both as a probe of the nature of the phase transition, as well as being a critical aspect of novel switching devices based on Mott insulators. Of much recent interest among this class of materials, is vanadium dioxide (VO2), a correlated semiconductor which exhibits a thermally induced MIT close to room temperature, and has also been shown to undergo an ultra-fast switching of conductivity by optical and electrical means. Among many of the experiments demonstrating an electrically triggered transition, however, the attendant phenomenon of Joule heating in the current channel raises questions about the triggering mechanism. To carefully address this issue, we explore the fabrication of three terminal field-effect devices, in which the resistance of a VO2 based channel may be modulated by a gate electric field in the absence of any significant current induced heating. In this talk we present details of the fabrication, the technical challenges involved in implementing them, and results of gated I-V measurements performed on these devices along with our interpretation of the observed effects.

  18. Measurement of a solid-state triple point at the metal-insulator transition in VO2.

    PubMed

    Park, Jae Hyung; Coy, Jim M; Kasirga, T Serkan; Huang, Chunming; Fei, Zaiyao; Hunter, Scott; Cobden, David H

    2013-08-22

    First-order phase transitions in solids are notoriously challenging to study. The combination of change in unit cell shape, long range of elastic distortion and flow of latent heat leads to large energy barriers resulting in domain structure, hysteresis and cracking. The situation is worse near a triple point, where more than two phases are involved. The well-known metal-insulator transition in vanadium dioxide, a popular candidate for ultrafast optical and electrical switching applications, is a case in point. Even though VO2 is one of the simplest strongly correlated materials, experimental difficulties posed by the first-order nature of the metal-insulator transition as well as the involvement of at least two competing insulating phases have led to persistent controversy about its nature. Here we show that studying single-crystal VO2 nanobeams in a purpose-built nanomechanical strain apparatus allows investigation of this prototypical phase transition with unprecedented control and precision. Our results include the striking finding that the triple point of the metallic phase and two insulating phases is at the transition temperature, Ttr = Tc, which we determine to be 65.0 ± 0.1 °C. The findings have profound implications for the mechanism of the metal-insulator transition in VO2, but they also demonstrate the importance of this approach for mastering phase transitions in many other strongly correlated materials, such as manganites and iron-based superconductors.

  19. Metal-Insulator Transitions in Epitaxial LaVO(3) and LaTiO(3) Films

    DTIC Science & Technology

    2012-08-01

    are insulating in the bulk—has led to an explosion of research activity in perovskite transition-metal oxide heterostructures. The most well-known...ADDRESSES U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 15. SUBJECT TERMS metal insulator transition, oxide ...effects must be duly taken into consideration when interpreting metallic behavior in these complex oxide heterostructures. This work is supported by the

  20. Scaling Theory of a Compressibility-Driven Metal-Insulator Transition in a Two-Dimensional Electron Fluid.

    PubMed

    Belitz, D; Kirkpatrick, T R

    2016-12-02

    We present a scaling description of a metal-insulator transition in two-dimensional electron systems that is driven by a vanishing compressibility rather than a vanishing diffusion coefficient. A small set of basic assumptions leads to a consistent theoretical framework that is compatible with existing transport and compressibility measurements, and allows us to make predictions for other observables. We also discuss connections between these ideas and other theories of transitions to an incompressible quantum fluid.

  1. First-order metal-insulator transition and infrared identification of shape-controlled magnetite nanocrystals

    NASA Astrophysics Data System (ADS)

    Zheng, Lei; Su, Wei; Qi, Zeming; Xu, Yang; Zhou, Min; Xie, Yi

    2011-12-01

    The first-order metal-insulator transition (MIT) in magnetite has been known for a long time but is still controversial in its nature. In this study, well-defined magnetite nanocrystals (NCs) with controllable size, shape and terminated surface are first employed to elucidate this important issue, and new discoveries such as a highly suppressed phase transition temperature are identified by monitoring the variable-temperature electric resistance and infrared spectroscopy. Significantly, by carefully comparing the infrared vibrational bands of the as-prepared magnetite NCs with octahedral and cubic shapes, respectively, we found that these two forms of magnetite NCs exhibited different transmittance changes and frequency shifts of the infrared characteristics, presumably due to the differences in the lattice distortions on the corresponding {001} and {111} terminal surfaces. This result produced evidence in support of the charge ordering of Fe atoms along the low dimensionality at octahedral B sites undergoing the MIT. Taken together, infrared identification was proposed to be an available characterization strategy for MIT, which can reflect more information on the elusive lattice distortion of crystallographic structure or exposed surfaces.

  2. Magnetic Superstructure and Metal-Insulator Transition in Mn-Substituted Sr3Ru2O7

    NASA Astrophysics Data System (ADS)

    Hossain, M. A.; Bohnenbuck, B.; Chuang, Y.-D.; Geck, J.; Tokura, Y.; Yoshida, Y.; Hussain, Z.; Keimer, B.; Sawatzky, G. A.; Damascelli, A.

    2010-03-01

    We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr3(Ru1-xMnx)2O7, performed at both Ru and Mn L-edges. Resonant magnetic superstructure reflections, which indicate an incipient instability of the parent compound, are detected below the transition. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x˜0.05 Mn substitution. In collaboration with A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley Lab), I. Zegkinoglou, M.W. Haverkort (MPI, Stuttgart), I.S. Elfimov, D.G. Hawthorn (UBC), R. Mathieu, S. Satow, H. Takagi (Tokyo), H.-H. Wu and C. Sch"ußler-Langeheine (Cologne).

  3. Metal-insulator transition in 3d transition-metal oxides with ABO 3 and A 2BO 4 type structures

    NASA Astrophysics Data System (ADS)

    Eisaki, H.; Ido, T.; Magoshi, K.; Mochizuki, M.; Yamatsu, H.; Ito, T.; Uchida, S.

    1991-12-01

    3d transition-metal oxides with perovskite and K 2NiF 4 crystal structures, (La,Sr)VO 3, (La,Sr)FeO 3, (La,Sr)CoO 3, LaNiO 3 and (La,Sr) 2NiO 4 systems are investigated focusing on the effect of carrier doping performed by the A-site ion substitution. Both (La,Sr)VO 3 and (La,Sr)CoO 3 systems show an insulator to metal transition by Sr substitution, however, the magnetic behavior differs drastically. The mid-infrared structure induced by Sr substitution is observed in the optical spectra of (La,Sr) 2NiO 4 system. Relation between the behavior of metal-insulator transition and the variation of the electronic and/or spin structure in these systems is discussed in comparison with the high-T c copper oxides.

  4. Heteroepitaxial VO2 thin films on GaN: Structure and metal-insulator transition characteristics

    NASA Astrophysics Data System (ADS)

    Zhou, You; Ramanathan, Shriram

    2012-10-01

    Monolithic integration of correlated oxide and nitride semiconductors may open up new opportunities in solid-state electronics and opto-electronics that combine desirable functional properties of both classes of materials. Here, we report on epitaxial growth and phase transition-related electrical properties of vanadium dioxide (VO2) thin films on GaN epitaxial layers on c-sapphire. The epitaxial relation is determined to be (010)vo2‖(0001)GaN‖(0001)A12O3 and [100]vo2‖[1¯21¯0]A12O3 from x-ray diffraction. VO2 heteroepitaxial growth and lattice mismatch are analyzed by comparing the GaN basal plane (0001) with the almost close packed corrugated oxygen plane in vanadium dioxide and an experimental stereographic projection describing the orientation relationship is established. X-ray photoelectron spectroscopy suggests a slightly oxygen rich composition at the surface, while Raman scattering measurements suggests that the quality of GaN layer is not significantly degraded by the high-temperature deposition of VO2. Electrical characterization of VO2 films on GaN indicates that the resistance changes by about four orders of magnitude upon heating, similar to epitaxial VO2 films grown directly on c-sapphire. It is shown that the metal-insulator transition could also be voltage-triggered at room temperature and the transition threshold voltage scaling variation with temperature is analyzed in the framework of a current-driven Joule heating model. The ability to synthesize high quality correlated oxide films on GaN with sharp phase transition could enable new directions in semiconductor-photonic integrated devices.

  5. Metal-Insulator Transition of c-Axis-Controlled V2O3 Thin Film

    NASA Astrophysics Data System (ADS)

    Shimazu, Yuichi; Okumura, Teppei; Tsuchiya, Takashi; Shimada, Atsushi; Tanabe, Kenji; Tokiwa, Kazuyasu; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

    2015-06-01

    We prepared c-axis-controlled V2O3 thin films by RF magnetron sputtering and proved their metal-insulator transition (MIT) in terms of electronic structure. The lattice constant of the c-axis depends on the film thickness and the lattice mismatch of the substrate and V2O3. MIT is observed at a temperature of ˜150 K in the V2O3 thin films with the lattice constants of c = 13.942 and 13.992 Å, although the V2O3 thin film with c = 13.915 Å exhibits metallic conductivity without MIT. The electron correlation energy, which corresponds to the energy difference between the lower Hubbard band and the upper Hubbard band, increases with increasing lattice constant of the c-axis. Bandwidths also depend on the lattice constant of the c-axis. The intensity of the a1g orbital around the Fermi level decreases with increasing lattice constant of the c-axis. These results suggest that the electron correlation interaction and bandwidths play important roles in the MIT of c-axis-controlled V2O3 thin films.

  6. Weak localization and the approach to metal-insulator transition in single crystalline germanium nanowires

    NASA Astrophysics Data System (ADS)

    Sett, Shaili; Das, K.; Raychaudhuri, A. K.

    2017-03-01

    We study the low-temperature electronic transport properties of single germanium nanowires (NWs) with diameters down to 45 nm to investigate the weak localization (WL) behavior and approach to metal-insulator transition (MIT) within them. The NWs (single crystalline) we investigate lie on the metallic side of the MIT with an extrapolated zero temperature conductivity {σ0} in the range 23 to 1790 (Ω cm)-1 and show a temperature-dependent conductivity which below 30 K can be described by a 3D WL behavior with Thouless length {{L}\\text{Th}}˜ {{T}-\\frac{p{2}}} and p˜ 4 . From the observed value of {σ0} and the value of the critical carrier concentration n c, it is observed that the approach to MIT can be described by the scaling equation {σ0}˜ {{≤ft(n-{{n}\\text{c}}\\right)}ν} with ν ≈ 0.6 , which is a value expected for an uncompensated system. The investigation establishes a NW size limit for the applicability of 3D scaling theories.

  7. Mobility engineering and a metal-insulator transition in monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Radisavljevic, Branimir; Kis, Andras

    2013-09-01

    Two-dimensional (2D) materials are a new class of materials with interesting physical properties and applications ranging from nanoelectronics to sensing and photonics. In addition to graphene, the most studied 2D material, monolayers of other layered materials such as semiconducting dichalcogenides MoS2 or WSe2 are gaining in importance as promising channel materials for field-effect transistors (FETs). The presence of a direct bandgap in monolayer MoS2 due to quantum-mechanical confinement allows room-temperature FETs with an on/off ratio exceeding 108. The presence of high- κ dielectrics in these devices enhanced their mobility, but the mechanisms are not well understood. Here, we report on electrical transport measurements on MoS2 FETs in different dielectric configurations. The dependence of mobility on temperature shows clear evidence of the strong suppression of charged-impurity scattering in dual-gate devices with a top-gate dielectric. At the same time, phonon scattering shows a weaker than expected temperature dependence. High levels of doping achieved in dual-gate devices also allow the observation of a metal-insulator transition in monolayer MoS2 due to strong electron-electron interactions. Our work opens up the way to further improvements in 2D semiconductor performance and introduces MoS2 as an interesting system for studying correlation effects in mesoscopic systems.

  8. Metal-insulator transition and the role of electron correlation in FeO2

    NASA Astrophysics Data System (ADS)

    Jang, Bo Gyu; Kim, Duck Young; Shim, Ji Hoon

    2017-02-01

    Iron oxide is a key compound to understand the state of the deep Earth. It has been believed that previously known oxides such as FeO and Fe2O3 will be dominant at the mantle conditions. However, the recent observation of FeO2 shed another light to the composition of the deep lower mantle (DLM), and thus understanding of the physical properties of FeO2 will be critical to model the DLM. Here, we report the electronic structure and structural properties of FeO2 by using density functional theory and dynamic mean-field theory. The crystal structure of FeO2 is composed of Fe2 + and O22 - dimers, where the Fe ions are surrounded by the octahedral O atoms. We found that FeO2 shows a metal-insulator transition (MIT) under high pressure. The MIT is not a Mott type but a band insulator type which is driven by the O2 dimer bond length change. However, the correlation effect of Fe 3 d orbitals should be considered to correctly describe O2 dimer bond length of FeO2 and the MIT.

  9. Metal-insulator transitions in LaTiO3 / CaTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Seo, Sung Seok A.; Lee, Ho Nyung

    2010-03-01

    Strongly correlated electrons at an interface of complex oxide heterostructures often show interesting behaviors that require an introduction of new physical concepts. For example, the metallic transport behavior found in the superlattices of a Mott insulator LaTiO3 and a band insulator SrTiO3 (STO) has established the concept of interfacial electronic reconstruction. In this work, we have studied the transport property of a new type of Mott/band insulator LaTiO3/CaTiO3 (LTO/CTO) superlattices grown by pulsed laser deposition (PLD). In order to rule out concerns about the PLD plume-triggered oxygen vacancies generated in STO substrates, which might influence transport measurement, and to investigate the effect of epitaxial strain, we have used insulating NdGaO3 substrates. While both LTO and CTO single films are highly insulating, we have observed intriguing metal-insulator transitions (MIT) in the LTO/CTO superlattices depending on the global LTO/CTO thickness ratio and temperature. (Note that LTO/STO superlattices are metallic at all temperatures (2-300 K)). In this talk, we will discuss the origin of the MIT in the scheme of self compensation mechanism of d-electrons at the hetero-interface between LTO and CTO.

  10. Unusual behaviour of thermal conductivity in vanadium dioxide across the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Hippalgaonkar, Kedar; Lee, Sangwook; Ko, Changhyun; Yang, Fan; Suh, Joonki; Liu, Kai; Wang, Kevin; Zhang, Xiang; Dames, Chris; Wu, Junqiao

    In an electrically conductive solid, the Wiedemann-Franz (WF) law requires the electronic contribution to thermal conductivity to be proportional to the product of electrical conductivity and absolute temperature , where the ratio is the Lorenz number, typically not much different from the Sommerfeld value L0 = 2.44x10-8 W-ohm-K-2 at room temperature. The WF law reflects a basic property of metals where charge and heat are both carried by the same quasiparticles that both experience elastic scattering. At temperatures below the Debye temperature, the WF law has been experimentally shown to be robust in conventional conductors, with violations theoretically predicted or experimentally observed in strongly correlated electron systems or Luttinger liquids. However, the experimentally observed violations are at very low temperatures. Here we report breakdown of the WF law in a strongly correlated metal, in which the electronic thermal conductivity and L nearly vanish at temperatures above room temperature, where the electronic thermal conductivity amounts to only <~5% of the value expected from the WF law. Unusual behaviour of thermal conductivity in vanadium dioxide across the metal-insulator transition.

  11. Charge and orbital orderings associated with metal-insulator transition in V6O13

    NASA Astrophysics Data System (ADS)

    Toriyama, T.; Nakayama, T.; Konishi, T.; Ohta, Y.

    2014-08-01

    Density-functional-theory-based electronic-structure calculations are carried out to elucidate the mechanism of the metal-insulator transition (MIT) of a Wadsley-phase vanadium oxide V6O13. We show that, at the MIT, the orbitals occupied by electrons are reconstructed in the single trellis layers of the V(1) ions, which occurs simultaneously with the transfer of electrons from the V(2) to V(3) ions in the double trellis layers, leaving the V(2) ions nonmagnetic. We discuss that these changes lead to the formation of spin-singlet state associated with the ordering of the dyz and dxz orbitals in the V(1) zigzag chain, together with the formation of the Mott-insulator state with frustrated spin degrees of freedom in the zigzag ladder of the dxy orbitals of the V(3) ions; possible antiferromagnetic ordering patterns are predicted for the latter state. Thus, the spin-singlet and antiferromagnetic states coexist in spatially separated regions at lowest temperatures. The band Jahn-Teller-type instability hidden in the single trellis layer, which is the orbital ordering instability in the strong correlation limit, is suggested to cause the MIT.

  12. Weak localization and the approach to metal-insulator transition in single crystalline germanium nanowires.

    PubMed

    Sett, Shaili; Das, K; Raychaudhuri, A K

    2017-03-22

    We study the low-temperature electronic transport properties of single germanium nanowires (NWs) with diameters down to 45 nm to investigate the weak localization (WL) behavior and approach to metal-insulator transition (MIT) within them. The NWs (single crystalline) we investigate lie on the metallic side of the MIT with an extrapolated zero temperature conductivity [Formula: see text] in the range 23 to 1790 [Formula: see text] cm)(-1) and show a temperature-dependent conductivity which below 30 K can be described by a 3D WL behavior with Thouless length [Formula: see text] and [Formula: see text]. From the observed value of [Formula: see text] and the value of the critical carrier concentration n c, it is observed that the approach to MIT can be described by the scaling equation [Formula: see text] with [Formula: see text], which is a value expected for an uncompensated system. The investigation establishes a NW size limit for the applicability of 3D scaling theories.

  13. Phase controlled metal-insulator transition in multi-leg quasiperiodic optical lattices

    NASA Astrophysics Data System (ADS)

    Maiti, Santanu K.; Sil, Shreekantha; Chakrabarti, Arunava

    2017-07-01

    A tight-binding model of a multi-leg ladder network with a continuous quasiperiodic modulation in both the site potential and the inter-arm hopping integral is considered. The model mimics optical lattices where ultra-cold fermionic or bosonic atoms are trapped in double well potentials. It is observed that, the relative phase difference between the on-site potential and the inter-arm hopping integral, which can be controlled by the tuning of the interfering laser beams trapping the cold atoms, can result in a mixed spectrum of one or more absolutely continuous subband(s) and point like spectral measures. This opens up the possibility of a re-entrant metal-insulator transition. The subtle role played by the relative phase difference mentioned above is revealed, and we corroborate it numerically by working out the multi-channel electronic transmission for finite two-, and three-leg ladder networks. The extension of the calculation beyond the two-leg case is trivial, and is discussed in the work.

  14. Charge Mediated Reversible Metal-Insulator Transition in Monolayer MoTe2 and WxMo1-xTe2 Alloy.

    PubMed

    Zhang, Chenxi; Kc, Santosh; Nie, Yifan; Liang, Chaoping; Vandenberghe, William G; Longo, Roberto C; Zheng, Yongping; Kong, Fantai; Hong, Suklyun; Wallace, Robert M; Cho, Kyeongjae

    2016-08-23

    Metal-insulator transitions in low-dimensional materials under ambient conditions are rare and worth pursuing due to their intriguing physics and rich device applications. Monolayer MoTe2 and WTe2 are distinguished from other TMDs by the existence of an exceptional semimetallic distorted octahedral structure (T') with a quite small energy difference from the semiconducting H phase. In the process of transition metal alloying, an equal stability point of the H and the T' phase is observed in the formation energy diagram of monolayer WxMo1-xTe2. This thermodynamically driven phase transition enables a controlled synthesis of the desired phase (H or T') of monolayer WxMo1-xTe2 using a growth method such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). Furthermore, charge mediation, as a more feasible method, is found to make the T' phase more stable than the H phase and induce a phase transition from the H phase (semiconducting) to the T' phase (semimetallic) in monolayer WxMo1-xTe2 alloy. This suggests that a dynamic metal-insulator phase transition can be induced, which can be exploited for rich phase transition applications in two-dimensional nanoelectronics.

  15. Multifractality and Conformal Invariance at 2D Metal-Insulator Transition in the Spin-Orbit Symmetry Class

    NASA Astrophysics Data System (ADS)

    Obuse, Hideaki; Subramaniam, Arvind; Furusaki, Akira; Gruzberg, Ilya; Ludwig, Andreas

    2007-03-01

    We study the multifractality of critical wave functions at boundaries and corners at the Anderson metal-insulator transition for noninteracting electrons in the two-dimensional (2D) spin-orbit (symplectic) universality class. We find that the multifractal exponents near a boundary are different from those in the bulk. The exponents at a corner are found to be directly related to those at a straight boundary through a relation arising from conformal invariance. This provides direct numerical evidence for conformal invariance at the 2D spin-orbit metal-insulator transition. We also show that the presence of boundaries modifies the multifractality of the whole sample even in the thermodynamic limit.

  16. Mg doping of thermochromic VO2 films enhances the optical transmittance and decreases the metal-insulator transition temperature

    NASA Astrophysics Data System (ADS)

    Mlyuka, N. R.; Niklasson, G. A.; Granqvist, C. G.

    2009-10-01

    Thermochromic films of MgxV1-xO2 were made by reactive dc magnetron sputtering onto heated glass. The metal-insulator transition temperature decreased by ˜3 K/at. %Mg, while the optical transmittance increased concomitantly. Specifically, the transmittance of visible light and of solar radiation was enhanced by ˜10% when the Mg content was ˜7 at. %. Our results point at the usefulness of these films for energy efficient fenestration.

  17. Magnetic and metal-insulator transitions in coupled spin-fermion systems

    DOE PAGES

    Mondaini, R.; Paiva, T.; Scalettar, R. T.

    2014-10-14

    We use quantum Monte Carlo to determine the magnetic and transport properties of coupled square lattice spin and fermionic planes as a model for a metal-insulator interface. Specifically, layers of Ising spins with an intra-layer exchange constant J interact with the electronic spins of several adjoining metallic sheets via a coupling JH. When the chemical potential cuts across the band center, that is, at half-filling, the Neel temperature of antiferromagnetic (J > 0) Ising spins is enhanced by the coupling to the metal, while in the ferromagnetic case (J < 0) the metallic degrees of freedom reduce the ordering temperature.more » In the former case, a gap opens in the fermionic spectrum, driving insulating behavior, and the electron spins also order. This induced antiferromagnetism penetrates more weakly as the distance from the interface increases, and also exhibits a non-monotonic dependence on JH. For doped lattices an interesting charge disproportionation occurs where electrons move to the interface layer to maintain half-filling there.« less

  18. Magnetic and metal-insulator transitions in coupled spin-fermion systems

    SciTech Connect

    Mondaini, R.; Paiva, T.; Scalettar, R. T.

    2014-10-14

    We use quantum Monte Carlo to determine the magnetic and transport properties of coupled square lattice spin and fermionic planes as a model for a metal-insulator interface. Specifically, layers of Ising spins with an intra-layer exchange constant J interact with the electronic spins of several adjoining metallic sheets via a coupling JH. When the chemical potential cuts across the band center, that is, at half-filling, the Neel temperature of antiferromagnetic (J > 0) Ising spins is enhanced by the coupling to the metal, while in the ferromagnetic case (J < 0) the metallic degrees of freedom reduce the ordering temperature. In the former case, a gap opens in the fermionic spectrum, driving insulating behavior, and the electron spins also order. This induced antiferromagnetism penetrates more weakly as the distance from the interface increases, and also exhibits a non-monotonic dependence on JH. For doped lattices an interesting charge disproportionation occurs where electrons move to the interface layer to maintain half-filling there.

  19. Magnetic and metal-insulator transitions in coupled spin-fermion systems

    NASA Astrophysics Data System (ADS)

    Mondaini, R.; Paiva, T.; Scalettar, R. T.

    2014-10-01

    We use quantum Monte Carlo method to determine the magnetic and transport properties of coupled square lattice spin and fermionic planes as a model for a metal-insulator interface. Specifically, layers of Ising spins with an intralayer exchange constant J interact with the electronic spins of several adjoining metallic sheets via a coupling JH. When the chemical potential cuts across the band center, that is, at half-filling, the Néel temperature of antiferromagnetic (J >0) Ising spins is enhanced by the coupling to the metal, while in the ferromagnetic case (J <0), the metallic degrees of freedom reduce the ordering temperature. In the former case, a gap opens in the fermionic spectrum, driving insulating behavior, and the electron spins also order. This induced antiferromagnetism penetrates more weakly as the distance from the interface increases, and also exhibits a nonmonotonic dependence on JH. For doped lattices, an interesting charge disproportionation occurs where electrons move to the interface layer to maintain half-filling there.

  20. Dynamically Babinet-invertible metasurface: a capacitive-inductive reconfigurable filter for terahertz waves using vanadium-dioxide metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Urade, Yoshiro; Nakata, Yosuke; Okimura, Kunio; Nakanishi, Toshihiro; Miyamaru, Fumiaki; Takeda, Mitsuo W.; Kitano, Masao

    2016-03-01

    This paper proposes a reconfigurable planar metamaterial that can be switched between capacitive and inductive responses using local changes in the electrical conductivity of its constituent material. The proposed device is based on Babinet's principle and exploits the singular electromagnetic responses of metallic checkerboard structures, which are dependent on the local electrical conductivity. Utilizing the heating-induced metal-insulator transition of vanadium dioxide ($\\mathrm{VO}_2$), the proposed metamaterial is designed to compensate for the effect of the substrate and is experimentally characterized in the terahertz regime. This reconfigurable metamaterial can be utilized as a switchable filter and as a switchable phase shifter for terahertz waves.

  1. Variation of optical conductivity spectra in the course of bandwidth-controlled metal-insulator transitions in pyrochlore iridates

    NASA Astrophysics Data System (ADS)

    Ueda, K.; Fujioka, J.; Tokura, Y.

    2016-06-01

    We spectroscopically investigate a series of pyrochlore iridates R2Ir2O7 (R : rare-earth and Y ions) where the metal-insulator transitions are induced by systematic bandwidth control via chemical substitutions of R ions. We establish the phase diagram of R2Ir2O7 , as endorsed by the variation of the optical conductivity spectra, in which the competing phases including paramagnetic insulator (PI), paramagnetic metal (PM), and antiferromagnetic insulator (AFI) show up as a function of bandwidth and temperature. For small R -ionic radius (R = Y-Sm), i.e., strongly correlated region, pronounced peaks on the edge of the optical gap are discerned below the magnetic transition temperature TN, which is attributable to exciton and magnon sideband absorptions. It turns out that the estimated nearest-neighbor exchange interaction increases as R -ionic radius increases, whereas TN monotonically decreases, indicating that the all-in all-out magnetic order arises from the interplay among several exchange interactions inherent to extended 5 d orbitals on the frustrated lattice. For larger R -ionic radius (R = Sm-Pr), i.e., relatively weakly correlated region, the optical conductivity spectra markedly change below 0.3 eV in the course of PM-AFI transition, implying that the magnetic order induces the insulating state. In particular, we have found distinct electrodynamics in the composition of R =Nd0.5Pr0.5 which is located on the boundary of the quantum PM-AFI transition, pointing to the possible emergence of unconventional topological electronic phases related possibly to the correlated Weyl electrons.

  2. Metal-insulator transition in the dimerized organic conductor κ -(BEDT-TTF)2Hg (SCN )2Br

    NASA Astrophysics Data System (ADS)

    Ivek, Tomislav; Beyer, Rebecca; Badalov, Sabuhi; Čulo, Matija; Tomić, Silvia; Schlueter, John A.; Zhilyaeva, Elena I.; Lyubovskaya, Rimma N.; Dressel, Martin

    2017-08-01

    The organic charge-transfer salt κ -(BEDT-TTF)2Hg (SCN )2Br is a quasi-two-dimensional metal with a half-filled conduction band at ambient conditions. When cooled below T =80 K , it undergoes a pronounced transition to an insulating phase where the resistivity increases many orders of magnitude. In order to elucidate the nature of this metal-insulator transition, we have performed comprehensive transport, dielectric and optical investigations. The findings are compared with other dimerized κ -(BEDT-TTF) salts, in particular the Cl analog, where a charge-order transition takes place at TCO=30 K .

  3. Tuning the metal-insulator transition in NdNiO3 heterostructures via Fermi surface instability and spin fluctuations

    NASA Astrophysics Data System (ADS)

    Dhaka, R. S.; Das, Tanmoy; Plumb, N. C.; Ristic, Z.; Kong, W.; Matt, C. E.; Xu, N.; Dolui, Kapildeb; Razzoli, E.; Medarde, M.; Patthey, L.; Shi, M.; Radović, M.; Mesot, Joël

    2015-07-01

    We employed in situ pulsed laser deposition (PLD) and angle-resolved photoemission spectroscopy (ARPES) to investigate the mechanism of the metal-insulator transition (MIT) in NdNiO3 (NNO) thin films, grown on NdGaO3(110) and LaAlO3(100) substrates. In the metallic phase, we observe three-dimensional hole and electron Fermi surface (FS) pockets formed from strongly renormalized bands with well-defined quasiparticles. Upon cooling across the MIT in NNO/NGO sample, the quasiparticles lose coherence via a spectral weight transfer from near the Fermi level to localized states forming at higher binding energies. In the case of NNO/LAO, the bands are apparently shifted upward with an additional holelike pocket forming at the corner of the Brillouin zone. We find that the renormalization effects are strongly anisotropic and are stronger in NNO/NGO than NNO/LAO. Our study reveals that substrate-induced strain tunes the crystal field splitting, which changes the FS properties, nesting conditions, and spin-fluctuation strength, and thereby controls the MIT via the formation of an electronic order parameter with QAF˜(1 /4 ,1 /4 ,1 /4 ±δ ) .

  4. Suppression of Structural Phase Transition in VO2 by Epitaxial Strain in Vicinity of Metal-insulator Transition

    NASA Astrophysics Data System (ADS)

    Yang, Mengmeng; Yang, Yuanjun; Bin Hong; Wang, Liangxin; Hu, Kai; Dong, Yongqi; Xu, Han; Huang, Haoliang; Zhao, Jiangtao; Chen, Haiping; Song, Li; Ju, Huanxin; Zhu, Junfa; Bao, Jun; Li, Xiaoguang; Gu, Yueliang; Yang, Tieying; Gao, Xingyu; Luo, Zhenlin; Gao, Chen

    2016-03-01

    Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films.

  5. Suppression of Structural Phase Transition in VO2 by Epitaxial Strain in Vicinity of Metal-insulator Transition

    PubMed Central

    Yang, Mengmeng; Yang, Yuanjun; Bin Hong; Wang, Liangxin; Hu, Kai; Dong, Yongqi; Xu, Han; Huang, Haoliang; Zhao, Jiangtao; Chen, Haiping; Song, Li; Ju, Huanxin; Zhu, Junfa; Bao, Jun; Li, Xiaoguang; Gu, Yueliang; Yang, Tieying; Gao, Xingyu; Luo, Zhenlin; Gao, Chen

    2016-01-01

    Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films. PMID:26975328

  6. Giant Electroresistance in Edge Metal-Insulator-Metal Tunnel Junctions Induced by Ferroelectric Fringe Fields

    PubMed Central

    Jung, Sungchul; Jeon, Youngeun; Jin, Hanbyul; Lee, Jung-Yong; Ko, Jae-Hyeon; Kim, Nam; Eom, Daejin; Park, Kibog

    2016-01-01

    An enormous amount of research activities has been devoted to developing new types of non-volatile memory devices as the potential replacements of current flash memory devices. Theoretical device modeling was performed to demonstrate that a huge change of tunnel resistance in an Edge Metal-Insulator-Metal (EMIM) junction of metal crossbar structure can be induced by the modulation of electric fringe field, associated with the polarization reversal of an underlying ferroelectric layer. It is demonstrated that single three-terminal EMIM/Ferroelectric structure could form an active memory cell without any additional selection devices. This new structure can open up a way of fabricating all-thin-film-based, high-density, high-speed, and low-power non-volatile memory devices that are stackable to realize 3D memory architecture. PMID:27476475

  7. Gold clusters on Nb-doped SrTiO3: effects of metal-insulator transition on heterogeneous Au nanocatalysis.

    PubMed

    Zhou, Miao; Feng, Yuan Ping; Zhang, Chun

    2012-07-21

    Doping induced metal-insulator transition (MIT) in transition-metal (TM) oxides has been the topic of continued interest outside the field of catalysis chemistry. In this paper, via ab initio (GGA+U) calculations, we show that Nb-doping induced MIT in SrTiO(3) causes a dimensionality crossover of supported Au clusters, and at the same time, greatly enhances the stability and catalytic activity of these clusters. Underlying the predicted high catalytic activity of Au clusters towards the CO oxidation is the MIT induced interaction between the O(2) antibonding 2π* orbital and Au conduction bands, leading to a shift in the population of electrons from Au to the antibonding orbital and the activation of the O(2) molecule. We expect these results to provide a new methodology for the control of catalytic performance of TM-oxide supported Au nanoclusters.

  8. Multistep metal insulator transition in VO{sub 2} nanowires on Al{sub 2}O{sub 3} (0001) substrates

    SciTech Connect

    Takami, Hidefumi; Kanki, Teruo E-mail: h-tanaka@sanken.osaka-u.ac.jp; Tanaka, Hidekazu E-mail: h-tanaka@sanken.osaka-u.ac.jp

    2014-01-13

    We observed a temperature- and voltage-induced multistep metal-insulator transition (MIT) in vanadium dioxide nanowires fabricated on Al{sub 2}O{sub 3} (0001) substrates. Nanowires with a width of 200 nm showed a multistep MIT that exhibited a resistivity change of nearly two orders of magnitude in a 0.5 K temperature step. These multistep resistivity jumps can be understood as a transition of a single domain, whose size is estimated to be around 50–70 nm from numerical calculation. We found that the temperature-induced isotropic conductive behavior of the nanowires becomes similar to the voltage-induced anisotropic one as their width decreases.

  9. Positive-bias gate-controlled metal-insulator transition in ultrathin VO2 channels with TiO2 gate dielectrics.

    PubMed

    Yajima, Takeaki; Nishimura, Tomonori; Toriumi, Akira

    2015-12-14

    The next generation of electronics is likely to incorporate various functional materials, including those exhibiting ferroelectricity, ferromagnetism and metal-insulator transitions. Metal-insulator transitions can be controlled by electron doping, and so incorporating such a material in transistor channels will enable us to significantly modulate transistor current. However, such gate-controlled metal-insulator transitions have been challenging because of the limited number of electrons accumulated by gate dielectrics, or possible electrochemical reaction in ionic liquid gate. Here we achieve a positive-bias gate-controlled metal-insulator transition near the transition temperature. A significant number of electrons were accumulated via a high-permittivity TiO2 gate dielectric with subnanometre equivalent oxide thickness in the inverse-Schottky-gate geometry. An abrupt transition in the VO2 channel is further exploited, leading to a significant current modulation far beyond the capacitive coupling. This solid-state operation enables us to discuss the electrostatic mechanism as well as the collective nature of gate-controlled metal-insulator transitions, paving the pathway for developing functional field effect transistors.

  10. Correlating the Energetics and Atomic Motions of the Metal-Insulator Transition of M1 Vanadium Dioxide

    PubMed Central

    Booth, Jamie M.; Drumm, Daniel W.; Casey, Phil S.; Smith, Jackson S.; Seeber, Aaron J.; Bhargava, Suresh K.; Russo, Salvy P.

    2016-01-01

    Materials that undergo reversible metal-insulator transitions are obvious candidates for new generations of devices. For such potential to be realised, the underlying microscopic mechanisms of such transitions must be fully determined. In this work we probe the correlation between the energy landscape and electronic structure of the metal-insulator transition of vanadium dioxide and the atomic motions occurring using first principles calculations and high resolution X-ray diffraction. Calculations find an energy barrier between the high and low temperature phases corresponding to contraction followed by expansion of the distances between vanadium atoms on neighbouring sub-lattices. X-ray diffraction reveals anisotropic strain broadening in the low temperature structure’s crystal planes, however only for those with spacings affected by this compression/expansion. GW calculations reveal that traversing this barrier destabilises the bonding/anti-bonding splitting of the low temperature phase. This precise atomic description of the origin of the energy barrier separating the two structures will facilitate more precise control over the transition characteristics for new applications and devices. PMID:27211303

  11. Multifractality and Conformal Invariance at 2D Metal-Insulator Transition in the Spin-Orbit Symmetry Class

    NASA Astrophysics Data System (ADS)

    Obuse, H.; Subramaniam, A. R.; Furusaki, A.; Gruzberg, I. A.; Ludwig, A. W. W.

    2007-04-01

    We study the multifractality (MF) of critical wave functions at boundaries and corners at the metal-insulator transition (MIT) for noninteracting electrons in the two-dimensional (2D) spin-orbit (symplectic) universality class. We find that the MF exponents near a boundary are different from those in the bulk. The exponents at a corner are found to be directly related to those at a straight boundary through a relation arising from conformal invariance. This provides direct numerical evidence for conformal invariance at the 2D spin-orbit MIT. The presence of boundaries modifies the MF of the whole sample even in the thermodynamic limit.

  12. Electrophoretic-like gating used to control metal-insulator transitions in electronically phase separated manganite wires.

    PubMed

    Guo, Hangwen; Noh, Joo H; Dong, Shuai; Rack, Philip D; Gai, Zheng; Xu, Xiaoshan; Dagotto, Elbio; Shen, Jian; Ward, T Zac

    2013-08-14

    Electronically phase separated manganite wires are found to exhibit controllable metal-insulator transitions under local electric fields. The switching characteristics are shown to be fully reversible, polarity independent, and highly resistant to thermal breakdown caused by repeated cycling. It is further demonstrated that multiple discrete resistive states can be accessed in a single wire. The results conform to a phenomenological model in which the inherent nanoscale insulating and metallic domains are rearranged through electrophoretic-like processes to open and close percolation channels.

  13. Metal insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

    NASA Astrophysics Data System (ADS)

    Silwal, Punam; Miao, Ludi; Stern, Ilan; Zhou, Xiaolan; Hu, Jin; Ho Kim, Dae

    2012-01-01

    We have grown epitaxial thin films of spinel NiCo2O4 on single crystalline MgAl2O4 (001) substrates by pulsed laser deposition. Magnetization measurement revealed hysteresis loops consistent with the reported ferrimagnetic order. The electrical transport exhibits a metallic behavior with the lowest resistivity of 0.8 mΩ cm and a metal insulator transition around the Néel temperature. The systematic variation in the properties of the films grown at different growth temperatures indicates a close relationship between the magnetic order and electrical transport.

  14. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    NASA Astrophysics Data System (ADS)

    Xun, Wei; Hao, Xiang; Pan, Tao; Zhong, Jia-Lin; Ma, Chun-Lan; Hou, Fang; Wu, Yin-Zhong

    2017-07-01

    Based on first-principles calculations, the BaTiO3(BTO) film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

  15. Voltage Control of Metal-insulator Transition and Non-volatile Ferroelastic Switching of Resistance in VOx/PMN-PT Heterostructures

    PubMed Central

    Nan, Tianxiang; Liu, Ming; Ren, Wei; Ye, Zuo-Guang; Sun, Nian X.

    2014-01-01

    The central challenge in realizing electronics based on strongly correlated electronic states, or ‘Mottronics', lies in finding an energy efficient way to switch between the distinct collective phases with a control voltage in a reversible and reproducible manner. In this work, we demonstrate that a voltage-impulse-induced ferroelastic domain switching in the (011)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates allows a robust non-volatile tuning of the metal-insulator transition in the VOx films deposited onto them. In such a VOx/PMN-PT heterostructure, the unique two-step electric polarization switching covers up to 90% of the entire poled area and contributes to a homogeneous in-plane anisotropic biaxial strain, which, in turn, enables the lattice changes and results in the suppression of metal-insulator transition in the mechanically coupled VOx films by 6 K with a resistance change up to 40% over a broad range of temperature. These findings provide a framework for realizing in situ and non-volatile tuning of strain-sensitive order parameters in strongly correlated materials, and demonstrate great potentials in delivering reconfigurable, compactable, and energy-efficient electronic devices. PMID:25088796

  16. Voltage control of metal-insulator transition and non-volatile ferroelastic switching of resistance in VOx/PMN-PT heterostructures.

    PubMed

    Nan, Tianxiang; Liu, Ming; Ren, Wei; Ye, Zuo-Guang; Sun, Nian X

    2014-08-04

    The central challenge in realizing electronics based on strongly correlated electronic states, or 'Mottronics', lies in finding an energy efficient way to switch between the distinct collective phases with a control voltage in a reversible and reproducible manner. In this work, we demonstrate that a voltage-impulse-induced ferroelastic domain switching in the (011)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates allows a robust non-volatile tuning of the metal-insulator transition in the VOx films deposited onto them. In such a VOx/PMN-PT heterostructure, the unique two-step electric polarization switching covers up to 90% of the entire poled area and contributes to a homogeneous in-plane anisotropic biaxial strain, which, in turn, enables the lattice changes and results in the suppression of metal-insulator transition in the mechanically coupled VOx films by 6 K with a resistance change up to 40% over a broad range of temperature. These findings provide a framework for realizing in situ and non-volatile tuning of strain-sensitive order parameters in strongly correlated materials, and demonstrate great potentials in delivering reconfigurable, compactable, and energy-efficient electronic devices.

  17. Voltage Control of Metal-insulator Transition and Non-volatile Ferroelastic Switching of Resistance in VOx/PMN-PT Heterostructures

    NASA Astrophysics Data System (ADS)

    Nan, Tianxiang; Liu, Ming; Ren, Wei; Ye, Zuo-Guang; Sun, Nian X.

    2014-08-01

    The central challenge in realizing electronics based on strongly correlated electronic states, or `Mottronics', lies in finding an energy efficient way to switch between the distinct collective phases with a control voltage in a reversible and reproducible manner. In this work, we demonstrate that a voltage-impulse-induced ferroelastic domain switching in the (011)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates allows a robust non-volatile tuning of the metal-insulator transition in the VOx films deposited onto them. In such a VOx/PMN-PT heterostructure, the unique two-step electric polarization switching covers up to 90% of the entire poled area and contributes to a homogeneous in-plane anisotropic biaxial strain, which, in turn, enables the lattice changes and results in the suppression of metal-insulator transition in the mechanically coupled VOx films by 6 K with a resistance change up to 40% over a broad range of temperature. These findings provide a framework for realizing in situ and non-volatile tuning of strain-sensitive order parameters in strongly correlated materials, and demonstrate great potentials in delivering reconfigurable, compactable, and energy-efficient electronic devices.

  18. Metal-insulator transition upon heating and negative-differential-resistive-switching induced by self-heating in BaCo{sub 0.9}Ni{sub 0.1}S{sub 1.8}

    SciTech Connect

    Fisher, B.; Genossar, J.; Chashka, K. B.; Patlagan, L.; Reisner, G. M.

    2014-04-14

    The layered compound BaCo{sub 1−x}Ni{sub x}S{sub 2−y} (0.05 < x < 0.2 and 0.05 < y < 0.2) exhibits an unusual first-order structural and electronic phase transition from a low-T monoclinic paramagnetic metal to a high-T tetragonal antiferromagnetic insulator around 200 K with huge hysteresis (∼40 K) and large volume change (∼0.01). Here, we report on unusual voltage-controlled resistive switching followed by current-controlled resistive switching induced by self-heating in polycrystalline BaCo{sub 1−x}Ni{sub x}S{sub 2−y} (nominal x = 0.1 and y = 0.2). These were due to the steep metal to insulator transition upon heating followed by the activated behavior of the resistivity above the transition. The major role of Joule heating in switching is supported by the absence of nonlinearity in the current as function of voltage, I(V), obtained in pulsed measurements, in the range of electric fields relevant to d.c. measurements. The voltage-controlled negative differential resistance around the threshold for switching was explained by a simple model of self-heating. The main difficulty in modeling I(V) from the samples resistance as function of temperature R(T) was the progressive increase of R(T), and to a lesser extend the decrease of the resistance jumps at the transitions, caused by the damage induced by cycling through the transitions by heating or self-heating. This was dealt with by following systematically R(T) over many cycles and by using the data of R(T) in the heating cycle closest to that of the self-heating one.

  19. Interplay between Ferroelastic and Metal-Insulator Phase Transitions in Strained Quasi-Two-Dimensional VO2 Nanoplatelets

    SciTech Connect

    Tselev, Alexander; Strelcov, Evgheni; Luk'yanchuk, Prof. Igor A.; Ivanov, Ilia N; Budai, John D; Tischler, Jonathan Zachary; Jones, Keith M; Proksch, Roger; Kalinin, Sergei V; Kolmakov, Andrei

    2010-01-01

    Formation of ferroelastic twin domains in VO_2 nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline vanadium dioxide (VO_2) quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and non-trivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that complete picture of the phase transitions in single-crystalline and disordered VO_2 structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

  20. Metal-insulator transition in variably doped (Bi(1-x)Sb(x))2Se3 nanosheets.

    PubMed

    Lee, Chee Huei; He, Rui; Wang, ZhenHua; Qiu, Richard L J; Kumar, Ajay; Delaney, Conor; Beck, Ben; Kidd, T E; Chancey, C C; Sankaran, R Mohan; Gao, Xuan P A

    2013-05-21

    Topological insulators are novel quantum materials with metallic surface transport but insulating bulk behavior. Often, topological insulators are dominated by bulk contributions due to defect induced bulk carriers, making it difficult to isolate the more interesting surface transport characteristics. Here, we report the synthesis and characterization of nanosheets of a topological insulator Bi2Se3 with variable Sb-doping levels to control the electron carrier density and surface transport behavior. (Bi(1-x)Sb(x))2Se3 thin films of thickness less than 10 nm are prepared by epitaxial growth on mica substrates in a vapor transport setup. The introduction of Sb in Bi2Se3 effectively suppresses the room temperature electron density from ∼4 × 10(13) cm(-2) in pure Bi2Se3 (x = 0) to ∼2 × 10(12) cm(-2) in (Bi(1-x)Sb(x))2Se3 at x ∼ 0.15, while maintaining the metallic transport behavior. At x ≳ ∼0.20, a metal-insulator transition (MIT) is observed, indicating that the system has transformed into an insulator in which the metallic surface conduction is blocked. In agreement with the observed MIT, Raman spectroscopy reveals the emergence of vibrational modes arising from Sb-Sb and Sb-Se bonds at high Sb concentrations, confirming the appearance of the Sb2Se3 crystal structure in the sample. These results suggest that nanostructured chalcogenide films with controlled doping can be a tunable platform for fundamental studies and electronic applications of topological insulator systems.

  1. Metal-insulator transition in Bi-Pb-Sr-Ca-Y-Cu-O caused by a change in the structural modulation

    NASA Astrophysics Data System (ADS)

    Fukushima, Noburu; Yoshiki, Masahiko

    1994-07-01

    A metal-insulator transition was observed in the layered cuprate Bi2-xPbxSr2Ca0.3Y0.7Cu2O8+d, where the carrier concentration is not changed but the structural modulation was relaxed with increasing lead content x. Resistivity measurements and x-ray-photoelectron-spectroscopy (XPS) valence-band spectra manifested the occurrence of the metal-insulator transition; XPS core-level spectra, together with the results of a chemical analysis, confirmed that in this system the degree of the electron filling is constant. This metal-insulator transition is believed to arise from the change in the Cu-O-Cu bonding angle, as well as those in some nonlayered transition-metal perovskites.

  2. Magnetic and Metal-Insulator Transition in natural Transition Metal Sulfides

    NASA Astrophysics Data System (ADS)

    Wang, Renxiong; Metz, Tristin; Liu, I.-Lin; Wang, Kefeng; Wang, Xiangfeng; Jeffries, J. R.; Saha, S. R.; Greene, R. L.; Paglione, J.; Santelli, C. C.; Post, J.,

    In collaboration with the Smithsonian Institution's National Museum of Natural History, we present detailed studies of a class of natural minerals with potential to harbor correlated behavior. Transition metal sulfide minerals, such as Bornite (Cu5FeS4), are an important family of compounds known for their thermoelectric properties. We will present low temperature experimental studies of magnetic transitions and focus on a compound that exhibits a metal to insulator transition concident with entrance to an antiferromagnetic ground state, suggesting a potentially interesting system with promise for realizing new correlated states of matter in a naturally occurring mineral.

  3. Magnetic Superstructure and Metal-Insulator Transition in Mn-Substituted Sr3 Ru 2 O 7

    NASA Astrophysics Data System (ADS)

    Hossain, M. A.; Zhu, Z. H.; Bohnenbuck, B.; Chuang, Y.-D.; Yoshida, Y.; Hussain, Z.; Keimer, B.; Elfimov, I. S.; Sawatzky, G. A.; Damascelli, A.

    2011-03-01

    We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr 3 (Ru 1-x Mn x)2 O7 , performed at both Ru and Mn L -edges. Resonant magnetic superstructure reflections together with ab-initio density functional theory calculations identify the ground state as a spin checkerboard with blocks of 4 spins up and 4 spins down. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x ~ 0.05 Mn substitution. Perhaps more important, our results suggest that the same checkerboard instability might be present already in the parent compound Sr 3 Ru 2 O7 . In collaboration with: A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley) I. Zegkinoglou, M.W. Haverkort (MPI) J. Geck, D.G. Hawthorn (UBC) R. Mathieu, Y. Tokura, S. Satow, H. Takagi (Tokyo) H.-H. Wu and C. Schussler-Langeheine (Cologne).

  4. Robust antiferromagnetic spin waves across the metal-insulator transition in hole-doped BaMn2As2

    DOE PAGES

    Ramazanoglu, M.; Sapkota, A.; Pandey, Abhishek; ...

    2017-06-01

    BaMn2 As2 is an antiferromagnetic insulator where a metal-insulator transition occurs with hole doping via the substitution of Ba with K. The metal-insulator transition causes only a small suppression of the Néel temperature (TN) and the ordered moment, suggesting that doped holes interact weakly with the Mn spin system. Powder inelastic neutron scattering measurements were performed on three different samples of Ba1 - xKxMn2 As2 with x = 0 , 0.125, and 0.25 to study the effect of hole doping and metallization on the spin dynamics. We compare the neutron intensities to a linear spin-wave theory approximation to the J1more » $-$ J2 $-$ Jc Heisenberg model. Hole doping is found to introduce only minor modifications to the exchange energies and spin gap. The changes observed in the exchange constants are consistent with the small drop of TN with doping.« less

  5. Effect of Structural Relaxation on the Metal-Insulator Transition in Heavily Underdoped YBa $_2 2 Cu _3 3 O _{7-delta }$ 7 - δ Single Crystals

    NASA Astrophysics Data System (ADS)

    Vovk, R. V.; Dobrovolskiy, O. V.; Nazyrov, Z. F.; Kotvitskaya, K. A.; Chroneos, A.

    2015-08-01

    We report the results of a study of the effect of structural relaxation on the basal-plane conductivity of heavily underdoped high- YBaCuO single crystals. An increase of the oxygen deficiency in YBaCuO has been found to strengthen localization effects and to lead to the realization of a transition of the metal-insulator type, which always precedes the superconducting transition. In addition, a 5-day room-temperature annealing of the samples has been revealed to result in a notable shift of the metal-insulator transition point toward higher temperatures.

  6. Electron lone pair distortion facilitated metal-insulator transition in β-Pb{sub 0.33}V{sub 2}O{sub 5} nanowires

    SciTech Connect

    Wangoh, L.; Quackenbush, N. F.; Marley, P. M.; Banerjee, S.; Sallis, S.; Fischer, D. A.; Woicik, J. C.; Piper, L. F. J.

    2014-05-05

    The electronic structure of β-Pb{sub 0.33}V{sub 2}O{sub 5} nanowires has been studied with x-ray photoelectron spectroscopy techniques. The recent synthesis of defect-free β-Pb{sub 0.33}V{sub 2}O{sub 5} nanowires resulted in the discovery of an abrupt voltage-induced metal insulator transition. First principle calculations predicted an additional V-O-Pb hybridized “in-gap” state unique to this vanadium bronze playing a significant role in facilitating the transition. We confirm the existence, energetic position, and orbital character of the “in-gap” state. Moreover, we reveal that this state is a hybridized Pb 6s–O 2p antibonding lone pair state resulting from the asymmetric coordination of the Pb{sup 2+} ions.

  7. High resolution Hall measurements across the VO2 metal-insulator transition reveal impact of spatial phase separation

    PubMed Central

    Yamin, Tony; Strelniker, Yakov M.; Sharoni, Amos

    2016-01-01

    Many strongly correlated transition metal oxides exhibit a metal-insulator transition (MIT), the manipulation of which is essential for their application as active device elements. However, such manipulation is hindered by lack of microscopic understanding of mechanisms involved in these transitions. A prototypical example is VO2, where previous studies indicated that the MIT resistance change correlate with changes in carrier density and mobility. We studied the MIT using Hall measurements with unprecedented resolution and accuracy, simultaneously with resistance measurements. Contrast to prior reports, we find that the MIT is not correlated with a change in mobility, but rather, is a macroscopic manifestation of the spatial phase separation which accompanies the MIT. Our results demonstrate that, surprisingly, properties of the nano-scale spatially-separated metallic and semiconducting domains actually retain their bulk properties. This study highlights the importance of taking into account local fluctuations and correlations when interpreting transport measurements in highly correlated systems. PMID:26783076

  8. Metal-insulator transition in the Hollandite vanadate K2V8O16 investigated by 51V NMR measurements

    NASA Astrophysics Data System (ADS)

    Okai, Katsunori; Itoh, Masayuki; Shimizu, Yasuhiro; Isobe, Masahiko; Yamaura, Jun-Ichi; Ueda, Yutaka

    2009-03-01

    51V NMR measurements have been made on powdered samples to investigate the metal-insulator (MI) transition and the local magnetic properties of the Hollandite vanadate K2V8O16 which undergoes the MI transition at TMI~170 K. An asymmetric 51V NMR spectrum in the metallic phase has the T-dependent negative Knight shift K. The two NMR spectra appears around TMI, showing the coexistence of the metallic and insulating phases in consistent with the two-step first-order transition. The temperature dependence of K and the 51V nuclear spin-lattice relaxation rate indicates the presence of the ferromagnetic spin fluctuations in the metallic phase. A 51V NMR spectrum observed below TMI has the temperature-independent K~0.35%, showing the presence of the nonmagnetic ground state.

  9. Critical metal-insulator transition due to nuclear quantum effects in Mn-doped GaAs

    NASA Astrophysics Data System (ADS)

    Bae, Soungmin; Raebiger, Hannes

    2016-12-01

    Mn-doped GaAs exhibits a critical metal-insulator transition at the Mn concentration of xcrit≈1 % . Our self-interaction corrected first principles calculation shows that for Mn concentrations x ≳1 % , hole carriers are delocalized in host valence states, and for x ≲1 % , holes tend to be trapped in impurity-band-like states. We further show that for a finite range of concentrations around xcrit the system exhibits a nonadiabatic superposition of these states, i.e., a mixing of electronic and nuclear wave functions. This means that the phase transition is continuous, and its criticality is caused by quantum effects of the atomic nuclei. In other words, the apparently electronic phase transition from the insulator to metal state cannot be described by electronic effects alone.

  10. Dynamically tracking the strain across the metal-insulator transition in VO2 measured using electromechanical resonators.

    PubMed

    Parikh, Pritesh; Chakraborty, Chitraleema; Abhilash, T S; Sengupta, Shamashis; Cheng, Chun; Wu, Junqiao; Deshmukh, Mandar M

    2013-10-09

    We study the strain state of doubly clamped VO2 nanobeam devices by dynamically probing resonant frequency of the nanoscale electromechanical device across the metal-insulator transition. Simultaneous resistance and resonance measurements indicate M1-M2 phase transition in the insulating state with a drop in resonant frequency concomitant with an increase in resistance. The resonant frequency increases by ~7 MHz with the growth of metallic domain (M2-R transition) due to the development of tensile strain in the nanobeam. Our approach to dynamically track strain coupled with simultaneous resistance and resonance measurements using electromechanical resonators enables the study of lattice-involved interactions more precisely than static strain measurements. This technique can be extended to other phase change systems important for device applications.

  11. Theory of the metal-insulator transition in Pr Ru4 P12 and Pr Fe4 P12

    NASA Astrophysics Data System (ADS)

    Curnoe, S. H.; Harima, H.; Takegahara, K.; Ueda, K.

    2004-12-01

    All symmetry-allowed couplings between the 4f2 -electron ground state doublet of trivalent praseodymium in PrRu4P12 and PrFe4P12 and displacements of the phosphorus, iron, or ruthenium ions are considered. Two types of displacements can change the crystal lattice from body-centred cubic to simple orthorhombic or to simple cubic. The first type lowers the point group symmetry from tetrahedral to orthorhombic, while the second type leaves it unchanged, with corresponding space group reductions Im3¯→Pmmm and Im3¯→Pm3¯ , respectively. In former case, the lower point group symmetry splits the degeneracy of the 4f2 doublet into states with opposite quadrupole moment, which then leads to antiquadrupolar ordering, as in PrFe4P12 . Either kind of displacement may conspire with nesting of the Fermi surface to cause the metal-insulator or partial metal-insulator transition observed in PrFe4P12 and PrRu4P12 . We investigate this scenario using band-structure calculations, and it is found that displacements of the phosphorus ions in PrRu4P12 (with space-group reduction Im3¯→Pm3¯ ) open a gap everywhere on the Fermi surface.

  12. Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

    NASA Astrophysics Data System (ADS)

    Torriss, B.; Margot, J.; Chaker, M.

    2017-01-01

    Samarium nickelate (SmNiO3) thin films were successfully synthesized on LaAlO3 and SrTiO3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing.

  13. Visualizing the interfacial evolution from charge compensation to metallic screening across the manganite metal-insulator transition.

    PubMed

    Mundy, Julia A; Hikita, Yasuyuki; Hidaka, Takeaki; Yajima, Takeaki; Higuchi, Takuya; Hwang, Harold Y; Muller, David A; Kourkoutis, Lena F

    2014-03-17

    Electronic changes at polar interfaces between transition metal oxides offer the tantalizing possibility to stabilize novel ground states yet can also cause unintended reconstructions in devices. The nature of these interfacial reconstructions should be qualitatively different for metallic and insulating films as the electrostatic boundary conditions and compensation mechanisms are distinct. Here we directly quantify with atomic-resolution the charge distribution for manganite-titanate interfaces traversing the metal-insulator transition. By measuring the concentration and valence of the cations, we find an intrinsic interfacial electronic reconstruction in the insulating films. The total charge observed for the insulating manganite films quantitatively agrees with that needed to cancel the polar catastrophe. As the manganite becomes metallic with increased hole doping, the total charge build-up and its spatial range drop substantially. Direct quantification of the intrinsic charge transfer and spatial width should lay the framework for devices harnessing these unique electronic phases.

  14. Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

    PubMed Central

    Torriss, B.; Margot, J.; Chaker, M.

    2017-01-01

    Samarium nickelate (SmNiO3) thin films were successfully synthesized on LaAlO3 and SrTiO3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing. PMID:28098240

  15. Temperature dependence of the first-order metal-insulator transition in VO2 and programmable critical temperature sensor

    NASA Astrophysics Data System (ADS)

    Kim, Bong-Jun; Lee, Yong Wook; Chae, Byung-Gyu; Yun, Sun Jin; Oh, Soo-Young; Kim, Hyun-Tak; Lim, Yong-Sik

    2007-01-01

    For VO2-based two-terminal devices, the first-order metal-insulator transition (MIT, jump) is controlled by an applied voltage and temperature, and an intermediate monoclinic metal phase between the MIT and the structural phase transition (SPT) is observed. The conductivity of this phase linearly increases with increasing temperature up to TSPT≈68°C and becomes maximum at TSPT. Optical microscopic observation reveals the absence of a local current path in the metal phase. The current uniformly flows throughout the surface of the VO2 film when the MIT occurs. This device can be used as a programmable critical temperature sensor where the applied voltage is controlled by a program.

  16. Role of thermal strain in the metal-insulator and structural phase transition of epitaxial VO2 films

    NASA Astrophysics Data System (ADS)

    Théry, V.; Boulle, A.; Crunteanu, A.; Orlianges, J. C.; Beaumont, A.; Mayet, R.; Mennai, A.; Cosset, F.; Bessaudou, A.; Fabert, M.

    2016-05-01

    The metal-insulator switching characteristics of VO2 play a crucial role in the performances of VO2-based devices. In this paper we study high-quality (010)-oriented epitaxial films grown on (001) sapphire substrates by means of electron-beam evaporation and investigate the role of interface defects and thermal strain on the parallel evolution of the metal-insulator transition (MIT) and structural phase transition (SPT) between the monoclinic (insulator) and rutile (metal) phases. It is demonstrated that the highly-mismatched VO2/Al2O3 interface promotes a domain-matching epitaxial growth process where the film grows in a strain-relaxed state and the lattice distortions are confined at the interface in regions with limited spatial extent. Upon cooling down from the growth temperature, tensile strain is stored in the films as a consequence of the thermal expansion mismatch between VO2 and Al2O3 . The thinnest films exhibit the highest level of tensile strain in the interfacial plane resulting in a shift of both the MIT and the SPT temperatures towards higher values, pointing to a stabilization of the monoclinic/insulating phase. Concomitantly, the electrical switching characteristics are altered (lower resistivity ratio and broader transition) as a result of the presence of structural defects located at the interface. The SPT exhibits a similar evolution with, additionally, a broader hysteresis due to the formation of an intermediate, strain-stabilized phase in the M1-R transition. Films with thickness ranging between 100-300 nm undergo a partial strain relaxation and exhibit the best performances, with a sharp (10°C temperature range) and narrow (hysteresis <4°C) MIT extending over more than four orders of magnitude in resistivity (6 ×104 ).

  17. Covalency, Excitons, Double Counting and the Metal-Insulator Transition in Transition Metal Oxides

    NASA Astrophysics Data System (ADS)

    Wang, Xin

    2012-02-01

    We present single-site dynamical mean-field studies of realistic models of transition metal oxides, including the cuprate superconductors and rare earth nickelates (in bulk and superlattice form). We include orbital multiplet effects and hybridization to ligands. We explicitly calculate the d-d exciton spectra for cuprates, finding sharp exciton lines in both metallic and insulating phases, which should be visible in experiments. We also find that the additional d3z^2-r^2 orbital does not contribute to an additional Fermi surface at any reasonable doping, in contradiction to previous slave-boson studies. The hybridization to ligands is shown to have crucial effects, for example suppressing the ferro-orbital order previously found in Hubbard model studies of nickelates. Hybridization to ligands is shown to be most naturally parametrized by the d-orbital occupancy. For cuprates and nickelates, insulating behavior is found to be present only for a very narrow range of d-occupancy, irrespective of the Coulomb repulsion. The d-occupancy predicted by standard band calculations is found to be very far from the values required to obtain an insulating phase, calling into question the interpretation of these materials as charge transfer insulators. [4pt] This work is done in collaboration with A.J. Millis, M.J. Han, C.A. Marianetti, L. de' Medici, and H.T. Dang, and is supported by NSF-DMR-1006282, the Army Office of Scientific Research, and the Condensed Matter Theory Center and CNAM at University of Maryland. [4pt] [1] X. Wang, H. T. Dang, and A. J. Millis, Phys. Rev. B 84, 014530 (2011).[0pt] [2] X. Wang, M. J. Han, L. de' Medici, C. A. Marianetti, and A. J. Millis, arXiv:1110.2782.[0pt] [3] M. J. Han, X. Wang, C. A. Marianetti, and A. J. Millis, Phys. Rev. Lett. 107, 206804 (2011).

  18. Metal-insulator transition and nonlinear optical responseof sputter-deposited V3O5 thin films

    NASA Astrophysics Data System (ADS)

    Rúa, Armando; Díaz, Ramón D.; Kumar, Nardeep; Lysenko, Sergiy; Fernández, Félix E.

    2017-06-01

    The compound V3O5, a member of the vanadium oxide Magnéli series, exhibits a metal-insulator transition near 430 K, the highest known temperature value among all vanadium oxides. It has been studied before mainly in single-crystal form, and for the very few cases in which thin films have been fabricated before, the procedure has required extensive post-deposition annealing of other oxides or vanadium metal at high temperatures in tightly controlled atmospheres. For the present work, V3O5 films were deposited directly on SiO2 glass substrates, without subsequent annealing, by DC magnetron sputtering. X-ray diffraction study of the samples evidenced oxygen deficiency, accommodated by oxygen vacancies. Resistivity measurements from 300 to 500 K revealed the metal-insulator transition by Tc ˜ 430 K, with an associated resistivity change by a factor of 20, and no detectable hysteresis in heating-cooling cycles, in agreement with most single-crystal studies. Resistivity values obtained were, however, lower than published results for bulk crystal values, particularly at temperatures below Tc. This was attributed to conduction electrons generated by the oxygen vacancies. Gradual resistivity increase in a very thin sample, through heating in air at temperatures up to 500 K, lends support to this argument. Using a pump-probe scattering technique, the V3O5 films were also probed for ultrafast nonlinear optical response. A reduction in the transient relative scattered light signal was recorded, which reached -10% within ˜800 fs. This observed response, likely related to the photoinduced insulator-to-metal phase transition, should stimulate additional interest in this material.

  19. Direct measurement of sheet resistance Rsquare in cuprate systems: evidence of a fermionic scenario in a metal-insulator transition.

    PubMed

    Orgiani, P; Aruta, C; Balestrino, G; Born, D; Maritato, L; Medaglia, P G; Stornaiuolo, D; Tafuri, F; Tebano, A

    2007-01-19

    The metal-insulator transition (MIT) has been studied in Ba(0.9)Nd(0.1)CuO(2+x)/CaCuO2 ultrathin cuprate structures. Such structures allow for the direct measurement of the 2D sheet resistance R( square), eliminating ambiguity in the definition of the effective thickness of the conducting layer in high temperature superconductors. The MIT occurs at room temperature for experimental values of R(square) close to the 25.8 kOmega universal quantum resistance. All data confirm the assumption that each CaCuO2 layer forms a 2D superconducting sheet within the superconducting block, which can be described as weak-coupled equivalent sheets in parallel.

  20. Resistivity of the insulating phase approaching the two-dimensional metal-insulator transition: The effect of spin polarization

    NASA Astrophysics Data System (ADS)

    Li, Shiqi; Sarachik, M. P.

    2017-01-01

    The resistivities of the dilute, strongly interacting two-dimensional electron systems in the insulating phase of a silicon MOSFET are the same for unpolarized electrons in the absence of magnetic field and for electrons that are fully spin polarized by the presence of an in-plane magnetic field. In both cases the resistivity obeys Efros-Shklovskii variable range hopping ρ (T ) =ρ0exp[(TES/T ) 1 /2] , with TE S and 1 /ρ0 mapping onto each other if one applies a shift of the critical density nc reported earlier. With and without magnetic field, the parameters TE S and 1 /ρ0=σ0 exhibit scaling consistent with critical behavior approaching a metal-insulator transition.

  1. The metal-insulator transition in the organic conductor β″-(BEDT-TTF)2Hg(SCN)2Cl

    NASA Astrophysics Data System (ADS)

    Li, Weiwu; Rose, Eva; Tran, Minh Vu; Hübner, Ralph; Łapiński, Andrzej; Świetlik, Roman; Torunova, Svetlana A.; Zhilyaeva, Elena I.; Lyubovskaya, Rimma N.; Dressel, Martin

    2017-08-01

    We explore the nature of the metal-insulator transition in the two-dimensional organic compound β″-(BEDT-TTF)2Hg(SCN)2Cl by x-ray, electrical transport, ESR, Raman, and infrared investigations. Magnetic and vibrational spectroscopy concurrently reveal a gradual dimerization along the stacking direction (a -b ) , setting in already at the crossover temperature of 150 K from the metallic to the insulating state. A spin gap of Δσ=47 meV is extracted. From the activated resistivity behavior below T = 55 K, a charge gap of Δρ=60 meV is derived. At TCO = 72 K, the C=C vibrational modes reveal the development of a charge-ordered state with a charge disproportionation of 2 δρ=0.34 e . In addition to a slight structural dimerization, charge-order causes stripes most likely perpendicular to the stacks.

  2. Effect of crystal-field splitting and interband hybridization on the metal-insulator transitions of strongly correlated systems

    NASA Astrophysics Data System (ADS)

    Poteryaev, Alexander I.; Ferrero, Michel; Georges, Antoine; Parcollet, Olivier

    2008-07-01

    We investigate a quarter-filled two-band Hubbard model involving a crystal-field splitting, which lifts the orbital degeneracy as well as an interorbital hopping (interband hybridization). Both terms are relevant to the realistic description of correlated materials such as transition-metal oxides. The nature of the Mott metal-insulator transition is clarified and is found to depend on the magnitude of the crystal-field splitting. At large values of the splitting, a transition from a two-band to a one-band metal is first found as the on-site repulsion is increased and is followed by a Mott transition for the remaining band, which follows the single-band (Brinkman-Rice) scenario well documented previously within dynamical mean-field theory. At small values of the crystal-field splitting, a direct transition from a two-band metal to a Mott insulator with partial orbital polarization is found, which takes place simultaneously for both orbitals. This transition is characterized by a vanishing of the quasiparticle weight for the majority orbital but has a first-order character for the minority orbital. It is pointed out that finite-temperature effects may easily turn the metallic regime into a bad metal close to the orbital polarization transition in the metallic phase.

  3. Comprehensive studies of interfacial strain and oxygen vacancy on metal-insulator transition of VO2 film

    NASA Astrophysics Data System (ADS)

    Fan, L. L.; Chen, S.; Liao, G. M.; Chen, Y. L.; Ren, H.; Zou, C. W.

    2016-06-01

    As a typical strong correlation material, vanadium dioxide (VO2) has attracted wide interest due to its particular metal-insulator transition (MIT) property. However, the relatively high critical temperature (T c) of ~68 °C seriously hinders its practical applications. Thus modulating the phase transition process and decreasing the T c close to room temperature have been hot topics for VO2 study. In the current work, we conducted a multi-approach strategy to control the phase transition of VO2 films, including the interfacial tensile/compressive strain and oxygen vacancies. A synchrotron radiation reciprocal space mapping technique was used to directly record the interfacial strain evolution and variations of lattice parameters. The effects of interfacial strain and oxygen vacancies in the MIT process were systematically investigated based on band structure and d-orbital electron occupation. It was suggested that the MIT behavior can be modulated through the combined effects of the interfacial strain and oxygen vacancies, achieving the distinct phase transition close to room temperature. The current findings not only provide better understanding for strain engineering and oxygen vacancies controlling phase transition behavior, but also supply a combined way to control the phase transition of VO2 film, which is essential for VO2 film based device applications in the future.

  4. β phase and γ-β metal-insulator transition in multiferroic BiFeO3

    NASA Astrophysics Data System (ADS)

    Palai, R.; Katiyar, R. S.; Schmid, H.; Tissot, P.; Clark, S. J.; Robertson, J.; Redfern, S. A. T.; Catalan, G.; Scott, J. F.

    2008-01-01

    We report on extensive experimental studies on thin film, single crystal, and ceramics of multiferroic bismuth ferrite BiFeO3 using differential thermal analysis, high-temperature polarized light microscopy, high-temperature and polarized Raman spectroscopy, high-temperature x-ray diffraction, dc conductivity, optical absorption and reflectivity, and domain imaging, and show that epitaxial (001) thin films of BiFeO3 are clearly monoclinic at room temperature, in agreement with recent synchrotron studies but in disagreement with all other earlier reported results. We report an orthorhombic order-disorder β phase between 820 and 925 (±5)°C , and establish the existence range of the cubic γ phase between 925 (±5) and 933 (±5)°C , contrary to all recent reports. We also report the refined Bi2O3-Fe2O3 phase diagram. The phase transition sequence rhombohedral-orthorhombic-cubic in bulk [monoclinic-orthorhombic-cubic in (001)BiFeO3 thin film] differs distinctly from that of BaTiO3 . The transition to the cubic γ phase causes an abrupt collapse of the band gap toward zero (insulator-metal transition) at the orthorhombic-cubic β-γ transition around 930°C . Our band structure models, high-temperature dc resistivity, and light absorption and reflectivity measurements are consistent with this metal-insulator transition.

  5. Critical Behavior in Doping-Driven Metal-Insulator Transition on Single-Crystalline Organic Mott-FET.

    PubMed

    Sato, Yoshiaki; Kawasugi, Yoshitaka; Suda, Masayuki; Yamamoto, Hiroshi M; Kato, Reizo

    2017-02-08

    We present the carrier transport properties in the vicinity of a doping-driven Mott transition observed at a field-effect transistor (FET) channel using a single crystal of the typical two-dimensional organic Mott insulator κ-(BEDT-TTF)2CuN(CN)2Cl (κ-Cl). The FET shows a continuous metal-insulator transition (MIT) as electrostatic doping proceeds. The phase transition appears to involve two-step crossovers, one in Hall measurement and the other in conductivity measurement. The crossover in conductivity occurs around the conductance quantum e(2)/h, and hence is not associated with "bad metal" behavior, which is in stark contrast to the MIT in half-filled organic Mott insulators or that in doped inorganic Mott insulators. Through in-depth scaling analysis of the conductivity, it is found that the above carrier transport properties in the vicinity of the MIT can be described by a high-temperature Mott quantum critical crossover, which is theoretically argued to be a ubiquitous feature of various types of Mott transitions.

  6. Thermopower analysis of the electronic structure around the metal-insulator transition in V1-xWxO2

    NASA Astrophysics Data System (ADS)

    Katase, Takayoshi; Endo, Kenji; Ohta, Hiromichi

    2014-10-01

    The electronic structure across the metal-insulator (MI) transition of electron-doped V1-xWxO2 epitaxial films (x =0-0.06) grown on α-Al2O3 substrates was studied by means of thermopower (S) measurements. Significant increase of |S | values accompanied by MI transition was observed, and the transition temperatures of S (TS) decreased with x in a good linear relation with MI transition temperatures. |S| values of V1-xWxO2 films at T>TS were constant at low values of 23μVK-1 independently of x, which reflects a metallic electronic structure, whereas those at T

  7. Studies on electric triggering of the metal-insulator transition in VO2 thin films between 77 K and 300 K

    NASA Astrophysics Data System (ADS)

    Yang, Zheng; Hart, Sean; Ko, Changhyun; Yacoby, Amir; Ramanathan, Shriram

    2011-08-01

    We investigate the electrically triggered metal-insulator transition (E-MIT) in VO2 thin films at temperatures far below the structural phase transition temperature (˜340 K). At 77 K, the maximum current jump observed across the E-MIT is nearly 300×. The threshold voltage for E-MIT decreases slightly from ˜2.0 V at 77 K to ˜1.1 V at 300 K across ˜200 nm thick films, which scales weakly over the temperature range of 77-300 K with an activation energy of ˜5 meV. The phase transition properties are found to be stable after over one thousand scans, indicating reproducible measurements. Analysis of the scaling behavior suggests that the observed weak temperature-dependence of the threshold voltages for E-MIT is smaller than that predicted for a purely current induced Joule heating effect and may include contribution from field effect or carrier injection under applied bias. The results are of potential relevance to the field of phase transition oxide electronics and further understanding of the transition mechanisms.

  8. Field Effect and Strongly Localized Carriers in the Metal-Insulator Transition Material VO(2).

    PubMed

    Martens, K; Jeong, J W; Aetukuri, N; Rettner, C; Shukla, N; Freeman, E; Esfahani, D N; Peeters, F M; Topuria, T; Rice, P M; Volodin, A; Douhard, B; Vandervorst, W; Samant, M G; Datta, S; Parkin, S S P

    2015-11-06

    The intrinsic field effect, the change in surface conductance with an applied transverse electric field, of prototypal strongly correlated VO(2) has remained elusive. Here we report its measurement enabled by epitaxial VO(2) and atomic layer deposited high-κ dielectrics. Oxygen migration, joule heating, and the linked field-induced phase transition are precluded. The field effect can be understood in terms of field-induced carriers with densities up to ∼5×10(13)  cm(-2) which are trongly localized, as shown by their low, thermally activated mobility (∼1×10(-3)  cm(2)/V s at 300 K). These carriers show behavior consistent with that of Holstein polarons and strongly impact the (opto)electronics of VO(2).

  9. Metal-insulator transitions induced by doping in LaNiO{sub 3}: LaNi{sub 0.95}M{sub 0.05}O{sub 3} (M = Mo, W, Sb, Ti, Cu, Zn) perovskites

    SciTech Connect

    Alvarez, I.; Veiga, M.L.; Pico, C.

    1998-03-01

    Structural characterization and electronic properties of the LaNi{sub 0.95}M{sub 0.05}O{sub 3} (M = Mo, W, Sb, Ti, Cu, Zn) perovskite-like system are reported. These compounds can be regarded as being derived from LaNiO{sub 3} by partial substitution of Ni{sup 3+} in this material by M{sup 6+}, M{sup 5+}, M{sup 4+}, or M{sup 2+} formal cations, with a partial reduction of Ni{sup 3+} to Ni{sup 2+} taking place. X-ray powder diffraction data were analyzed by means of the Rietveld method and show that all the title materials present perovskite-type structure with a rhombohedral (S.G. R{bar 3}c) or orthorhombic (S.G. Pbnm) symmetry, depending on the nature of the M cation. In all cases, Ni and M cations are placed at random in octahedral B-sites of perovskite structure. Electrical resistivity measurements (four probe method) show metal-to-insulator (M-I) transitions for M = Mo, W, Ti, Cu, Zn at temperatures of about 50K and a semiconductor behavior for the Sb sample in the whole temperature range explored. Magnetic susceptibility measurements show the presence of weak ferromagnetic interactions for M = Sb and Pauli paramagnetism for the remaining compounds.

  10. Novel Metal-Insulator Transition at the SmTiO3/SrTiO3 Interface

    NASA Astrophysics Data System (ADS)

    Ahadi, Kaveh; Stemmer, Susanne

    2017-06-01

    We report on a metal-insulator transition (MIT) that is observed in an electron system at the SmTiO3/SrTiO3 interface. This MIT is characterized by an abrupt transition at a critical temperature, below which the resistance changes by more than an order of magnitude. The temperature of the transition systematically depends on the carrier density, which is tuned from ˜1 ×1014 to 3 ×1014 cm-2 by changing the SmTiO3 thickness. An analysis of the transport properties shows non-Fermi-liquid behavior and mass enhancement as the carrier density is lowered. We compare the MIT characteristics with those of known MITs in other material systems and show that they are distinctly different in several aspects. We tentatively conclude that both long-range Coulomb interactions and the fixed charge at the polar interface are likely to play a role in this MIT. The strong dependence on the carrier density makes this MIT of interest for field-tunable devices.

  11. Linear-in-temperature resistivity close to a topological metal insulator transition in ultra-multi valley fcc-ytterbium

    NASA Astrophysics Data System (ADS)

    Enderlein, Carsten; Fontes, Magda; Baggio-Saitovich, Elisa; Continentino, Mucio A.

    2016-01-01

    The semimetal-to-semiconductor transition in fcc-Yb under modest pressure can be considered a picture book example of a metal-insulator transition of the Lifshitz type. We have performed transport measurements at low temperatures in the closest vicinity of the transition and related DFT calculations of the Fermi surface. Our resistivity measurements show a linear temperature dependence with an unusually low dρ / dT at low temperatures approaching the MIT. The calculations suggest fcc-ytterbium being an ultra-multi valley system with 24 electron and 6 hole pockets in the Brillouin zone. Such Fermi surface topology naturally supports the appearance of strongly correlated phases. An estimation of the quasiparticle-enhanced effective mass shows that the scattering rate is by at least two orders of magnitude lower than in other materials which exhibit linear-in-T behavior at a quantum critical point. However, we cannot exclude an excessive effective mass enhancement, when the van Hove singularity touches the Fermi level.

  12. Dynamic phase coexistence and non-Gaussian resistance fluctuations in VO2 near the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Samanta, Sudeshna; Raychaudhuri, A. K.; Zhong, Xing; Gupta, A.

    2015-11-01

    We have carried out an extensive investigation on the resistance fluctuations (noise) in an epitaxial thin film of VO2 encompassing the metal-insulator transition (MIT) region to investigate the dynamic phase coexistence of metal and insulating phases. Both flicker noise as well as the Nyquist noise (thermal noise) were measured. The experiments showed that flicker noise, which has a 1 /f spectral power dependence, evolves with temperature in the transition region following the evolution of the phase fractions and is governed by activated kinetics. Importantly, closer to the insulating end of the transition, when the metallic phase fraction is low, the magnitude of the noise shows an anomaly and a strong non-Gaussian component of noise develops. In this region, the local electron temperature (as measured through the Nyquist noise thermometry) shows a deviation from the equilibrium bath temperature. It is proposed that this behavior arises due to current crowding where a substantial amount of the current is carried through well separated small metallic islands leading to a dynamic correlated current path redistribution and an enhanced effective local current density. This leads to a non-Gaussian component to the resistance fluctuation and an associated local deviation of the electron temperature from the bath. Our experiment establishes that phase coexistence leads to a strong inhomogeneity in the region of MIT that makes the current transport strongly inhomogeneous and correlated.

  13. Metal-insulator transition and magnetic fluctuations in polycrystalline Ru1 -xRhxP investigated by 31P NMR

    NASA Astrophysics Data System (ADS)

    Li, Shang; Kobayashi, Yoshiaki; Itoh, Masayuki; Hirai, Daigorou; Takagi, Hidenori

    2017-04-01

    31P NMR measurements have been made on polycrystalline samples to study a metal-insulator (MI) transition and magnetic fluctuations in Ru1 -xRhxP which has metallic (M), pseudogap (PG), insulating (I), and superconducting (SC) phases. We find that RuP undergoes a crossover from the high-temperature (high-T ) M phase to the PG phase with the pseudo spin-gap behavior probed by the nuclear spin-lattice relaxation rate at TPG=330 K . The first-order MI transition is observed to take place from the PG phase to the low-T nonmagnetic I phase with the spin-gap energy of 1250 K at TMI=270 K . In the PG phase of Ru1 -xRhxP with 0 ≤x <0.45 , an analysis based on the modified Korringa relation, which is applicable to an itinerant paramagnet with weak electron correlation, shows that antiferromagnetic (AFM) fluctuations described in the random-phase approximation are enhanced in the low-T and low-x region. Around the PG-M phase boundary at xc˜0.45 , there is the SC phase whose normal state has negligible electron-electron interaction. We discuss the MI transition, the crossover from the M phase to the PG phase, and the magnetic properties of each phase based on the band structure.

  14. Superconductor-Metal-Insulator transition in two dimensional Ta thin Films

    NASA Astrophysics Data System (ADS)

    Park, Sun-Gyu; Kim, Eunseong

    2013-03-01

    Superconductor-insulator transition has been induced by tuning film thickness or magnetic field. Recent electrical transport measurements of MoGe, Bi, Ta thin films revealed an interesting intermediate metallic phase which intervened superconducting and insulating phases at certain range of magnetic field. Especially, Ta thin films show the characteristic IV behavior at each phase and the disorder tuned intermediate metallic phase [Y. Li, C. L. Vicente, and J. Yoon, Physical Review B 81, 020505 (2010)]. This unexpected metallic phase can be interpreted as a consequence of vortex motion or contribution of fermionic quasiparticles. In this presentation, we report the scaling behavior during the transitions in Ta thin film as well as the transport measurements in various phases. Critical exponents v and z are obtained in samples with wide ranges of disorder. These results reveal new universality class appears when disorder exceeds a critical value. Dynamical exponent z of Superconducting sample is found to be 1, which is consistent with theoretical prediction of unity. z in a metallic sample is suddenly increased to be approximately 2.5. This critical exponent is much larger than the value found in other system and theoretical prediction. We gratefully acknowledge the financial support by the National Research Foundation of Korea through the Creative Research Initiatives.

  15. Reversible metal-insulator transition of Ar-irradiated LaAl O3 /SrTi O3 interfaces

    NASA Astrophysics Data System (ADS)

    Aurino, P. P.; Kalabukhov, A.; Tuzla, N.; Olsson, E.; Klein, A.; Erhart, P.; Boikov, Y. A.; Serenkov, I. T.; Sakharov, V. I.; Claeson, T.; Winkler, D.

    2015-10-01

    The conducting state of a quasi-two-dimensional electron gas (q2DEG), formed at the heterointerface between the two wide-bandgap insulators LaAl O3 (LAO) and SrTi O3 , can be made completely insulating by low-energy, 150-eV, A r+ irradiation. The metallic behavior of the interface can be recovered by high-temperature oxygen annealing. The electrical transport properties of the recovered q2DEG are exactly the same as before the irradiation. Microstructural investigations confirm that the transition is not due to physical etching or crystal lattice distortion of the LAO film below its critical thickness. They also reveal a correlation between electrical state, LAO film surface amorphization, and argon ion implantation. The experimental results are in agreement with density functional theory calculations of Ar implantation and migration in the LAO film. This suggests that the metal-insulator transition may be caused by charge trapping in the defect amorphous layer created during the ion irradiation.

  16. Influence of oxygen flow rate on metal-insulator transition of vanadium oxide thin films grown by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Ma, Xu; Liu, Xinkun; Li, Haizhu; Zhang, Angran; Huang, Mingju

    2017-03-01

    High-quality vanadium oxide ( VO2) films have been fabricated on Si (111) substrates by radio frequency (RF) magnetron sputtering deposition method. The sheet resistance of VO2 has a significant change (close to 5 orders of magnitude) in the process of the metal-insulator phase transition (MIT). The field emission-scanning electron microscope (FE-SEM) results show the grain size of VO2 thin films is larger with the increase of oxygen flow. The X-ray diffraction (XRD) results indicate the thin films fabricated at different oxygen flow rates grow along the (011) crystalline orientation. As the oxygen flow rate increases from 3 sccm to 6 sccm, the phase transition temperature of the films reduces from 341 to 320 K, the width of the thermal hysteresis loop decreases from 32 to 9 K. The thin films fabricated in the condition of 5 sccm have a high temperature coefficient of resistance (TCR) -3.455%/K with a small resistivity of 2.795 ρ/Ω cm.

  17. Mg-doped VO2 nanoparticles: hydrothermal synthesis, enhanced visible transmittance and decreased metal-insulator transition temperature.

    PubMed

    Zhou, Jiadong; Gao, Yanfeng; Liu, Xinling; Chen, Zhang; Dai, Lei; Cao, Chuanxiang; Luo, Hongjie; Kanahira, Minoru; Sun, Chao; Yan, Liuming

    2013-05-28

    This paper reports the successful preparation of Mg-doped VO2 nanoparticles via hydrothermal synthesis. The metal-insulator transition temperature (T(c)) decreased by approximately 2 K per at% Mg. The Tc decreased to 54 °C with 7.0 at% dopant. The composite foils made from Mg-doped VO2 particles displayed excellent visible transmittance (up to 54.2%) and solar modulation ability (up to 10.6%). In addition, the absorption edge blue-shifted from 490 nm to 440 nm at a Mg content of 3.8 at%, representing a widened optical band gap from 2.0 eV for pure VO2 to 2.4 eV at 3.8 at% doping. As a result, the colour of the Mg-doped films was modified to increase their brightness and lighten the yellow colour over that of the undoped-VO2 film. A first principle calculation was conducted to understand how dopants affect the optical, Mott phase transition and structural properties of VO2.

  18. A persistent metal-insulator transition at the surface of an oxygen-deficient, epitaxial manganite film.

    PubMed

    Snijders, Paul C; Gao, Min; Guo, Hangwen; Cao, Guixin; Siemons, Wolter; Gao, Hongjun; Ward, Thomas Z; Shen, Jian; Gai, Zheng

    2013-10-21

    The oxygen stoichiometry has a large influence on the physical and chemical properties of complex oxides. Most of the functionality in e.g. catalysis and electrochemistry depends in particular on control of the oxygen stoichiometry. In order to understand the fundamental properties of intrinsic surfaces of oxygen-deficient complex oxides, we report on in situ temperature dependent scanning tunnelling spectroscopy experiments on pristine oxygen deficient, epitaxial manganite films. Although these films are insulating in subsequent ex situ in-plane electronic transport experiments at all temperatures, in situ scanning tunnelling spectroscopic data reveal that the surface of these films exhibits a metal-insulator transition (MIT) at 120 K, coincident with the onset of ferromagnetic ordering of small clusters in the bulk of the oxygen-deficient film. The surprising proximity of the surface MIT transition temperature of nonstoichiometric films with that of the fully oxygenated bulk suggests that the electronic properties in the surface region are not significantly affected by oxygen deficiency in the bulk. This carries important implications for the understanding and functional design of complex oxides and their interfaces with specific electronic properties in catalysis, oxide electronics and electrochemistry.

  19. Monolayer MoS2 metal insulator transition based memcapacitor modeling with extension to a ternary device

    NASA Astrophysics Data System (ADS)

    Khan, Abdul Karim; Lee, Byoung Hun

    2016-09-01

    Memcapacitor model based on its one possible physical realization is developed and simulated in order to know its limitation before making a real device. The proposed device structure consists of vertically stacked dielectric layer and MoS2 monolayer between two external metal plates. The Metal Insulator Transition (MIT) phenomenon of MoS2 monolayer is represented in terms of percolation probabilty which is used as the system state. Cluster based site percolation theory is used to mimic the MIT of MoS2 which shows slight discontinuous change in MoS2 monolayer conductivity. The metal to insulator transition switches the capacitance of the device in hysterical way. An Ioffe Regel criterion is used to determine the MIT state of MoS2 monolayer. A good control of MIT time in the range of psec is also achieved by changing a single parameter in the model. The model shows memcapacitive behavior with an edge of fast switching (in psec range) over the previous general models. The model is then extended into vertical cascaded version which behaves like a ternary device instead of binary.

  20. Anisotropic phase separation through the metal-insulator transition in amorphous Mo-Ge and Fe-Ge alloys

    SciTech Connect

    Regan, Michael J.

    1993-12-01

    Since an amorphous solid is often defined as that which lacks long-range order, the atomic structure is typically characterized in terms of the high-degree of short-range order. Most descriptions of vapor-deposited amorphous alloys focus on characterizing this order, while assuming that the material is chemically homogeneous beyond a few near neighbors. By coupling traditional small-angle x-ray scattering which probes spatial variations of the electron density with anomalous dispersion which creates a species-specific contrast, one can discern cracks and voids from chemical inhomogeneity. In particular, one finds that the chemical inhomogeneities which have been previously reported in amorphous FexGe1-x and MoxGe1-x are quite anisotropic, depending significantly on the direction of film growth. With the addition of small amounts of metal atoms (x<0.2), no films appear isotropic nor homogeneous through the metal/insulator transition. The results indicate that fluctuations in the growth direction play a pivotal role in preventing simple growth models of a columnar structure or one that evolves systematically as it grows. The anomalous scattering measurements identify the metal atoms (Fe or Mo) as the source of the anisotropy, with the Ge atoms distributed homogeneously. The author has developed a method for using these measurements to determine the compositions of the phase-separating species. The results indicate phase separation into an amorphous Ge and an intermetallic phase of stoichiometry close to FeGe2or MoGe3. Finally, by manipulating the deposited power flux and rates of growth, FexGe1-x films which have the same Fe composition x can be grown to different states of phase separation. These results may help explain the difficulty workers have had in isolating the metal/insulator transition for these and other vapor-deposited amorphous alloys.

  1. Plasmonic induced transparency in a coupled system composed of metal-insulate-metal stub and trapezoid cavity resonator

    NASA Astrophysics Data System (ADS)

    Zheng, Pengfei; Yang, Huimin; Jiao, Linsen; Fan, Meiyong; Yun, Binfeng; Cui, Yiping

    2017-08-01

    A plasmonic induced transparency system constructed by a metal-insulate-metal stub coupled with a trapezoid cavity resonator was proposed. The results show that the spectra of different narrow modes in the trapezoid resonator can overlap with the broad stub mode and induce the plasmonic induced transparency effect. However, some of them cannot produce a plasmonic induced transparency effect because there is hardly any near field overlap between the trapezoid cavity mode and the stub mode, which was proved by the mode field distributions in the coupled resonator system. The ;disappeared; plasmonic induced transparency can be reproduced by changing the relative position between the stub and trapezoid resonator. Also the coupling strength can be modulated by this method to manipulate the plasmonic induced transparency and slow light effect.

  2. Modulation of metal-insulator transitions by field-controlled strain in NdNiO3/SrTiO3/PMN-PT (001) heterostructures

    PubMed Central

    Heo, Seungyang; Oh, Chadol; Eom, Man Jin; Kim, Jun Sung; Ryu, Jungho; Son, Junwoo; Jang, Hyun Myung

    2016-01-01

    The band width control through external stress has been demonstrated as a useful knob to modulate metal-insulator transition (MIT) in RNiO3 as a prototype correlated materials. In particular, lattice mismatch strain using different substrates have been widely utilized to investigate the effect of strain on transition temperature so far but the results were inconsistent in the previous literatures. Here, we demonstrate dynamic modulation of MIT based on electric field-controlled pure strain in high-quality NdNiO3 (NNO) thin films utilizing converse-piezoelectric effect of (001)-cut - (PMN-PT) single crystal substrates. Despite the difficulty in the NNO growth on rough PMN-PT substrates, the structural quality of NNO thin films has been significantly improved by inserting SrTiO3 (STO) buffer layers. Interestingly, the MIT temperature in NNO is downward shifted by ~3.3 K in response of 0.25% in-plane compressive strain, which indicates less effective TMI modulation of field-induced strain than substrate-induced strain. This study provides not only scientific insights on band-width control of correlated materials using pure strain but also potentials for energy-efficient electronic devices. PMID:26916618

  3. Modulation of metal-insulator transitions by field-controlled strain in NdNiO3/SrTiO3/PMN-PT (001) heterostructures

    NASA Astrophysics Data System (ADS)

    Heo, Seungyang; Oh, Chadol; Eom, Man Jin; Kim, Jun Sung; Ryu, Jungho; Son, Junwoo; Jang, Hyun Myung

    2016-02-01

    The band width control through external stress has been demonstrated as a useful knob to modulate metal-insulator transition (MIT) in RNiO3 as a prototype correlated materials. In particular, lattice mismatch strain using different substrates have been widely utilized to investigate the effect of strain on transition temperature so far but the results were inconsistent in the previous literatures. Here, we demonstrate dynamic modulation of MIT based on electric field-controlled pure strain in high-quality NdNiO3 (NNO) thin films utilizing converse-piezoelectric effect of (001)-cut - (PMN-PT) single crystal substrates. Despite the difficulty in the NNO growth on rough PMN-PT substrates, the structural quality of NNO thin films has been significantly improved by inserting SrTiO3 (STO) buffer layers. Interestingly, the MIT temperature in NNO is downward shifted by ~3.3 K in response of 0.25% in-plane compressive strain, which indicates less effective TMI modulation of field-induced strain than substrate-induced strain. This study provides not only scientific insights on band-width control of correlated materials using pure strain but also potentials for energy-efficient electronic devices.

  4. Modulation of metal-insulator transitions by field-controlled strain in NdNiO3/SrTiO3/PMN-PT (001) heterostructures.

    PubMed

    Heo, Seungyang; Oh, Chadol; Eom, Man Jin; Kim, Jun Sung; Ryu, Jungho; Son, Junwoo; Jang, Hyun Myung

    2016-02-26

    The band width control through external stress has been demonstrated as a useful knob to modulate metal-insulator transition (MIT) in RNiO3 as a prototype correlated materials. In particular, lattice mismatch strain using different substrates have been widely utilized to investigate the effect of strain on transition temperature so far but the results were inconsistent in the previous literatures. Here, we demonstrate dynamic modulation of MIT based on electric field-controlled pure strain in high-quality NdNiO3 (NNO) thin films utilizing converse-piezoelectric effect of (001)-cut Pb(Mg(1/3)Nb(2/3)O3-(PbTiO3) (PMN-PT) single crystal substrates. Despite the difficulty in the NNO growth on rough PMN-PT substrates, the structural quality of NNO thin films has been significantly improved by inserting SrTiO3 (STO) buffer layers. Interestingly, the MIT temperature in NNO is downward shifted by ~3.3 K in response of 0.25% in-plane compressive strain, which indicates less effective TMI modulation of field-induced strain than substrate-induced strain. This study provides not only scientific insights on band-width control of correlated materials using pure strain but also potentials for energy-efficient electronic devices.

  5. Heteroepitaxial VO{sub 2} thin films on GaN: Structure and metal-insulator transition characteristics

    SciTech Connect

    Zhou You; Ramanathan, Shriram

    2012-10-01

    Monolithic integration of correlated oxide and nitride semiconductors may open up new opportunities in solid-state electronics and opto-electronics that combine desirable functional properties of both classes of materials. Here, we report on epitaxial growth and phase transition-related electrical properties of vanadium dioxide (VO{sub 2}) thin films on GaN epitaxial layers on c-sapphire. The epitaxial relation is determined to be (010){sub vo{sub 2}} parallel (0001){sub GaN} parallel (0001){sub A1{sub 2O{sub 3}}} and [100]{sub vo{sub 2}} parallel [1210]{sub GaN} parallel [0110]{sub A1{sub 2O{sub 3}}} from x-ray diffraction. VO{sub 2} heteroepitaxial growth and lattice mismatch are analyzed by comparing the GaN basal plane (0001) with the almost close packed corrugated oxygen plane in vanadium dioxide and an experimental stereographic projection describing the orientation relationship is established. X-ray photoelectron spectroscopy suggests a slightly oxygen rich composition at the surface, while Raman scattering measurements suggests that the quality of GaN layer is not significantly degraded by the high-temperature deposition of VO{sub 2}. Electrical characterization of VO{sub 2} films on GaN indicates that the resistance changes by about four orders of magnitude upon heating, similar to epitaxial VO{sub 2} films grown directly on c-sapphire. It is shown that the metal-insulator transition could also be voltage-triggered at room temperature and the transition threshold voltage scaling variation with temperature is analyzed in the framework of a current-driven Joule heating model. The ability to synthesize high quality correlated oxide films on GaN with sharp phase transition could enable new directions in semiconductor-photonic integrated devices.

  6. Orbital electronic occupation effect on metal-insulator transition in Ti x V1-x O2

    NASA Astrophysics Data System (ADS)

    Huang, Kang; Meng, Yifan; Xu, XiaoFeng; Chen, Pingping; Lu, Aijiang; Li, Hui; Wu, Binhe; Wang, Chunrui; Chen, Xiaoshuang

    2017-09-01

    A series of Ti x V1-x O2 (0%  ⩽  x  ⩽  4.48%) thin films on c-plane sapphire substrates have been fabricated by co-sputtering oxidation solutions, and the metal-insulator transition temperature (T MIT) of Ti x V1-x O2 films rises monotonically at the rate of 1.64 K/at.% Ti. The x-ray diffraction measurement results show that, after Ti4+ ion doping, the rutile structure expands along the c r axis while shrinking along the a r and b r axis simultaneously. It makes the V-O bond length shorter, which is believed to upshift the π * orbitals. The rising of π * orbitals in Ti-doped VO2 has been illustrated by ultraviolet-infrared spectroscopy and first-principles calculation. With the Ti4+ ion doping concentration increasing, the energy levels of π * orbitals are elevated and the electronic occupation of π * orbitals decreases, which weakens the shielding for the strong electron-electron correlations in the d|| orbital and result in the T MIT rising. The research reveals that the T MIT of VO2 can be effected by the electronic occupancy of π * orbitals in a rutile state, which is helpful for developing VO2-based thermal devices.

  7. Metal-insulator transition in tin doped indium oxide (ITO) thin films: Quantum correction to the electrical conductivity

    NASA Astrophysics Data System (ADS)

    Kaushik, Deepak Kumar; Kumar, K. Uday; Subrahmanyam, A.

    2017-01-01

    Tin doped indium oxide (ITO) thin films are being used extensively as transparent conductors in several applications. In the present communication, we report the electrical transport in DC magnetron sputtered ITO thin films (prepared at 300 K and subsequently annealed at 673 K in vacuum for 60 minutes) in low temperatures (25-300 K). The low temperature Hall effect and resistivity measurements reveal that the ITO thin films are moderately dis-ordered (kFl˜1; kF is the Fermi wave vector and l is the electron mean free path) and degenerate semiconductors. The transport of charge carriers (electrons) in these disordered ITO thin films takes place via the de-localized states. The disorder effects lead to the well-known `metal-insulator transition' (MIT) which is observed at 110 K in these ITO thin films. The MIT in ITO thin films is explained by the quantum correction to the conductivity (QCC); this approach is based on the inclusion of quantum-mechanical interference effects in Boltzmann's expression of the conductivity of the disordered systems. The insulating behaviour observed in ITO thin films below the MIT temperature is attributed to the combined effect of the weak localization and the electron-electron interactions.

  8. Metal-insulator transition of valence-controlled VO2 thin film prepared by RF magnetron sputtering using oxygen radical

    NASA Astrophysics Data System (ADS)

    Suetsugu, Takaaki; Shimazu, Yuichi; Tsuchiya, Takashi; Kobayashi, Masaki; Minohara, Makoto; Sakai, Enju; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

    2016-06-01

    We have prepared b-axis-oriented VO2 thin films by RF magnetron sputtering using oxygen radicals as the reactive gas. The VO2 thin films consist of a mixed-valence V3+/V4+ state formed by oxygen vacancies. The V3+ ratio strongly depends on the film thickness and the oxygen partial pressure of the radical gun during deposition. The lattice constant of the b-axis increases and the metal-insulator transition (MIT) temperature decreases with decreasing V3+ ratio, although the VO2 thin films with a high V3+ ratio of 42% do not exhibit MIT. The bandwidths and spectral weights of V 3d a1g and \\text{e}\\text{g}σ bands at around the Fermi level, which correspond to the insulating phase at 300 K, are smaller in the VO2 thin films with a low V3+ ratio. These results indicate that the control of the mixed-valence V3+/V4+ state is important for the MIT of b-axis-oriented VO2 thin films.

  9. Metal-insulator transition in RbC60 polymer fulleride studied by ESR and electron-spin relaxation

    NASA Astrophysics Data System (ADS)

    Atsarkin, V. A.; Demidov, V. V.; Vasneva, G. A.

    1997-10-01

    The ESR intensity, line shape, and longitudinal electron-spin relaxation in the polymer phase of the RbC60 fulleride are investigated in the temperature range 4.2metal-insulator transition region (25-50 K). It is found that below 50 K the ESR line can be separated into two Lorentzian components ascribed to conduction electrons and some localized paramagnetic centers (with concentration of about 0.03 per formula unit) with allowance made for the relaxation bottleneck. The decrease of the conduction-electron susceptibility obeys an activation law with the characteristic energy Δ/kB=80+/-10 K related to the opening of a gap 2Δ~100 cm -1. The same quantity is found by analyzing both longitudinal and transverse relaxation caused by fluctuations of internal fields with correlation time τc~ exp(2Δ/kBT). Below 25 K, the temperature dependencies of the linewidth and the relaxation times change abruptly, revealing the development of a new ordered state. The nature of this state is discussed.

  10. Variable-range hopping conduction and metal-insulator transition in amorphous RexSi1-x thin films

    NASA Astrophysics Data System (ADS)

    Lisunov, K. G.; Vinzelberg, H.; Arushanov, E.; Schumann, J.

    2011-09-01

    Resistivity, ρ(T), of the amorphous RexSi1-x thin films with x = 0.285-0.351 is investigated in the interval of T ~ 300-0.03 K. At x = 0.285-0.324 the activated behavior of ρ(T) is governed by the Mott and the Shklovskii-Efros variable-range hopping (VRH) conduction mechanisms in different temperature intervals and the three-dimensional regime of the hopping. Between x = 0.328 and 0.351 the activationless dependence of ρ(T) takes place. The critical behavior of the characteristic VRH temperatures and of the Coulomb gap, Δ, pertinent to proximity to the metal-insulator transition at the critical value of xc ≈ 0.327, is observed. The analysis of the critical behavior of Δ yields directly the critical exponent of the dielectric permittivity, η = 2.1 ± 0.2, in agreement with the theoretical prediction, η = 2. On the other hand, the values of the critical exponent of the correlation length ν ~ 0.8-1.1 close to the expected value of unity can be obtained from the analysis of the critical behavior of the VRH characteristic temperatures under an additional assumption of a strong underbarrier scattering of hopping charge carriers in conditions, when the concentration of scattering centers considerably exceeds the concentration of sites involved in the hopping.

  11. Suppression of the metal-insulator transition temperature in thin La0.7Sr0.3MnO3 films

    NASA Astrophysics Data System (ADS)

    Angeloni, M.; Balestrino, G.; Boggio, N. G.; Medaglia, P. G.; Orgiani, P.; Tebano, A.

    2004-12-01

    In this paper, we illustrate an approach to discriminate between epitaxial strain and other factors responsible for the decrease of the metal-insulator transition temperature (TP) in thin La0.7Sr0.3MnO3 films grown by pulsed laser deposition. Using this approach, we have estimated the effect of the biaxial strain on TP. Ultrathin films, independent of epitaxial strain, do not show any metal-insulator transition over the full temperature range. This finding confirms the existence of an interface dead layer. The strain-independent decrease in TP, relative to its bulk value, observed for a much wider thickness range (up to about 1000Å) can most likely be attributed to oxygen deficiency.

  12. A Review on Disorder-Driven Metal-Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials.

    PubMed

    Wang, Jiang-Jing; Xu, Ya-Zhi; Mazzarello, Riccardo; Wuttig, Matthias; Zhang, Wei

    2017-07-27

    Metal-insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the underlying mechanism of most MITs is an interplay of electron correlation effects (Mott type) and disorder effects (Anderson type), and to disentangle the two effects is difficult. Recent progress on the crystalline Ge₁Sb₂Te₄ (GST) compound provides compelling evidence for a disorder-driven MIT. In this work, we discuss the presence of strong disorder in GST, and elucidate its effects on electron localization and transport properties. We also show how the degree of disorder in GST can be reduced via thermal annealing, triggering a disorder-driven metal-insulator transition. The resistance switching by disorder tuning in crystalline GST may enable novel multilevel data storage devices.

  13. Electronic properties and the nature of metal-insulator transition in NdNiO3 prepared at ambient oxygen pressure

    NASA Astrophysics Data System (ADS)

    Hooda, M. K.; Yadav, C. S.

    2016-06-01

    We report the electronic properties of the NdNiO3, prepared at the ambient oxygen pressure condition. The metal-insulator transition temperature is observed at 192 K, but the low temperature state is found to be less insulating compared to the NdNiO3 prepared at high oxygen pressure. The electric resistivity, Seebeck coefficient and thermal conductivity of the compound show large hysteresis below the metal-insulator transition. The large value of the effective mass (m*~8me) in the metallic state indicates the narrow character of the 3d band. The electric conduction at low temperatures (T=2-20 K) is governed by the variable range hopping of the charge carriers.

  14. Compositionally controlled metal-insulator transition in Tl{sub 2-x}In{sub x}TeO{sub 6}

    SciTech Connect

    Siritanon, Theeranun; Sleight, A.W.; Subramanian, M.A.

    2011-04-15

    Tl{sub 2}TeO{sub 6} and In{sub 2}TeO{sub 6} are both known to crystallize in the Na{sub 2}SiF{sub 6}-type structure. We find Tl{sub 2}TeO{sub 6} is metallic, whereas In{sub 2}TeO{sub 6} is an insulator. We have prepared a complete Tl{sub 2-x}In{sub x}TeO{sub 6} series in a search for a compositionally controlled metal-insulator transition that might be expected if a complete solid solution can be obtained. Unit cell edges and volume vary monotonically with no indication of a miscibility gap. The metal-insulator transition occurs at an x value of about 1.4, which can be rationalized on a percolation model. No superconductivity could be detected down to 5 K. -- Graphical abstract: A complete solid solution between Tl{sub 2}TeO{sub 6} and In{sub 2}TeO{sub 6} is formed. A compositionally controlled metal-insulator transition occurs in Tl{sub 2-x}In{sub x}TeO{sub 6} at an x value of about 1.5. No superconductivity could be detected down to 5 K. Display Omitted Research highlights: {yields} A complete solid solution between Tl{sub 2}TeO{sub 6} and In{sub 2}TeO{sub 6} is formed. {yields} A compositionally controlled metal-insulator transition occurs in Tl{sub 2-x}In{sub x}TeO{sub 6} at an x value of about 1.5, which can be rationalized on a percolation model. {yields} No superconductivity could be detected down to 5 K.

  15. Mg doping of thermochromic VO{sub 2} films enhances the optical transmittance and decreases the metal-insulator transition temperature

    SciTech Connect

    Mlyuka, N. R.; Niklasson, G. A.; Granqvist, C. G.

    2009-10-26

    Thermochromic films of Mg{sub x}V{sub 1-x}O{sub 2} were made by reactive dc magnetron sputtering onto heated glass. The metal-insulator transition temperature decreased by {approx}3 K/at. %Mg, while the optical transmittance increased concomitantly. Specifically, the transmittance of visible light and of solar radiation was enhanced by {approx}10% when the Mg content was {approx}7 at. %. Our results point at the usefulness of these films for energy efficient fenestration.

  16. Localization-driven metal-insulator transition in epitaxial hole-doped Nd1-x Sr x NiO3 ultrathin films

    NASA Astrophysics Data System (ADS)

    Wang, Le; Chang, Lei; Yin, Xinmao; Rusydi, Andrivo; You, Lu; Zhou, Yang; Fang, Liang; Wang, Junling

    2017-01-01

    Advances in thin film growth technologies make it possible to obtain ultra-thin perovskite oxide films and open the window for controlling novel electronic phases for use in functional nanoscale electronics, such as switches and sensors. Here, we study the thickness-dependent transport characteristics of high-quality ultrathin Nd0.9Sr0.1NiO3 (Sr-NNO) films, which were grown on LaAlO3 (0 0 1) single-crystal substrates by using pulsed laser deposition method. Thick Sr-NNO films (25 unit cells) exhibit metallic behavior with the electrical resistivity following the T  n (n  <  2) law corresponding to a non-Fermi liquid system, while a temperature driven metal-insulator transition (MIT) is observed with films of less than 15 unit cells. The transition temperature increases with reducing film thickness, until the insulating characteristic is observed even at room temperature. The emergence of the insulator ground state can be attributed to weak localization driven MIT expected by considering Mott-Ioffe-Regel limit. Furthermore, the magneto-transport study of Sr-NNO ultrathin films also confirms that the observed MIT is due to the disorder-induced localization rather than the electron-electron interactions.

  17. Doping-driven metal-insulator transitions and charge orderings in the extended Hubbard model

    NASA Astrophysics Data System (ADS)

    Kapcia, K. J.; Robaszkiewicz, S.; Capone, M.; Amaricci, A.

    2017-03-01

    We perform a thorough study of the extended Hubbard model featuring local and nearest-neighbor Coulomb repulsion. Using the dynamical mean-field theory we investigated the zero-temperature phase diagram of this model as a function of the chemical doping. The interplay between local and nonlocal interactions drives a variety of phase transitions connecting two distinct charge-ordered insulators, i.e., half filled and quarter filled, a charge-ordered metal and a Mott-insulating phase. We characterize these transitions and the relative stability of the solutions and we show that the two interactions conspire to stabilize the quarter-filled charge-ordered phase.

  18. Mechanisms of spin-flipping and metal-insulator transition in nano-Fe3O4

    NASA Astrophysics Data System (ADS)

    Dito Fauzi, Angga; Aziz Majidi, Muhammad; Rusydi, Andrivo

    2017-04-01

    Fe3O4 is a half-metallic ferrimagnet with {{T}\\text{C}}∼ 860 K exhibiting metal-insulator transition (MIT) at  ∼120 K. In bulk form, the saturation magnetization is 0.6 Tesla (∼471 emu cm‑3). A recent experimental study has shown that the saturation magnetization of nano-Fe3O4 thin films can achieve up to  ∼760 emu cm‑3, attributed to spin-flipping of Fe ions at tetrahedral sites assisted by oxygen vacancies (V O). Such a system has shown to have higher MIT temperature (∼150 K). The spin-flipping is a new phenomenon in Fe3O4, while the MIT is a long-standing one. Here, we propose a model and calculations to investigate the mechanisms of both phenomena. Our results show that, for the system without V O, the ferrimagnetic configuration is energetically favorable. Remakably, upon inclusion of V O, the ground-state configuration switches into ferromagnetic. As for the MIT, by proposing temperature dependences of some hopping integrals in the model, we demonstrate that the system without and with V O undergo the MIT in slightly different ways, leading to higher MIT temperature for the system with V O, in agreement with the experimental data. Our results also show that the MIT in both systems occur concomitantly with the redistribution of electrons among the three Fe ions in each Fe3O4 formula unit. As such temperature dependences of hopping integrals may arise due to dynamic Jahn–Teller effects, our phenomenological theory may provide a way to reconcile existing theories relating the MIT to the structural transition and the charge ordering.

  19. Attenuated total reflection response to wavelength tuning of plasmon-induced transparency in a metal-insulator-metal structure.

    PubMed

    Matsunaga, Kouki; Watanabe, Takeshi; Neo, Yoichiro; Matsumoto, Takahiro; Tomita, Makoto

    2016-11-15

    We experimentally demonstrated a plasmon-induced transparency in a metal-insulator-metal (MIM) structure based on the attenuated total reflection (ATR) response. Here, the MIM waveguide (MIMWG) mode and the surface plasmon polariton (SPP) resonance mode acted as low- and high-Q resonance modes, respectively. The dependence of the resonance angles of SPP and MIMWG mode resonances on the incident wavelength differed, which allowed the coupling condition between the two modes to be tuned via the wavelength. When the resonance angles of the two modes coincided, the ATR response showed a symmetric plasmon-induced transparency spectrum; in contrast, when the resonance angles were detuned, the ATR exhibited a sharp asymmetric spectrum characteristic to off-resonance Fano interference.

  20. Tunable Anderson metal-insulator transition in quantum spin-Hall insulators

    NASA Astrophysics Data System (ADS)

    Chen, Chui-Zhen; Liu, Haiwen; Jiang, Hua; Sun, Qing-feng; Wang, Ziqiang; Xie, X. C.

    2015-06-01

    We numerically study disorder effects in the Bernevig-Hughes-Zhang (BHZ) model, and we find that the Anderson transition of a quantum spin-Hall insulator (QSHI) is determined by model parameters. The BHZ Hamiltonian is equivalent to two decoupled spin blocks that belong to the unitary class. In contrast to the common belief that a two-dimensional unitary system scales to an insulator except at certain critical points, we find, through calculations scaling properties of the localization length, level statistics, and participation ratio, that a possible exotic metallic phase emerges between the QSHI and normal insulator phases in the InAs/GaSb-type BHZ model. On the other hand, direct transition from a QSHI to a normal insulator is found in the HgTe/CdTe-type BHZ model. Furthermore, we show that the metallic phase originates from the Berry phase and can survive both inside and outside the gap.

  1. Proton spin-lattice relaxation mechanisms and the metal-insulator transition in cerium hydrides

    NASA Astrophysics Data System (ADS)

    Zamir, D.; Barnes, R. G.; Salibi, N.; Cotts, R. M.; Phua, T.-T.; Torgeson, D. R.; Peterson, D. T.

    1984-01-01

    Nuclear-magnetic-resonance (NMR) experiments have been done on cerium hydride (CeHx) samples to search for correlations between NMR properties and known electrical conductivity changes as a function of hydrogen concentration and temperature. Data are presented for the 1H spin-lattice relaxation rate R1 (=1T1) and some line shapes for 2.10<=x<=2.92 for temperatures from about 100 to 375 K. Although two 1H resonances are observed at some temperatures, proton spin-lattice relaxation is characterized by a single relaxation time at each x and T. To a good approximation R1=AT+R, where AT is attributed to direct dipolar coupling between protons and the electronic magnetic dipole moment of Ce3+, and R is an essentially temperature-independent term attributed to indirect [Ruderman-Kittel-Kasuya-Yosida (RKKY)] coupling to the Ce3+ moment. The AT term is so large that for most experiments the proton-proton dipolar and proton-conduction-electron couplings are negligible. The x dependence of the constant A is consistent with the dipolar coupling. The constant R decreases in a steep manner as x is increased above x~2.65 just below the regime 2.75transition occurs in CeHx. It is proposed that R~Nd(EF) and that the RKKY interaction includes coupling through the d-band density of states. The marked decreases in R1 and in the electrical conductivity that are associated with the concentration-dependent transition are thus attributed to the vanishing electron density of states at the Fermi surface. No temperature-dependent transition in R1 is found. Results are consistent with a Mott transition model in which the electron donors are hydrogen vacancies.

  2. Universal role of quantum uncertainty in Anderson metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Cheng, W. W.; Zhang, Z. J.; Gong, L. Y.; Zhao, S. M.

    2016-07-01

    We explore quantum uncertainty, based on Wigner-Yanase skew information, in various one-dimensional single-electron wave functions. For the power-law function and eigenfunctions in the Aubry-André model, the electronic localization properties are well-defined. For them, we find that quantum uncertainty is relatively small and large for delocalized and localized states, respectively. And around the transition points, the first-order derivative of the quantum uncertainty exhibits singular behavior. All these characters can be used as signatures of the transition from a delocalized phase to a localized one. With this criterion, we also study the quantum uncertainty in one-dimensional disorder system with long-range correlated potential. The results show that the first-order derivative of spectrum-averaged quantum uncertainty is minimal at a certain correlation exponent αm for a finite system, and has perfect finite-size scaling behaviors around αm. By extrapolating αm, the threshold value αc ≃ 1.56 ± 0.02 is obtained for the infinite system. Thus we give another perspective and propose a consistent interpretation for the discrepancies about localization property in the long-range correlated potential model. These results suggest that the quantum uncertainty can provide us with a new physical intuition to the localization transition in these models.

  3. Ferromagnetic-nonmagnetic and metal-insulator phase transitions at the interfaces of KTaO{sub 3} and PbTiO{sub 3}

    SciTech Connect

    Yang, Yi; Chen, Jin-Feng; Hu, Lei; Lin, Chen-Sheng; Cheng, Wen-Dan

    2014-10-21

    We studied the electronic and magnetic properties of hole doped KTaO{sub 3}/PbTiO{sub 3} interface using density functional theory methods. Ferromagnetic-nonmagnetic phase transition and metal-insulator phase transition occur simultaneously at the interface with ferroelectric polarization reversal. Furthermore, these two transitions are coupled with each other because hole doping with large concentration of holes gives rise to ferromagnetism. The interfacial magnetization, which is proportional to hole concentration at the interface, can be tuned by ferroelectric polarization, leading to strong intrinsic magnetoelectric effect at the interface of originally nonmagnetic KTaO{sub 3} and PbTiO{sub 3}.

  4. Intrinsic evolutions of optical functions, band gap, and higher-energy electronic transitions in VO2 film near the metal-insulator transition region

    NASA Astrophysics Data System (ADS)

    Li, W. W.; Yu, Q.; Liang, J. R.; Jiang, K.; Hu, Z. G.; Liu, J.; Chen, H. D.; Chu, J. H.

    2011-12-01

    Transmittance spectra of (011) vanadium dioxide (VO2) film have been studied in the temperature range of 45-80 °C. Owing to increasing carrier concentration, the near-infrared extinction coefficient and optical conductivity around metal-insulator transition (MIT) rapidly increase with the temperature. Moreover, three electronic transitions can be uniquely assigned and show the hysteresis behavior near the MIT region. It was found that the optical band gap decreases from 0.457 to 0.042 eV before the MIT, then reduces to zero for the metal state. This confirms the fact that the a1g and egπ bands are moved close and finally overlap with the temperature.

  5. Localization, mobility edges, and metal-insulator transition in a class of one-dimensional slowly varying deterministic potentials

    NASA Astrophysics Data System (ADS)

    Das Sarma, S.; He, Song; Xie, X. C.

    1990-03-01

    We study the localization properties of the one-dimensional nearest-neighbor tight-binding Schrödinger equation, un+1+un-1+Vnun=Eun, where the on-site potential Vn is neither periodic (the ``Bloch'' case) nor random (the ``Anderson'' case), but is aperiodic or pseudorandom. In particular, we consider in detail a class of slowly varying potential with a typical example being Vn=λ cos(παnν) with 0<ν<1. We develop an asymptotic semiclassical technique to calculate exactly (in the large-n limit) the density of states and the Lyapunov exponent for this model. We also carry out numerical work involving direct diagonalization and recursive transfer-matrix calculations to study localization properties of the model. Our theoretical results are essentially in exact agreement with the numerical results. Our most important finding is that, for λ<2, there is a metal-insulator transition in this one-dimensional model (ν<1) with the mobility edges located at energies Ec=+/-||2-λ||. Eigenstates at the band center (||E||<||Ec||) are all extended whereas the band-edge states (||E||>||Ec||) are all localized. Another interesting finding is that, in contrast to higher-dimensional random-disorder situations, the density of states, D(E), in this model is not necessarily smooth through the mobility edge, but may diverge according to D(E)~||E-Ec||-δ. The Lyapunov exponent γ (or, the inverse localization length) behaves at Ec as γ(E)~||E-Ec||β, with β=1-δ. We solve the exact critical behavior of the general model, deriving analytic expressions for D(E), γ(E), and the exponents δ and β. We find that λ, α, and ν are all irrelevant variables in the renormalization-group sense for the localization critical properties of the model. We also give detailed numerical results for a number of different forms of Vn.

  6. Ultracold fermions in a one-dimensional bipartite optical lattice: Metal-insulator transitions driven by shaking

    NASA Astrophysics Data System (ADS)

    Di Liberto, M.; Malpetti, D.; Japaridze, G. I.; Morais Smith, C.

    2014-08-01

    We theoretically investigate the behavior of a system of fermionic atoms loaded in a bipartite one-dimensional optical lattice that is under the action of an external time-periodic driving force. By using Floquet theory, an effective model is derived. The bare hopping coefficients are renormalized by zeroth-order Bessel functions of the first kind with different arguments for the nearest-neighbor and next-nearest-neighbor hopping. The insulating behavior characterizing the system at half filling in the absence of driving is dynamically suppressed, and for particular values of the driving parameter the system becomes either a standard metal or an unconventional metal with four Fermi points. The existence of the four-Fermi-point metal relies on the fact that, as a consequence of the shaking procedure, the next-nearest-neighbor hopping coefficients become significant compared to the nearest-neighbor ones. We use the bosonization technique to investigate the effect of on-site Hubbard interactions on the four-Fermi-point metal-insulator phase transition. Attractive interactions are expected to enlarge the regime of parameters where the unconventional metallic phase arises, whereas repulsive interactions reduce it. This metallic phase is known to be a Luther-Emery liquid (spin-gapped metal) for both repulsive and attractive interactions, contrary to the usual Hubbard model, which exhibits a Mott-insulator phase for repulsive interactions. Ultracold fermions in driven one-dimensional bipartite optical lattices provide an interesting platform for the realization of this long-studied four-Fermi-point unconventional metal.

  7. Synchronization of pairwise-coupled, identical, relaxation oscillators based on metal-insulator phase transition devices: A model study

    NASA Astrophysics Data System (ADS)

    Parihar, Abhinav; Shukla, Nikhil; Datta, Suman; Raychowdhury, Arijit

    2015-02-01

    Computing with networks of synchronous oscillators has attracted wide-spread attention as novel materials and device topologies have enabled realization of compact, scalable and low-power coupled oscillatory systems. Of particular interest are compact and low-power relaxation oscillators that have been recently demonstrated using MIT (metal-insulator-transition) devices using properties of correlated oxides. Further the computational capability of pairwise coupled relaxation oscillators has also been shown to outperform traditional Boolean digital logic circuits. This paper presents an analysis of the dynamics and synchronization of a system of two such identical coupled relaxation oscillators implemented with MIT devices. We focus on two implementations of the oscillator: (a) a D-D configuration where complementary MIT devices (D) are connected in series to provide oscillations and (b) a D-R configuration where it is composed of a resistor (R) in series with a voltage-triggered state changing MIT device (D). The MIT device acts like a hysteresis resistor with different resistances in the two different states. The synchronization dynamics of such a system has been analyzed with purely charge based coupling using a resistive (RC) and a capacitive (CC) element in parallel. It is shown that in a D-D configuration symmetric, identical and capacitively coupled relaxation oscillator system synchronizes to an anti-phase locking state, whereas when coupled resistively the system locks in phase. Further, we demonstrate that for certain range of values of RC and CC, a bistable system is possible which can have potential applications in associative computing. In D-R configuration, we demonstrate the existence of rich dynamics including non-monotonic flows and complex phase relationship governed by the ratios of the coupling impedance. Finally, the developed theoretical formulations have been shown to explain experimentally measured waveforms of such pairwise coupled

  8. Accumulation capacitance frequency dispersion of III-V metal-insulator-semiconductor devices due to disorder induced gap states

    SciTech Connect

    Galatage, R. V.; Zhernokletov, D. M.; Dong, H.; Brennan, B.; Hinkle, C. L.; Wallace, R. M.; Vogel, E. M.

    2014-07-07

    The origin of the anomalous frequency dispersion in accumulation capacitance of metal-insulator-semiconductor devices on InGaAs and InP substrates is investigated using modeling, electrical characterization, and chemical characterization. A comparison of the border trap model and the disorder induced gap state model for frequency dispersion is performed. The fitting of both models to experimental data indicate that the defects responsible for the measured dispersion are within approximately 0.8 nm of the surface of the crystalline semiconductor. The correlation between the spectroscopically detected bonding states at the dielectric/III-V interface, the interfacial defect density determined using capacitance-voltage, and modeled capacitance-voltage response strongly suggests that these defects are associated with the disruption of the III-V atomic bonding and not border traps associated with bonding defects within the high-k dielectric.

  9. Martensitic accommodation strain and the metal-insulator transition in manganites

    NASA Astrophysics Data System (ADS)

    Podzorov, V.; Kim, B. G.; Kiryukhin, V.; Gershenson, M. E.; Cheong, S.-W.

    2001-10-01

    In this paper, we report polarized optical microscopy and electrical transport studies of manganese oxides that reveal that the charge ordering transition in these compounds exhibits typical signatures of a martensitic transformation. We demonstrate that specific electronic properties of charge-ordered manganites stem from a combination of martensitic accommodation strain and effects of strong electron correlations. This intrinsic strain is strongly affected by the grain boundaries in ceramic samples. Consistently, our studies show a remarkable enhancement of low field magnetoresistance and the grain size effect on the resistivity in polycrystalline samples and suggest that the transport properties of this class of manganites are governed by the charge-disordered insulating phase stabilized at low temperature by virtue of martensitic accommodation strain. High sensitivity of this phase to strains and magnetic field leads to a variety of striking phenomena, such as unusually high magnetoresistance (1010%) in low magnetic fields.

  10. Quantum transport in 3D Weyl semimetals: Is there a metal-insulator transition?

    NASA Astrophysics Data System (ADS)

    Ziegler, Klaus

    2016-12-01

    We calculate the transport properties of three-dimensional Weyl fermions in a disordered environment. The resulting conductivity depends only on the Fermi energy and the scattering rate. First we study the conductivity at the spectral node for a fixed scattering rate and obtain a continuous transition from an insulator at weak disorder to a metal at stronger disorder. Within the self-consistent Born approximation the scattering rate depends on the Fermi energy. Then it is crucial that the limits of the conductivity for a vanishing Fermi energy and a vanishing scattering rate do not commute. As a result, there is also metallic behavior in the phase with vanishing scattering rate and only a quantum critical point remains as an insulating phase. The latter turns out to be a critical fixed point in terms of a renormalization-group flow.

  11. Exotic topological states near a quantum metal-insulator transition in pyrochlore iridates

    NASA Astrophysics Data System (ADS)

    Tian, Zhaoming

    Pyrochlore iridates have attracted great interest as prime candidates that may host topologically nontrivial states, spin ice ordering and quantum spin liquid states, in particular through the interplay between different degrees of freedom, such as local moments and mobile electrons. Based on our extensive study using our high quality single crystals, we will discuss such examples, i.e. chiral spin liquid in a quadratic band touching state, Weyl semimetallic state and chiral domain wall transport nearby a quantum insulator-semimetal transition in pyrochlore iridates. This work is based on the collaboration with Nakatsuji Satoru, Kohama Yoshimitsu, Tomita Takahiro, Kindo Koichi, Jun J. Ishikawa, Balents Leon, Ishizuka Hiroaki, Timothy H. Hsieh. ZM. Tian was supported by JSPS Postdoctoral Fellowship (No.P1402).

  12. Volume-based considerations for the metal-insulator transition of CMR oxides

    SciTech Connect

    Neumeier, J.J. |; Hundley, M.F.; Cornelius, A.L.; Andres, K.

    1998-03-01

    The sensitivity of {rho} [electrical resistivity] to changes in volume which occur through: (1) applied pressure, (2) variations in temperature, and (3) phase transitions, is evaluated for some selected CMR oxides. It is argued that the changes in volume associated with phase changes are large enough to produce self pressures in the range of 0.18 to 0.45 GPa. The extreme sensitivity of the electrical resistivity to pressure indicates that these self pressures are responsible for large features in the electrical resistivity and are an important component for occurrence the metallicity below {Tc}. It is suggested that this is related to a strong volume dependence of the electron phonon coupling in the CMR oxides.

  13. Three-dimensional electronic structures and the metal-insulator transition in Ruddlesden-Popper iridates

    NASA Astrophysics Data System (ADS)

    Yamasaki, A.; Fujiwara, H.; Tachibana, S.; Iwasaki, D.; Higashino, Y.; Yoshimi, C.; Nakagawa, K.; Nakatani, Y.; Yamagami, K.; Aratani, H.; Kirilmaz, O.; Sing, M.; Claessen, R.; Watanabe, H.; Shirakawa, T.; Yunoki, S.; Naitoh, A.; Takase, K.; Matsuno, J.; Takagi, H.; Sekiyama, A.; Saitoh, Y.

    2016-09-01

    In this study, we systematically investigate three-dimensional (3D) momentum (ℏ k )-resolved electronic structures of Ruddlesden-Popper-type iridium oxides Srn +1IrnO3 n +1 using soft-x-ray (SX) angle-resolved photoemission spectroscopy (ARPES). Our results provide direct evidence of an insulator-to-metal transition that occurs upon increasing the dimensionality of the IrO2-plane structure. This transition occurs when the spin-orbit-coupled jeff=1 /2 band changes its behavior in the dispersion relation and moves across the Fermi energy. In addition, an emerging band along the Γ (0,0,0)-R (π ,π ,π ) direction is found to play a crucial role in the metallic characteristics of SrIrO3. By scanning the photon energy over 350 eV, we reveal the 3D Fermi surface in SrIrO3 and kz-dependent oscillations of photoelectron intensity in Sr3Ir2O7 . In contrast to previously reported results obtained using low-energy photons, folded bands derived from lattice distortions and/or magnetic ordering make significantly weak (but finite) contributions to the k -resolved photoemission spectrum. At the first glance, this leads to the ambiguous result that the observed k -space topology is consistent with the unfolded Brillouin zone (BZ) picture derived from a nonrealistic simple square or cubic Ir lattice. Through careful analysis, we determine that a superposition of the folded and unfolded band structures has been observed in the ARPES spectra obtained using photons in both ultraviolet and SX regions. To corroborate the physics deduced using low-energy ARPES studies, we propose to utilize SX-ARPES as a powerful complementary technique, as this method surveys more than one whole BZ and provides a panoramic view of electronic structures.

  14. Tuning the metal-insulator transition in d1 and d2 perovskites by epitaxial strain: A first-principles-based study

    NASA Astrophysics Data System (ADS)

    Sclauzero, Gabriele; Dymkowski, Krzysztof; Ederer, Claude

    2016-12-01

    We investigate the effect of epitaxial strain on the Mott metal-insulator transition (MIT) in perovskite systems with d1 and d2 electron configurations of the transition metal (TM) cation. We first discuss the general trends expected from the changes in the crystal-field splitting and in the hopping parameters that are induced by epitaxial strain. We argue that the strain-induced crystal-field splitting generally favors the Mott-insulating state, whereas the strain-induced changes in the hopping parameters favor the metallic state under compressive strain and the insulating state under tensile strain. Thus the two effects can effectively cancel each other under compressive strain, while they usually cooperate under tensile strain, in this case favoring the insulating state. We then validate these general considerations by performing electronic structure calculations for several d1 and d2 perovskites, using a combination of density functional theory (DFT) and dynamical mean-field theory (DMFT). We isolate the individual effects of strain-induced changes in either hopping or crystal-field by performing DMFT calculations where we fix one type of parameter to the corresponding unstrained DFT values. These calculations confirm our general considerations for SrVO3 (d1) and LaVO3 (d2), whereas the case of LaTiO3 (d1) is distinctly different, due to the strong effect of the octahedral tilt distortion in the underlying perovskite crystal structure. Our results demonstrate the possibility to tune the electronic properties of correlated TM oxides by using epitaxial strain, which allows to control the strength of electronic correlations and the vicinity to the Mott MIT.

  15. Tuning the metal-insulator transition in NdNiO3 thin films

    NASA Astrophysics Data System (ADS)

    Shiyani, T.; Shekhada, K. G.; Savaliya, C. R.; Markna, J. H.

    2017-05-01

    The RNiO3 (R is rare earth) perovskites are famous for their metal to insulator transition (MIT). The temperature can be transformed and depends on the nature of the rare earth. The MIT in thin films and heterostructures of RNiO3 propose the chance to control the MIT as a function of thickness via strain using different substrates. We have reported the electrical transport properties of NdNiO3/NdGaO3, and NNO/NGO/STO structures. These structures were fabricated by pulsed laser deposition (PLD) method. The temperature of the MIT changes from 155K to 195 K. The electrical resistivity of the heterostructures undergoes MIT, depending on the thickness and deposition conditions. Thickness and deposition temperature were found to have a great impact on the electrical transport properties. The shift in TMI changes with thickness and it larger for thinner NdNiO3. The MIT of NNO thin films is responsive to strain and its partial relaxation creates an inhomogeneous strain field that broadens the MIT. This study may be potentially applicable to Mott transistor devices.

  16. Directing colloidal assembly and a metal-insulator transition using quenched-disordered polymeric networks

    NASA Astrophysics Data System (ADS)

    Phan, Anh; Jadrich, Ryan; Schweizer, Kenneth

    2015-03-01

    Replica integral equation and effective medium theory methods are employed to elucidate how to massively reconfigure a colloidal assembly and realize equilibrium states of high electrical conductivity at low physical volume fractions. This is achieved by employing variable mesh size networks of rigid rod or semiflexible polymers as a templating internal field. By exploiting bulk phase separation frustration and the tunable competing processes of colloid adsorption on the low dimensional network and fluctuation-driven colloid clustering in the pore spaces, distinct spatial organizations of greatly enhanced particle contacts can be achieved. As a result, a continuous, but very abrupt, transition from an insulating to metallic-like state can be realized via a small change of either the colloid-template or colloid-colloid attraction strength. Polymer conformational fluctuations are found to significantly modify the physical adsorption process and hence the ability of colloids to organize along the filamentary network strands. Qualitatively new physical behavior can emerge as the pore size approaches the colloid diameter, reflecting strong frustrating constraints of the template on colloidal assembly.

  17. Tunneling Spectroscopy of Amorphous Magnetic Rare Earth-Si Alloys near the Metal-Insulator Transition

    NASA Astrophysics Data System (ADS)

    Xiong, P.; Zink, B. L.; Tran, M. Q.; Gebala, A. E.; Wilcox, E. M.; Hellman, F.; Dynes, R. C.

    1997-03-01

    Amorphous dilute magnetic semiconductors exhibit striking differences in the electrical and magneto-transport behavior from their crystalline or nonmagnetic analogs.(F. Hellman et al., Phys. Rev. Lett. 77, 4652 (1996).) Magnetic impurities cause a large suppression of conductivity below 50 K in a-Si_xGd_1-x and a-Si_xTb_1-x relative to the nonmagnetic a-Si_xY_1-x (x ~ 0.85-0.9). Application of a magnetic field increases the conductivity by orders of magnitude. We have fabricated good quality tunnel junctions on a-Si:Gd and the nonmagnetic a-Si:Y to probe the electronic density of states in these two systems. We present the results of the tunneling spectroscopy and its magnetic field dependence for a series of the two alloys at different compositions. We will discuss the correlation between the tunneling spectra and the transport properties and its implications on the possible origin of the magnetic field tuned insulator-metal transition in a-Si:Gd. Research Supported by ONR Grant No. N000149151320 and NSF Grant No. DMR-9208599.

  18. Topological textures and metal-insulator transition in Reentrant Integer Quantum Hall Effect: role of disorder

    NASA Astrophysics Data System (ADS)

    Lyanda-Geller, Yuli; Simion, George

    2015-03-01

    We investigate a ground state of the two-dimensional (2D) electron liquid in the presence of disorder for Landau level filling factors, for which the re-entrant integer quantum Hall effect is observed. Our particular interest is the range of filling factors, which in a clean 2D system is favorable to formation of the two-electron (2e) bubble crystal. For the smooth random potential due to charged impurities placed far away from the 2D gas, the ground state is a lightly distorted 2e bubble crystal. However, for positively or negatively charged residual impurities located approximately within about three magnetic lengths from the 2D electrons, the ground state contains charged 2e complexes formed either by positively charged impurity and 3e defect bubble, or negatively charged impurity and 2e defect bubble. In the vicinity of 1e and 3e defect bubbles, the 2e bubbles of the crystal change their shape from round to elongated forming hedgehog (for 1e defect) or vortex (for 3e defect) textures. The topological textures due to these complexes interact with vortex and hedgehog excitations, generated as temperature increases that are not bound by residual impurities. The temperature of insulator to metal transition calculated with both bound and unbound defects agrees with experiment. Research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010544.

  19. Magnetism and Metal-Insulator Transition in Fe(Sb1−xTex)2

    SciTech Connect

    Petrovic, C.; Hu, R.; Mitrovic, V.F.

    2009-02-09

    We have investigated structural, magnetic, and transport properties of Fe(Sb{sub 1-x}Te{sub x}){sub 2} single crystals. Whereas metallic ground state is induced for x = 0.001, canted antiferromagnetism is observed for 0.1 {le} x {le} 0.4 with an intermediate ferromagnetic phase for x = 0.2. With higher Te doping, semiconducting behavior is restored and the variable range hopping conduction mechanism dominates at low temperatures for 0.4 {le} x {le} 0.6. We discuss our results within the framework of inverted metal to insulator in correlated electron insulators.

  20. Stress-induced self-rolled metal/insulator bifilm microtube with micromesh walls

    NASA Astrophysics Data System (ADS)

    Lee, Kook-Nyung; Seo, Yeong-Tai; Lee, Min-Ho; Jung, Suk-Won; Kim, Yong-Kweon; Kim, Jung-Mu; Kyeong Seong, Woo

    2013-01-01

    A metal/insulator microtube with micromesh walls was constructed using stress-assisted self-rolling technology. The mesh-sidewall Pt/Ti/SiO2 microtube was self-formed by a tensile-stressed metal Pt/Ti film deposited onto a pre-patterned SiO2 micromesh layer. The microtube measured about 25 µm in diameter and was longer than 7 mm. The sidewall of the microtube was a square mesh, 5-20 µm long, and was electrically connected to electrical pads for electrical conductance measurement. The electrical resistance of the rolled-up microtube was measured to be 250-350 Ω when the microtube resistor's length was around 540 µm. The real-time measurement of the conductance change of the microtube with a Pt resistor could monitor the temperature change generated by heat injection. The microtube with micromesh walls is expected to be an interesting structure that has promising potential for use in electronics, chemical and biological applications.

  1. The Unusual Metal-Insulator Transition in Ca(2-x)Sr(x)RuO(4)

    NASA Astrophysics Data System (ADS)

    Rice, T. Maurice

    2002-03-01

    The isoelectronic compounds Ca_2-xSr_xRuO4 offer a rare opportunity to follow the evolution of the electronic structure from a multiband metal, Sr_2RuO_4, to a Mott insulator, Ca_2RuO_4. The evolution is not at all monotonic but proceeds through a series of intermediate regions with unexpected behavior [1]. Sr_2RuO4 is a good metal with the 4 electrons in the t_2g-subshell of the Ru^4+-ions distributed equally in 3 bands. These in turn separate into a d_xy-band which disperses in both directions in the RuO_2-planes and d_xz/d_yz-bands dispersing only in one direction. The hybridization between these components occurs only through very weak interplanar processes. Substituting Ca for Sr leads to band narrowing through a rotation of the RuO_4-octahedra. A series of electronic structure calculations [2] using the LDA+DMFT method to incorporate strong correlations, predict an unusual state with 3 electrons localizing in the narrower d_xz/d_yz bands while the last electron remains itinerant in the broader d_xy-band. The observation of a strongly enhanced and temperature dependent spin susceptibility in the metallic state at x=0.5 is attributed to the S=1/2 local moments of the localized hole in the d_xz/d_yz-orbitals. The superexchange interaction between the local moments is strongly dependent on the specific orbital occupation and so glassy behavior in the orbital ordering can account for the glassy behavior observed in the susceptibility in the range 0.2 < x < 0.5. The final transition to a Mott insulator at x < 0.2 is driven by a compression of the RuO_4-octahedra and a switch to an electronic configuration with a filled d_xy-orbital and 2 electrons in the d_xz/d_yz orbitals which has a S=1 local moment expected for a Ru^4+-ion. [1] S. Nakatsuji and Y. Maeno, Phys. Rev. Lett. 84, 2666 (2000). [2] V.I. Anisimov, I.A. Nekrasov, D.E. Kondakov, T.M. Rice, and M. Sigrist, cond-mat0107095 and Eur. Phys. Jour. B (in press).

  2. Metal-Insulator Transitions.

    ERIC Educational Resources Information Center

    Mott, Nevill

    1978-01-01

    Explains how changes in temperature, pressure, magnetic field or alloy composition can affect the electronic band structure of substances, leading in some cases to dramatic changes in conductivity. (GA)

  3. Metal-Insulator Transitions.

    ERIC Educational Resources Information Center

    Mott, Nevill

    1978-01-01

    Explains how changes in temperature, pressure, magnetic field or alloy composition can affect the electronic band structure of substances, leading in some cases to dramatic changes in conductivity. (GA)

  4. Observations of a metal-insulator transition and strong surface states in Bi2-x SbxSe3 thin films.

    PubMed

    Zhang, Cheng; Yuan, Xiang; Wang, Kai; Chen, Zhi-Gang; Cao, Baobao; Wang, Weiyi; Liu, Yanwen; Zou, Jin; Xiu, Faxian

    2014-11-05

    High-quality thin films of the topological insulator Bi2-xSbxSe3 are grown by molecular beam epitaxy. A metal-insulator transition along with strong surface states - revealed by Shubnikov-de Haas oscillations - is observed as the Sb concentration is increased. This system represents a widely tunable platform for achieving high surface conduction, suppressing the bulk influence, and manipulating the band structure of topological insulators. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Electrolysis-induced protonation of VO2 thin film transistor for the metal-insulator phase modulation

    NASA Astrophysics Data System (ADS)

    Katase, Takayoshi; Endo, Kenji; Ohta, Hiromichi

    2016-02-01

    Compared to state-of-the-art modulation techniques, protonation is the most ideal to control the electrical and optical properties of transition metal oxides (TMOs) due to its intrinsic non-volatile operation. However, the protonation of TMOs is not typically utilized for solid-state devices because of imperative high-temperature annealing treatment in hydrogen source. Although one solution for room temperature (RT) protonation of TMOs is liquid-phase electrochemistry, it is unsuited for practical purposes due to liquid-leakage problem. Herein we demonstrate solid-state RT-protonation of vanadium dioxide (VO2), which is a well-known thermochromic TMO. We fabricated the three terminal thin-film-transistor structure on an insulating VO2 film using a water-infiltrated nanoporous glass, which serves as a solid electrolyte. For gate voltage application, water electrolysis and protonation/deprotonation of VO2 film surface occurred, leading to reversible metal-insulator phase conversion of ~11-nm-thick VO2 layer. The protonation was clearly accompanied by the structural change from an insulating monoclinic to a metallic tetragonal phase. Present results offer a new route for the development of electro-optically active solid-state devices with TMO materials by engineering RT protonation.

  6. Role of long range Coulomb interaction near the disorder driven metal-insulator transition in Ga1-xMnxAs

    NASA Astrophysics Data System (ADS)

    Mahmoudian, S.; Miranda, E.; Dobrosavljevic, V.

    2013-03-01

    Surprising signatures of interaction effects on disorder-driven localization have recently been observed by scanning tunneling microscopy of Ga1-xMnxAs, where visualizing the electronic wave function near the metal-insulator transition revealed[1] a pronounced suppression of the local tunneling density of states (LDOS) and enhanced localization only near the Fermi energy. These features highlight the limitation of the non-interacting picture, and point to the crucial importance of the long-range Coulomb interaction. Here, we implement a theoretical approach based on the recently developed Typical-Medium Theory,[2] the conceptually simplest approach to interaction-localization. We show that the presence of long-range Coulomb interaction leads to the simultaneous opening of a soft pseudogap in both the typical (geometrically averaged) and the average (algebraically averaged) LDOS, as the transition is approached. This result is consistent with the experimentally observed features of the STM spectra, suggesting new experiments that should be performed to fully characterize the quantum critical behavior at the metal-insulator transition

  7. Fano response induced by the interference between localized plasmons and interface reflections in metal-insulator-metal waveguide structure

    NASA Astrophysics Data System (ADS)

    Li, Hong-Ju; Wang, Ling-Ling; Zhai, Xiang

    2016-06-01

    The original Fano response induced by the interference between the localized plasmons and interface-reflected surface plasmon polaritons in a single metal-insulator-metal waveguide with two parallel separated metal strips is predicted theoretically through the coupled mode theory combined with the Fano function. The prominent asymmetric line shape resulting from the coupling between the discrete dipole resonance formed between metal strips and an interface-reflected-induced continuum is confirmed by the performed numerical simulations. The novel Fano spectrum is tuned easily by varying the length and coupling distance of metal strips. By introducing another separated metal strip, the outstanding double Fano behavior is obtained, and the corresponding underlying physics is illustrated. In particular, based on the performed refractive index sensing spectra, the high sensitivity of 855 nm/RIU and figure of merit up to 30 are achieved via the double Fano resonance. Undoubtedly, such ingenious structure may benefit the fabrications of nano-integrated plasmonic devices for optical switching and sensing.

  8. Ground-state oxygen holes and the metal-insulator transition in the negative charge-transfer rare-earth nickelates

    NASA Astrophysics Data System (ADS)

    Bisogni, Valentina; Catalano, Sara; Green, Robert J.; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Strocov, Vladimir N.; Zubko, Pavlo; Balandeh, Shadi; Triscone, Jean-Marc; Sawatzky, George; Schmitt, Thorsten

    2016-10-01

    The metal-insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal-insulator transition in terms of bond disproportionation.

  9. Metal-insulator transition in the hollandite K2V8O16 with a frustrated zigzag ladder probed by V51 NMR

    NASA Astrophysics Data System (ADS)

    Shimizu, Yasuhiro; Okai, Katsunori; Itoh, Masayuki; Isobe, Masahiro; Yamaura, Jun-Ichi; Yamauchi, Touru; Ueda, Yutaka

    2011-04-01

    We report the experimental results of V51 NMR measurements on the hollandite K2V8O16 consisting of a frustrated zigzag ladder with the orbital degrees of freedom. The metal-insulator transition is found to involve the spin-singlet formation by the V51 Knight shift K, the nuclear spin-lattice relaxation rate 1/T1, and the spin-echo decay rate 1/T2 measurements. In the insulating state, the anisotropic electric-field gradient supports the dxy orbital order with the spin singlet along the chain. The dxy orbital is magnetically most active in the metallic state, as observed by the anisotropic Knight shift, which suggests the strong electron correlation in the dxy band. Despite the large enhancement of the spin susceptibility, no apparent spin correlation is developed in the frustrated metallic state. Pressure suppresses the electron correlation continuously, as highlighted in the decrease of the metal-insulator transition and the spin susceptibility keeping the largest dxy contribution in the metallic state. A robust spin-singlet insulating phase with the large spin gap and paramagnetic spins appears above 1 GPa, which suggests a competition of the charge-orbital ordering pattern.

  10. Ground-state oxygen holes and the metal-insulator transition in the negative charge-transfer rare-earth nickelates.

    PubMed

    Bisogni, Valentina; Catalano, Sara; Green, Robert J; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Strocov, Vladimir N; Zubko, Pavlo; Balandeh, Shadi; Triscone, Jean-Marc; Sawatzky, George; Schmitt, Thorsten

    2016-10-11

    The metal-insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d(8) configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal-insulator transition in terms of bond disproportionation.

  11. Changes in the electronic structure and spin dynamics across the metal-insulator transition in LaLa1-xSrxCoO3

    DOE PAGES

    Smith, R. X.; Hoch, M. J. R.; Moulton, W. G.; ...

    2016-01-25

    The magnetoelectronic properties of La1-xSrxCoO3, which include giant magnetoresistance, are strongly dependent on the level of hole doping. The system evolves, with increasing x, from a spin glass insulator to a metallic ferromagnet with a metal-insulator (MI) transition at xC ~ 0.18. Nanoscale phase separation occurs in the insulating phase and persists, to some extent, into the just-metallic phase. The present experiments at 4.2 K have used 139La NMR to investigate the transition from hopping dynamics for x < xC to Korringa-like ferromagnetic metal behavior for x > xC. A marked decrease in the spin-lattice relaxation rate is found inmore » the vicinity of xC as the MI transition is crossed. Lastly, this behavior is accounted for in terms of the evolution of the electronic structure and dynamics with cluster size.« less

  12. Effects of low-energy excitations on spectral properties at higher binding energy: the metal-insulator transition of VO(2).

    PubMed

    Gatti, Matteo; Panaccione, Giancarlo; Reining, Lucia

    2015-03-20

    The effects of electron interaction on spectral properties can be understood in terms of coupling between excitations. In transition-metal oxides, the spectral function close to the Fermi level and low-energy excitations between d states have attracted particular attention. In this work we focus on photoemission spectra of vanadium dioxide over a wide (10 eV) range of binding energies. We show that there are clear signatures of the metal-insulator transition over the whole range due to a cross coupling of the delocalized s and p states with low-energy excitations between the localized d states. This coupling can be understood by advanced calculations based on many-body perturbation theory in the GW approximation. We also advocate the fact that tuning the photon energy up to the hard-x-ray range can help to distinguish fingerprints of correlation from pure band-structure effects.

  13. Low-temperature oriented growth of vanadium dioxide films on CoCrTa metal template on Si and vertical metal-insulator transition

    SciTech Connect

    Okimura, Kunio; Mian, Md.Suruz

    2012-09-15

    The authors achieved oriented growth of vanadium dioxide (VO{sub 2}) films on CoCrTa metal template grown on an Si substrate. Low-temperature ({approx}250 Degree-Sign C) deposition of VO{sub 2} films using inductively coupled-plasma-assisted sputtering technique realized an abrupt interface between VO{sub 2} and CoCrTa layers, suppressing the oxidation and diffusion of metal components. The films revealed a metal-insulator transition with resistance change of over 2 orders of magnitude. The CoCrTa film, in which Co hexagonal crystalline grains with c-axis orientation were surrounded by segregated Cr and Ta, serves for the oriented growth of VO{sub 2} crystalline film, enabling higher orders of transition in resistance and low voltage switching, even for the vertical (out-of-plane) direction.

  14. Tuning the metal-insulator transition via epitaxial strain and Co doping in NdNiO{sub 3} thin films grown by polymer-assisted deposition

    SciTech Connect

    Yao, Dan; Shi, Lei Zhou, Shiming; Liu, Haifeng; Zhao, Jiyin; Li, Yang; Wang, Yang

    2016-01-21

    The epitaxial NdNi{sub 1-x}Co{sub x}O{sub 3} (0 ≤ x ≤ 0.10) thin films on (001) LaAlO{sub 3} and (001) SrTiO{sub 3} substrates were grown by a simple polymer-assisted deposition technique. The co-function of the epitaxial strain and Co doping on the metal-insulator transition in perovskite nickelate NdNiO{sub 3} thin films is investigated. X-ray diffraction and scanning electron microscopy reveal that the as-prepared thin films exhibit good crystallinity and heteroepitaxy. The temperature dependent resistivities of the thin films indicate that both the epitaxial strain and Co doping lower the metal-insulator (MI) transition temperature, which can be treated as a way to tune the MI transition. Furthermore, under the investigated Co-doping levels, the MI transition temperature (T{sub MI}) shifts to low temperatures with Co content increasing under both compressive and tensile strain, and the more distinction is in the former situation. When x is increased up to 0.10, the insulating phase is completely suppressed under the compressive strain. With the strain increases from compression to tension, the resistivities are enhanced both in the metal and insulating regions. However, the Co-doping effect on the resistivity shows a more complex situation. As Co content x increases from zero to 0.10, the resistivities are reduced both in the metal and insulating regions under the tensile strain, whereas they are enhanced in the high-temperature metal region under the compressive strain. Based on the temperature dependent resistivity in the metal regions, it is suggested that the electron-phonon coupling in the films becomes weaker with the increase of both the strain and Co-doping.

  15. Cu(Ir1 − xCrx)2S4: a model system for studying nanoscale phase coexistence at the metal-insulator transition

    PubMed Central

    Božin, E. S.; Knox, K. R.; Juhás, P.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.

    2014-01-01

    Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood. Despite their ubiquity, they are hard to study because they produce weak diffuse signals in most measurements. Here we propose Cu(Ir1 − xCrx)2S4 as a model system, where robust local structural signals lead to key new insights. We demonstrate a hitherto unobserved coexistence of an Ir4+ charge-localized dimer phase and Cr-ferromagnetism. The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates. We suggest that the presence of quenched strain from dopant ions acts as an arbiter deciding between the competing ground states. PMID:24518384

  16. Improved metal-insulator-transition characteristics of ultrathin VO{sub 2} epitaxial films by optimized surface preparation of rutile TiO{sub 2} substrates

    SciTech Connect

    Martens, Koen; Aetukuri, Nagaphani; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.

    2014-02-24

    Key to the growth of epitaxial, atomically thin films is the preparation of the substrates on which they are deposited. Here, we report the growth of atomically smooth, ultrathin films of VO{sub 2} (001), only ∼2 nm thick, which exhibit pronounced metal-insulator transitions, with a change in resistivity of ∼500 times, at a temperature that is close to that of films five times thicker. These films were prepared by pulsed laser deposition on single crystalline TiO{sub 2}(001) substrates that were treated by dipping in acetone, HCl and HF in successive order, followed by an anneal at 700–750  °C in flowing oxygen. This pretreatment removes surface contaminants, TiO{sub 2} defects, and provides a terraced, atomically smooth surface.

  17. Unusual valence state and metal-insulator transition in BaV10O15 probed by hard x-ray photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Yoshino, T.; Okawa, M.; Kajita, T.; Dash, S.; Shimoyama, R.; Takahashi, K.; Takahashi, Y.; Takayanagi, R.; Saitoh, T.; Ootsuki, D.; Yoshida, T.; Ikenaga, E.; Saini, N. L.; Katsufuji, T.; Mizokawa, T.

    2017-02-01

    We have studied the electronic structure of BaV10O15 across the metal-insulator transition with V trimerization by means of hard-x-ray photoemission spectroscopy (HAXPES) and mean-field calculations. The V 2 p HAXPES indicates V2.5 +-V3 + charge fluctuation in the metallic phase, and V2+-V3+ charge order in the insulating phase. The V2.5 +-V3 + charge fluctuation is consistent with the mean-field solution where a V 3 d a1 g electron is shared by two V sites with face-sharing VO6 octahedra. The valence-band HAXPES of the metallic phase exhibits pseudogap opening at the Fermi level associated with the charge fluctuation, and a band gap ˜200 meV is established in the insulating phase due to the switching of charge correlation.

  18. Substrate-mediated strain effect on the role of thermal heating and electric field on metal-insulator transition in vanadium dioxide nanobeams

    PubMed Central

    Kim, Min-Woo; Jung, Wan-Gil; Hyun-Cho; Bae, Tae-Sung; Chang, Sung-Jin; Jang, Ja-Soon; Hong, Woong-Ki; Kim, Bong-Joong

    2015-01-01

    Single-crystalline vanadium dioxide (VO2) nanostructures have recently attracted great attention because of their single domain metal-insulator transition (MIT) nature that differs from a bulk sample. The VO2 nanostructures can also provide new opportunities to explore, understand, and ultimately engineer MIT properties for applications of novel functional devices. Importantly, the MIT properties of the VO2 nanostructures are significantly affected by stoichiometry, doping, size effect, defects, and in particular, strain. Here, we report the effect of substrate-mediated strain on the correlative role of thermal heating and electric field on the MIT in the VO2 nanobeams by altering the strength of the substrate attachment. Our study may provide helpful information on controlling the properties of VO2 nanobeam for the device applications by changing temperature and voltage with a properly engineered strain. PMID:26040637

  19. Metal-insulator transition characteristics of vanadium dioxide thin films synthesized by ultrasonic nebulized spray pyrolysis of an aqueous combustion mixture

    NASA Astrophysics Data System (ADS)

    Bharathi, R.; Naorem, Rameshwari; Umarji, A. M.

    2015-08-01

    We report the synthesis of high quality vanadium dioxide (VO2) thin films by a novel spray pyrolysis technique, namely ultrasonic nebulized spray pyrolysis of aqueous combustion mixture (UNSPACM). This simple and cost effective two step process involves synthesis of a V2O5 film on an LaAlO3 substrate followed by a controlled reduction to form single phase VO2. The formation of M1 phase (P21/c) is confirmed by Raman spectroscopic studies. A thermally activated metal-insulator transition (MIT) was observed at 61 ^\\circ C, where the resistivity changes by four orders of magnitude. Activation energies for the low conduction phase and the high conduction phase were obtained from temperature variable resistance measurements. The infrared spectra also show a dramatic change in reflectance from 13% to over 90% in the wavelength range of 7-15 μ m. This indicates the suitability of the films for optical switching applications at infrared frequencies.

  20. Thickness-dependent evolution of structure, electronic structure, and metal-insulator transition in ultrathin V2O3(0001) films on Ag(001)

    NASA Astrophysics Data System (ADS)

    Kundu, Asish K.; Menon, Krishnakumar S. R.

    2017-05-01

    Epitaxial hexagonal V2O3(0001) films were grown on cubic Ag(001) substrate for coverages ranging from 1-20 monolayers equivalent (MLE) and have studied their structure, electronic structure and the metal-insulator transition (MIT) using Low Energy Electron Diffraction (LEED), X-ray Photoelectron Spectroscopy (XPS) and Angle-Resolved Photoemission Spectroscopy (ARPES) techniques. Detailed LEED and XPS study reveal that, for the lower film coverages (∼1 MLE), a complex (coexisting phase of) vanadium oxide is formed while from 3 MLE coverage onwards, three-dimensional crystallites of V2O3 grows epitaxially. Our LEED results also show that the hexagonal surface of V2O3(0001) is stabilizing on top of square symmetry substrate by the formation of twin-domain structure, where each domain is rotated by 90o. Our photoemission results show that the surface of V2O3 is more insulating than its bulk, similar to the case of many strongly correlated oxide surfaces which is discussed based on the valence band electronic structure with varying probing depth. Evolution of the surface electronic structure was also studied as a function of the film thickness. Further, the effect of lattice strain, film thickness and the domain formation on the metal-insulator transition (MIT) are discussed. The change in the orbital occupancy of (a1 g, egπ) and (egπ, egπ) orbitals of V 3 d, a vanishing of quasiparticle (QP) peak and opening an energy gap at the Fermi level is observed below a critical temperature as a consequence of the MIT.

  1. Distinctive Finite Size Effects on the Phase Diagram and Metal-insulator Transitions of Tungsten-doped Vanadium(IV) Oxide

    SciTech Connect

    L Whittaker; T Wu; C Patridge; S Ganapathy; S Banerjee

    2011-12-31

    The influence of finite size in altering the phase stabilities of strongly correlated materials gives rise to the interesting prospect of achieving additional tunability of solid-solid phase transitions such as those involved in metal-insulator switching, ferroelectricity, and superconductivity. We note here some distinctive finite size effects on the relative phase stabilities of insulating (monoclinic) and metallic (tetragonal) phases of solid-solution W{sub x}V{sub 1-x}O{sub 2}. Ensemble differential scanning calorimetry and individual nanobelt electrical transport measurements suggest a pronounced hysteresis between metal {yields} insulator and insulator {yields} metal phase transformations. Both transitions are depressed to lower critical temperatures upon the incorporation of substitutional tungsten dopants but the impact on the former transition seems far more prominent. In general, the depression in the critical temperatures upon tungsten doping far exceeds corresponding values for bulk W{sub x}V{sub 1-x}O{sub 2} of the same composition. Notably, the depression in phase transition temperature saturates at a relatively low dopant concentration in the nanobelts, thought to be associated with the specific sites occupied by the tungsten substitutional dopants in these structures. The marked deviations from bulk behavior are rationalized in terms of a percolative model of the phase transition taking into account the nucleation of locally tetragonal domains and enhanced carrier delocalization that accompany W{sup 6+} doping in the W{sub x}V{sub 1-x}O{sub 2} nanobelts.

  2. Localization of metal-induced gap states at the metal-insulator interface: origin of flux noise in SQUIDs and superconducting qubits.

    PubMed

    Choi, SangKook; Lee, Dung-Hai; Louie, Steven G; Clarke, John

    2009-11-06

    The origin of magnetic flux noise in superconducting quantum interference devices with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 20 years. This noise limits the decoherence time of superconducting qubits. A consensus has emerged that the noise arises from fluctuating spins of localized electrons with an areal density of 5x10(17) m(-2). We show that, in the presence of potential disorder at the metal-insulator interface, some of the metal-induced gap states become localized and produce local moments. A modest level of disorder yields the observed areal density.

  3. Localization of metal-induced gap states at the metal-insulator interface: Origin of flux noise in SQUIDs and superconducting qubits

    SciTech Connect

    Choi, SangKook; Lee, Dung-Hai; Louie, Steven G.; Clarke, John

    2009-10-10

    The origin of magnetic flux noise in Superconducting Quantum Interference Devices with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 20 years. This noise limits the decoherence time of superconducting qubits. A consensus has emerged that the noise arises from fluctuating spins of localized electrons with an areal density of 5 x 10(17)m(-2). We show that, in the presence of potential disorder at the metal-insulator interface, some of the metal-induced gap states become localized and produce local moments. A modest level of disorder yields the observed areal density.

  4. Orbital magnetic field driven metal-insulator transition in spinless extended Falicov-Kimball model on a triangular lattice

    NASA Astrophysics Data System (ADS)

    Yadav, Umesh K.

    2017-01-01

    Ground state properties of spinless, extended Falicov-Kimball model (FKM) on a finite size triangular lattice with orbital magnetic field normal to the lattice are studied using numerical diagonalization and Monte-Carlo simulation methods. We show that the ground state configurations of localized electrons strongly depend on the magnetic field. Magnetic field induces a metal to insulator transition accompanied by segregated phase to an ordered regular phase except at density nf = 1 / 2 of localized electrons. It is proposed that magnetic field can be used as a new tool to produce segregated phase which was otherwise accessible only either with correlated hopping or with large on-site interactions.

  5. Tunable metal-insulator transition in Nd1-xYxNiO3 (x = 0.3, 0.4) perovskites thin film at near room temperature

    NASA Astrophysics Data System (ADS)

    Shao, Tao; Qi, Zeming; Wang, Yuyin; Li, Yuanyuan; Yang, Mei; Wang, Yu; Zhang, Guobin; Liu, Miao

    2015-07-01

    Metal-insulator transition (MIT) occurs due to the charge disproportionation and lattice distortions in rare-earth nickelates. Existing studies revealed that the MIT behavior of rare-earth nickelates is fairly sensitive to external stress/pressure, suggesting a viable route for MIT strain engineering. Unlike applying extrinsic strain, the MIT can also be modulated by through rare-earth cation mixing, which can be viewed as intrinsic quantum stress. We choose Nd1-XYXNiO3 (x = 0.3, 0.4) perovskites thin films as a prototype system to exhibit the tunable sharp MIT at near room temperature. By adjusting Y concentration, the transition temperature of the thin films can be changed within the range of 340-360 K. X-ray diffraction, X-ray absorption fine structure (XAFS), and in situ infrared spectroscopy are employed to probe the structural and optical property variation affected by composition and temperature. The infrared transmission intensity decreases with temperature across the MIT, indicating a pronounced thermochromic effect. Meanwhile, the XAFS result exhibits that the crystal atomistic structure changes accompanying with the Y atoms incorporation and MIT phase transition. The heavily doped Y atoms result in the pre-edge peak descent and Ni-O bond elongation, suggesting an enhanced charge disproportionation effect and the weakening of hybridization between Ni-3d and O-2p orbits.

  6. Hopping conduction in p-type MoS{sub 2} near the critical regime of the metal-insulator transition

    SciTech Connect

    Park, Tae-Eon; Jang, Chaun E-mail: presto@kist.re.kr; Suh, Joonki; Wu, Junqiao; Seo, Dongjea; Park, Joonsuk; Lin, Der-Yuh; Huang, Ying-Sheng; Choi, Heon-Jin; Chang, Joonyeon E-mail: presto@kist.re.kr

    2015-11-30

    We report on temperature-dependent charge and magneto transport of chemically doped MoS{sub 2}, p-type molybdenum disulfide degenerately doped with niobium (MoS{sub 2}:Nb). The temperature dependence of the electrical resistivity is characterized by a power law, ρ(T) ∼ T{sup −0.25}, which indicates that the system resides within the critical regime of the metal-insulator (M-I) transition. By applying high magnetic field (∼7 T), we observed a 20% increase in the resistivity at 2 K. The positive magnetoresistance shows that charge transport in this system is governed by the Mott-like three-dimensional variable range hopping (VRH) at low temperatures. According to relationship between magnetic-field and temperature dependencies of VRH resistivity, we extracted a characteristic localization length of 19.8 nm for MoS{sub 2}:Nb on the insulating side of the M-I transition.

  7. Role of temperature-dependent O-p-Fe-d hybridization parameter in the metal-insulator transition of Fe3O4: a theoretical study

    NASA Astrophysics Data System (ADS)

    Fauzi, A. D.; Majidi, M. A.; Rusydi, A.

    2017-04-01

    We propose a simple tight-binding based model for Fe3O4 that captures the preference of ferrimagnetic over ferromagnetic spin configuration of the system. Our model is consistent with previous theoretical and experimental studies suggesting that the system is half metallic, in which spin polarized electrons hop only among the Fe B sites. To address the metal-insulator transition (MIT) we propose that the strong correlation among electrons, which may also be influenced by the electron-phonon interactions, manifest as the temperature-dependence of the O-p-Fe-d hybridization parameter, particularly Fe-d belonging to one of the Fe B sites (denoted as {t}{{FeB}-{{O}}}(2)). By proposing that this parameter increases as the temperature decreases, our density-of-states calculation successfully captures a gap opening at the Fermi level, transforming the system from half metal to insulator. Within this model along with the corresponding choice of parameters and a certain profile of the temperature dependence of {t}{{FeB}-{{O}}}(2), we calculate the resistivity of the system as a function of temperature. Our calculation result reveals the drastic uprising trend of the resistivity profile as the temperature decreases, with the MIT transition temperature located around 100 K, which is in agreement with experimental data.

  8. Charge Disproportionation without Charge Transfer in the Rare-Earth-Element Nickelates as a Possible Mechanism for the Metal-Insulator Transition

    NASA Astrophysics Data System (ADS)

    Johnston, Steve; Mukherjee, Anamitra; Elfimov, Ilya; Berciu, Mona; Sawatzky, George A.

    2014-03-01

    We study a model for the metal-insulator (M-I) transition in the rare-earth-element nickelates RNiO3, based upon a negative charge transfer energy and coupling to a rocksaltlike lattice distortion of the NiO6 octahedra. Using exact diagonalization and the Hartree-Fock approximation we demonstrate that electrons couple strongly to these distortions. For small distortions the system is metallic, with a ground state of predominantly d8L character, where L_ denotes a ligand hole. For sufficiently large distortions (δdNi-O˜0.05-0.10 Å), however, a gap opens at the Fermi energy as the system enters a periodically distorted state alternating along the three crystallographic axes, with (d8L_2)S =0(d8)S=1 character, where S is the total spin. Thus the M-I transition may be viewed as being driven by an internal volume "collapse" where the NiO6 octahedra with two ligand holes shrink around their central Ni, while the remaining octahedra expand accordingly, resulting in the (1/2, 1/2, 1/2) superstructure observed in x-ray diffraction in the insulating phase. This insulating state is an example of charge ordering achieved without any actual movement of the charge.

  9. Pressure dependence of the metal-insulator transition in κ-(BEDT-TTF)2Hg(SCN)2Cl: optical and transport studies

    NASA Astrophysics Data System (ADS)

    Löhle, A.; Rose, E.; Singh, S.; Beyer, R.; Tafra, E.; Ivek, T.; Zhilyaeva, E. I.; Lyubovskaya, R. N.; Dressel, M.

    2017-02-01

    The two-dimensional organic conductor κ-(BEDT-TTF)2-Hg(SCN)2Cl exhibits a pronounced metal-insulator transition at {{T}\\text{CO}}=30 K. From the splitting of the molecular vibrations, the phase transition can be unambiguously assigned to charge-ordering with 2{δρ}=0.2e . We have investigated the pressure evolution of this behavior by temperature-dependent electrical transport measurements and optical investigations applying hydrostatic pressure up to 12 kbar. The data reveal a mean-field like down-shift of {{T}\\text{CO}}≤ft( p\\right) with a critical pressure of {{p}c}=0.7+/- 0.1 kbar and a metallic state above the suppression of the charge-ordered state; no traces of superconductivity could be identified down to T  =  1.5 K. As the charge order {δρ} sets in abruptly with decreasing temperature, its size remains unaffected by pressure. However, the fraction of charge imbalanced molecules decreases until it is completely absent above 1.6 kbar.

  10. Charge disproportionation without charge transfer in the rare-earth nickelates as a possible mechanism for the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Johnston, Steven; Mukherjee, Anamitra; Elfimov, Ilya; Berciu, Mona; Sawatzky, George

    2014-03-01

    We study a model for the metal-insulator (MI) transition in the rare-earth nickelates RNiO3, based upon a negative charge transfer energy and coupling to a rock-salt like lattice distortion of the NiO6 octahedra. Using exact diagonalization and the Hartree-Fock approximation we demonstrate that electrons couple strongly to these distortions. For small distortions the system is metallic, with ground state of predominantly d8 ligand character, where ligand denotes a ligand hole. For sufficiently large distortions (δdNi - O ~ 0 . 05 - 0 . 10 Å), however, a gap opens at the Fermi energy as the system enters a periodically distorted state alternating along the three crystallographic axes, with (d8 ligand2) S = 0(d8) S = 1 character, where S is the total spin. Thus the MI transition may be viewed as being driven by an internal volume ``collapse'' where the NiO6 octahedra with two ligand holes shrink around their central Ni, while the remaining octahedra expand accordingly, resulting in the superstructure observed in x-ray diffraction in the insulating phase. This insulating state is an example of charge ordering achieved without any actual movement of the charge, similar to that reported in a prior DMFT study.

  11. Interfacial reaction between metal-insulator transition material NbO2 thin film and wide band gap semiconductor GaN

    NASA Astrophysics Data System (ADS)

    Posadas, Agham; Kvit, Alexander; Demkov, Alexander

    Materials that undergo a metal-insulator transition (MIT) are potentially useful for a wide variety of applications including electronic and opto-electronic switches, memristors, sensors, and coatings. In most such materials, the MIT is driven by temperature. In one such material, NbO2, the MIT mechanism is primarily of the Peierls-type, in which the dimerization of the Nb atoms without electron correlation causes the transition from metallic to semiconducting. We describe our initial work at combining NbO2 and GaN in epitaxial form, which could be potentially useful in resistive switching devices operating at very high temperatures. We grow NbO2 films on GaN(0001)/Si(111) substrates using reactive molecular beam epitaxy from a metal evaporation source and molecular oxygen. X-ray diffraction shows that the films are found to grow with a single out of plane orientation but with three symmetry-related orientation domains in the plane. In situ x-ray photoelectron spectroscopy confirms that the phase pure NbO2 is formed but that a chemical reaction occurs between the GaN and NbO2 during the growth forming a polycrystalline interfacial layer. We perform STEM-EELS analysis of the film and the interface to further elucidate their chemical and structural properties.

  12. Pressure dependence of the metal-insulator transition in κ-(BEDT-TTF)2Hg(SCN)2Cl: optical and transport studies.

    PubMed

    Löhle, A; Rose, E; Singh, S; Beyer, R; Tafra, E; Ivek, T; Zhilyaeva, E I; Lyubovskaya, R N; Dressel, M

    2017-02-08

    The two-dimensional organic conductor κ-(BEDT-TTF)2-Hg(SCN)2Cl exhibits a pronounced metal-insulator transition at [Formula: see text] K. From the splitting of the molecular vibrations, the phase transition can be unambiguously assigned to charge-ordering with [Formula: see text]. We have investigated the pressure evolution of this behavior by temperature-dependent electrical transport measurements and optical investigations applying hydrostatic pressure up to 12 kbar. The data reveal a mean-field like down-shift of [Formula: see text] with a critical pressure of [Formula: see text] kbar and a metallic state above the suppression of the charge-ordered state; no traces of superconductivity could be identified down to T  =  1.5 K. As the charge order [Formula: see text] sets in abruptly with decreasing temperature, its size remains unaffected by pressure. However, the fraction of charge imbalanced molecules decreases until it is completely absent above 1.6 kbar.

  13. Sudden slowing down of charge carrier dynamics at the Mott metal-insulator transition in kappa-(D{sub 8}-BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br.

    SciTech Connect

    Brandenburg, J.; Muller, J.; Schlueter, J. A.

    2012-02-01

    We investigate the dynamics of correlated charge carriers in the vicinity of the Mott metal-insulator (MI) transition in the quasi-two-dimensional organic charge-transfer salt {kappa}-(D{sub 8}-BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br by means of fluctuation (noise) spectroscopy. The observed 1/f-type fluctuations are quantitatively very well described by a phenomenological model based on the concept of non-exponential kinetics. The main result is a correlation-induced enhancement of the fluctuations accompanied by a substantial shift of spectral weight to low frequencies in the vicinity of the Mott critical endpoint. This sudden slowing down of the electron dynamics, observed here in a pure Mott system, may be a universal feature of MI transitions. Our findings are compatible with an electronic phase separation in the critical region of the phase diagram and offer an explanation for the not yet understood absence of effective mass enhancement when crossing the Mott transition.

  14. Synthetic beta-K(0.33)V2O5 nanorods: a metal-insulator transition in vanadium oxide bronze.

    PubMed

    Zhang, Xiaodong; Yan, Wensheng; Xie, Yi

    2011-12-02

    We found a linear relationship between the metal-insulator transition (MIT) temperature and the A(+) ionic radius of the beta-A(0.33)V(2)O(5) bronze family, leading our attention to beta-K(0.33)V(2)O(5) which has been neglected for a long time. We have introduced a facile hydrothermal method to obtain the single-crystalline beta-K(0.33)V(2)O(5) nanorods. As expected, both the temperature-dependence of the resistivity and magnetization demonstrated MITs at about 72 K for beta-K(0.33)V(2)O(5), thus matching well with the linear relationship described above. The beta-K(0.33)V(2)O(5) was assigned as a new member of the beta-A(0.33)V(2)O(5) bronze family for their similar crystal and electronic structures and their MIT property; this addition enriches the beta-A(0.33)V(2)O(5) bronze family.

  15. Localization length and impurity dielectric susceptibility in the critical regime of the metal-insulator transition in homogeneously doped p-type Ge

    SciTech Connect

    Watanabe, Michio; Itoh, Kohei M.; Ootuka, Youiti; Haller, Eugene E.

    2000-07-15

    We have determined the localization length {xi} and the impurity dielectric susceptibility {chi}{sub imp} as a function of Ga acceptor concentrations (N) in nominally uncompensated {sup 70}Ge:Ga just below the critical concentration (N{sub c}) for the metal-insulator transition. Both {xi} and {chi}{sub imp} diverge at N{sub c} according to the functions {xi}{proportional_to}(1-N/N{sub c}){sup -{nu}} and {chi}{sub imp}{proportional_to}(N{sub c}/N-1){sup -{zeta}}, respectively, with {nu}=1.2{+-}0.3 and {zeta}=2.3{+-}0.6 for 0.99N{sub c}

  16. Chromium-niobium co-doped vanadium dioxide films: Large temperature coefficient of resistance and practically no thermal hysteresis of the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Miyazaki, Kenichi; Shibuya, Keisuke; Suzuki, Megumi; Sakai, Kenichi; Fujita, Jun-ichi; Sawa, Akihito

    2016-05-01

    We investigated the effects of chromium (Cr) and niobium (Nb) co-doping on the temperature coefficient of resistance (TCR) and the thermal hysteresis of the metal-insulator transition of vanadium dioxide (VO2) films. We determined the TCR and thermal-hysteresis-width diagram of the V1-x-yCrxNbyO2 films by electrical-transport measurements and we found that the doping conditions x ≳ y and x + y ≥ 0.1 are appropriate for simultaneously realizing a large TCR value and an absence of thermal hysteresis in the films. By using these findings, we developed a V0.90Cr0.06Nb0.04O2 film grown on a TiO2-buffered SiO2/Si substrate that showed practically no thermal hysteresis while retaining a large TCR of 11.9%/K. This study has potential applications in the development of VO2-based uncooled bolometers.

  17. Controlled modulation of hard and soft X-ray induced tunneling currents utilizing coaxial metal-insulator-metal probe tips

    DOE PAGES

    Cummings, Marvin; Shirato, Nozomi; Kersell, Heath; ...

    2017-01-05

    Here, the effect of a local external electric field on the barrier potential of a tunneling gap is studied utilizing an emerging technique, synchrotron x-ray scanning tunneling microscopy. Here, we demonstrate that the shape of the potential barrier in the tunneling gap can be altered by a localized external electric field, generated by voltages placed on the metallic outer shield of a nanofabricated coaxial metal-insulator-metal tip, resulting in a controlled linear modulation of the tunneling current. Experiments at hard and soft x-ray synchrotron beamlines reveal that both the chemical contrast and magnetic contrast signals measured by the tip can bemore » drastically enhanced, resulting in improved local detection of chemistry and magnetization at the surface.« less

  18. Massive Temperature-Induced Metal—Insulator Transition in Individual Nanowires of a Non-Stoichiometric Vanadium Oxide Bronze

    SciTech Connect

    Patridge, C.; Wu, T; Jaye, C; Ravel, B; Takeuchi, E; Fischer, D; Sambandamurthy, G; Banerjee, S

    2010-01-01

    Metal-insulator transitions in strongly correlated materials, induced by varying either temperature or dopant concentration, remain a topic of enduring interest in solid-state chemistry and physics owing to their fundamental importance in answering longstanding questions regarding correlation effects. We note here the unprecedented observation of a four-orders-of-magnitude metal-insulator transition in single nanowires of {delta}-K{sub x}V{sub 2}O{sub 5}, when temperature is varied, which thus represents a rare new addition to the pantheon of materials exhibiting pronounced metal-insulator transitions in proximity to room temperature.

  19. Metal-Insulator Transition and the Temperature of the Pseudogap Anomaly Opening in Praseodymium Doped Y1-zPrzBa2Cu3O7-δ Single Crystals

    NASA Astrophysics Data System (ADS)

    Vovk, R. V.; Nazyrov, Z. F.; Goulatis, I. L.; Chroneos, A.; Pinto Simoes, V. M.

    2013-02-01

    The influence of praseodymium doping on the electrical resistivity in the ab-plane of Y1-zPrzBa2Cu3O7-δ single crystals, is investigated. It is determined that as the concentration of praseodymium (0.0 ≤ z ≤ 0.5) is rising there occurs a significant shift of the temperature regions, corresponding to the metal-insulator transitions, as well as to the regime of the implementation of the pseudogap anomaly. The part of the curves related to the metal-insulator transition are well described by means of an asymptotic dependence that corresponds to the implementation of a quantum critical regime in the system, the so-called law of the "one third".

  20. Simultaneous metal-insulator and antiferromagnetic transitions in orthorhombic perovskite iridate S r0.94I r0.78O2.68 single crystals

    NASA Astrophysics Data System (ADS)

    Zheng, H.; Terzic, J.; Ye, Feng; Wan, X. G.; Wang, D.; Wang, Jinchen; Wang, Xiaoping; Schlottmann, P.; Yuan, S. J.; Cao, G.

    2016-06-01

    The orthorhombic perovskite SrIr O3 is a semimetal, an intriguing exception in iridates where the strong spin-orbit interaction coupled with electron correlations tends to impose an insulating state. We report results of our investigation of bulk single-crystal S r0.94I r0.78O2.68 or Ir-deficient, orthorhombic perovskite SrIr O3 . It retains the same crystal structure as stoichiometric SrIr O3 but exhibits a sharp, simultaneous antiferromagnetic (AFM) and metal-insulator (MI) transition occurring in the basal-plane resistivity at 185 K. Above it, the basal-plane resistivity features an extended regime of almost linear temperature dependence up to 800 K but the strong electronic anisotropy renders an insulating behavior in the out-of-plane resistivity. The Hall resistivity undergoes an abrupt sign change and grows below 40 K, which along with the Sommerfeld constant of 20 mJ /mol K2 suggests a multiband effect. All results including our first-principles calculations underscore a delicacy of the paramagnetic, metallic state in SrIr O3 that is in close proximity to an AFM insulating state. The contrasting ground states in isostructural S r0.94I r0.78O2.68 and SrIr O3 illustrate a critical role of lattice distortions and Ir deficiency in rebalancing the ground state in the iridates. Finally, the concurrent AFM and MI transitions reveal a direct correlation between the magnetic transition and formation of an activation gap in the iridate, which is conspicuously absent in S r2Ir O4 .

  1. Metal-insulator transition in Ba3Fe1 -xRu2 +xO9 : Interplay between site disorder, chemical percolation, and electronic structure

    NASA Astrophysics Data System (ADS)

    Middey, S.; Aich, Payel; Meneghini, C.; Mukherjee, K.; Sampathkumaran, E. V.; Siruguri, V.; Mahadevan, P.; Ray, Sugata

    2016-11-01

    Perovskites containing barium metal at the A site often take up unusual hexagonal structures having more than one type of possible sites for the B cation to occupy. This opens up various different B -B - or B -O-B -type connectivities and consequent physical properties which are naturally missing in cubic perovskites. BaRuO3 is one such system where doping of Ru (4 d4 ) by other transition metals (Mn +) creates similar conditions, giving rise to various M -Ru interactions. Interestingly, the 6 H hexagonal structure of doped barium ruthenate triple perovskite (Ba3M Ru2O9 ) seems to possess some internal checks because within the structure M ion always occupies the 2 a site and Ru goes to the 4 f site, allowing only M -O-Ru 180∘ and Ru-O-Ru 90∘ interactions to occur. The only exception is observed in the case of the Fe dopant, which allows us to study almost the full Ba3Fe1 -xRu2 +xO9 series of compounds with wide ranges of x because here Fe ions have the ability to freely go to the 4 f sites and Ru readily takes up the 2 a positions. Therefore, here one has the opportunity to probe the evolution of electronic and magnetic properties as a function of doping by going from BaRuO3 (paramagnetic metal) to BaFeO3 (ferromagnetic insulator). Our detailed experimental and theoretical results show that the series does exhibit a percolative metal-insulator transition with an accompanying but not coincidental magnetic transition as a function of x .

  2. Universality classes of metal-insulator transitions in strongly correlated electron systems and mechanism of high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Imada, Masatoshi

    2005-08-01

    We study three regimes of the Mott transitions characterized by classical, marginally quantum, and quantum. In the classical regime, the quantum degeneracy temperature is lower than the critical temperature of the Mott transition Tc , below which the first-order transition occurs. The quantum regime describes the Tc=0 boundary of the continuous transition. The marginal quantum region appears sandwiched by these two regimes. The classical transition is described by the Ising universality class. However, the Ginzburg-Landau-Wilson scheme breaks down when the quantum effects dominate. The marginal quantum critical region is categorized to an unusual universality class, where the order parameter exponent β , the susceptibility exponent γ , and the field exponent δ are given by β=d/2 , γ=2-d/2 , and δ=4/d , respectively, with d being the spatial dimensionality. It is shown that the transition is always at the upper critical dimension irrespective of the spatial dimensions. Therefore the mean-field exponents and the hyperscaling description become both valid at any dimension. The obtained universality classes agree with the recent experimental results on the Mott criticality in organic conductors such as κ-(ET)2Cu[N(CN)2]Cl and transition-metal compounds such as V2O3 . The marginal quantum criticality is characterized by the critically enhanced electron-density fluctuations at small wave number. The characteristic energy scale of the density fluctuation extends to the order of the Mott gap in contrast to the spin and orbital fluctuation scales and causes various unusual properties. The mode coupling theory shows that the marginal quantum criticality further generates non-Fermi-liquid properties in the metallic side. The effects of the long-range Coulomb force in the filling-control Mott transition are also discussed. A mechanism of high-temperature superconductivity emerges from the density fluctuations at small wave number inherent in the marginal quantum

  3. Transport properties and metal-insulator transition in oxygen deficient LaNiO3: a density functional theory study

    NASA Astrophysics Data System (ADS)

    Misra, D.; Kundu, T. K.

    2016-09-01

    Density functional theory with appropriate functional has been employed to investigate the metal to insulator transition in oxygen deficient LaNiO3-x (x = 0.0, 0.25, 0.5, 1.0) compounds. While the metallic nature of LaNiO3 is characterized by the low temperature Fermi liquid behavior of resistivity and a finite density of states at the Fermi level, the density of states and the transport properties clearly identify LaNiO2.75 as a semiconductor, and LaNiO2.5 as an insulator, which is followed by another insulator to semiconductor transition with further increase of x to ‘1’ in LaNiO2. This oxygen vacancy controlled metal to insulator transition is explained on the basis of non-adiabatic polaronic transport. From the covalency metric calculation of the chemical bonding and the Bader charge transfer analysis, this metal to insulator transition is attributed to the enhanced covalent part in the chemical bonding and reduced charge transfer from Ni to O atoms in LaNiO3-x compounds.

  4. LETTER TO THE EDITOR: The Mott metal - insulator transition in the two-dimensional Hubbard model at half-filling with lifetime effects within the moment approach

    NASA Astrophysics Data System (ADS)

    Rodríguez-Núñez, J. J.; Schafroth, S.

    1998-06-01

    We explore the effect of the self-energy, 0953-8984/10/23/002/img5, having a single pole, 0953-8984/10/23/002/img6, with spectral weight 0953-8984/10/23/002/img7 and quasi-particle lifetime 0953-8984/10/23/002/img8, on the density of states. We obtain the set of parameters 0953-8984/10/23/002/img6, 0953-8984/10/23/002/img7, and 0953-8984/10/23/002/img8 by means of the moment approach (exact sum rules) of Nolting. Due to our choice of self-energy, the system is not a Fermi liquid for any value of the interaction, a result which also holds in the moment approach of Nolting without lifetime effects. Our self-energy satisfies the Kramers - Kronig relationships since it is analytic in one of the complex half-planes. By increasing the value of the local interaction, 0953-8984/10/23/002/img12, at half-filling 0953-8984/10/23/002/img13, there is a transition from a paramagnetic metal to a paramagnetic insulator (a Mott metal - insulator transition) for values of 0953-8984/10/23/002/img12 of the order of 0953-8984/10/23/002/img15 (W is the bandwidth) which is in agreement with numerical results for finite lattices and for an infinite number of dimensions 0953-8984/10/23/002/img16. These results expose the main weakness of the spherical approximation of Nolting: a finite gap for any finite value of the interaction, i.e., an insulator for any finite value of 0953-8984/10/23/002/img12. Lifetime effects are absolutely indispensable to making our scheme work better than that based on improving the narrowing band factor, 0953-8984/10/23/002/img18, beyond that obtained from the spherical approximation of Nolting.

  5. Metal-Insulator-Semiconductor Photodetectors

    PubMed Central

    Lin, Chu-Hsuan; Liu, Chee Wee

    2010-01-01

    The major radiation of the Sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III–V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows. PMID:22163382

  6. Metal-insulator-semiconductor photodetectors.

    PubMed

    Lin, Chu-Hsuan; Liu, Chee Wee

    2010-01-01

    The major radiation of the sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III-V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

  7. Charge driven metal-insulator transitions in LaMnO3|SrTiO3 (111) superlattices

    NASA Astrophysics Data System (ADS)

    Cossu, F.; Tahini, H. A.; Singh, N.; Schwingenschlögl, U.

    2017-06-01

    Interfaces of perovskite oxides, due to the strong interplay between the lattice, charge and spin degrees of freedom, can host various phase transitions, which is particularly interesting if these transitions can be tuned by external fields. Recently, ferromagnetism was found together with a seemingly insulating state in superlattices of manganites and titanates. We therefore study the (111) oriented (\\text{LaMnO}_3)6-x\\vert(\\text{SrTiO}_3)6+x~(x = -0.5, 0, 0.5) superlattices by means of ab initio calculations, predicting a ferromagnetic ground state due to double exchange in all cases. We shed light on the ferromagnetic coupling in the LaMnO3 region and at the interfaces. The insulating states of specific superlattices can be understood on the basis of Jahn-Teller modes and electron/hole doping.

  8. Metal-insulator transition in CuIr2S4: XAS results, structure revisited, electronic structure proposed

    NASA Astrophysics Data System (ADS)

    Croft, Mark

    2006-03-01

    Interestingly, the magnetism in the spinel compound Fe3O4 (loadstone), constitutes the correlated electron material/problem of the greatest antiquity known to man. The Verwy transition problem in Fe3O4 is, by comparison, young at only 67 years of age. Recently experimental and theoretical insights into such exotic magnetic, charge, and orbital orderings in transition metal (T) spinel compounds have been rapidly emerging. The leitmotifs in these works involve: frustrated tripartite crossing 1D chains of edge-sharing T-ligand octahedra; T-d(t2g) orbital ordering onto subsets of these chains which involve d-d overlap; dimmer formation on these chains; and/or charge ordering on the chains dependent on band filling. Understanding the low temperature structural and metal (M) to insulator (I) transition in the spinel compound CuIr2S4 provides a key link in the generalization to other such systems. S K-edge X-ray absorption spectroscopy (XAS) measurements across this M-I transition reflect a dramatic Ir d-electronic state redistribution^1. These results stimulated a detailed re-evaluation of the of I-phase crystal structure in terms of: decoupled chains of IrS6 octahedra along the (110)-type directions; and an Ir^3+ (Ir^4+-Ir^4+) Ir^3+ repeat pattern ordering, where the (Ir^4+-Ir^4+) pair forms a dimmer. Further, the electronic state changes, evidenced by the XAS, motivated a model in which the I-phase involves: an orbital ordering of the highest lying t2g electron into 1D chains; the 3/4 filling of this 1D band dictating the periodicity of the orbital/charge ordering; and the direct t2g-t2g dimmer bonding production of an antibonding state prominent in the S-K edge spectrum. The generalization of these concepts to other transition metal spinels will be addressed. ^1M. Croft, W. Caliebe, H. Woo, T. A. Tyson, D. Sills, Y. S. Hor, S-W. Cheong, V. Kiryukhin, and S-J. Oh, Phys. Rev. B 67 (Rapid Comm.), 201102 (2003)

  9. Metal-insulator transition in Nd{sub 1−x}Eu{sub x}NiO{sub 3}: Entropy change and electronic delocalization

    SciTech Connect

    Jardim, R. F. Andrade, S.; Barbeta, V. B.; Escote, M. T.; Cordero, F.; Torikachvili, M. S.

    2015-05-07

    The metal-insulator (MI) phase transition in Nd{sub 1–x}Eu{sub x}NiO{sub 3}, 0 ≤ x ≤ 0.35, has been investigated through the pressure dependence of the electrical resistivity ρ(P, T) and measurements of specific heat C{sub P}(T). The MI transition temperature (T{sub MI}) increases with increasing Eu substitution and decreases with increasing pressure. Two distinct regions for the Eu dependence of dT{sub MI}/dP were found: (i) for x ≤ 0.15, dT{sub MI}/dP is nearly constant and ∼−4.3 K/kbar; (ii) for x ≥ 0.15, dT{sub MI}/dP increases with x and it seems to reach a saturation value ∼−6.2 K/kbar for the x = 0.35 sample. This change is accompanied with a strong decrease in the thermal hysteresis in ρ(P, T) between the cooling and warming cycles, observed in the vicinity of T{sub MI}. The entropy change (ΔS) at T{sub MI} for the sample x = 0, estimated by using the dT{sub MI}/dP data and the Clausius-Clapeyron equation, resulted in ΔS ∼ 1.2 J/mol K, a value in line with specific heat measurements. When the Eu concentration is increased, the antiferromagnetic (AF) and the MI transitions are separated in temperature, permitting that an estimate of the entropy change due to the AF/Paramagnetic transition be carried out, yielding ΔS{sub M} ∼ 200 mJ/mol K. This value is much smaller than that expected for a s = 1/2 spin system. The analysis of ρ(P, T) and C{sub P}(T) data indicates that the entropy change at T{sub MI} is mainly due to the electronic delocalization and not related to the AF transition.

  10. Size-dependent metal-insulator transition in platinum-dispersed silicon dioxide thin film: A candidate for future non-volatile memory

    NASA Astrophysics Data System (ADS)

    Chen, Albert B. K.

    Non-volatile random access memories (NVRAM) are promising data storage and processing devices. Various NVRAM, such as FeRAM and MRAM, have been studied in the past. But resistance switching random access memory (RRAM) has demonstrated the most potential for replacing flash memory in use today. In this dissertation, a novel RRAM material design that relies upon an electronic transition, rather than a phase change (as in chalcogenide Ovonic RRAM) or a structural change (such in oxide and halide filamentary RRAM), is investigated. Since the design is not limited to a single material but applicable to general combinations of metals and insulators, the goal of this study is to use a model material to delineate the intrinsic features of the electronic metal/insulator transition in random systems and to demonstrate their relevance to reliable memory storage and retrieval. We fabricated amorphous SiO2 thin films embedded with randomly dispersed Pt atoms. Macroscopically, this random material exhibits a percolation transition in electric conductivity similar to the one found in various insulator/metal granular materials. However, at Pt concentrations well below the bulk percolation limit, a distinct insulator to metal transition occurs in the thickness direction as the film thickness falls below electron's "diffusion" distance, which is the tunneling distance at 0K. The thickness-triggered metal- to-insulator transition (MIT) can be similarly triggered by other conditions: (a) a changing Pt concentration (a concentration-triggered MIT), (b) a changing voltage/polarity (voltage-triggered MIT), and (c) an UV irradiation (photon-triggered MIT). The resistance switching characteristics of this random material were further investigated in several device configurations under various test conditions. These include: materials for the top and bottom electrodes, fast pulsing, impedance spectroscopy, static stressing, retention, fatigue and temperature from 10K to 448K. The SiO2-Pt

  11. Field-dependent perpendicular magnetic anisotropy and interfacial metal-insulator transition in CoFeB/MgO systems

    NASA Astrophysics Data System (ADS)

    Barsukov, Igor; Fu, Yu; Safranski, C.; Chen, Yu-Jin; Youngblood, B.; Goncalves, A.; Sampaio, L.; Arias, R.; Spasova, M.; Farle, M.; Krivorotov, I.

    2015-03-01

    The CoFeB/MgO systems play a central role in magnetic tunnel junction devices due to the high tunneling magnetoresistance ratio. A strong perpendicular anisotropy (PMA) and voltage-controlled anisotropy are beneficial for spintronics application. We study PMA in thin films of Ta/Co20Fe60B20/MgO in the thickness range of 0.9-2.5 nm and find that it can be best described by the first two order terms. Surprisingly, we find PMA to be strongly field-dependent. Our results show that the field dependence has significant implications for determining and customizing magnetic anisotropy in spintronic applications. Our data suggest that it can be caused by an inhomogeneous interfacial spin pinning with a possibly ferrimagnetic phase at the CoFeB/MgO interface. We perform magnetometry and transport measurements and find a magnetization peak and resistance transitions at 160K, which are consistent with the presence of an interfacial oxide phase undergoing a Morin-like transition.

  12. Superconductivity and crystal structural origins of the metal-insulator transition in Ba6 -xSrxNb10O30 tetragonal tungsten bronzes

    NASA Astrophysics Data System (ADS)

    Kolodiaznyi, Taras; Sakurai, Hiroya; Isobe, Masaaki; Matsushita, Yoshitaka; Forbes, Scott; Mozharivskyj, Yurij; Munsie, Timothy J. S.; Luke, Graeme M.; Gurak, Mary; Clarke, David R.

    2015-12-01

    Ba6 -xSrxNb10O30 solid solution with 0 ≤ x ≤6 forms the filled tetragonal tungsten bronze (TTB) structure. The Ba-end member crystallizes in the highest symmetry P 4 /m b m space group (a =b =12.5842 (18 )Å and c =3.9995 (8 )Å ) and so do all the compositions with 0 ≤ x ≤5 . The Sr-end member of the solid solution crystallizes in the tentatively assigned A m a m space group (a *=17.506 (4 )Å , b *=34.932 (7 )Å , and c *=7.7777 (2 )Å ). The latter space group is related to the parent P 4 /m b m TTB structure as a * ≈ √{2 }a ,b * ≈2 √{2 }a ,c *=2 c . Low-temperature specific heat measurements indicate that the Ba-rich compositions with x ≤2 are conventional BCS superconductors with TC ≤1.6 K and superconducting energy gaps of ≤0.38 meV. The values of the TC in the cation-filled Nb-based TTBs reported here are comparable with those of the unfilled KxWO3 and NaxWO3 TTBs having large alkali ion deficiency. As the unit cell volume decreases with increasing x , an unexpected metal-insulator transition (MIT) in Ba6 -xSrxNb10O30 occurs at x ≥3 . We discuss the possible origins of the MIT in terms of the carrier concentration, symmetry break, and Anderson localization.

  13. Theory of the magnetic and metal-insulator transitions in RNiO3 bulk and layered structures.

    PubMed

    Lau, Bayo; Millis, Andrew J

    2013-03-22

    A slave rotor--Hartree-Fock formalism is presented for studying the properties of the p-d model describing perovskite transition metal oxides, and a flexible and efficient numerical formalism is developed for its solution. The methodology is shown to yield, within a unified formulation, the significant aspects of the rare-earth nickelate phase diagram, including the paramagnetic metal state observed for the LaNiO3 and the correct ground-state magnetic order of insulating compounds. It is then used to elucidate ground state changes occurring as morphology is varied from bulk to strained and unstrained thin-film form. For ultrathin films, epitaxial strain and charge transfer to the apical out-of-plane oxygen sites are shown to have significant impact on the phase diagram.

  14. Theory of the Magnetic and Metal-Insulator Transitions in RNiO3 Bulk and Layered Structures

    NASA Astrophysics Data System (ADS)

    Lau, Bayo; Millis, Andrew J.

    2013-03-01

    A slave rotor—Hartree-Fock formalism is presented for studying the properties of the p-d model describing perovskite transition metal oxides, and a flexible and efficient numerical formalism is developed for its solution. The methodology is shown to yield, within a unified formulation, the significant aspects of the rare-earth nickelate phase diagram, including the paramagnetic metal state observed for the LaNiO3 and the correct ground-state magnetic order of insulating compounds. It is then used to elucidate ground state changes occurring as morphology is varied from bulk to strained and unstrained thin-film form. For ultrathin films, epitaxial strain and charge transfer to the apical out-of-plane oxygen sites are shown to have significant impact on the phase diagram.

  15. Theory of the magnetic and metal-insulator transitions in RNiO3 bulk and layered

    NASA Astrophysics Data System (ADS)

    Lau, Bayo; Millis, Andrew J.

    2013-03-01

    A slave rotor-Hartree Fock formalism is presented for studying the properties of the p-d model describing perovskite transition metal oxides, and a flexible and efficient numerical formalism is developed for its solution. The methodology is shown to yield, within an unified formulation, the significant aspects of the rare earth nickelate phase diagram, including the paramagnetic metal state observed for the LaNiO3 and the correct ground-state magnetic order of insulating compounds. It is then used to elucidate ground state changes occurring as morphology is varied from bulk to strained and un-strained thin-film form. For ultrathin films, epitaxial strain and charge-transfer to the apical out-of-plane oxygen sites are shown to have significant impact on the phase diagram. This effort is supported by US National Science Foundation under grant NSF-DMR-1006282

  16. Directing Colloidal Assembly and a Metal-Insulator Transition Using a Quench-Disordered Porous Rod Template

    NASA Astrophysics Data System (ADS)

    Jadrich, Ryan B.; Schweizer, Kenneth S.

    2014-11-01

    Replica and effective-medium theory methods are employed to elucidate how to massively reconfigure a colloidal assembly to achieve globally homogeneous, strongly clustered, and percolated equilibrium states of high electrical conductivity at low physical volume fractions. A key idea is to employ a quench-disordered, large-mesh rigid-rod network as a templating internal field. By exploiting bulk phase separation frustration and the tunable competing processes of colloid adsorption on the low-dimensional network and fluctuation-driven colloid clustering in the pore spaces, two distinct spatial organizations of greatly enhanced particle contacts can be achieved. As a result, a continuous, but very abrupt, transition from an insulating to metallic-like state can be realized via a small change of either the colloid-template or colloid-colloid attraction strength. The approach is generalizable to more complicated template or colloidal architectures.

  17. Key role of lattice symmetry in the metal-insulator transition of NdNiO3 films

    SciTech Connect

    Zhang, Jack Y.; Kim, Honggyu; Mikheev, Evgeny; Hauser, Adam J.; Stemmer, Susanne

    2016-04-01

    Here, bulk NdNiO3 exhibits a metal-to-insulator transition (MIT) as the temperature is lowered that is also seen in tensile strained films. In contrast, films that are under a large compressive strain typically remain metallic at all temperatures. To clarify the microscopic origins of this behavior, we use position averaged convergent beam electron diffraction in scanning transmission electron microscopy to characterize strained NdNiO3 films both above and below the MIT temperature. We show that a symmetry lowering structural change takes place in case of the tensile strained film, which undergoes an MIT, but is absent in the compressively strained film. Using space group symmetry arguments, we show that these results support the bond length disproportionation model of the MIT in the rare-earth nickelates. Furthermore, the results provide insights into the non-Fermi liquid phase that is observed in films for which the MIT is absent.

  18. Key role of lattice symmetry in the metal-insulator transition of NdNiO3 films

    PubMed Central

    Zhang, Jack Y.; Kim, Honggyu; Mikheev, Evgeny; Hauser, Adam J.; Stemmer, Susanne

    2016-01-01

    Bulk NdNiO3 exhibits a metal-to-insulator transition (MIT) as the temperature is lowered that is also seen in tensile strained films. In contrast, films that are under a large compressive strain typically remain metallic at all temperatures. To clarify the microscopic origins of this behavior, we use position averaged convergent beam electron diffraction in scanning transmission electron microscopy to characterize strained NdNiO3 films both above and below the MIT temperature. We show that a symmetry lowering structural change takes place in case of the tensile strained film, which undergoes an MIT, but is absent in the compressively strained film. Using space group symmetry arguments, we show that these results support the bond length disproportionation model of the MIT in the rare-earth nickelates. Furthermore, the results provide insights into the non-Fermi liquid phase that is observed in films for which the MIT is absent. PMID:27033955

  19. Key role of lattice symmetry in the metal-insulator transition of NdNiO3 films

    DOE PAGES

    Zhang, Jack Y.; Kim, Honggyu; Mikheev, Evgeny; ...

    2016-04-01

    Here, bulk NdNiO3 exhibits a metal-to-insulator transition (MIT) as the temperature is lowered that is also seen in tensile strained films. In contrast, films that are under a large compressive strain typically remain metallic at all temperatures. To clarify the microscopic origins of this behavior, we use position averaged convergent beam electron diffraction in scanning transmission electron microscopy to characterize strained NdNiO3 films both above and below the MIT temperature. We show that a symmetry lowering structural change takes place in case of the tensile strained film, which undergoes an MIT, but is absent in the compressively strained film. Usingmore » space group symmetry arguments, we show that these results support the bond length disproportionation model of the MIT in the rare-earth nickelates. Furthermore, the results provide insights into the non-Fermi liquid phase that is observed in films for which the MIT is absent.« less

  20. The metal-insulator transition in vanadium dioxide: A view at bulk and surface contributions for thin films and the effect of annealing

    NASA Astrophysics Data System (ADS)

    Yin, W.; West, K. G.; Lu, J. W.; Pei, Y.; Wolf, S. A.; Reinke, P.; Sun, Y.

    2009-06-01

    Vanadium dioxide is investigated as potential oxide barrier in spin switches, and in order to incorporate VO2 layers in complex multilayer devices, it is necessary to understand the relation between bulk and surface/interface properties. Highly oriented VO2 thin films were grown on (0001) sapphire single crystal substrates with reactive bias target ion beam deposition. In the analysis of the VO2 films, bulk-sensitive methods [x-ray diffraction (XRD) and transport measurements] and surface sensitive techniques [photoelectron spectroscopy (PES) and scanning tunneling microscopy and spectroscopy] were employed. The samples were subjected to heating cycles with annealing temperatures of up to 425 and 525K. Prior to annealing the VO2 films exhibit the transition from the monoclinic to the tetragonal phase with the concurrent change in conductivity by more than a factor of 103 and their phase purity is confirmed by XRD. Annealing to 425K and thus cycling across the metal-insulator transition (MIT) temperature has no impact on the bulk properties of the VO2 film but the surface undergoes irreversible electronic changes. The observation of the valence band with PES during the annealing illustrates that the surface adopts a partially metallic character, which is retained after cooling. Annealing to a higher temperature (525K ) triggers a modification of the bulk, which is evidenced by a considerable reduction in the MIT characteristics, and a degradation in crystallite morphology. The local measurement of the conductivity with scanning tunneling spectroscopy shows the transition of the surface from predominantly semiconducting surface prior to annealing to a surface with an overwhelming contribution from metallic sections afterward. The spatial distribution of metallic regions cannot be linked in a unique manner to the crystallite size or location within the crystallites. The onset of oxygen depletion at the surface is held responsible for this behavior. The onset of bulk

  1. Metal-insulator transition of the two-band Hubbard model in infinite dimension and its relevance to a strongly correlated electron system: NiS2-xSex

    NASA Astrophysics Data System (ADS)

    Watanabe, H.; Doniach, S.

    1998-02-01

    We report a study of metal-insulator transition of a strongly correlated two-band Hubbard model using a dynamical mean-field theory approach. We find that the Mott transition appears at half filling even at T=0 in contrast to the one-band Hubbard model. The transition is characterized by the development of a ``Kondo-like'' peak near Fermi level. We also find a signature of the coexistence of metallic and antiferromagnetic phases from the study of the single-particle Green's function and the magnetic long-range order due to the superexchange coupling between the correlated electrons. We then suggest the relevance of our results to the metal-insulator transition and the recent angle-resolved photoemission measurements of NiS2-xSex. We also study the effect of carrier doping and the comparison of our findings with the experimental results suggests the possible importance of departures from stoichiometry associated with the Se substitution. The relevance of our results to high-temperature superconductivity is also discussed.

  2. Localization of Metal-Induced Gap States at the Metal-Insulator Interface: Origin of Flux Noise in SQUIDs and Superconducting Qubits

    NASA Astrophysics Data System (ADS)

    Choi, Sangkook; Lee, Dung-Hai; Louie, Steven G.; Clarke, John

    2010-03-01

    The origin of magnetic flux noise in dc Superconducting Quantum Interference Devices (SQUIDs) with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 25 years. This noise limits both the low frequency performance of SQUIDs and the decoherence time of flux-sensitive superconducting qubits, making scaling-up for quantum computing problematic. Recent calculations and experiments indicate that the noise is generated by electrons that randomly reverse their spin directions. Their areal density of ˜ 5 x 10^17 m-2 is relatively insensitive to the nature of the superconductor and substrate. Here, we propose that the local magnetic moments originate in metal-induced gap states (MIGSs) localized by potential disorder at the metal-insulator interface. MIGSs are particularly sensitive to such disorder, so that the localized states have a Coulomb repulsion sufficiently large to make them singly occupied. Our calculations demonstrate that a modest level of disorder generates the required areal density of localized moments. This result suggests that magnetic flux noise could be reduced by fabricating superconductor-insulator interfaces with less disorder. Support: NSF DMR07-05941, US DOE De-AC02-05CH11231, Samsung Foundation, Teragrid, NERSC.

  3. Spin-orbit contribution to the Hall coefficient approaching the metal-insulator transition: An explanation for the critical behavior of Ge:Sb

    NASA Astrophysics Data System (ADS)

    Castner, T. G.

    1990-09-01

    It is demonstrated that the band spin-orbit contribution to the Hall conductivity σyx can qualitatively explain the critical behavior of the Hall coefficient RH for Ge:Sb reported by Field and Rosenbaum. The spin-orbit contribution to σyx for n-type Ge has been experimentally determined by Chazalviel and leads to an R-1H versus (n/nc-1) dependence that is consistent with the Ge:Sb data. This result demonstrates a significant extraordinary contribution to RH for some very weakly paramagnetic metal-insulator systems when closely approaching the critical density nc.

  4. Magnetotransport properties of strained Ga0.95Mn0.05As epilayers close to the metal-insulator transition: Description using Aronov-Altshuler three-dimensional scaling theory

    NASA Astrophysics Data System (ADS)

    Honolka, J.; Masmanidis, S.; Tang, H. X.; Awschalom, D. D.; Roukes, M. L.

    2007-06-01

    The magnitude of the anisotropic magnetoresistance (AMR) and the longitudinal resistance in compressively strained Ga0.95Mn0.05As epilayers were measured down to temperatures as low as 30mK . Below temperatures of 3K , the conductivity decreases ∝T1/3 over 2 orders of magnitude in temperature. The conductivity can be well described within the framework of a three-dimensional scaling theory of Anderson’s transition in the presence of spin scattering in semiconductors. It is shown that the samples are on the metallic side but very close to the metal-insulator transition. At lowest temperatures, a decrease in the AMR effect is observed, which is assigned to changes in the coupling between the remaining itinerant carriers and the local Mn 5/2 -spin moments.

  5. Phase coexistence near the metal-insulator transition in a compressively strained NdNi O3 film grown on LaAl O3 : Scanning tunneling, noise, and impedance spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Bisht, Ravindra Singh; Samanta, Sudeshna; Raychaudhuri, A. K.

    2017-03-01

    We report an observation of phase coexistence near the metal-insulator transition (MIT) in a film of NdNi O3 grown on crystalline substrate LaAl O3 . This was established through a combination of three techniques, namely, scanning tunneling spectroscopy, 1 /f noise spectroscopy, and impedance spectroscopy experiments. The spatially resolved scanning tunneling spectroscopy showed that the two coexisting phases have different types of density of states (DOS) at the Fermi level. One phase showed a depleted DOS close to EF with a small yet finite correlation gap, while the other coexisting phase showed a metal-like DOS that had no depletion. The existence of the phase separation leads to a jump in the resistance fluctuation (as seen through 1 /f noise spectroscopy) at the transition, and, notably, the fluctuation becomes non-Gaussian when there is a phase separation even in the metallic phase. This was corroborated by the impedance spectroscopy, which showed a broad hump in capacitance at the transition region as a signature of the existence of two phases that have widely different electrical conductivities. The phase separation starts well within the metallic phase much above the transition temperature and makes the sample electronically "inhomogeneous" in nanoscopic scale close to the transition. We discuss certain scenarios that lead to such a phase separation in the general context of strongly correlated oxides.

  6. Infrared spectroscopic study of the local structural changes across the metal insulator transition in nickel-doped GdBaCo{sub 2}O{sub 5.5}

    SciTech Connect

    Yasodha, P.; Premila, M.; Bharathi, A.; Valsakumar, M.C.; Rajaraman, R.; Sundar, C.S.

    2010-11-15

    Phonons in GdBaCo{sub 2}O{sub 5.5} have been identified using infrared spectroscopy and their mode assignments have been carried out using ab initio lattice dynamical calculations. Metal insulator transitions in undoped and nickel-doped GdBaCo{sub 2}O{sub 5.5} have been probed using infrared absorption spectroscopy. The phonon modes corresponding to the bending mode of the CoO{sub 6} octahedra/pyramids are seen to soften, broaden and develop an asymmetry across the insulator-metal transition pointing to extensive electron phonon interaction effects in these systems. Correlated changes of the phonon line shape parameters associated with the transition indicate a suppression of T{sub MIT} with increased nickel doping of the cobalt sublattice. Temperature dependence of the octahedral stretching mode frequencies in undoped GdBaCo{sub 2}O{sub 5.5} points to distinct structural distortions accompanying the high temperature metallic transition. - Graphical abstract: Softening of the bending mode across T{sub MIT}.

  7. Changes in the electronic structure and spin dynamics across the metal-insulator transition in LaLa1-xSrxCoO3

    SciTech Connect

    Smith, R. X.; Hoch, M. J. R.; Moulton, W. G.; Kuhns, P. L.; Reyes, A. P.; Boebinger, G. S.; Zheng, H.; Mitchell, J. F.

    2016-01-25

    The magnetoelectronic properties of La1-xSrxCoO3, which include giant magnetoresistance, are strongly dependent on the level of hole doping. The system evolves, with increasing x, from a spin glass insulator to a metallic ferromagnet with a metal-insulator (MI) transition at xC ~ 0.18. Nanoscale phase separation occurs in the insulating phase and persists, to some extent, into the just-metallic phase. The present experiments at 4.2 K have used 139La NMR to investigate the transition from hopping dynamics for x < xC to Korringa-like ferromagnetic metal behavior for x > xC. A marked decrease in the spin-lattice relaxation rate is found in the vicinity of xC as the MI transition is crossed. Lastly, this behavior is accounted for in terms of the evolution of the electronic structure and dynamics with cluster size.

  8. Tunable metal-insulator transition in Nd{sub 1−x}Y{sub x}NiO{sub 3} (x = 0.3, 0.4) perovskites thin film at near room temperature

    SciTech Connect

    Shao, Tao; Qi, Zeming Wang, Yuyin; Li, Yuanyuan; Yang, Mei; Zhang, Guobin; Wang, Yu; Liu, Miao

    2015-07-13

    Metal-insulator transition (MIT) occurs due to the charge disproportionation and lattice distortions in rare-earth nickelates. Existing studies revealed that the MIT behavior of rare-earth nickelates is fairly sensitive to external stress/pressure, suggesting a viable route for MIT strain engineering. Unlike applying extrinsic strain, the MIT can also be modulated by through rare-earth cation mixing, which can be viewed as intrinsic quantum stress. We choose Nd{sub 1−X}Y{sub X}NiO{sub 3} (x = 0.3, 0.4) perovskites thin films as a prototype system to exhibit the tunable sharp MIT at near room temperature. By adjusting Y concentration, the transition temperature of the thin films can be changed within the range of 340–360 K. X-ray diffraction, X-ray absorption fine structure (XAFS), and in situ infrared spectroscopy are employed to probe the structural and optical property variation affected by composition and temperature. The infrared transmission intensity decreases with temperature across the MIT, indicating a pronounced thermochromic effect. Meanwhile, the XAFS result exhibits that the crystal atomistic structure changes accompanying with the Y atoms incorporation and MIT phase transition. The heavily doped Y atoms result in the pre-edge peak descent and Ni-O bond elongation, suggesting an enhanced charge disproportionation effect and the weakening of hybridization between Ni-3d and O-2p orbits.

  9. Finite-size driven topological and metal-insulator transition in (Bi1-xInx)2 Se3thin films

    NASA Astrophysics Data System (ADS)

    Salehi, Maryam; Shapourian, Hassan; Koirala, Nikesh; Brahlek, Matthew; Moon, Jisoo; Oh, Seongshik

    In a topological insulator (TI), if one of its heavy elements is replaced by a light one, the spin-orbit coupling (SOC) strength decreases and eventually the TI transforms into a normal insulator beyond a critical level of substitution.This is the standard description of the topological phase transition (TPT). However, this notion of TPT, driven solely by the SOC (or something equivalent), is not complete for finite size samples considering that the thickness of the topological surface states diverges at the critical point. Here, on specially-engineered (BixIn1-x)2 Se3 thin films, using systematic transport measurments we show that not only the SOC but also the finite sample size can induce TPT. This study sheds light on the role of spatial confinement as an extra tuning parameter controlling the topological critical point.

  10. Magnetism variations and susceptibility hysteresis at the metal-insulator phase transition temperature of VO2 in a composite film containing vanadium and tungsten oxides

    NASA Astrophysics Data System (ADS)

    Akande, Amos A.; Rammutla, Koena E.; Moyo, Thomas; Osman, Nadir S. E.; Nkosi, Steven S.; Jafta, Charl J.; Mwakikunga, Bonex W.

    2015-02-01

    We report on the magnetic property of 0.67-WO3+0.33-VOx mixture film deposit on the corning glass substrate using the chemical sol-gel and atmospheric pressure chemical vapor deposition (APCVD) methods. The XRD and Raman spectroscopy confirm species of both materials, and the morphological studies with FIB-SEM and TEM reveal segregation of W and V atoms. XPS reveals that V4+ from VO2 forms only 11% of the film; V3+ in the form of V2O3 form 1% of the film, 21% is V5+ from V2O5 and 67% is given to W6+ from WO3. The analysis of the ESR data shows some sharp changes in the magnetism near the metal-to-insulator (MIT), which could be theoretically interpreted as the ordering or alignment of electron spins from net moment nature to parallel alignment of magnetic moment. The derivatives of magnetic susceptibility established the thermally induced magnetic property: two distinct transitions of 339 K for heating data and 338 K for cooling data for 151.2 mT field were obtained. Similar results were also obtained for 308.7 mT field, 336 K for heating data and 335 K for cooling data. VSM results confirm a paramagnetic phase with a small amount of magnetically ordered phase.

  11. Role of tetravalent ion in metal-insulator transition in (La{sub 0.1}Ca{sub 0.9})(Mn{sub 1-x}Ti{sub x})O{sub 3}

    SciTech Connect

    Taguchi, Hideki; Sonoda, Masanori; Nagao, Mahiko; Kido, Hiroyasu

    1996-11-01

    Perovskite-type (La{sub 0.1}Ca{sub 0.9})(Mn{sub 1-x}Ti{sub x})O{sub 3} (0 {le} x {le} 0.9) has the orthorhombic GdFeO{sub 3}-type structure with the space group Pnma. With increasing x, the average (Mn, Ti)-O distance increases linearly and the average angles for (Mn,Ti)-O-(Mn, Ti) decrease slightly. The electrical resistivity ({rho}) of all manganates was measured in the temperature range from 10 to 953 K. All manganates are n-type semiconductors at low temperature. At high temperature, the manganates exhibit a metal-insulator transition in the range O{le}x{le}0.3. d{rho}/dT in the metallic region depends on the composition. From these results, it is considered that the Ti{sup 4+} ion makes the cation-anion-cation overlap integrals ({Delta}{sub cac}{sup {pi}} and {Delta}{sub cac}{sup {sigma}}) weaken.

  12. Controlling the sharpness of metal-insulator transition in epitaxial (La1-xPrx)0.67Ca0.33MnO3 (0 ≤ x ≤ 0.35) films

    NASA Astrophysics Data System (ADS)

    Chen, Pingfan; Huang, Zhen; Tan, Xuelian; Chen, Binbin; Zhi, Bowen; Gao, Guanyin; Chen, Feng; Wu, Wenbin

    2014-10-01

    We report that epitaxial strain and chemical doping can be used cooperatively to tune the sharpness of metal-insulator transition (MIT) in epitaxial (La1-xPrx)0.67Ca0.33MnO3 (LPCMO) films. Compared to multiple MITs in anisotropically strained LPCMO/(LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7(001)C (LSAT) films with a phase-separated ground state, the lattice-matched LPCMO/NdGaO3(110)Or (NGO) films show a sharp MIT near the Curie temperature (TC), with a ferromagnetic-metallic ground state. The sharpness of MIT, as evaluated by the temperature coefficient of resistance (TCR), can be two times larger in LPCMO/NGO films than in LPCMO/LSAT films. Moreover, for LPCMO/NGO films, TCR greatly relies on the Pr doping level x, where a maximum TCR value of 88.17% K-1 can be obtained at x = 0.25, but shows less dependence on the film thicknesses. These results suggest that the combination of epitaxial strain and chemical doping could be employed to control not only the ground state of the manganite films, but the sharpness of MIT at various TC, providing the feasibility to design manganite-based infrared devices in a broad temperature range.

  13. Relationship between superconductor and metal-insulator transitions in a large class of tetragonal 1:2:3 cuprates Ca-R-Ba-Cu-O (R=La,Nd)

    NASA Astrophysics Data System (ADS)

    Goldschmidt, D.; Knizhnik, A.; Direktovitch, Y.; Reisner, G. M.; Eckstein, Y.

    1995-11-01

    We report superconductor and transport properties of a large class of tetragonal 1:2:3 cuprates represented by the chemical formula (CaxR1-x)[Ba3-z-xRz-(1-x)]Cu3Oy, where R=La or Nd and existing as high-purity materials in a large range of z and x. At a given z, these materials maintain, through compensating cosubstitutions, a constant charge Q of the noncopper cations (Q=6+z) independent of x. By accurate control of oxygen content y, both cation and anion charge sources were kept constant. Under these isoelectronic conditions (constant electron concentration n) big changes in transition temperature Tc, resistivity ρ and thermopower (TEP) S occur, suggesting that the microscopic hole density in the CuO2 planes h changes. Having a single Tmaxc (maximal Tc), this material family behaves as a single material. Besides, for all values of Q, x, and y and for each R we show that Tc, ρ, and S can each be represented by a single curve when plotted as a function of y-yM-I(Q,x), where yM-I denotes the value of y at the metal-insulator (M-I) transition. Therefore, there exists a one to one correspondence between h and y-yM-I, but there is no straightforward relation between h and n. We found an empirical formula describing the functional dependence of yM-I on Q and x. This allows one to estimate yM-I, Tc, ρ, and S in many materials. Our results are interpreted in terms of a simple band picture which is modified to consider the existence of low-mobility states in the vicinity of EF. This accounts for the relatively low TEP at the M-I transition.

  14. Physical and electrical properties of induced high-k ZrHfO crystallization with ZrN cap by high power impulse magnetron sputtering for metal-gate metal-insulator-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Tsai, Jung-Ruey; Juan, Pi-Chun; Lin, Cheng-Li; Lin, Guo-Cheng

    2017-01-01

    Metal-gate TiN/ZrN/ZrHfO/p-Si metal-insulator-semiconductor (MIS) structures have been fabricated in this work. The physical and electrical properties were characterized. The crystallization of high-k ZrHfO thin-film is induced by high power impulse magnetron sputtering (HIPIMS) during the deposition of ZrN capping layer. The binding energies and depth profiles were investigated by X-ray photoelectron spectroscopy (XPS). It is found that Zr and Hf out-diffusion from high-k dielectric in samples with HIPIMS is lesser than those in samples with the conventional DC magnetron sputtering (DCMS). The dielectric constant which strongly relates to the tetragonal phase becomes higher and the flatband voltage shift shows smaller by using the HIPIMS method than by the conventional DCMS. The cation and anion vacancies have been investigated by the defect reaction model.

  15. Nonadiabatic effects in a generalized Jahn-Teller lattice model: Heavy and light polarons, pairing, and the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Majerníková, Eva; Riedel, J.; Shpyrko, S.

    2002-05-01

    The self-consistent ground state polaron potential of one-dimensional lattice of two-level molecules with spinless electrons and two dispersionless phonon modes with linear coupling and quantum phonon-assisted (nonadiabatic) transitions between the levels is found anharmonic in phonon displacements. As a function of these, the potential shows a crossover from two nonequivalent broad minima to a single narrow minimum which correspond to the positions of the levels in the ground state. Generalized variational approach respecting the mixing of levels (reflection) via a variational parameter implies prominent nonadiabatic effects: (i) In the limit of the symmetric E⊗e Jahn-Teller situation they cause transition between the regime of the predominantly one-level ``heavy'' polaron and a ``light'' polaron oscillating between the levels due to phonon assistance with almost vanishing polaron displacement. Vanishing polaron selflocalization implies enhancement of the electron transfer due to decrease of the ``heavy'' polaron mass (undressing) at the point of the transition. There can occur pairing of ``light'' polarons due to exchange of virtual phonons. Continuous transition to new energy ground state close to the transition from ``heavy'' polaron phase to ``light'' (bi)polaron phase occurs. In the ``heavy'' phase, we have found anomalous (anharmonic) enhancements of quantum fluctuations of the phonon coordinate, conjugated momentum and their product in the ground state as functions of the effective coupling which reach their maxima at E⊗e JT symmetry. They decrease rapidly to their harmonic values as soon as the ``light'' phase is stabilized. (ii) Nonadiabatic dependence of the polaron mass (Debye-Waller screening) on the optical phonon frequency appears. (iii) The contribution of Rabi oscillations to the transfer enhances significantly quantum shift of the insulator-metal transition line to higher values of the critical effective electron-phonon coupling supporting so

  16. Raman scattering investigation across the magnetic and metal-insulator transition in rare earth nickelate RNiO3 ( R=Sm , Nd) thin films

    NASA Astrophysics Data System (ADS)

    Girardot, C.; Kreisel, J.; Pignard, S.; Caillault, N.; Weiss, F.

    2008-09-01

    We report a temperature-dependent Raman scattering investigation of thin-film rare earth nickelates SmNiO3 , NdNiO3 , and Sm0.60Nd0.40NiO3 which present a metal-to-insulator (MI) transition at TMI and an antiferromagnetic-paramagnetic Néel transition at TN . Our results provide evidence that all investigated samples present a structural phase transition at TMI but the Raman signature across TMI is significantly different for NdNiO3 (TMI=TN) compared to SmNiO3 and Sm0.60Nd0.40NiO3 (TMI≠TN) . It is namely observed that the paramagnetic-insulator phase (TNtransition. The observed behavior might well be a general feature for all rare earth nickelates with TMI≠TN and illustrates intriguing coupling mechanism in the TN

  17. The metal-insulator transition in nanocrystalline Pr0.67Ca0.33MnO3: the correlation between supercooling and kinetic arrest.

    PubMed

    Rawat, R; Chaddah, P; Bag, Pallab; Das, Kalipada; Das, I

    2012-10-17

    The transition and hysteresis widths of a disorder broadened first order magnetic transition vary in H-T space which influences the co-existing phase fraction at low temperature arising due to kinetic arrest of the first order transition. We explored the role of change in the relative width of the supercooling/superheating band and kinetic arrest band for a ferromagnetic metallic to antiferromagnetic insulating transition. It is shown that for a correlated kinetic arrest and supercooling bands, the topology of the devitrification curves (or transformation across the (H(K),T(K)) band during warming) changes with the change in the relative width of these two bands. In addition to this, for a broader kinetic arrest band, the transformation temperature across the superheating band under constant H now depends on the arrested phase fraction. These predictions have been tested on nanocrystalline Pr(0.67)Ca(0.33)MnO(3), which is known to show a large variation in hysteresis width in H-T space. This is the first report where correlation between the kinetic arrest band and the supercooling band has been shown experimentally, in contrast to the universal observation of anticorrelation reported so far.

  18. Theoretical study of the thickness dependence of the metal-insulator transition in Bi2Sr2Co2O8 nanosheets

    NASA Astrophysics Data System (ADS)

    Huang, Xiaokun; Zhang, Weiyi

    2017-07-01

    The bulk Bi2Sr2Co2O8 crystal is an insulator at low temperature and experiences an insulator-metal transition at TC≈60 K . The new experiment showed that TC increases to 140 K for a mechanically exfoliated nanosheet of four blocks and is beyond room temperature for nanosheets thinner than four blocks. We show that the thickness-dependent insulator-metal transition observed in Bi2Sr2Co2O8 nanosheets can naturally be explained by the strongly correlated low-spin-state insulator (LS state) and intermediate-spin-low-spin-state metal (IS-LS state). In particular, the energy difference between the LS state and IS-LS state qualitatively reproduces the trend of the transition temperature with the nanosheet thickness. The predicted transition temperature of a nanosheet with three blocks is only slightly above room temperature, a result that can be used to check our proposed mechanism. Further experiments on the distinct magnetotransport properties and spin-fluctuation behaviors of the LS state and IS-LS state are also very helpful to resolve the issue. The weak interblock binding is also consistent with the layer-resolved partial densities of states.

  19. Electric field effect near the metal-insulator transition of a two-dimensional electron system in SrTiO3

    NASA Astrophysics Data System (ADS)

    Ahadi, Kaveh; Shoron, Omor F.; Marshall, Patrick B.; Mikheev, Evgeny; Stemmer, Susanne

    2017-02-01

    SmTiO3/SrTiO3 interfaces exhibit a two-dimensional electron system with carrier densities in the order of 3 × 1014 cm-2 due to the polar discontinuity at the interface. Here, electric field effect is used to investigate an electron system at this interface whose carrier density has been depleted substantially by the gate metal and by reducing the thickness of the SmTiO3. At zero applied gate voltage, the sheet resistance exceeds the quantum resistance, h/e2, by more than an order of magnitude, and the SrTiO3 channel is in the hopping transport regime. The electric field modulates the carrier density in the channel, which approaches the transition to a metal at positive gate bias. The channel resistances are found to scale by a single parameter that depends on the gate voltage, similar to two-dimensional electron systems in high-quality semiconductors.

  20. Thermoelectric effect across the metal-insulator domain walls in VO2 microbeams.

    PubMed

    Cao, J; Fan, W; Zheng, H; Wu, J

    2009-12-01

    We report on measurements of Seebeck effect in single-crystal VO(2) microbeams across their metal-insulator phase transition. One-dimensionally aligned metal-insulator domain walls were reversibly created and eliminated along single VO(2) beams by varying temperature, which allows for accurate extraction of the net contribution to the Seebeck effect from these domain walls. We observed significantly lower Seebeck coefficient in the metal-insulator coexisting regime than predicted by a linear combination of contributions from the insulator and metal domains. This indicates that the net contribution of the domain walls has an opposite sign from that of the insulator and metal phases separately. Possible origins that may be responsible for this unexpected effect were discussed in the context of complications in this correlated electron material.

  1. Electric field induced metal-insulator transition in VO2 thin film based on FTO/VO2/FTO structure

    NASA Astrophysics Data System (ADS)

    Hao, Rulong; Li, Yi; Liu, Fei; Sun, Yao; Tang, Jiayin; Chen, Peizu; Jiang, Wei; Wu, Zhengyi; Xu, Tingting; Fang, Baoying

    2016-03-01

    A VO2 thin film has been prepared using a DC magnetron sputtering method and annealing on an F-doped SnO2 (FTO) conductive glass substrate. The FTO/VO2/FTO structure was fabricated using photolithography and a chemical etching process. The temperature dependence of the I-V hysteresis loop for the FTO/VO2/FTO structure has been analyzed. The threshold voltage decreases with increasing temperature, with a value of 9.2 V at 20 °C. The maximum transmission modulation value of the FTO/VO2/FTO structure is 31.4% under various temperatures and voltages. Optical modulation can be realized in the structure by applying an electric field.

  2. Metal-Insulator-Semiconductor Nanowire Network Solar Cells.

    PubMed

    Oener, Sebastian Z; van de Groep, Jorik; Macco, Bart; Bronsveld, Paula C P; Kessels, W M M; Polman, Albert; Garnett, Erik C

    2016-06-08

    Metal-insulator-semiconductor (MIS) junctions provide the charge separating properties of Schottky junctions while circumventing the direct and detrimental contact of the metal with the semiconductor. A passivating and tunnel dielectric is used as a separation layer to reduce carrier recombination and remove Fermi level pinning. When applied to solar cells, these junctions result in two main advantages over traditional p-n-junction solar cells: a highly simplified fabrication process and excellent passivation properties and hence high open-circuit voltages. However, one major drawback of metal-insulator-semiconductor solar cells is that a continuous metal layer is needed to form a junction at the surface of the silicon, which decreases the optical transmittance and hence short-circuit current density. The decrease of transmittance with increasing metal coverage, however, can be overcome by nanoscale structures. Nanowire networks exhibit precisely the properties that are required for MIS solar cells: closely spaced and conductive metal wires to induce an inversion layer for homogeneous charge carrier extraction and simultaneously a high optical transparency. We experimentally demonstrate the nanowire MIS concept by using it to make silicon solar cells with a measured energy conversion efficiency of 7% (∼11% after correction), an effective open-circuit voltage (Voc) of 560 mV and estimated short-circuit current density (Jsc) of 33 mA/cm(2). Furthermore, we show that the metal nanowire network can serve additionally as an etch mask to pattern inverted nanopyramids, decreasing the reflectivity substantially from 36% to ∼4%. Our extensive analysis points out a path toward nanowire based MIS solar cells that exhibit both high Voc and Jsc values.

  3. Millimeter Wave Metal-Insulator-Metal Detector/Mixer Diode.

    DTIC Science & Technology

    1983-12-01

    AO-A138 391 MILLIMETER WAVE METAL-INSULATOR- METAL DETECTOR /MIXER 1/1 DIODE(VI NORTH CAROLIN A AGRICULTURAL A NO TECHNI CA L STATE UNIV GREENSRO. C TV...163-A I V AFWAL-TR-83-1179 MILLIMETER WAVE METAL-INSULATOR- METAL DETECTOR /MIXER DIODE CHUNG YU NORTH CAROLINA A&T STATE UNIVERSITY GREENSBORO, NORTH...TITLE (ad subsorle.I S. TYPE CrjflT&PEO OER MILLIMETER WAVE May, 1981--July, 1983 METAL-INSULATOR- METAL DETECTOR /MIXER G. PERFORMING ORG. REPORT

  4. Slow light in metal-insulator-metal waveguide by negative Goos-Hänchen shift

    NASA Astrophysics Data System (ADS)

    Oh, Geum-Yoon; Chheang, Vuthy; Kim, Doo-Gun; Kim, Tae-Ryong; Jun, Li; Kim, Hong-Seung; Choi, Young-Wan

    2014-12-01

    We demonstrated group velocity delay using a metal-insulator-metal structure for slow light that would be very simple to fabricate. A negative Goos-Hänchen shift of the surface plasmon resonance can be caused by incident radiation while reflecting, resulting in a general group delay. Using this phenomenon, we induced a group delay of 70 fs using a very simple 20-μm-long waveguide.

  5. Nano-optical investigations of the metal-insulator phase behavior of individual VO(2) microcrystals.

    PubMed

    Jones, Andrew C; Berweger, Samuel; Wei, Jiang; Cobden, David; Raschke, Markus B

    2010-05-12

    Despite the relatively simple stoichiometry and structure of VO(2), many questions regarding the nature of its famous metal-insulator transition (MIT) remain unresolved. This is in part due to the prevailing use of polycrystalline film samples and the limited spatial resolution in most studies, hindering access to and control of the complex phase behavior and its inevitable spatial inhomogeneities. Here, we investigate the MIT and associated nanodomain formation in individual VO(2) microcrystals subject to substrate stress. We employ symmetry-selective polarization Raman spectroscopy to identify crystals that are strain-stabilized in either the monoclinic M1 or M2 insulating phase at room-temperature. Raman measurements are further used to characterize the phase dependence on temperature, identifying the appearance of the M2 phase during the MIT. The associated formation and spatial evolution of rutile (R) metallic domains is studied with nanometer-scale spatial resolution using infrared scattering-scanning near-field optical microscopy (s-SNOM). We deduce that even for small crystals of VO(2), the MIT is influenced by the competition between the R, M1, and M2 crystal phases with their different lattice constants subjected to the external substrate-induced stress. The results have important implications for the interpretation of the investigations of conventional polycrystalline thin films where the mutual interaction of constituent crystallites may affect the nature of the MIT in VO(2).

  6. Suppression of the metal-insulator transition by magnetic field in (Pr{sub 1−y}Y{sub y}){sub 0.7}Ca{sub 0.3}CoO{sub 3} (y = 0.0625)

    SciTech Connect

    Naito, Tomoyuki Fujishiro, Hiroyuki; Nishizaki, Terukazu; Kobayashi, Norio; Hejtmánek, Jiří; Knížek, Karel; Jirák, Zdeněk

    2014-06-21

    The (Pr{sub 1−y}Y{sub y}){sub 0.7}Ca{sub 0.3}CoO{sub 3} compound (y = 0.0625, T{sub MI-SS}=40 K), at the lower limit for occurrence of the first-order metal-insulator (MI) and simultaneous spin-state (SS) transitions, has been studied using electrical resistivity and magnetization measurements in magnetic fields up to 17 T. The isothermal experiments demonstrate that the low-temperature insulating phase can be destabilized by an applied field and the metallic phase returns well below the transition temperature T{sub MI-SS}. The reverse process with decreasing field occurs with a significant hysteresis. The temperature scans taken at fixed magnetic fields reveal a parabolic-like decrease in T{sub MI-SS} with increasing field strength and a complete suppression of the MI-SS transition in fields above 9 T.

  7. Gravitationally induced quantum transitions

    NASA Astrophysics Data System (ADS)

    Landry, A.; Paranjape, M. B.

    2016-06-01

    In this paper, we calculate the probability for resonantly inducing transitions in quantum states due to time-dependent gravitational perturbations. Contrary to common wisdom, the probability of inducing transitions is not infinitesimally small. We consider a system of ultracold neutrons, which are organized according to the energy levels of the Schrödinger equation in the presence of the Earth's gravitational field. Transitions between energy levels are induced by an oscillating driving force of frequency ω . The driving force is created by oscillating a macroscopic mass in the neighborhood of the system of neutrons. The neutron lifetime is approximately 880 sec while the probability of transitions increases as t2. Hence, the optimal strategy is to drive the system for two lifetimes. The transition amplitude then is of the order of 1.06 ×10-5, and hence with a million ultracold neutrons, one should be able to observe transitions.

  8. Robust Interfacial Exchange Bias and Metal-Insulator Transition Influenced by the LaNiO3 Layer Thickness in La0.7Sr0.3MnO3/LaNiO3 Superlattices.

    PubMed

    Zhou, Guowei; Song, Cheng; Bai, Yuhao; Quan, Zhiyong; Jiang, Fengxian; Liu, Wenqing; Xu, Yongbing; Dhesi, Sarnjeet S; Xu, Xiaohong

    2017-01-25

    Artificial heterostructures based on LaNiO3 (LNO) have been widely investigated with the aim to realize the insulating antiferromagnetic state of LNO. In this work, we grew [(La0.7Sr0.3MnO3)5-(LaNiO3)n]12 superlattices on (001)-oriented SrTiO3 substrates by pulsed laser deposition and observed an unexpected exchange bias effect in field-cooled hysteresis loops. Through X-ray absorption spectroscopy and magnetic circular dichroism experiments, we found that the charge transfer at the interfacial Mn and Ni ions can induce a localized magnetic moment. A remarkable increase of exchange bias field and a transition from metal to insulator were simultaneously observed upon decreasing the thickness of the LNO layer, indicating the antiferromagnetic insulator state in 2 unit cells LNO ultrathin layers. The robust exchange bias of 745 Oe in the superlattice is caused by an interfacial localized magnetic moment and an antiferromagnetic state in the ultrathin LNO layer, pinning the ferromagnetic La0.7Sr0.3MnO3 layers together. Our results demonstrate that artificial interface engineering is a useful method to realize novel magnetic and transport properties.

  9. High efficient unidirectional surface plasmon excitation utilizing coupling between metal-insulator-metal waveguide and metal-insulator interface

    NASA Astrophysics Data System (ADS)

    Huang, Zhixiang; Xu, Ke; Pan, Deng

    2017-04-01

    A new structure is proposed, which can realize parallel coupling between metal-insulator-metal (MIM) waveguide and plasmon on metal-insulator (MI) interface. An example for wavelength of 680 nm shows the coupling efficiency can be high as 82%, with short coupling length of 1.2 μm. By using MIM waveguide with proper length, a unidirectional plasmon generator is realized. The generator shows excitation efficiency as high as 78%, with high extinction ratio as 1:170. It also shows a good tolerance for the wavelength. The results are of vital importance for optical integration and unidirectional plasmon excitation.

  10. Metal-insulator-metal capacitor using electrosprayed nanoparticles

    NASA Astrophysics Data System (ADS)

    Véliz, Bremnen; Bermejo, Sandra; Coll, Arnau; Castañer, Luis

    2014-07-01

    An electrospray technique has been used to deposit SiO2 nanoparticles as insulator layer of a metal-insulator-metal device. Impedance spectroscopy measurements show that a 4.4 factor increase in capacitance is achieved compared to a continuous dielectric layer of the same permittivity and dimensions.

  11. Abrupt Depletion Layer Approximation for the Metal Insulator Semiconductor Diode.

    ERIC Educational Resources Information Center

    Jones, Kenneth

    1979-01-01

    Determines the excess surface change carrier density, surface potential, and relative capacitance of a metal insulator semiconductor diode as a function of the gate voltage, using the precise questions and the equations derived with the abrupt depletion layer approximation. (Author/GA)

  12. Abrupt Depletion Layer Approximation for the Metal Insulator Semiconductor Diode.

    ERIC Educational Resources Information Center

    Jones, Kenneth

    1979-01-01

    Determines the excess surface change carrier density, surface potential, and relative capacitance of a metal insulator semiconductor diode as a function of the gate voltage, using the precise questions and the equations derived with the abrupt depletion layer approximation. (Author/GA)

  13. Non percolative nature of the metal-insulator transition and persistence of local Jahn-Teller distortions in the rhombohedral regime of La1-xCaxMnO3

    DOE PAGES

    Shatnawi, Mouath; Bozin, Emil S.; Mitchell, J. F.; ...

    2016-04-25

    Evolution of the average and local crystal structure of Ca-doped LaMnO3 has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations (x = 0.18,0.22). Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of MnO6 octahedra across the OR transition at TS~720 K. The study utilizedmore » explicit two-phase PDF structural modeling, revealing that away from TMI there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to CaMnO3. The results hence do not support the percolative scenario for the MI transition in La1–xCaxMnO3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO3 that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only ~1 nm with observably smaller distortions. In the x = 0.22 sample local JT distortions are found to persist across the OR transition and deep into the R phase (up to ~1050 K), where they are crystallographically prohibited. As a result, their magnitude and subnanometer spatial extent remain unchanged.« less

  14. Non percolative nature of the metal-insulator transition and persistence of local Jahn-Teller distortions in the rhombohedral regime of La1-xCaxMnO3

    SciTech Connect

    Shatnawi, Mouath; Bozin, Emil S.; Mitchell, J. F.; Billinge, Simon J. L.

    2016-04-25

    Evolution of the average and local crystal structure of Ca-doped LaMnO3 has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations (x = 0.18,0.22). Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of MnO6 octahedra across the OR transition at TS~720 K. The study utilized explicit two-phase PDF structural modeling, revealing that away from TMI there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to CaMnO3. The results hence do not support the percolative scenario for the MI transition in La1–xCaxMnO3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO3 that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only ~1 nm with observably smaller distortions. In the x = 0.22 sample local JT distortions are found to persist across the OR transition and deep into the R phase (up to ~1050 K), where they are crystallographically prohibited. As a result, their magnitude and subnanometer spatial extent remain unchanged.

  15. Non percolative nature of the metal-insulator transition and persistence of local Jahn-Teller distortions in the rhombohedral regime of La1-xCaxMnO3

    SciTech Connect

    Shatnawi, Mouath; Bozin, Emil S.; Mitchell, J. F.; Billinge, Simon J. L.

    2016-04-25

    Evolution of the average and local crystal structure of Ca-doped LaMnO3 has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations (x = 0.18,0.22). Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of MnO6 octahedra across the OR transition at TS~720 K. The study utilized explicit two-phase PDF structural modeling, revealing that away from TMI there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to CaMnO3. The results hence do not support the percolative scenario for the MI transition in La1–xCaxMnO3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO3 that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only ~1 nm with observably smaller distortions. In the x = 0.22 sample local JT distortions are found to persist across the OR transition and deep into the R phase (up to ~1050 K), where they are crystallographically prohibited. As a result, their magnitude and subnanometer spatial extent remain unchanged.

  16. All-optical logic gates in plasmonic metal-insulator-metal nanowaveguide with slot cavity resonator

    NASA Astrophysics Data System (ADS)

    Dolatabady, Alireza; Granpayeh, Nosrat

    2017-04-01

    We demonstrate the compact all-optical logic XOR and OR gates in subwavelength plasmonic metal-insulator-metal waveguides with slot cavity resonators, especially for telecommunication wavelengths, with an extinction ratio of 25 dB, which can provide nanoscale logic integrated circuits. The gates behavior is based on suppression or enhancement of resonant modes in a slot cavity resonator induced by a change in position of input ports. The performance of the gates is discussed analytically and verified by the numerical method of finite-difference time-domain (FDTD).

  17. Carrier tuning the metal-insulator transition of epitaxial La0.67Sr0.33MnO3 thin film on Nb doped SrTiO3 substrate

    NASA Astrophysics Data System (ADS)

    Zhan, J. M.; Li, P. G.; Liu, H.; Tao, S. L.; Ma, H.; Shen, J. Q.; Pan, M. J.; Zhang, Z. J.; Wang, S. L.; Yuan, G. L.

    2016-04-01

    La0.67Sr0.33MnO3 (LSMO) thin films were deposited on (001)SrTiO3(STO) and n-type doped Nb:SrTiO3(NSTO) single crystal substrates respectively. The metal to insulator transition temperature(TMI) of LSMO film on NSTO is lower than that on STO, and the TMI of LSMO can be tuned by changing the applied current in the LSMO/NSTO p-n junction. Such behaviors were considered to be related to the carrier concentration redistribution in LSMO film caused by the change of depletion layer thickness in p-n junction which depends greatly on the applied electric field. The phenomenon could be used to configure artificial devices and exploring the underlying physics.

  18. Low-voltage current noise in long quantum superconductor/insulator/normal-metal/insulator/superconductor junctions.

    SciTech Connect

    Kopnin, N. B.; Galperin, Y. M.; Vinokur, V.; Materials Science Division; Helsinki Univ. Tech.; L.D. Landau Inst. for Theoretical Physics; Univ. Oslo; A.F. Ioffe Physico-Tech. Inst. of Russian Academy of Sciences

    2007-01-01

    The current noise in long superconductor/insulator/normal-metal/insulator/superconductor junctions at low temperatures is sensitive to the population of the subgap states, which is far from equilibrium even at low bias voltages. A nonequilibrium distribution is established due to an interplay between voltage-driven interlevel Landau-Zener transitions and intralevel inelastic relaxation. The Fano factor (the ratio of the zero-frequency noise to the dc current) is enhanced drastically, being proportional to the number of times which a particle flies along the Andreev trajectory before it escapes from the level due to inelastic scattering. For weak Landau-Zener transitions, the enhancement is even larger due to a smaller dc current.

  19. Mott metal-insulator transition on compressible lattices.

    PubMed

    Zacharias, Mario; Bartosch, Lorenz; Garst, Markus

    2012-10-26

    The critical properties of the finite temperature Mott end point are drastically altered by a coupling to crystal elasticity, i.e., whenever it is amenable to pressure tuning. Similar as for critical piezoelectric ferroelectrics, the Ising criticality of the electronic system is preempted by an isostructural instability, and long-range shear forces suppress microscopic fluctuations. As a result, the end point is governed by Landau criticality. Its hallmark is, thus, a breakdown of Hooke's law of elasticity with a nonlinear strain-stress relation characterized by a mean-field exponent. Based on a quantitative estimate, we predict critical elasticity to dominate the temperature range ΔT*/T(c)≃8%, close to the Mott end point of κ-(BEDT-TTF)(2)X.

  20. Mott Metal-Insulator Transition on Compressible Lattices

    NASA Astrophysics Data System (ADS)

    Zacharias, Mario; Bartosch, Lorenz; Garst, Markus

    2012-10-01

    The critical properties of the finite temperature Mott end point are drastically altered by a coupling to crystal elasticity, i.e., whenever it is amenable to pressure tuning. Similar as for critical piezoelectric ferroelectrics, the Ising criticality of the electronic system is preempted by an isostructural instability, and long-range shear forces suppress microscopic fluctuations. As a result, the end point is governed by Landau criticality. Its hallmark is, thus, a breakdown of Hooke’s law of elasticity with a nonlinear strain-stress relation characterized by a mean-field exponent. Based on a quantitative estimate, we predict critical elasticity to dominate the temperature range ΔT*/Tc≃8%, close to the Mott end point of κ-(BEDT-TTF)2X.

  1. Infrared-transmittance tunable metal-insulator conversion device with thin-film-transistor-type structure on a glass substrate

    NASA Astrophysics Data System (ADS)

    Katase, Takayoshi; Endo, Kenji; Ohta, Hiromichi

    2017-05-01

    Infrared (IR) transmittance tunable metal-insulator conversion was demonstrated on a glass substrate by using thermochromic vanadium dioxide (VO2) as the active layer in a three-terminal thin-film-transistor-type device with water-infiltrated glass as the gate insulator. Alternative positive/negative gate-voltage applications induce the reversible protonation/deprotonation of a VO2 channel, and two-orders of magnitude modulation of sheet-resistance and 49% modulation of IR-transmittance were simultaneously demonstrated at room temperature by the metal-insulator phase conversion of VO2 in a non-volatile manner. The present device is operable by the room-temperature protonation in an all-solid-state structure, and thus it will provide a new gateway to future energy-saving technology as an advanced smart window.

  2. Plasmonic mode interferences and Fano resonances in Metal-Insulator- Metal nanostructured interface

    PubMed Central

    Nicolas, Rana; Lévêque, Gaëtan; Marae-Djouda, Joseph; Montay, Guillame; Madi, Yazid; Plain, Jérôme; Herro, Ziad; Kazan, Michel; Adam, Pierre-Michel; Maurer, Thomas

    2015-01-01

    Metal-insulator-metal systems exhibit a rich underlying physics leading to a high degree of tunability of their spectral properties. We performed a systematic study on a metal-insulator-nanostructured metal system with a thin 6 nm dielectric spacer and showed how the nanoparticle sizes and excitation conditions lead to the tunability and coupling/decoupling of localized and delocalized plasmonic modes. We also experimentally evidenced a tunable Fano resonance in a broad spectral window 600 to 800 nm resulting from the interference of gap modes with white light broad band transmitted waves at the interface playing the role of the continuum. By varying the incident illumination angle shifts in the resonances give the possibility to couple or decouple the localized and delocalized modes and to induce a strong change of the asymmetric Fano profile. All these results were confirmed with a crossed comparison between experimental and theoretical measurements, confirming the nature of different modes. The high degree of control and tunability of this plasmonically rich system paves the way for designing and engineering of similar systems with numerous applications. In particular, sensing measurements were performed and a figure of merit of 3.8 was recorded ranking this sensor among the highest sensitive in this wavelength range. PMID:26399425

  3. Optical control of capacitance in a metal-insulator-semiconductor diode with embedded metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Mikhelashvili, V.; Ankonina, G.; Kauffmann, Y.; Atiya, G.; Kaplan, W. D.; Padmanabhan, R.; Eisenstein, G.

    2017-06-01

    This paper describes a metal-insulator-semiconductor (MIS) capacitor with flat capacitance voltage characteristics and a small quadratic voltage capacitance coefficient. The device characteristics resemble a metal-insulator-metal diode except that here the capacitance depends on illumination and exhibits a strong frequency dispersion. The device incorporates Fe nanoparticles (NPs), mixed with SrF2, which are embedded in an insulator stack of SiO2 and HfO2. Positively charged Fe ions induce dipole type traps with an electronic polarization that is enhanced by photogenerated carriers injected from the substrate and/or by inter nanoparticle exchange of carriers. The obtained characteristics are compared with those of five other MIS structures: two based on Fe NPs, one with and the other without SrF2 sublayers. Additionally, devices contain Co NPs embedded in SrF2 sublayers, and finally, two structures have no NPs, with one based on a stack of SiO2 and HfO2 and the other which also includes SrF2. Only structures containing Fe NPs, which are incorporated into SrF2, yield a voltage independent capacitance, the level of which can be changed by illumination. These properties are essential in radio frequency/analog mixed signal applications.

  4. Optical control of capacitance in a metal-insulator-semiconductor diode with embedded metal nanoparticles.

    PubMed

    Mikhelashvili, V; Ankonina, G; Kauffmann, Y; Atiya, G; Kaplan, W D; Padmanabhan, R; Eisenstein, G

    2017-06-07

    This paper describes a metal-insulator-semiconductor (MIS) capacitor with flat capacitance voltage characteristics and a small quadratic voltage capacitance coefficient. The device characteristics resemble a metal-insulator-metal diode except that here the capacitance depends on illumination and exhibits a strong frequency dispersion. The device incorporates Fe nanoparticles (NPs), mixed with SrF2, which are embedded in an insulator stack of SiO2 and HfO2. Positively charged Fe ions induce dipole type traps with an electronic polarization that is enhanced by photogenerated carriers injected from the substrate and/or by inter nanoparticle exchange of carriers. The obtained characteristics are compared with those of five other MIS structures: two based on Fe NPs, one with and the other without SrF2 sublayers. Additionally, devices contain Co NPs embedded in SrF2 sublayers, and finally, two structures have no NPs, with one based on a stack of SiO2 and HfO2 and the other which also includes SrF2. Only structures containing Fe NPs, which are incorporated into SrF2, yield a voltage independent capacitance, the level of which can be changed by illumination. These properties are essential in radio frequency/analog mixed signal applications.

  5. A difference in using atomic layer deposition or physical vapour deposition TiN as electrode material in metal-insulator-metal and metal-insulator-silicon capacitors.

    PubMed

    Groenland, A W; Wolters, R A M; Kovalgin, A Y; Schmitz, J

    2011-09-01

    In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the MIM capacitors the bottom electrode is a patterned 100 nm TiN layer (called BE type 1), deposited via sputtering, while MIS capacitors have a flat bottom electrode (called BE type 2-silicon substrate). A high quality 50-100 nm thick SiO2 layer, made by inductively-coupled plasma CVD at 150 degrees C, is deposited as a dielectric on top of both types of bottom electrodes. BE type 1 (MIM) capacitors have a varying from low to high concentration of structural defects in the SiO2 layer. BE type 2 (MIS) capacitors have a low concentration of structural defects and are used as a reference. Two sets of each capacitor design are fabricated with the TiN top electrode deposited either via physical vapour deposition (PVD, i.e., sputtering) or atomic layer deposition (ALD). The MIM and MIS capacitors are electrically characterized in terms of the leakage current at an electric field of 0.1 MV/cm (I leak) and for different structural defect concentrations. It is shown that the structural defects only show up in the electrical characteristics of BE type 1 capacitors with an ALD TiN-based top electrode. This is due to the excellent step coverage of the ALD process. This work clearly demonstrates the sensitivity to process-induced structural defects, when ALD is used as a step in process integration of conductors on insulation materials.

  6. Superconducting tantalum nitride-based normal metal-insulator-superconductor tunnel junctions

    SciTech Connect

    Chaudhuri, S.; Maasilta, I. J.

    2014-03-24

    We report the development of superconducting tantalum nitride (TaN{sub x}) normal metal-insulator-superconductor (NIS) tunnel junctions. For the insulating barrier, we used both AlO{sub x} and TaO{sub x} (Cu-AlO{sub x}-Al-TaN{sub x} and Cu-TaO{sub x}-TaN{sub x}), with both devices exhibiting temperature dependent current-voltage characteristics which follow the simple one-particle tunneling model. The superconducting gap follows a BCS type temperature dependence, rendering these devices suitable for sensitive thermometry and bolometry from the superconducting transition temperature T{sub C} of the TaN{sub x} film at ∼5 K down to ∼0.5 K. Numerical simulations were also performed to predict how junction parameters should be tuned to achieve electronic cooling at temperatures above 1 K.

  7. Mid-infrared intersubband polaritons in dispersive metal-insulator-metal resonators

    SciTech Connect

    Manceau, J.-M. Ongarello, T.; Colombelli, R.; Zanotto, S.; Sorba, L.; Tredicucci, A.; Biasiol, G.

    2014-08-25

    We demonstrate room-temperature strong coupling between a mid-infrared (λ = 9.9 μm) intersubband transition and the fundamental cavity mode of a metal-insulator-metal resonator. Patterning of the resonator surface enables surface-coupling of the radiation and introduces an energy dispersion which can be probed with angle-resolved reflectivity. In particular, the polaritonic dispersion presents an accessible energy minimum at k = 0 where—potentially—polaritons can accumulate. We also show that it is possible to maximize the coupling of photons into the polaritonic states and—simultaneously—to engineer the position of the minimum Rabi splitting at a desired value of the in-plane wavevector. This can be precisely accomplished via a simple post-processing technique. The results are confirmed using the temporal coupled mode theory formalism and their significance in the context of the strong critical coupling concept is highlighted.

  8. Metal-insulator quantum critical point beneath the high Tc superconducting dome

    PubMed Central

    Sebastian, Suchitra E.; Harrison, N.; Altarawneh, M. M.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Lonzarich, G. G.; Hardy, W. N.

    2010-01-01

    An enduring question in correlated systems concerns whether superconductivity is favored at a quantum critical point (QCP) characterized by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high Tc cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultrastrong magnetic fields to measure quantum oscillations in underdoped YBa2Cu3O6+x, revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in Tc in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centered at a critical Fermi surface instability. PMID:20304800

  9. Tunable color filters based on metal-insulator-metal resonators.

    PubMed

    Diest, Kenneth; Dionne, Jennifer A; Spain, Merrielle; Atwater, Harry A

    2009-07-01

    We report a method for filtering white light into individual colors using metal-insulator-metal resonators. The resonators are designed to support photonic modes at visible frequencies, and dispersion relations are developed for realistic experimental configurations. Experimental results indicate that passive Ag/Si(3)N(4)/Au resonators exhibit color filtering across the entire visible spectrum. Full field electromagnetic simulations were performed on active resonators for which the resonator length was varied from 1-3 microm and the output slit depth was systematically varied throughout the thickness of the dielectric layer. These resonators are shown to filter colors based on interference between the optical modes within the dielectric layer. By careful design of the output coupling, the resonator can selectively couple to intensity maxima of different photonic modes and, as a result, preferentially select any of the primary colors. We also illustrate how refractive index modulation in metal-insulator-metal resonators can yield actively tunable color filters. Simulations using lithium niobate as the dielectric layer and the top and bottom Ag layers as electrodes, indicate that the output color can be tuned over the visible spectrum with an applied field.

  10. Strain-induced metal-semiconductor transition observed in atomic carbon chains

    NASA Astrophysics Data System (ADS)

    La Torre, A.; Botello-Mendez, A.; Baaziz, W.; Charlier, J.-C.; Banhart, F.

    2015-03-01

    Carbyne, the sp1-hybridized phase of carbon, is still a missing link in the family of carbon allotropes. While the bulk phases of carbyne remain elusive, the elementary constituents, that is, linear chains of carbon atoms, have already been observed using the electron microscope. Isolated atomic chains are highly interesting one-dimensional conductors that have stimulated considerable theoretical work. Experimental information, however, is still very limited. Here we show electrical measurements and first-principles transport calculations on monoatomic carbon chains. When the 1D system is under strain, the chains are semiconducting corresponding to the polyyne structure with alternating bond lengths. Conversely, when the chain is unstrained, the ohmic behaviour of metallic cumulene with uniform bond lengths is observed. This confirms the recent prediction of a metal-insulator transition that is induced by strain. The key role of the contacting leads explains the rectifying behaviour measured in monoatomic carbon chains in a nonsymmetric contact configuration.

  11. Vacancy-Induced Semiconductor-Insulator-Metal Transitions in Nonstoichiometric Nickel and Tungsten Oxides.

    PubMed

    Wang, Qi; Puntambekar, Ajinkya; Chakrapani, Vidhya

    2016-11-09

    Metal-insulator transitions in strongly correlated oxides induced by electrochemical charging have been attributed to formation of vacancy defects. However, the role of native defects in affecting these transitions is not clear. Here, we report a new type of phase transition in p-type, nonstoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition along with the complete reversal of conductivity from p- to n-type at room temperature induced by electrochemical charging in a Li(+)-containing electrolyte. Direct observation of vacancy-ion interactions using in situ near-infrared photoluminescence spectroscopy show that the transition is a result of passivation of native nickel (cationic) vacancy defects and subsequent formation of oxygen (anionic) vacancy defects driven by Li(+) insertion into the lattice. Changes in the oxidation states of nickel due to defect interactions probed by X-ray photoemission spectroscopy support the above conclusions. In contrast, n-type, nonstoichiometric tungsten oxide shows only insulator-to-metal transition, which is a result of oxygen vacancy formation. The defect-property correlations shown here in these model systems can be extended to other oxides.

  12. Magnetotransport in metal/insulating-ferromagnet heterostructures: Spin Hall magnetoresistance or magnetic proximity effect

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Ma, L.; Shi, Z.; Fan, W. J.; Zheng, Jian-Guo; Evans, R. F. L.; Zhou, S. M.

    2015-08-01

    We study the anomalous Hall-like effect (AHLE) and the effective anisotropic magnetoresistance (EAMR) in antiferromagnetic γ -IrMn3/Y3Fe5O12(YIG ) and Pt/YIG heterostructures. For γ -IrMn3/YIG , the EAMR and the AHLE resistivity change sign with temperature due to the competition between the spin Hall magnetoresistance (SMR) and the magnetic proximity effect (MPE) induced by the interfacial antiferromagnetic uncompensated magnetic moment. In contrast, for Pt/YIG, the AHLE resistivity changes sign with temperature whereas no sign change is observed in the EAMR. This is because the MPE and the SMR play a dominant role in the AHLE and the EAMR, respectively. As different types of galvanomagnetic properties, the AHLE and the EAMR have proved vital in disentangling the MPE and the SMR in metal/insulating-ferromagnet heterostructures.

  13. Electrode modulated capacitance-electric field nonlinearity in metal-insulator-metal capacitors

    NASA Astrophysics Data System (ADS)

    Austin, D. Z.; Holden, K. E. K.; Hinz, J.; Conley, J. F.

    2017-06-01

    Metals with low enthalpy of oxide formation (ΔHox) are used to examine the influence of the metal/dielectric interface, in the absence of a significant interfacial layer oxide (ILO), on the voltage nonlinearity of capacitance for metal-insulator-metal capacitors. For both atomic layer deposited Al2O3 and HfO2 dielectrics, Ag electrode devices show the lowest quadratic electric field coefficient of capacitance (αECC), followed in increasing order by Au, Pd, and Ni. The difference between the metals is greater for thinner dielectrics, which is consistent with increased influence of the interface. In addition, with decreasing dielectric thickness the quadratic voltage field coefficient of capacitance increases, whereas αECC decreases. It is proposed that the thickness dependencies are due to an interaction between vertical compression of the dielectric under an applied bias and the concomitant lateral expansion induced stress that is concentrated near the interface. Through this interaction, the metal interface inhibits lateral expansion of the dielectric resulting in a reduced αECC. Indeed, αECC is found to increase with the increasing lattice mismatch at the metal/dielectric interface, likely due to edge dislocations. Finally, Al, a high ΔHox metal, is found to fit the trend for Al2O3 but not for HfO2, due to the formation of a thin reduced-k ILO at the HfO2/Al interface. These results suggest that minimization of metal/dielectric lattice mismatch may be a route to ultra-low nonlinearity in highly scaled metal-insulator-metal devices.

  14. Structural and electronic transitions in G e2S b2T e5 induced by ion irradiation damage

    NASA Astrophysics Data System (ADS)

    Privitera, S. M. S.; Mio, A. M.; Smecca, E.; Alberti, A.; Zhang, W.; Mazzarello, R.; Benke, J.; Persch, C.; La Via, F.; Rimini, E.

    2016-09-01

    G e2S b2T e5 polycrystalline films either in the trigonal stable phase or in the metastable rock-salt structure have been irradiated with 150 keV Ar+ ions. The effects of disorder are studied by electrical, optical, and structural measurements and density functional theory (DFT) simulations. In the metastable structure, the main effect of ion irradiation is a progressive amorphization, with an optical threshold at a fluence of 3 ×1013c m-2 . For the trigonal structure, a metal-insulator transition and a crystalline transition to rock-salt structure occur prior to amorphization, which requires a fluence of 8 ×1013c m-2 . The bonds of Te atoms close to the van der Waals gaps, present in the trigonal phase and identified by Raman spectroscopy, change as a function of the disorder induced by the irradiation. Comparison with DFT simulations shows that ion irradiation leads to the gradual filling of the van der Waals gaps with displaced Ge and Sb lattice atoms, giving rise first to a metal-insulator transition (9 % of displaced atoms) correlated to the modification of the Te bonds and then induces a structural transition to the metastable rock-salt phase (15 % of displaced atoms). The data presented here not only show the possibility to tune the degree of order, and therefore the electrical properties and the structure of phase change materials by ion irradiation, but also underline the importance of the van der Waals gaps in determining the transport mechanisms and the stability of the crystalline structure.

  15. Tuning the metal-insulator crossover and magnetism in SrRuO3 by ionic gating

    PubMed Central

    Yi, Hee Taek; Gao, Bin; Xie, Wei; Cheong, Sang-Wook; Podzorov, Vitaly

    2014-01-01

    Reversible control of charge transport and magnetic properties without degradation is a key for device applications of transition metal oxides. Chemical doping during the growth of transition metal oxides can result in large changes in physical properties, but in most of the cases irreversibility is an inevitable constraint. Here we report a reversible control of charge transport, metal-insulator crossover and magnetism in field-effect devices based on ionically gated archetypal oxide system - SrRuO3. In these thin-film devices, the metal-insulator crossover temperature and the onset of magnetoresistance can be continuously and reversibly tuned in the range 90–250 K and 70–100 K, respectively, by application of a small gate voltage. We infer that a reversible diffusion of oxygen ions in the oxide lattice dominates the response of these materials to the gate electric field. These findings provide critical insights into both the understanding of ionically gated oxides and the development of novel applications. PMID:25308251

  16. Tuning the metal-insulator crossover and magnetism in SrRuO3 by ionic gating

    DOE PAGES

    Yi, Hee Taek; Gao, Bin; Xie, Wei; ...

    2014-10-13

    Reversible control of charge transport and magnetic properties without degradation is a key for device applications of transition metal oxides. Chemical doping during the growth of transition metal oxides can result in large changes in physical properties, but in most of the cases irreversibility is an inevitable constraint. We report a reversible control of charge transport, metal-insulator crossover and magnetism in field-effect devices based on ionically gated archetypal oxide system - SrRuO3. In these thin-film devices, the metal-insulator crossover temperature and the onset of magnetoresistance can be continuously and reversibly tuned in the range 90–250 K and 70–100 K, respectively,more » by application of a small gate voltage. We infer that a reversible diffusion of oxygen ions in the oxide lattice dominates the response of these materials to the gate electric field. These findings provide critical insights into both the understanding of ionically gated oxides and the development of novel applications.« less

  17. Tuning the metal-insulator crossover and magnetism in SrRuO3 by ionic gating

    SciTech Connect

    Yi, Hee Taek; Gao, Bin; Xie, Wei; Cheong, Sang -Wook; Podzorov, Vitaly

    2014-10-13

    Reversible control of charge transport and magnetic properties without degradation is a key for device applications of transition metal oxides. Chemical doping during the growth of transition metal oxides can result in large changes in physical properties, but in most of the cases irreversibility is an inevitable constraint. We report a reversible control of charge transport, metal-insulator crossover and magnetism in field-effect devices based on ionically gated archetypal oxide system - SrRuO3. In these thin-film devices, the metal-insulator crossover temperature and the onset of magnetoresistance can be continuously and reversibly tuned in the range 90–250 K and 70–100 K, respectively, by application of a small gate voltage. We infer that a reversible diffusion of oxygen ions in the oxide lattice dominates the response of these materials to the gate electric field. These findings provide critical insights into both the understanding of ionically gated oxides and the development of novel applications.

  18. Transport and screen blockage characteristics of reflective metallic insulation materials

    SciTech Connect

    Brocard, D.N.

    1984-01-01

    In the event of a LOCA within a nuclear power plant, it is possible for insulation debris to be generated by the break jet. Such debris has the potential for PWR sump screen (or BWR RHR suction inlet) blockage and thus can affect the long-term recirculation capability. In addition to the variables of break jet location and orientation, the types and quantities of debris which could be generated are dependent on the insulation materials employed. This experimental investigation was limited to reflective metallic insulation and components thereof. The study was aimed at determining the flow velocities needed to transport the insulation debris to the sump screens and the resulting modes of screen blockage. The tests revealed that thin metallic foils (0.0025 in. and 0.004 in.) could transport at low flow velocities, 0.2 to 0.5 ft/sec. Thicker foils (0.008 in.) transported at higher velocities, 0.4 to 0.8 ft/sec, and as fabricated half cylinder insulation units required velocities in excess of 1.0 ft/sec for transport. The tests also provided information on screen blockage patterns that showed blockage could occur at the lower portion of the screen as foils readily flipped on the screen when reaching it.

  19. Metal-Insulator Photocathode Heterojunction for Directed Electron Emission

    SciTech Connect

    Droubay, Timothy C.; Chambers, Scott A.; Joly, Alan G.; Hess, Wayne P.; Nemeth, Karoly; Harkay, Katherine C.; Spentzouris, Linda

    2014-02-14

    New photocathode materials capable of producing intense and directed electron pulses are needed for development of next generation light sources and dynamic transmission electron microscopy. Ideal photocathodes should have high photoemission quantum efficiency (QE) and be capable of delivering collimated and well-shaped pulses of consistent charge under high-field operating conditions. High-brightness and low-intrinsic emittance electron pulses have been predicted for hybrid metal-insulator photocathode designs constructed from three to four monolayer MgO films on atomically flat silver. Here we use angle-resolved photoelectron spectroscopy to confirm directional photoemission and a large increase in QE under ultraviolet laser excitation of an ultrathin MgO film on Ag(001). We observe new low-binding energy photoemission, not seen for Ag(001), and greater electron emission in the normal direction. Under 4.66 eV laser excitation, the photoemission quantum efficiency of the MgO/Ag(001) hybrid photocathode is a factor of seven greater than that for clean Ag(001).

  20. Metal-insulator-metal plasmonic absorbers: influence of lattice.

    PubMed

    Chen, Yiting; Dai, Jin; Yan, Min; Qiu, Min

    2014-12-15

    We experimentally demonstrate three kinds of metal-insulator-metal based plasmonic absorbers consisting of arrays of gold nanodisks distributed in different lattices, including square, triangular and honeycomb lattices. It's found that resonances originated from localized surface plasmon undergo little changes with respect to different lattice distributions of the nanodisks. The interparticle coupling results in a minor bandwidth broadening of the fundamental mode. Different from square- and triangular-lattice absorbers, honeycomb-lattice absorber possesses a unique red-shifting (with respect to incident angles) narrow-band high-order mode, which originates from coupling of incident light to propagating surface plasmon polariton (SPP) waves. Similar high-order mode can also be generated in square-lattice absorber by increasing the period so that a smaller reciprocal lattice vector can be introduced to excite the SPP mode. Furthermore, we show that two types of resonances can interact and create Fano-type resonances. The simulation results agree well with the experimental results.

  1. Optical transmission theory for metal-insulator-metal periodic nanostructures

    NASA Astrophysics Data System (ADS)

    Blanchard-Dionne, Andre-Pierre; Meunier, Michel

    2017-01-01

    A semi-analytical formalism for the optical properties of a metal-insulator-metal periodic nanostructure using coupled-mode theory is presented. This structure consists in a dielectric layer in between two metallic layers with periodic one-dimensional nanoslit corrugation. The model is developed using multiple-scattering formalism, which defines transmission and reflection coefficients for each of the interface as a semi-infinite medium. Total transmission is then calculated using a summation of the multiple paths of light inside the structure. This method allows finding an exact solution for the transmission problem in every dimension regime, as long as a sufficient number of diffraction orders and guided modes are considered for the structure. The resonant modes of the structure are found to be related to the metallic slab only and to a combination of both the metallic slab and dielectric layer. This model also allows describing the resonant behavior of the system in the limit of a small dielectric layer, for which discontinuities in the dispersion curves are found. These discontinuities result from the out-of-phase interference of the different diffraction orders of the system, which account for field interaction for both inner interfaces of the structure.

  2. Optical properties of non-dilute metal insulator composites

    NASA Astrophysics Data System (ADS)

    Tuncer, Enis; Niklasson, Gunnar A.

    2008-09-01

    The description of the optical properties of metal-insulator composites in the non-dilute region is a long standing problem. In this letter we extract the spectral density function of cobalt-amorphous aluminum oxide composites from optical and near-infrared data. The spectral functions are accurately computed numerically with the help of a recently developed technique. It is observed that the spectral features of the prepared composites change with increasing cobalt content. For low concentrations of cobalt, only one depolarization peak is found that corresponds to the Maxwell Garnett approximation. For concentrations higher than 11% cobalt, three effective depolarization factors are resolved that move towards low spectral parameter values with increasing cobalt content. Such a multi-peak structure arises naturally in fractal equivalent circuit models for the optical properties. A comparison with a deterministic fractal model is presented to illustrate the strength of the spectral density representation and to better comprehend our results. We conclude that the observed behavior gives important information on the relation of the optical characteristics to the composite micro-structure.

  3. Optical transmission theory for metal-insulator-metal periodic nanostructures

    NASA Astrophysics Data System (ADS)

    Blanchard-Dionne, Andre-Pierre; Meunier, Michel

    2016-11-01

    A semi-analytical formalism for the optical properties of a metal-insulator-metal periodic nanostructure using coupled-mode theory is presented. This structure consists in a dielectric layer in between two metallic layers with periodic one-dimensional nanoslit corrugation. The model is developed using multiple-scattering formalism, which defines transmission and reflection coefficients for each of the interface as a semi-infinite medium. Total transmission is then calculated using a summation of the multiple paths of light inside the structure. This method allows finding an exact solution for the transmission problem in every dimension regime, as long as a sufficient number of diffraction orders and guided modes are considered for the structure. The resonant modes of the structure are found to be related to the metallic slab only and to a combination of both the metallic slab and dielectric layer. This model also allows describing the resonant behavior of the system in the limit of a small dielectric layer, for which discontinuities in the dispersion curves are found. These discontinuities result from the out-of-phase interference of the different diffraction orders of the system, which account for field interaction for both inner interfaces of the structure.

  4. Direct observation of nanoscale Peltier and Joule effects at metal-insulator domain walls in vanadium dioxide nanobeams.

    PubMed

    Favaloro, Tela; Suh, Joonki; Vermeersch, Bjorn; Liu, Kai; Gu, Yijia; Chen, Long-Qing; Wang, Kevin X; Wu, Junqiao; Shakouri, Ali

    2014-05-14

    The metal to insulator transition (MIT) of strongly correlated materials is subject to strong lattice coupling, which brings about the unique one-dimensional alignment of metal-insulator (M-I) domains along nanowires or nanobeams. Many studies have investigated the effects of stress on the MIT and hence the phase boundary, but few have directly examined the temperature profile across the metal-insulating interface. Here, we use thermoreflectance microscopy to create two-dimensional temperature maps of single-crystalline VO2 nanobeams under external bias in the phase coexisting regime. We directly observe highly localized alternating Peltier heating and cooling as well as Joule heating concentrated at the M-I domain boundaries, indicating the significance of the domain walls and band offsets. Utilizing the thermoreflectance technique, we are able to elucidate strain accumulation along the nanobeam and distinguish between two insulating phases of VO2 through detection of the opposite polarity of their respective thermoreflectance coefficients. Microelasticity theory was employed to predict favorable domain wall configurations, confirming the monoclinic phase identification.

  5. Deep-level spectroscopy in metal-insulator-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Kurtz, A.; Muñoz, E.; Chauveau, J. M.; Hierro, A.

    2017-02-01

    In this study we present a method for measuring bulk traps using deep-level spectroscopy techniques in metal-insulator-semiconductor (MIS) structures. We will focus on deep-level transient spectroscopy (DLTS), although this can be extended to deep-level optical spectroscopy (DLOS) and similar techniques. These methods require the modulation of a depletion region either from a Schottky junction or from a highly asymmetric p-n junction, junctions that may not be realizable in many current material systems. This is the case of wide-bandgap semiconductor families that present a doping asymmetry or have a high residual carrier concentration or surface carrier accumulation, such as InGaN or ZnO. By adding a thin insulating layer and forming an MIS structure this problem can be circumvented and DLTS/DLOS can be performed under certain conditions. A model for the measurement of bulk traps in MIS structures is thus presented, focusing on the similarities with standard DLTS, maintaining when possible links to existing knowledge on DLTS and related techniques. The model will be presented from an equivalent circuit point of view. The effect of the insulating layer on DLTS is evaluated by a combination of simulations and experiments, developing methods for the measurement of these type of devices. As a validation, highly doped ZnO:Ga MIS devices have been successfully characterized and compared with a reference undoped sample using the methods described in this work, obtaining the same intrinsic levels previously reported in the literature but in material doped as high as 1× {{10}18} cm-3.

  6. Resonant modes in metal/insulator/metal metamaterials: An analytical study on near-field couplings

    NASA Astrophysics Data System (ADS)

    Ma, Shaojie; Xiao, Shiyi; Zhou, Lei

    2016-01-01

    Metamaterials (MTMs) in a metal/insulator/metal (MIM) configuration have drawn much attention recently, but the resonances in such systems are still not fully understood. Here, we employ a rigorous mode expansion method to analytically study the resonance properties of a model MIM MTM where the top metallic layer consists of an array of metallic stripes. Our analyses, supported by full-wave simulations and microwave experiments, provide a unified platform to understand the resonances in such systems, in which two previously established models are found valid only at certain extreme conditions. In particular, the resonance in such a system undergoes a transition from a vertical Fabry-Pérot type to a transverse type as the spacer thickness shrinks, and the resonance frequency saturates at a particular value in the thin-spacer limit. Finally, we derive a set of analytical formulas to describe how the essential properties (i.e., resonance frequency and quality factor) of the resonance depend on the structural details of the system and verify these analytical relationships by full-wave simulations in MIM systems with complex microstructures.

  7. Hot plasmonic electron-driven catalytic reactions on patterned metal-insulator-metal nanostructures.

    PubMed

    Kim, Sun Mi; Lee, Changhwan; Goddeti, Kalyan C; Park, Jeong Young

    2017-08-17

    The smart design of plasmonic nanostructures offers a unique capability for the efficient conversion of solar energy into chemical energy by strong interactions with resonant photons through the excitation of surface plasmon resonance, which increases the prospect of using sunlight in environmental and energy applications. Here, we show that the catalytic activity of CO oxidation can be tuned by using new model systems: two-dimensional (2D) arrays of metal-insulator-metal (MIM) plasmonic nanoislands designed to efficiently shuttle hot plasmonic electrons. Hot plasmonic electrons are generated upon the absorption of photons on noble metals, followed by the injection of these hot electrons into the Pt nanoparticles through tunneling or Schottky emission mechanisms, depending on the energy of the hot electrons. We found that these MIM nanostructures exhibit higher catalytic activity (i.e. by 40-110%) under light irradiation, revealing a significant impact on the catalytic activity for CO oxidation. The thickness dependence of the enhancement of catalytic activity on the oxide layers is consistent with the tunneling mechanism of hot electron flows. The results imply that surface plasmon-induced hot electron flows by light absorption significantly influence the catalytic activity of CO oxidation.

  8. Negative capacitance in optically sensitive metal-insulator-semiconductor-metal structures

    NASA Astrophysics Data System (ADS)

    Mikhelashvili, V.; Padmanabhan, R.; Meyler, B.; Yofis, S.; Eisenstein, G.

    2016-12-01

    We report a strong negative capacitance effect in back to back combination of a metal-insulator-semiconductor (MIS) structure and a metal-semiconductor junction, which is fabricated on an n type Silicon-on-Insulator substrate. The MIS capacitor comprises a SiO2-HfO2 insulator stack with embedded Pt nanoparticles. The capacitor undergoes a voltage stress process and thereby turns into a varactor and a photodetector. The negative capacitance is observed only under illumination in structures that employ a Schottky back contact. A symmetric double or an asymmetric single negative capacitance peak is observed depending on the nature of illumination. The phenomenon is attributed to the modulation of the semiconductor conductance due to photo generated carriers and their incorporation in trapping/de-trapping processes on interfacial and post filamentation induced defects in the insulator stack. The frequency range of the observed effect is limited to 100 kHz. Large ratios of light to dark and maximum to minimum of negative capacitances as well as of the obtained sensitivity to the applied voltage are, respectively, 105, more than 100, and 10-15. These were measured at 10 kHz under illumination at 365 nm with a power of 2.5 × 10-6 W.

  9. Effect of thermal treatment on the performance of ZnO based metal-insulator-semiconductor ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Ali, Ghusoon M.; Chakrabarti, P.

    2010-07-01

    The article reports fabrication, characterization, and testing of the performance of ZnO-based metal-insulator-semiconductor (MIS) Schottky barrier ultraviolet photodetectors under varying thermal treatment. The ZnO thin film was grown on p-type Si ⟨100⟩ substrate by using sol-gel technique. The electrical and optical characteristics of MIS photodetector were studied. The study revealed that the performance of the device improves with increasing postmetal deposition annealing temperature up to 250 °C approximately. For annealing temperature beyond 250 °C the performance of the device degrades drastically. The variation in the electrical and photoresponse properties of MIS photodetector can be attributed to combined effects of interfacial reaction and phase transition during the annealing process.

  10. Fano Resonance Based on Metal-Insulator-Metal Waveguide-Coupled Double Rectangular Cavities for Plasmonic Nanosensors

    PubMed Central

    Zhang, Zhidong; Luo, Liang; Xue, Chenyang; Zhang, Wendong; Yan, Shubin

    2016-01-01

    A refractive index sensor based on metal-insulator-metal (MIM) waveguides coupled double rectangular cavities is proposed and investigated numerically using the finite element method (FEM). The transmission properties and refractive index sensitivity of various configurations of the sensor are systematically investigated. An asymmetric Fano resonance lineshape is observed in the transmission spectra of the sensor, which is induced by the interference between a broad resonance mode in one rectangular and a narrow one in the other. The effect of various structural parameters on the Fano resonance and the refractive index sensitivity of the system based on Fano resonance is investigated. The proposed plasmonic refractive index sensor shows a maximum sensitivity of 596 nm/RIU. PMID:27164101

  11. High-channel-count plasmonic filter with the metal-insulator-metal Fibonacci-sequence gratings.

    PubMed

    Gong, Yongkang; Liu, Xueming; Wang, Leiran

    2010-02-01

    Fibonacci-sequence gratings based on metal-insulator-metal waveguides are proposed. The spectrum properties of this structure are numerically investigated by using the transfer matrix method. Numerical results demonstrate that the proposed structure can generate high-channel-count plasmonic stop bands and can find significant applications in highly integrated dense wavelength division multiplexing networks.

  12. Model of coherent transport in metal-insulator-midband gap semiconductor-insulator-semiconductor structure

    NASA Astrophysics Data System (ADS)

    Abramov, I. I.; Danilyuk, A. L.

    1997-08-01

    A kinetic model of coherent transport with self-organized carrier transfer via midband gap semiconductor states in metal-insulator-midband gap semiconductor-insulator-semiconductor structure at room temperature is proposed. The coherent transport at room temperature can be a result of continuous oscillations of charge carriers at midband gap semiconductor states.

  13. Peltier effect in normal metal-insulator-heavy fermion metal junctions

    NASA Astrophysics Data System (ADS)

    Goltsev, A. V.; Rowe, D. M.; Kuznetsov, V. L.; Kuznetsova, L. A.; Min, Gao

    2003-04-01

    A theoretical study has been undertaken of the Peltier effect in normal metal-insulator-heavy fermion metal junctions. The results indicate that, at temperatures below the Kondo temperature, such junctions can be used as electronic microrefrigerators to cool the normal metal electrode and are several times more efficient in cooling than the normal metal-heavy fermion metal junctions.

  14. Local bias-induced phase transitions

    SciTech Connect

    Seal, Katyayani; Baddorf, Arthur P.; Jesse, Stephen; Kalinin, Sergei V.; Nikiforov, Maxim; Proksch, Roger; Rodriguez, Brian J.; Maksymovych, Petro; Kholkin, Andrei L.

    2008-11-27

    Electrical bias-induced phase transitions underpin a wide range of applications from data storage to energy generation and conversion. The mechanisms behind these transitions are often quite complex and in many cases are extremely sensitive to local defects that act as centers for local transformations or pinning. Furthermore, using ferroelectrics as an example, we review methods for probing bias-induced phase transitions and discuss the current limitations and challenges for extending the methods to field-induced phase transitions and electrochemical reactions in energy storage, biological and molecular systems.

  15. Local bias-induced phase transitions

    DOE PAGES

    Seal, Katyayani; Baddorf, Arthur P.; Jesse, Stephen; ...

    2008-11-27

    Electrical bias-induced phase transitions underpin a wide range of applications from data storage to energy generation and conversion. The mechanisms behind these transitions are often quite complex and in many cases are extremely sensitive to local defects that act as centers for local transformations or pinning. Furthermore, using ferroelectrics as an example, we review methods for probing bias-induced phase transitions and discuss the current limitations and challenges for extending the methods to field-induced phase transitions and electrochemical reactions in energy storage, biological and molecular systems.

  16. Interfacial engineering of metal-insulator-semiconductor junctions for efficient and stable photoelectrochemical water oxidation

    NASA Astrophysics Data System (ADS)

    Digdaya, Ibadillah A.; Adhyaksa, Gede W. P.; Trześniewski, Bartek J.; Garnett, Erik C.; Smith, Wilson A.

    2017-06-01

    Solar-assisted water splitting can potentially provide an efficient route for large-scale renewable energy conversion and storage. It is essential for such a system to provide a sufficiently high photocurrent and photovoltage to drive the water oxidation reaction. Here we demonstrate a photoanode that is capable of achieving a high photovoltage by engineering the interfacial energetics of metal-insulator-semiconductor junctions. We evaluate the importance of using two metals to decouple the functionalities for a Schottky contact and a highly efficient catalyst. We also illustrate the improvement of the photovoltage upon incidental oxidation of the metallic surface layer in KOH solution. Additionally, we analyse the role of the thin insulating layer to the pinning and depinning of Fermi level that is responsible to the resulting photovoltage. Finally, we report the advantage of using dual metal overlayers as a simple protection route for highly efficient metal-insulator-semiconductor photoanodes by showing over 200 h of operational stability.

  17. Ultra-thin broadband nanostructured insulator-metal-insulator-metal plasmonic light absorber.

    PubMed

    Hubarevich, Aliaksandr; Kukhta, Aliaksandr; Demir, Hilmi Volkan; Sun, Xiaowei; Wang, Hong

    2015-04-20

    An ultra-thin nanostructured plasmonic light absorber with an insulator-metal-insulator-metal (IMIM) architecture is designed and numerically studied. The IMIM structure is capable to absorb up to about 82.5% of visible light in a broad wavelength range of 300-750 nm. The absorption by the bottom metal is only 6% of that of the top metal. The results show that the IMIM architecture has weak dependence of the angle of the incident light. Interestingly, by varying the top insulator material the optical absorption spectrum can be shifted more than 180 nm as compared to the conventional air-metal-insulator-metal structure. The IMIM structure can be applied for different plasmonic devices with improved performance.

  18. Theoretical analysis of the characteristic impedance in metal-insulator-metal plasmonic transmission lines.

    PubMed

    Nejati, Hamid; Beirami, Ahmad

    2012-03-15

    We propose a closed form formulation for the impedance of the metal-insulator-metal (MIM) plasmonic transmission lines by solving the Maxwell's equations. We provide approximations for thin and thick insulator layers sandwiched between metallic layers. In the case of very thin dielectric layer, the surface waves on both interfaces are strongly coupled resulting in an almost linear dependence of the impedance of the plasmonic transmission line on the thickness of the insulator layer. On the other hand, for very thick insulator layer, the impedance does not vary with the insulator layer thickness due to the weak-coupling/decoupling of the surface waves on each metal-insulator interface. We demonstrate the effectiveness of our proposed formulation using two test scenarios, namely, almost zero reflection in T-junction and reflection from line discontinuity in the design of Bragg reflectors, where we compare our formulation against previously published results.

  19. Investigation of high efficiency silicon MINP solar cells. [metal-insulator n/p

    NASA Technical Reports Server (NTRS)

    Olsen, L. C.; Addis, F. W.

    1986-01-01

    This paper includes results of both theoretical and experimental studies of silicon metal insulator n/p cells. Performance calculations are described which give expected efficiencies as a function of base resistivity. Fabrication and characterization of cells are discussed, and detailed analyses of current loss mechanisms are presented. Using 0.2-ohm cm FZ material and Mg tunneling contacts, AM 1 efficiencies in the range of 16.5-17 percent have been achieved.

  20. Modeling, Fabrication, and Electrical Testing of Metal-Insulator-Metal Diode

    DTIC Science & Technology

    2011-12-01

    K. Design and Develop- ment of Batch Fabricatable Metal-Insulator-Metal Diode and Microstrip Slot Antenna as Rectenna Elements. Sensors and...rectifying radiation absorbed by a nano- antenna designed for the terahertz frequency range (visible and infrared wavelengths) (1, 2). For this application...referred to as “rectification reversal” is due to the switching between Fowler-Nordheim and direct tunneling. Rectification reversal can be explained by

  1. Flexible perovskite solar cells based on the metal-insulator-semiconductor structure.

    PubMed

    Wei, Jing; Li, Heng; Zhao, Yicheng; Zhou, Wenke; Fu, Rui; Pan, Huiyue; Zhao, Qing

    2016-09-14

    The metal-insulator-semiconductor (MIS) structure is applied to perovskite solar cells, in which the traditional compact layer TiO2 is replaced by Al2O3 as the hole blocking material to realize an all-low-temperature process. Flexible devices based on this structure are also realized with excellent flexibility, which hold 85% of their initial efficiency after bending 100 times.

  2. Metal-Insulator-Metal Diode Process Development for Energy Harvesting Applications

    DTIC Science & Technology

    2010-04-01

    performed using a high -temperature deposition and ion milling process . I-V measurements will be performed on General Order of Operations: 1...Fabricate MIM diodes using one of two processes a. Low-temperature deposition recipes in conjunction with a lift-off process b. High -temperature...Metal-Insulator-Metal Diode Process Development for Energy Harvesting Applications by Matthew Chin, Stephen Kilpatrick, and Dr. Richard

  3. Investigation of high efficiency silicon MINP solar cells. [metal-insulator n/p

    NASA Technical Reports Server (NTRS)

    Olsen, L. C.; Addis, F. W.

    1986-01-01

    This paper includes results of both theoretical and experimental studies of silicon metal insulator n/p cells. Performance calculations are described which give expected efficiencies as a function of base resistivity. Fabrication and characterization of cells are discussed, and detailed analyses of current loss mechanisms are presented. Using 0.2-ohm cm FZ material and Mg tunneling contacts, AM 1 efficiencies in the range of 16.5-17 percent have been achieved.

  4. Novel Way to Characterize Metal-Insulator-Metal Devices via Nanoindentation: Preprint

    SciTech Connect

    Periasamy, P.; Packard, C. E.; O?Hayre, R. P.; Berry, J. J.; Parilla, P. A.; Ginley, D. S.

    2011-07-01

    Metal-Insulator-Metal (MIM) devices are crucial components for applications ranging from optical rectennas for harvesting sunlight to infrared detectors. To date, the relationship between materials properties and device performance in MIM devices is not fully understood, partly due to the difficulty in making and reproducing reliable devices. One configuration that is popular due to its simplicity and ease of fabrication is the point-contact diode where a metal tip serves as one of the metals in the MIM device. The intrinsic advantage of the point-contact configuration is that it is possible to achieve very small contact areas for the device thereby allowing very high-frequency operation. In this study, precise control over the contact area and penetration depth of an electrically conductive tip into a metal/insulator combination is achieved using a nanoindenter with in-situ electrical contact resistance measurement capabilities. A diamond probe tip, doped (degeneratively) with boron for conductivity, serves as the point contact and second 'metal' (b-Diamond) of the MIM diode. The base layer consists of Nb/Nb2O5 thin films on Si substrates and serves as the first metal /insulator combination of the MIM structure. The current-voltage response of the diodes is measured under a range of conditions to assess the validity and repeatability of the technique. Additionally, we compare the results of this technique to those acquired using a bent-wire approach and find that Nb/Nb2O5/b-Diamond MIM devices show an excellent asymmetry (60-300) and nonlinearity values (~6-9). This technique shows great promise for screening metal-insulator combinations for performance without the uncertainty that stems from a typical bent-wire point-contact.

  5. Optical Properties of Some Metal-Insulator Composites.

    NASA Astrophysics Data System (ADS)

    Noh, Tae Won

    Ni-MgO granular composites were prepared by coprecipitation of NiO-MgO solid solutions and their preferential reduction in a hydrogen atmosphere. Measured reflection spectra of the composites were better described by the Effective Medium Approximation (EMA) than by the Maxwell-Garnett theory (MGT). The conductivities and the dielectric constants were derived by a Kramers-Kronig transformation, and they showed a qualitative agreement with the EMA. In the far -infrared region, the percolation transition was observed in the reflection spectra, and also seen in the derived conductivities and the dielectric constants. The far-infrared absorption of Ag-smoke--teflon composites was studied. Because of the high resistivity of the oxide layer, the far-infrared electric dipole absorption was enhanced by three or four orders of magnitude, and it became comparable to the magnetic dipole absorption. The effects of the oxide coating on the infrared and visible absorption of silver smoke were also studied using Ag-smoke --KBr composites. In the infrared and visible region, the complete Mie theory gave better descriptions of our experimental results than the MGT. Comparison of our experimental data and the Mie calculation showed that the oxide coating on the particles did not strongly affect the extinction coefficient of the Ag-smoke--KBr composite in the near-infrared and visible range. The "anomalous" far-infrared absorption of small metal particles was investigated thoroughly using oxide -free Ag--teflon composites and Ag-smoke--teflon composites. For the oxide-free Ag particles, large enhancement of the absorption coefficient over the prediction of the MGT was observed and explained by enhancement of magnetic dipole absorption based on the increase of the eddy current paths due to clustering. For the Ag-smoke--teflon composite, excellent agreement between the experimental absorption and the MGT was obtained when the particle size distribution and oxide coating were taken into

  6. Electroluminescence from metal-insulator-semiconductor tunneling diodes using compressively strained Ge on Si0.5Ge0.5 virtual substrates.

    PubMed

    Manna, Santanu; Aluguri, Rakesh; Das, Samaresh; Singha, Rajkumar; Ray, Samit K

    2013-11-18

    Direct band gap optical transition in compressively strained Ge film is demonstrated for the first time under current injection through a metal-insulator-semiconductor diode structure. The compressively strained Ge layer is grown on the relaxed Si0.5Ge0.5 substrate by solid source molecular beam epitaxy. The electroluminescence of direct band gap emission from strained Ge film and TO phonon assisted transition in Si and SiGe from the virtual substrate is observed under different current injections. The signature of heavy hole and light hole splitting in valence band is observed in the electroluminescence spectra from strained Ge layer. The temperature dependent electroluminescence characteristics have been studied over a temperature range of 10-300 K. AC frequency modulation for the Ge direct band electroluminescence has been studied to improve the emission efficiency over the DC bias.

  7. Metal-insulator transition in V/sub 1-x/Mn/sub x/O/sub 2-2x/F/sub 2x/ (O < x less than or equal to 0. 10). Study of structural, magnetic, and electrical properties

    SciTech Connect

    Akroune, A.; Casalot, A.

    1987-05-01

    V/sub 1-x/Mn/sub x/O/sub 2-2x/F/sub 2x/ samples (O < x less than or equal to 0.10) have been prepared by solid state reaction in sealed platinum tubes. The metal in equilibrium insulator transition occurs at a quickly decreasing temperatures as MnF/sub 2/ increases. The crystallographic, magnetic, transport properties, and DTA have been determined and discussed.

  8. Shattering transitions in collision-induced fragmentation

    NASA Astrophysics Data System (ADS)

    Krapivsky, P. L.; Ben-Naim, E.

    2003-08-01

    We investigate the kinetics of nonlinear collision-induced fragmentation. We obtain the fragment mass distribution analytically by utilizing its traveling wave behavior. The system undergoes a shattering transition in which a finite fraction of the mass is lost to infinitesimal fragments (dust). The nature of the shattering transition depends on the fragmentation process. When the larger of the two colliding fragments splits, the transition is discontinuous and the entire mass is transformed into dust at the transition point. When the smaller fragment splits, the transition is continuous with the dust gaining mass steadily on the account of the fragments. At the transition point, the fragment mass distribution diverges algebraically for small masses, c(m)˜m-α, with α=1.201 91… .

  9. Metal-insulator-metal photomonitor for optical waveguides at telecom wavelengths

    NASA Astrophysics Data System (ADS)

    Ishii, Satoshi; Baghdasaryan, Hovik; Marciniak, Marian; Otomo, Akira

    2016-12-01

    A compact photodetector for an optical waveguide that is easy to integrate is necessary for optical on-chip devices. We demonstrate that a metallic contact covering an optical waveguide can monitor guided light in the 680 to 1550 nm wavelength range without blocking it. The contact is made of Au, titania, and Ti thin films that form a metal-insulator-metal structure. A concise design and facile fabrication process make our device particularly suitable for optical waveguides made of insulators such as polymers and dielectrics.

  10. Metal-insulator-semi-conductor studies of lead telluride. [capacitance and conductance-voltage characteristics

    NASA Technical Reports Server (NTRS)

    Lilly, D. A.; Joslin, D. E.; Kan, H. K. A.

    1976-01-01

    The capacitance and conductance-voltage characteristics were measured on metal-insulator-semiconductor capacitors fabricated with zirconium dioxide films on single-crystal lead telluride. At 77 K, on both n- and p-type substrates, evidence of surface potential control was obtained. Comparison of the measured capacitance-voltage characteristics with those calculated from the equilibrium solution of the one-dimensional Poisson equation indicated qualitative agreement, although the slope of the measured capacitance in the region near the capacitance minimum was less steep than calculated.

  11. Metal-insulator-semi-conductor studies of lead telluride. [capacitance and conductance-voltage characteristics

    NASA Technical Reports Server (NTRS)

    Lilly, D. A.; Joslin, D. E.; Kan, H. K. A.

    1976-01-01

    The capacitance and conductance-voltage characteristics were measured on metal-insulator-semiconductor capacitors fabricated with zirconium dioxide films on single-crystal lead telluride. At 77 K, on both n- and p-type substrates, evidence of surface potential control was obtained. Comparison of the measured capacitance-voltage characteristics with those calculated from the equilibrium solution of the one-dimensional Poisson equation indicated qualitative agreement, although the slope of the measured capacitance in the region near the capacitance minimum was less steep than calculated.

  12. Memory Impedance in TiO2 based Metal-Insulator-Metal Devices

    PubMed Central

    Qingjiang, Li; Khiat, Ali; Salaoru, Iulia; Papavassiliou, Christos; Hui, Xu; Prodromakis, Themistoklis

    2014-01-01

    Large attention has recently been given to a novel technology named memristor, for having the potential of becoming the new electronic device standard. Yet, its manifestation as the fourth missing element is rather controversial among scientists. Here we demonstrate that TiO2-based metal-insulator-metal devices are more than just a memory-resistor. They possess resistive, capacitive and inductive components that can concurrently be programmed; essentially exhibiting a convolution of memristive, memcapacitive and meminductive effects. We show how non-zero crossing current-voltage hysteresis loops can appear and we experimentally demonstrate their frequency response as memcapacitive and meminductive effects become dominant. PMID:24682245

  13. Dispersion of metal-insulator-metal plasmon polaritons probed by cathodoluminescence imaging spectroscopy

    SciTech Connect

    Kuttge, Martin; Cai, Wei; Garcia de Abajo, F. Javier; Polman, Albert

    2009-07-15

    Cathodoluminescence imaging spectroscopy is used to excite and characterize the resonant modes of Fabry-Perot resonators for surface plasmon polaritons confined in a metal-insulator-metal (MIM) geometry. The smallest MIM plasmon wavelength derived from the observed mode pattern is found to be 160 nm in cavities with a 10 nm SiO{sub 2} layer for a free-space wavelength of 645 nm. The measured wavelength agrees well with values from analytical dispersion relation calculations. Calculations of the excitation probability show that the resonant excitation of MIM plasmons depends strongly on the electron energy due to phase retardation effects resulting from the finite electron velocity.

  14. Electrically induced phase transition in α -(BEDT-TTF)2I3 : Indications for Dirac-like hot charge carriers

    NASA Astrophysics Data System (ADS)

    Peterseim, T.; Ivek, T.; Schweitzer, D.; Dressel, M.

    2016-06-01

    The two-dimensional organic conductor α -(BEDT-TTF)2I3 undergoes a metal-insulator transition at TCO=135 K due to electronic charge ordering. We have conducted time-resolved investigations of its electronic properties in order to explore the field- and temperature-dependent dynamics. At a certain threshold field, the system switches from a low-conducting to a high-conducting state, accompanied by a negative differential resistance. Our time-dependent infrared investigations indicate that close to TCO, the strong electric field pushes the crystal into a metallic state with optical properties similar to the one for T >TCO . Well into the insulating state, however, at T =80 K , the spectral response evidences a completely different electronically induced high-conducting state. Applying a two-state model of hot electrons explains the observations by excitation of charge carriers with a high mobility. They resemble the Dirac-like charge carriers with a linear dispersion of the electronic bands found in α -(BEDT-TTF)2I3 at high pressure. Extensive numerical simulations quantitatively reproduce our experimental findings in all details.

  15. Low-Power All-Optical Bistable Device of Twisted-Nematic Liquid Crystal Based on Surface Plasmons in a Metal-Insulator-Metal Structure

    NASA Astrophysics Data System (ADS)

    Tien Thanh, Pham; Tanaka, Daisuke; Fujimura, Ryushi; Takanishi, Yoichi; Kajikawa, Kotaro

    2013-01-01

    A low-power all-optical bistable device of twisted-nematic liquid crystal (TN-LC) is reported, on the basis of coupled surface plasmons (SPs) in a metal-insulator-metal (MIM) structure. The lowest threshold switching illumination was 0.3 mW/mm2, which is much lower than the value we previously reported for a similar all-optical TN-LC device based on the coupled SPs in a gold grating. The threshold illumination is lower at higher temperature up to the phase transition. The TN-LC device is promising for two-dimensional optical memories or spatial light modulators, since the structure is simple and free from electronic circuits.

  16. Metallic, insulating and superconducting states in κ-ET2X systems, where ET is the BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) molecule

    NASA Astrophysics Data System (ADS)

    Ivanov, Valery A.; Ugolkova, Elena A.; Zhuravlev, Mikhail Ye.

    1998-08-01

    An electronic structure and normal and superconducting properties are reviewed for layered organic materials on the basis of bis(ethylenedithio)tetrathiafulvalene molecule (BEDT-TTF, hereafter ET) with essential intraET electron and cross-dimer κ-packing in ET-plane. The metall-insulator phase transition is derived for realistic model of κ-ET2X salts. Based on the Fermi-surface topology and electron correlations the d-symmetry of superconducting order parameter is obtained with interplay between its nodes on the Fermi surface and superconducting phase characteristics. The results are in agreement with measured nonactivated temperature dependencies of NMR-relaxation rate of central carbon 13C spins in ET and superconducting specific heat.

  17. Insulator charging limits direct current across tunneling metal-insulator-semiconductor junctions

    SciTech Connect

    Vilan, Ayelet

    2016-01-07

    Molecular electronics studies how the molecular nature affects the probability of charge carriers to tunnel through the molecules. Nevertheless, transport is also critically affected by the contacts to the molecules, an aspect that is often overlooked. Specifically, the limited ability of non-metallic contacts to maintain the required charge balance across the fairly insulating molecule often have dramatic effects. This paper shows that in the case of lead/organic monolayer-silicon junctions, a charge balance is responsible for an unusual current scaling, with the junction diameter (perimeter), rather than its area. This is attributed to the balance between the 2D charging at the metal/insulator interface and the 3D charging of the semiconductor space-charge region. A derivative method is developed to quantify transport across tunneling metal-insulator-semiconductor junctions; this enables separating the tunneling barrier from the space-charge barrier for a given current-voltage curve, without complementary measurements. The paper provides practical tools to analyze specific molecular junctions compatible with existing silicon technology, and demonstrates the importance of contacts' physics in modeling charge transport across molecular junctions.

  18. All-Graphene Planar Self-Switching MISFEDs, Metal-Insulator-Semiconductor Field-Effect Diodes

    PubMed Central

    Al-Dirini, Feras; Hossain, Faruque M.; Nirmalathas, Ampalavanapillai; Skafidas, Efstratios

    2014-01-01

    Graphene normally behaves as a semimetal because it lacks a bandgap, but when it is patterned into nanoribbons a bandgap can be introduced. By varying the width of these nanoribbons this band gap can be tuned from semiconducting to metallic. This property allows metallic and semiconducting regions within a single Graphene monolayer, which can be used in realising two-dimensional (2D) planar Metal-Insulator-Semiconductor field effect devices. Based on this concept, we present a new class of nano-scale planar devices named Graphene Self-Switching MISFEDs (Metal-Insulator-Semiconductor Field-Effect Diodes), in which Graphene is used as the metal and the semiconductor concurrently. The presented devices exhibit excellent current-voltage characteristics while occupying an ultra-small area with sub-10 nm dimensions and an ultimate thinness of a single atom. Quantum mechanical simulation results, based on the Extended Huckel method and Nonequilibrium Green's Function Formalism, show that a Graphene Self-Switching MISFED with a channel as short as 5 nm can achieve forward-to-reverse current rectification ratios exceeding 5000. PMID:24496307

  19. Quantum criticality at the Anderson transition: A typical medium theory perspective

    NASA Astrophysics Data System (ADS)

    Mahmoudian, Samiyeh; Tang, Shao; Dobrosavljević, Vladimir

    2015-10-01

    We present a complete analytical and numerical solution of the typical medium theory (TMT) for the Anderson metal-insulator transition. This approach self-consistently calculates the typical amplitude of the electronic wave functions, thus representing the conceptually simplest order-parameter theory for the Anderson transition. We identify all possible universality classes for the critical behavior, which can be found within such a mean-field approach. This provides insights into how interaction-induced renormalizations of the disorder potential may produce qualitative modifications of the critical behavior. We also formulate a simplified description of the leading critical behavior, thus obtaining an effective Landau theory for Anderson localization.

  20. Fingerprints of the field-induced Berezinskii-Kosterlitz-Thouless transition in quasi-two-dimensional quantum magnets

    NASA Astrophysics Data System (ADS)

    Orendáčová, Alžbeta

    The two-dimensional (2d) easy-plane (XY) model provides a prototypical description of 2d systems exhibiting topological excitations, which drive the Berezinskii-Kosterlitz-Thouless (BKT) transition that occurs in 2d superfluids, electron plasmas, Josephson junction arrays, ultracold atomic 2d Bose gasses, etc. The excitations in the 2d XY model are spin waves and vortices. In the BKT scenario, at low temperatures, all vortices (V) and antivortices (AV) are bound to V-AV pairs, and spin waves dominate in this quasi-long-range-ordered phase with an infinite correlation length, ξ, and an algebraic decay of correlations. At a critical temperature, TBKT, the V-AV pairs start to unbind, driving the transition to a free vortex phase above TBKT, characterized by an exponential divergence of ξ. Vortices remain stable also in quantum 2d anisotropic Heisenberg systems with a very weak XY anisotropy. The BKT scenario appears even in 2d isotropic Heisenberg magnets due to frustration or an external magnetic field. I will focus on quasi-2d spin 1/2 Heisenberg antiferromagnets with extremely weak spin anisotropy. These highly anisotropic layered Cu(II) organo-metallic insulators with relatively low saturation fields, about 6 T, enabled a comprehensive study in a wide range of magnetic fields and temperatures. A response of all compounds to the application of a magnetic field mimics 2d behavior with fingerprints of a field-induced Berezinskii-Kosterlitz-Thouless phase transition. ITMS 26220120005, VEGA 1/0143/13 and APVV-14-0073 are acknowledged for a financial support.

  1. Contemporary research of dynamically induced phase transitions

    NASA Astrophysics Data System (ADS)

    Hull, L. M.

    2017-01-01

    Dynamically induced phase transitions in metals, within the present discussion, are those that take place within a time scale characteristic of the shock waves and any reflections or rarefactions involved in the loading structure along with associated plastic flow. Contemporary topics of interest include the influence of loading wave shape, the effect of shear produced by directionality of the loading relative to the sample dimensions and initial velocity field, and the loading duration (kinetic effects, hysteresis) on the appearance and longevity of a transformed phase. These topics often arise while considering the loading of parts of various shapes with high explosives, are typically two or three-dimensional, and are often selected because of the potential of the transformed phase to significantly modify the motion. In this paper, we look at current work on phase transitions in metals influenced by shear reported in the literature, and relate recent work conducted at Los Alamos on iron's epsilon phase transition that indicates a significant response to shear produced by reflected elastic waves. A brief discussion of criteria for the occurrence of stress induced phase transitions is provided. Closing remarks regard certain physical processes, such as fragmentation and jet formation, which may be strongly influenced by phase transitions.

  2. Contemporary Research of Dynamically Induced Phase Transitions

    NASA Astrophysics Data System (ADS)

    Hull, Lawrence

    2015-06-01

    Dynamically induced phase transitions in metals, within the present discussion, are those that take place within a time scale characteristic of the shock waves and any reflections or rarefactions involved in the loading structure along with associated plastic flow. Contemporary topics of interest include the influence of loading wave shape, the effect of shear produced by directionality of the loading relative to the sample dimensions and initial velocity field, and the loading duration (kinetic effects, hysteresis) on the appearance and longevity of a transformed phase. These topics often arise while considering the loading of parts of various shapes with high explosives, are typically two or three-dimensional, and are often selected because of the potential of the transformed phase to significantly modify the motion. In this paper, we look at current work on phase transitions in metals influenced by shear reported in the literature, and relate recent work conducted at Los Alamos on iron's epsilon phase transition that indicates a significant response to shear produced by reflected elastic waves. A brief discussion of criteria for the occurrence of stress induced phase transitions is provided. Closing remarks regard certain physical processes, such as fragmentation and jet formation, which may be strongly influenced by phase transitions. Supported by the DoD/DOE Joint Munitions Technology Development Program.

  3. High-field Overhauser dynamic nuclear polarization in silicon below the metal-insulator transition.

    PubMed

    Dementyev, Anatoly E; Cory, David G; Ramanathan, Chandrasekhar

    2011-04-21

    Single crystal silicon is an excellent system to explore dynamic nuclear polarization (DNP), as it exhibits a continuum of properties from metallic to insulating as a function of doping concentration and temperature. At low doping concentrations DNP has been observed to occur via the solid effect, while at very high-doping concentrations an Overhauser mechanism is responsible. Here we report the hyperpolarization of (29)Si in n-doped silicon crystals, with doping concentrations in the range of (1-3) × 10(17) cm(-3). In this regime exchange interactions between donors become extremely important. The sign of the enhancement in our experiments and its frequency dependence suggest that the (29)Si spins are directly polarized by donor electrons via an Overhauser mechanism within exchange-coupled donor clusters. The exchange interaction between donors only needs to be larger than the silicon hyperfine interaction (typically much smaller than the donor hyperfine coupling) to enable this Overhauser mechanism. Nuclear polarization enhancement is observed for a range of donor clusters in which the exchange energy is comparable to the donor hyperfine interaction. The DNP dynamics are characterized by a single exponential time constant that depends on the microwave power, indicating that the Overhauser mechanism is a rate-limiting step. Since only about 2% of the silicon nuclei are located within 1 Bohr radius of the donor electron, nuclear spin diffusion is important in transferring the polarization to all the spins. However, the spin-diffusion time is much shorter than the Overhauser time due to the relatively weak silicon hyperfine coupling strength. In a 2.35 T magnetic field at 1.1 K, we observed a DNP enhancement of 244 ± 84 resulting in a silicon polarization of 10.4 ± 3.4% following 2 h of microwave irradiation.

  4. Metal-insulator transition in a weakly interacting disordered electron system

    NASA Astrophysics Data System (ADS)

    Ekuma, C. E.; Yang, S.-X.; Terletska, H.; Tam, K.-M.; Vidhyadhiraja, N. S.; Moreno, J.; Jarrell, M.

    2015-11-01

    The interplay of interactions and disorder is studied using the Anderson-Hubbard model within the typical medium dynamical cluster approximation. Treating the interacting, nonlocal cluster self-energy [Σc[G ˜] (i ,j ≠i ) ] up to second order in the perturbation expansion of interactions, U2, with a systematic incorporation of nonlocal spatial correlations and diagonal disorder, we explore the initial effects of electron interactions (U ) in three dimensions. We find that the critical disorder strength (WcU), required to localize all states, increases with increasing U ; implying that the metallic phase is stabilized by interactions. Using our results, we predict a soft pseudogap at the intermediate W close to WcU and demonstrate that the mobility edge (ωɛ) is preserved as long as the chemical potential, μ , is at or beyond the mobility edge energy.

  5. Disordered systems and the metal-insulator transition: A super universality class

    NASA Astrophysics Data System (ADS)

    Hofstetter, E.

    1998-05-01

    The critical behavior of three-dimensional disordered systems is investigated by analyzing the spectral fluctuations of the energy spectrum. Our results suggest that the initial symmetries (orthogonal, unitary, and symplectic) are broken by the disorder at the critical point. The critical behavior, determined by the symmetry at the critical point, should therefore be independent of the previous invariances and be described by a ``super'' universality class. This result is strongly supported by the fact that we obtain the same critical exponent ν~=1.35 in the three cases: orthogonal, unitary, and symplectic.

  6. Magnetism and metal-insulator transition in oxygen deficient SrTiO3

    NASA Astrophysics Data System (ADS)

    Lopez-Bezanilla, Alejandro; Ganesh, P.; Littlewood, Peter

    2015-03-01

    We report new findings in the electronic structure and magnetism of oxygen vacancies in SrTiO3. By means of first-principles calculations we show that the appearance of magnetism in oxygen-deficient SrTiO3 is not determined solely by the presence of a single oxygen vacancy but by the density of free carriers and the relative proximity of the vacant sites. While an isolated vacancy behaves as a non-magnetic double donor, manipulation of the doping conditions allows the stability of a single donor state with emergent local moments. Strong local lattice distortions enhance the binding of this state. Consequently we find that the free-carrier density and strain are fundamental components to obtaining trapped spin-polarized electrons in oxygen-deficient SrTiO3, which may have important implications in the design of switchable magneto-optic devices. AL-B and PBL were supported by DOE-BES under Contract No. DE-AC02-06CH11357. PG was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT- Battelle, LLC, for the US Department of Energy.

  7. Mesoscopic Effects and Metal-Insulator Transition in Vanadium Oxide Nanowires

    DTIC Science & Technology

    2012-07-08

    with those of other recent studies implies that M2 is generically present in  thin   films  and bulk  samples below  ,  though  this  fact has not been...electrical  contacts. For  example, we succeeded  in growing high quality epitaxial VO2  films , by physical vapor transport using a  V2O5  source, on...Investigations were performed with a view to making such devices in the surface, or in thin crystals, of vanadium dioxide. This required developing

  8. Magnetism and Metal-Insulator Transition in Oxygen Deficient SrTiO3

    DOE PAGES

    Lopez-Bezanilla, Alejandro; Ganesh, Panchapakesan; Littlewood, Peter B.

    2015-09-08

    First-principles calculations to study the electronic and magnetic properties of bulk, oxygen-deficient SrTiO3 (STO) under different doping conditions and densities have been conducted. The appearance of magnetism in oxygen-deficient STO is not determined solely by the presence of a single oxygen vacancy but by the density of free carriers and the relative proximity of the vacant sites. We find that while an isolated vacancy behaves as a nonmagnetic double donor, manipulation of the doping conditions allows the stability of a single-donor state, with emergent local moments coupled ferromagnetically by carriers in the conduction band. Strong local lattice distortions enhance themore » binding of this state. As a result, the energy of the in-gap local moment can be further tuned by orthorhombic strain. Consequently we find that the free-carrier density and strain are fundamental components to obtaining trapped spin-polarized electrons in oxygen-deficient STO, which may have important implications in the design of optical devices.« less

  9. Metal-insulator transition in Au-NiO-Ni dual Schottky nanojunctions.

    PubMed

    Sun, Jia-Lin; Zhao, Xingchen; Zhu, Jia-Lin

    2009-11-11

    Ni nanowire arrays were fabricated through electrochemical deposition on a template. After a nanoscale NiO layer was formed on the top of the nanowires, a layer of Au paint was coated on the top of the nanowire arrays to construct Au-NiO-Ni dual Schottky nanojunctions, and the structure was characterized at different scales. Within a small range of voltages, extraordinary current jumps were observed at room temperature and at 77 K. The resistance switch effect can be repeated at room temperature, while switching is irreversible at low temperature. The significant change in resistance of the samples does not require doping and may find future applications.

  10. Magnetism and Metal-Insulator Transition in Oxygen Deficient SrTiO3

    SciTech Connect

    Lopez-Bezanilla, Alejandro; Ganesh, Panchapakesan; Littlewood, Peter B.

    2015-09-08

    First-principles calculations to study the electronic and magnetic properties of bulk, oxygen-deficient SrTiO3 (STO) under different doping conditions and densities have been conducted. The appearance of magnetism in oxygen-deficient STO is not determined solely by the presence of a single oxygen vacancy but by the density of free carriers and the relative proximity of the vacant sites. We find that while an isolated vacancy behaves as a nonmagnetic double donor, manipulation of the doping conditions allows the stability of a single-donor state, with emergent local moments coupled ferromagnetically by carriers in the conduction band. Strong local lattice distortions enhance the binding of this state. As a result, the energy of the in-gap local moment can be further tuned by orthorhombic strain. Consequently we find that the free-carrier density and strain are fundamental components to obtaining trapped spin-polarized electrons in oxygen-deficient STO, which may have important implications in the design of optical devices.

  11. Coulomb interactions and the metal-insulator transition in p-SiGe

    NASA Astrophysics Data System (ADS)

    Coleridge, P. T.; Lapointe, J.; Williams, R. L.; Zawadzki, P.

    2001-10-01

    Magnetoresistance data in p-SiGe samples is analysed using the Renormalisation Group theories of Finkel'stein and Castellani et al. The interaction parameter, γ2 is found to be of order one or larger than one, sufficient to explain the metallic behaviour in terms of delocalising Coulomb interaction corrections.

  12. Thickness-dependent metal-insulator transition in epitaxial SrRuO3 ultrathin films

    DOE PAGES

    Shen, Xuan; Qiu, Xiangbiao; Su, Dong; ...

    2015-01-06

    Transport characteristics of ultrathin SrRuO₃ films, deposited epitaxially on TiO₂-terminated SrTiO₃ (001) single-crystal substrates, were studied as a function of film thickness. Evolution from a metallic to an insulating behavior is observed as the film thickness decreases from 20 to 4 unit cells. In films thicker than 4 unit cells, the transport behavior obeys the Drude low temperature conductivity with quantum corrections, which can be attributed to weak localization. Fitting the data with 2-dimensional localization model indicates that electron-phonon collisions are the main inelastic relaxation mechanism. In the film of 4 unit cells in thickness, the transport behavior follows variablemore » range hopping model, indicating a strongly localized state. As a result, magnetoresistance measurements reveal a likely magnetic anisotropy with the magnetic easy axis along the out-of-plane direction.« less

  13. The metal-insulator phase transition in mixed potassium-rubidium electro-sodalites.

    PubMed

    Madsen, Georg K H

    2004-09-01

    The collapse under pressure of the antiferromagnetic ground state of the potassium-rubidium electro-sodalite is studied using the linearized augmented plane wave with local orbitals method. Special considerations needed for setting up this basis for systems such as the electro-sodalites are discussed. It is demonstrated that the magnetism collapses at a unit-cell volume similar to potassium electro-sodalite and rubidium electro-sodalite. A critical pressure of 8 GPa is predicted. The mechanism behind the collapse is a mixing of the F-center states with the highly diffuse unoccupied p states of the alkali atoms.

  14. Compact silicon photonic waveguide modulator based on the vanadium dioxide metal-insulator phase transition.

    PubMed

    Briggs, Ryan M; Pryce, Imogen M; Atwater, Harry A

    2010-05-24

    We have integrated lithographically patterned VO2 thin films grown by pulsed laser deposition with silicon-on-insulator photonic waveguides to demonstrate a compact in-line absorption modulator for use in photonic circuits. Using single-mode waveguides at lambda=1550 nm, we show optical modulation of the guided transverse-electric mode of more than 6.5 dB with 2 dB insertion loss over a 2-microm active device length. Loss is determined for devices fabricated on waveguide ring resonators by measuring the resonator spectral response, and a sharp decrease in resonator quality factor is observed above 70 degrees C, consistent with switching of VO2 to its metallic phase. A computational study of device geometry is also presented, and we show that it is possible to more than double the modulation depth with modified device structures.

  15. Resistance noise at the metal-insulator transition in thermochromic VO2 films

    NASA Astrophysics Data System (ADS)

    Topalian, Zareh; Li, Shu-Yi; Niklasson, Gunnar A.; Granqvist, Claes G.; Kish, Laszlo B.

    2015-01-01

    Thermochromic VO2 films were prepared by reactive DC magnetron sputtering onto heated sapphire substrates and were used to make 100-nm-thick samples that were 10 μm wide and 100 μm long. The resistance of these samples changed by a factor ˜2000 in the 50 < Ts < 70 °C range of temperature Ts around the "critical" temperature Tc between a low-temperature semiconducting phase and a high-temperature metallic-like phase of VO2. Power density spectra S(f) were extracted for resistance noise around Tc and demonstrated unambiguous 1/f behavior. Data on S(10 Hz)/Rs2 scaled as Rsx, where Rs is sample resistance; the noise exponent x was -2.6 for Ts < Tc and +2.6 for Ts > Tc. These exponents can be reconciled with the Pennetta-Trefán-Reggiani theory [Pennetta et al., Phys. Rev. Lett. 85, 5238 (2000)] for lattice percolation with switching disorder ensuing from random defect generation and healing in steady state. Our work hence highlights the dynamic features of the percolating semiconducting and metallic-like regions around Tc in thermochromic VO2 films.

  16. An Exploration and Optimization of the Metal Insulator Transition in Vanadium Dioxide Thin Films

    DTIC Science & Technology

    2009-12-02

    Standard Form 298 (Rev. 8 /98) REPORT DOCUMENTATION PAGE Prescribed by ANSI Std. Z39.18 Form Approved OMB No. 0704-0188 The public reporting...ELEMENT NUMBER 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 6. AUTHOR(S) 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8 . PERFORMING...NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT 13 . SUPPLEMENTARY NOTES 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: a. REPORT

  17. Temperature Dependent Low Frequency Optical and DC Transport Near a Metal Insulator Transition

    NASA Astrophysics Data System (ADS)

    Kohlman, R. S.; Epstein, A. J.; Tanner, D. B.; Ihas, G. G.; Ishiguro, T.; Kaneko, H.; Min, Y. G.; MacDiarmid, A. G.

    1996-03-01

    We report measurements of the temperature dependent far infrared (10-100 cm-1) reflectance and milliKelvin transport of highly conducting polyaniline doped with d,1-camphorsulfonic acid (PAN-CSA) and polypyrrole doped with hexafluorophosphate (PPy-PF_6). With decreasing T (to ~ 200 K), the reflectance initially increases for ω > 20 cm-1 and decreases at lower frequencies. As T is further decreased, there is a continuous reduction in the reflection. There is no indication of a gap opening at low temperatures in contrast to earlier reports for PPy-PF_6.^1 These results will be discussed along with mK magnetotransport measurements for ``metallic'' PAN-CSA samples that have a negative magnetoresistance similar to metallic PPy-PF6 ^2 and other nonmetallic samples, indicating the importance of weak localization channels for transport in highly conducting polymers. ^*Supported in part by NIST ATP 1993-01-0149 and NSF DMR-9403894. ^1K. Lee, et al., Synth. Met. 68, 287 (1995). ^2J. C. Clark, et al., Synth. Met. 69, 215 (1995).

  18. Nonequilibrium theory of a hot-electron bolometer with normal metal-insulator-superconductor tunnel junction

    SciTech Connect

    Golubev, Dmitri; Kuzmin, Leonid

    2001-06-01

    The operation of the hot-electron bolometer with normal metal-insulator-superconductor (NIS) tunnel junction as a temperature sensor is analyzed theoretically. The responsivity and the noise equivalent power (NEP) of the bolometer are obtained numerically for typical experimental parameters. Relatively simple approximate analytical expressions for these values are derived. The time constant of the device is also found. We demonstrate that the effect of the electron cooling by the NIS junction, which serves as a thermometer, can improve the sensitivity. This effect is also useful in the presence of the finite background power load. We discuss the effect of the correlation of the shot noise and the heat flow noise in the NIS junction. {copyright} 2001 American Institute of Physics.

  19. Metal-insulator-semiconductor heterostructures for plasmonic hot-carrier optoelectronics.

    PubMed

    García de Arquer, F Pelayo; Konstantatos, Gerasimos

    2015-06-01

    Plasmonic hot-electron devices are attractive candidates for light-energy harvesting and photodetection applications. For solid state devices, the most compact and straightforward architecture is the metal-semiconductor Schottky junction. However convenient, this structure introduces limitations such as the elevated dark current associated to thermionic emission, or constraints for device design due to the finite choice of materials. In this work we theoretically consider the metal-insulator-semiconductor heterojunction as a candidate for plasmonic hot-carrier photodetection and solar cells. The presence of the insulating layer can significantly reduce the dark current, resulting in increased device performance with predicted solar power conversion efficiencies up to 9%. For photodetection, the sensitivity can be extended well into the infrared by a judicious choice of the insulating layer, with up to 300-fold expected enhancement in detectivity.

  20. A four-port plasmonic quasi-circulator based on metal-insulator-metal waveguides.

    PubMed

    Wen, Kunhua; Yan, Lianshan; Pan, Wei; Luo, Bin; Guo, Zhen; Guo, Yinghui

    2012-12-17

    A metal-insulator-metal (MIM)-based four-port quasi-circulator consisting of four bus waveguides and eight narrow inside/outside slits is proposed without using nonreciprocity. Once the input port is defined, only a specific output port could be obtained by proper the design of parameters of the waveguides and slits. Simulation results based on finite-different time-domain (FDTD) method demonstrate that the transmittance at the center wavelength of the appropriate output port can reach 0.63 while those of the other two output ports are lower than 0.06. Through adjusting the slits spacing or optimizing the insulator material in the slits, the isolation of the circulator could be further improved with a slight sacrifice of the transmission. Such structure could also be used for wavelength demultiplexing with the center wavelength determined by the length of the bus waveguides and slits.

  1. Passive and active metasurface based on metal-insulator-metal structures

    NASA Astrophysics Data System (ADS)

    Takahara, Junichi; Liu, Tianji; Hatada, Hideaki; Nagasaki, Yusuke; Miyata, Masashi; Kaijima, Akira

    2016-11-01

    A metal-insulator-metal (MIM) structure is a fundamental plasmonic structure that has been studied widely since the early stage of plasmonics. It enables us to confine surface plasmon polariton (SPP) and concentrate light into nano-space beyond the diffraction limit. A finite-length MIM structure is considered to be a Fabry-Perot resonator of SPP as a nanocavity. Here, we review our recent studies about active metasurface based on a reconfigurable metal-air-metal (MAM) nanocavity which modify reflection or absorption spectra in scattering by changing a gap distance. Such reconfigurable MAM nanocavity becomes promising candidate for various applications such as plasmonic color or sky radiator from visible to infrared range.

  2. Plasmonic optical convergence microcavity based on the metal-insulator-metal microstructure

    NASA Astrophysics Data System (ADS)

    Wen, J.; Wang, W. J.; Li, N.; Li, Z. F.; Lu, W.

    2017-06-01

    With the increasing demand of low noise detection, the dimension of detectors are becoming smaller and smaller to reduce the dark current while sacrificing the detection efficiency. Here, a metal-insulator-metal (MIM) optical microcavity is proposed to converge light from tens of micrometers to several micrometers with little divergence. The measured transmission peaks show obvious dependence on the top metallic grating parameters, indicating the surface plasmon polariton resonance inside the cavity. Scanning near-field optical microscopy reveals the output profile around the exit holes. Polarization selective transmission has been demonstrated. If combined with a photodetector, the MIM microcavity, due to its light convergence capability, would provide a possibility to reduce the detector's active dimension down to 1-2 μm while retaining high quantum efficiency by keeping a large light collection area.

  3. Functional metal-insulator-metal top contacts for Si-based color photodetectors

    NASA Astrophysics Data System (ADS)

    Butun, Serkan; Aydin, Koray

    2016-12-01

    Here, we report on Si-based color photodetectors using monolithically integrated metal-insulator-metal Fabry-Perot cavity top contacts. Contacts were formed by depositing Ag/SiO2/Ag layers with different oxide thicknesses for each color. This allowed controlling the transmission band position and width while maintaining the high conductivity. We have obtained over 55% external quantum efficiency for different colors both numerically and experimentally. The FWHM was less than 50 nm and the rejection ratio was an order of magnitude for each color. The total transmission through these top contacts exceeded that of dye filters used in conventional color CCDs and CMOS imaging arrays. In addition, these contacts performed similarly to recently proposed plasmonic hole array filters without the necessity of complicated fabrication steps like FIB milling and e-beam lithography. This type of top contacts can serve as a cheap alternative to dye filters used in contemporary devices without making the fabrication complicated.

  4. A simple formulation for magnetoresistance in metal-insulator granular films with increased current

    NASA Astrophysics Data System (ADS)

    Boff, M. A. S.; Canto, B.; Baibich, M. N.; Pereira, L. G.

    2013-02-01

    We studied the tunnel magnetoresistance in metal/insulator granular films when the applied current is varied. The tunnel magnetoresistance shows a strong modification related to a non-Ohmic behaviour of theses materials. It was verified that spin-dependent tunnelling is the main mechanism for magnetoresistance at low applied current. However, when the current is high, another mechanism gets to be important: it is independent of the magnetization and is associated to variable range hopping between metallic grains. In this work, we propose a simple modification of Inoue and Maekawa's model for tunnelling magnetoresistance in granulars, rewriting the expression for resistance as a function of magnetic field and temperature, also taking into account the two different contributions.

  5. Optical magnetism and plasmonic Fano resonances in metal-insulator-metal oligomers.

    PubMed

    Verre, R; Yang, Z J; Shegai, T; Käll, M

    2015-03-11

    The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructures has recently been a subject of great interest. The concept is based on designing structures that support plasmon modes with electron oscillation patterns that imitate current loops, that is, magnetic dipoles. However, the magnetic resonances are typically spectrally narrow, thereby limiting their applicability in, for example, metamaterial designs. We show that a significantly broader magnetic response can be realized in plasmonic pentamers constructed from metal-insulator-metal (MIM) sandwich particles. Each MIM unit acts as a magnetic meta-atom and the optical magnetism is rendered quasi-broadband through hybridization of the in-plane modes. We demonstrate that scattering spectra of individual MIM pentamers exhibit multiple Fano resonances and a broad subradiant spectral window that signals the magnetic interaction and a hierarchy of coupling effects in these intricate three-dimensional nanoparticle oligomers.

  6. Si nanowire metal-insulator-semiconductor photodetectors as efficient light harvesters.

    PubMed

    Bae, Joonho; Kim, Hyunjin; Zhang, Xiao-Mei; Dang, Cuong H; Zhang, Yue; Choi, Young Jin; Nurmikko, Arto; Wang, Zhong Lin

    2010-03-05

    Novel ITO-Si nanowire (NW) metal-insulator-semiconductor (MIS) photodetectors were fabricated by using n-type Si NWs as detection units and ITO films as top gate electrodes. Measurements on the Si NW based device reveal a significant photoresponse, including photocurrent generation with an external quantum efficiency (EQE) of approximately 35% at a peak wavelength of 600 nm at zero external bias, and with an EQE of 70% at a peak wavelength of 800 nm at - 0.5 V bias. The NW device shows a flat and low reflectance and almost constant EQE up to a 60 degrees incident angle of illumination, demonstrating efficient visible-light harvesting by the Si NW antenna.

  7. Frequency selective heterojunction metal-insulator-metal mirror for surface plasmons

    NASA Astrophysics Data System (ADS)

    Hwang, Yongsop; Shin, Jonghwa; Kim, Jae-Eun; Park, Hae Yong; Kee, Chul-Sik

    2011-06-01

    The authors introduce a mode-gap mirror for surface plasmon polaritons in a metal-insulator-metal (MIM) structure. At the heterojunction of MIMs which consists of two MIMs of different insulators, it is shown that a mode gap exists for a certain frequency range and the junction works as an effective mirror. Transmission and reflection properties of plasmonic modes at the interface of the heterojunction are investigated, and explained by the band theory. By showing that the mirror has high reflection and transmission of nearly zero, it is verified that the frequency range in which no plasmonic modes exist is an actual mode-gap range. It is also shown that by varying both the thickness and the dielectric constant of the insulator layer, one can select the frequency range in which the reflection coefficient is greater than 0.9.

  8. Metal-Insulator-Semiconductor Diode Consisting of Two-Dimensional Nanomaterials.

    PubMed

    Jeong, Hyun; Oh, Hye Min; Bang, Seungho; Jeong, Hyeon Jun; An, Sung-Jin; Han, Gang Hee; Kim, Hyun; Yun, Seok Joon; Kim, Ki Kang; Park, Jin Cheol; Lee, Young Hee; Lerondel, Gilles; Jeong, Mun Seok

    2016-03-09

    We present a novel metal-insulator-semiconductor (MIS) diode consisting of graphene, hexagonal BN, and monolayer MoS2 for application in ultrathin nanoelectronics. The MIS heterojunction structure was fabricated by vertically stacking layered materials using a simple wet chemical transfer method. The stacking of each layer was confirmed by confocal scanning Raman spectroscopy and device performance was evaluated using current versus voltage (I-V) and photocurrent measurements. We clearly observed better current rectification and much higher current flow in the MIS diode than in the p-n junction and the metal-semiconductor diodes made of layered materials. The I-V characteristic curve of the MIS diode indicates that current flows mainly across interfaces as a result of carrier tunneling. Moreover, we observed considerably high photocurrent from the MIS diode under visible light illumination.

  9. Phase modulation in horizontal metal-insulator-silicon-insulator-metal plasmonic waveguides.

    PubMed

    Zhu, Shiyang; Lo, G Q; Kwong, D L

    2013-04-08

    An extremely compact Si phase modulator is proposed and validated, which relies on effective modulation of the real part of modal index of horizontal metal-insulator-Si-insulator-metal plasmonic waveguides by a voltage applied between the metal cover and the Si core. Proof-of-concept devices are fabricated on silicon-on-insulator substrates using standard complementary metal-oxide-semiconductor technology using copper as the metal and thermal silicon dioxide as the insulator. A modulator with a 1-μm-long phase shifter inserted in an asymmetric Si Mach-Zehnder interferometer exhibits 9-dB extinction ratio under a 6-V/10-kHz voltage swing. Numerical simulations suggest that high speed and low driving voltage could be achieved by shortening the distance between the Si core and the n(+)-contact and by using a high-κ dielectric as the insulator, respectively.

  10. Nanoscale temperature sensor based on Fano resonance in metal-insulator-metal waveguide

    NASA Astrophysics Data System (ADS)

    Kong, Yan; Wei, Qi; Liu, Cheng; Wang, Shouyu

    2017-02-01

    In order to realize temperature measurements with high sensitivity using compact structure, a nanoscale metal-insulator-metal waveguide based sensor combining with Fano resonance is proposed in this paper. Sealed ethanol in resonant cavity is adopted to further improve sensing performance. Additionally, dual resonant cavity based configuration is designed to generate a Fano-based sharp and asymmetric spectrum, providing high figure of merit in measurements. Moreover, structural parameters are optimized considering both transmission rate and spectral peak width. Certified by numerical calculation, sensitivity of 0.36 nm/°C is acquired with the optimized structure, indicating the designed sensor can play an important role in the nano-integrated plasmonic devices for high-accurate temperature detection.

  11. Enhancing metal-insulator-insulator-metal tunnel diodes via defect enhanced direct tunneling

    SciTech Connect

    Alimardani, Nasir; Conley, John F.

    2014-08-25

    Metal-insulator-insulator-metal tunnel diodes with dissimilar work function electrodes and nanolaminate Al{sub 2}O{sub 3}-Ta{sub 2}O{sub 5} bilayer tunnel barriers deposited by atomic layer deposition are investigated. This combination of high and low electron affinity insulators, each with different dominant conduction mechanisms (tunneling and Frenkel-Poole emission), results in improved low voltage asymmetry and non-linearity of current versus voltage behavior. These improvements are due to defect enhanced direct tunneling in which electrons transport across the Ta{sub 2}O{sub 5} via defect based conduction before tunneling directly through the Al{sub 2}O{sub 3}, effectively narrowing the tunnel barrier. Conduction through the device is dominated by tunneling, and operation is relatively insensitive to temperature.

  12. Decay and propagation properties of symmetric surface plasmon polariton mode in metal-insulator-metal waveguide

    NASA Astrophysics Data System (ADS)

    Yang, Hongyan; Li, Jianqing; Xiao, Gongli

    2017-07-01

    Decay and propagation properties of symmetric surface plasmon polariton (SPP) mode based on metal-insulator-metal (MIM) waveguide are investigated numerically. SPP mode is excited through a dipole embedded in Al2 O3 layer of Au /Al2 O3 / Au structure. We demonstrate that the distance between the dipole and Al2 O3 / Au interface is an important tunable parameter to influence the decay properties. The electric/magnetic field intensity horizontal and vertical decay lengths of symmetric SPP mode are 19 nm and 24 nm, respectively. Moreover, the propagation length along Al2 O3 / Au interface of symmetric SPP mode depends on Al2 O3 layer thickness. The maximal propagation length reaches 0.608 μm with Al2 O3 layer thickness of 100 nm. These values can provide a theoretical reference for designing a high-performance SPP source using Au /Al2 O3 / Au structure.

  13. Andreev Reflections in Micrometer-Scale Normal Metal-Insulator-Superconductor Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Lowell, Peter J.; O'Neil, Galen C.; Underwood, Jason M.; Ullom, Joel N.

    2011-11-01

    Understanding the subgap behavior of Normal metal-Insulator-Superconductor (NIS) tunnel junctions is important in order to be able to accurately model the thermal properties of the junctions. Hekking and Nazarov (Phys. Rev. B 49:6847, 1994) developed a theory in which NIS subgap current in thin-film structures can be modeled by multiple Andreev reflections. In their theory, the current due to Andreev reflections depends on the junction area and the junction resistance area product. We have measured the current due to Andreev reflections in NIS tunnel junctions for various junction sizes and junction resistance area products and found that the multiple reflection theory is in agreement with our data.

  14. Microrefrigeration by a pair of normal metal/insulator/superconductor junctions

    NASA Technical Reports Server (NTRS)

    Leivo, M. M.; Pekola, J. P.; Averin, D. V.

    1995-01-01

    We suggest and demonstrate experimentally that two normal metal/insulator/superconductor (NIS) tunnel junctions combined in series to form a symmetric SINIS structure can operate as an efficient Peltier refrigerator. Specifically, it is shown that the SINIS structure with normal-state junction resistences of 1.0 and 1.1 kOmega is capable of reaching a temperature of about 100 mK starting from 300 mK. We estimate the corresponding cooling power to be 1.5 pW per total junction area of 0.8 micrometers(exp 2) at T = 300 mK. This cooling power density implies that scaling of junction area up to about 1 mm(exp 2) should bring the cooling power into the microW range.

  15. Anisotropic Strain Induced Directional Metallicity in Highly Epitaxial LaBaCo2O5.5+δ Thin Films on (110) NdGaO3

    NASA Astrophysics Data System (ADS)

    Ma, Chunrui; Han, Dong; Liu, Ming; Collins, Gregory; Wang, Haibin; Xu, Xing; Lin, Yuan; Jiang, Jiechao; Zhang, Shengbai; Chen, Chonglin

    2016-11-01

    Highly directional-dependent metal-insulator transition is observed in epitaxial double perovskite LaBaCo2O5.5+δ films. The film exhibit metallic along [100], but remain semiconducting along [010] under application of a magnetic field parallel to the surface of the film. The physical origin for the properties is identified as in-plane tensile strain arising from oxygen vacancies. First-principle calculations suggested the tensile strain drastically alters the band gap, and the vanishing gap opens up [100] conduction channels for Fermi-surface electrons. Our observation of strain-induced highly directional-dependent metal-insulator transition may open up new dimension for multifunctional devices.

  16. Anisotropic Strain Induced Directional Metallicity in Highly Epitaxial LaBaCo2O5.5+δ Thin Films on (110) NdGaO3

    PubMed Central

    Ma, Chunrui; Han, Dong; Liu, Ming; Collins, Gregory; Wang, Haibin; Xu, Xing; Lin, Yuan; Jiang, Jiechao; Zhang, Shengbai; Chen, Chonglin

    2016-01-01

    Highly directional-dependent metal-insulator transition is observed in epitaxial double perovskite LaBaCo2O5.5+δ films. The film exhibit metallic along [100], but remain semiconducting along [010] under application of a magnetic field parallel to the surface of the film. The physical origin for the properties is identified as in-plane tensile strain arising from oxygen vacancies. First-principle calculations suggested the tensile strain drastically alters the band gap, and the vanishing gap opens up [100] conduction channels for Fermi-surface electrons. Our observation of strain-induced highly directional-dependent metal-insulator transition may open up new dimension for multifunctional devices. PMID:27869137

  17. Anisotropic Strain Induced Directional Metallicity in Highly Epitaxial LaBaCo2O5.5+δ Thin Films on (110) NdGaO3.

    PubMed

    Ma, Chunrui; Han, Dong; Liu, Ming; Collins, Gregory; Wang, Haibin; Xu, Xing; Lin, Yuan; Jiang, Jiechao; Zhang, Shengbai; Chen, Chonglin

    2016-11-21

    Highly directional-dependent metal-insulator transition is observed in epitaxial double perovskite LaBaCo2O5.5+δ films. The film exhibit metallic along [100], but remain semiconducting along [010] under application of a magnetic field parallel to the surface of the film. The physical origin for the properties is identified as in-plane tensile strain arising from oxygen vacancies. First-principle calculations suggested the tensile strain drastically alters the band gap, and the vanishing gap opens up [100] conduction channels for Fermi-surface electrons. Our observation of strain-induced highly directional-dependent metal-insulator transition may open up new dimension for multifunctional devices.

  18. Anisotropic strain induced directional metallicity in highly epitaxial LaBaCo2O5.5+δ thin films on (110) NdGaO3

    DOE PAGES

    Ma, Chunrui; Han, Dong; Liu, Ming; ...

    2016-11-21

    Highly directional-dependent metal-insulator transition is observed in epitaxial double perovskite LaBaCo2O5.5+δ films. The film exhibit metallic along [100], but remain semiconducting along [010] under application of a magnetic field parallel to the surface of the film. The physical origin for the properties is identified as in-plane tensile strain arising from oxygen vacancies. First-principle calculations suggested the tensile strain drastically alters the band gap, and the vanishing gap opens up [100] conduction channels for Fermi-surface electrons. Lastly, our observation of strain-induced highly directional-dependent metal-insulator transition may open up new dimension for multifunctional devices.

  19. Disorder-induced structural transitions in topological insulating Ge-Sb-Te compounds

    SciTech Connect

    Kim, Jeongwoo; Jhi, Seung-Hoon

    2015-05-21

    The mechanism for the fast switching between amorphous, metastable, and crystalline structures in chalcogenide phase-change materials has been a long-standing puzzle. Based on first-principles calculations, we study the atomic and electronic properties of metastable Ge{sub 2}Sb{sub 2}Te{sub 5} and investigate the atomic disorder to understand the transition between crystalline hexagonal and cubic structures. In addition, we study the topological insulating property embedded in these compounds and its evolution upon structural changes and atomic disorder. We also discuss the role of the surface-like states arising from the topological insulating property in the metal-insulator transition observed in the hexagonal structure.

  20. Noise induced transitions in rugged energy landscapes

    NASA Astrophysics Data System (ADS)

    Pradas, Marc; Duncan, Andrew; Kalliadasis, Serafim; Pavliotis, Greg

    2016-11-01

    External or internal random fluctuations are ubiquitous in many physical and technological systems and can play a key role in their dynamics often inducing a wide variety of complex spatiotemporal phenomena, including noise-induced spatial patterns and noise-induced phase transitions. Many of these phenomena can be modelled by noisy multiscale systems characterized by the presence of a wide range of different time- and lengthscales interacting nontrivially with each other. Here we analyse the effects of additive noise on systems that are described in terms of a rugged energy landscape, modelled as a slowly-varying multiscale potential perturbed by periodic multiscale fluctuations. Some examples of this problem include the dynamics of sessile droplets on heterogeneous substrates, crystallization and the evolution of protein folding. We demonstrate that the interplay between noise and the small scale fluctuations in the potential can give rise to a dramatically different bifurcation structure and dynamical behaviour compared to that of the original, unperturbed model. For instance, we observe several nontrivial and largely unexpected dynamic-state transitions controlled by the noise intensity. We characterize these transitions in terms of critical exponents.

  1. Anisotropic strain induced directional metallicity in highly epitaxial LaBaCo2O5.5+δ thin films on (110) NdGaO3

    SciTech Connect

    Ma, Chunrui; Han, Dong; Liu, Ming; Collins, Gregory; Wang, Haibin; Xu, Xing; Lin, Yuan; Jiang, Jiechao; Zhang, Shengbai; Chen, Chonglin

    2016-11-21

    Highly directional-dependent metal-insulator transition is observed in epitaxial double perovskite LaBaCo2O5.5+δ films. The film exhibit metallic along [100], but remain semiconducting along [010] under application of a magnetic field parallel to the surface of the film. The physical origin for the properties is identified as in-plane tensile strain arising from oxygen vacancies. First-principle calculations suggested the tensile strain drastically alters the band gap, and the vanishing gap opens up [100] conduction channels for Fermi-surface electrons. Lastly, our observation of strain-induced highly directional-dependent metal-insulator transition may open up new dimension for multifunctional devices.

  2. Pulsed laser-induced oxygen deficiency at TiO{sub 2} surface: Anomalous structure and electrical transport properties

    SciTech Connect

    Nakajima, Tomohiko; Tsuchiya, Tetsuo; Kumagai, Toshiya

    2009-09-15

    We have studied pulsed laser-induced oxygen deficiencies at rutile TiO{sub 2} surfaces. The crystal surface was successfully reduced by excimer laser irradiation, and an oxygen-deficient TiO{sub 2-{delta}} layer with 160 nm thickness was formed by means of ArF laser irradiation at 140 mJ/cm{sup 2} for 2000 pulses. The TiO{sub 2-{delta}} layer fundamentally maintained a rutile structure, though this structure was distorted by many stacking faults caused by the large oxygen deficiency. The electrical resistivity of the obtained TiO{sub 2-{delta}} layer exhibited unconventional metallic behavior with hysteresis. A metal-insulator transition occurred at 42 K, and the electrical resistivity exceeded 10{sup 4} OMEGA cm below 42 K. This metal-insulator transition could be caused by bipolaronic ordering derived from Ti-Ti pairings that formed along the stacking faults. The constant magnetization behavior observed below 42 K is consistent with the bipolaronic scenario that has been observed previously for Ti{sub 4}O{sub 7}. These peculiar electrical properties are strongly linked to the oxygen-deficient crystal structure, which contains many stacking faults formed by instantaneous heating during excimer laser irradiation. - Graphical abstract: A pulsed laser-irradiated TiO{sub 2-{delta}} substrate showed an unconventional metallic phase, with hysteresis over a wide range of temperatures and a metal-insulator transition at 42 K.

  3. Pressure induced quantum phase transitions in metallic oxides and pnictides

    NASA Astrophysics Data System (ADS)

    Fallah Tafti, Fazel

    Quantum phase transitions occur as a result of competing ground states. The focus of the present work is to understand quantum criticality and its consequences when the competition is between insulating and metallic ground states. Metal-insulator transitions are studied by means of electronic transport measurements and quantum critical points are approached by applying hydrostatic pressure in two different compounds namely Eu2Ir22O 7 and FeCrAs. The former is a ternary metal oxide and the latter is a ternary metal pnictide. A major component of this work was the development of the ultra-high pressure measurements by means of Anvil cells. A novel design is introduced which minimizes the alignment accessory components hence, making the cell more robust and easier to use. Eu2Ir22O7 is a ternary metal oxide and a member of the pyrochlore iridate family. Resistivity measurements under pressure in moissanite anvil cells show the evolution of the ground state of the system from insulating to metallic. The quantum phase transition at Pc ˜ 6 GPa appears to be continuous. A remarkable correspondence is revealed between the effect of the hydrostatic pressure on Eu2Ir22O7 and the effect of chemical pressure by changing the R size in the R2Ir2O7 series. This suggests that in both cases the tuning parameter controls the t2g bandwidth of the iridium 5d electrons. Moreover, hydrostatic pressure unveils a curious cross-over from incoherent to conventional metallic behaviour at a T* > 150 K in the neighbourhood of Pc, suggesting a connection between the high and low temperature phases. The possibility of a topological semi-metallic ground state, predicted in recent theoretical studies, is explained. FeCrAs is a ternary metal pnictide with Fermi liquid specific heat and susceptibility behaviour but non-metallic non-Fermi liquid resistivity behaviour. Characteristic properties of the compound are explained and compared to those of superconducting pnictides. Antiferromagnetic (AFM

  4. Germanium Metal - Insulator - Semiconductor Field Effect Transistors Utilizing a Germanium Nitride Gate Insulator.

    NASA Astrophysics Data System (ADS)

    Rosenberg, James Jordan

    The work presented in this thesis provides new information on three distinct but related topics. Firstly, it describes a technique for growing thin films of germanium nitride on germanium--a previously unexplored semiconductor -insulator system. Secondly, it describes electrical measurements made on metal-Ge(,3)N(,4)-Ge capacitors which demonstrate that this metal-insulator-semiconductor (MIS) system is of high quality. Thirdly, it describes a process by which n-channel germanium metal-insulator-semiconductor field effect transistors (MISFETs) have been fabricated. The motivations for exploring this new MIS system (e.g. basic physics of germanium inversion layers, higher performance MISFETs, etc.) are also described. The growth technique described here and the films produced by it possess several distinct advantages over previous methods of obtaining insulating films on germanium. The growth technique itself is simple. It involves no elaborate or expensive equipment, and is essentially identical in its execution (although not in its chemical process) to conventional techniques for obtaining an insulator on silicon (i.e. thermal oxidation of silicon). The film growth technique yields very reproducible results (in terms of film thickness and refractive index) from wafer to wafer. The physical properties of the film itself are also attractive. It is far more chemically stable than germanium oxide, and is quite process compatible. It is resistant to many chemicals encountered in typical processing cycles, but also can be readily patterned in hot phosphoric acid, which does not appreciably attack germanium. Electrical measurements on MIS capacitors indicate that the density of fast states at the germanium-germanium nitride interface is quite low. The interface state density is less than or equal to 1 x 10('11)/cm('2)-eV from midgap to within 0.15 eV of the conduction band edge, as determined by variable frequency capacitance measurements. The MISFETs fabricated for this

  5. Shear induced phase transitions induced in edible fats

    NASA Astrophysics Data System (ADS)

    Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.

    2003-03-01

    The food industry crystallizes fats under different conditions of temperature and shear to obtain products with desired crystalline phases. Milk fat, palm oil, cocoa butter and chocolate were crystallized from the melt in a temperature controlled Couette cell. Synchrotron x-ray diffraction studies were conducted to examine the role of shear on the phase transitions seen in edible fats. The shear forces on the crystals induced acceleration of the alpha to beta-prime phase transition with increasing shear rate in milk fat and palm oil. The increase was slow at low shear rates and became very strong above 360 s-1. In cocoa butter the acceleration between beta-prime-III and beta-V phase transition increased until a maximum of at 360 s-1, and then decreased, showing competition between enhanced heat transfer and viscous heat generation.

  6. Theoretical model of homogeneous metal-insulator-metal perfect multi-band absorbers for the visible spectrum

    NASA Astrophysics Data System (ADS)

    Kajtár, G.; Kafesaki, M.; Economou, E. N.; Soukoulis, C. M.

    2016-02-01

    We present a rigorous study of the perfect absorption properties of metal-insulator-metal (MIM) structures in the visible spectrum. We provide a derivation (based on the transfer matrix method) and analysis of the conditions for which the perfect absorption occurs. We show that these conditions are fulfilled when the incident wave excites the eigenmodes of the structure. The quantitative analysis allows us to design specific perfect absorbers for our needs. The analytical model is verified by rigorous simulations based on rigorous coupled wave analysis, which demonstrate also the angle and polarization insensitivity of the absorption properties of such a structure. Employing the MIM approach and results, we also investigate and demonstrate multiple perfect absorption bands and broad-band absorption in properly designed multilayer metal-insulator systems.

  7. Fluoride dielectric films on InP for metal-insulator-semiconductor applications

    NASA Astrophysics Data System (ADS)

    Paul, T. K.; Bose, D. N.

    1990-04-01

    This paper describes the characteristics of thin fluoride films on InP which are used as dielectric for metal-insulator-semiconductor (MIS) devices. Films of Ba1-xSrxF2 (x=0.0, 0.5, 0.83, and 1.0) were deposited by sublimation of mixtures of BaF2 and SrF2 in vacuum under 10-5 Torr pressure. The composition of the films was deduced from x-ray diffraction and energy dispersion analysis by x-ray studies. The electrical activation energies of the films determined between 120 and 300 K were found to be 3.5-22.0×10-3 eV , depending on composition and temperature. The resistivity of the films was in the range of 5.0×1011 to 5.0×1012 Ω cm with the breakdown fields greater than 5.0×105 V cm-1 . The interface state density obtained was as low as 5×1010 cm-2 eV-1 with annealed BaF2 films. Scanning electron microscope studies showed that annealing caused development of cracks resulting in decreased film resistivity. Auger studies gave evidence of broadening of the interface and outdiffusion from the substrate due to annealing.

  8. Magnetic Nanoparticles in "Amorphous Ferromagnetic Metal-Insulator" Nanogranular thin Films

    NASA Astrophysics Data System (ADS)

    Granovsky, A.; Kalinin, Yu.; Sitnikov, A.; Stognei, O.

    A lot of factors limit possible applications of magnetic nanoparticles in medicine for drug delivery and magnetic hyperthermia therefore it is of primary importance to understand influence of classical and quantum-size effects, surface layers, interparticle distance, shape of nanoparticles on their magnetic properties. Magnetic nanogranular thin films, known also as nanocomposites, can be considered as a convenient model for such investigations as it is possible to tune easily many of mentioned above parameters by varying of the fabrication conditions. The ion-beam sputtering technique has been developed to prepare "amorphous ferromagnetic metal-insulator" nanocomposites with different concentration and parameters simultaneously in one technological cycle. This feature is achieved by using of a composite target (consisting of a metal and dielectric parts) with an asymmetric arrangement of the dielectric parts on the metal base. Influence of sputtering conditions and post-fabrication treatment on structural, magnetic, electrical and magnetotransport properties of magnetic nanocomposites in a wide range of metal volume fraction and distance between magnetic nanoparticles is being discussed.

  9. A transparent electrochromic metal-insulator switching device with three-terminal transistor geometry

    PubMed Central

    Katase, Takayoshi; Onozato, Takaki; Hirono, Misako; Mizuno, Taku; Ohta, Hiromichi

    2016-01-01

    Proton and hydroxyl ion play an essential role for tuning functionality of oxides because their electronic state can be controlled by modifying oxygen off-stoichiometry and/or protonation. Tungsten trioxide (WO3), a well-known electrochromic (EC) material for smart window, is a wide bandgap insulator, whereas it becomes a metallic conductor HxWO3 by protonation. Although one can utilize electrochromism together with metal-insulator (MI) switching for one device, such EC-MI switching cannot be utilized in current EC devices because of their two-terminal structure with parallel-plate configuration. Here we demonstrate a transparent EC-MI switchable device with three-terminal TFT-type structure using amorphous (a-) WO3 channel layer, which was fabricated on glass substrate at room temperature. We used water-infiltrated nano-porous glass, CAN (calcium aluminate with nano-pores), as a liquid-leakage-free solid gate insulator. At virgin state, the device was fully transparent in the visible-light region. For positive gate voltage, the active channel became dark blue, and electrical resistivity of the a-WO3 layer drastically decreased with protonation. For negative gate voltage, deprotonation occurred and the active channel returned to transparent insulator. Good cycleability of the present transparent EC-MI switching device would have potential for the development of advanced smart windows. PMID:27174791

  10. Thin-film composite materials as a dielectric layer for flexible metal-insulator-metal capacitors.

    PubMed

    Tiwari, Jitendra N; Meena, Jagan Singh; Wu, Chung-Shu; Tiwari, Rajanish N; Chu, Min-Ching; Chang, Feng-Chih; Ko, Fu-Hsiang

    2010-09-24

    A new organic-organic nanoscale composite thin-film (NCTF) dielectric has been synthesized by solution deposition of 1-bromoadamantane and triblock copolymer (Pluronic P123, BASF, EO20-PO70-EO20), in which the precursor solution has been achieved with organic additives. We have used a sol-gel process to make a metal-insulator-metal capacitor (MIM) comprising a nanoscale (10 nm-thick) thin-film on a flexible polyimide (PI) substrate at room temperature. Scanning electron microscope and atomic force microscope revealed that the deposited NCTFs were crack-free, uniform, highly resistant to moisture absorption, and well adhered on the Au-Cr/PI. The electrical properties of 1-bromoadamantane-P123 NCTF were characterized by dielectric constant, capacitance, and leakage current measurements. The 1-bromoadamantane-P123 NCTF on the PI substrate showed a low leakage current density of 5.5 x 10(-11) A cm(-2) and good capacitance of 2.4 fF at 1 MHz. In addition, the calculated dielectric constant of 1-bromoadamantane-P123 NCTF was 1.9, making them suitable candidates for use in future flexible electronic devices as a stable intermetal dielectric. The electrical insulating properties of 1-bromoadamantane-P123 NCTF have been improved due to the optimized dipole moments of the van der Waals interactions.

  11. Refractive Index Sensor Based on Fano Resonances in Metal-Insulator-Metal Waveguides Coupled with Resonators.

    PubMed

    Tang, Yue; Zhang, Zhidong; Wang, Ruibing; Hai, Zhenyin; Xue, Chenyang; Zhang, Wendong; Yan, Shubin

    2017-04-06

    A surface plasmon polariton refractive index sensor based on Fano resonances in metal-insulator-metal (MIM) waveguides coupled with rectangular and ring resonators is proposed and numerically investigated using a finite element method. Fano resonances are observed in the transmission spectra, which result from the coupling between the narrow-band spectral response in the ring resonator and the broadband spectral response in the rectangular resonator. Results are analyzed using coupled-mode theory based on transmission line theory. The coupled mode theory is employed to explain the Fano resonance effect, and the analytical result is in good agreement with the simulation result. The results show that with an increase in the refractive index of the fill dielectric material in the slot of the system, the Fano resonance peak exhibits a remarkable red shift, and the highest value of sensitivity (S) is 1125 nm/RIU, RIU means refractive index unit. Furthermore, the coupled MIM waveguide structure can be integrated with other photonic devices at the chip scale. The results can provide a guide for future applications of this structure.

  12. Angular dependence of optical modes in metal-insulator-metal coupled quantum well infrared photodetector

    SciTech Connect

    Jing, YouLiang; Li, ZhiFeng Chen, PingPing; Zhou, XiaoHao; Wang, Han; Li, Ning; Lu, Wei; Li, Qian

    2016-04-15

    We report the dependence of the near-field optical modes in metal-insulator-metal quantum well infrared photodetector (MIM-QWIP) on the incident angles. Three optical modes are observed and attributed to the 2nd- and the 3rd-order surface plasmon polariton (SPP) modes and the localized surface polariton (LSP) mode. In addition to the observation of a responsivity enhancement of 14 times by the LSP mode, the varying pattern of the three modes against the incident angle are revealed, in which the LSP mode is fixed while the 2nd SPP mode splits into two branches and the 3rd SPP mode red-shifts. The detailed mechanisms are analyzed and numerically simulated. The results fit the experiments very well, demonstrating the wavevector coupling effect between the incident light and the metal gratings on the SPP modes. Our work will pave the way to fully understanding the influence of incident angles on a detector’s response for applying the MIM-QWIP to focal plane arrays.

  13. Angular dependence of optical modes in metal-insulator-metal coupled quantum well infrared photodetector

    NASA Astrophysics Data System (ADS)

    Jing, YouLiang; Li, ZhiFeng; Li, Qian; Chen, PingPing; Zhou, XiaoHao; Wang, Han; Li, Ning; Lu, Wei

    2016-04-01

    We report the dependence of the near-field optical modes in metal-insulator-metal quantum well infrared photodetector (MIM-QWIP) on the incident angles. Three optical modes are observed and attributed to the 2nd- and the 3rd-order surface plasmon polariton (SPP) modes and the localized surface polariton (LSP) mode. In addition to the observation of a responsivity enhancement of 14 times by the LSP mode, the varying pattern of the three modes against the incident angle are revealed, in which the LSP mode is fixed while the 2nd SPP mode splits into two branches and the 3rd SPP mode red-shifts. The detailed mechanisms are analyzed and numerically simulated. The results fit the experiments very well, demonstrating the wavevector coupling effect between the incident light and the metal gratings on the SPP modes. Our work will pave the way to fully understanding the influence of incident angles on a detector's response for applying the MIM-QWIP to focal plane arrays.

  14. Optimal design of resonant enhanced quantum dot infrared photodetector based on metal-insulator-metal microcavity

    NASA Astrophysics Data System (ADS)

    Wang, Han; Jing, Youliang; Li, Mengyao; Li, Liang; Zhen, Honglou

    2015-11-01

    The design of quantum dot infrared photodetector (QDIP) based on metal-insulator-metal (MIM) microcavity in which the quantum dot (QD) is sandwiched between a planar metallic film and a metallic stripe is reported. By a finite difference time-domain (FDTD) method, the light coupling efficiency spectra and enhancement factor are numerically calculated. The results exhibit that the total electric field concentrated in metal-metal region is strongly enhanced when the resonant frequency of microcavity is equal to the QD's peak response frequency. This enhancement effect mainly originates from the resonant coupling of incident photons into microcavity forming the surface plasmonic mode. The optimization of structural parameters for MIM microcavity is discussed, demonstrating an optimal structure of quantum dot infrared photodetector with the coupling efficiency improved nearly 7 times compared with conventional mesa QDIPs. So, it is deduced that a favorable performance of device such as high quantum efficiency and infrared responsivity is possible. Finally, the detector shows the potential application in the infrared sensing and imaging, as well as integrating with other electronic and optoelectronic device for the sub-wavelength size.

  15. Amorphous silicon enhanced metal-insulator-semiconductor contacts for silicon solar cells

    NASA Astrophysics Data System (ADS)

    Bullock, J.; Cuevas, A.; Yan, D.; Demaurex, B.; Hessler-Wyser, A.; De Wolf, S.

    2014-10-01

    Carrier recombination at the metal-semiconductor contacts has become a significant obstacle to the further advancement of high-efficiency diffused-junction silicon solar cells. This paper provides the proof-of-concept of a procedure to reduce contact recombination by means of enhanced metal-insulator-semiconductor (MIS) structures. Lightly diffused n+ and p+ surfaces are passivated with SiO2/a-Si:H and Al2O3/a-Si:H stacks, respectively, before the MIS contacts are formed by a thermally activated alloying process between the a-Si:H layer and an overlying aluminum film. Transmission/scanning transmission electron microscopy (TEM/STEM) and energy dispersive x-ray spectroscopy are used to ascertain the nature of the alloy. Idealized solar cell simulations reveal that MIS(n+) contacts, with SiO2 thicknesses of ˜1.55 nm, achieve the best carrier-selectivity producing a contact resistivity ρc of ˜3 mΩ cm2 and a recombination current density J0c of ˜40 fA/cm2. These characteristics are shown to be stable at temperatures up to 350 °C. The MIS(p+) contacts fail to achieve equivalent results both in terms of thermal stability and contact characteristics but may still offer advantages over directly metallized contacts in terms of manufacturing simplicity.

  16. Analytical and experimental investigation of electrical characteristics of a metallic insulation GdBCO coil.

    PubMed

    Yang, D G; Choi, Y H; Kim, Y G; Song, J B; Lee, H G

    2016-03-01

    This paper presents results, experimental and analytical, of the electrical characteristics of GdBCO single-pancake coils co-wound with a brass tape as metallic insulation (MI coil). The GdBCO pancakes were subjected to sudden discharge, charge-discharge, and over-current tests. The sudden discharge and charge-discharge test results of the MI coil demonstrated that MI coils can be charged and discharged significantly faster than non-insulated coils that are wound only with GdBCO tape. In over-current tests at 150 A (1.25I(c)), the MI coil exhibited better electrical behavior, i.e., self-protecting features, than its counterpart co-wound with Kapton tape, an insulator. Moreover, the experimental and analytical results are in agreement, validating the use of a concise equivalent parallel-RL circuit model for the MI coil to characterize its electrical behavior. Overall, the MI winding technique is highly promising to help build compact, mechanically robust, and self-protecting magnets composed of REBCO pancake coils. With no organic material in the winding, MI REBCO pancakes will be immune to neutron radiation damage, making the MI winding technique a viable option for fusion reactors, such as for toroidal field, poroidal field magnets, and central solenoid.

  17. Elastoplasmonic interaction in metal-insulator-metal localized surface plasmon systems

    NASA Astrophysics Data System (ADS)

    Mrabti, Abdelali; Lévêque, Gaëtan; Akjouj, Abdellatif; Pennec, Yan; Djafari-Rouhani, Bahram; Nicolas, Rana; Maurer, Thomas; Adam, Pierre-Michel

    2016-08-01

    We investigate theoretically and numerically the coupling between elastic and localized surface plasmon modes in a system of gold nanocylinders separated from a thin gold film by a dielectric spacer of few nanometers thickness. That system supports plasmon modes confined in between the bottom of the nanocylinder and the top of the gold film, which arise from the formation of interference patterns by short-wavelength metal-insulator-metal propagating plasmon. First, we present the plasmonic properties of the system though computer-simulated extinction spectra and field maps associated to the different optical modes. Next, a simple analytical model is introduced, which allows to correctly reproduce the shape and wavelengths of the plasmon modes. This model is used to investigate the efficiency of the coupling between an elastic deformation and the plasmonic modes. In the last part of the paper, we present the full numerical simulations of the elastic properties of the system, and then compute the acousto-plasmonic coupling between the different plasmon modes and five acoustic modes of very different shape. The efficiency of the coupling is assessed first by evaluating the modulation of the resonance wavelength, which allows comparison with the analytical model, and finally in term of time-modulation of the transmission spectra on the full visible range, computed for realistic values of the deformation of the nanoparticle.

  18. Analytical and experimental investigation of electrical characteristics of a metallic insulation GdBCO coil

    NASA Astrophysics Data System (ADS)

    Yang, D. G.; Choi, Y. H.; Kim, Y. G.; Song, J. B.; Lee, H. G.

    2016-03-01

    This paper presents results, experimental and analytical, of the electrical characteristics of GdBCO single-pancake coils co-wound with a brass tape as metallic insulation (MI coil). The GdBCO pancakes were subjected to sudden discharge, charge-discharge, and over-current tests. The sudden discharge and charge-discharge test results of the MI coil demonstrated that MI coils can be charged and discharged significantly faster than non-insulated coils that are wound only with GdBCO tape. In over-current tests at 150 A (1.25Ic), the MI coil exhibited better electrical behavior, i.e., self-protecting features, than its counterpart co-wound with Kapton tape, an insulator. Moreover, the experimental and analytical results are in agreement, validating the use of a concise equivalent parallel-RL circuit model for the MI coil to characterize its electrical behavior. Overall, the MI winding technique is highly promising to help build compact, mechanically robust, and self-protecting magnets composed of REBCO pancake coils. With no organic material in the winding, MI REBCO pancakes will be immune to neutron radiation damage, making the MI winding technique a viable option for fusion reactors, such as for toroidal field, poroidal field magnets, and central solenoid.

  19. Metal-insulator-silicon-insulator-metal waveguides compatible with standard CMOS technology.

    PubMed

    Kwon, Min-Suk

    2011-04-25

    Metal-insulator-silicon-insulator-metal (MISIM) waveguides are proposed and investigated theoretically. They are hybrid plasmonic waveguides, and light is highly confined to the insulator between the metal and silicon. As compared to previous ones, they are advantageous since they may be realized in a simple way by using current standard CMOS technology and their insulator is easily replaceable without affecting the metal and silicon. First, their structure and fabrication process are explained, both of which are compatible with standard CMOS technology. Then, the characteristics of the single MISIM waveguide whose insulator has its original or an adjusted refractive index are analyzed. The analysis demonstrates that its characteristics are comparable to those of previous hybrid plasmonic waveguides and that they are very effectively tuned by changing the refractive index of the insulator. Finally, the characteristics of the two coupled MISIM waveguides are analyzed. Through the analysis, it is obtained how close or far apart they are for efficient power transfer or low crosstalk. MISIM-waveguide-based devices may play an important role in connecting Si-based photonic and electronic circuits.

  20. AlN/GaN Metal Insulator Semiconductor Field Effect Transistor on Sapphire Substrate

    NASA Astrophysics Data System (ADS)

    Seo, Sanghyun; Ghose, Kaustav; Zhao, Guang Yuan; Pavlidis, Dimitris

    AlN/GaN Metal Insulator Semiconductor Field Effect Transistors (MISFETs) were designed, simulated and fabricated. DC, S-parameter and power measurements were also performed. Drift-diffusion simulations using DESSIS compared AlN/GaN MISFETs and Al32Ga68N/GaN Heterostructure FETs (HFETs) with the same geometries. The simulation results show the advantages of AlN/GaN MISFETs in terms of higher saturation current, lower gate leakage and higher transconductance than AlGaN/GaN HFETs. First results from fabricated AlN/GaN devices with 1μm gate length and 200μm gate width showed a maximum drain current density of ˜380mA/mm and a peak extrinsic transconductance of 85mS/mm. S-parameter measurements showed that currentgain cutoff frequency (fT) and maximum oscillation frequency (fmax) were 5.85GHz and 10.57GHz, respectively. Power characteristics were measured at 2GHz and showed output power density of 850mW/mm with 23.8% PAE at VDS=15V. To the authors knowledge this is the first report of a systematic study of AlN/GaN MISFETs addressing their physical modeling and experimental high-frequency characteristics including the power performance.