Download or read book Phase Field Study of Metal Insulator Transition in Strongly Correlated Vanadium Dioxide written by Yin Shi and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Vanadium dioxide (VO2) is a strongly correlated system which exhibits an intriguing metal-insulator transition (MIT) accompanied by a structural transition at a temperature slightly above the room temperature. It offers potential novel device applications such as sensors, Mott field-effect transistors, and memristors, which desire guidance from mesoscopic theoretical modeling. Based on symmetry consideration, we formulate a mesoscopic phase-field model of the MIT explicitly incorporating both structural and electronic instabilities as well as free electrons and holes. We employ this model to investigate the MIT in mesoscale VO2 subject to various stimuli such as heat, stress/strain, electric field, doping, electric current, and light. First, the temperature-stress/strain phase diagrams of VO2 nanobeams and thin films under different mechanical boundary conditions are calculated consistently, which show good agreement with existing experimental observations. We also calculate the temperature-radius phase diagrams of VO2 nanoparticles and nanofibers. Second, in a VO2 slab under an electric field in an open-circuit configuration, an abrupt universal resistive transition is shown to occur inside the supercooling region, in sharp contrast to the conventional Landau-Zener smooth electric breakdown. Third, the temperature-dopant-concentration phase diagrams of VO2 doped with various metal ions are calculated consistent with the experiments. Furthermore, hole doping in VO2 may induce a metastable metallic monoclinic phase, which could be stabilized through geometrical confinement and the size effect in VO2-VO_{2-delta} bilayers leading to the decoupling of the electronic and structural phase transitions. Fourth, we demonstrate that the electric current may drive the MIT isothermally via the current-induced electron correlation weakening, inducing a few-nanosecond ultrafast resistive switching consistent with experimental measurements. The isothermal temperature-current phase diagram is further calculated and the current is also found able to drive domain walls to move. Fifth, dynamic processes of the MIT in VO2 illuminated by femtosecond laser pulses are simulated, showing the emergence of the transient metallic monoclinic phase and the bias-induced shrinkage of the photoinduced metallic phase. We also prove that during a generic metal-insulator transition, a nonequilibrium homogeneous state may be unstable against charge density modulations with certain wavelengths, and thus evolves to the equilibrium phase through transient electronic phase separation. This transient electronic phase separation is shown to take place in VO2 upon photoexcitation.
Download or read book Ultrafast Far infrared Studies of Vanadates Multiple Routes for an Insulator to Metal Transition written by Mengkun Liu and published by . This book was released on 2012 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The metal insulator transition in vanadates has been studied for decades and yet new discoveries still spring up revealing new physics, especially among two of the most studied members: Vanadium sesquioxide (V2 0 3 ) and Vanadium dioxide (VO2 ). Although subtleties abound, both of the materials have first order insulator to metal phase transitions that are considered to be related to strong electron-electron (e-e) correlation. Further, ultrafast spectroscopy of strongly correlated materials has generated great interest in the field given the potential to dynamically distinguish the difference between electronic (spin) response versus lattice responses due to the associated characteristic energy and time scales.In this thesis, I mainly focus on utilizing ultrafast optical and THz spectroscopy to study phase transition dynamics in high quality V2 0 3 and VO2 thin films epitaxially grown on different substrates. The main findings of the thesis are:(1) Despite the fact that the insulator to metal transition (IMT) in V2 03 is electron-correlation driven, lattice distortion plays an important role. Coherent oscillations in the far-infrared conductivity are observed resulting from coherent acoustic phonon modulation of the bandwidth W. The same order of lattice distortion induces less of an effect on the electron transport in VO 2 in comparison to V2 03 . This is directly related to the difference in latent heat of the phase transitions in VO2 and V2 03 .(2) It is possible for the IMT to occur with very little structural change in epitaxial strained VO2 films, like in the case of Cr doped or strained V2 03 . However, in V02 , this necessitates a large strain which is only possible by clamping to a substrate with larger c axis parameter through epitaxial growth. This is demonstrated for VO 2 films on TiO2 substrates.(3) Initiating an ultrafast photo-induced insulator-to-metal transition (IMT) is not only possible with above bandgap excitation, but also possible with high-field far-infrared excitation. With the help of the field enhancement in metamaterial split ring resonator gaps, we obtain picosecond THz electric field transients of several MV/cm which is sufficient to drive the insulator to metal transition in V0 2 .
Download or read book Proceedings of the 8th International Conference on Attosecond Science and Technology written by Argenti and published by Springer Nature. This book was released on 2024 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt: This open access volume brings together selected papers from the 8th International Conference on Attosecond Science and Technology. The contributions within represent the latest advances in attosecond science, covering recent progress in ultrafast electron dynamics in atoms, molecules, clusters, surfaces, solids, nanostructures and plasmas, as well as the generation of sub-femtosecond XUV and X-ray pulses, either through table-top laser setups or with X-ray free-electron lasers. In addition to highlighting key advances and outlining the state of the field, the conference and its proceedings serve to introduce junior researchers to the community, promote collaborations, and represent the global and topical diversity of the field.
Download or read book Correlated Oxides Material Physics and Devices written by You Zhou and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this work we study the metal-insulator transition in vanadium dioxide and samarium nickelate and the application of such transitions in electronic devices. Chapter 1 provides an introduction to the Mott metal-insulator transition mechanisms and an overview of the interplay between various degrees of freedom in correlated oxides. The phase transition in vanadium dioxide is presented as an example to emphasize the overarching electron-phonon and electron-electron interaction driven transition mechanisms. In Chapter 2, we describe the growth and structure-functionality relationship of thin film transition metal oxides. Chapter 3 goes on to examine the mechanism of voltage-triggered metal-insulator transition in vanadium dioxide two-terminal threshold switches through dynamic studies. Chapter 4 delves into the mechanism of conductance modulation in electrolyte-gated vanadium dioxide transistors, which reveals the importance of electrochemical effects versus electrostatic effects in these devices. Utilizing the idea of electrochemical doping, we designed and realized a strongly correlated insulating phase in samarium nickel oxide through electron doping with hydrogen and lithium interstitials in Chapter 5. Such techniques can be extended to other materials to achieve reversible and controllable carrier doping with high concentration to study the related physics.
Download or read book Vanadium Oxide Phase Transitions written by Ilya Valmianski and published by . This book was released on 2017 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vanadium oxides are a prototypical family of highly correlated oxides. In his dissertation, I present the study of two vanadium oxides in particular, V2O3 and VO2, which undergo simultaneously both a structural phase transition and a metal to insulator transition. While traditionally these phase transitions were studied in equilibrium, bulk, or in meso/macro-scale devices, in my work I focused on different modalities: fast, small, and strained. In my work on fast time scales during photoexcitation of V2O3 we found a novel meta-stable intermediate state that appears due to symmetry change in the monoclinic phase. This change occurs in the proximity of high temperature rhombohedral domains on length scales similar to those of electronic correlation. Our finding shows that the electronic and structural transitions in V2O3 have similar length scales but very different time scales. In VO2 and V2O3 nanoscale devices, we found a length-scale competition between Joule heating and electric field driven current induced metal to insulator transition. We proposed a novel thermoelectric model and performed simulations using finite element methods. Our modeling showed that the transition is highly inhomogeneous and the resulting filaments are surface bound with thermal gradients generating Seebeck electric fields on the order of 1000 V/cm. Finally, we studied pressurized and strained thin films in V2O3 and discovered strong strain relaxation for pressures of up to 500 MPa, which cause a deviation of thin film Pressure-Temperature phase diagram from bulk behavior. This strain relaxation relies on the difference between the structural and morphological length scales, which allows the formation of strain relaxing creases. Once those creases are fully strained, the thin films respond similarly to bulk samples.
Download or read book Experiments on a Strongly Correlated Material written by T. Serkan Kasirga and published by . This book was released on 2013 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: The metal-insulator transition(MIT) in vanadium dioxide(VO2) has attracted waves of attention after its rst observation by Morin in 1959. There are several reasons for the interest in this material. First, its metal-insulator transition is at an easily accessible temperature which allows investigators to study the eect of strong elec- tronic correlations with little eort. Second reason is VO2 oers many applications, although most of them are mundane, a few may have signicant eects on dierent areas of technology. However, even after over half a century there is still a debate about the nature of the MIT and non of the applications proposed have been realized. The main culprit for this is the diculties in studying the bulk crystals of VO2. In bulk crystals, defects in the crystal, impurities and domain structure causes irrepro- ducible results. This combined with the theoretical challenges made studying VO2 and realization of applications impractical. However, recent discovery of the growth technique for growing the nano-scale crystals, revitalized the interest in VO2. In this dissertation I present the experimental studies that we performed on VO2. I discussed the ndings from three major studies we performed; photoresponse, nd- ing the strain-temperature phase diagram and hydrogen doping of VO2. We used scanning photocurrent microscopy technique to reveal the light-matter interaction in VO2. Suspended nanobeam devices are used in the experiments and results revealed that photoresponse of VO2 is dominated by the thermal eects and there is no pho- tovoltaic contribution. Results are published in Nature Nanotechnology in 2012 . In the second study, we determined the strain-temperature phase stability diagram of VO2. This is the rst ever determination of the phase diagram of a solid state phase transition. Also our studies revealed that the triple point coincides with the critical point, which has important implications for both theoretical studies of the MIT in VO2 and for its applications. Results of this study is published in Nature in 2013. Last study presented here is the hydrogen doping of VO2. There is not much known about hydrogenation of VO2. However our initial studies revealed very high anisotropy of diusion and mechanism other than diusion eecting the hydrogen motion in the VO2 crystal. There is also a chapter on previous studies and a general introduction to the MIT in VO2. Appendices contain detailed information about the experiment setups, crystal growth techniques and device fabrication techniques. I believe studies presented here with the recent advances in the eld had an important contribution to our understanding of the MIT in VO2 and brought us closer to the realization of tantalizing applications.
Download or read book Principles of Nano Optics written by Lukas Novotny and published by Cambridge University Press. This book was released on 2012-09-06 with total page 583 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fully revised and in its second edition, this standard reference on nano-optics is ideal for graduate students and researchers alike.
Download or read book The Control of Metal insulator Transition in Vanadium Dioxide written by Naga Phani B. Aetukuri and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The external control of the conductivity of correlated oxides is one of the most promising avenues towards realizing energy-efficient electronic devices. One of the prime candidates for such devices, vanadium dioxide (VO2), undergoes a temperature-driven metal-insulator transition (MIT) near room temperature (~340 K) with a concomitant change in crystal symmetry. First, using epitaxial strain provided by a variable thickness RuO2 buffer layer, we vary the MIT transition temperature of VO2 (001) films continuously from ~285 to ~345 K. We show, using strain-, polarization- and temperature-dependent x-ray absorption spectroscopy, in conjunction with x-ray diffraction and electrical transport measurements, that the transition temperature (TMIT) of VO2 is controlled by the orbital occupancy in its metallic state. Our results furthermore indicate that the magnitude of the structural distortion across the transition is also directly related to the orbital occupation in the metallic state. This work opens up the possibility of controlling the nature of the conducting state in atomically thin VO2 layers by manipulating the orbital occupancy by, for example, hetero-structural engineering. In a related study, we have used a combination of electron-beam and optical lithography to fabricate lateral two-terminal nano-devices from VO2 films deposited on TiO2 (001) substrates without RuO2 buffer layers. In these devices, we show that the transition can also be engendered by the application of modest electric fields, several orders of magnitude below the electric breakdown field, making this phenomenon potentially useful for two or three terminal switches. The delay time before switching is found to decrease with increasing electric field and temperature. We discuss whether these results indicate the transition is dominated by electronic or by Joule heating effects. These results demonstrate the possibility of triggering an MIT at low voltages and, therefore, at low energies, which is essential for device applications. Finally, we also discuss MIT in VO2-TiO2 based hetero-structures. We show that the temperature-driven MIT persists in VO2 films as thin as 1.8 nm.
Download or read book Synthesis and Structural Magnetic Thermal and Transport Properties of Several Transition Metal Oxides and Aresnides written by and published by . This book was released on 2010 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oxide compounds containing the transition metal vanadium (V) have attracted a lot of attention in the field of condensed matter physics owing to their exhibition of interesting properties including metal-insulator transitons, structural transitions, ferromagnetic and an- tiferromagnetic orderings, and heavy fermion behavior. Binary vanadium oxides VnO2n-1 where 2 ≤ n ≤ 9 have triclinic structures and exhibit metal-insulator and antiferromagnetic transitions.[1–6] The only exception is V7O13 which remains metallic down to 4 K.[7] The ternary vanadium oxide LiV2O4 has the normal spinel structure, is metallic, does not un- dergo magnetic ordering and exhibits heavy fermion behavior below 10 K.[8] CaV2O4 has an orthorhombic structure[9, 10] with the vanadium spins forming zigzag chains and has been suggested to be a model system to study the gapless chiral phase.[11, 12] These provide great motivation for further investigation of some known vanadium compounds as well as to ex- plore new vanadium compounds in search of new physics. This thesis consists, in part, of experimental studies involving sample preparation and magnetic, transport, thermal, and x- ray measurements on some strongly correlated eletron systems containing the transition metal vanadium. The compounds studied are LiV2O4, YV4O8, and YbV4O8. The recent discovery of superconductivity in RFeAsO1-xFx (R = La, Ce, Pr, Gd, Tb, Dy, Sm, and Nd), and AFe2As2 (A = Ba, Sr, Ca, and Eu) doped with K, Na, or Cs at the A site with relatively high Tc has sparked tremendous activities in the condensed matter physics community and a renewed interest in the area of superconductivity as occurred following the discovery of the layered cuprate high Tc superconductors in 1986. To discover more supercon- ductors with hopefully higher Tc’s, it is extremely important to investigate compounds having crystal structures related to the compounds showing high Tc superconductivity. Along with the vanadium oxide compounds described before, this thesis describes our investigations of magnetic, structural, thermal and transport properties of EuPd2Sb2 single crystals which have a crystal structure closely related to the AFe2As2 compounds and also a study of the reaction kinetics of the formation of LaFeAsO1-xFx.
Download or read book Theory of Metal Insulator Transition in Strongly Correlated Electron Systems written by and published by . This book was released on 1994 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Emerging Nanoelectronic Devices written by An Chen and published by John Wiley & Sons. This book was released on 2015-01-27 with total page 570 pages. Available in PDF, EPUB and Kindle. Book excerpt: Emerging Nanoelectronic Devices focuses on the future direction of semiconductor and emerging nanoscale device technology. As the dimensional scaling of CMOS approaches its limits, alternate information processing devices and microarchitectures are being explored to sustain increasing functionality at decreasing cost into the indefinite future. This is driving new paradigms of information processing enabled by innovative new devices, circuits, and architectures, necessary to support an increasingly interconnected world through a rapidly evolving internet. This original title provides a fresh perspective on emerging research devices in 26 up to date chapters written by the leading researchers in their respective areas. It supplements and extends the work performed by the Emerging Research Devices working group of the International Technology Roadmap for Semiconductors (ITRS). Key features: • Serves as an authoritative tutorial on innovative devices and architectures that populate the dynamic world of “Beyond CMOS” technologies. • Provides a realistic assessment of the strengths, weaknesses and key unknowns associated with each technology. • Suggests guidelines for the directions of future development of each technology. • Emphasizes physical concepts over mathematical development. • Provides an essential resource for students, researchers and practicing engineers.
Download or read book Optical Techniques for Solid State Materials Characterization written by Rohit P. Prasankumar and published by CRC Press. This book was released on 2020-06-30 with total page 748 pages. Available in PDF, EPUB and Kindle. Book excerpt: With chapters written by pioneering experts in various optical techniques, this comprehensive reference provides detailed descriptions of basic and advanced optical techniques commonly used to study materials, from the simple to the complex. It explains how to use the techniques to acquire, analyze, and interpret data for gaining insight into ma
Download or read book Tunable Spin charge Conversion in Vanadium Dioxide written by Taqiyyah Sariyah Safi and published by . This book was released on 2019 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spin-based electronic devices rely on the interplay of spin and charge degree of freedom of electrons and are emerging as a promising beyond CMOS technology. Fast, scalable, low energy consumption magnetic memories and nonvolatile spin logic devices have been demonstrated utilizing spin-orbit-torque based magnetization switching. A large, pure spin current is crucial for these applications and significant effort is geared towards finding materials with large charge-to-spin conversion efficiency to exploit the full potential of spintronics. The charge-to-spin conversion efficiency is an inherent property of the spintronics materials and cannot be easily modified without changing the chemical or structural properties of the material. To date most of the explored materials, have significant electrical conductivity and are in their pure, stable, intrinsic structural form. Most importantly, they exhibit negligible variation in the electrical and structural properties. In this thesis we investigate spin-charge conversion efficiency in the transition metal oxide, vanadium dioxide (VO2), which exhibits structural phase transition subject to external stimuli. We demonstrate tunable charge-to-spin conversions in this material across the phase transition. Vanadium dioxide is a prototypical metal-insulator transition material and has the unique property of a dramatic and abrupt structural phase transition under external stimuli such as heat, strain, and electric field etc. Due to its unique properties, it has gained much interest from both fundamental research and applications perspective but its spin related properties remain largely unexplored. In this thesis, we demonstrate the successful tuning of charge-spin conversion efficiency via the metal-insulator transition in this quintessential strongly correlated electron compound. We inject a pure spin current through ferromagnetic resonance driven spin pumping and measure the temperature dependent inverse spin Hall effect voltage across VO2 We found a swift, dramatic change in the spin pumping signal (decrease by >80%) and charge-spin conversion efficiency (increase by five times) upon transition. The swift, dramatic change in the structural and electrical properties of this material therefore provides additional knobs to modulate the conversion efficiency. This work leads to extra flexibilities in spintronic device design and opens up new avenues for variable spintronics.
Download or read book Proceedings of the National Academy of Sciences of the United States of America written by and published by . This book was released on 2006 with total page 1250 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Thermodynamic Studies of Metal insulator Transitions in Organic Charge transfer Salts written by Elena Aurelia Gati and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis aimed at identifying and understanding the interplay of charge and lattice degrees of freedom at metal-insulator transitions that are driven by strong electron correlations, i.e., Mott and charge-order metal-insulator transitions. To this end, measurements of the thermal expansion were performed, which have proven to be particularly suited to deliver insight into the role of lattice degrees of freedom in strongly correlated electron systems. Prime examples of such systems are the herein studied organic charge-transfer salts which stand out by a high tunability of the interaction strength. The central topic of this thesis was the investigation of the universal behavior of the pressure-induced finite-temperature Mott critical endpoint in the organic charge-transfer salt kappa-(BEDT-TTF)2Cu[N(CN)2]Cl. In the present work, it was proven experimentally that lattice effects play a crucial role for the universal behavior, in contrast to the assumption made in previous works.
Download or read book Mott Insulators written by Sindhunil Barman Roy and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "There have been many recent developments in the physics and materials science of Mott insulators, especially their recognition as emergent materials for important and innovative device applications such as information processing and storage, and the possibilities of even further applications in optical and thermal switches, thermo-chromic devices, gas sensors and even solar cell applications. Aimed at advanced undergraduate students of physics, chemistry, materials science, and electrical and electronics engineering, this book introduces the subject and reviews present knowledge in the field, enabling students and researchers to get acquainted with this very interesting and emerging area of science and technology. Professional researchers in academic institutions and industries already engaged in the programmes of correlated electron materials and devices will also find this title of use." -- Prové de l'editor.
Download or read book The Physics of Phase Transitions written by Pierre Papon and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Physics of Phase Transitions occupies an important place at the crossroads of several fields central to materials sciences. This second edition incorporates new developments in the states of matter physics, in particular in the domain of nanomaterials and atomic Bose-Einstein condensates where progress is accelerating. New information and application examples are included. This work deals with all classes of phase transitions in fluids and solids, containing chapters on evaporation, melting, solidification, magnetic transitions, critical phenomena, superconductivity, and more. End-of-chapter problems and complete answers are included.
