scholarly journals Direct measurement of ferroelectric polarization in a tunable semimetal

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sergio C. de la Barrera ◽  
Qingrui Cao ◽  
Yang Gao ◽  
Yuan Gao ◽  
Vineetha S. Bheemarasetty ◽  
...  
Keyword(s):  
Electric Fields ◽  
Spontaneous Polarization ◽  
Electrical Conductance ◽  
Metallic State ◽  
Transition Metal Dichalcogenide ◽  
Free Carriers ◽  
Electric Dipoles ◽  
Valence Bands ◽  
Density Of Electrons ◽  
Ferroelectric Switching

AbstractFerroelectricity, the electrostatic counterpart to ferromagnetism, has long been thought to be incompatible with metallicity due to screening of electric dipoles and external electric fields by itinerant charges. Recent measurements, however, demonstrated signatures of ferroelectric switching in the electrical conductance of bilayers and trilayers of WTe2, a semimetallic transition metal dichalcogenide with broken inversion symmetry. An especially promising aspect of this system is that the density of electrons and holes can be continuously tuned by an external gate voltage. This degree of freedom enables measurement of the spontaneous polarization as free carriers are added to the system. Here we employ capacitive sensing in dual-gated mesoscopic devices of bilayer WTe2 to directly measure the spontaneous polarization in the metallic state and quantify the effect of free carriers on the polarization in the conduction and valence bands, separately. We compare our results to a low-energy model for the electronic bands and identify the layer-polarized states that contribute to transport and polarization simultaneously. Bilayer WTe2 is thus shown to be a fully tunable ferroelectric metal and an ideal platform for exploring polar ordering, ferroelectric transitions, and applications in the presence of free carriers.

Paraelektrische Resonanz und dielektrische Dispersion von Wasser in Beryll-Einkristallen / Paraelectric Resonance and Dielectric Dispersion of Water in Beryl Single Crystals

1974 ◽  
Vol 29 (11) ◽  
pp. 1558-1571
Author(s):  
H.-J. Rehm
Keyword(s):  
Electric Fields ◽  
Resonance Effect ◽  
Theoretical Description ◽  
Tunnel Effect ◽  
Zero Field ◽  
Zero Field Splitting ◽  
A Value ◽  
Axis Parallel ◽  
Electric Dipoles ◽  
The One

Paraelectric resonance spectra of beryl crystals are observed in the X-band region between 5 and 20 kV/cm under the condition that the external electric field F[101̅0]. Additional dielectric measurements show, that the paraelectric centres are the monomeric water molecules in the beryl cavities. For water dipoles in beryl only two orientations of the molecular a-axis relative to the crystal C6-axis are possible, and only those with their a-axis parallel to the C6-axis contribute to the paraelectric resonance effect. The electric moment vector µ of these latter molecules may rotate in the (0001)-crystal plane, i. e. around their own a-axis, and has a value of (1.9 ± 0.2) D. A theoretical description of paraelectric resonance is presented for a simplified model: the electric dipoles have 6 equivalent equilibrium positions along the [101̅0]-directions, tunnel effect and external electric fields remove the site degeneracy and we observe a molecular Stark splitting. We calculate a value of (2.0 ± 0.4) GHz for the zero-field splitting in the one-parameter Hamiltonian model.

scholarly journals Significantly Improved Electrical Properties of Crosslinked Polyethylene Modified by UV-Initiated Grafting MAH

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 62 ◽  
Author(s):  
Xin-Dong Zhao ◽  
Hong Zhao ◽  
Wei-Feng Sun
Keyword(s):  
Electric Fields ◽  
Carrier Transport ◽  
Elevated Temperatures ◽  
Dielectric Breakdown ◽  
Breakdown Strength ◽  
Electrical Conductance ◽  
Electrical Current ◽  
Underlying Mechanism ◽  
Polar Group ◽  
Frenkel Effect

Direct current (DC) electrical performances of crosslinked polyethylene (XLPE) have been evidently improved by developing graft modification technique with ultraviolet (UV) photon-initiation. Maleic anhydride (MAH) molecules with characteristic cyclic anhydride were successfully grafted to polyethylene molecules under UV irradiation, which can be efficiently realized in industrial cable production. The complying laws of electrical current varying with electric field and the Weibull statistics of dielectric breakdown strength at altered temperature for cable operation were analyzed to study the underlying mechanism of improving electrical insulation performances. Compared with pure XLPE, the appreciably decreased electrical conductivity and enhanced breakdown strength were achieved in XLPE-graft-MAH. The critical electric fields of the electrical conduction altering from ohm conductance to trap-limited mechanism significantly decrease with the increased testing temperature, which, however, can be remarkably raised by grafting MAH. At elevated temperatures, the dominant carrier transport mechanism of pure XLPE alters from Poole–Frenkel effect to Schottky injection, while and XLPE-graft-MAH materials persist in the electrical conductance dominated by Poole–Frenkel effect. The polar group of grafted MAH renders deep traps for charge carriers in XLPE-graft-MAH, and accordingly elevate the charge injection barrier and reduce charge mobility, resulting in the suppression of DC electrical conductance and the remarkable amelioration of insulation strength. The well agreement of experimental results with the quantum mechanics calculations suggests a prospective strategy of UV initiation for polar-molecule-grafting modification in the development of high-voltage DC cable materials.

On oscillating electric dipoles immersed in a hot plasma

1968 ◽  
Vol 2 (3) ◽  
pp. 437-448 ◽  
Author(s):  
S. R. Watson
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Electric Fields ◽  
Plasma Frequency ◽  
Velocity Distribution Function ◽  
Electron Velocity ◽  
Electron Velocity Distribution ◽  
Electron Velocity Distribution Function ◽  
Hot Plasma ◽  
Electric Dipoles

In this paper the electric fields of an infinitesimal dipole oscillating in a hot plasma are derived in the absence of an external magnetic field; explicit expressions are obtained by making an approximation on the background electron velocity distribution function. These results are applied to investigate the resonance observed at the plasma frequency, and to estimate the radiation resistance of the dipole.

Tunneling emission of electrons from semiconductors’ valence bands in high electric fields

2006 ◽  
Vol 40 (9) ◽  
pp. 1036-1042 ◽  
Author(s):  
V. D. Kalganov ◽  
N. V. Mileshkina ◽  
E. V. Ostroumova
Keyword(s):  
Electric Fields ◽  
Valence Bands ◽  
High Electric Fields

scholarly journals Giant reversible, facet-dependent, structural changes in a correlated-electron insulator induced by ionic liquid gating

2015 ◽  
Vol 112 (4) ◽  
pp. 1013-1018 ◽  
Author(s):  
Jaewoo Jeong ◽  
Nagaphani B. Aetukuri ◽  
Donata Passarello ◽  
Steven D. Conradson ◽  
Mahesh G. Samant ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Electric Fields ◽  
Room Temperature ◽  
Structural Changes ◽  
Electron System ◽  
Metallic State ◽  
Crystal Facet ◽  
Correlated Electron ◽  
High Electric Fields ◽  
Insulating Phase

The use of electric fields to alter the conductivity of correlated electron oxides is a powerful tool to probe their fundamental nature as well as for the possibility of developing novel electronic devices. Vanadium dioxide (VO2) is an archetypical correlated electron system that displays a temperature-controlled insulating to metal phase transition near room temperature. Recently, ionic liquid gating, which allows for very high electric fields, has been shown to induce a metallic state to low temperatures in the insulating phase of epitaxially grown thin films of VO2. Surprisingly, the entire film becomes electrically conducting. Here, we show, from in situ synchrotron X-ray diffraction and absorption experiments, that the whole film undergoes giant, structural changes on gating in which the lattice expands by up to ∼3% near room temperature, in contrast to the 10 times smaller (∼0.3%) contraction when the system is thermally metallized. Remarkably, these structural changes are fully reversible on reverse gating. Moreover, we find these structural changes and the concomitant metallization are highly dependent on the VO2 crystal facet, which we relate to the ease of electric-field–induced motion of oxygen ions along chains of edge-sharing VO6 octahedra that exist along the (rutile) c axis.

Structurally ferroelectric SrMgF4

2001 ◽  
Vol 58 (1) ◽  
pp. 34-37 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Crystal Structure ◽  
Curie Temperature ◽  
Spontaneous Polarization ◽  
Two Dimensional ◽  
Acta Cryst ◽  
Ferroelectric Switching

The crystal structure of 0.06% Ce-doped SrMgF4, strontium magnesium tetrafluoride, reported by Ishizawa et al. [(2001), Acta Cryst. C57, 784–786]  is shown to satisfy the structural criteria for ferroelectricity and to have a predicted Curie temperature T c ≃ l450 K. The estimated spontaneous polarization P s ≃ 11 × 10−2 C m−2 is consistent with classification as a two-dimensional ferroelectric in which minor Δx and major Δy, Δz atomic coordinate component displacements are required for ferroelectric switching.

scholarly journals Possible strain induced Mott gap collapse in 1T-TaS2

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Kunliang Bu ◽  
Wenhao Zhang ◽  
Ying Fei ◽  
Zongxiu Wu ◽  
Yuan Zheng ◽  
...  
Keyword(s):  
Optical Excitation ◽  
Strain Engineering ◽  
Tuning Parameter ◽  
Metallic State ◽  
Transition Metal Dichalcogenide ◽  
Electronic Density ◽  
Fundamental Interest ◽  
Insulator Metal Transition ◽  
Mott Gap ◽  
Layered Transition Metal

AbstractTuning the electronic properties of a matter is of fundamental interest in scientific research as well as in applications. Recently, the Mott insulator-metal transition has been reported in a pristine layered transition metal dichalcogenide 1T-TaS$${}_{2}$$2, with the transition triggered by an optical excitation, a gate controlled intercalation, or a voltage pulse. However, the sudden insulator-metal transition hinders an exploration of how the transition evolves. Here, we report the strain as a possible new tuning parameter to induce Mott gap collapse in 1T-TaS$${}_{2}$$2. In a strain-rich area, we find a mosaic state with distinct electronic density of states within different domains. In a corrugated surface, we further observe and analyze a smooth evolution from a Mott gap state to a metallic state. Our results shed new lights on the understanding of the insulator-metal transition and promote a controllable strain engineering on the design of switching devices in the future.

scholarly journals The MoSeS dynamic omnigami paradigm for smart shape and composition programmable 2D materials

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Joel Berry ◽  
Simeon Ristić ◽  
Songsong Zhou ◽  
Jiwoong Park ◽  
David J. Srolovitz
Keyword(s):  
Electric Fields ◽  
Flexible Electronics ◽  
2D Materials ◽  
Strain Engineering ◽  
Transition Metal Dichalcogenide ◽  
3D Objects ◽  
Novel Material ◽  
Shape Programming ◽  
Composition Programming ◽  
New Applications

AbstractThe properties of 2D materials can be broadly tuned through alloying and phase and strain engineering. Shape programmable materials offer tremendous functionality, but sub-micron objects are typically unachievable with conventional thin films. Here we propose a new approach, combining phase/strain engineering with shape programming, to form 3D objects by patterned alloying of 2D transition metal dichalcogenide (TMD) monolayers. Conjugately, monolayers can be compositionally patterned using non-flat substrates. For concreteness, we focus on the TMD alloy MoSe$${}_{2c}$$2cS$${}_{2(1-c)}$$2(1−c); i.e., MoSeS. These 2D materials down-scale shape/composition programming to nanoscale objects/patterns, provide control of both bending and stretching deformations, are reversibly actuatable with electric fields, and possess the extraordinary and diverse properties of TMDs. Utilizing a first principles-informed continuum model, we demonstrate how a variety of shapes/composition patterns can be programmed and reversibly modulated across length scales. The vast space of possible designs and scales enables novel material properties and thus new applications spanning flexible electronics/optics, catalysis, responsive coatings, and soft robotics.

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