An eigenstate formulation of the magnetotelluric impedance tensor

Geophysics ◽  
1982 ◽  
Vol 47 (8) ◽  
pp. 1204-1214 ◽  
Author(s):  
Dwight E. Eggers
Keyword(s):  
Electric Fields ◽  
Degrees Of Freedom ◽  
Homogeneous Medium ◽  
Real Space ◽  
Conventional Approach ◽  
Impedance Tensor ◽  
Electric And Magnetic Fields ◽  
Coordinate Rotation ◽  
Rotation Methods ◽  
Transverse Electromagnetic

An important step in the interpretation of magnetotelluric (MT) data is the extraction of scalar parameters from the impedance tensor Z, the transfer function which relates the observed horizontal magnetic and electric fields. The conventional approach defines parameters in terms of elements of a coordinate‐rotated tensor. The rotation angle is chosen such that Z′(θ) approximates in some sense the form for a two‐dimensional (2-D) subsurface conductivity distribution, with zero elements on the diagonal. There are two major problems with this approach. (1) Apparent resistivities, defined from the off‐diagonal elements of the rotated tensor, are independent of the trace of Z. It is problematic that apparent resistivities, the parameters for which we have physical analogs and which are most heavily used in interpretation, are insensitive to the addition of an arbitrary constant on the diagonal of Z. (2) The conventional parameter set is incomplete; there are two degrees of freedom in Z which are transparent to all parameters. Through a variation of the classical eigenstate formulation of a matrix, it is shown that in general there exist two, and only two, polarization states for which the electric and magnetic fields have the same polarization at perpendicular orientations. For each eigenstate the magnetic and electric fields are related by a scalar, the eigenvalue for that state. This scalar relationship between fields is of identical form to the solution for transverse electromagnetic (TEM) waves in a homogeneous medium and thus provides a physically more satisfactory basis for defining apparent resistivity than the conventional approach using the off‐diagonal elements of the coordinate‐rotated impedance tensor. The eigenstate and coordinate‐rotation methods yield identical results in the limited cases of 1-D and 2-D subsurface conductivity distributions. The eigenstates provide the basis for new definitions of parameters as concise, closed expressions which are complete and more amenable to interpretational insight. The polarization ellipses defined by the eigenstates provide a concise display in real space of all the information contained in the impedance tensor.

Simulation-based assessment of coupled frequency response of magneto-electro-elastic auxetic multifunctional structures subjected to various electromagnetic circuits

2021 ◽  
pp. 146442072110219
Author(s):  
Vinyas Mahesh ◽  
Vishwas Mahesh ◽  
Dineshkumar Harursampath ◽  
Ahmed E Abouelregal
Keyword(s):  
Electric Fields ◽  
Solid Mechanics ◽  
Natural Frequencies ◽  
Comsol Multiphysics ◽  
Simulation Based ◽  
Electric And Magnetic Fields ◽  
Auxetic Structures ◽  
Triangular Elements ◽  
Benchmark Solutions ◽  
Free Vibration Response

This article deals with the modeling of magneto-electro-elastic auxetic structures and developing a methodology in COMSOL Multiphysics® to assess the free vibration response of such structures when subjected to various electromagnetic circuit conditions. The triple energy interaction between elastic, magnetic, and electric fields are established in the COMSOL Multiphysics® using structural mechanics and electromagnetic modules. The multiphase magneto-electro-elastic material with different percentages of piezoelectric and piezomagnetic phases are used as the material. In the solid mechanics module, the piezoelectric and piezomagnetic materials were created in stress-charge and stress-magnetization forms, respectively. The electric and magnetic fields are defined in COMSOL Multiphysics® through electromagnetic equations. Further, the customized controlled meshing constituted of free tetrahedral and triangular elements is adapted to trade-off between the accuracy and the computational expenses. The eigenvalue analysis is performed to obtain the natural frequencies of the MEE re-entrant auxetic structures. Also, the efficiency of smart auxetic structures over conventional honeycomb structures is presented throughout the manuscript. In addition, the discrepancy in the natural frequencies of the structures considering coupled and uncoupled state is also illustrated. It is believed that the modeling procedure and its outcomes serve as benchmark solutions for further design and analysis of smart auxetic magneto-electro-elastic structures.

scholarly journals A chiral switchable photovoltaic ferroelectric 1D perovskite

2020 ◽  
Vol 6 (9) ◽  
pp. eaay4213 ◽  
Author(s):  
Yang Hu ◽  
Fred Florio ◽  
Zhizhong Chen ◽  
W. Adam Phelan ◽  
Maxime A. Siegler ◽  
...  
Keyword(s):  
Electric Fields ◽  
Mirror Symmetry ◽  
Degrees Of Freedom ◽  
Electrical Measurements ◽  
Temperature Dependent ◽  
Paraelectric Phase Transition ◽  
Strongly Coupled ◽  
Yield Phenomena ◽  
Hybrid Perovskite ◽  
Low Dimensional

Spin and valley degrees of freedom in materials without inversion symmetry promise previously unknown device functionalities, such as spin-valleytronics. Control of material symmetry with electric fields (ferroelectricity), while breaking additional symmetries, including mirror symmetry, could yield phenomena where chirality, spin, valley, and crystal potential are strongly coupled. Here we report the synthesis of a halide perovskite semiconductor that is simultaneously photoferroelectricity switchable and chiral. Spectroscopic and structural analysis, and first-principles calculations, determine the material to be a previously unknown low-dimensional hybrid perovskite (R)-(−)-1-cyclohexylethylammonium/(S)-(+)-1 cyclohexylethylammonium) PbI3. Optical and electrical measurements characterize its semiconducting, ferroelectric, switchable pyroelectricity and switchable photoferroelectric properties. Temperature dependent structural, dielectric and transport measurements reveal a ferroelectric-paraelectric phase transition. Circular dichroism spectroscopy confirms its chirality. The development of a material with such a combination of these properties will facilitate the exploration of phenomena such as electric field and chiral enantiomer–dependent Rashba-Dresselhaus splitting and circular photogalvanic effects.

scholarly journals Realization of acoustic spin transport in metasurface waveguides

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Yang Long ◽  
Danmei Zhang ◽  
Chenwen Yang ◽  
Jianmin Ge ◽  
Hong Chen ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Electromagnetic Waves ◽  
Degrees Of Freedom ◽  
Transport Processes ◽  
Angular Momenta ◽  
Transverse Electromagnetic ◽  
Spin Texture ◽  
Momentum Coupling ◽  
Practical Implications ◽  
Spin Momentum

Abstract Spin angular momentum enables fundamental insights for topological matters, and practical implications for information devices. Exploiting the spin of carriers and waves is critical to achieving more controllable degrees of freedom and robust transport processes. Yet, due to the curl-free nature of longitudinal waves distinct from transverse electromagnetic waves, spin angular momenta of acoustic waves in solids and fluids have never been unveiled only until recently. Here, we demonstrate a metasurface waveguide for sound carrying non-zero acoustic spin with tight spin-momentum coupling, which can assist the suppression of backscattering when scatters fail to flip the acoustic spin. This is achieved by imposing a soft boundary of the π reflection phase, realized by comb-like metasurfaces. With the special-boundary-defined spin texture, the acoustic spin transports are experimentally manifested, such as the suppression of acoustic corner-scattering, the spin-selected acoustic router with spin-Hall-like effect, and the phase modulator with rotated acoustic spin.

Nonlinear nanoelectrodynamics of a Weyl metal

2021 ◽  
Vol 118 (48) ◽  
pp. e2116366118
Author(s):  
Yinming Shao ◽  
Ran Jing ◽  
Sang Hoon Chae ◽  
Chong Wang ◽  
Zhiyuan Sun ◽  
...  
Keyword(s):  
Electric Fields ◽  
Mirror Symmetry ◽  
Density Functional ◽  
Near Field ◽  
Surface States ◽  
Real Space ◽  
Resonance Structure ◽  
Nonlinear Conductivity ◽  
Weyl Semimetal ◽  
Photocurrent Spectroscopy

Chiral Weyl fermions with linear energy-momentum dispersion in the bulk accompanied by Fermi-arc states on the surfaces prompt a host of enticing optical effects. While new Weyl semimetal materials keep emerging, the available optical probes are limited. In particular, isolating bulk and surface electrodynamics in Weyl conductors remains a challenge. We devised an approach to the problem based on near-field photocurrent imaging at the nanoscale and applied this technique to a prototypical Weyl semimetal TaIrTe4. As a first step, we visualized nano-photocurrent patterns in real space and demonstrated their connection to bulk nonlinear conductivity tensors through extensive modeling augmented with density functional theory calculations. Notably, our nanoscale probe gives access to not only the in-plane but also the out-of-plane electric fields so that it is feasible to interrogate all allowed nonlinear tensors including those that remained dormant in conventional far-field optics. Surface- and bulk-related nonlinear contributions are distinguished through their “symmetry fingerprints” in the photocurrent maps. Robust photocurrents also appear at mirror-symmetry breaking edges of TaIrTe4 single crystals that we assign to nonlinear conductivity tensors forbidden in the bulk. Nano-photocurrent spectroscopy at the boundary reveals a strong resonance structure absent in the interior of the sample, providing evidence for elusive surface states.

scholarly journals Synthetic Gauge Structures in Real Space in a Ring lattice

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Kunal K. Das ◽  
Miroslav Gajdacz
Keyword(s):  
Degrees Of Freedom ◽  
Real Space ◽  
Physical Motion ◽  
Physical Universe ◽  
Subatomic Particles ◽  
Internal States ◽  
Synthetic Gauge Fields ◽  
Fundamental Forces ◽  
Spatially Varying ◽  
Internal Degrees Of Freedom

Abstract Emergence of fundamental forces from gauge symmetry is among our most profound insights about the physical universe. In nature, such symmetries remain hidden in the space of internal degrees of freedom of subatomic particles. Here we propose a way to realize and study gauge structures in real space, manifest in external degrees of freedom of quantum states. We present a model based on a ring-shaped lattice potential, which allows for both Abelian and non-Abelian constructs. Non trivial Wilson loops are shown possible via physical motion of the system. The underlying physics is based on the close analogy of geometric phase with gauge potentials that has been utilized to create synthetic gauge fields with internal states of ultracold atoms. By scaling up to an array with spatially varying parameters, a discrete gauge field can be realized in position space, and its dynamics mapped over macroscopic size and time scales.

scholarly journals Time-resolved observation of spin-charge deconfinement in fermionic Hubbard chains

Science ◽  
2020 ◽  
Vol 367 (6474) ◽  
pp. 186-189 ◽  
Author(s):  
Jayadev Vijayan ◽  
Pimonpan Sompet ◽  
Guillaume Salomon ◽  
Joannis Koepsell ◽  
Sarah Hirthe ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Spatial Separation ◽  
Real Space ◽  
Quantum Gas ◽  
Interacting Particles ◽  
Time Resolved ◽  
One Dimensional ◽  
Quantum Numbers ◽  
Charge Correlations ◽  
The Individual

Elementary particles carry several quantum numbers, such as charge and spin. However, in an ensemble of strongly interacting particles, the emerging degrees of freedom can fundamentally differ from those of the individual constituents. For example, one-dimensional systems are described by independent quasiparticles carrying either spin (spinon) or charge (holon). Here, we report on the dynamical deconfinement of spin and charge excitations in real space after the removal of a particle in Fermi-Hubbard chains of ultracold atoms. Using space- and time-resolved quantum gas microscopy, we tracked the evolution of the excitations through their signatures in spin and charge correlations. By evaluating multipoint correlators, we quantified the spatial separation of the excitations in the context of fractionalization into single spinons and holons at finite temperatures.

scholarly journals Electret formation in transition metal oxides by electrochemical amorphization

2020 ◽  
Vol 12 (1) ◽  
Author(s):  
Yong-Jin Kim ◽  
Chan-Ho Yang
Keyword(s):  
Transition Metal ◽  
Metal Oxides ◽  
Charge Density ◽  
Electric Fields ◽  
Transition Metal Oxides ◽  
Degrees Of Freedom ◽  
Permanent Magnets ◽  
Underlying Mechanism ◽  
Diffusion Reaction ◽  
Wide Range

AbstractTransition metal oxides (TMOs) are an important class of materials that show a wide range of functionalities involving spin, charge, and lattice degrees of freedom. The strong correlation between electrons in d-orbitals and the multivalence nature give rise to a variety of exotic electronic states ranging from insulator to superconductor and cause intriguing phase competition phenomena. Despite a burst of research on the multifarious functionalities in TMOs, little attention has been paid to the formation and integration of an electret—a type of quasi-permanent electric field generator useful for nanoscale functional devices as an electric counterpart to permanent magnets. Here, we find that an electret can be created in LaMnO3 thin films by tip-induced electric fields, with a considerable surface height change, via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. The temporal evolution of the surface height, charge density, and electric potential are systematically examined by scanning probe microscopy. The underlying mechanism is theoretically analyzed based on a drift-diffusion-reaction model, suggesting that positively charged particles, which are likely protons produced by the dissociation of water, play crucial roles as trapped charges and a catalysis to trigger amorphization. Our finding opens a new horizon for multifunctional TMOs.

DIAGRAMS FOR MAGNETOTELLURIC DATA

Geophysics ◽  
1976 ◽  
Vol 41 (4) ◽  
pp. 766-770 ◽  
Author(s):  
F. E. M. Lilley
Keyword(s):  
Impedance Tensor ◽  
Two Dimensional ◽  
Magnetotelluric Data ◽  
One Dimensional ◽  
Magnetic Components ◽  
Strike Direction ◽  
Electric And Magnetic Fields ◽  
The Relationship ◽  
Special Case ◽  
Phase Differences

Observed magnetotelluric data are often transformed to the frequency domain and expressed as the relationship [Formula: see text]where [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text] represent electric and magnetic components measured along two orthogonal axes (in this paper, for simplicity, to be north and east, respectively). The elements [Formula: see text] comprise the magnetotelluric impedance tensor, and they are generally complex due to phase differences between the electric and magnetic fields. All quantities in equation (1) are frequency dependent. For the special case of “two‐dimensional” geology (where structure can be described as having a certain strike direction along which it does not vary), [Formula: see text] with [Formula: see text]. For the special case of “one‐dimensional” geology (where structure varies with depth only, as if horizontally layered), [Formula: see text] and [Formula: see text].

A time‐domain EM system measuring the step response of the ground

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 1010-1026 ◽  
Author(s):  
G. F. West ◽  
J. C. Macnae ◽  
Y. Lamontagne
Keyword(s):  
Magnetic Fields ◽  
Impulse Response ◽  
Electric Fields ◽  
Time Domain ◽  
Wide Band ◽  
Step Response ◽  
System Function ◽  
Response Measurement ◽  
Resistivity Method ◽  
Electric And Magnetic Fields

A wide‐band time‐domain EM system, known as UTEM, which uses a large fixed transmitter and a moving receiver has been developed and used extensively in a variety of geologic environments. The essential characteristics that distinguish it from other systems are that its system function closely approximates a stepfunction response measurement and that it can measure both electric and magnetic fields. Measurement of step rather than impulse response simplifies interpretation of data amplitudes, and improves the detection of good conductors in the presence of poorer ones. Measurement of electric fields provides information about lateral conductivity contrasts somewhat similar to that obtained by the gradient array resistivity method.

scholarly journals Magnetotellurics with a remote magnetic reference

Geophysics ◽  
1979 ◽  
Vol 44 (1) ◽  
pp. 53-68 ◽  
Author(s):  
T. D. Gamble ◽  
W. M. Goubau ◽  
J. Clarke
Keyword(s):  
Magnetic Field ◽  
Standard Deviation ◽  
Magnetic Fields ◽  
Apparent Resistivity ◽  
The Other ◽  
Impedance Tensor ◽  
Free Data ◽  
Electric And Magnetic Fields ◽  
Conventional Methods ◽  
The Magnetic Field

Magnetotelluric measurements were performed simultaneously at two sites 4.8 km apart near Hollister, California. SQUID magnetometers were used to measure fluctuations in two orthogonal horizontal components of the magnetic field. The data obtained at each site were analyzed using the magnetic fields at the other site as a remote reference. In this technique, one multiplies the equations relating the Fourier components of the electric and magnetic fields by a component of magnetic field from the remote reference. By averaging the various crossproducts, estimates of the impedance tensor not biased by noise are obtained, provided there are no correlations between the noises in the remote channels and noises in the local channels. For some data, conventional methods of analysis yielded estimates of apparent resistivities that were biased by noise by as much as two orders of magnitude. Nevertheless, estimates of the apparent resistivity obtained from these same data, using the remote reference technique, were consistent with apparent resistivities calculated from relatively noise‐free data at adjacent periods. The estimated standard deviation for periods shorter than 3 sec was less than 5 percent, and for 87 percent of the data, was less than 2 percent. Where data bands overlapped between periods of 0.33 sec and 1 sec, the average discrepancy between the apparent resistivities was 1.8 percent.

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