Mechanisms

2021 ◽  
pp. 32-125
Author(s):  
Vladimir Z. Kresin ◽  
Sergei G. Ovchinnikov ◽  
Stuart A. Wolf
Keyword(s):  
Superconducting State ◽  
Degrees Of Freedom ◽  
Pair Correlation ◽  
Three Dimensional ◽  
Layered Materials ◽  
Spin Fluctuations ◽  
Strong Electron ◽  
Hubbard Hamiltonian ◽  
Electron Phonon Interaction ◽  
Phonon Mechanism

This chapter introduces the general concepts of pair correlation, and superconductivity as a strong non-adiabatic phenomenon. Phonon, electronic, and magnetic mechanisms play the major roles; each of them can serve as the origin of the superconducting state. Speaking of the phonon mechanism, it is essential that an explicit expression for Tc depend on the intensity of the electron–phonon interaction. In principle, the electron–phonon mechanism can provide high values of Tc, up to room temperature. Pioneering work by Little, who introduced the electronic mechanism, is described. The mechanism has been analysed for one-dimensional, two-dimensional, and three-dimensional systems. The plasmon mechanism can play a role for layered materials. The superconducting state can be provided by magnetic degrees of freedom. The band limit with spin fluctuations and the regime of strong electron correlations are described. The Hubbard Hamiltonian and the t − J model are the ingredients of the approach.

scholarly journals Low Energy Electrodynamics of CrI3 Layered Ferromagnet

2021 ◽  
Author(s):  
Luca Tomarchio ◽  
Salvatore Macis ◽  
Lorenzo Mosesso ◽  
Loi T. Nguyen ◽  
Antonio Grilli ◽  
...  
Keyword(s):  
Optical Properties ◽  
Degrees Of Freedom ◽  
Near Infrared ◽  
Effective Interaction ◽  
Blue Shift ◽  
Ferromagnetic Phase ◽  
Phonon Modes ◽  
Strong Electron ◽  
Spin Lattice ◽  
Electron Phonon Interaction

Abstract We report on the optical properties from terahertz (THz) to Near-Infrared (NIR) of the layered magnetic compound CrI3 at various temperatures, both in the para- magnetic and ferromagnetic phase. In the NIR spectral range, we have observed an insulating electronic gap around 1.1 eV which strongly hardens with decreasing temperature. The blue shift observed represents a record in insulating materials and it is a fingerprint of a strong electron-phonon interaction. Moreover, a further gap hardening is observed below the Curie temperature, indicating the establishment of an effective interaction between electrons and magnetic degrees of freedom in the ferromagnetic phase. This interaction is confirmed by the disappearance of some phonon modes in the same phase as expected from a spin-lattice interaction theory. Therefore, the optical properties of CrI3 reveal a complex interaction among electronic, phononic and magnetic degrees of freedom, opening many possibilities for its use in 2-Dimensional heterostructures.

scholarly journals Low energy electrodynamics of CrI3 layered ferromagnet

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Luca Tomarchio ◽  
Salvatore Macis ◽  
Lorenzo Mosesso ◽  
Loi T. Nguyen ◽  
Antonio Grilli ◽  
...  
Keyword(s):  
Optical Properties ◽  
Degrees Of Freedom ◽  
Near Infrared ◽  
Effective Interaction ◽  
Blue Shift ◽  
Ferromagnetic Phase ◽  
Phonon Modes ◽  
Strong Electron ◽  
Spin Lattice ◽  
Electron Phonon Interaction

AbstractWe report on the optical properties from terahertz (THz) to Near-Infrared (NIR) of the layered magnetic compound CrI3 at various temperatures, both in the paramagnetic and ferromagnetic phase. In the NIR spectral range, we observe an insulating electronic gap around 1.1 eV which strongly hardens with decreasing temperature. The blue shift observed represents a record in insulating materials and it is a fingerprint of a strong electron-phonon interaction. Moreover, a further gap hardening is observed below the Curie temperature, indicating the establishment of an effective interaction between electrons and magnetic degrees of freedom in the ferromagnetic phase. Similar interactions are confirmed by the disappearance of some phonon modes in the same phase, as expected from a spin-lattice interaction theory. Therefore, the optical properties of CrI3 reveal a complex interaction among electronic, phononic and magnetic degrees of freedom, opening many possibilities for its use in 2-Dimensional heterostructures.

scholarly journals Ferroelectricity Modulates Polaronic Coupling at Multiferroic Interfaces

2022 ◽  
Author(s):  
Marius-Adrian Husanu ◽  
Dana Popescu ◽  
Luminita Hrib ◽  
Raluca Negrea ◽  
Cosmin Istrate ◽  
...  
Keyword(s):  
Colossal Magnetoresistance ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Charge Carriers ◽  
Ferroelectric Polarization ◽  
Interfacial Region ◽  
Electron Phonon Interaction ◽  
Band Filling ◽  
Multiferroic Heterostructures ◽  
Beyond Cmos

Abstract Physics of the multiferroic interfaces is currently understood mostly within a phenomenological framework including screening of the polarization field and depolarizing charges. Largely unexplored still remains the band dependence of the interfacial charge modulation, as well as the associated changes of the electron-phonon interaction, coupling the charge and lattice degrees of freedom. Here, multiferroic heterostructures of the colossal-magnetoresistance manganite La1-xSrxMnO3 buried under ferroelectric BaTiO3 and PbZrxTi1-xO3 are explored using soft-X-ray angle-resolved photoemission. The experimental band dispersions from the buried La1-xSrxMnO3 identify coexisting two-dimensional hole and three-dimensional electron charge carriers. The ferroelectric polarization modulates their charge density, changing the band filling and orbital occupation in the interfacial region. Furthermore, these changes in the carrier density affect the coupling of the 2D holes and 3D electrons with the lattice which forms large Froelich polarons inherently reducing mobility of the charge carriers. We find that the fast dynamic response of electrons makes them much more efficient in screening of the electron-lattice interaction compared to the holes. Our k-resolved results on the orbital occupancy, band filling and electron-lattice interaction in multiferroic oxide heterostructures modulated by the ferroelectric polarization disclose most fundamental physics of these systems needed for further progress of beyond-CMOS ferro-functional electronics.

scholarly journals Bosonic Spectral Function and the Electron-Phonon Interaction in HTSC Cuprates

2010 ◽  
Vol 2010 ◽  
pp. 1-64 ◽  
Author(s):  
E. G. Maksimov ◽  
M. L. Kulić ◽  
O. V. Dolgov
Keyword(s):  
Spectral Function ◽  
Spin Fluctuations ◽  
Strongly Correlated ◽  
Phonon Interaction ◽  
Strong Electron ◽  
Optimal Doping ◽  
Electron Phonon Interaction ◽  
Wave Pairing ◽  
Range Part ◽  
D Wave

In this paper we discuss experimental evidence related to the structure and origin of the bosonic spectral function in high-temperature superconducting (HTSC) cuprates at and near optimal doping. Global properties of , such as number and positions of peaks, are extracted by combining optics, neutron scattering, ARPES and tunnelling measurements. These methods give evidence for strong electron-phonon interaction (EPI) with in cuprates near optimal doping. We clarify how these results are in favor of the modified Migdal-Eliashberg (ME) theory for HTSC cuprates near optimal doping. In Section 2 we discuss theoretical ingredients—such as strong EPI, strong correlations—which are necessary to explain the mechanism of d-wave pairing in optimally doped cuprates. These comprise the ME theory for EPI in strongly correlated systems which give rise to the forward scattering peak. The latter is supported by the long-range part of EPI due to the weakly screened Madelung interaction in the ionic-metallic structure of layered HTSC cuprates. In this approach EPI is responsible for the strength of pairing while the residual Coulomb interaction and spin fluctuations trigger the d-wave pairing.

EPR INVESTIGATION OF La0.7Ca0.3MnO3: EVIDENCE OF SPIN-GLASS FORMATION

2002 ◽  
Vol 16 (01n02) ◽  
pp. 47-56 ◽  
Author(s):  
G. NARSINGA RAO ◽  
Y. BABU ◽  
M. D. SASTRY ◽  
D. SURESH BABU ◽  
J. W. CHEN
Keyword(s):  
Curie Temperature ◽  
Experimental Evidence ◽  
Spin Glass ◽  
Glass Formation ◽  
Spin Fluctuations ◽  
Magnetization Curves ◽  
Phonon Interaction ◽  
Strong Electron ◽  
Phase Line ◽  
Electron Phonon Interaction

EPR investigations on La 0.7 Ca 0.3 MnO 3 were carried out in the temperature range from 14 K to 300 K. The important observations are: (i) a coincidence of resistivity maxima with the disappearance of paramagnetic EPR line I, which suggests that there exists a strong electron–phonon interaction, (ii) the appearance of an "out of phase" line near the Curie temperature T c due to the formation of spin clusters consisting of Mn3+ and Mn4+ ions, and (iii) the appearance of an intense EPR line III and the splitting of FC and ZFC magnetization curves below 160 K, ascribed to local magnetic frustrations. The above EPR observations provide experimental evidence for the co existence of spin fluctuations and magnetic disorders in this sample, which leads to the formation of spin-glass features below T c .

scholarly journals Design, Fabrication, and Testing of a Novel 3D 3-Fingered Electrothermal Microgripper with Multiple Degrees of Freedom

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 444
Author(s):  
Guoning Si ◽  
Liangying Sun ◽  
Zhuo Zhang ◽  
Xuping Zhang
Keyword(s):  
Degrees Of Freedom ◽  
Dynamic Properties ◽  
Three Dimensional ◽  
Polyimide Film ◽  
Zebrafish Embryos ◽  
Multiple Degrees Of Freedom ◽  
Electrothermal Actuator ◽  
3D Space ◽  
Pick And Place

This paper presents the design, fabrication, and testing of a novel three-dimensional (3D) three-fingered electrothermal microgripper with multiple degrees of freedom (multi DOFs). Each finger of the microgripper is composed of a V-shaped electrothermal actuator providing one DOF, and a 3D U-shaped electrothermal actuator offering two DOFs in the plane perpendicular to the movement of the V-shaped actuator. As a result, each finger possesses 3D mobilities with three DOFs. Each beam of the actuators is heated externally with the polyimide film. The durability of the polyimide film is tested under different voltages. The static and dynamic properties of the finger are also tested. Experiments show that not only can the microgripper pick and place microobjects, such as micro balls and even highly deformable zebrafish embryos, but can also rotate them in 3D space.

scholarly journals Asymmetry in Three-Dimensional Sprinting with and without Running-Specific Prostheses

Symmetry ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 580
Author(s):  
Anna Lena Emonds ◽  
Katja Mombaur
Keyword(s):  
Degrees Of Freedom ◽  
Body Position ◽  
Three Dimensional ◽  
Problem Formulation ◽  
Contact Phase ◽  
Individual Level ◽  
Lower Trunk ◽  
Floating Base ◽  
The Asymmetry ◽  
Limb Asymmetry

As a whole, human sprinting seems to be a completely periodic and symmetrical motion. This view is changed when a person runs with a running-specific prosthesis after a unilateral amputation. The aim of our study is to investigate differences and similarities between unilateral below-knee amputee and non-amputee sprinters—especially with regard to whether asymmetry is a distracting factor for sprint performance. We established three-dimensional rigid multibody models of one unilateral transtibial amputee athlete and for reference purposes of three non-amputee athletes. They consist of 16 bodies (head, ipper, middle and lower trunk, upper and lower arms, hands, thighs, shanks and feet/running specific prosthesis) with 30 or 31 degrees of freedom (DOFs) for the amputee and the non-amputee athletes, respectively. Six DOFs are associated with the floating base, the remaining ones are rotational DOFs. The internal joints are equipped with torque actuators except for the prosthetic ankle joint. To model the spring-like properties of the prosthesis, the actuator is replaced by a linear spring-damper system. We consider a pair of steps which is modeled as a multiphase problem with each step consisting of a flight, touchdown and single-leg contact phase. Each phase is described by its own set of differential equations. By combining motion capture recordings with a least squares optimal control problem formulation including constraints, we reconstructed the dynamics of one sprinting trial for each athlete. The results show that even the non-amputee athletes showed less symmetrical sprinting than expected when examined on an individual level. Nevertheless, the asymmetry is much more pronounced in the amputee athlete. The amputee athlete applies larger torques in the arm and trunk joints to compensate the asymmetry and experiences a destabilizing influence of the trunk movement. Hence, the inter-limb asymmetry of the amputee has a significant effect on the control of the sprint movement and the maintenance of an upright body position.

Three-dimensional asymmetric maximum weight lifting prediction considering dynamic joint strength

2021 ◽  
pp. 095441192098703
Author(s):  
Rahid Zaman ◽  
Yujiang Xiang ◽  
Jazmin Cruz ◽  
James Yang
Keyword(s):  
Experimental Data ◽  
Degrees Of Freedom ◽  
Inverse Dynamics ◽  
Three Dimensional ◽  
Optimization Method ◽  
Weight Lifting ◽  
Joint Torque ◽  
Maximum Weight ◽  
Angular Velocities ◽  
Asymmetric Lifting

In this study, the three-dimensional (3D) asymmetric maximum weight lifting is predicted using an inverse-dynamics-based optimization method considering dynamic joint torque limits. The dynamic joint torque limits are functions of joint angles and angular velocities, and imposed on the hip, knee, ankle, wrist, elbow, shoulder, and lumbar spine joints. The 3D model has 40 degrees of freedom (DOFs) including 34 physical revolute joints and 6 global joints. A multi-objective optimization (MOO) problem is solved by simultaneously maximizing box weight and minimizing the sum of joint torque squares. A total of 12 male subjects were recruited to conduct maximum weight box lifting using squat-lifting strategy. Finally, the predicted lifting motion, ground reaction forces, and maximum lifting weight are validated with the experimental data. The prediction results agree well with the experimental data and the model’s predictive capability is demonstrated. This is the first study that uses MOO to predict maximum lifting weight and 3D asymmetric lifting motion while considering dynamic joint torque limits. The proposed method has the potential to prevent individuals’ risk of injury for lifting.

Determination of the Workspace of a Three-Degrees-of-Freedom Parallel Manipulator Using a Three-Dimensional Computer-Aided-Design Software Package and the Concept of Virtual Chains1

2015 ◽  
Vol 8 (2) ◽  
Author(s):  
Andrew Johnson ◽  
Xianwen Kong ◽  
James Ritchie
Keyword(s):  
Computer Aided Design ◽  
Parallel Manipulator ◽  
Degrees Of Freedom ◽  
Graphical Representation ◽  
Three Dimensional ◽  
Parallel Manipulators ◽  
Workspace Analysis ◽  
Computer Aided ◽  
Aided Design

The determination of workspace is an essential step in the development of parallel manipulators. By extending the virtual-chain (VC) approach to the type synthesis of parallel manipulators, this technical brief proposes a VC approach to the workspace analysis of parallel manipulators. This method is first outlined before being illustrated by the production of a three-dimensional (3D) computer-aided-design (CAD) model of a 3-RPS parallel manipulator and evaluating it for the workspace of the manipulator. Here, R, P and S denote revolute, prismatic and spherical joints respectively. The VC represents the motion capability of moving platform of a manipulator and is shown to be very useful in the production of a graphical representation of the workspace. Using this approach, the link interferences and certain transmission indices can be easily taken into consideration in determining the workspace of a parallel manipulator.

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