scholarly journals Study of effective coupling between charge degrees of freedom in low dimensional hole-doped quantum antiferromagnets

2020 ◽  
Author(s):  
Suraka Bhattacharjee ◽  
Ranjan Chaudhury
Keyword(s):  
Degrees Of Freedom ◽  
Coulomb Repulsion ◽  
Detailed Comparison ◽  
Zero Temperature ◽  
Quantum Antiferromagnets ◽  
Stiffness Constant ◽  
In Doping ◽  
Charge Correlations ◽  
Drude Weight ◽  
Low Dimensional

Expressions for generalized charge stiffness constant at zero temperature are derived corresponding to low dimensional hole doped quantum antiferromagnets, describable by the t-J-like models, with a view to understanding fermionic pairing possibilities and charge couplings in the itinerant antiferromagnetic systems. A detailed comparison between spin and charge correlations and couplings are presented in both strong and weak coupling limits. The result highlights that the charge and spin couplings show very similar behaviour in the over-doped region in both the dimensions, whereas they show a completely different trend in the lower doping regimes. A qualitative equivalence of generalized charge stiffness constant with the effective Drude weight and Coulomb interaction is established based on the comparison with other theoretical and experimental results. The fall in charge stiffness with increase in doping then implies reduction in the magnitude of effective Coulomb repulsion between the mobile carriers. This leads to an enhanced possibility of fermionic pairing with increase in doping in the possible presence of some other attraction producing mechanism from a source outside the t-J-like models. Moreover, under certain conditions in the optimal doping region, the t-J-like models themselves are able to produce attractive interaction for pairing.

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 Optimizing the structure and movement of a robotic bat with biological kinematic synergies

2018 ◽  
Vol 37 (10) ◽  
pp. 1233-1252 ◽  
Author(s):  
Jonathan Hoff ◽  
Alireza Ramezani ◽  
Soon-Jo Chung ◽  
Seth Hutchinson
Keyword(s):  
Principal Component Analysis ◽  
Topological Structure ◽  
Degrees Of Freedom ◽  
Dimensional Space ◽  
Principal Component ◽  
Biologically Inspired ◽  
Wing Kinematics ◽  
Wing Motion ◽  
Kinematic Synergies ◽  
Low Dimensional

In this article, we present methods to optimize the design and flight characteristics of a biologically inspired bat-like robot. In previous, work we have designed the topological structure for the wing kinematics of this robot; here we present methods to optimize the geometry of this structure, and to compute actuator trajectories such that its wingbeat pattern closely matches biological counterparts. Our approach is motivated by recent studies on biological bat flight that have shown that the salient aspects of wing motion can be accurately represented in a low-dimensional space. Although bats have over 40 degrees of freedom (DoFs), our robot possesses several biologically meaningful morphing specializations. We use principal component analysis (PCA) to characterize the two most dominant modes of biological bat flight kinematics, and we optimize our robot’s parametric kinematics to mimic these. The method yields a robot that is reduced from five degrees of actuation (DoAs) to just three, and that actively folds its wings within a wingbeat period. As a result of mimicking synergies, the robot produces an average net lift improvesment of 89% over the same robot when its wings cannot fold.

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 $\bm{\widehat{{\rm U}(1)}\times\widehat{{\rm SU}({\lc m})}_{1}}$ THEORY AND c=m W1+∞ MINIMAL MODELS IN THE HIERARCHICAL QUANTUM HALL EFFECT

2000 ◽  
Vol 15 (06) ◽  
pp. 915-926 ◽  
Author(s):  
MARINA HUERTA
Keyword(s):  
Hall Effect ◽  
Quantum Hall Effect ◽  
Degrees Of Freedom ◽  
Central Charge ◽  
Quantum Hall ◽  
Detailed Comparison ◽  
Conformal Field Theories ◽  
Minimal Models ◽  
Conformal Field ◽  
Group Flow

Two classes of Conformal Field Theories have been proposed to describe the Hierarchical Quantum Hall Effect: the multicomponent bosonic theory, characterized by the symmetry [Formula: see text] and the W1+∞ minimal models with central charge c=m. In spite of having the same spectrum of edge excitations, they manifest differences in the degeneracy of the states and in the quantum statistics, which call for a more detailed comparison between them. Here, we describe their detailed relation for the general case, c=m and extend the methods previously published for c≤3. Specifically, we obtain the reduction in the number of degrees of freedom from the multicomponent Abelian theory to the minimal models by decomposing the characters of the [Formula: see text] representations into those of the c=mW1+∞ minimal models. Furthermore, we find the Hamiltonian whose renormalization group flow interpolates between the two models, having the W1+∞ minimal models as an infrared fixed point.

Spin Hall Effect Induced by Sound

2012 ◽  
Vol 190 ◽  
pp. 117-120
Author(s):  
I.I. Lyapilin
Keyword(s):  
Degrees Of Freedom ◽  
Spin Current ◽  
Coherent Motion ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Spin Coherence ◽  
Nanoscale Systems ◽  
The Subject ◽  
Normal Current ◽  
Low Dimensional

Transport of electronic spins in low-dimensional and nanoscale systems is the subject of thenovel and quickly developing eld of spintronics. The possibility of coherent spin manipulationrepresents an ultimate goal of this eld. Typically, spin transport is strongly aected by couplingof spin and orbital degrees of freedom. The inuence of the spin orbit interaction is twofold.The momentum relaxation due to the scattering of carriers, inevitably leads to spin relaxationand destroys the spin coherence. On the other hand, the controlled orbital motion of carrierscan result in a coherent motion of their spins. Thus, the spin orbit coupling is envisaged as apossible tool for spin controling in electronic devices. In particular, it is possible to generatespin polarization and spin currents by applying electric eld, the phenomenon known as thespin-Hall eect (SHE) [1- 3]. The eect is manifested in the form of a spin current directedperpendicular to the normal current, which takes place in an electric eld.

RECENT APPLICATIONS OF THE DMRG METHOD

2006 ◽  
Vol 20 (19) ◽  
pp. 2624-2635
Author(s):  
KAREN HALLBERG
Keyword(s):  
Degrees Of Freedom ◽  
Mean Field Theory ◽  
Mean Field ◽  
Finite Size ◽  
Strongly Correlated Systems ◽  
Strongly Correlated ◽  
Correlated Systems ◽  
Infinite Dimensional ◽  
Low Dimensional ◽  
Time Dependent Problems

Since its inception, the DMRG method has been a very powerful tool for the calculation of physical properties of low-dimensional strongly correlated systems. It has been adapted to obtain dynamical properties and to consider finite temperature, time-dependent problems, bosonic degrees of freedom, the treatment of classical problems and non-equilibrium systems, among others. We will briefly review the method and then concentrate on its latest developments, describing some recent successful applications. In particular we will show how the dynamical DMRG can be used together with the Dynamical Mean Field Theory (DMFT) to solve the associated impurity problem in the infinite-dimensional Hubbard model. This method is used to obtain spectral properties of strongly correlated systems. With this algorithm, more complex problems having a larger number of degrees of freedom can be considered and finite-size effects can be minimized.

Near Integrability in Low Dimensional Gross–Neveu Models

2011 ◽  
Vol 66 (8-9) ◽  
pp. 468-480 ◽  
Author(s):  
Ognyan Christov
Keyword(s):  
Lie Algebras ◽  
Degrees Of Freedom ◽  
Normal Forms ◽  
Kam Theory ◽  
Higher Dimensions ◽  
Low Dimensional ◽  
Three Degrees Of Freedom

Abstract The low-dimensional Gross-Neveu models are studied. For the systems, related to the Lie algebras so(4), so(5), sp(4), sl(3), we prove that they have Birkhoff-Gustavson normal forms which are integrable and non-degenerate in Kolmogorov-Arnold-Moser (KAM) theory sense. Unfortunately, this is not the case for systems with three degrees of freedom, related to the Lie algebras so(6) ~ sl(4), so(7), sp(6); their Birkhoff-Gustavson normal forms are proven to be non-integrable in the Liouville sense. The last result can easily be extended to higher dimensions.

scholarly journals Centre manifolds of forced dynamical systems

1991 ◽  
Vol 32 (4) ◽  
pp. 401-436 ◽  
Author(s):  
S. M. Cox ◽  
A. J. Roberts
Keyword(s):  
Dynamical System ◽  
Dynamical Systems ◽  
Degrees Of Freedom ◽  
Rational Approach ◽  
Centre Manifold ◽  
Formal Scheme ◽  
Dimensional Models ◽  
Centre Manifolds ◽  
Low Dimensional ◽  
Sivashinsky Equation

AbstractCentre manifolds arise in a rational approach to the problem of forming low-dimensional models of dynamical systems with many degrees of freedom. When a dynamical system with a centre manifold is subject to a small forcing, F, there are two effects: to displace the centre manifold; and to alter the evolution thereon. We propose a formal scheme for calculating the centre manifold of such a forced dynamical system. Our formalism permits the calculation of these effects, with errors of order |F|2. We find that the displacement of the manifold allows a reparameterisation of its description, and we describe two “natural” ways in which this can be carried out. We give three examples: an introductory example; a five-mode model of the atmosphere to display the quasi-geostrophic approximation; and the forced Kuramoto-Sivashinsky equation.

Characterization of Grain Boundary Geometry in the TEM, Exemplified in Si Thin Films

2012 ◽  
Vol 186 ◽  
pp. 7-12 ◽  
Author(s):  
János L. Lábár ◽  
Ákos K. Kiss ◽  
Silke Christiansen ◽  
Fritz Falk
Keyword(s):  
Thin Films ◽  
Degrees Of Freedom ◽  
Sample Surface ◽  
High Energy ◽  
High Energy Density ◽  
Glass Substrates ◽  
Low Dimensional ◽  
Si Films ◽  
Alternative Routes

A method is presented here for complete geometrical characterization of grain boundaries, based on measurement of thin films in the TEM. First, the three parameters, characterizing the misorientation of the two neighboring grains are determined from convergent beam electron diffraction (CBED). Next, the last two (of the total five macroscopic degrees of freedom) parameters are determined from bright field (BF) images to describe the orientation of the boundary plane between them. Ambiguity in the tilt direction of the plane is resolved from BF images recorded at two distinct goniometer settings. Application of the method is demonstrated in Silicon thin films. GB-plane distribution in a thin film is not necessarily identical to the distribution of similar planes in bulk materials. It was observed in low dimensional fcc metals (wires or thin films) that energy minimization of GBs can follow two (mainly alternative) routes. Either low energy planes (like {111}) are formed in 3 boundaries, or alternatively, it is observed that the GB plane has a general index (and high energy density) but it ends at both free surfaces of the sample, resulting in a GB, almost normal to the sample surface, minimizing the total area of the GB. We observed that this later type of planes is mainly characteristic of non-3 boundaries in thin Si films, crystallized from melt on glass substrates (separated by a thin SiN barrier layer). This observation is important for the expected recombination properties of the multicrystalline Si (m-Si) in planned solar cell (SC) applications.

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