35,090 research outputs found
Uncovering the mechanism of the impurity-selective Mott transition in paramagnetic VO
While the phase diagrams of the one- and multi-orbital Hubbard model have
been well studied, the physics of real Mott insulators is often much richer,
material dependent, and poorly understood. In the prototype Mott insulator
VO, chemical pressure was initially believed to explain why the
paramagnetic-metal to antiferromagnetic-insulator transition temperature is
lowered by Ti doping while Cr doping strengthens correlations, eventually
rendering the high-temperature phase paramagnetic insulating. However, this
scenario has been recently shown both experimentally and theoretically to be
untenable. Based on full structural optimization, we demonstrate via the charge
self-consistent combination of density functional theory and dynamical
mean-field theory that changes in the VO phase diagram are driven
by defect-induced local symmetry breakings resulting from dramatically
different couplings of Cr and Ti dopants to the host system. This finding
emphasizes the high sensitivity of the Mott metal-insulator transition to the
local environment and the importance of accurately accounting for the
one-electron Hamiltonian, since correlations crucially respond to it.Comment: 5 pages, 5 figures, supplementary informatio
Information Transmission using the Nonlinear Fourier Transform, Part III: Spectrum Modulation
Motivated by the looming "capacity crunch" in fiber-optic networks,
information transmission over such systems is revisited. Among numerous
distortions, inter-channel interference in multiuser wavelength-division
multiplexing (WDM) is identified as the seemingly intractable factor limiting
the achievable rate at high launch power. However, this distortion and similar
ones arising from nonlinearity are primarily due to the use of methods suited
for linear systems, namely WDM and linear pulse-train transmission, for the
nonlinear optical channel. Exploiting the integrability of the nonlinear
Schr\"odinger (NLS) equation, a nonlinear frequency-division multiplexing
(NFDM) scheme is presented, which directly modulates non-interacting signal
degrees-of-freedom under NLS propagation. The main distinction between this and
previous methods is that NFDM is able to cope with the nonlinearity, and thus,
as the the signal power or transmission distance is increased, the new method
does not suffer from the deterministic cross-talk between signal components
which has degraded the performance of previous approaches. In this paper,
emphasis is placed on modulation of the discrete component of the nonlinear
Fourier transform of the signal and some simple examples of achievable spectral
efficiencies are provided.Comment: Updated version of IEEE Transactions on Information Theory, vol. 60,
no. 7, pp. 4346--4369, July, 201
Information Transmission using the Nonlinear Fourier Transform, Part I: Mathematical Tools
The nonlinear Fourier transform (NFT), a powerful tool in soliton theory and
exactly solvable models, is a method for solving integrable partial
differential equations governing wave propagation in certain nonlinear media.
The NFT decorrelates signal degrees-of-freedom in such models, in much the same
way that the Fourier transform does for linear systems. In this three-part
series of papers, this observation is exploited for data transmission over
integrable channels such as optical fibers, where pulse propagation is governed
by the nonlinear Schr\"odinger equation. In this transmission scheme, which can
be viewed as a nonlinear analogue of orthogonal frequency-division multiplexing
commonly used in linear channels, information is encoded in the nonlinear
frequencies and their spectral amplitudes. Unlike most other fiber-optic
transmission schemes, this technique deals with both dispersion and
nonlinearity directly and unconditionally without the need for dispersion or
nonlinearity compensation methods. This first paper explains the mathematical
tools that underlie the method.Comment: This version contains minor updates of IEEE Transactions on
Information Theory, vol. 60, no. 7, pp. 4312--4328, July 201
Information Transmission using the Nonlinear Fourier Transform, Part II: Numerical Methods
In this paper, numerical methods are suggested to compute the discrete and
the continuous spectrum of a signal with respect to the Zakharov-Shabat system,
a Lax operator underlying numerous integrable communication channels including
the nonlinear Schr\"odinger channel, modeling pulse propagation in optical
fibers. These methods are subsequently tested and their ability to estimate the
spectrum are compared against each other. These methods are used to compute the
spectrum of various signals commonly used in the optical fiber communications.
It is found that the layer-peeling and the spectral methods are suitable
schemes to estimate the nonlinear spectra with good accuracy. To illustrate the
structure of the spectrum, the locus of the eigenvalues is determined under
amplitude and phase modulation in a number of examples. It is observed that in
some cases, as signal parameters vary, eigenvalues collide and change their
course of motion. The real axis is typically the place from which new
eigenvalues originate or are absorbed into after traveling a trajectory in the
complex plane.Comment: Minor updates to IEEE Transactions on Information Theory, vol. 60,
no. 7, pp. 4329--4345, July 201
Dimensional tuning of electronic states under strong and frustrated interactions
We study a model of strongly interacting spinless fermions on an anisotropic
triangular lattice. At half-filling and the limit of strong repulsive
nearest-neighbor interactions, the fermions align in stripes and form an
insulating state. When a particle is doped, it either follows a one-dimensional
free motion along the stripes or fractionalizes perpendicular to the stripes.
The two propagations yield a dimensional tuning of the electronic state. We
study the stability of this phase and derive an effective model to describe the
low-energy excitations. Spectral functions are presented which can be used to
experimentally detect signatures of the charge excitations.Comment: 4pages 4figures included. to appear in Phys. Rev. Lett. vol. 10
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