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7,977 results on '"Sayyad A"'

206. Numerical and Experimental Analysis of Profile Complexity in Aluminum Extrusion

Author

Chekotu, Josiah Cherian, Qamar, Sayyad Zahid, Qamar, Sayyad Basim, Cavas-Martínez, Francisco, Series Editor, Chaari, Fakher, Series Editor, di Mare, Francesca, Series Editor, Gherardini, Francesco, Series Editor, Haddar, Mohamed, Series Editor, Ivanov, Vitalii, Series Editor, Kwon, Young W., Series Editor, Trojanowska, Justyna, Series Editor, and Abdel Wahab, Magd, editor

Published
2022
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224. Pairing and non-Fermi liquid behavior in partially flat-band systems

Author

Sayyad, Sharareh, Huang, Edwin W., Kitatani, Motoharu, Vaezi, Mohammad-Sadegh, Nussinov, Zohar, Vaezi, Abolhassan, and Aoki, Hideo

Subjects
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Abstract

While multiband systems are usually considered for flat-band physics, here we study one-band models that have flat portions in the dispersion to explore correlation effects in the 2D repulsive Hubbard model in an intermediate coupling regime. The FLEX+DMFT~(the dynamical mean-field theory combined with the fluctuation exchange approximation) is used to show that we have a crossover from ferromagnetic to antiferromagnetic spin fluctuations as the band filling is varied, which triggers a crossover from triplet to singlet pairings with a peculiar filling dependence that is dominated by the size of the flat region in the dispersion. A curious manifestation of the flat part appears as larger numbers of nodal lines associated with pairs extended in real space. We further detect non-Fermi liquid behavior in the momentum distribution function, frequency dependence of the self-energy and spectral function. These indicate correlation physics peculiar to flat-band systems., Comment: 7+2 pages

Published
2019
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225. SO(4) FLEX+DMFT formalism with SU(2)$\otimes$SU(2)-symmetric impurity solver for superconductivity in the repulsive Hubbard model

Author

Sayyad, Sharareh, Tsuji, Naoto, Capone, Massimo, and Aoki, Hideo

Subjects
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Abstract

Here we have developed a FLEX+DMFT formalism, where the symmetry properties of the system are incorporated by constructing a SO(4) generalization of the conventional fluctuation-exchange approximation (FLEX) coupled self-consistently to the dynamical mean-field theory (DMFT). Along with this line, we emphasize that the SO(4) symmetry is the lowest group-symmetry that enables us to investigate superconductivity and antiferromagnetism on an equal footing. We have imposed this by decomposing the electron operator into auxiliary fermionic and slave-boson constituents that respect SU(2)$_{\rm spin}\otimes$SU(2)$_{\eta{\rm spin}}$. This is used not in a mean-field treatment as in the usual slave-boson formalisms, but instead in the DMFT impurity solver with an SU(2)$_{\rm spin}\otimes$SU(2)$_{\eta{\rm spin}}$ hybridization function to incorporate the FLEX-generated bath information into DMFT iterations. While there have been attempts such as the doublon-less SU(2) slave-boson formalism, the present "full-SU(2)" slave-boson formalism is expected to provide a new platform for addressing the underlying physics for various quantum orders, which compete with each other and can coexist., Comment: 12+15 pages

Published
2019

226. Characterizing dissociative motion in time-resolved x-ray scattering from gas-phase diatomic molecules

Author

Ware, MR, Glownia, JM, Al-Sayyad, N, O'Neal, JT, and Bucksbaum, PH

Subjects
Physics - Atomic Physics
Abstract

Time-resolved x-ray scattering (TRXS) measures internuclear separations in a molecule following laser-induced photoexcitation. The molecular dynamics induced by the excitation laser may lie on one or several bound or dissociative electronic states. TRXS from these states can be difficult to isolate because they generally overlap in the angle-resolved x-ray scattering pattern $I(x,y,{\tau})$, where ${\tau}$ is the pump-probe delay and $x,y$ are the physical pixel positions. Here we show how standard transform methods can isolate the dynamics from individual states. We form the temporal Fourier transform, $\tilde{I}(x,y,{\omega})$$=\int_{-\infty}^{\infty} d\tau e^{-i\omega\tau} I(x,y,\tau)$. This frequency-resolved x-ray scattering (FRXS) signal segregates the bound states according to their vibrational frequencies, ${\omega}_i$, and also displays dissociative states along straight lines ${\omega}=vQ$, where the slope $v$ is the rate of increase of the internuclear distance and $Q$ is the momentum transfer between the incident and scattered x-ray photon. We derive this relation and use FRXS to extract state-specific dynamics from experimental TRXS from molecular iodine following a 520 nm pump. Dynamics observed include one- and two-photon dissociation of the $^{1}{\Pi}_{u}$ and $^{1}{\Sigma}_{g}^{+}$ excited states, and vibrational wave packets on the B ($^{3}{\Pi}_{0u}^{+}$)state., Comment: 18 pages, 9 figures

Published
2019
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