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Subir Sachdev - One of the best experts on this subject based on the ideXlab platform.
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linear in temperature resistivity in the limit of zero temperature from the time reparameterization soft mode
Annals of Physics, 2020Co-Authors: Haoyu Guo, Subir SachdevAbstract:Abstract The most puzzling aspect of the ‘strange metal’ behavior of correlated electron compounds is that the linear in temperature resistivity often extends down to low temperatures, lower than natural Microscopic Energy scales. We consider recently proposed deconfined critical points (or phases) in models of electrons in large dimension lattices with random nearest-neighbor exchange interactions. The criticality is in the class of Sachdev–Ye–Kitaev models, and exhibits a time reparameterization soft mode representing gravity in dual holographic theories. We compute the low temperature resistivity in a large M limit of models with SU( M ) spin symmetry, and find that the dominant temperature dependence arises from this soft mode. The resistivity is linear in temperature down to zero temperature at the critical point, with a co-efficient universally proportional to the product of the residual resistivity and the co-efficient of the linear in temperature specific heat. We argue that the time reparameterization soft mode offers a promising and generic mechanism for resolving the strange metal puzzle.
Haoyu Guo - One of the best experts on this subject based on the ideXlab platform.
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linear in temperature resistivity in the limit of zero temperature from the time reparameterization soft mode
Annals of Physics, 2020Co-Authors: Haoyu Guo, Subir SachdevAbstract:Abstract The most puzzling aspect of the ‘strange metal’ behavior of correlated electron compounds is that the linear in temperature resistivity often extends down to low temperatures, lower than natural Microscopic Energy scales. We consider recently proposed deconfined critical points (or phases) in models of electrons in large dimension lattices with random nearest-neighbor exchange interactions. The criticality is in the class of Sachdev–Ye–Kitaev models, and exhibits a time reparameterization soft mode representing gravity in dual holographic theories. We compute the low temperature resistivity in a large M limit of models with SU( M ) spin symmetry, and find that the dominant temperature dependence arises from this soft mode. The resistivity is linear in temperature down to zero temperature at the critical point, with a co-efficient universally proportional to the product of the residual resistivity and the co-efficient of the linear in temperature specific heat. We argue that the time reparameterization soft mode offers a promising and generic mechanism for resolving the strange metal puzzle.
Jan Vorberger - One of the best experts on this subject based on the ideXlab platform.
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lattice dynamics and ultrafast Energy flow between electrons spins and phonons in a 3d ferromagnet
Physical Review Research, 2021Co-Authors: Daniela Zahn, Florian Jakobs, Yoav William Windsor, Helene Seiler, Thomas Vasileiadis, Tim A Butcher, Dieter Engel, U Atxitia, Jan Vorberger, Ralph ErnstorferAbstract:This work provides a consistent description of the Microscopic Energy flow during the ultrafast demagnetization of nickel by combining experimental results for the lattice heating with atomistic spin dynamics simulations.
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electron phonon coupling and Energy flow in a simple metal beyond the two temperature approximation
Physical Review X, 2016Co-Authors: Lutz Waldecker, Ralph Ernstorfer, Roman Bertoni, Jan VorbergerAbstract:The electron-phonon coupling and the corresponding Energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitored by femtosecond electron diffraction. The electron-phonon coupling strength is obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a twotemperature model (TTM) deviates significantly from the ab initio values. We introduce a nonthermal lattice model (NLM) for describing nonthermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principles calculations except the phonon-phonon coupling strength, the prediction of the Energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the Microscopic Energy flow even for simple metals like aluminium and that the determination of the electronphonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.
V Lavin - One of the best experts on this subject based on the ideXlab platform.
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efficient nd3 yb3 Energy transfer processes in high phonon Energy phosphate glasses for 1 0 μm yb3 laser
Journal of Applied Physics, 2011Co-Authors: F Riveralopez, C.k. Jayasankar, P Babu, Ch Basavapoornima, V LavinAbstract:Efficient Nd3+→Yb3+ resonant and phonon-assisted Energy transfer processes have been observed in phosphate glasses and have been studied using steady-state and time-resolved optical spectroscopies. Results indicate that the Energy transfer occurs via nonradiative electric dipole-dipole processes and is enhanced with the concentration of Yb3+ acceptor ions, having an efficiency higher than 75% for the glass doped with 1 mol% of Nd2O3 and 4 mol% of Yb2O3. The luminescence decay curves show a nonexponential character and the Energy transfer Microscopic parameter calculated with the Inokuti-Hirayama model gives a value of 240 × 10−40 cm6 s−1, being one of the highest reported in the literature for Nd3+-Yb3+ co-doped matrices. From the steady-state experimental absorption and emission cross-sections, a general expression for estimating the Microscopic Energy transfer parameter is proposed based upon the theoretical methods developed by Miyakawa and Dexter and Tarelho et al. This expression takes into account a...
Ralph Ernstorfer - One of the best experts on this subject based on the ideXlab platform.
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lattice dynamics and ultrafast Energy flow between electrons spins and phonons in a 3d ferromagnet
Physical Review Research, 2021Co-Authors: Daniela Zahn, Florian Jakobs, Yoav William Windsor, Helene Seiler, Thomas Vasileiadis, Tim A Butcher, Dieter Engel, U Atxitia, Jan Vorberger, Ralph ErnstorferAbstract:This work provides a consistent description of the Microscopic Energy flow during the ultrafast demagnetization of nickel by combining experimental results for the lattice heating with atomistic spin dynamics simulations.
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electron phonon coupling and Energy flow in a simple metal beyond the two temperature approximation
Physical Review X, 2016Co-Authors: Lutz Waldecker, Ralph Ernstorfer, Roman Bertoni, Jan VorbergerAbstract:The electron-phonon coupling and the corresponding Energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitored by femtosecond electron diffraction. The electron-phonon coupling strength is obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a twotemperature model (TTM) deviates significantly from the ab initio values. We introduce a nonthermal lattice model (NLM) for describing nonthermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principles calculations except the phonon-phonon coupling strength, the prediction of the Energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the Microscopic Energy flow even for simple metals like aluminium and that the determination of the electronphonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.