The Experts below are selected from a list of 43377 Experts worldwide ranked by ideXlab platform
Leon Balents - One of the best experts on this subject based on the ideXlab platform.
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electronic instabilities of kagome metals saddle points and Landau Theory
Physical Review B, 2021Co-Authors: Takamori Park, Leon BalentsAbstract:The newly discovered family of kagome metals $A$V${}_{3}$Sb${}_{5}$ ($A$=K,Cs,Rb) has recently gained wide attention. Here, the authors study these materials using a general continuum model and utilize renormalization group and mean field Theory methods to identify mechanisms that can lead to the experimentally observed charge density wave ordering. The authors find that the charge density wave is the primary density wave instability in certain cases but could also be induced by a leading orbital current or spin density wave order.
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Landau Theory of charge and spin ordering in the nickelates
Physical Review Letters, 2011Co-Authors: Sungbin Lee, Ru Chen, Leon BalentsAbstract:Guided by experiment and band structure, we introduce and study a phenomenological Landau Theory for the unusual charge and spin ordering associated with the Mott transition in the perovskite nickelates, with chemical formula $R{\mathrm{NiO}}_{3}$, where $R=\mathrm{Pr}$, Nd,Sm, Eu, Ho, Y, and Lu. While the Landau Theory has general applicability, we show that for the most conducting materials, $R=\mathrm{Pr}$, Nd, both types of order can be understood in terms of a nearly nested spin-density wave. Furthermore, we argue that in this regime, the charge ordering is reliant upon the orthorhombic symmetry of the sample, and therefore proportional to the magnitude of the orthorhombic distortion. The first order nature of the phase transitions is also explained. We briefly show by example how the Theory is readily adapted to modified geometries such as nickelate films.
H Toki - One of the best experts on this subject based on the ideXlab platform.
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color confinement quark pair creation and dynamical chiral symmetry breaking in the dual ginzburg Landau Theory
Nuclear Physics, 1995Co-Authors: Hideo Suganuma, Shoichi Sasaki, H TokiAbstract:Abstract We study the color confinement, the q q pair creation and the dynamical chiral-symmetry breaking of nonperturbative QCD by using the dual Ginzburg-Landau Theory, where the dual Higgs mechanism plays an essential role in the nonperturbative dynamics in the infrared region. As a result of the dual Meissner effect, the linear static quark potential, which characterizes the quark confinement, is obtained in the long distance within the quenched approximation. We obtain a simple expression for the string tension similar to the energy per unit length of a vortex in the superconductivity physics. The dynamical effect of light quarks on the quark confining potential is investigated in terms of the infrared screening effect due to the pair creation or the cut of the hadronic string. The screening length of the potential is estimated by using the Schwinger formula for the q q pair creation. We introduce the corresponding infrared cutoff to the strong long-range correlation factor in the gluon propagator as a dynamical effect of light quarks, and obtain a compact formula for the quark potential including the screening effect in the infrared region. We investigate the dynamical chiral-symmetry breaking by using the Schwinger-Dyson equation in the dual Ginzburg-Landau Theory, where the gluon propagator includes the nonperturbative effect related to the color confinement. We find a large enhancement of the chiral-symmetry breaking by the dual Higgs mechanism, which supports the close relation between the color confinement and the chiral-symmetry breaking. The dynamical quark mass, the pion decay constant and the quark condensate are well reproduced by using the consistent values of the gauge coupling constant and the QCD scale parameter with the perturbative QCD and the quark confining potential. The light-quark confinement is also roughly examined in terms of the disappearance of physical poles in the light-quark propagator by using the smooth extrapolation of the quark mass function to the time-like momentum region.
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color confinement quark pair creation and dynamical chiral symmetry breaking in the dual ginzburg Landau Theory
arXiv: High Energy Physics - Phenomenology, 1993Co-Authors: Hideo Suganuma, Shoichi Sasaki, H TokiAbstract:We study the color confinement, the $q$-$\bar q$ pair creation and the dynamical chiral-symmetry breaking of nonperturbative QCD by using the dual Ginzburg-Landau Theory, where QCD-monopole condensation plays an essential role on the nonperturbative dynamics in the infrared region. As a result of the dual Meissner effect, the linear static quark potential, which characterizes the quark confinement, is obtained in the long distance within the quenched approximation. We obtain a simple expression for the string tension similar to the energy per unit length of a vortex in the superconductivity physics. The dynamical effect of light quarks on the quark confining potential is investigated in terms of the infrared screening effect due to the $q$-$\bar q$ pair creation or the cut of the hadronic string. The screening length of the potential is estimated by using the Schwinger formula for the $q$-$\bar q$ pair creation. We introduce the corresponding infrared cutoff to the strong long-range correlation factor in the gluon propagator as a dynamical effect of light quarks, and obtain a compact formula of the quark potential including the screening effect in the infrared region. We investigate the dynamical chiral-symmetry breaking by using the Schwinger-Dyson equation, where the gluon propagator includes the nonperturbative effect related to
Mark K Transtrum - One of the best experts on this subject based on the ideXlab platform.
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vortex nucleation in superconductors within time dependent ginzburg Landau Theory in two and three dimensions role of surface defects and material inhomogeneities
Physical Review B, 2020Co-Authors: Alden Pack, Jared Carlson, Spencer Wadsworth, Mark K TranstrumAbstract:We use time-dependent Ginzburg-Landau Theory to study the nucleation of vortices in type-II superconductors in the presence of both geometric and material inhomogeneities. The superconducting Meissner state is metastable up to a critical magnetic field, known as the superheating field. For a uniform surface and homogeneous material, the superheating transition is driven by a nonlocal critical mode in which an array of vortices simultaneously penetrate the surface. In contrast, we show that even a small amount of disorder localizes the critical mode and can have a significant reduction in the effective superheating field for a particular sample. Vortices can be nucleated by either surface roughness or local variations in material parameters, such as ${T}_{c}$. Our approach uses a finite-element method to simulate a cylindrical geometry in two dimensions and a film geometry in two and three dimensions. We combine saddle-node bifurcation analysis along with a fitting procedure to evaluate the superheating field and identify the unstable mode. We demonstrate agreement with previous results for homogeneous geometries and surface roughness and extend the analysis to include variations in material properties. Finally, we show that in three dimensions, surface divots not aligned with the applied field can increase the superheating field. We discuss implications for fabrication and performance of superconducting resonant frequency cavities in particle accelerators.
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ginzburg Landau Theory of the superheating field anisotropy of layered superconductors
Physical Review B, 2016Co-Authors: Danilo B Liarte, Mark K Transtrum, James P SethnaAbstract:We investigate the effects of material anisotropy on the superheating field of layered superconductors. We provide an intuitive argument both for the existence of a superheating field, and its dependence on anisotropy, for $\ensuremath{\kappa}=\ensuremath{\lambda}/\ensuremath{\xi}$ (the ratio of magnetic to superconducting healing lengths) both large and small. On the one hand, the combination of our estimates with published results using a two-gap model for ${\mathrm{MgB}}_{2}$ suggests high anisotropy of the superheating field near zero temperature. On the other hand, within Ginzburg-Landau Theory for a single gap, we see that the superheating field shows significant anisotropy only when the crystal anisotropy is large and the Ginzburg-Landau parameter $\ensuremath{\kappa}$ is small. We then conclude that only small anisotropies in the superheating field are expected for typical unconventional superconductors near the critical temperature. Using a generalized form of Ginzburg Landau Theory, we do a quantitative calculation for the anisotropic superheating field by mapping the problem to the isotropic case, and present a phase diagram in terms of anisotropy and $\ensuremath{\kappa}$, showing type I, type II, or mixed behavior (within Ginzburg-Landau Theory), and regions where each asymptotic solution is expected. We estimate anisotropies for a number of different materials, and discuss the importance of these results for radio-frequency cavities for particle accelerators.
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superheating field of superconductors within ginzburg Landau Theory
Physical Review B, 2011Co-Authors: Mark K Transtrum, Gianluigi Catelani, James P SethnaAbstract:We study the superheating field of a bulk superconductor within Ginzburg-Landau Theory, which is valid near the critical temperature. We calculate, as functions of the Ginzburg-Landau parameter $\ensuremath{\kappa}$, the superheating field ${H}_{\mathrm{sh}}$ and the critical momentum ${k}_{c}$ characterizing the wavelength of the instability of the Meissner state to flux penetration. By mapping the two-dimensional linear stability Theory into a one-dimensional eigenfunction problem for an ordinary differential equation, we solve the problem numerically. We demonstrate agreement between the numerics and analytics, and show convergence to the known results at both small and large $\ensuremath{\kappa}$. We discuss the implications of the results for superconducting rf cavities used in particle accelerators.
James P Sethna - One of the best experts on this subject based on the ideXlab platform.
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ginzburg Landau Theory of the superheating field anisotropy of layered superconductors
Physical Review B, 2016Co-Authors: Danilo B Liarte, Mark K Transtrum, James P SethnaAbstract:We investigate the effects of material anisotropy on the superheating field of layered superconductors. We provide an intuitive argument both for the existence of a superheating field, and its dependence on anisotropy, for $\ensuremath{\kappa}=\ensuremath{\lambda}/\ensuremath{\xi}$ (the ratio of magnetic to superconducting healing lengths) both large and small. On the one hand, the combination of our estimates with published results using a two-gap model for ${\mathrm{MgB}}_{2}$ suggests high anisotropy of the superheating field near zero temperature. On the other hand, within Ginzburg-Landau Theory for a single gap, we see that the superheating field shows significant anisotropy only when the crystal anisotropy is large and the Ginzburg-Landau parameter $\ensuremath{\kappa}$ is small. We then conclude that only small anisotropies in the superheating field are expected for typical unconventional superconductors near the critical temperature. Using a generalized form of Ginzburg Landau Theory, we do a quantitative calculation for the anisotropic superheating field by mapping the problem to the isotropic case, and present a phase diagram in terms of anisotropy and $\ensuremath{\kappa}$, showing type I, type II, or mixed behavior (within Ginzburg-Landau Theory), and regions where each asymptotic solution is expected. We estimate anisotropies for a number of different materials, and discuss the importance of these results for radio-frequency cavities for particle accelerators.
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superheating field of superconductors within ginzburg Landau Theory
Physical Review B, 2011Co-Authors: Mark K Transtrum, Gianluigi Catelani, James P SethnaAbstract:We study the superheating field of a bulk superconductor within Ginzburg-Landau Theory, which is valid near the critical temperature. We calculate, as functions of the Ginzburg-Landau parameter $\ensuremath{\kappa}$, the superheating field ${H}_{\mathrm{sh}}$ and the critical momentum ${k}_{c}$ characterizing the wavelength of the instability of the Meissner state to flux penetration. By mapping the two-dimensional linear stability Theory into a one-dimensional eigenfunction problem for an ordinary differential equation, we solve the problem numerically. We demonstrate agreement between the numerics and analytics, and show convergence to the known results at both small and large $\ensuremath{\kappa}$. We discuss the implications of the results for superconducting rf cavities used in particle accelerators.
L Bessais - One of the best experts on this subject based on the ideXlab platform.
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magnetocaloric properties and Landau Theory of dy 0 5 sr 1 x ca x 0 5 mno 3 0 x 0 3 manganites at cryogenic temperatures
Chemical Physics Letters, 2017Co-Authors: R Hamdi, A Tozri, E Dhahri, L BessaisAbstract:Abstract Magnetic entropy change of Dy 0.5 (Sr 1−x Ca x ) 0.5 MnO 3 nanoparticles (0 ≤ x ≤ 0.3) was analyzed at low temperatures to investigate the magnetic refrigeration as a promising tool for hydrogen liquefaction. These samples depict interesting values of maximum magnetic entropy change and large relative cooling power, especially for x = 0.3 sample (about 169 J/Kg). It could be a promising candidate for magnetic refrigeration at cryogenic temperatures. Landau Theory presents a discord between the experimental magnetic entropy change and the theoretical one. This disagreement is tending to be in accordance as Ca substitution is increasing and also with augmenting the applied magnetic field.
