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Difficulty in the Fermi-Liquid-Based Theory for the In-Plane Magnetic Anisotropy in Untwinned High-T_c Superconductor
Recently, Eremin and Manske [1] presented a oneband Fermi-liquid theory for
the in-plane magnetic anisotropy in untwinned high-Tc superconductor
YBa2Cu3O6:85 (YBCO). They claimed that they found good agreement with inelastic
neutron scattering (INS) spectra. In this Comment, we point out that their
conclusion on this important problem may be questionable due to an error in
logic about the orthorhombicity delta_0 characterizing the lattice structure of
YBCO. In Ref. [1], a single band at delta_0>0 is proved to be in accordance
with the angle resolved photoemission spectroscopy (ARPES) on untwinned YBCO.
But in their Erratum in PRL[3], they admit that delta_0= -0.03 was used to fit
the INS data. Hence publications [1,3] contain errors that we believe
invalidate their approach.Comment: This is a Comment on the paper of I. Eremin, and D. Manske, Phys.
Rev. Lett. 94, 067006(2005
Analysis on the Invariant Properties of Constitutive Equations of Hydrodynamics in the Transformation between Different Reference Systems
The velocities of the same fluid particle observed in two different reference
systems are two different quantities and they are not equal when the two
reference systems have translational and rotational movements relative to each
other. Thus, the velocity is variant. But, we prove that the divergences of the
two different velocities are always equal, which implies that the divergence of
velocity is invariant. Additionally, the strain rate tensor and the gradient of
temperature are invariant but, the vorticity and gradient of velocity are
variant. Only the invariant quantities are employed to construct the
constitutive equations used to calculate the stress tensor and heat flux
density, which are objective quantities and thus independent of the reference
system. Consequently, the forms of constitutive equations keep unchanged when
the corresponding governing equations are transformed between different
reference systems. Additionally, we prove that the stress is a second-order
tensor since its components in different reference systems satisfy the
transformation relationship.Comment: Analyses with rigorous mathematical proofs on several classical
subjects of hydrodynamic
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