140 research outputs found
Gauge invariance, massless modes and topology of gauge fields in multi-band superconductors
Multi-phase physics is a new physics of multi-gap superconductors. Multi-band
superconductors exhibit many interesting and novel properties. We investigate
the dynamics of the phase-difference mode and show that this mode yields a new
excitation mode. The phase-difference mode is represented as an abelian vector
field. There are massless modes when the number of gaps is greater than three
and the Josephson term is frustrated. The fluctuation of phase-difference modes
with non-trivial topology leads to the existence of a fractional-quantum flux
vortex in a magnetic field. A superconductor with a fractional-quantum flux
vortex is regarded as a topological superconductor with the integer Chern
number.Comment: Proceedings of the 12th Asia and Pacific Physics Conference (2013
Field resilient superconductivity in atomic layer crystalline materials
The recent study [S. Yoshizawa et al., Nature Communications 12, 1 (2021)]
reported the field resilient superconductivity, that is, the enhancement of an
in-plane critical magnetic field exceeding the paramagnetic
limiting field in an atomic layer crystalline ()-In on
a Si(111) substrate. The present article elucidates the origin of the observed
field resilient noncentrosymmetric superconductivity in the highly crystalline
two dimensional material. We developed the quasiclassical theory by
incorporating the Fermi surface anisotropy together with an anisotropic spin
splitting specific to atomic layer crystalline systems. The enhancement of the
rescaled by the critical temperature at zero field occurs not
only due to the disorder effect but also to an anisotropic non-ideal Rashba
spin texture depending on the field direction. We also study the parity mixing
effect to show the enhancement of is limited in the
moderately clean regime because of the fragile -wave pairing against
nonmagnetic scattering in the case of the dominant odd parity component of a
pair wavefunction. Furthermore, from the analysis of the transition line, we
identify the field resilience factor taking account of the scattering and
suppression of paramagnetic effects and discuss the origin of the field
resilient superconductivity. Through the fitting of the data,
the normal state electron scattering is discussed, mainly focusing on the role
of atomic steps on a Si(111) surface.Comment: 13 pages, 6 figures, 1 tabl
Reply to "Comment on 'Isotope effect in multi-band and multi-channel attractive systems and inverse isotope effect in iron-based superconductors'"
The Comment insists on the following: in our model it is assumed that the
effective interactions have specific energy ranges within the single band with
a cutoff at \omega_1 for the phononic part and a range from \omega_1 to
\omega_2 in the AF channel. Our reply is that we assume that V_i(k,k')\neq 0 if
|\xi_k|<\omega_i and |\xi_{k'}|<\omega_i, and otherwise V_i(k,k')= 0 (i=1,2),
as stated in our paper. This is the model of BCS type with two attractive
interactions, and this assumption is the characteristic of the BCS
approximation. The claim "the integration limits have been modified such that
the AF channel mediated pairing sets in where the ph-channel pairing terminates
and is limited at an energy given by \omega_j=\omega_{AF}" in the Comment is
wrong. We describe the model and the method to solve the gap equation in more
detail
Madelung Energy of the Valence Skipping Compound BaBiO
Several elements show valence skip fluctuation, for instance, Tl forms the
compounds in valence states +1 and +3, and Bi forms in +3 and +5 states. This
kind of fluctuation gives rise to a negative effective attractive interaction
and the Kondo effect. In the compounds of valence skipping elements, the
carrier doping will induce superconductivity with high critical temperature.
For example, BaKBiO shows high which is unlikely from the
conventional electron-phonon mechanism. The reason for the missing of some
valence states in such valence skip compounds remains a mystery. We have
performed the evaluation of the Madelung potential for BaBiO, and have
shown for the first time that charge-ordered state is stabilized if we take
into account the polarization of the oxygen charge. We argue that the effective
Coulomb interaction energy may be negative evaluating the local excitation
energy
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