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Register a new userComment on ``Anisotropic s-wave superconductivity: comparison with experiments on MgB_2 [A. I. Posazhennikova, T. Dahm and K. Maki, cond-mat/0204272; submitted to Europhys. Lett.]
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An analytical result for the renormalization of the jump of the heat capacity Delta C/C_N by the anisotropy of the order parameter is derived within the framework of the very recent model proposed by Posazhennikova, Dahm and Maki [cond-mat/0204272, submitted to Europhys. Lett.], for both oblate and prolate anisotropy. The graph of Delta C/C_N versus the ratio of the gaps on the equator and the pole of the Fermi surface, Delta_e/Delta_p, allows a direct determination of the gap anisotropy parameter Delta_e/Delta_p by fitting data from specific heat measurements Delta C/C_N. Using the experimental value Delta C/C_N=0.82 +/- 10% by Wang, Plackowski, and Junod [Physica C 355 (2001) 179] we find Delta_e/Delta_p = 4.0.
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A recent e-print (cond-mat/0604532) presented a proposed Comment to Applied Physics Letters on our publication Appl. Phys. Lett. 88, 162503 (2006), cond-mat/0603260. Here is our Response. As the proposed Comment has now been rejected by Applied Physics Letters, neither the Comment nor the Response will be published in Applied Physics Letters in this form.
The lower critical field $H_{c1}$ has been carefully measured on a well shaped cylindrical sample of the new superconductor $MgB_2$ fabricated by high pressure synthesis. The penetration depth $lambda$ is calculated from the $H_{c1}$ data. It is found that a linear relation of $H_{c1}(T)$ appears in whole temperature region below $T_c$. Furthermore a finite slope of $dH_{c1}/dT$ and $dlambda(T)/dT$ remains down to the lowest temperature (2 K). These are inconsistent with the expectation for a widely thought s-wave superconductivity in $MgB_2$.
In cond-mat/0107371, Mendonca proposes that diffusion can change the universality class of a parity-conserving reaction-diffusion process. In this comment we suggest that this cannot happen, due to symmetry arguments. We also present numerical results from lattice simulations which support these arguments, and mention a previous result supporting this conclusion.
In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors, in which superconductivity may coexist with magnetism, and only a few examples are known, when superconductivity itself induces spontaneous magnetism. The most known compounds are Sr$_2$RuO$_4$ and some noncentrosymmetric superconductors. Here, we report the finding of a narrow dome of a novel $s+is$ superconducting (SC) phase with broken time-reversal symmetry (BTRS) inside the broad $s$-wave SC region of the centrosymmetric multiband superconductor Ba$_{rm 1-x}$K$_{rm x}$Fe$_2$As$_2$ ($0.7 lesssim x lesssim 0.85$). We observe spontaneous magnetic fields inside this dome using the muon spin relaxation ($mu$SR) technique. Furthermore, our detailed specific heat study reveals that the BTRS dome appears very close to a change in the topology of the Fermi surface (Lifshitz transition). With this, we experimentally demonstrate the emergence of a novel quantum state due to topological changes of the electronic system.
We show that the {it gapped} triplet superconductivity, i.e., a triplet superconductor with triplet order parameter, can be realized in strong spin-orbit-coupled quantum wells in proximity to $s$-wave superconductor. It is revealed that with the singlet order parameter induced from the superconducting proximity effect, in quantum wells, not only can the triplet pairings arise due to the spin-orbit coupling, but also the triplet order parameter can be induced due to the repulsive effective electron-electron interaction, including the electron-electron Coulomb and electron-phonon interactions. This is a natural extension of the work of de Gennes, in which the repulsive-interaction-induced singlet order parameter arises in the normal metal in proximity to $s$-wave superconductor [Rev. Mod. Phys. {bf 36}, 225 (1964)]. Specifically, we derive the effective Bogoliubov-de Gennes equation, in which the self-energies due to the effective electron-electron interactions contribute to the singlet and triplet order parameters. It is further shown that for the singlet order parameter, it is efficiently suppressed due to this self-energy renormalization; whereas for the triplet order parameter, it is the $p$-wave ($p_xpm ip_y$) one with the ${bf d}$-vector parallel to the effective magnetic field due to the spin-orbit coupling. Finally, we perform the numerical calculation in InSb (100) quantum wells. Specifically, we reveal that the Coulomb interaction is much more important than the electron-phonon interaction at low temperature. Moreover, it shows that with proper electron density, the minimum of the renormalized singlet and the maximum of the induced triplet order parameters are comparable, and hence can be experimentally distinguished.
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