اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSuperconducting states of the quasi-2D Holstein model: Effects of vertex and non-local corrections
104
0
0.0
(
0
)
تأليف
J.P.Hague
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
I investigate superconducting states in a quasi-2D Holstein model using the dynamical cluster approximation (DCA). The effects of spatial fluctuations (non-local corrections) are examined and approximations neglecting and incorporating lowest-order vertex corrections are computed. The approximation is expected to be valid for electron-phonon couplings of less than the bandwidth. The phase diagram and superconducting order parameter are calculated. Effects which can only be attributed to theories beyond Migdal--Eliashberg theory are present. In particular, the order parameter shows momentum dependence on the Fermi-surface with a modulated form and s-wave order is suppressed at half-filling. The results are discussed in relation to Hohenbergs theorem and the BCS approximation.
قيم البحث
اقرأ أيضاً
The pairing glue of high-$T_{rm c}$ superconductivity in heavily electron-doped (e-doped) FeSe, in which hole-pockets are absent, has been an important unsolved problem. Here, we focus on a heavily e-doped bulk superconductor Li$_{1-x}$Fe$_x$OHFeSe (
$T_{rm c} sim 40$K). We construct a multiorbital model beyond the rigid band approximation and analyze the spin and orbital fluctuations by taking both vertex corrections (VCs) and self-energy into consideration. Without e-doping ($x=0$), the ferro-orbital order without magnetism in FeSe is reproduced by the VCs.The orbital order quickly disappears when the hole-pocket vanishes at $x sim 0.03$. With increasing $x$ further, the spin fluctuations remain small, whereas orbital fluctuations gradually increase with $x$ due to the VCs. The negative feedback due to the self-energy is crucial to explain experimental phase diagram. Thanks to both vertex and self-energy corrections, the orbital-fluctuation-mediated $s_{++}$-wave state appears for a wide doping range, consistent with experiments.
We theoretically study the local density of states in superconducting proximity structure where two superconducting terminals are attached to a side surface of a normal-metal wire. Using the quasiclassical Greens function method, the energy spectrum
is obtained for both of spin-singlet $s$-wave and spin-triplet $p$-wave junctions. In both of the cases, the decay length of the proximity effect at the zero temperature is limited by a depairing effect due to inelastic scatterings. In addition to the depairing effect, in $p$-wave junctions, the decay length depends sensitively on the transparency at the junction interfaces, which is a unique property to odd-parity superconductors where the anomalous proximity effect occurs.
The thermal conductivity of the heavy-fermion superconductor CeCoIn_5 has been studied in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of the thermal conductivity which is characteristic of a superconducting gap with node
s along the (+-pi,+-pi)-directions is resolved. The thermal conductivity measurement also reveals a first order transition at H_c2, indicating a Pauli limited superconducting state. These results indicate that the symmetry most likely belongs to d_{x^2-y^2}, implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.
Oxygen NMR is used to probe the local influence of nonmagnetic Zn and magnetic Ni impurities in the superconducting state of optimally doped high Tc YBa2Cu3O7. Zn and Ni induce a staggered paramagnetic polarization, similar to that evidenced above Tc
, with a typical extension xi=3 cell units for Zn and xi>=3 for Ni. In addition, Zn is observed to induce a local density of states near the Fermi Energy in its neighbourhood, which also decays over about 3 cell units. Its magnitude decreases sharply with increasing temperature. This allows direct comparison with the STM observations done in BiSCO.
In the framework of a multiorbital Hubbard model description of superconductivity, a matrix formulation of the superconducting pairing interaction that has been widely used is designed to treat spin, charge and orbital fluctuations within a random ph
ase approximation (RPA). In terms of Feynman diagrams, this takes into account particle-hole ladder and bubble contributions as expected. It turns out, however, that this matrix formulation also generates additional terms which have the diagrammatic structure of vertex corrections. Here we examine these terms and discuss the relationship between the matrix-RPA superconducting pairing interaction and the Feynman diagrams that it sums.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
