Quasiparticle interference in heavy Fermion superconductor CeCoIn_5

We investigate the quasiparticle interference in the heavy Fermion superconductor CeCoIn_5 as direct method to confirm the d-wave gap symmetry. The ambiguity between d_{xy} and d_{x^2-y^2} symmetry remaining from earlier specific heat and thermal transport investigations has been resolved in favor of the latter by the observation of a spin resonance that can occur only in d_{x^2-y^2} symmetry. However these methods are all indirect and depend considerably on theoretical interpretation. Here we propose that quasiparticle interference (QPI) spectroscopy by scanning tunneling microscopy (STM) can give a direct fingerprint of the superconducting gap in real space which may lead to a definite conclusion on its symmetry for CeCoIn_5 and related 115 compounds. The QPI pattern for both magnetic and nonmagnetic impurities is calculated for the possible d-wave symmetries and characteristic differences are found that may be identified by STM method.Comment: 7 pages, 4 figure

Polar Kerr effect from a time-reversal symmetry breaking unidirectional charge density wave

We analyze the Hall conductivity $\sigma_{xy}(\omega)$ of a charge ordered state with momentum $\mathbf{Q}=(0,2Q)$ and calculate the intrinsic contribution to the Kerr angle $\Theta_K$ using the fully reconstructed tight-binding band structure for layered cuprates beyond the low energy hot spots model and particle hole symmetry. We show that such a unidirectional charge density wave (CDW), which breaks time reversal symmetry as recently put forward by Wang and Chubukov [Phys. Rev. B {\bf 90}, 035149 (2014)], leads to a nonzero polar Kerr effect as observed experimentally. In addition, we model a fluctuating CDW via a large quasiparticle damping of the order of the CDW gap and discuss possible implications for the pseudogap phase. We can qualitatively reproduce previous measurements of underdoped cuprates but making quantitative connections to experiments is hampered by the sensitivity of the polar Kerr effect with respect to the complex refractive index $n(\omega)$.Comment: 6 pages, 4 figure

Evolution of the multiband RKKY interaction: Application to iron pnictides and chalcogenides

The indirect RKKY interaction in iron pnictide and chalcogenide metals is calculated for a simplified four bands Fermi surface (FS) model. We investigate the specific multi-band features and show that distinct length scales of the RKKY oscillations appear. For the regular lattice of the local moments, the generalized RKKY interaction is defined in momentum space. We consider its momentum dependence in paramagnetic and spin density wave (SDW) phases, discuss its implications for the possible type of magnetic order and compare it to the results obtained from more realistic tight-binding type Fermi surface model. Our finding can give important clues on the magnetic ordering of the 4f- iron based superconductors.Comment: 18 pages, 8 figure

Surface state tunneling signatures in two-component superconductor UPt3_3

Quasiparticle interference (QPI) imaging of Bogoliubov excitations in quasi-two dimensional unconventional superconductors has become a powerful technique for measuring the superconducting gap and its symmetry. Here, we present the extension of this method to three-dimensional superconductors and analyze the expected QPI spectrum for the two-component heavy fermion superconductor UPt$_3$ whose gap structure is still controversial. Starting from a 3D electronic structure and the three proposed chiral gap models $E_{1g,u}$ or $E_{2u}$, we perform a slab calculation that determines the 2D continuum Bogoliubov- de Gennes (BdG) surface quasiparticle bands and in addition the in-gap flat-band Andreev bound states that lead to surface Weyl arcs connecting the projected gap nodes. Both features are very distinct for the three models, in particular the most prominent $E_{2u}$ candidate is singled out by the existence of {\it two} Weyl arcs due to the double monopole node points. The signature of these distinct surface bound and continuum states that is left in QPI is derived and discussed. We show that it provides a fingerprint that may finally determine the true nodal structure of UPt$_3$ superconductor.Comment: 6 pages, 4 figure