We show that effective superconducting orders generally emerge at low energy in the superconducting state of graphene with conventionally defined pairing symmetry . We study such a particular interesting example, the d x 2 −y 2 + id ′ xy spin singlet pairing superconducting state in graphene, which can be generated by electronic correlation as well as induced through a proximity effect with a d-wave superconductor. We find that effectively the d-wave state is a state with mixed s-wave and exotic p + ip-wave pairing orders at low energy. This remarkable property leads to distinctive superconducting gap functions and novel behavior of the Andreev conductance spectra.

A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechanism for superconductivity. For iron pnictide superconductors, the s ± -pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies (E 2 ) below T c . On the other hand, the s ++ -pairing symmetry expects a broad spin excitation enhancement at an energy above 2 below T c . Although the resonance has been observed in iron pnictide superconductors at an energy below 2 consistent with the s ± -pairing symmetry, the mode has also been interpreted as arising from the s ++ -pairing symmetry with E 2 due to its broad energy width and the large uncertainty in determining the SC gaps. Here we use inelastic neutron scattering to reveal a sharp resonance at E = 7 meV in SC NaFe 0.935 Co 0.045 As (T c = 18 K). On warming towards T c , the mode energy hardly softens while its energy width increases rapidly. By comparing with calculated spin-excitation spectra within the s ± and s ++ -pairing symmetries, we conclude that the ground-state resonance in NaFe 0.935 Co 0.045 As is only consistent with the s ± pairing, and is inconsistent with the s ++ -pairing symmetry.

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Magnetization measurements and time-of-flight neutron powder-diffraction studies on the hightemperature (300-980 K) magnetism and crystal structure (321-1200 K) of a pulverized YCrO3 single crystal have been performed. Temperature-dependent inverse magnetic susceptibility coincides with a piecewise linear function with five regimes, with which we fit a Curie-Weiss law and calculate the frustration factor f . The fit results indicate a formation of magnetic polarons between 300 and 540 K and a very strong magnetic frustration. By including one factor η that represents the degree of spin interactions into the Brillouin function, we can fit well the applied-magnetic-field dependence of magnetization. No structural phase transition was observed from 321 to 1200 K. The average thermal expansions of lattice configurations (a, b, c, and V ) obey well the Grüneisen approximations with an anomaly appearing around 900 K, implying an isosymmetric structural phase transition, and display an anisotropic character along the crystallographic a, b, and c axes with the incompressibility K a 0 > K c 0 > K b 0 . It is interesting to find that at 321 K, the local distortion size ∆(O2) ≈ 1.96∆(O1) ≈ 4.32∆(Y) ≈ 293.89∆(Cr). Based on the refined Y-O and Cr-O bond lengths, we deduce the local distortion environments and modes of Y, Cr, O1, and O2 ions. Especially, the Y and O2 ions display obvious atomic displacement and charge subduction, which may shed light on the dielectric property of the YCrO3 compound. Additionally, by comparing Kramers Mn 3+ with non-Kramers Cr 3+ ions, it is noted that being a Kramers or non-Kramers ion can strongly affect the local distortion size, whereas, it may not be able to change the detailed distortion mode. arXiv:2001.09573v1 [cond-mat.str-el]

We apply the recently formulated torque equilibrium spin wave theory (TESWT) to compute the 1/S -order interacting K -edge bimagnon resonant inelastic x-ray scattering (RIXS) spectra of an anisotropic triangular lattice antiferromagnet with Dzyaloshinskii-Moriya (DM) interaction. We extend the interacting torque equilibrium formalism, incorporating the effects of DM interaction, to appropriately account for the zero-point quantum fluctuation that manifests as the emergence of spin Casimir effect in a noncollinear spin spiral state. Using inelastic neutron scattering data from Cs 2 CuCl 4 we fit the 1/S corrected TESWT dispersion to extract exchange and DM interaction parameters. We use these new fit coefficients alongside other relevant model parameters to investigate, compare, and contrast the effects of spatial anisotropy and DM interaction on the RIXS spectra at various points across the magnetic Brillouin zone. We highlight the key features of the bi-and trimagnon RIXS spectrum at the two inequivalent rotonlike points, M(0, 2π/ √3) and M (π, π/ √ 3), whose behavior is quite different from an isotropic triangular lattice system. While the roton RIXS spectrum at the M point undergoes a spectral downshift with increasing anisotropy, the peak at the M location loses its spectral strength without any shift. With the inclusion of DM interaction the spiral phase is more stable and the peak at both M and M point exhibits a spectral upshift. Our calculation offers a practical example of how to calculate interacting RIXS spectra in a non-collinear quantum magnet using TESWT. Our findings provide an opportunity to experimentally test the predictions of interacting TESWT formalism using RIXS, a spectroscopic method currently in vogue. PACS number(s): 78.70. Ck, 75.10.Jm