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Register a new userAnalysis of Magnetic Field-Angle Dependent Electronic Raman Scattering to Probe the Superconducting Gap
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We study the field-angle resolved electronic Raman scattering in 2-dimensional d-wave superconducting vortex states theoretically by quasi-classical approximation, the so-called Doppler-shift method. An analytic expression is obtained for the field angle dependence of the Raman scattering amplitude at zero temperature. After numerical integration, we obtain the scattering intensity for various field angles by changing the Raman shift energy. Field-angle resolved electronic Raman scattering turns out to be an effective method for probing unconventional superconducting gap structures. It shows a novel phenomenon: reversal of extrema as a function of frequency without changing temperature or field magnitude.
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We report Raman scattering spectra for single crystals of overdoped Tl2Ba2CuO6+d (Tl-2201) at low temperatures. It was observed that the pair-breaking peaks in A1g and B1g spectra radically shift to lower energy with carrier doping. We interpret it as s-wave component mixing into d-wave, although the crystal structure is tetragonal. Since similar phenomena were observed also in YBa2Cu3Oy and Bi2Sr2CaCu2Oz, we conclude that s-wave mixing is a common property for overdoped high-Tc superconductors.
Inelastic neutron scattering provides a probe for studying the spin and momentum structure of the superconducting gap. Here, using a two-orbital model for the Fe-pnicitide superconductors and an RPA-BCS approximation for the dynamic spin susceptibility, we explore the scattering response for various gaps that have been proposed.
Electronic Raman scattering with in and out of (ab) plane polarizations have been performed on HgBa2Ca2Cu3O8+d in a slightly underdoped single crystal with a critical temperature Tc=122 K. We find that the d-wave pairing gap at the antinodes is higher in energy (14 kBTc) than in other cuprates and that it varies very slowly up to Tc. This hints at a strong coupling nature of the pairing mechanism. Interestingly, we reveal that the pairing-gap feature in the Raman response displays a complex peak-dip-hump structure, in a fashion reminiscent of what observed by angle resolved photo-emission spectroscopy in Bi2Sr2CaCu2O8+d (Bi-2212). We detect two other distinct superconducting peaks at 5kBTc and 7kBTc when probing respectively around the nodes and on the whole Fermi surface. Finally we establish that the pairing gap at the antinodes is detected both for (ab) plane and for c-axis light polarizations. This shows that the quasiparticle dynamics along the c-axis is intimately connected to the antinodal one in the (ab) plane.
Pure electronic Raman spectra with no phonon structures superimposed to the electronic continuum, are reported, in optimally doped HgBa_{2}CaCu_{2}O_{6+delta } single crystals (T_{c }=126 K). As a consequence, the spectra in the A_{1g }, B_{1g } and B_{2g } symmetries, including the crucial low energy frequency dependence of the electronic scattering, are directly and reliably measured. The B_{2g } and, most strikingly, the B_{1g } spectra exhibit a strong intrinsic linear term, which suggests that the nodes are shifted from the [110] and [1bar{1}0] directions, a result inconsistent with a pure d_{x^{2}-y^{2}} model.
For YBa_2Cu_3O_{6+delta} and Bi_2Sr_2CaCu_2O_8 superconductors, electronic Raman scattering from high- and low-energy excitations has been studied in relation to the hole doping level, temperature, and energy of the incident photons. For underdoped superconductors, it is concluded that short range antiferromagnetic (AF) correlations persist with hole doping and doped single holes are incoherent in the AF environment. Above the superconducting (SC) transition temperature T_c the system exhibits a sharp Raman resonance of B_1g symmetry and about 75 meV energy and a pseudogap for electron-hole excitations below 75 meV, a manifestation of a partially coherent state forming from doped incoherent quasi-particles. The occupancy of the coherent state increases with cooling until phase ordering at T_c produces a global SC state.
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