46 research outputs found

    Spin-Orbital Entanglement and the Breakdown of Singlets and Triplets in Sr2RuO4 Revealed by Spin- and Angle-Resolved Photoemission Spectroscopy

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    Spin-orbit coupling has been conjectured to play a key role in the low-energy electronic structure of Sr2RuO4. By using circularly polarized light combined with spin-and angle-resolved photoemission spectroscopy, we directly measure the value of the effective spin-orbit coupling to be 130 +/- 30 meV. This is even larger than theoretically predicted and comparable to the energy splitting of the d(xy) and d(xz,yz) orbitals around the Fermi surface, resulting in a strongly momentum-dependent entanglement of spin and orbital character in the electronic wavefunction. As demonstrated by the spin expectation value calculated for a pair of electrons with zero total momentum, the classification of the Cooper pairs in terms of pure singlets or triplets fundamentally breaks down, necessitating a description of the unconventional superconducting state of Sr2RuO4 in terms of these newly found spin-orbital entangled eigenstates

    Broken time-reversal symmetry probed by muon spin relaxation in the caged type superconductor Lu5Rh6Sn18

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    The superconducting state of the caged type compound Lu5Rh6Sn18 has been investigated by using magnetization, heat capacity, and muon spin relaxation or rotation (?SR) measurements, and the results interpreted on the basis of the group theoretical classifications of the possible pairing symmetries and a simple model of the resulting quasiparticle spectra. Our zero-field ?SR measurements clearly reveal the spontaneous appearance of an internal magnetic field below the transition temperature, which indicates that the superconducting state in this material is characterized by broken time-reversal symmetry. Further, the analysis of the temperature dependence of the magnetic penetration depth measured using the transverse-field ?SR measurements suggests an isotropic s?wave character for the superconducting gap. This is in agreement with the heat capacity behavior, and we show that it can be interpreted in terms of a nonunitary triplet state with point nodes and an open Fermi surface

    Important Roles of Te 5p and Ir 5d Spin-orbit Interactions on the Multi-band Electronic Structure of Triangular Lattice Superconductor Ir1-xPtxTe2

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    We report an angle-resolved photoemission spectroscopy (ARPES) study on a triangular lattice superconductor Ir1−x_{1-x}Ptx_{x}Te2_2 in which the Ir-Ir or Te-Te bond formation, the band Jahn-Teller effect, and the spin-orbit interaction are cooperating and competing with one another. The Fermi surfaces of the substituted system are qualitatively similar to the band structure calculations for the undistorted IrTe2_2 with an upward chemical potential shift due to electron doping. A combination of the ARPES and the band structure calculations indicates that the Te 5p5p spin-orbit interaction removes the px/pyp_x/p_y orbital degeneracy and induces px±ipyp_x \pm ip_y type spin-orbit coupling near the A point. The inner and outer Fermi surfaces are entangled by the Te 5p5p and Ir 5d5d spin-orbit interactions which may provide exotic superconductivity with singlet-triplet mixing.Comment: 10 pages, 4 figure

    Spin polarization in photoemission from the cuprate superconductor Bi2Sr2CaCu2O8+delta

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    Photoelectrons produced from the excitation of spin-degenerate states in solids can have a sizable spin polarization, which is related to the phase of interfering channels in the photoemission matrix elements. Such spin polarization can be measured by spin-resolved photoemission spectroscopy to gain information about the transitions and the Wigner time delay of the process. Incorporating strongly correlated electron systems into this paradigm could yield a novel means of extracting phase information crucial to understanding the mechanism of their emergent behavior. In this work, we present, as a case study, experimental measurements of the cuprate superconductor Bi2Sr2CaCu2O8+delta by spin-resolved photoemission while maintaining full angular and energy resolution. A spin polarization of at least 10% is observed, which is related to the phase of the photoelectron wave function

    Unconventional superconductivity in the cage type compound Sc5_5Rh6_6Sn18_{18}

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    We have examined the superconducting ground state properties of the caged type compound Sc5_5Rh6_6Sn18_{18} using magnetization, heat capacity, and muon-spin relaxation or rotation (μ\muSR) measurements. Magnetization measurements indicate type-II superconductivity with an upper critical field μ0Hc2(0)\mu_0H_{c2}(0) = 7.24 T. The zero-field cooled and field cooled susceptibility measurements unveil an onset of diamagnetic signal below TcT_{\bf c} = 4.4 K. The interpretation of the heat capacity results below TcT_{\bf c} using the α−\alpha-BCS model unveils the value of α\alpha = 2.65, which gives the dimensionless ratio 2Δ(0)/kBTc\Delta(0)/k_B T_{\bf c} = 5.3, intimating that Sc5_5Rh6_6Sn18_{18} is a strong-coupling BCS superconductor. The zero-field μ\muSR measurements in the longitudinal geometry exhibit a signature of a spontaneous appearance of the internal magnetic field below the superconducting transition temperature, indicating that the superconducting state is characterized by the broken time-reversal symmetry (TRS). We have compared the results of broken TRS in Sc5_5Rh6_6Sn18_{18} with that observed in R5_5Rh6_6Sn18_{18} (R = Lu and Y).Comment: 6 pages, 4 figures. arXiv admin note: text overlap with arXiv:1411.687

    Stabilizing Even-Parity Chiral Superconductivity in Sr2_2RuO4_4

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    Strontium ruthenate (Sr2_2RuO4_4) has long been thought to host a spin-triplet chiral pp-wave superconducting state. However, the singletlike response observed in recent spin-susceptibility measurements casts serious doubts on this pairing state. Together with the evidence for broken time-reversal symmetry and a jump in the shear modulus c66c_{66} at the superconducting transition temperature, the available experiments point towards an even-parity chiral superconductor with kz(kx±iky)k_z(k_x\pm ik_y)-like EgE_g symmetry, which has consistently been dismissed based on the quasi-two-dimensional electronic structure of Sr2_2RuO4_4. Here, we show how the orbital degree of freedom can encode the two-component nature of the EgE_g order parameter, allowing for a local orbital-antisymmetric spin-triplet state that can be stabilized by on-site Hund's coupling. We find that this exotic EgE_g state can be energetically stable once a complete, realistic three-dimensional model is considered, within which momentum-dependent spin-orbit coupling terms are key. This state naturally gives rise to Bogoliubov Fermi surfaces.Comment: 6+10 pages, 5 figure
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