New Journal of Physics Surface and bulk electronic structure of the unconventional superconductor Sr 2 RuO 4 : unusual splitting of the β band (original) (raw)
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New Journal of Physics, 2012
We present an angle-resolved photoemission study of the surface and bulk electronic structure of the single layer ruthenate Sr 2 RuO 4 . As the early studies by photoemission and scanning tunneling microscopy were confronted with a problem of surface reconstruction, surface ageing was previously proposed as a possible remedy to access the bulk states. Here, we suggest an alternative way by demonstrating that, in the case of Sr 2 RuO 4 , circularly polarized light can be used to disentangle the signals from the bulk and surface layers, thus opening the possibility to investigate many-body interactions both in bulk and surface bands. The proposed procedure results in improved momentum resolution, which enabled us to detect an unexpected splitting of the surface β band. We discuss the origin of the splitting of the β band and the possible connection with the Rashba effect at the surface. 6 Present address: Diamond
mK-STM Studies of the Temperature- and Field-dependence of the Quasiparticle Spectrum of Sr2RuO4
Atomic-resolution scanning tunneling spectroscopy is used to study the spectrum of quasiparticle states in superconducting Sr2RuO4. The measured temperature dependence of the quasiparticle spectrum is consistent with a multi-band superconducting order parameter with one band exhibiting a line of nodes, if a constant density of states offset can be ascribed to a surface effect. In magnetic fields H < Hc2, a vortex lattice, square and oriented parallel to the 110 direction of the RuO2 lattice, is detected by spectroscopic imaging. Each vortex exhibits one flux quantum and a strong zero-bias conductance peak. PACS numbers: 68.37.Ef, 74.20.Rp, 74.70.Pq Sr 2 RuO 4 displays an exotic form of superconductivity at temperatures below 1.45 K [1, 2]. Because of the independence of the spin susceptibility on temperature below T c , the Cooper pairs are believed to be in a spin triplet 'equal spin pairing' (ESP) state. Muon spin rotation studies also show a time-reversal-symmetry breaking (spontaneous magnetization) signal which is also consistent with spin-triplet superconductivity .
Physica C: Superconductivity, 1997
We have performed high-resolution angle-resolved photoemission spectroscopy of a non-cuprate layered superconductor Sr2RuO 4 to study the electronic structure near the Fermi level (EF). The result shows an extended van Hove singularity (vHs) along the Ru-O bonding direction just like the cuprate, regardless of the character of the electronic states at EF. This suggests that the extended vHs is a general electronic structure of a two dimensional correlated d-electron metal. We also have found that the observed Fermi surface topology (one electron-like Fermi surface sheet centered at 1" point and two hole-like ones centered at X point) is qualitatively different from the calculated Fermi surface topology (two electron-like Fermi sheets centered at F point and one hole-like one centered at X point) in the consequence of the existence of the vHs.
The surface of Sr2Ru0.9Mo0.1O4: a LEED and STM study
Surface Science, 2003
In the unconventional superconductor Sr2RuO4, substitution of a small amount of Mo for Ru destroys the superconducting state. We have used low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) to study the cleaved (100) surface of the Mo-doped strontium ruthenate: Sr2Ru0.9Mo0.1O4. Excellent LEED patterns indicate a well-ordered surface similar to Sr2RuO4. The analysis of LEED-I(V) spectra revealed that
Fermi surface of Sr 2RuO 4 studied by two-dimensional angle resolved photoelectron spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 1998
The shape of the Fermi surface of the Sr2RuO4, the first noncuprate superconductor, has been directly observed by twodimensional angle resolved photoelectron spectroscopy (2D-ARPES) technique using a display-type hemispherical mirror analyzer. The gross shape of the Fermi surface agrees with previous band calculations. The photoelectron angular distribution pattern of the Fermi level shows that the Fermi surface is composed of orbitals with dxy, dyz, and dzx-like symmetries which agree well with those predicted by previous band calculations and are in contrast to dx2_y2 symmetry of the high-T c superconductors.
Renormalized band structure of Sr 2 RuO 4 : A quasiparticle tight-binding approach
We derive an effective quasiparticle tight-binding model which is able to describe with high accuracy the low-energy electronic structure of Sr 2 RuO 4 obtained by means of low temperature angle resolved photoemission spectroscopy. Such an approach is applied to determine the momentum and orbital dependent effective masses and velocities of the electron quasiparticles close to the Fermi level. We demonstrate that the model can provide, among the various computable physical quantities, a very good agreement with the experimentally measured specific heat coefficient and compares well with the plasma frequency estimated from local density calculations. Its use is underlined as a realistic input in the analysis of the possible electronic mechanisms related to the superconducting state of Sr 2 RuO 4 .
Phenomenological theory of the 3 Kelvin phase in Sr2RuO4
Journal of The Physical Society of Japan, 2001
We model the 3 K-phase of Sr 2 RuO 4 with Ru-metal inclusion as interface state with locally enhanced transition temperatures. The resulting 3 K-phase must have a dierent pairing symmetry than the bulk phase of Sr 2 RuO 4 , because the symmetry at the interface is lower than in the bulk. It is invariant under time reversal and a second transition, in general, above the onset of bulk superconductivity is expected where time reversal symmetry is broken. The nucleation of the 3 K-phase exhibits a ''capillary eect'' which can lead to frustration phenomena for the superconducting states on dierent Ru-inclusions. Furthermore, the phase structure of the pair wave function gives rise to zero-energy quasiparticle states which would be visible in quasiparticle tunneling spectra. Additional characteristic properties are associated with the upper critical eld H c2 . The 3 K-phase has a weaker anisotropy of H c2 between the inplane and z-axis orientation than the bulk superconducting phase. This is connected with the more isotropic nature Ru-metal which yields a stronger orbital depairing eect for the inplane magnetic eld than in the strongly layered Sr 2 RuO 4 . An anomalous temperature dependence for the z-axis critical eld is found due to the coupling of the magnetic eld to the order parameter texture at the interface. Various other experiments are discussed and new measurements are suggested.
Evaluation of Spin-Triplet Superconductivity in Sr2RuO4
Journal of the Physical Society of Japan, 2012
This review presents a summary and evaluations of the superconducting properties of the layered ruthenate Sr 2 RuO 4 as they are known in the autumn of 2011. This paper appends the main progress that has been made since the preceding review by Mackenzie and Maeno was published in 2003. Here, special focus is placed on the critical evaluation of the spin-triplet, odd-parity pairing scenario applied to Sr 2 RuO 4. After an introduction to superconductors with possible odd-parity pairing, accumulated evidence for the pairing symmetry of Sr 2 RuO 4 is examined. Then, significant recent progress on the theoretical approaches to the superconducting pairing by Coulomb repulsion is reviewed. A section is devoted to some experimental properties of Sr 2 RuO 4 that seem to defy simple explanations in terms of currently available spin-triplet scenario. The next section deals with some new developments using eutectic boundaries and micro-crystals, which reveals novel superconducting phenomena related to chiral edge states, odd-frequency pairing states, and half-fluxoid states. Some of these properties are intimately connected with the properties as a topological superconductor. The article concludes with a summary of knowledge emerged from the study of Sr 2 RuO 4 that are now more widely applied to understand the physics of other unconventional superconductors, as well as with a brief discussion of relatively unexplored but promising areas of ongoing and future studies of Sr 2 RuO 4 .
Electron magnetic resonance imaging of the Fermi surface of Sr2RuO4
Physica C: Superconductivity, 2001
We have carried out detailed angle dependent studies of the normal state microwave (40±112 GHz) magneto-conductivity of several single crystal samples of the perovskite superconductor Sr 2 RuO 4. As previously reported [Phys. Rev. Lett. 84 (2000) 3374], we observe a series of resonant absorptions which we attribute to cyclotron resonance of quasiparticles belonging to the three well-known Fermi surfaces for this material. From the angle dependence, we con®rm the two-dimensional character of these resonances, i.e. the cyclotron frequencies scale as the inverse cosine of the angle between the magnetic ®eld and the normal to the conducting layers. Furthermore, by performing measurements on several samples, and in dierent electromagnetic ®eld con®gurations, we are able to couple to dierent cyclotron modes (harmonics) which derive from deformations (warpings) of the Fermi surfaces from perfect cylinders. These mode couplings will be discussed in the light of recent angle dependent de Haas±van Alphen measurements.