Optical Properties of High-Temperature Superconductors

Tanner, D. B.; Timusk, T.

doi:10.1142/9789814439688_0005

Cited by 190 publications

(256 citation statements)

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“…In the case of YBCO, displayed in Fig. 2c and d, both σ and ǫ are frequency independent at high temperatures (metallic behavior) but reveal a pronounced dispersion at 5 K. A strong increase of σ is seen towards the lowest frequencies, similar to that observed in all high-Tc's and connected to uncondensed (normal) carriers [15,16]; such dispersion leads to a peak in the temperature dependence of the conductivity, in case of our film -around 50 K for the frequency of 25 cm −1 . The dielectric permittivity ǫ shows in the SC state a divergent dispersion ǫ ∝ −(1/ω) 2 which represents the dielectric response of the zero-frequency deltafunction in the conductivity spectrum, responsible for the infinite DC conductivity [14].…”

supporting

confidence: 59%

Suppression of superconductivity in YBCO/LCMO superlattices

Chen

Gorshunov

Cristiani

et al. 2004

Solid State Communications

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The competition of superconductivity and magnetism in superlattices composed of alternating YBa2Cu3O 7−d and La0.67Ca0.33MnO3 thin films is investigated using low-energy optical spectroscopy. The thickness of the superconducting YBCO layers is varied from 30 nm to 20 nm while the thickness of the magnetic LCMO layers is kept constant at 20 nm. We clearly observe that the superconducting condensate density in the superconducting state of superlattice is drastically reduced by the magnetic subsystem which may be connected with proximity effects that distort the gap symmetry and thus suppress superconductivity. PACS numbers: 72.25.Mk; 74.78.Bz; 75.70.Cn; Since the early 1960s the interplay of superconductivity (SC) and ferromagnetism (FM) has continuously drawn attention [1]. At first glance SC and FM exclude each other because the magnetic exchange field breaks the Cooper pairs. Nevertheless the possible coexistence of both phenomena due to a spatially modulated order parameter was suggested by Fulde, Ferrell, Larkin and Ovchinnikov [2]; the correspondent state was never observed in conventional SC. A good way to study the effect is to bring the nano-sized layers of the two materials into contact and to view the SC-FM interaction on the level of the proximity effects. The exploration of multilayer systems composed of alternating conventional SC and metallic FM layers was subject of recent reviews [3,4].In the last years artificially grown superlattices (SLs) consisting of high-T c superconductors and manganese oxides which exhibit the phenomenon of colossal magnetoresistance have attracted increasing interests for various reasons. On one hand, SLs were developed as an important tool to explore the interplay between the two antagonistic SC and FM ground states, and on the other hand the injection of spin-polarized carriers can lead to new SC switching devices [5]. Due to the structural similarity of the two classes of perovskite compounds, it is possible to construct a unique combination of SC cuprate and strongly FM manganese layers. It has been demonstrated by different groups [6,7,8,9] that although SC and FM are preserved in each subsystem, the superconducting transition temperature T c and the Curie temperature of the magnetic ordering T mag are considerably suppressed. Transport and magnetization measurements clearly indicate that spin-polarized quasiparticle injection in YBa 2 Cu 3 O 7−d /La 0.67 Ca 0.33 MnO 3 (YBCO/LCMO) SL can strongly decrease T c and the critical current J c [10,11]. Particularly interesting is the almost complete spin polarization in LCMO and the low carrier density in YBCO which seems to be suppressed even further in the case of SL, as was shown by optical spectroscopy [12]. The advantage of optical techniques is that one can directly monitor the temperature dependence of the "strength" of the conducting and supercon- ducting condensates expressed by the spectral weight, i.e. the area under the dynamical conductivity spectrum. Up to now, however, optical measurements failed to even de...

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supporting

confidence: 59%

Suppression of superconductivity in YBCO/LCMO superlattices

Chen

Gorshunov

Cristiani

et al. 2004

Solid State Communications

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“…(ii) The quasiparticle dispersion has a bandwidth of order J, is almost flat near (π, 0) and (0, π), and the general structure agrees with the recent photoemission results. (iii) The remaining spectral weight is mostly distributed in the energy range corresponding to the mid-infrared absorption universally observed in the optical experiments of the high T c cuprates 11 . (iv) There is tentative evidence indicating that the quasiparticle band found in the one-hole case remains fairly robust under the finite doping.…”

Section: Introductionmentioning

confidence: 78%

Quasiparticle structure and coherent propagation in thet-Jz-J⊥
Gan
¹
,
Hedegård
²

1996
Phys. Rev. B
5
1
19
0
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Numerical studies, from variational calculation to exact diagonalization, all indicate that the quasiparticle generated by introducing one hole into a two-dimensional quantum antiferromagnet has the same nature as a string state in the t − Jz model. Based on this observation, we attempt to visualize the quasiparticle formation and subsequent coherent propagation at low energy by studying the generalized t − Jz − J ⊥ model in which we first diagonalize the t − Jz model and then perform a degenerate perturbation in J ⊥ . We construct the quasiparticle state and derive an effective Hamiltonian describing the coherent propagation of the quasiparticle and its interaction with the spin wave excitations in the presence of the Néel order. We expect that qualitative properties of the quasiparticle remain intact when analytically continuing J ⊥ from the anisotropic J ⊥ < Jz to the isotropic J ⊥ = Jz limit, despite the fact that the spin wave excitations change from gapful to gapless. Extrapolating to J ⊥ = Jz, our quasiparticle dispersion and spectral weight compare well with the exact numerical results for small clusters.

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“…Let us now make contact with the experimentally observed characteristics of the midinfrared spectra in the doped perovskites (for an review of the experimental and theoretical work on the optical conductivity see Refs. [63,35,59,2]). Needless to say, that it is out of the scope of our ten-site cluster diagonalization study to give a quantitative theoretical description of the complex optical properties of particular copper and nickel oxides.…”

Section: Optical Conductivitymentioning

confidence: 99%

Optical absorption and single-particle excitations in the two-dimensional Holsteint−Jmodel

1998

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To discuss the interplay of electronic and lattice degrees of freedom in systems with strong Coulomb correlations we have performed an extensive numerical study of the two-dimensional Holstein t-J model. The model describes the interaction of holes, doped in a quantum antiferromagnet, with a dispersionsless optical phonon mode. We apply finite-lattice Lanczos diagonalization, combined with a well-controlled phonon Hilbert space truncation, to the Hamiltonian. The focus is on the dynamical properties. In particular we have evaluated the single-particle spectral function and the optical con-

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Optical Properties of High-Temperature Superconductors

Cited by 190 publications

References 0 publications

Suppression of superconductivity in YBCO/LCMO superlattices

Suppression of superconductivity in YBCO/LCMO superlattices

Quasiparticle structure and coherent propagation in thet-Jz-J⊥
Gan
¹
,
Hedegård
²

1996
Phys. Rev. B
5
1
19
0
View full text Add to dashboard Cite

Optical absorption and single-particle excitations in the two-dimensional Holsteint−Jmodel

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Optical Properties of High-Temperature Superconductors

Cited by 190 publications

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Suppression of superconductivity in YBCO/LCMO superlattices

Suppression of superconductivity in YBCO/LCMO superlattices

Quasiparticle structure and coherent propagation in thet-Jz-J⊥Gan1, Hedegård2 1996Phys. Rev. B51190View full textAdd to dashboardCite

Optical absorption and single-particle excitations in the two-dimensional Holsteint−Jmodel

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Quasiparticle structure and coherent propagation in thet-Jz-J⊥
Gan
¹
,
Hedegård
²

1996
Phys. Rev. B
5
1
19
0
View full text Add to dashboard Cite