Direct Observation of k∥ and k⊥ Stripe Excitations in La2−x Sr x CuO4

J. Phys.: Condens. Matter

Takayanagi

Hayamizu

et al. 2013

The individual k|| and k ⊥ stripe excitations in fluctuating spin-charge stripes have not been observed yet. Raman scattering has a unique selection rule that the combination of two electric field directions of incident and scattered light determines the observed symmetry. If we set, for example, two electric fields to two possible stripe directions, we can observe the fluctuating stripe as if it is static. Using the different symmetry selection rule between the B1g two-magnon scattering and the B1g and B2g isotropic electronic scattering, we succeeded to obtain the k|| and k ⊥ strip magnetic excitations separately in La2−xSrxCuO4. Only the k ⊥ stripe excitations appear in the wide-energy isotropic electronic Raman scattering, indicating that the charge transfer is restricted to the direction perpendicular to the fluctuating stripe. This surprising restriction is reminiscent of the Burgers vector of an edge dislocation in metal. The edge dislocation easily slides perpendicularly to an inserted stripe and causes ductility in metal. Hence charges at the edge of a stripe move together with the edge dislocation perpendicularly to the stripe, while other charges are localized. A looped edge dislocation has lower energy than a single edge dislocation. The superconducting coherence length is close to the inter-charge stripe distance at x ≤ 0.2. Therefore we conclude that Cooper pairs are formed at looped edge dislocations. The restricted charge transfer direction naturally explains the opening of a pseudogap around (0, π) for the stripe parallel to the b axis and the reconstruction of the Fermi surface to have a flat plane near (0, π). They break the four-fold rotational symmetry. Furthermore the systematic experiments revealed the carrier density dependence of the isotropic and anisotropic electronic excitations, the spin density wave and/or charge density wave gap near (π/2, π/2), and the strong coupling between the electronic states near (π/2, π/2) and the zone boundary phonons at (π, π).

“…17. The B 1g and B 2g gap energies are consistent with the reported results 82,86,90,94,96 . The B 2g gap energies are located between the B 1 and B 3 peak energies at x ≤ 0.15.…”

supporting

confidence: 91%

Superconducting pairing and the pseudogap in the nematic dynamical stripe phase of La_2−xSr_xCuO₄

J. Phys.: Condens. Matter

Takayanagi

Hayamizu

et al. 2013

“…Magnetic scattering arises from two mechanisms, two-magnon scattering and highenergy electronic scattering. The two mechanisms have different symmetries [14]. Using the difference we disclosed the following results.…”

Section: Introductionmentioning

confidence: 93%

“…In the previous conference (Superstripes 2011) we presented the direct observation of individual k|| and k ⊥ stripe magnetic excitations in a fluctuating spincharge stripe state utilizing high-energy Raman scattering [14]. The advantage of Raman scattering is the unique selection rule which is determined by two Cartesian vectors parallel to the electric fields of incident and scattered light.…”

Section: Introductionmentioning

confidence: 99%

“…The spin-charge stripe structure [1,2,3,4,5,6,7,8,9] in the hole-doped high temperature superconducting cuprate has been intensively investigated, because it has a strong possibility to solve the superconducting mechanism [10,11,12,13]. In the previous conference (Superstripes 2011) we presented the direct observation of individual k|| and k ⊥ stripe magnetic excitations in a fluctuating spincharge stripe state utilizing high-energy Raman scattering [14]. The advantage of Raman scattering is the unique selection rule which is determined by two Cartesian vectors parallel to the electric fields of incident and scattered light.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Raman Studies of Anisotropic Magnetic Excitations in Fluctuating Nematic Striped La2−x Sr x CuO4 and the Comparison to Uniform Nd2−x Ce x CuO4

Takayanagi

Hayamizu

et al. 2013

J Supercond Nov Magn

Self Cite

The mechanism of the high temperature holedoped superconductivity was investigated by Raman scattering. The Raman selection rule is unique, so that anisotropic magnetic excitations in a fluctuating spincharge stripe can be detected as if it is static. We use different Raman selection rules for two kinds of magnetic Raman scattering processes, two-magnon scattering and high-energy electronic scattering. In order to confirm the difference, the Raman spectra of striped La 2−x Sr x CuO 4 (LSCO) and non-striped Nd 2−x Ce x CuO 4 (NCCO) were compared. The main results in LSCO are (1) magnetic excitations are presented by individual energy dispersions for the k|| stripe and the k ⊥ stripe, (2) the charge transfer is allowed only in the direction perpendicular to the stripe. The direction is the same as S. Sugai Department of Physics, Art and Science, Petroleum Institute, P.O. Box 2533, Abu Dhabi, UAE Tel.: +971-26075257 E-mail: ssugai@pi.ac.ae Department of Physics, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan Y. Takayanagi Department of Physics, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan N. Hayamizu Department of Physics, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan Y. Sone Department of Physics, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan N. Nakagawa Department of Physics, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan T. Muroi Department of Physics, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan the Burgers vector of an edge dislocation. Hence we assume that a charge moves together with the edge dislocation of the charge stripe. The superconducting coherence length is close to the inter-charge stripe distance at x < 0.2. Therefore we propose a model that superconducting pairs are formed in the edge dislocations. The binding energy is related to the stripe formation energy.

“…It is preferable to find the relation between χ (ω) and σ (ω), because the low-energy Raman spectra are derived from the coherent parts which have no correlation. The B 1g and B 2g Raman spectra have a large hump from 1000 to 3500 cm −1 [30,31]. The intensity is enhanced as temperature decreases from 300 to 5 K. From the carrier density dependence of the low-energy edge, we assigned the hump to the separated dispersion segments of the spin wave in the k direction perpendicular to the spin-charge stripe [30,31] based on the calculation by Seibold and Lorenzana [32,33].…”

Section: Introductionmentioning

confidence: 98%

Correlation between Raman sum and optical conductivity sum in La_2−xSr_xCuO₄

J. Phys.: Condens. Matter

Nohara

Shiozaki

et al. 2013

In a strongly correlated electron system, the single-particle spectral function changes into a coherent peak and incoherent humps which extend over 1 eV. The incoherent parts lose the symmetry and k dependence, so that the Raman spectra with different symmetries become identical and they are expressed by the optical conductivity. We found that the B1g and B2g spectra in La(2-x)Sr(x)CuO4 become identical above 2000 cm(-1) in the underdoped phase, if Fleury-Loudon type B1g two-magnon scattering is removed. The first Raman susceptibility moment correlates with the generalized optical conductivity moment. The good correlation arises from the incoherent states of a hump from 1000 to 4000 cm(-1). The hump is the only structure of the incoherent electronic states in the mid-infrared absorption spectra below 1.4 eV at low carrier densities. The energy is twice the separated dispersion segments of the spin wave in the k(perpendicular) stripe direction. The incoherent state is formed by the magnetic excitations created by the hole hopping in the antiferromagnetic spin stripes in the real space picture.