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Hazra S, Bag R, Singh S, Kini RN. Terahertz spectroscopic signature of the charge density wave in the spin-ladder compound, Sr 14Cu 24O 41. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:275601. [PMID: 32155612 DOI: 10.1088/1361-648x/ab7e5e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We provide spectroscopic evidence for the charge density wave (CDW) phason mode at ≈0.93 THz in the two-leg, spin-1/2 ladders of Sr14Cu24O41 using terahertz time-domain spectroscopy. We find that annealing in an oxygen atmosphere or doping with a low concentration of Co (≾1%) does not affect the CDW phason mode. However, Co doping at higher concentrations (10%), wherein the Co enters the ladder layers, destabilizes the CDW. We believe that the suppression of the CDW phase is due to an increase in intraladder overlap integrals through the shrinkage of interplane distance upon Co doping.
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Affiliation(s)
- Soumitra Hazra
- Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Maruthamala P.O. Vithura, Kerala 695551, India
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Yu XJ, Diao CZ, Venkatesan T, Breese MBH, Rusydi A. A soft x-ray-ultraviolet (SUV) beamline and diffractometer for resonant elastic scattering and ultraviolet-vacuum ultraviolet reflectance at the Singapore synchrotron light source. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:113113. [PMID: 30501296 DOI: 10.1063/1.5043341] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Accepted: 10/23/2018] [Indexed: 05/22/2023]
Abstract
A new beamline and a six-circle UHV diffractometer have been constructed at the Singapore Synchrotron Light Source with a broad energy coverage from 3.5 to 1500 eV. The beamline is optimized for ultraviolet-vacuum-ultraviolet optical reflectivity and resonant soft X-ray scattering with medium energy resolution over a broad energy range, achieved by using a self-focusing monochromator consisting of a plane mirror and three variable line spacing gratings. The unique character of the diffractometer comprises 4-circles in the vertical plane and 2-circles in the horizontal plane. Thirteen motions are available inside the UHV chamber with a base pressure of 1 × 10-9 mbar. Two sample holders working independently over a temperature range of 37 K-400 K are controlled by a closed-cycle cryostat, while the bottom holder inside a high field compact pulsed magnet is available for measurements requiring a magnetic field.
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Affiliation(s)
- X J Yu
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - C Z Diao
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - T Venkatesan
- NUSSNI-NanoCore, National University of Singapore, Singapore 117576, Singapore
| | - M B H Breese
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - A Rusydi
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
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3
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Chi X, Huang Z, Asmara TC, Han K, Yin X, Yu X, Diao C, Yang M, Schmidt D, Yang P, Trevisanutto PE, Whitcher TJ, Venkatesan T, Breese MBH, Rusydi A. Large Enhancement of 2D Electron Gases Mobility Induced by Interfacial Localized Electron Screening Effect. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1707428. [PMID: 29667241 DOI: 10.1002/adma.201707428] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 02/13/2018] [Indexed: 06/08/2023]
Abstract
The interactions between delocalized and localized charges play important roles in correlated electron systems. Here, using a combination of transport measurements, spectroscopic ellipsometry (SE), and X-ray absorption spectroscopy (XAS) supported by theoretical calculations, we reveal the important role of interfacial localized charges and their screening effects in determining the mobility of (La0.3 Sr0.7 )(Al0.65 Ta0.35 )O3 /SrTiO3 (LSAT/SrTiO3 ) interfaces. When the LSAT layer thickness reaches the critical value of 5 uc, the insulating interface abruptly becomes conducting, accompanied by the appearance of a new midgap state. This midgap state emerges at ≈1 eV below the Ti t2g band and shows a strong character of Ti 3dxy - O 2p hybridization. Increasing the LSAT layer from 5 to 18 uc, the number of localized charges increases, resulting in an enhanced screening effect and higher mobile electron mobility. This observation contradicts the traditional semiconductor interface where the localized charges always suppress the carrier mobility. These results demonstrate a new strategy to probe localized charges and mobile electrons in correlated electronic systems and highlight the important role of screening effects from localized charges in improving the mobile electron mobility at complex oxide interfaces.
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Affiliation(s)
- Xiao Chi
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Zhen Huang
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
| | - Teguh C Asmara
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
| | - Kun Han
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
| | - Xinmao Yin
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Xiaojiang Yu
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - Caozheng Diao
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - Ming Yang
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore
- Institute of Materials Research and Engineering, A*-STAR, 2 Fusionopolis Way, Singapore, 138634, Singapore
| | - Daniel Schmidt
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - Ping Yang
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - Paolo E Trevisanutto
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - T J Whitcher
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
| | - T Venkatesan
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
- National University of Singapore Graduate School for Integrative Sciences and Engineering (NGS), 28 Medical Drive, Singapore, 117456, Singapore
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117583, Singapore
| | - Mark B H Breese
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
| | - Andrivo Rusydi
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore
- Department of Physics, National University of Singapore, Singapore, 117542, Singapore
- NUSSNI-NanoCore, National University of Singapore, Singapore, 117576, Singapore
- National University of Singapore Graduate School for Integrative Sciences and Engineering (NGS), 28 Medical Drive, Singapore, 117456, Singapore
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Rusydi A, Goos A, Binder S, Eich A, Botril K, Abbamonte P, Yu X, Breese MBH, Eisaki H, Fujimaki Y, Uchida S, Guerassimova N, Treusch R, Feldhaus J, Reininger R, Klein MV, Rübhausen M. Electronic screening-enhanced hole pairing in two-leg spin ladders studied by high-resolution resonant inelastic x-ray scattering at Cu M edges. PHYSICAL REVIEW LETTERS 2014; 113:067001. [PMID: 25148343 DOI: 10.1103/physrevlett.113.067001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Indexed: 05/23/2023]
Abstract
We study the electronic screening mechanisms of the effective Coulomb on-site repulsion in hole-doped Sr(14)Cu(24)O(41) compared to undoped La(6)Ca(8)Cu(24)O(41) using polarization dependent high-resolution resonant inelastic x-ray scattering at Cu M edges. By measuring the energy of the effective Coulomb on-site repulsion and the spin excitations, we estimate superexchange and hopping matrix element energies along rungs and legs, respectively. Interestingly, hole doping locally screens the Coulomb on-site repulsion reducing it by as much as 25%. We suggest that the increased ratio of the electronic kinetic to the electronic correlation energy contributes to the local superexchange mediated pairing between holes.
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Affiliation(s)
- A Rusydi
- Institut für Angewandte Physik, Universität Hamburg, Jungiusstraße 11, D-20355 Hamburg, Germany and Center for Free Electron Laser Science (CFEL), Notkestraße 85, D-22607 Hamburg, Germany and NUSSNI-NanoCore, Department of Physics, National University of Singapore, Singapore 117542, Singapore and Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore
| | - A Goos
- Institut für Angewandte Physik, Universität Hamburg, Jungiusstraße 11, D-20355 Hamburg, Germany and Center for Free Electron Laser Science (CFEL), Notkestraße 85, D-22607 Hamburg, Germany
| | - S Binder
- Institut für Angewandte Physik, Universität Hamburg, Jungiusstraße 11, D-20355 Hamburg, Germany and Center for Free Electron Laser Science (CFEL), Notkestraße 85, D-22607 Hamburg, Germany
| | - A Eich
- Institut für Angewandte Physik, Universität Hamburg, Jungiusstraße 11, D-20355 Hamburg, Germany and Center for Free Electron Laser Science (CFEL), Notkestraße 85, D-22607 Hamburg, Germany
| | - K Botril
- Institut für Angewandte Physik, Universität Hamburg, Jungiusstraße 11, D-20355 Hamburg, Germany and Center for Free Electron Laser Science (CFEL), Notkestraße 85, D-22607 Hamburg, Germany
| | - P Abbamonte
- Physics Department and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - X Yu
- Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore
| | - M B H Breese
- NUSSNI-NanoCore, Department of Physics, National University of Singapore, Singapore 117542, Singapore and Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore
| | - H Eisaki
- Nanoelectronics Research Institute, AIST, 1-1-1 Central 2, Umezono, Tsukuba, Ibaraki 305-8568, Japan
| | - Y Fujimaki
- Department of Superconductivity, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan
| | - S Uchida
- Department of Superconductivity, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan
| | - N Guerassimova
- Photon Science, DESY, Notkestraße 85, D-22607 Hamburg, Germany
| | - R Treusch
- Photon Science, DESY, Notkestraße 85, D-22607 Hamburg, Germany
| | - J Feldhaus
- Photon Science, DESY, Notkestraße 85, D-22607 Hamburg, Germany
| | - R Reininger
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - M V Klein
- Physics Department and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - M Rübhausen
- Institut für Angewandte Physik, Universität Hamburg, Jungiusstraße 11, D-20355 Hamburg, Germany and Center for Free Electron Laser Science (CFEL), Notkestraße 85, D-22607 Hamburg, Germany and NUSSNI-NanoCore, Department of Physics, National University of Singapore, Singapore 117542, Singapore
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Fink J, Schierle E, Weschke E, Geck J. Resonant elastic soft x-ray scattering. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2013; 76:056502. [PMID: 23563216 DOI: 10.1088/0034-4885/76/5/056502] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Resonant (elastic) soft x-ray scattering (RSXS) offers a unique element, site and valence specific probe to study spatial modulations of charge, spin and orbital degrees of freedom in solids on the nanoscopic length scale. It is not only used to investigate single-crystalline materials. This method also enables one to examine electronic ordering phenomena in thin films and to zoom into electronic properties emerging at buried interfaces in artificial heterostructures. During the last 20 years, this technique, which combines x-ray scattering with x-ray absorption spectroscopy, has developed into a powerful probe to study electronic ordering phenomena in complex materials and furthermore delivers important information on the electronic structure of condensed matter. This review provides an introduction to the technique, covers the progress in experimental equipment, and gives a survey on recent RSXS studies of ordering in correlated electron systems and at interfaces.
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Affiliation(s)
- J Fink
- Leibniz-Institute for Solid State and Materials Research Dresden, PO Box 270116, D-01171 Dresden, Germany.
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Rusydi A, Dhar S, Barman AR, Qi DC, Motapothula M, Yi JB, Santoso I, Feng YP, Yang K, Dai Y, Yakovlev NL, Ding J, Wee ATS, Neuber G, Breese MBH, Ruebhausen M, Hilgenkamp H, Venkatesan T. Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti1-xTaxO2 (x~0.05) thin films. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2012; 370:4927-4943. [PMID: 22987036 DOI: 10.1098/rsta.2012.0198] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We report room-temperature ferromagnetism (FM) in highly conducting, transparent anatase Ti(1-x)Ta(x)O(2) (x∼0.05) thin films grown by pulsed laser deposition on LaAlO(3) substrates. Rutherford backscattering spectrometry (RBS), X-ray diffraction, proton-induced X-ray emission, X-ray absorption spectroscopy (XAS) and time-of-flight secondary-ion mass spectrometry indicated negligible magnetic contaminants in the films. The presence of FM with concomitant large carrier densities was determined by a combination of superconducting quantum interference device magnetometry, electrical transport measurements, soft X-ray magnetic circular dichroism (SXMCD), XAS and optical magnetic circular dichroism, and was supported by first-principles calculations. SXMCD and XAS measurements revealed a 90 per cent contribution to FM from the Ti ions, and a 10 per cent contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites, though carrier activation was only 50 per cent at 5 per cent Ta concentration, implying compensation by cationic defects. The role of the Ti vacancy (V(Ti)) and Ti(3+) was studied via XAS and X-ray photoemission spectroscopy, respectively. It was found that, in films with strong FM, the V(Ti) signal was strong while the Ti(3+) signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localized magnetic moments, V(Ti) sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to FM in wide-band-gap semiconducting oxides without any magnetic elements.
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Affiliation(s)
- A Rusydi
- NUSNNI-NanoCore, National University of Singapore, Republic of Singapore.
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Thorsmølle VK, Homes CC, Gozar A, Blumberg G, van Mechelen JLM, Kuzmenko AB, Vanishri S, Marin C, Rønnow HM. Phonon energy gaps in the charged incommensurate planes of the spin-ladder Sr14Cu24O41 compound by Raman and infrared spectroscopy. PHYSICAL REVIEW LETTERS 2012; 108:217401. [PMID: 23003300 DOI: 10.1103/physrevlett.108.217401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Indexed: 06/01/2023]
Abstract
The terahertz (THz) excitations in the quantum spin-ladder system Sr14Cu24O41 have been determined along the c axis using THz time-domain, Raman, and infrared spectroscopy. Low-frequency infrared and Raman active modes are observed above and below the charge-ordering temperature T(co) is approximately equal to 200 K over a narrow interval approximately equal to 1-2 meV approximately equal to 8-16 cm(-1)). A new infrared mode at approximately equal to 1 meV develops below approximately equal to 100 K. The temperature dependence of these modes shows that they are coupled to the charge- and spin-density-wave correlations in this system. These low-energy features are conjectured to originate in the gapped sliding motion of the chain and ladder subsystems, which are both incommensurate and charged.
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Affiliation(s)
- V K Thorsmølle
- Laboratory for Photonics and Interfaces, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
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Schlappa J, Chang CF, Hu Z, Schierle E, Ott H, Weschke E, Kaindl G, Huijben M, Rijnders G, Blank DHA, Tjeng LH, Schüssler-Langeheine C. Resonant soft x-ray scattering from stepped surfaces of SrTiO3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:035501. [PMID: 22179392 DOI: 10.1088/0953-8984/24/3/035501] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We studied the resonant diffraction signal from stepped surfaces of SrTiO(3) at the Ti 2p → 3d (L(2,3)) resonance in comparison with x-ray absorption (XAS) and specular reflectivity data. The steps on the surface form an artificial superstructure suitable as a model system for resonant soft x-ray diffraction. A small step density on the surface is sufficient to produce a well defined diffraction peak. We determined the optical parameters of the sample across the resonance and found that the differences between the energy dependence of the x-ray absorption signal, the specular reflectivity and the step-related peak reflect the different quantities probed in these signals. When recorded at low incidence or detection angles, XAS and specular reflectivity spectra are strongly distorted by the changes of the angle of total reflection with energy. The resonant diffraction spectrum is less affected and can be used as a spectroscopic probe even in less favorable geometries.
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Affiliation(s)
- J Schlappa
- II. Physikalisches Institut, Universität zu Köln, Köln, Germany.
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Rusydi A, Ku W, Schulz B, Rauer R, Mahns I, Qi D, Gao X, Wee ATS, Abbamonte P, Eisaki H, Fujimaki Y, Uchida S, Rübhausen M. Experimental observation of the crystallization of a paired holon state. PHYSICAL REVIEW LETTERS 2010; 105:026402. [PMID: 20867721 DOI: 10.1103/physrevlett.105.026402] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2008] [Revised: 11/14/2009] [Indexed: 05/29/2023]
Abstract
An excitation at 201 meV is observed in the doped-hole ladder cuprate Sr14Cu24O41, using ultraviolet resonance Raman scattering with incident light at 3.7 eV polarized along the rungs. The excitation is of charge nature, with a temperature independent excitation energy, and can be understood via an intraladder pair-breaking process. The intensity tracks closely the order parameter of the charge density wave in the ladder CDW(L), but persists above its transition temperature T(CDW(L)), indicating a strong local pairing above the T(CDW(L)). The 201 meV excitation vanishes in La6Ca8Cu24O(41+δ), and La5Ca9Cu24O41 which are samples with no holes in the ladders. Our results suggest that the doped holes in the ladder are composite bosons consisting of paired holons that order below T(CDW).
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Affiliation(s)
- A Rusydi
- NanoCore, Department of Physics, Faculty of Science, National University of Singapore, 117542, Singapore.
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Ma C, Yang HX, Zeng LJ, Zhang Y, Wang LL, Chen L, Xiong R, Shi J, Li JQ. Structural modulation and hole distribution in Sr(14-x)Ca(x)Cu(24)O(41). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:215606. [PMID: 21825555 DOI: 10.1088/0953-8984/21/21/215606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Structural properties and hole distribution in the spin-ladder compound Sr(14-x)Ca(x)Cu(24)O(41) have been extensively investigated by transmission electron microscopy (TEM). The complex electron diffraction patterns and high-resolution TEM observations reveal a clear incommensurate structural modulation along the c-axis direction attributable to two mismatched sublattices; this modulation strongly depends on hole distribution in the compounds. The fine structures of the O K and Cu L(2,3) ionization edges for the Sr(14-x)Ca(x)Cu(24)O(41) compounds recorded under different conditions indicate that more doped holes reside in the chains than the ladders, and that substituting Ca for Sr atoms results in a charge redistribution between the chains and ladders. Based on the experimental findings, the theoretical results, including the partial density of states and optical conductivity spectra calculated by the density functional theory, are also discussed.
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Affiliation(s)
- C Ma
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
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Raichle M, Reehuis M, André G, Capogna L, Sofin M, Jansen M, Keimer B. Incommensurate spin-density modulation in a copper oxide chain compound with commensurate charge order. PHYSICAL REVIEW LETTERS 2008; 101:047202. [PMID: 18764362 DOI: 10.1103/physrevlett.101.047202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2008] [Indexed: 05/26/2023]
Abstract
Neutron diffraction has been used to determine the magnetic structure of Na8Cu5O10, a stoichiometric compound containing chains based on edge-sharing CuO4 plaquettes. The chains are doped with 2/5 hole per Cu site and exhibit long-range commensurate charge order with an onset well above room temperature. Below TN=23 K, the neutron data indicate long-range collinear magnetic order with a spin-density modulation whose propagation vector is commensurate along, and incommensurate perpendicular to, the chains. Competing interchain exchange interactions are discussed as a possible origin of the incommensurate magnetic order.
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Affiliation(s)
- M Raichle
- Max Planck Institute for Solid State Research, Heisenbergstr. 1, D-70569 Stuttgart, Germany
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