9,757 research outputs found
Quasiparticle spectroscopy and high-field phase diagrams of cuprate superconductors -- An investigation of competing orders and quantum criticality
We present scanning tunneling spectroscopic and high-field thermodynamic
studies of hole- and electron-doped (p- and n-type) cuprate superconductors.
Our experimental results are consistent with the notion that the ground state
of cuprates is in proximity to a quantum critical point (QCP) that separates a
pure superconducting (SC) phase from a phase comprised of coexisting SC and a
competing order, and the competing order is likely a spin-density wave (SDW).
The effect of applied magnetic field, tunneling current, and disorder on the
revelation of competing orders and on the low-energy excitations of the
cuprates is discussed.Comment: 10 pages, 5 figures. Accepted for publication in the International
Journal of Modern Physics B. (Correspondence author: Nai-Chang Yeh, e-mail:
[email protected]
Interfacial strain in AlxGa1–xAs layers on GaAs
Detailed analysis of x-ray rocking curves was used to determine the depth profile of strain and composition in a 2500-Å-thick layer of AlxGa1–xAs grown by metalorganic chemical vapor deposition on 100 GaAs. The x value and layer thickness were in good agreement with the values expected from growth parameters. The presence of a transition region, 280 Å thick, was detected by the rocking curve. In this region, the Al concentration varies smoothly from 0 to 0.87. Measurement and control of the sharpness of such interfaces has important implications for heterojunction devices
Dimensionality of superconductivity in the infinite-layer high-temperature cuprate Sr0.9M0.1CuO2 (M = La, Gd)
The high magnetic field phase diagram of the electron-doped infinite layer
high-temperature superconducting (high-T_c) compound Sr_{0.9}La_{0.1}CuO_2 was
probed by means of penetration depth and magnetization measurements in pulsed
fields to 60 T. An anisotropy ratio of 8 was detected for the upper critical
fields with H parallel (H_{c2}^{ab}) and perpendicular (H_{c2}^c) to the CuO_2
planes, with H_{c2}^{ab} extrapolating to near the Pauli paramagnetic limit of
160 T. The longer superconducting coherence length than the lattice constant
along the c-axis indicates that the orbital degrees of freedom of the pairing
wavefunction are three dimensional. By contrast, low-field magnetization and
specific heat measurements of Sr_{0.9}Gd_{0.1}CuO_2 indicate a coexistence of
bulk s-wave superconductivity with large moment Gd paramagnetism close to the
CuO_2 planes, suggesting a strong confinement of the spin degrees of freedom of
the Cooper pair to the CuO_2 planes. The region between H_{c2}^{ab} and the
irreversibility line in the magnetization, H_{irr}^{ab}, is anomalously large
for an electron-doped high-T_c cuprate, suggesting the existence of additional
quantum fluctuations perhaps due to a competing spin-density wave order.Comment: 4 pages, 4 figures, submitted to Phys. Rev. B, Rapid Communications
(2004). Corresponding author: Nai-Chang Yeh (E-mail: [email protected]
Experimental investigation of the competing orders and quantum criticality in hole- and electron-doped cuprate superconductors
We investigate the issues of competing orders and quantum criticality in cuprate superconductors via experimental studies of the high-field thermodynamic phase diagrams and the quasiparticle tunneling spectroscopy. Substantial field-induced quantum fluctuations are found in all cuprates investigated, and the corresponding correlation with quasiparticle spectra suggest that both electron- (n-type) and hole-doped (p-type) cuprate superconductors are in close proximity to a quantum critical point that separates a pure superconducting (SC) phase from a phase consisting of coexisting SC and a competing order. We further suggests that the relevant competing order is likely a spin-density wave (SDW) or a charge density wave (CDW), which can couple efficiently to an in-plane Cu-O bond stretching longitudinal optical (LO) phonon mode in the p-type cuprates but not in the n-type cuprates. This cooperative interaction may account for the pseudogap phenomenon above T, only in the p-type cuprate superconductors
Infrared studies of a La_(0.67)Ca_(0.33)MnO_3 single crystal: Optical magnetoconductivity in a half-metallic ferromagnet
The infrared reflectivity of a La_(0.67)Ca_(0.33)MnO_3 single crystal is studied over a broad range of temperatures (78–340 K), magnetic fields (0–16 T), and wave numbers (20–9000cm^(-1)). The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near 5000cm-1 in the ferromagnetic state below the Curie temperature T_C=307K. Various features of the optical conductivity bear striking resemblance to recent theoretical predictions based on the interplay between the double exchange interaction and the Jahn-Teller electron-phonon coupling. A large optical magnetoconductivity is observed near T_C
Infrared Studies of a La_{0.67}Ca_{0.33}MnO_3 Single Crystal: Optical Magnetoconductivity in a Half-Metallic Ferromagnet
The infrared reflectivity of a single crystal
is studied over a broad range of temperatures (78-340 K), magnetic fields (0-16
T), and wavenumbers (20-9000 cm). The optical conductivity gradually
changes from a Drude-like behavior to a broad peak feature near 5000 cm
in the ferromagnetic state below the Curie temperature . Various
features of the optical conductivity bear striking resemblance to recent
theoretical predictions based on the interplay between the double exchange
interaction and the Jahn-Teller electron-phonon coupling. A large optical
magnetoconductivity is observed near .Comment: 4 pages, 4 figures, Latex, PostScript; The 7th Joint MMM-Intermag
Conference,San Francisco, January 6-9, 1998; The Int. Conf. on Strongly
Correlated Electron Systems, Paris, July 15-18,199
Macroscopic evidence for quantum criticality and field-induced quantum fluctuations in cuprate superconductors
We present macroscopic experimental evidence for field-induced microscopic
quantum fluctuations in different hole- and electron-type cuprate
superconductors with varying doping levels and numbers of CuO layers per
unit cell. The significant suppression of the zero-temperature in-plane
magnetic irreversibility field relative to the paramagnetic field in all
cuprate superconductors suggests strong quantum fluctuations due to the
proximity of the cuprates to quantum criticality.Comment: 3 figures. To appear in Phys. Rev. B, Rapid Communications (2007).
For correspondence, contact: Nai-Chang Yeh (e-mail: [email protected]
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