15,322 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]
Vortex pinning by cylindrical defects in type-II superconductors: Numerical solutions to the Ginzburg-Landau equations
We numerically integrate the one-dimensional, cylindrically symmetric Ginzburg-Landau equations to calculate the spatial variation of the order parameter and supercurrents for a vortex trapped by a cylindrical defect. We use the resulting field distributions to estimate the pinning energy, and make use of the vortex/two-dimensional boson analogy to calculate the depinning temperature. The microscopic behavior oi the fields depends on the size, and the conductivity of the cylindrical defect appears to be important for the pinning
Investigating the Physical Origin of Unconventional Low-Energy Excitations and Pseudogap Phenomena in Cuprate Superconductors
We investigate the physical origin of unconventional low-energy excitations
in cuprate superconductors by considering the effect of coexisting competing
orders (CO) and superconductivity (SC) and of quantum fluctuations and other
bosonic modes on the low-energy charge excitation spectra. By incorporating
both SC and CO in the bare Green's function and quantum phase fluctuations in
the self-energy, we can consistently account for various empirical findings in
both the hole- and electron-type cuprates, including the excess subgap
quasiparticle density of states, ``dichotomy'' in the fluctuation-renormalized
quasiparticle spectral density in momentum space, and the occurrence and
magnitude of a low-energy pseudogap being dependent on the relative gap
strength of CO and SC. Comparing these calculated results with experiments of
ours and others, we suggest that there are two energy scales associated with
the pseudogap phenomena, with the high-energy pseudogap probably of magnetic
origin and the low-energy pseudogap associated with competing orders.Comment: 10 pages, 5 figures. Invited paper for the 2006 Taiwan International
Conference on Superconductivity. Correspondence author: Nai-Chang Yeh
(e-mail: [email protected]
Two-dimensional matrix algorithm using detrended fluctuation analysis to distinguish Burkitt and diffuse large B-cell lymphoma
Copyright © 2012 Rong-Guan Yeh et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.A detrended fluctuation analysis (DFA) method is applied to image analysis. The 2-dimensional (2D) DFA algorithms is proposed
for recharacterizing images of lymph sections. Due to Burkitt lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL), there
is a significant different 5-year survival rates after multiagent chemotherapy. Therefore, distinguishing the difference between BL
and DLBCL is very important. In this study, eighteen BL images were classified as group A, which have one to five cytogenetic
changes. Ten BL images were classified as group B, which have more than five cytogenetic changes. Both groups A and B BLs are
aggressive lymphomas, which grow very fast and require more intensive chemotherapy. Finally, ten DLBCL images were classified
as group C. The short-term correlation exponent α1 values of DFA of groups A, B, and C were 0.370 ± 0.033, 0.382 ± 0.022, and
0.435 ± 0.053, respectively. It was found that α1 value of BL image was significantly lower (P < 0.05) than DLBCL. However, there
is no difference between the groups A and B BLs. Hence, it can be concluded that α1 value based on DFA statistics concept can
clearly distinguish BL and DLBCL image.National Science Council (NSC) of Taiwan the Center for Dynamical Biomarkers and
Translational Medicine, National Central University, Taiwan (also sponsored by National Science Council)
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]
A parallel VLSI architecture for a digital filter of arbitrary length using Fermat number transforms
A parallel architecture for computation of the linear convolution of two sequences of arbitrary lengths using the Fermat number transform (FNT) is described. In particular a pipeline structure is designed to compute a 128-point FNT. In this FNT, only additions and bit rotations are required. A standard barrel shifter circuit is modified so that it performs the required bit rotation operation. The overlap-save method is generalized for the FNT to compute a linear convolution of arbitrary length. A parallel architecture is developed to realize this type of overlap-save method using one FNT and several inverse FNTs of 128 points. The generalized overlap save method alleviates the usual dynamic range limitation in FNTs of long transform lengths. Its architecture is regular, simple, and expandable, and therefore naturally suitable for VLSI implementation
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