934 research outputs found
Quantum Impurities in the Two-Dimensional Spin One-Half Heisenberg Antiferromagnet
The study of randomness in low-dimensional quantum antiferromagnets is at the
forefront of research in the field of strongly correlated electron systems, yet
there have been relatively few experimental model systems. Complementary
neutron scattering and numerical experiments demonstrate that the spin-diluted
Heisenberg antiferromagnet La2Cu(1-z)(Zn,Mg)zO4 is an excellent model material
for square-lattice site percolation in the extreme quantum limit of spin
one-half. Measurements of the ordered moment and spin correlations provide
important quantitative information for tests of theories for this complex
quantum-impurity problem.Comment: 11 pages, 3 figures. NOTE: possible errors in PDF version of Fig. 1.
View postscript version of figure if possibl
Quantitative Test of SO(5) Symmetry in the Vortex State of
By numerically solving models with competing superconducting and
antiferromagnetic orders, we study the magnetic field dependence of the
antiferromagnetic moment in both the weak and strong field regimes. Through a
omparison with the neutron scattering results of Kang et al and Matsuura et
al.on , we conclude that this system is close to a
SO(5) symmetric critical point. We also make a quantitative prediction on
increasing the upper critical field and the superconducting transition
temperature by applying an in-plane magnetic field.Comment: 4 pages, 3 figures v3: final version PRL 92, 107002 (2004
Electron-phonon interaction in n-doped cuprates: an Inelastic X-ray Scattering study
Inelastic x-ray scattering (IXS) with very high (meV) energy resolution has
become a valuable spectroscopic tool, complementing the well established
coherent inelastic neutron scattering (INS) technique for phonon dispersion
investigations. In the study of crystalline systems IXS is a viable alternative
to INS, especially in cases where only small samples are available. Using IXS,
we have measured the phonon dispersion of Nd_{1.86}Ce_{0.14}CuO_{4+\delta}
along the [x,0,0] and [x,x,0] in-plane directions. Compared to the undoped
parent compound, the two highest longitudinal optical (LO) phonon branches are
shifted to lower energies because of Coulomb-screening effects brought about by
the doped charge carriers. An additional anomalous softening of the highest
branch is observed around q=(0.2,0,0). This anomalous softening, akin to what
has been observed in other compounds, provides evidence for a strong
electron-phonon coupling in the electron-doped high-temperature
superconductors.Comment: Proceedings of the SATT11 conference, Vietri sul Mare - Italy (March
2002); accepted for publication on Int. J. Mod. Phys.
Non-Markovian effect on the quantum discord
We study the non-Markovian effect on the dynamics of the quantum discord by
exactly solving a model consisting of two independent qubits subject to two
zero-temperature non-Markovian reservoirs, respectively. Considering the two
qubits initially prepared in Bell-like or extended Werner-like states, we show
that there is no occurrence of the sudden death, but only instantaneous
disappearance of the quantum discord at some time points, in comparison to the
entanglement sudden death in the same range of the parameters of interest. It
implies that the quantum discord is more useful than the entanglement to
describe quantum correlation involved in quantum systems.Comment: 5 pages, 5 figure
Spin correlations in the electron-doped high-transition-temperature superconductor Nd{2-x}Ce{x}CuO{4+/-delta}
High-transition-temperature (high-Tc) superconductivity develops near
antiferromagnetic phases, and it is possible that magnetic excitations
contribute to the superconducting pairing mechanism. To assess the role of
antiferromagnetism, it is essential to understand the doping and temperature
dependence of the two-dimensional antiferromagnetic spin correlations. The
phase diagram is asymmetric with respect to electron and hole doping, and for
the comparatively less-studied electron-doped materials, the antiferromagnetic
phase extends much further with doping [1, 2] and appears to overlap with the
superconducting phase. The archetypical electron-doped compound
Nd{2-x}Ce{x}CuO{4\pm\delta} (NCCO) shows bulk superconductivity above x \approx
0.13 [3, 4], while evidence for antiferromagnetic order has been found up to x
\approx 0.17 [2, 5, 6]. Here we report inelastic magnetic neutron-scattering
measurements that point to the distinct possibility that genuine long-range
antiferromagnetism and superconductivity do not coexist. The data reveal a
magnetic quantum critical point where superconductivity first appears,
consistent with an exotic quantum phase transition between the two phases [7].
We also demonstrate that the pseudogap phenomenon in the electron-doped
materials, which is associated with pronounced charge anomalies [8-11], arises
from a build-up of spin correlations, in agreement with recent theoretical
proposals [12, 13].Comment: 5 pages, 4 figure
Expression of estrogen receptor (ER)-alpha and ER-beta in normal and malignant prostatic epithelial cells: regulation by methylation and involvement in growth regulation
The aim of the current study is to demonstrate normal and malignant prostatic epithelial cells (PrECs) as targets for receptor-mediated estrogenic and antiestrogenic action. Using an improved protocol, we have successfully isolated and maintained highly enriched populations of normal PrECs from ultrasound-guided peripheral zone biopsies, individually determined to be morphologically normal. Semiquantitative reverse transcription-PCR analyses were used to determine whether transcripts of estrogen receptor (ER)-alpha and those of ER-beta were expressed in our normal PrEC primary cultures, in a commercially available PrEC preparation (PrEC; Clontech), in an immortalized PrEC line established from a benign prostatic hyperplasia specimen (BPH-1), and in three prostatic cancer cell lines (LNCaP, PC-3, and DU145). Expression levels of ER-alpha and ER-beta transcripts were related to those of two estrogen-responsive genes [progesterone receptor (PR) and pS2], at the message levels, to gain insights into the functionality of the ER subtypes in PrECs. Interestingly, only transcripts of ER-beta, but not those of ER-alpha, were found in our primary cultures of normal PrECs, along with both PR and pS2 mRNA. These data strongly suggest that estrogen action was signaled exclusively via ER-beta in normal human PrECs. In contrast, PrEC (Clontech) and BPH-1 cells expressed both ER-alpha and ER-beta transcripts and no PR nor pS2 mRNA in PrEC and only a minimal level of PR mRNA in BPH-1. Among the three prostate cancer cell lines, LNCaP expressed ER-beta mRNA along with transcripts of PR and pS2, DU145 expressed messages of ER-beta and PR, and PC-3 cells exhibited ER-alpha, ER-beta, and pS2 mRNA. Thus, unlike normal PrECs, expression patterns of these genes in malignant PrECs are more variable. Treatment of prostate cancer cells with demethylation agents effectively reactivated the expression of ER-alpha mRNA in LNCaP and DU145 and that of pS2 message in DU145. These findings provide experimental evidence that ER-alpha gene silencing in prostate cancer cells, and perhaps also in normal PrECs, are caused by DNA hypermethylation. To evaluate the potential of using antiestrogens as prostate cancer therapies, we have assessed the growth-inhibitory action of estrogens (estradiol and diethylstilbestrol) and antiestrogens (4-hydroxy-tamoxifen and ICI-182,780) on PC-3 and DU-145 cells. In PC-3 cells, which express both ER subtypes, estrogens as well as antiestrogens are effective inhibitors. In contrast, in DU145 cells, which express only ER-beta, antiestrogens, but not estrogens, are growth inhibitors. By comparison, ICI 182,780 is the more effective cell growth inhibitor. Importantly, the ICI 182,780-induced antiproliferative effects were reversed by cotreatment of DU145 cells with an ER-beta antisense oligonucleotide, hence lending additional support to a central role played by ER-beta in mediating growth-inhibitory action of antiestrogens
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