48 research outputs found
Momentum Dependent Charge Excitations of Two-Leg Ladder: Resonant Inelastic X-ray Scattering of (La,Sr,Ca)14Cu24O41
Momentum dependent charge excitations of a two-leg ladder are investigated by
resonant inelastic x-ray scattering of (La,Sr,Ca)14Cu24O41. In contrast to the
case of a square lattice, momentum dependence of the Mott gap excitation of the
ladder exhibits little change upon hole-doping, indicating the formation of
hole pairs. Theoretical calculation based on a Hubbard model qualitatively
explains this feature. In addition, experimental data shows intraband
excitation as continuum intensity below the Mott gap and it appears at all the
momentum transfers simultaneously. The intensity of the intraband excitation is
proportional to the hole concentration of the ladder, which is consistent with
optical conductivity measurements.Comment: 7 page
Field-induced magnetic order in LaSrCuO (x = 0.10, 0.115, 0.13) studied by in-plane thermal conductivity measurements
We have measured the thermal conductivity in the -plane of
LaSrCuO ( 0.10, 0.115, 0.13) in magnetic fields up to 14 T
parallel to the c-axis and also parallel to the -plane. By the application
of magnetic fields parallel to the c-axis, the thermal conductivity has been
found to be suppressed at low temperatures below the temperature
which is located above the superconducting transition temperature and is almost
independent of the magnitude of the magnetic field. The suppression is marked
in 0.10 and 0.13, while it is small in 0.115. Furthermore, no
suppression is observed in the 1 % Zn-substituted
LaSrCuZnO with 0.115. Taking into
account the experimental results that the temperature dependence of the
relative reduction of the thermal conductivity is quite similar to the
temperature dependence of the intensity of the incommensurate magnetic Bragg
peak corresponding to the static stripe order and that the Zn substitution
tends to stabilize the static order, it is concluded that the suppression of
the thermal conductivity in magnetic fields is attributed to the development of
the static stripe order. The present results suggest that the field-induced
magnetic order in LaSrCuO originates from the pinning of the
dynamical stripes of spins and holes by vortex cores.Comment: 8 pages, 5 figures. Fig. 1 has been modifie
Diet and Energy-Sensing Inputs Affect TorC1-Mediated Axon Misrouting but Not TorC2-Directed Synapse Growth in a Drosophila Model of Tuberous Sclerosis
The Target of Rapamycin (TOR) growth regulatory system is influenced by a number of different inputs, including growth factor signaling, nutrient availability, and cellular energy levels. While the effects of TOR on cell and organismal growth have been well characterized, this pathway also has profound effects on neural development and behavior. Hyperactivation of the TOR pathway by mutations in the upstream TOR inhibitors TSC1 (tuberous sclerosis complex 1) or TSC2 promotes benign tumors and neurological and behavioral deficits, a syndrome known as tuberous sclerosis (TS). In Drosophila, neuron-specific overexpression of Rheb, the direct downstream target inhibited by Tsc1/Tsc2, produced significant synapse overgrowth, axon misrouting, and phototaxis deficits. To understand how misregulation of Tor signaling affects neural and behavioral development, we examined the influence of growth factor, nutrient, and energy sensing inputs on these neurodevelopmental phenotypes. Neural expression of Pi3K, a principal mediator of growth factor inputs to Tor, caused synapse overgrowth similar to Rheb, but did not disrupt axon guidance or phototaxis. Dietary restriction rescued Rheb-mediated behavioral and axon guidance deficits, as did overexpression of AMPK, a component of the cellular energy sensing pathway, but neither was able to rescue synapse overgrowth. While axon guidance and behavioral phenotypes were affected by altering the function of a Tor complex 1 (TorC1) component, Raptor, or a TORC1 downstream element (S6k), synapse overgrowth was only suppressed by reducing the function of Tor complex 2 (TorC2) components (Rictor, Sin1). These findings demonstrate that different inputs to Tor signaling have distinct activities in nervous system development, and that Tor provides an important connection between nutrient-energy sensing systems and patterning of the nervous system
1/8 anomaly in the excess-oxygen-doped La<sub>1.8</sub>Nd<sub>0.2</sub>Cu<sub>1-y</sub>Zn<sub>y</sub>O<sub>4+δ</sub>
We have found the 1/8 anomaly, namely, the anomalous suppression of
superconductivity at p (the hole concentration per Cu) = 1/8 in the
excess-oxygen-doped La_1.8_Nd_0.2_Cu_1-y_Zn_y_O_4+\delta_, where the excess
oxygen is doped by the electrochemical technique and the phase separation of
the excess oxygen is suppressed. The 1/8 anomaly has become marked by the 1 %
substitution of Zn for Cu. The muon-spin-relaxation measurements have revealed
that the magnetic correlation develops at low temperatures below about 50 K in
both Zn-free and 1 % Zn-substituted samples with p = 1/8. Clear precession of
muon spins suggesting the formation of a long-range magnetic order has been
observed below 1 K in the 1 % Zn-substituted sample with p = 1/8. These results
are consistent with the stripe-pinning model.Comment: 8 pages, 10 figures, to be published in Phys. Rev.