Phonon Spectroscopy by Electric Measurements of Coupled Quantum Dots

We propose phonon spectroscopy by electric measurements of the low-temperature conductance of coupled-quantum dots, specifically employing dephasing of the quantum electronic transport by the phonons. The setup we consider consists of a T-shaped double-quantum-dot (DQD) system in which only one of the dots (dot 1) is connected to external leads and the other (dot 2) is coupled solely to the first one. For noninteracting electrons, the differential conductance of such a system vanishes at a voltage located in-between the energies of the bonding and the anti-bonding states, due to destructive interference. When electron-phonon (e-ph) on the DQD is invoked, we find that, at low temperatures, phonon emission taking place on dot 1 does not affect the interference, while phonon emission from dot 2 suppresses it. The amount of this suppression, as a function of the bias voltage, follows the effective e-ph coupling reflecting the phonon density of states and can be used for phonon spectroscopy.Comment: 9 pages, 6 figure

Evolution of a collapsing and exploding Bose-Einstein condensate in different trap symmetries

Based on the time-dependent Gross-Pitaevskii equation we study the evolution of a collapsing and exploding Bose-Einstein condensate in different trap symmetries to see the effect of confinement on collapse and subsequent explosion, which can be verified in future experiments. We make prediction for the evolution of the shape of the condensate and the number of atoms in it for different trap symmetries (cigar to pancake) as well as in the presence of an optical lattice potential. We also make prediction for the jet formation in different cases when the collapse is suddenly terminated by changing the scattering length to zero via a Feshbach resonance.Comment: 8 pages, 11 ps figures, Physical Review

Magnetic pyroxenes LiCrGe2O6 and LiCrSi2O6: dimensionality crossover in a non-frustrated S=3/2 Heisenberg model

The magnetism of magnetoelectric $S$ = 3/2 pyroxenes LiCrSi$_2$O$_6$ and LiCrGe$_2$O$_6$ is studied by density functional theory (DFT) calculations, quantum Monte Carlo (QMC) simulations, neutron diffraction, as well as low-field and high-field magnetization measurements. In contrast with earlier reports, we find that the two compounds feature remarkably different, albeit non-frustrated magnetic models. In LiCrSi$_2$O$_6$, two relevant exchange integrals, $J_1 \simeq$ 9 K along the structural chains and $J_{\text{ic1}}$ $\simeq$ 2 K between the chains, form a 2D anisotropic honeycomb lattice. In contrast, the spin model of LiCrGe$_2$O$_6$ is constituted of three different exchange couplings. Surprisingly, the leading exchange $J_{\text{ic1}}$ $\simeq$ 2.3 K operates between the chains, while $J_1$ $\simeq$ 1.2 K is about two times smaller. The additional interlayer coupling $J_{\text{ic2}}$ $\simeq$ $J_1$ renders this model 3D. QMC simulations reveal excellent agreement between our magnetic models and the available experimental data. Underlying mechanisms of the exchange couplings, magnetostructural correlations, as well as implications for other pyroxene systems are discussed.Comment: 11 pages, 8 figures, 3 tables + Supplementary informatio

The UW solution for canine kidney preservation: Its specific effect on renal hemodynamics and microvasculature

The preservation effects of UW solution on renal hemodynamics and microvascular systems were studied in canine kidney autografts. In 72-hr UW-preserved kidneys, the microvessels of both cortex and medulla were completely visualized with silicon rubber compound 1 hr after reperfusion. Histology also showed extremely well-preserved arterioglomerular and tubular systems. These results were correlated with good renal blood flow, prompt recovery of posttransplant graft function, and 100% two-week survival of dogs. In contrast, kidneys preserved for 72 hr with Euro-Collins solution showed necrotic and obstructive changes of the microvasculature and deterioration of renal hemodynamics. In 120-hr UW-preserved kidneys, the microcirculation of the medullary region became poor after reflow when there was fairly intact perfusion of the cortical region, indicating an ischemia-related intrarenal blood flow maldistribution. The 120-hr kidneys subsequently failed in spite of having a good blood flow and morphologically well-maintained microvasculature after reperfusion. These data demonstrated that much, but not all, of the beneficial effect of UW solution in kidney preservation might be attributed to its remarkable protection of renal microvasculature. Correction of intrarenal blood maldistribution caused by a discrepancy in tolerance to ischemia of the vascular and tubular systems might be important in successfully preserving the kidney for 120 hr. © 1989 by Williams & Wilkins

Structural, orbital, and magnetic order in vanadium spinels

Vanadium spinels (ZnV_2O_4, MgV_2O_4, and CdV_2O_4) exhibit a sequence of structural and magnetic phase transitions, reflecting the interplay of lattice, orbital, and spin degrees of freedom. We offer a theoretical model taking into account the relativistic spin-orbit interaction, collective Jahn-Teller effect, and spin frustration. Below the structural transition, vanadium ions exhibit ferroorbital order and the magnet is best viewed as two sets of antiferromagnetic chains with a single-ion Ising anisotropy. Magnetic order, parametrized by two Ising variables, appears at a tetracritical point.Comment: v3: streamlined introductio

Fluctuation Theorem with Information Exchange: Role of Correlations in Stochastic Thermodynamics

We establish the fluctuation theorem in the presence of information exchange between a nonequilibrium system and other degrees of freedom such as an observer and a feedback controller, where the amount of information exchange is added to the entropy production. The resulting generalized second law sets the fundamental limit of energy dissipation and energy cost during the information exchange. Our results apply not only to feedback-controlled processes but also to a much broader class of information exchanges, and provides a unified framework of nonequilibrium thermodynamics of measurement and feedback control.Comment: To appear in PR

Macroscopic quantum tunneling and phase diffusion in a La2−x_{2-x}Srx_xCuO4_4 intrinsic Josephson junction stack

We performed measurements of switching current distribution in a submicron La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) intrinsic Josephson junction (IJJ) stack in a wide temperature range. The escape rate saturates below approximately 2\,K, indicating that the escape event is dominated by a macroscopic quantum tunneling (MQT) process with a crossover temperature $T^{*}\approx2\,$K. We applied the theory of MQT for IJJ stacks, taking into account dissipation and the phase re-trapping effect in the LSCO IJJ stack. The theory is in good agreement with the experiment both in the MQT and in the thermal activation regimes.Comment: 9 pages, 7 figure