Modeling the underlying mechanisms for organic memory devices: Tunneling, electron emission and oxygen adsorbing

We present a combined experimental and theoretical study to get insight into both memory and negative differential resistance (NDR) effect in organic memory devices. The theoretical model we propose is simply a one-dimensional metallic island array embedding within two electrodes. We use scattering operator method to evaluate the tunneling current among the electrode and islands to establish the basic bistable I-V curves for several devices. The theoretical results match the experiments very well, and both memory and NDR effect could be understood comprehensively. The experimental correspondence, say, the experiment of changing the pressure of oxygen, is addressed as well.Comment: 5 pages, 3 figure

Checkerboard charge density wave and pseudogap in high-TcT_{c} cuprates

We consider the scenario where a 4-lattice constant, rotationally symmetric charge density wave (CDW) is present in the underdoped cuprates. We prove a theorem that puts strong constraint on the possible form factor of such a CDW. We demonstrate, within mean-field theory, that a particular form factor within the allowed class describes the angle-resolved photoemission and scan tunneling spectroscopy well. We conjecture that the ``large pseudogap'' in cuprates is the consequence of this type of charge density wave.Comment: We add a new section II on the symmetry property of the checkerboard CD

Phonon Effects on Spin-Charge Separation in One Dimension

Phonon effects on spin-charge separation in one dimension are investigated through the calculation of one-electron spectral functions in terms of the recently developed cluster perturbation theory together with an optimized phonon approach. It is found that the retardation effect due to the finiteness of phonon frequency suppresses the spin-charge separation and eventually makes it invisible in the spectral function. By comparing our results with experimental data of TTF-TCNQ, it is observed that the electron-phonon interaction must be taken into account when interpreting the ARPES data.Comment: 5 pages, 5 figures, minor differences with the published version in Physical Review Letter

Reversal of Thermal Rectification in Quantum Systems

We study thermal transport in anisotropic Heisenberg spin chains using the quantum master equation. It is found that thermal rectification changes sign when the external homogeneous magnetic field is varied. This reversal also occurs when the magnetic field becomes inhomogeneous. Moreover, we can tune the reversal of rectification by temperatures of the heat baths, the anisotropy and size of the spin chains.Comment: 4 pages, 7 figure