Counter Patent

Circuit for measuring wide range of pulse rates by utilizing high capacity counte

Circuit counts pulses and indicates time of occurrence of slow pulses

Counter includes one section which counts the first several pulses, and a second section which counts pulses from a clock between the beginning of a sampling interval and the receipt of the first pulse by the circuit. The number of clock pulses indicates receipt time of the first pulse

Transport through anisotropic magnetic molecules with partially ferromagnetic leads: Spin-charge conversion and negative differential conductance

We theoretically investigate inelastic transport through anisotropic magnetic molecules weakly coupled to one ferromagnetic and one nonmagnetic lead. We find that the current is suppressed over wide voltage ranges due to spin blockade. In this system, spin blockade is associated with successive spin flips of the molecular spins and depends on the anisotropy energy barrier. This leads to the appearance of a window of bias voltages between the Coulomb blockade and spin blockade regimes where the current is large and to negative differential conductance at low temperatures. Remarkably, negative differential conductance is also present close to room temperature. Spin-blockade behavior is accompanied by super-Poissonian shot noise, like in nonmagnetic quantum dots. Finally, we show that the charge transmitted through the molecule between initial preparation in a certain spin state and infinite time very strongly depends on the initial spin state in certain parameter ranges. Thus the molecule can act as a spin-charge converter, an effect potentially useful as a read-out mechanism for molecular spintronics.Comment: 8 pages with 5 figures, version as publishe

Spin amplification, reading, and writing in transport through anisotropic magnetic molecules

Inelastic transport through a single magnetic molecule weakly coupled to metallic leads is studied theoretically. We consider dynamical processes that are relevant for writing, storing, and reading spin information in molecular memory devices. Magnetic anisotropy is found to be crucial for slow spin relaxation. In the presence of anisotropy we find giant spin amplification: The spin accumulated in the leads if a bias voltage is applied to a molecule prepared in a spin-polarized state can be made exponentially large in a characteristic energy divided by temperature. For one ferromagnetic and one paramagnetic lead the molecular spin can be reversed by applying a bias voltage even in the absence of a magnetic field. We propose schemes for reading and writing spin information based on our findings.Comment: 5+ pages with 5 figure

Doping dependence of the Neel temperature in Mott-Hubbard antiferromagnets: Effect of vortices

The rapid destruction of long-range antiferromagnetic order upon doping of Mott-Hubbard antiferromagnetic insulators is studied within a generalized Berezinskii-Kosterlitz-Thouless renormalization group theory in accordance with recent calculations suggesting that holes dress with vortices. We calculate the doping-dependent Neel temperature in good agreement with experiments for high-Tc cuprates. Interestingly, the critical doping where long-range order vanishes at zero temperature is predicted to be xc ~ 0.02, independently of any energy scales of the system.Comment: 4 pages with 3 figures included, minor revisions, to be published in PR

Theory for Magnetism and Triplet Superconductivity in LiFeAs

Superconducting pnictides are widely found to feature spin-singlet pairing in the vicinity of an antiferromagnetic phase, for which nesting between electron and hole Fermi surfaces is crucial. LiFeAs differs from the other pnictides by (i) poor nesting properties and (ii) unusually shallow hole pockets. Investigating magnetic and pairing instabilities in an electronic model that incorporates these differences, we find antiferromagnetic order to be absent. Instead we observe almost ferromagnetic fluctuations which drive an instability toward spin-triplet p-wave superconductivity.Comment: Published versio