Dissipative tunneling at finite temperature

A simple theory is presented for the influence of a weakly coupled interaction system on the tunneling of a particle out of a metastable well. It is based on the standard model of momentum and energy transfer to an infinite set of oscillators and is applied to the case of phase tunneling in a Josephson contact. The distribution of the energy transfer and in particular the Debye-Waller factor for elastic processes is determined by the imaginary part of the dielectric function. For small damping γ the main influence of dissipation on the total tunneling probability is contained in a factor exp —AMγ(Δq)². The numerical coefficientA and the distance Δq under the barrier depend on the considered tunneling state andA(T) vanishes at a temperatureT ^* above which classical activation prevails. The tunneling probability of any level is therefore predicted to increase with temperature. In additional general expressions are derived for the correlation functions of a damped quantum oscillator in terms of the classical response of the interaction system.     

Spin polarized photoemission from NiMnSb

Spin polarized photoemission experiments are reported on NiMnSb which has been predicted to be a halfmetallic ferromagnet. The 100% polarization near photothreshold has not been observed. If an energy gap in the minority electron density-of-states should exist, it will be smaller than 0.5 eV.     

Analysis of spin polarized tunneling results

We report spin polarized tunneling results for Fe which confirm the original work of Tedrow et al. at MIT, and also use the data to illustrate an analysis which determines, with only qualitative reference to theoretical calculations, the true polarization index of the sample, provided the polarization is not too small.     

Microscopic calculations of spin polarized neutron matter at finite temperature

The properties of spin polarized neutron matter are studied both at zero and finite temperature within the framework of the Brueckner–Hartree–Fock formalism, using the Argonne v18 nucleon–nucleon interaction. The free energy, energy and entropy per particle are calculated for several values of the spin polarization, densities and temperatures together with the magnetic susceptibility of the system. The results show no indication of a ferromagnetic transition at any density and temperature.     

Spin tunneling in junctions with disordered ferromagnets

We provide compelling evidence to establish that, contrary to one's elementary guess, the tunneling spin polarization (TSP) of amorphous CoFeB is larger than that of fcc CoFeB. First-principles atomic and electronic structure calculations reveal striking agreement between the measured TSP and the predicted s-electron spin polarization. Given the disordered structure of the ternary alloy, not only do these results strongly endorse our communal understanding of tunneling through AlO(x), but they also portray the key concepts that demand primary consideration in such complex systems.     

Spin transport in the XXZ chain at finite temperature and momentum

We investigate the role of momentum for the transport of magnetization in the spin-1/2 Heisenberg chain above the isotropic point at finite temperature and momentum. Using numerical and analytical approaches, we analyze the autocorrelations of density and current and observe a finite region of the Brillouin zone with diffusive dynamics below a cutoff momentum, and a diffusion constant independent of momentum and time, which scales inversely with anisotropy. Lowering the temperature over a wide range, starting from infinity, the diffusion constant is found to increase strongly while the cutoff momentum for diffusion decreases. Above the cutoff momentum diffusion breaks down completely.     

相互作用量子点的自旋相关输运

介绍了与磁性电极耦合的量子点的近藤共振、单电子能级自旋劈裂、磁化和线性电导等物理性质．研究结果显示，当磁性电极磁矩取向相同的时候，线性电导在低温下呈现双峰结构．而近藤共振和单电子能级的自旋劈裂都可以通过电极的内部磁化强度来控制，可以用来产生自旋阀效应．     

Spin detection and manipulation with scanning tunneling microscopy

Over the past few decades, spin detection and manipulation at the atomic scale using scanning tunneling microcopy has matured, which has opened the possibility of realizing spin-based functional devices with single atoms and molecules.This article reviews the principle of spin polarized scanning tunneling microscopy and inelastic tunneling spectroscopy,which are used to measure the static spin structure and dynamic spin excitation, respectively. Recent progress will be presented, including complex spin structure, magnetization of single atoms and molecules, as well as spin excitation of single atoms, clusters, and molecules. Finally, progress in the use of spin polarized tunneling current to manipulate an atomic magnet is discussed.     

Zero bias tunneling conductance for high field superconductors

The zero bias tunneling conductance is investigated theoretically and shown to be a promising experimental tool for detecting first order phase transitions in high field superconductors. We calculate and evaluate numerically the zero bias tunneling conductance for arbitrary spin orbital mean free path. In doing the calculations we distinguish between thin films in a parallel field and high?-value materials in a perpendicular field. In the former case anomalous properties appear for sufficient long spin orbital mean free path. Finally we determine the minimum spin orbital mean free path which is compatible with a first order phase transition and show that it is much smaller than commonly believed.     

Coherence length effects in zero bias tunneling anomalies

Experiments were performed with Al-Al₂O₃-Al tunnel junctions fabricated by a new procedure supposed to produce a slight impurity layer inside the Al electrode. Impurities displaced at distances less than about 100 Å from the junction surface were found to be effective in causing zero bias anomalies.     

Spin and polarized current from Coulomb blockaded quantum dots

We report measurements of spin transitions for GaAs quantum dots in the Coulomb blockade regime and compare ground and excited state transport spectroscopy to direct measurements of the spin polarization of emitted current. Transport spectroscopy reveals both spin-increasing and spin-decreasing transitions, as well as higher-spin ground states, and allows g factors to be measured down to a single electron. The spin of emitted current in the Coulomb blockade regime, measured using spin-sensitive electron focusing, is found to be polarized along the direction of the applied magnetic field regardless of the ground state spin transition.     

Spin polarized quantum pump effect in zigzag graphene nanoribbons

The spin polarized adiabatic quantum pump effect in zigzag graphene nanoribbons has been numerically analyzed. Since the ground state of such a ribbon is antiferromagnetic (the opposite spin electrons are located on the opposite edges of the ribbon), the spin currents can be generated in this system with the help of the quantum pump effect when symmetry between the opposite spin states is broken. Two methods of this breaking by means of defects at the ribbon edge and the transverse electric field have been proposed. It has been shown that the generation of not only the electron and spin currents, but also the purely spin current is possible in both cases.