arXiv subjects

A. J. Epstein

Publications and source records attributed to A. J. Epstein.

3 recordsLinked to original sources

arXiv2011

Electrical spin injection from an organic-based ferrimagnet in a hybrid organic/inorganic heterostructure

We report the successful extraction of spin polarized current from the organic-based room temperature ferrimagnetic semiconductor V[TCNE]x (x~2, TCNE: tetracyanoethylene; TC ~ 400 K, EG ~ 0.5 eV, s ~ 10-2 S/cm) and its subsequent injection into a GaAs/AlGaAs light-emitting diode (LED). The spin current tracks the magnetization of V[TCNE]x~2, is weakly temperature dependent, and exhibits heavy hole / light hole asymmetry. This result has implications for room temperature spintronics and the use of inorganic materials to probe spin physics in organic and molecular systems.

cond-mat.mtrl-sci↗

arXiv1999

Distribution of time-constants for tunneling through a 1D Disordered Chain

The dynamics of electronic tunneling through a disordered 1D chain of finite length is considered. We calculate distributions of the transmission coefficient T, Wigner delay time and, $τ_ϕ$ and the transport time, $τ_t=Tτ_ϕ$. The central bodies of these distributions have a power-law form, what can be understood in terms of the resonant tunneling through localised states.

cond-mat.dis-nn↗

arXiv1998

Hopping Conductivity of a Nearly-1d Fractal: a Model for Conducting Polymers

We suggest treating a conducting network of oriented polymer chains as an anisotropic fractal whose dimensionality D=1+εis close to one. Percolation on such a fractal is studied within the real space renormalization group of Migdal and Kadanoff. We find that the threshold value and all the critical exponents are strongly nonanalytic functions of εas εtends to zero, e.g., the critical exponent of conductivity is ε^{-2}\exp (-1-1/ε). The distribution function for conductivity of finite samples at the percolation threshold is established. It is shown that the central body of the distribution is given by a universal scaling function and only the low-conductivity tail of distribution remains $ε$-dependent. Variable range hopping conductivity in the polymer network is studied: both DC conductivity and AC conductivity in the multiple hopping regime are found to obey a quasi-1d Mott law. The present results are consistent with electrical properties of poorly conducting polymers.

cond-mat.dis-nn↗