Electrical spin injection and detection in an InAs quantum well

We demonstrate fully electrical detection of spin injection in InAs quantum wells. A spin polarized current is injected from a NiFe thin film to a two-dimensional electron gas (2DEG) made of InAs based epitaxial multi-layers. Injected spins accumulate and diffuse out in the 2DEG, and the spins are electrically detected by a neighboring NiFe electrode. The observed spin diffusion length is 1.8 um at 20 K. The injected spin polarization across the NiFe/InAs interface is 1.9% at 20 K and remains at 1.4% even at room temperature. Our experimental results will contribute significantly to the realization of a practical spin field effect transistor

Phase Dependent Thermopower in Andreev Interferometers

We report measurements of the thermopower S of mesoscopic Andreev interferometers, which are hybrid loops with one arm fabricated from a superconductor (Al), and one arm from a normal metal (Au). S depends on the phase of electrons in the interferometer, oscillating as a function of magnetic flux with a period of one flux quantum (= h/2e). The magnitude of S increases as the temperature T is lowered, reaching a maximum around T = 0.14 K, and decreases at lower temperatures. The symmetry of S oscillations with respect to magnetic flux depends on the topology of the sample.Comment: 4 pages, 4 figure

Synaptic Characteristics of an Ultrathin Hexagonal Boron Nitride (h-BN) Diffusive Memristor

Nano-sized two-terminal memristor exhibiting volatile threshold switching (TS) is a promising candidate for the emulation of biological synaptic functions to realize efficient neuromorphic computing systems. The Ca2+ dynamics play a vital role in generating a temporal response for neural functions by changing the synaptic weight of biological synapses. Herein, a thinnest synaptic device is fabricated demonstrating drift dynamics of Ag+ migration through the exfoliated h-BN sheets, which emulates neuromorphic computing operations. The TS characteristics with a large ION/OFF up to ≈105 lead to bio-synaptic applications, including short-term and long-term memory. The experimental realization of the synaptic behavior is demonstrated with paired-pulse facilitation (PPF), spike-rate-dependent plasticity (SRDP), and transition from short-term plasticity (STP) to long-term plasticity (LTP). The transition from STP to LTP in this synaptic device verifies the Atkinson and Shiffrin psychological model of human brain learning experimentally. The input pulses with different spike-times are used to replicate the synaptic functionalities. The two-terminal diffusive memristors constructed with thin sheets of 2D-flexible h-BN resistive materials may lead to flexible neuromorphic devices for biological applications11Nsciescopu

High-frequency impedance of single-walled carbon nanotube networks on transparent flexible substrate

Transparent and flexible networks with randomly distributed single-walled carbon nanotubes (SWCNTs) are emerging as novel materials for various applications, particularly as electronic materials. We investigate the frequency-dependent impedance measurements up to 20 GHz, of single-walled carbon nanotube networks on transparent and flexible substrates, by using two different techniques: two probe and Corbino reflectometry setups. The thickness and roughness of the thin film of SWCNT are examined by AFM. The impedance measurements show the cut-off frequency increases with increasing the density of SWCNT. The log-log plot of low frequency impedance as a function of the cut-off frequency shows the same slope in both measuring techniques. The slope is independent on sample geometries, which is characteristic of a totally disordered system. The cut-off frequencies observed by the Corbino reflectometry technique are 3 orders of magnitude higher than those observed by two-probe technique even for the same SWCNTs density network. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimPeer ReviewedPostprint (published version