Spin Filtering through Single-Wall Carbon Nanotubes Functionalized with Single-Stranded DNA

High spin polarization materials or spin filters are key components in spintronics, a niche subfield of electronics where carrier spins play a functional role. Carrier transmission through these materials is "spin selective" i.e. these materials are able to discriminate between "up" and "down" spins. Common spin filters include transition metal ferromagnets and their alloys, with typical spin selectivity (or, polarization) ~50% or less. Here we consider carrier transport in an archetypical one-dimensional molecular hybrid in which a single wall carbon nanotube (SWCNT) is wrapped around by single stranded deoxyribonucleic acid (ssDNA). By magnetoresistance measurements we show that this system can act as a spin filter with maximum spin polarization approaching ~74% at low temperatures, significantly larger than transition metals under comparable conditions. Inversion asymmetric helicoidal potential of the charged ssDNA backbone induces a Rashba spin-orbit interaction in the SWCNT channel and polarizes carrier spins. Our results are consistent with recent theoretical work that predicted spin dependent conductance in ssDNA-SWCNT hybrid. Ability to generate highly spin polarized carriers using molecular functionalization can lead to magnet-less and contact-less spintronic devices in the future. This can eliminate the conductivity mismatch problem and open new directions for research in organic spintronics.Comment: Supplementary information file is available for free from the journal websit

Issues pertaining to D'yakonov-Perel' spin relaxation in quantum wire channels

We elucidate the origin and nature of the D'yakonov-Perel' spin relaxation in a quantum wire structure, showing (analytically) that there are three necessary conditions for it to exist: (i) transport must be multi-channeled, (ii) there must be a Rashba spin orbit interaction in the wire, and (iii) there must also be a Dresselhaus spin orbit interaction. Therefore, the only effective way to completely eliminate the D'yakonov-Perel' relaxation in compound semiconductor channels with structural and bulk inversion asymmetry is to ensure strictly single channeled transport. In view of that, recent proposals in the literature that advocate using multi-channeled quantum wires for spin transistors appear ill-advised

Spin transport in nanowires

We study high-field spin transport of electrons in a quasi one-dimensional channel of a $GaAs$ gate controlled spin interferometer (SPINFET) using a semiclassical formalism (spin density matrix evolution coupled with Boltzmann transport equation). Spin dephasing (or depolarization) is predominantly caused by D'yakonov-Perel' relaxation associated with momentum dependent spin orbit coupling effects that arise due to bulk inversion asymmetry (Dresselhaus spin orbit coupling) and structural inversion asymmetry (Rashba spin orbit coupling). Spin dephasing length in a one dimensional channel has been found to be an order of magnitude higher than that in a two dimensional channel. This study confirms that the ideal configuration for a SPINFET is one where the ferromagnetic source and drain contacts are magnetized along the axis of the channel. The spin dephasing length in this case is about 22.5 microns at lattice temperature of 30K and 10 microns at lattice temperature of 77 K for an electric field of 2 kV/cm. Spin dephasing length has been found to be weakly dependent on the driving electric field and strongly dependent on the lattice temperature

Decay of spin polarized hot carrier current in a quasi one-dimensional spin valve structure

We study the spatial decay of spin polarized hot carrier current in a spin-valve structure consisting of a semiconductor quantum wire flanked by half-metallic ferromagnetic contacts. The current decays because of D'yakonov-Perel' spin relaxation in the semiconductor caused by Rashba spin orbit interaction. The associated relaxation length is found to decrease with increasing lattice temperature (in the range 30-77 K) and exhibit a non-monotonic dependence on the electric field driving the current. The relaxation lengths are several tens of microns which are at least an order of magnitude larger than what has been theoretically calculated for two-dimensional structures at comparable temperatures, Rashba interaction strengths and electric fields. This improvement is a consequence of one-dimensional carrier confinement that does not necessarily suppress carrier scattering, but nevertheless suppresses D'yakonov-Perel' spin relaxation.Comment: 2 figures. Submitted to Appl. Phys. Let

A Calder\'on-Zygmund estimate with applications to generalized Radon transforms and Fourier integral operators

We prove a Calder\'on-Zygmund type estimate which can be applied to sharpen known regularity results on spherical means, Fourier integral operators and generalized Radon transforms

Transverse spin relaxation time in organic molecules: A possible platform for fault tolerant room temperature quantum computing

We report measurement of the ensemble averaged transverse spin relaxation time (T2*) in bulk and few molecules of the organic semiconductor tris(8-hydroxyquinolinolato aluminum) or Alq3. This system exhibits two characteristic T2* times, the longer of which is temperature-independent and the shorter is temperature-dependent, indicating that the latter is most likely limited by spin-phonon interaction. Based on the measured data, we infer that the single particle T2 time is long enough to meet Knill's criterion for fault tolerant quantum computing, even at room temperature. Alq3 is also an optically active organic and we propose a simple optical scheme for spin qubit read out. Moreover, we found that the temperature-dependent T2* time is considerably shorter in bulk Alq3 powder than in few molecules confined in 1-2 nm sized cavities, which is suggestive of a new type of ``phonon bottleneck effect''. This is very intriguing for organic molecules where carriers are always localized over individual molecules but the phonons are delocalized

Diagnostics of atmospheric pressure capillary DBD oxygen plasma jet

Atmospheric pressure capillary dielectric barrier oxygen discharge plasma jet is developed to generate non-thermal plasma using unipolar positive pulse power supply. Both optical and electrical techniques are used to investigate the characteristics of the produced plasma as function of applied voltage and gas flow rate. Analytical results obtained from the optical emission spectroscopic data reveal the gas temperature, rotational temperature, excitation temperature and electron density. Gas temperature and rotational temperature are found to decrease with increasing oxygen flow rate but increase linearly with applied voltage. It is exposed that the electron density is boosting up with enhanced applied voltage and oxygen flow rate, while the electron excitation temperature is reducing with rising oxygen flow rate. Electrical characterization demonstrates that the discharge frequency is falling with flow rate but increasing with voltage. The produced plasma is applied preliminarily to study the inactivation yield of Fusarium oxysporum infected potato samples

Spin relaxation in a nanowire organic spin valve: Observation of extremely long spin relaxation times

We report spin valve behavior in an organic nanowire consisting of three layers - cobalt, Alq3 and nickel - all nominally 50 nm in diameter. Based on the data, we conclude that the dominant spin relaxation mechanism in Alq3 is the Elliott-Yafet mode. Despite the very short momentum relaxation time, the spin relaxation time is found to be very long - at least a few milliseconds - and relatively temperature independent up to 100 K. To our knowledge, this is the first demonstration of an organic nanoscale spin valve, as well as the first determination of the primary spin relaxation mechanism in organics. The unusually long spin relaxation time makes these materials ideal platforms for some areas of spintronics.Comment: Resolution of some figures has suffered in an effort to reduce the file siz

Spin Transport in Organic Semiconductors: A Brief Overview of the First Eight Years

In this article we briefly review the current state of the experimental research on spin polarized transport in organic semiconductors. These systems, which include small molecular weight compounds and polymers, are central in the rapidly maturing area of organic electronics. A great deal of effort has been invested in the last eight years toward understanding spin injection and transport in organics. These developments have opened up the possibility of realizing a new family of organic spintronic devices which will blend the chemical versatility of organic materials with spintronic functionalities.Comment: 67 pages, 12 figures. Invited book chapter to appear in "Nanoelectronics: Fabrication, Interconnects and Device Structures" (Taylor and Francis). Comments welcome

Spin Filtering with Poly-T Wrapped Single Wall Carbon Nanotubes

Spin filtering is an essential operation in spintronics that allows creation and detection of spin polarized carriers. Transition metal ferromagnets are used as spin filters in most cases, though their spin filtering efficiency is only around ~50%, thereby limiting the efficiency of spintronic devices. Recently, chiral systems such as DNA have been shown to exhibit efficient spin filtering, a phenomenon often dubbed as "chirality induced spin selectivity" (CISS). In this work, we consider single wall carbon nanotubes helically wrapped with single stranded poly-T DNA. By magnetoresistance measurements we show that this system exhibits significant spin polarization of ~80%, which could be attributed to the Rashba spin-orbit interaction induced by the inversion asymmetric helical potential of the DNA. Observed spin polarization is larger than that reported before for d(GT)15 strands. Such systems allow tailoring spin polarization by chemical means and also allow extremely localized creation and detection of spin polarization without any magnetic element and could lead to extreme miniaturization and compact integration of spintronic devices and circuits