Resolution of Single Spin-Flips of a Single Proton

The spin magnetic moment of a single proton in a cryogenic Penning trap was coupled to the particle's axial motion with a superimposed magnetic bottle. Jumps in the oscillation frequency indicate spin-flips and were identified using a Bayesian analysis.Comment: accepted for publication by Phys. Rev. Lett., submitted 6.June.201

Magnetic Field tuning of low energy spin dynamics in the single-atomic magnet Li2_2(Li1−x_{1-x}Fex_x)N

We present a systematic 57Fe-Moessbauer study on highly diluted Fe centers in Li2(Li1-xFex)N single-crystals as a function of temperature and magnetic field applied transverse and longitudinal with respect to the single-ion anisotropy axis. Below 30 K the Fe centers exhibit a giant magnetic hyperfine field of E_A = 70.25(2)T parallel to the axis of strongest electric field gradient Vzz = -154.0(1) V/A2. Fluctuations of the magnetic hyperfine field are observed between 50K and 300K and described by the Blume two-level relaxation model. From the temperature dependence of the uctuation rate an Orbach spin-lattice relaxation process is deduced. An Arrhenius analysis yields a single thermal activation barrier of E_A = 570(6)K and an attempt frequency nu_0 = 309(10) GHz. Moessbauer spectroscopy studies with applied transverse magnetic fields up to 5T reveal a large increase of the uctuation rate by more than one order of magnitude. In longitudinal magnetic fields a splitting of the uctuation rate into two branches is observed consistent with a Zeeman induced modifcation of the energy levels. The experimental observations are qualitatively reproduced by a single-ion effective spin Hamiltonian analysis assuming a Fe1+ d7 charge state with unquenched orbital moment and a J = 7=2 ground state. It is demonstrated that a weak axial single-ion anisotropy D of the order of a few Kelvin can cause a two orders of magnitude larger energy barrier for longitudinal spin fluctuations.Comment: 19 pages, 17 figures

Demonstration of the Double Penning Trap Technique with a Single Proton

Spin flips of a single proton were driven in a Penning trap with a homogeneous magnetic field. For the spin-state analysis the proton was transported into a second Penning trap with a superimposed magnetic bottle, and the continuous Stern-Gerlach effect was applied. This first demonstration of the double Penning trap technique with a single proton suggests that the antiproton magnetic moment measurement can potentially be improved by three orders of magnitude or more

Hybrid graphene nematic liquid crystal light scattering device.

A hybrid graphene nematic liquid crystal (LC) light scattering device is presented. This device exploits the inherent poly-crystallinity of chemical vapour deposited (CVD) graphene films to induce directional anchoring and formation of LC multi-domains. This thereby enables efficient light scattering without the need for crossed polarisers or separate alignment layers/additives. The hybrid LC device exhibits switching thresholds at very low electric fields (< 1 V μm(-1)) and repeatable, hysteresis free characteristics. This exploitation of LC alignment effects on CVD graphene films enables a new generation of highly efficient nematic LC scattering displays as well as many other possible applications.Funding from the EPSRC (Grant No. EP/K016636/1, GRAPHTED) is acknowledged. P.R.K. acknowledges funding from Cambridge Commonwealth Trust (CCT) and the Lindemann Trust Fellowship. A.A.K would like to thank the Higher Education of Pakistan (HEC) and the CCT for financial support. A.C.V. acknowledges funding from the Cambridge Conacyt Scholarship and the Roberto Rocca Fellowship. A.K. would like to thank the Luys Educational Foundation and Hovnanian Foundation for scholarships.This is the author accepted manuscript. The final version is available from the Royal Society of Chemistry via http://dx.doi.org/10.1039/c5nr04094

Transfer-free graphene passivation of sub 100 nm thin Pt and Pt–Cu electrodes for memristive devices

Memristive switches are among the most promising building blocks for future neuromorphic computing. These devices are based on a complex interplay of redox reactions on the nanoscale. Nanoionic phenomena enable non-linear and low-power resistance transition in ultra-short programming times. However, when not controlled, the same electrochemical reactions can result in device degradation and instability over time. Two-dimensional barriers have been suggested to precisely manipulate the nanoionic processes. But fabrication-friendly integration of these materials in memristive devices is challenging.Here we report on a novel process for graphene passivation of thin platinum and platinum/copper electrodes. We also studied the level of defects of graphene after deposition of selected oxides that are relevant for memristive switching

Atomic layer deposited oxide films as protective interface layers for integrated graphene transfer

The transfer of chemical vapour deposited (CVD) graphene from its parent growth catalyst has become a bottleneck for many of its emerging applications. The sacrificial polymer layers that are typically deposited onto graphene for mechanical support during transfer are challenging to fully remove and hence leave graphene and subsequent device interfaces contaminated. Here, we report on the use of atomic layer deposited (ALD) oxide films as protective interface and support layers during graphene transfer. The method avoids any direct contact of the graphene with polymers and through the use of thicker ALD layers (≥100nm), polymers can be eliminated from the transfer-process altogether. The ALD film can be kept as a functional device layer, facilitating integrated device manufacturing. We demonstrate back-gated field effect devices based on single-layer graphene transferred with a protective Al2O3 film onto SiO2 that show significantly reduced charge trap and residual carrier densities. We critically discuss the advantages and challenges of processing graphene/ALD bilayer structures.We acknowledge funding from EPSRC (Grant No. EP/K016636/1, GRAPHTED) and ERC (Grant No. 279342, InsituNANO). ACV acknowledges the Conacyt Cambridge Scholarship and Roberto Rocca Fellowship. JAA-W acknowledges the support of his Research Fellowships from the Royal Commission for the Exhibition of 1851 and Churchill College, Cambridge. RSW acknowledges a Research Fellowship from St. John's College, Cambridge and a Marie Skłodowska-Curie Individual Fellowship (Global) under grant ARTIST (no. 656870) from the European Union's Horizon 2020 research and innovation programme

Contactless graphene conductivity mapping on a wide range of substrates with terahertz time-domain reflection spectroscopy.

We demonstrate how terahertz time-domain spectroscopy (THz-TDS) operating in reflection geometry can be used for quantitative conductivity mapping of large area chemical vapour deposited graphene films on sapphire, silicon dioxide/silicon and germanium. We validate the technique against measurements performed with previously established conventional transmission based THz-TDS and are able to resolve conductivity changes in response to induced back-gate voltages. Compared to the transmission geometry, measurement in reflection mode requires careful alignment and complex analysis, but circumvents the need of a terahertz transparent substrate, potentially enabling fast, contactless, in-line characterisation of graphene films on non-insulating substrates such as germanium.H.L. and J.A.Z. acknowledge financial support from the EPSRC (Grant No. EP/L019922/1). P.B.W. acknowledges EPSRC Cambridge NanoDTC EP/G037221/1. R.D., H.E.B. and D. R. acknowledge financial support from the EPSRC (Grant No. EP/J017671/1, Coherent Terahertz Systems). S.H. acknowledges funding from the EPSRC (Grant No. EP/K016636/1, GRAPHTED)

Graphene based plasmonic terahertz amplitude modulator operating above 100 MHz

The terahertz (THz) region of the electromagnetic spectrum holds great potential in many fields of study, from spectroscopy to biomedical imaging, remote gas sensing, and high speed communication. To fully exploit this potential, fast optoelectronic devices such as amplitude and phase modulators must be developed. In this work, we present a room temperature external THz amplitude modulator based on plasmonic bow-tie antenna arrays with graphene. By applying a modulating bias to a back gate electrode, the conductivity of graphene is changed, which modifies the reflection characteristics of the incoming THz radiation. The broadband response of the device was characterized by using THz time-domain spectroscopy, and the modulation characteristics such as the modulation depth and cut-off frequency were investigated with a 2.0 THz single frequency emission quantum cascade laser. An optical modulation cut-off frequency of 105 ± 15 MHz is reported. The results agree well with a lumped element circuit model developed to describe the device.R.D., Y.R., H.E.B., and D.A.R. acknowledge financial support from the Engineering and Physical Sciences Research Council (Grant No. EP/J017671/1, Coherent Terahertz Systems). P.B.-W. and S.H. acknowledge financial support from the Engineering and Physical Sciences Research Council (Grant Nos. EP/K016636/1, GRAPHTED). H.L. and J.A.Z. acknowledge financial support from the Engineering and Physical Sciences Research Council (Grant No. EP/L019922/1)