Author(s): S. Gardonio, M. Karolak, T. O. Wehling, L. Petaccia, S. Lizzit, A. Goldoni, A. I. Lichtenstein, and C. Carbone
We report photoemission experiments revealing the valence electron spectral function of Mn, Fe, Co, and Ni atoms on the Ag (100) surface. The series of spectra shows splittings of higher energy features which decrease with the filling of the 3d shell and a highly nonmonotonic evolution of spectral w...
[Phys. Rev. Lett. 110, 186404] Published Fri May 03, 2013
Author(s): Lan Meng, Wen-Yu He, Hong Zheng, Mengxi Liu, Hui Yan, Wei Yan, Zhao-Dong Chu, Keke Bai, Rui-Fen Dou, Yanfeng Zhang, Zhongfan Liu, Jia-Cai Nie, and Lin He
Theoretical research has predicted that a ripple of graphene generates an effective gauge field on its low-energy electronic structure and could lead to Landau quantization. Here, we demonstrate using a combination of an experimental method (scanning tunneling microscopy) and a theoretical approach ...
[Phys. Rev. B 87, 205405] Published Fri May 03, 2013
Heralded entanglement between solid-state qubits separated by three metres
Nature 497, 7447 (2013). doi:10.1038/nature12016
Authors: H. Bernien, B. Hensen, W. Pfaff, G. Koolstra, M. S. Blok, L. Robledo, T. H. Taminiau, M. Markham, D. J. Twitchen, L. Childress & R. Hanson
Quantum entanglement between spatially separated objects is one of the most intriguing phenomena in physics. The outcomes of independent measurements on entangled objects show correlations that cannot be explained by classical physics. As well as being of fundamental interest, entanglement is a unique resource for quantum information processing and communication. Entangled quantum bits (qubits) can be used to share private information or implement quantum logical gates. Such capabilities are particularly useful when the entangled qubits are spatially separated, providing the opportunity to create highly connected quantum networks or extend quantum cryptography to long distances. Here we report entanglement of two electron spin qubits in diamond with a spatial separation of three metres. We establish this entanglement using a robust protocol based on creation of spin–photon entanglement at each location and a subsequent joint measurement of the photons. Detection of the photons heralds the projection of the spin qubits onto an entangled state. We verify the resulting non-local quantum correlations by performing single-shot readout on the qubits in different bases. The long-distance entanglement reported here can be combined with recently achieved initialization, readout and entanglement operations on local long-lived nuclear spin registers, paving the way for deterministic long-distance teleportation, quantum repeaters and extended quantum networks.
Flu papers spark row over credit for data
Nature 497, 7447 (2013). http://www.nature.com/doifinder/10.1038/497014a
Authors: Declan Butler & David Cyranoski
Rush to publish on H7N9 avian flu upsets Chinese scientists.
Dr.jens.bredemaybe
Dr.jens.bredeWow.... really... what you are allowed to sell as SP-STM these days...
Nature Physics. doi:10.1038/nphys2610
Authors: Manuela Garnica, Daniele Stradi, Sara Barja, Fabian Calleja, Cristina Díaz, Manuel Alcamí, Nazario Martín, Amadeo L. Vázquez de Parga, Fernando Martín & Rodolfo Miranda
Inducing magnetism in graphene holds great promises, such as controlling the exchange interaction with a gate electrode and generating exotic magnetic phases. Coating graphene with magnetic molecules or atoms has so far mostly lead to decreased graphene mobility. In the present work, we show that Pt-porphyrins adsorbed on graphene lead to an enhanced mobility and to gate-dependent magnetism. We report that porphyrins can be donor or acceptor, depending on graphene s initial doping. The porphyrins transfer charge and ionize around the charged impurities on graphene, decreasing the graphene doping and increasing its mobility. In addition, ionized porphyrins carry a magnetic moment. Using the sensitivity of mesoscopic transport to magnetism, in particular the superconducting proximity effect and conductance fluctuations, we explore the magnetic order induced in graphene by the interacting magnetic moments of the ionized porphyrins. Among the signatures of magnetism, we find two-terminal-magnetoresistance fluctuations with an odd component, a tell-tale sign of time reversal symmetry breaking at zero field, that does not exist in uncoated graphene sample. When graphene is connected to superconducting electrodes, the induced magnetism leads to a gate-voltage-dependent suppression of the supercurrent, modified magnetic interference patterns, and gate-voltage-dependent magnetic hysteresis. The magnetic signatures are greatest for long superconductor graphene superconductor junctions and for samples with the highest initial doping, compatible with a greater number of ionized and thus magnetic porphyrins. Our findings suggest that long-range magnetism is induced through graphene by the ionized porphyrins magnetic moment. This magnetic interaction is controlled by the density of carriers in graphene, a tunability that could be exploited in spintronic applications.
Using first-principles calculations we demonstrate sizable exchange coupling between a magnetic molecule and a magnetic substrate via a graphene layer. As a model system we consider cobaltocene (CoCp$_2$) adsorbed on graphene deposited on Ni(111). We find that the magnetic coupling between the molecule and the substrate is antiferromagnetic and varies considerably depending on the molecule structure, the adsorption geometry, and the stacking of graphene on Ni(111). We show how this coupling can be tuned by intercalating a magnetic monolayer, e.g. Fe or Co, between graphene and Ni(111). We identify the leading mechanism responsible for the coupling to be the spatial and energy matching of the frontier orbitals of CoCp$_2$ and graphene close to the Fermi level, and we demonstrate the role of graphene as an electronic decoupling layer, yet allowing spin communication between molecule and substrate.
A multi-terminal device based on a carbon nanotube quantum dot was used at very low tem- perature to probe a single electronic and nuclear spin embedded in a bis-phthalocyanine Terbium (III) complex (TbPc2). A spin-valve signature with large conductance jumps was found when two molecules were strongly coupled to the nanotube. The application of a transverse field separated the magnetic signal of both molecules and enabled single-shot read-out of the Terbium nuclear spin. The Landau-Zener (LZ) quantum tunneling probability was studied as a function of field sweep rate, establishing a good agreement with the LZ equation and yielding the tunnel splitting \Delta. It was found that ? increased linearly as a function of the transverse field. These studies are an essential prerequisite for the coherent manipulation of a single nuclear spin in TbPc2.
Magnetic molecules possess a high potential as building blocks for the design of spintronic devices. Moreover, the use of molecular materials opens the way for the controlled use of bottom-up, e.g. supramolecular, processing techniques combining massively parallel self-fabrication with conventional top-down nanostructuring techniques. The development of solid state spintronic devices based on the giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), and spin valve effects has revolutionized the field of magnetic memory applications. Recently, organic semiconductors were inserted into nanometer sized tunnel junctions allowing enhancement of spin reversal, giant magneto-resistance behaviour was observed in single non-magnetic molecules coupled to magnetic electrodes, and the use of the quantum tunnelling properties of single-molecule magnets (SMMs) in hybrid devices was proposed. Herein, we present an original device in which a non-magnetic molecular quantum dot, made of a single-wall carbon nanotube (SWCNT) contacted with non-magnetic electrodes, is laterally coupled via supramolecular interactions to a TbPc2-SMM (Pc = phthalocyanine), which provides a localized magnetic moment. The conductance through the SWCNT is modulated by sweeping the magnetic field, exhibiting magnetoresistance ratios up to 300% between fully polarized and non-polarized SMMs below 1 K. We thus demonstrate the functionality of a supramolecular spin valve without magnetic leads. Our results open up prospects of circuit-integration and implementation of new device capabilities.
Evolution of Landau levels into edge states in graphene
Nature Communications 4, 1744 (2013). doi:10.1038/ncomms2767
Authors: Guohong Li, Adina Luican-Mayer, Dmitry Abanin, Leonid Levitov & Eva Y. Andrei
Author(s): L. El-Kareh, P. Sessi, T. Bathon, and M. Bode
We report on low-temperature scanning tunneling spectroscopy investigations of the (√3×√3) Bi/Ag(111)R30° surface alloy which provides a giant Rashba-type spin splitting. We observed spectroscopic features that are assigned to two Rashba-split bands. Quantum interference mapping shows that backscatt...
[Phys. Rev. Lett. 110, 176803] Published Tue Apr 23, 2013
Author(s): Fernando de Juan, Juan L. Mañes, and María A. H. Vozmediano
We revise the tight-binding approach to strained or curved graphene in the presence of external probes such as photoemission or scanning tunneling microscopy experiments. We show that extra terms arise in the continuum limit of the tight-binding Hamiltonian which cannot be accounted for by changes i...
[Phys. Rev. B 87, 165131] Published Tue Apr 23, 2013
Dr.jens.bredetheory. more toward break junction experiments. Does anyone know these guys?
We investigate theoretically the effects of intrinsic spin-relaxation on the spin-dependent transport through a single-molecule magnet (SMM), which is weakly coupled to ferromagnetic leads. The tunnel magnetoresistance (TMR) is obtained by means of the rate-equation approach including not only the sequential but also the cotunneling processes. It is shown that the TMR is strongly suppressed by the fast spin-relaxation in the sequential region and can vary from a large positive to slight negative value in the cotunneling region. Moreover, with an external magnetic field along the easy-axis of SMM, a large negative TMR is found when the relaxation strength increases. Finally, in the high bias voltage limit the TMR for the negative bias is slightly larger than its characteristic value of the sequential region, however it can become negative for the positive bias caused by the fast spin-relaxation.
High-fidelity readout and control of a nuclear spin qubit in silicon
Nature 496, 7445 (2013). doi:10.1038/nature12011
Authors: Jarryd J. Pla, Kuan Y. Tan, Juan P. Dehollain, Wee H. Lim, John J. L. Morton, Floris A. Zwanenburg, David N. Jamieson, Andrew S. Dzurak & Andrea Morello
Detection of nuclear spin precession is critical for a wide range of scientific techniques that have applications in diverse fields including analytical chemistry, materials science, medicine and biology. Fundamentally, it is possible because of the extreme isolation of nuclear spins from their environment. This isolation also makes single nuclear spins desirable for quantum-information processing, as shown by pioneering studies on nitrogen-vacancy centres in diamond. The nuclear spin of a 31P donor in silicon is very promising as a quantum bit: bulk measurements indicate that it has excellent coherence times and silicon is the dominant material in the microelectronics industry. Here we demonstrate electrical detection and coherent manipulation of a single 31P nuclear spin qubit with sufficiently high fidelities for fault-tolerant quantum computing. By integrating single-shot readout of the electron spin with on-chip electron spin resonance, we demonstrate quantum non-demolition and electrical single-shot readout of the nuclear spin with a readout fidelity higher than 99.8 per cent—the highest so far reported for any solid-state qubit. The single nuclear spin is then operated as a qubit by applying coherent radio-frequency pulses. For an ionized 31P donor, we find a nuclear spin coherence time of 60 milliseconds and a one-qubit gate control fidelity exceeding 98 per cent. These results demonstrate that the dominant technology of modern electronics can be adapted to host a complete electrical measurement and control platform for nuclear-spin-based quantum-information processing.
Author(s): S. Javaid, S. Lebègue, B. Detlefs, F. Ibrahim, F. Djeghloul, M. Bowen, S. Boukari, T. Miyamachi, J. Arabski, D. Spor, J. Zegenhagen, W. Wulfhekel, W. Weber, E. Beaurepaire, and M. Alouani
van der Waals (vdW) interactions within density functional theory are shown to strongly reduce the distance between manganese phthalocyanine (MnPc) and a Cu(001) surface to that found by x-ray standing wave experiments. Thus, the physisorbed ground state that is predicted within the generalized-grad...
[Phys. Rev. B 87, 155418] Published Wed Apr 17, 2013
Dr.jens.bredetheory
Dr.jens.bredepoint defects generated by "overheating" graphene foil
Here we report a facile method to generate a high density of point defects in graphene on metal foil and show how the point defects affect the electronic structures of graphene layers. Our scanning tunneling microscopy (STM) measurements, complemented by first principle calculations, reveal that the point defects result in both the intervalley and intravalley scattering of graphene. The Fermi velocity is reduced in the vicinity area of the defect due to the enhanced scattering. Additionally, our analysis further points out that periodic point defects can tailor the electronic properties of graphene by introducing a significant bandgap, which opens an avenue towards all-graphene electronics.
Dr.jens.bredeXue army
A violation of the uncertainty principle implies a violation of the second law of thermodynamics
Nature Communications 4, 1670 (2013). doi:10.1038/ncomms2665
Authors: Esther Hänggi & Stephanie Wehner
Author(s): Mehmet Z. Baykara, Milica Todorović, Harry Mönig, Todd C. Schwendemann, Özhan Ünverdi, Lucia Rodrigo, Eric I. Altman, Rubén Pérez, and Udo D. Schwarz
The influence of defects on the local structural, electronic, and chemical properties of a surface oxide on Cu(100) were investigated using atomic resolution three-dimensional force mapping combined with tunneling current measurements and ab initio density functional theory. Results reveal that the ...
[Phys. Rev. B 87, 155414] Published Fri Apr 12, 2013
Dr.jens.bredeJust for the title.
If God did not exist - people would invent one. The development of human civilization requires mechanisms promoting cooperation and social order. One of these mechanisms is based on the idea that everything we do is seen and judged by God - bad deeds will be punished, while good ones will be rewarded. The Information Age has now fueled the dream that God-like omniscience and omnipotence can be created by man.
Dr.jens.bredehere we go again: this time silicene
We performed low temperature scanning tunneling microscopy (STM) and spectroscopy (STS) studies on the electronic properties of (R3xR3)R30{\deg} phase of silicene on Ag(111) surface. We found the existence of Dirac Fermion chirality through the observation of -1.5 and -1.0 power law decay of quasiparticle interference (QPI) patterns. Moreover, in contrast to the trigonal warping of Dirac cone in graphene, we found that the Dirac cone of silicene is hexagonally warped, which is further confirmed by density functional calculations and explained by the unique superstructure of silicene. Our results demonstrate that the (R3xR3)R30{\deg} phase is an ideal system to investigate the unique Dirac Fermion properties of silicene.
