Nanoscience: Single-atom data storage
Nature 543, 7644 (2017). doi:10.1038/543189a
Authors: Roberta Sessoli
The ultimate limit of classical data storage is a single-atom magnetic bit. Researchers have now achieved the writing and reading of individual atoms whose magnetic information can be retained for several hours. See Letter p.226
Author(s): Tomoya Asaba, B. J. Lawson, Colin Tinsman, Lu Chen, Paul Corbae, Gang Li, Y. Qiu, Y. S. Hor, Liang Fu, and Lu Li
Quantum computers need new materials to protect their delicate quantum states. Evidence for such a material—a topological superconductor—has been detected as a breaking of rotational symmetry in a crystal of Nb-doped Bi2Se3.
[Phys. Rev. X 7, 011009] Published Fri Jan 27, 2017
Author(s): Rocco P. Fornari, Paul W. M. Blom, and Alessandro Troisi
We describe charge transport along a polymer chain with a generic theoretical model depending in principle on tens of parameters, reflecting the chemistry of the material. The charge carrier states are obtained from a model Hamiltonian that incorporates different types of disorder and electronic str…
[Phys. Rev. Lett. 118, 086601] Published Fri Feb 24, 2017
Nature Physics. doi:10.1038/nphys4047
Authors: Vedran Jelic, Krzysztof Iwaszczuk, Peter H. Nguyen, Christopher Rathje, Graham J. Hornig, Haille M. Sharum, James R. Hoffman, Mark R. Freeman & Frank A. Hegmann
Author(s): M. D. Jenkins, Y. Duan, B. Diosdado, J. J. García-Ripoll, A. Gaita-Ariño, C. Giménez-Saiz, P. J. Alonso, E. Coronado, and F. Luis
We study the quantum spin dynamics of nearly isotropic Gd3+ ions entrapped in polyoxometalate molecules and diluted in crystals of a diamagnetic Y3+ derivative. The full energy-level spectrum and the orientations of the magnetic anisotropy axes have been determined by means of continuous-wave electr…
[Phys. Rev. B 95, 064423] Published Wed Feb 22, 2017
Nature Chemistry 9, 213 (2017). doi:10.1038/nchem.2662
Authors: Oleksandr Stetsovych, Martin Švec, Jaroslav Vacek, Jana Vacek Chocholoušová, Andrej Jančařík, Jiří Rybáček, Krzysztof Kosmider, Irena G. Stará, Pavel Jelínek & Ivo Starý
Flat, prochiral molecules form chiral adsorbates on achiral surfaces, but such assemblies are globally racemic. Now, it is shown that this mirror symmetry can be broken through stereocontrolled on-surface synthesis. Enantiopure helicene molecules can be transformed into flat, enantiofacially adsorbed products through a cascade of reactions on Ag(111) monitored by high-resolution scanning probe microscopy.
Magnetic skyrmions are nanoscale windings of the spin configuration that hold great promise for technology due to their topology-related properties and extremely reduced sizes. After the recent observation at room temperature of sub-100 nm skyrmions stabilized by interfacial chiral interaction in magnetic multilayers, several pending questions remain to be solved, notably about the means to nucleate individual compact skyrmions or the exact nature of their motion. In this study, a method leading to the formation of magnetic skyrmions in a micrometer-sized nanotrack using homogeneous current injection is evidenced. Spin-transfer-induced motion of these small electricalcurrent-generated skyrmions is then demonstrated and the role of the out-of-plane magnetic field in the stabilization of the moving skyrmions is also analysed. The results of these experimental observations of spin torque induced motion are compared to micromagnetic simulations reproducing a granular type, non-uniform magnetic multilayer, in order to address the particularly important role of the magnetic inhomogeneities on the current-induced motion of sub-100 nm skyrmions, for which the material grains size is comparable to the skyrmion diameter.
Author(s): S. N. Rebec, T. Jia, C. Zhang, M. Hashimoto, D.-H. Lu, R. G. Moore, and Z.-X. Shen
To elucidate the mechanisms behind the enhanced Tc in monolayer (1 ML) FeSe on SrTiO3 (STO), we grew highly strained 1 ML FeSe on the rectangular (100) face of rutile TiO2, and observed the coexistence of replica bands and superconductivity with a Tc of 63 K. From the similar Tc between this system …
[Phys. Rev. Lett. 118, 067002] Published Fri Feb 10, 2017
Knowledge of the topology of the electronic ground state of materials has led to deep insights to novel phenomena such as the integer quantum Hall effect and fermion-number fractionalization, as well as other properties of matter. Joining two insulators of different topological classes produces fascinating boundary states in the band gap. Another exciting recent development is the bottom-up synthesis (from molecular precursors) of graphene nanoribbons (GNRs) with atomic precision control of their edge and width. Here we connect these two fields, and show for the first time that semiconducting GNRs of different width, edge, and end termination belong to different topological classes. The topology of GNRs is protected by spatial symmetries and dictated by the terminating unit cell. We have derived explicit formula for their topological invariants, and show that localized junction states developed between two GNRs of distinct topology may be tuned by lateral junction geometry. The topology of a GNR can be further modified by dopants, such as a periodic array of boron atoms. In a superlattice consisted of segments of doped and pristine GNRs, the junction states are stable spin centers, forming a Heisenberg antiferromagnetic spin 1/2 chain with tunable exchange interaction. The discoveries here are not only of scientific interest for studies of quasi one-dimensional systems, but also open a new path for design principles of future GNR-based devices through their topological characters.
Among all transition metals, Palladium (Pd) has the highest density of states at the Fermi energy yet does not fulfill the Stoner criterion for ferromagnetism. However, its close vicinity to magnetism renders it a nearly ferromagnetic metal, which hosts paramagnons, strongly damped spin fluctuations. In this letter we compare the total and the differential conductance of mono-atomic Pd and Cobalt (Co) contacts between Pd electrodes. Transport measurements reveal a conductance for Co of 1 $G_0$ , while for Pd we obtain 2 $G_0$. The differential conductance of mono-atomic Pd contacts shows a drop with increasing bias, which gives rise to a peculiar {$\Lambda$}-shaped spectrum. Supported by theoretical calculations we correlate this finding with the life time of hot quasi-particles in Pd which is strongly influenced by paramagnon scattering. In contrast to this, Co adatoms locally induce magnetic order and transport through single cobalt atoms remains unaffected by paramagnon scattering, consistent with theory.
Direct observation of spin-layer locking by local Rashba effect in monolayer semiconducting PtSe<sub>2</sub> film
Nature Communications, Published online: 31 January 2017; doi:10.1038/ncomms14216
Spin polarization in non-magnetic solids has mainly been limited to non-centrosymmetric materials. Here, the authors identify a helical spin texture in the centrosymmetric semiconductor platinum diselenide, and suggest it arises from a local dipole induced Rashba effect rather than the usual spin-splitting.
We report direct evidence for quintuplet spin states in a particular kind of reduced TiO2 anatase obtained by the mild oxidation of TiB2 under hydrothermal conditions. Continuous-wave and pulse EPR spectroscopy at X and Q band frequencies provide compelling evidence for the presence of S=2 states, stable in a wide range of temperatures up to room temperature. A tentative model, corroborated by spin-polarized DFT calculations, is proposed, which consists of four ferromagnetically interacting Ti3+ ions with distances ranging from 0.5 nm to 0.8 nm and tetrahedral arrangement.
Spinoff: Ferromagnetically interacting Ti3+ centers leading to stable S=2 states in TiO2 anatase are generated through the solvothermal oxidation of TiB2. This nanomaterial corresponds to a particular form of reduced, blue-colored TiO2 (structure and contour plot of 2D transient EPR nutation spectra shown).
Author(s): Jianhui Wang, Yigal Meir, and Yuval Gefen
A topological insulator with beveled, as opposed to sharp, edges might lose the attributes that make it attractive for applications.
[Phys. Rev. Lett. 118, 046801] Published Thu Jan 26, 2017
Author(s): Zhumin Han (韩竹敏), Gregory Czap, Chen Xu (徐晨), Chi-lun Chiang (蔣季倫), Dingwang Yuan (袁定旺), Ruqian Wu, and W. Ho
Using a scanning tunneling microscope, researchers detect coupled vibrations between two molecules.
[Phys. Rev. Lett. 118, 036801] Published Thu Jan 19, 2017
<i>p</i>-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor
Nature Communications, Published online: 19 January 2017; doi:10.1038/ncomms14024
Unconventional superconductivity may be triggered when graphene is deposited on a high temperature superconductor. Here, Di Bernardo et al. observe spectroscopic evidence for p-wave superconductivity in single layer graphene on an electron-doped cuprate superconductor.
We have studied the temporal evolution of a quantum system subjected to strong dissipation at ultra-low temperatures where the system-bath interaction represents the leading energy scale. In this regime, theory predicts the time evolution of the system to follow a generalization of the classical Smoluchowski description, the quantum Smoluchowski equation, thus, exhibiting quantum Brownian motion characteristics. For this purpose, we have investigated the phase dynamics of a superconducting tunnel junction in the presence of high damping. We performed current-biased measurements on the small-capacitance Josephson junction of a scanning tunneling microscope placed in a low impedance environment at milli-Kelvin temperatures. We can describe our experimental findings by a quantum diffusion model with high accuracy in agreement with theoretical predications based on the quantum Smoluchowski equation. In this way we experimentally demonstrate that quantum systems subjected to strong dissipation follow quasi-classical dynamics with significant quantum effects as the leading corrections.
