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Voltage-driven v.s. Current-driven Spin Torque in Anisotropic Tunneling Junctions  [PDF]
A. Manchon
Physics , 2011, DOI: 10.1109/TMAG.2011.2157108
Abstract: Non-equilibrium spin transport in a magnetic tunnel junction comprising a single magnetic layer in the presence of interfacial spin-orbit interaction (SOI) is studied theoretically. The interfacial SOI generates a spin torque of the form {\bf T}=T_{||}{\bf M}x({\bf z}x{\bf M})+T_{\bot}{\bf z}x{\bf M}, even in the absence of an external spin polarizer. For thick and large tunnel barriers, the torque reduces to the perpendicular component, $T_{\bot}$, which can be electrically tuned by applying a voltage across the insulator. In the limit of thin and low tunnel barriers, the in-plane torque $T_{||}$ emerges, proportional to the tunneling current density. Experimental implications on magnetic devices are discussed.
Charge Tunneling Rates in Ultrasmall Junctions  [PDF]
Gert-Ludwig Ingold,Yu. V. Nazarov
Physics , 2005,
Abstract: 1. Introduction 2. Description of the environment 3. Electron tunneling rates for single tunnel junctions 4. Examples of electromagnetic environments 5. Tunneling rates in Josephson junctions 6. Double junction and single electron transistor 7. Microscopic foundation
The Origin of Tunneling Anisotropic Magnetoresistance in Break Junctions  [PDF]
J. D. Burton,R. F. Sabirianov,J. P. Velev,O. N. Mryasov,E. Y. Tsymbal
Physics , 2007, DOI: 10.1103/PhysRevB.76.144430
Abstract: First-principles calculations of electron tunneling transport in Ni and Co break junctions reveal strong dependence of the conductance on the magnetization direction, an effect known as tunneling anisotropic magnetoresistance (TAMR). The origin of this phenomenon stems from resonant states localized in the electrodes near the junction break. The energy and broadening of these states is strongly affected by the magnetization orientation due to spin-orbit coupling, causing TAMR to be sensitive to bias voltage on a scale of a few mV. Our results bear a resemblance to recent experimental data and suggest that TAMR driven by resonant states is a general phenomenon typical for magnetic broken contacts and other experimental geometries where a magnetic tip is used to probe electron transport.
An RF-Driven Josephson Bifurcation Amplifier for Quantum Measurements  [PDF]
I. Siddiqi,R. Vijay,F. Pierre,C. M. Wilson,M. Metcalfe,C. Rigetti,L. Frunzio,M. H. Devoret
Physics , 2003, DOI: 10.1103/PhysRevLett.93.207002
Abstract: We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of an RF-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. The main advantages of this new amplifier are speed, high-sensitivity, low back-action, and the absence of on-chip dissipation. Pulsed microwave reflection measurements on nanofabricated Al junctions show that actual devices attain the performance predicted by theory.
Tuning the conductance of molecular junctions: transparent versus tunneling regimes  [PDF]
J. Ferrer,V. M. Garcia-Suarez
Physics , 2008, DOI: 10.1103/PhysRevB.80.085426
Abstract: We present a theoretical study of the transport characteristics of molecular junctions, where first-row diatomic molecules are attached to (001) gold and platinum electrodes. We find that the conductance of all of these junctions is of the order of the conductance quantum unit $G_0$, spelling out that they belong to the transparent regime. We further find that the transmission coefficients show wide plateaus as a function of the energy, instead of the usual sharp resonances that signal the molecular levels in the tunneling regime. We use Caroli's model to show that this is a rather generic property of the transparent regime of a junction, which is driven by a strong effective coupling between the delocalized molecular levels and the conduction channels at the electrodes. We analyse the transmission coefficients and chemical bonding of gold/Benzene and gold/Benzene-dithiolate (BDT) junctions to understand why the later show large resistances, while the former are highly conductive.
Tunneling conductance of graphene NIS junctions  [PDF]
Subhro Bhattacharjee,K. Sengupta
Physics , 2006, DOI: 10.1103/PhysRevLett.97.217001
Abstract: We show that in contrast to conventional normal metal-insulator-superconductor (NIS) junctions, the tunneling conductance of a NIS junction in graphene is an oscillatory function of the effective barrier strength of the insulating region, in the limit of a thin barrier. The amplitude of these oscillations are maximum for aligned Fermi surfaces of the normal and superconducting regions and vanishes for large Fermi surface mismatch. The zero-bias tunneling conductance, in sharp contrast to its counterpart in conventional NIS junctions, becomes maximum for a finite barrier strength. We also suggest experiments to test these predictions.
Perpendicular current-driven magnetization switching in free layer of magnetic tunneling junctions and MRAM
磁随机存储器中垂直电流驱动的磁性隧道结自由层的磁化翻转

Peng Zi-Long,Han Xiu-Feng,Zhao Su-Fen,Wei Hong-Xiang,Du Guan-Xiang,Zhan Wen-Shan,
彭子龙
,韩秀峰,赵素芬,魏红祥,杜关祥,詹文山

物理学报 , 2006,
Abstract: A new method of readout and writing process driven by perpendicular current in magnetoresistantive random access memory (MRAM) based on the magnetic tunneling junction is reported, and its schematic structure and operation are described.
Driven Tunneling: Chaos and Decoherence  [PDF]
Peter Hanggi,Sigmund Kohler,Thomas Dittrich
Physics , 1999,
Abstract: Chaotic tunneling in a driven double-well system is investigated in absence as well as in the presence of dissipation. As the constitutive mechanism of chaos-assisted tunneling, we focus on the dynamics in the vicinity of three-level crossings in the quasienergy spectrum. The coherent quantum dynamics near the crossing is described satisfactorily by a three-state model. It fails, however, for the corresponding dissipative dynamics, because incoherent transitions due to the interaction with the environment indirectly couple the three states in the crossing to the remaining quasienergy states. The asymptotic state of the driven dissipative quantum dynamics partially resembles the, possibly strange, attractor of the corresponding damped driven classical dynamics, but also exhibits characteristic quantum effects.
Tunneling spectroscopy for ferromagnet/superconductor junctions  [PDF]
Igor Zutic,Oriol T. Valls
Physics , 1999, DOI: 10.1103/PhysRevB.61.1555
Abstract: In tunneling spectroscopy studies of ferromagnet/superconductor (F/S) junctions, the effects of spin polarization, Fermi wavevector mismatch (FWM) between the F and S regions, and interfacial resistance play a crucial role. We study the low bias conductance spectrum of these junctions, governed by Andreev reflection at the F/S interface. We consider both d- and s-wave superconductors as well as mixed states of the $d+is$ form. We present results for a range of values of the relevant parameters and find that a rich variety of features appears, depending on pairing state and other conditions. We show that in the presence of FWM, spin polarization can enhance Andreev reflection and give rise to a zero bias conductance peak for an s-wave superconductor.
Theory of Tunneling for Rough Junctions  [PDF]
M. B. Walker
Physics , 1999, DOI: 10.1103/PhysRevB.60.9283
Abstract: A formally exact expression for the tunneling current, for its separation into specular and diffuse components, and for its directionality, is given for a thick tunnel junction with rough interfaces in terms of the properties of appropriately defined scattering amplitudes. An approximate evaluation yields the relative magnitudes of the specular and diffuse components, and the angular dependence of the diffuse component, in terms of certain statistical properties of the junction interfaces.
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