arXiv subjects

M. Jonson

Publications and source records attributed to M. Jonson.

At least 55 records · Page 3Linked to original sources

arXiv2007

Thermoelectrical manipulation of nano-magnets

We propose a device that can operate as a magneto-resistive switch or oscillator. The device is based on a spin-thermo-electronic control of the exchange coupling of two strong ferromagnets through a weakly ferromagnetic spacer. We show that the local Joule heating due to a high concentration of current in a magnetic point contact or a nanopillar can be used to reversibly drive the weak ferromagnet through its Curie point and thereby exchange-decouple the strongly ferromagnetic layers, which have an antiparallel ground state. Such a spin-thermionic parallel-to-antiparallel switching causes magnetoresistance oscillations where the frequency can be controlled by proper biasing from essentially DC to GHz.

cond-mat.mes-hall↗

arXiv2007

Electronic superlattices in corrugated graphene

We theoretically investigate electron transport through corrugated graphene ribbons and show how the ribbon curvature leads to an electronic superlattice with a period set by the corrugation wave length. Transport through the ribbon depends sensitively on the superlattice band structure which, in turn, strongly depends on the geometry of the deformed sheet. In particular, we find that for ribbon widths where the transverse level separation is comparable to the the band edge energy, a strong current switching occurs as function of an applied backgate voltage. Thus, artificially corrugated graphene sheets or ribbons can be used for the study of Dirac fermions in periodic potentials. Furthermore, this provides an additional design paradigm for graphene-based electronics.

cond-mat.mes-hall↗

arXiv2006

Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts

We consider the electrical current through a magnetic point contact in the limit of a strong inelastic scattering of electrons. In this limit local Joule heating of the contact region plays a decisive role in determining the transport properties of the point contact. We show that if an applied constant bias voltage exceeds a critical value, the stationary state of the system is unstable, and that periodic, non-harmonic oscillations in time of both the electrical current through the contact and the local temperature in the contact region develop spontaneously. Our estimations show that the necessary experimental conditions for observing such oscillations with characteristic frequencies in the range $10^8 ÷10^9$ Hz can easily be met. We also show a possibility to manipulate upon the magnetization direction of a magnetic grain coupled through a point contact to a bulk ferromagnetic by exciting the above-mentioned thermal-electric oscillations.

cond-mat.mtrl-sci↗

arXiv2006

Electronic Aharonov-Bohm Effect Induced by Quantum Vibrations

Mechanical displacements of a nanoelectromechanical system (NEMS) shift the electron trajectories and hence perturb phase coherent charge transport through the device. We show theoretically that in the presence of a magnetic feld such quantum-coherent displacements may give rise to an Aharonov-Bohm-type of effect. In particular, we demonstrate that quantum vibrations of a suspended carbon nanotube result in a positive nanotube magnetoresistance, which decreases slowly with the increase of temperature. This effect may enable one to detect quantum displacement fluctuations of a nanomechanical device.

cond-mat.mes-hall↗

arXiv2005

Single-interface superconductivity in two-layer semiconductor heterostructures

We have discovered superconductivity in the two-layer semiconducting monochalcogenide heterostrutures PbTe/PbS, PbTe/PbSe and PbTe/YbS. By comparing data from two-layer samples with data from single monochalcogenide films we conclude that the superconductivity is connected with the interface between the two semiconductors. Evidence for the low dimensional nature of the superconducting interlayer is presented and a model that explains the appearance of single-interface superconductivity is proposed.

cond-mat.supr-con↗

arXiv2005

Spintronics of a Nanoelectromechanical Shuttle

We consider effects of the spin degree of freedom on the nanomechanics of a single-electron transistor (SET) containing a nanometer-sized metallic cluster suspended between two magnetic leads. It is shown that in such a nanoelectromechanical SET(NEM-SET) the onset of an electromechanical instability leading to cluster vibrations and "shuttle" transport of electrons between the leads can be controlled by an external magnetic field. Different stable regimes of this spintronic NEM-SET operation are analyzed. Two different scenarios for the onset of shuttle vibrations are found.

cond-mat.mes-hall↗

arXiv2005

Giant oscillations of the density of states and the conductance in a ferromagnetic conductor coupled to two superconductors

Giant oscillations of the density of electronic states and the differential conductance of a superconductor-ferromagnet-superconductor structure are predicted for the case when the exchange energy, $I_0$, due to the interaction between the electron spin and the spontaneous moment of the ferromagnet is smaller than the superconductor energy gap, $Δ$. The effect is due to the extremely large degeneration of the energy level $ε= I_0$ when the superconductor phase difference $ϕ$ is close to odd multiple of $π$ ($ε$ is the electron energy measured from the Fermi-energy). This quantum interference effect persists even in long ferromagnetic bridges whose length much exceeds the ''magnetic length'' ($\hbar v_{F}/I_{0}$ in the ballistic regime and $\sqrt{\hbar D/I_0}$ in the diffusive regime; $D$ is the electron diffusion constant). The predicted effect allows a direct spectroscopy of Andreev levels in the ferromagnet as well as a direct measurement of the exchange energy,$I_0$.

cond-mat.mes-hall↗

arXiv2005

Electromechanical instability in suspended carbon nanotubes

We have theoretically investigated electromechanical properties of freely suspended carbon nanotubes when a current is injected into the tubes using a scanning tunneling microscope. We show that a shuttle-like electromechanical instability can occur if the bias voltage exceeds a dissipation-dependent threshold value. An instability results in large amplitude vibrations of the carbon nanotube bending mode, which modify the current-voltage characteristics of the system.

cond-mat.mes-hall↗

arXiv2005

Coulomb Promotion of Spin-Dependent Tunnelling

We study transport of spin-polarized electrons through a magnetic single-electron transistor (SET) in the presence of an external magnetic field. Assuming the SET to have a nanometer size central island with a single electron level we find that the interplay on the island between coherent spin-flip dynamics and Coulomb interactions can make the Coulomb correlations promote rather than suppress the current through the device. We find the criteria for this new phenomenon -- Coulomb promotion of spin-dependent tunnelling -- to occur.

cond-mat.mes-hall↗

arXiv2004

Influence of the Rashba effect on the Josephson current through a superconductor/Luttinger liquid/superconductor tunnel junction

The Josephson current through a 1D quantum wire with Rashba spin-orbit and electron-electron interactions is calculated. We show that the interplay of Rashba and Zeeman interactions gives rise to a supercurrent through the 1D conductor that is anomalous in the sense that it persists in the absence of any phase difference between the two superconducting leads to which it is attached. The electron dispersion asymmetry induced by the Rashba interaction in a Luttinger-liquid wire plays a significant role for poorly transmitting junctions. It is shown that for a weak or moderate electron-electron interaction the spectrum of plasmonic modes confined to the normal part of the junction becomes quasi-random in the presence of dispersion asymmetry.

cond-mat.supr-con↗

arXiv2004

Spin-Dependent Transport of Electrons in a Shuttle Structure

We consider "shuttling" of spin-polarized electrons between two magnetic electrodes (half-metals) by a movable dot with a single electronic level. If the magnetization of the electrodes is antiparallel we show that the transmittance of the system can be changed by orders of magnitude if an external magnetic field, perpendicular to the polarization of the electronic spins, is applied. A giant magnetotransmittance effect can be achieved for weak external fields of order $1÷10$ Oe.

cond-mat.mes-hall↗

arXiv2004

Quantum Shuttle Phenomena in a Nanoelectromechanical Single-Electron Transistor

An analytical analysis of quantum shuttle phenomena in a nanoelectromechanical single-electron transistor has been performed in the realistic case, when the electron tunnelling length is much greater than the amplitude of the zero point oscillations of the central island. It is shown that when the dissipation is below a certain threshold value, the vibrational ground state of the central island is unstable. The steady-state into which this instability develops is studied. It is found that if the electric field ${\cal E}$ between the leads is much greater than a characteristic value ${\cal E}_q$, the quasiclassical shuttle picture is recovered, while if ${\cal E}\ll{\cal E}_q$ a new quantum regime of shuttle vibrations occurs. We show that in the latter regime small quantum fluctuations result in large (i.e. finite in the limit $\hbar \to 0$) shuttle vibrations.

cond-mat.mes-hall↗

arXiv2003

Resonant microwave properties of a voltage-biased single-Cooper-pair transistor

We consider the microwave dynamics and transport properties of a voltage-biased single-Cooper-pair transistor. The dynamics is shown to be strongly affected by interference between multiple microwave-induced inter-level transitions. As a result the magnitude and direction of the dc Josephson current are extremely sensitive to small variations of the bias voltage and to changes in the frequency of the microwave field.

cond-mat.mes-hall↗

arXiv2003

Giant lasing effect in magnetic nanoconductors

We propose a new principle for a compact solid-state laser in the 1-100 THz regime. This is a frequency range where attempts to fabricate small size lasers up till now have met severe technical problems. The proposed laser is based on a new mechanism for creating spin-flip processes in ferromagnetic conductors. The mechanism is due to the interaction of light with conduction electrons; the interaction strength, being proportional to the large exchange energy, exceeds the Zeeman interaction by orders of magnitude. On the basis of this interaction, a giant lasing effect is predicted in a system where a population inversion has been created by tunneling injection of spin-polarized electrons from one ferromagnetic conductor to another -- the magnetization of the two ferromagnets having different orientations. Using experimental data for ferromagnetic manganese perovskites with nearly 100% spin polarization we show the laser frequency to be in the range 1-100 THz. The optical gain is estimated to be of order 10^7 cm^{-1}, which exceeds the gain of conventional semiconductor lasers by 3 or 4 orders of magnitude. A relevant experimental study is proposed and discussed.

cond-mat↗

arXiv2002

Quantum Precursor of Shuttle Instability

The effects of a coupling between the quantized mechanical vibrations of a quantum dot and coherent tunneling of electrons through a single level in the dot are studied. The equation of motion for the reduced density operator describing the vibrational degree of freedom is obtained. It is shown that that the expectation value of the displacement is an oscillating function of time with an exponentially increasing amplitude, which is the signature of a quantum shuttle instability.

cond-mat.mes-hall↗

arXiv2002

Electrical Manipulation of Nanomagnets

We demonstrate a possibility to manipulate the magnetic coupling between two nanomagnets with a help of ac electric field. In the scheme suggested the magnetic coupling in question is mediated by a magnetic particle contacting with both of the nanomagnets through the tunnel barriers. The electric field providing a successive suppression of the barriers leads to pumping of magnetization through the mediating particle. Time dependent dynamics of the particle magnetization allows to to switch between ferro- and antiferromagnetic couplings.

cond-mat.mes-hall↗

arXiv2002

Mechanical Cooper pair transportation as a source of long distance superconducting phase coherence

Transportation of Cooper-pairs by a movable single Cooper-pair-box placed between two remote superconductors is shown to establish coherent coupling between them. This coupling is due to entanglement of the movable box with the leads and is manifested in the supression of quantum fluctuations of the relative phase of the order parameters of the leads. It can be probed by attaching a high resistance Josephson junction between the leads and measuring the current through this junction. The current is suppressed with increasing temperature.

cond-mat.mes-hall↗

arXiv2002

Vibrational Instability due to Coherent Tunneling of Electrons

Effects of a coupling between the mechanical vibrations of a quantum dot placed between the two leads of a single electron transistor and coherent tunneling of electrons through a single level in the dot has been studied. We have found that for bias voltages exceeding a certain critical value a dynamical instability occurs and mechanical vibrations of the dot develop into a stable limit cycle. The current-voltage characteristics for such a transistor were calculated and they seem to be in a reasonably good agreement with recent experimental results for the single $C_{60}$-molecule transistor by Park et al.(Nature {\bf 407,} (2000) 57).

cond-mat.mes-hall↗