Influence of dissipation on one- and two-dimensional quantum tunneling

The influence of low-frequency oscillations of the medium on the particle tunneling probability is investigated in a system with a selected tunneling coordinate, when the two-well tunnel potential takes the form of two parabolas of the same frequency. With parallel or antiparallel tunneling of two interacting particles, taking the interaction with the medium into account has no qualitative effect on the process. Quantitatively, however, the medium always influences the parallel motion of the tunneling particles and does not influence the action along the basic trajectory (R₁=−R₂) with antiparallel motion of the tunneling particles. Penzensk State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 103–107, July, 1998.     

Deconfinement and dissipation in quantum Hall Josephson tunneling

The zero-bias tunneling resonance in quantum Hall bilayer systems is investigated via numerical simulations of the classical two-dimensional XY model with a symmetry-breaking field. Disorder is included in the model and is shown to nucleate strings of overturned spins proliferated through the system, with unpaired vortices and antivortices at their end points. This string glass state supports low-energy excitations which lead to anomalously large dissipation in tunneling, as observed in experiment. The effect of an in-plane magnetic field is discussed.     

Decoherence and entanglement in coherent quantum tunneling of magnetization with dissipation

We study the coherent quantum tunneling of magnetization, for example, in a biaxial molecular magnet with dissipation of the environment which results in the suppression of the tunneling and therefore the decoherence of superposition of macroscopic quantum states in terms of the general spin-boson model. The degree of entanglement between the magnet and the environment is evaluated explicitly with the help of reduced density matrix. We show an interesting relation that the degree of entanglement approaches maximum value when the coherent tunneling is suppressed completely.     

Superconducting tunneling on Chevrel phase thin films

Electron tunneling spectroscopy has been applied for the investigation of Cu_1.8Mo₆S₈, PbMo_6.35S₈ and LaMo₆S₈ d.c. getter-sputtered thin films. Cryogenically deposited Al₂O₃ as the artificial barrier with Al counter-electrode formed the tunnel junctions. The energy gap Δ₀ and the ratio 2Δ₀/k_BT_c were determined from the differential conductance dJ/dV vs. voltage V. Preliminary measurements showed phonon structure in LaMo₆S₈ films.     

Atomic tunneling states with dissipation in glasses: temperature-dependent two-level systems

By taking account of the influence of dissipation on atomic tunneling states in glasses, we introduce a density of states of two-level systems which is non-linearly temperature dependent. Based on this model, we can explain the “excess T³” anomaly in the specific heat and the “plateau” in the thermal conductivity of glasses.     

Influence of trap-assisted tunneling on trap-assisted tunneling current in double gate tunnel field-effect transistor

Trap-assisted tunneling(TAT) has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor(TFET). In this paper, we assess subthreshold performance of double gate TFET(DG-TFET) through a band-to-band tunneling(BTBT) model, including phonon-assisted scattering and acoustic surface phonons scattering. Interface state density profile(D_(it)) and the trap level are included in the simulation to analyze their effects on TAT current and the mechanism of gate leakage current.     

Dynamics and dissipation induced by single-electron tunneling in carbon nanotube nanoelectromechanical systems

We demonstrate the effect of single-electron tunneling (SET) through a carbon nanotube quantum dot on its nanomechanical motion. We find that the frequency response and the dissipation of the nanoelectromechanical system to SET strongly depends on the electronic environment of the quantum dot, in particular, on the total dot capacitance and the tunnel coupling to the metal contacts. Our findings suggest that one could achieve quality factors of 10(6) or higher by choosing appropriate gate dielectrics and/or by improving the tunnel coupling to the leads.     

Model study of dissipation in quantum phase transitions

We consider a prototypical system of an infinite range transverse field Ising model coupled to a bosonic bath. By integrating out the bosonic degrees, an effective anisotropic Heisenberg model is obtained for the spin system. The phase diagram of the latter is calculated as a function of coupling to the heat bath and the transverse magnetic field. Collective excitations at low temperatures are assessed within a spin-wave like analysis that exhibits a vanishing energy gap at the quantum critical point. We also discuss the possible realization and application of the model in different physical systems.     

Influence of barrier parameters on tunneling in ferromagnet-insulator-ferromagnet contacts

The contribution of electrons moving at large angles to the barrier junction plane to the tunnel current is calculated. This contribution turns out to be small only if the Fermi energy of the electrons equals several electron volts. Otherwise, specifically, when the Fermi energy is no higher than 1–2 eV, this contribution dominates in high and thin potential barriers. It is found that the tunnel magnetic resistance in ferromagnet-insulator-ferromagnet contacts correlates with this contribution. It is this correlation that is responsible for a decrease in this contribution as the potential barriers get lower and thicker.     

Quantum tunneling via quantum geometric phase

A new geometric phase is proposed by considering both the energy and momentum conservation, where the corresponding dynamical phases have two parts differently from the conventional calculations for the phase. The results are applied to quantum tunneling process, which is helpful to distinguish the concept about the tunneling time.     

Local spectroscopy and atomic imaging of tunneling current, forces, and dissipation on graphite

Theory predicts that the currents in scanning tunneling microscopy (STM) and the attractive forces measured in atomic force microscopy (AFM) are directly related. Atomic images obtained in an attractive AFM mode should therefore be redundant because they should be similar to STM. Here, we show that while the distance dependence of current and force is similar for graphite, constant-height AFM and STM images differ substantially depending on the distance and bias voltage. We perform spectroscopy of the tunneling current, the frequency shift, and the damping signal at high-symmetry lattice sites of the graphite (0001) surface. The dissipation signal is about twice as sensitive to distance as the frequency shift, explained by the Prandtl-Tomlinson model of atomic friction.     

The effects of forcing and dissipation on phase transitions in thin granular layers

Recent experimental and computational studies of vibrated thin layers of identical spheres have shown transitions to ordered phases similar to those seen in equilibrium systems. Motivated by these results, we carry out simulations of hard inelastic spheres forced by homogenous white noise. We find a transition to an ordered state of the same symmetry as that seen in the experiments, but the clear phase separation observed in the vibrated system is absent. Simulations of purely elastic spheres also show no evidence for phase separation. We show that the energy injection in the vibrated system is dramatically different in the different phases, and suggest that this creates an effective surface tension not present in the equilibrium or randomly forced systems. We do find, however, that inelasticity suppresses the onset of the ordered phase with random forcing, as is observed in the vibrating system, and that the amount of the suppression is proportional to the degree of inelasticity. The suppression depends on the details of the energy injection mechanism, but is completely eliminated when inelastic collisions are replaced by uniform system-wide energy dissipation.     

Influence of dynamic power dissipation on Si MRM modulation characteristics

We experimentally observe that Si micro-ring modulator(MRM) modulation characteristics are strongly influenced by the modulation data rate and the data pattern and determine this influence is due to the temperature increase caused by dynamic power dissipation within the Si MRM device. We also quantitatively determine the amount of Si MRM resonance wavelength shift due to different modulation data rates, data patterns, and modulation voltages. Our results should be of great help for achieving reliable and optimal modulation characteristics for Si MRMs.