Tunneling Transitions Research Articles

Magnetic excitation and readout of methyl group tunnel coherence

Methyl groups are ubiquitous in synthetic materials and biomolecules. At sufficiently low temperature, they behave as quantum rotors and populate only the rotational ground state. In a symmetric potential, the three localized substates are degenerate and become mixed by the tunnel overlap to delocalized states separated by the tunnel splitting ν t . Although ν t can be inferred by several techniques, coherent superposition of the tunnel-split states and direct measurement of ν t have proven elusive. Here, we show that a nearby electron spin provides a handle on the tunnel transition, allowing for its excitation and readout. Unlike existing dynamical nuclear polarization techniques, our experiment transfers polarization from the electron spin to methyl proton spins with an efficiency that is independent of the magnetic field and does not rely on an unusually large tunnel splitting. Our results also demonstrate control of quantum states despite the lack of an associated transition dipole moment.

Spin Hall effect of tunneling mode in one-dimensional photonic crystal based on frustrated total internal reflection

The spin Hall effect of light (SHEL) upon reflection and refraction of p and s waves in one-dimensional photonic crystal (1DPC) tunneling mode based on frustrated total internal reflection (FTIR) is investigated in this paper. We discuss the SHEL in three different cases based on both theoretical derivation and simulation. These results have demonstrated that the SHEL in 1DPC can be enhanced significantly when the designed 1DPC structure simultaneously satisfies both high reflection coefficient of p-wave and high transmission rate of s-wave. A transverse shift of 28.47 μm (equivalent to 45λin length) can be achieved in the structure without any amplification method, which is much larger than those previously reported in literature.

Redox Control of Charge Transport in Vertical Ferrocene Molecular Tunnel Junctions

Summary Controlling charge transport through molecular tunnel junctions is of crucial importance for exploring basic physical and chemical mechanisms at the molecular level and realizing the applications of molecular devices. Here, through a combined experimental and theoretical investigation, we demonstrate redox control of cross-plane charge transport in a vertical gold/self-assembled monolayer (SAM)/graphene tunnel junction composed of a ferrocene-based SAM. When an oxidant/reductant or electrochemical control is applied to the outside surface of the neutral single-layer graphene top electrode, reversible redox reactions of ferrocene groups take place with charges crossing the graphene layer. This leads to counter anions on the outer surface of graphene, which balance the charges of ferrocene cations in the oxidized state. Correspondingly, the junctions switch between a high-conductance, neutral state with asymmetrical characteristics and a low-conductance, oxidized state with symmetrical characteristics, yielding a large on/off ratio (>100).

The effect of pressure on the negative thermal expansion of solid methane

The effect of pressure on thermal expansion of solid CH4 is calculated for the low-temperature region where the contributions from phonons and librons can be neglected and only the rotational tunnelling modes are essential. The effect of pressure is shown to increase the magnitude of the peaks of the negative thermal expansion and shifts the positions of the peaks to the low-temperature region, which goes asymptotically to zero temperature with increasing pressure. The Gruneisen thermodynamical parameter for the rotational tunnelling modes is calculated. It is large, negative, and increases in magnitude with rising pressure.

Commensuration effects in layered nanoparticle solids

We have developed HiNTS, the {\bf Hi}erarchical {\bf N}anoparticle {\bf T}ransport {\bf S}imulator, and adapted it to study commensuration effects in two classes of Nanoparticle (NP) solids: (1) a bilayer NP solid (BNS) with an energy offset, and (2) a BNS as part of a Field-Effect Transistor (FET). HiNTS integrates the ab initio characterization of single NPs with the phonon-assisted tunneling transition model of the NP-NP transitions into a Kinetic Monte Carlo based simulation of the charge transport in NP solids. First, we studied a BNS with an inter-layer energy offset $\Delta$, possibly caused by a fixed electric field. Our results include the following. (1) In the independent energy-offset model, we observed the emergence of commensuration effects when scanning the electron filling factor $FF$ across integer values. These commensuration effects were profound as they reduced the mobility by several orders of magnitude. We analyzed these commensuration effects in a five dimensional parameter space, as a function of the on-site charging energy $E_C$, energy offset $\Delta$, the disorder $D$, the electron filling factor $FF$, and the temperature $k_{B}T$. We demonstrated the complexity of our model by showing that at integer filling factors $FF$ commensuration effects are present in some regions of the parameter space, while they vanish in other regions, thus defining distinct dynamical phases of the model. We determined the phase boundaries between these dynamical phases. (2) Using these results as a foundation, we shifted our focus to the experimentally much-studied NP-FETs. NP-FETs are also characterized by an inter-layer energy offset $\Delta$, which, in contrast to our first model, is set by the gate voltage $V_G$ and thereby related to the electron filling $FF$. We demonstrated the emergence of commensuration effects and distinct dynamical phases in these NP-FETs.

Research on Fire Smoke Controlling Effect of Submarine Road Tunnel Based on FDS

Taking submarine road tunnel as the research objective, numerical calculation model of fire smoke controlling in rectangular underwater tunnel was established by FDS. The adaptability of lateral concentrated exhaust mode in tunnels of variable widths is obtained according to analysis of smoke distribution and smoke exhausting efficiency under different working conditions. The results are as follows: The increase of width results in the decrease of smoke exhausting efficiency. In the four-lane dual-directional tunnel, the smoke exhausting efficiency is 83.4%; while that of twelve-lane dual-directional tunnel is only 55.2%. The wind velocity is higher in the area near the lateral exhaust valves; and which is lower in the area far from the exhaust valves. The influence of wind velocity for lateral exhaust valves is limited. With the increase of width, the wind velocity of cross-section decreases dramatically. In a four-lane dual-directional tunnel, the wind velocity of the right wall decreases by 32%, and that in twelve-lane dual-directional tunnel decreases by 59.6%. For large-span rectangular tunnels of eight-lane dual-directional or even wider ones, the lateral centralized exhaust mode shows poor fire smoke controlling effect.

P4-IPsec: Site-to-Site and Host-to-Site VPN With IPsec in P4-Based SDN

In this work, we present P4-IPsec, a concept for IPsec in software-defined networks (SDN) using P4 programmable data planes. The prototype implementation features ESP in tunnel mode and supports different cipher suites. P4-capable switches are programmed to serve as IPsec tunnel endpoints. We also provide a client agent to configure tunnel endpoints on Linux hosts so that site-to-site and host-to-site application scenarios can be supported which are the base for virtual private networks (VPNs). While traditional VPNs require complex key exchange protocols like IKE to set up and renew tunnel endpoints, P4-IPsec benefits from an SDN controller to accomplish these tasks. One goal of this experimental work is to investigate how well P4-IPsec can be implemented on existing P4 switches. We present a prototype for the BMv2 P4 software switch, evaluate its performance, and publish its source code on GitHub. We explain why we could not provide a useful implementation with the NetFPGA SUME board. For the Edgecore Wedge 100BF-32X Tofino-based switch, we presented two prototype implementations to cope with a missing crypto unit. As another contribution of this paper, we provide technological background of P4 and IPsec and give a comprehensive review of security applications in P4, IPsec in SDN, and IPsec data plane implementations. According to our knowledge, P4-IPsec is the first implementation of IPsec for P4-based SDN.

Quantum Cosmology with Many Fluids and the Choice of Cosmological Time

In this work we propose the quantization of a cosmological model describing the primordial universe filled with five barotropic fluids, namely: radiation, dust, vacuum, cosmic strings and domain walls. We intend to identify which fluid is best suited to provide phenomenologically the temporal variable in accordance with the observable universe. Through the Galerkin spectral method and the finite difference method in the Crank-Nicolson scheme (vacuum case), the quantum cosmological solutions are obtained and compared. We, also, compare the quantum cosmological solutions with the corresponding classical ones. The vacuum case is especially interesting because it provides a tunneling transition mechanism from the quantum to the classical phase and the possibility of calculating quantum tunneling probabilities.

Macroscopic quantum coherent effects induced by electric current in dynamics of lanthanide based single molecule toroics

The dynamics of a quantum system with a large toroidal moment under the influence of a time-dependent electric current coupled with the toroidal moment is considered. The possibility of observing the quasi-anyonic excitations, the Bloch type oscillations in the precession motion of the toroidal moment, the Stark-type resonances, and the tunnel transitions between different precession modes are discussed.

Study of the Molecular Bending in Azobenzene Self-Assembled Monolayers Observed by Tip-Enhanced Raman Spectroscopy in Scanning Tunneling Mode

Tip-enhanced Raman spectroscopy (TERS) is capable of amplifying the extremely weak Raman response of azobenzene self-assembled monolayers (SAMs), thus allowing for the chemical characterization of ...

Atom-pair tunneling and quantum phase transition in asymmetry double-well trap in strong-interaction regime**Project supported by the National Natural Science Foundation of China (Grant No. 11075099).

The quantum effect of nonlinear co-tunnelling process, which is dependent on atom-pair tunneling and asymmetry of an double-well trap, is studied by using an asymmetrical extended Bose–Hubbard model. Due to the existence of atom-pair tunneling that describes quantum phenomena of ultracold atom-gas clouds in an asymmetrical double-well trap, the asymmetrical extended Bose–Hubbard model is better than the previous Bose–Hubbard model model by comparing with the experimental data cited from the literature. The dependence of dynamics and quantum phase transition on atom-pair tunneling and asymmetry are investigated. Importantly, it shows that the asymmetry of the extended Bose–Hubbard model, corresponding to the bias between double wells, leads to a number of resonance tunneling processes, which tunneling is renamed conditional resonance tunneling, and corrects the atom-number parity effect by controlling the bias between double wells.

Features of Tunneling Current in Superlattices with Electrical Domains

Abstract—The tunneling electron transport in GaAs/AlAs and InAs/AlSb superlattices with electric domains at room temperature is studied. At voltages above the threshold for the formation of domains, a series of maxima on the current–voltage characteristics, almost equidistant in voltage, and current hysteresis during direct and reverse voltage sweeps were found. An explanation is proposed relating the origin of these maxima to tunnel transitions between quantum wells in a triangular domain, assisted by the emission of optical phonons, and hysteresis with a transition between modes with a moving and static domain. The large asymmetry of the transition times between domain modes was found.

Charge State of Metallic Nanoparticles on a Conducting Substrate

The charge state of a disordered system of metallic nanoparticles on a conducting substrate is analyzed. The theoretical model that describes thermostimulated tunnel transitions of electrons between the particles and also the electron transitions between the particles and the substrate due to the difference in the work functions has been built. The model takes into account the interaction of the charges of the nearest particles and also the interaction of the particle charges with the image charges in the substrate. The Monte Carlo computer simulation for this model makes it possible to obtain the distribution pattern of the charge in structures with different nanoparticle density in a one-layer coating on the substrate at various values of the dielectric permittivity of the environment and various values of the difference of the work functions of particles and the substrate. The numerical results for structures with Ni and Pt nanoparticles on a carbon substrate, which are often used as catalysts of chemical processes, are presented as an example.

Photon-Assisted Electron Transmission through a Quantum Point Contact

The theory of coherent photon-assisted electron transmission through a one-dimensional smooth barrier is successfully used to model the results of measuring the terahertz photoconductivity of a tunneling point contact in a two-dimensional electron gas. For this barrier in a deeper tunneling mode, photon steps in the curve of the transmission coefficient versus initial electron energy were found. Their position is determined by the terahertz photon energy.

Simulation of the quantum dynamics of indistinguishable bosons with the method of coupled coherent states

Computer simulations of many-body quantum dynamics of indistinguishable particles is a challenging task for computational physics. In this paper we demonstrate that the method of coupled coherent states (CCS) developed previously for multidimensional quantum dynamics of distinguishable particles can be used to study indistinguishable bosons in the second quantisation formalism. To prove its validity, the technique termed here coupled coherent states for indistinguishable bosons (CCSB) is tested on two model problems. The first is a system-bath problem consisting of a tunnelling mode coupled to a harmonic bath, previously studied by CCS and other methods in distinguishable representation in 20 dimensions. The harmonic bath is comprised of identical oscillators, and may be second quantised for use with CCSB, so that this problem may be thought of as a bosonic bath with an impurity. The cross-correlation function for the dynamics of the system and Fourier transform spectrum compare extremely well with a benchmark calculation, which none of the prior methods of studying the problem achieved. The second model problem involves 100 bosons in a shifted harmonic trap. Breathing oscillations in the 1-body density are calculated and shown to compare favourably to a multiconfigurational time-dependent Hartree for bosons calculation, demonstrating the applicability of the method as a new formally exact way to study the quantum dynamics of Bose-Einstein condensates.

Combined configuration-enthalpy model describing radiation-optical responses in chalcogenide semiconductor glasses

Combined configuration-enthalpy model evolving free energy configuration-coordinate and thermodynamic enthalpy diagrams is developed to describe the phenomenology of optical responses in structural metastability of chalcogenide semiconductor glasses of As-S system activated under prolonged physical ageing and high-energy γ-irradiation. The developed approach foresees glass stabilization in ground-state multibasin formed by rejuvenation-induced, irradiation-induced and/or most stable annealing-induced basins, interlinked by thermally-activated over-barrier jumping and through-barrier tunneling transitions. Effect of high-energy γ-irradiation in glasses is described due to vertical transitions of atomic sites into excited state followed by non-radiative relaxation into irradiation-induced glass ground state. This approach based on interlinked enthalpic and configuration-coordinate diagrams allows complete parameterization of optical responses related to induced metastable states, defined in blue (bleaching) or red (darkening) shifts in the transmission spectra of As-S glasses detected in the region of their fundamental optical absorption edge.

Polarized Raman analyzes of (RE3+) doped fluorotellurite glass and ceramics

Several trivalent Rare Earths ions (RE3+) doped glasses and a ceramic with the following stoichiometry 85TeO2-10PbF2-2.5AlF3-2.5REF3 (TPA); RE3+ = (Nd3+, Gd3+ and Yb3+) were studied by polarized Raman Spectroscopy and vibrational analysis. The motivation of this investigation was the understanding of the structural characteristics of the TPA glasses and ceramics. The analysis was done by a detailed band fitting study, the results of which show the combined existence of TeO4 trigonal bipyramid, TeO3+1 and TeO3 trigonal pyramid groups. Furthermore, all the bands associated with the Te–O–Te vibration mode and heavy metal fluorides such as PbF2, AlF3 and REF3 have been assigned and identified with a comparison to previous results in the literature. Finally, a discussion about the Boson Band behavior and corresponding analysis was conducted. Possible origins of the Boson Band are a combination of interaction between light, optical phonons, the tunnelling modes, and the relaxation states. It has been found that non-bridging anion atoms and disordered structures influence Boson bands below 100 cm−1. The thermal treatment for the ceramic process decreased the intensity of Boson bands, likely caused by the destruction of non-bridging anion atoms and their’ inhomogeneous cohesion.

Modulation and splitting of three-body radiative heat flux via graphene/SiC core-shell nanoparticles

We theoretically demonstrate the modulation and splitting of radiative heat flux in a three-body system consisting of graphene/SiC core-shell (GSCS) nanoparticles on the basis of their highly tunable polarizabilities, which play a dominant role in the coupling of localized surface resonance. The excitation of multiple photon tunneling modes enables the radiative heat transfer to be controlled in different scenarios. Using the dependence of photon tunneling on the Fermi level and radius of the intermediate GSCS nanoparticle, such a many-body system not only holds the potential to be a near-field thermal modulator with a thermal modulation ratio greater than 40, but also allows the heat splitting effect with the ratio over 99 when the intermediate particle becomes the hot source. This work may facilitate dynamical thermal management in a many-body system, and can also benefit the plasmonics community in the near future.

Effect of fine-tuning pore structures on the dynamics of confined water

Confinement of water in sub-nanometer pores strongly alters its vibrational dynamics from that of bulk water. The effect of confinement can, furthermore, be finely tuned by small changes in the size and symmetry of the confining pore. Using inelastic neutron scattering (INS), we recently studied the dynamics of water confined in the channels of beryl and cordierite in which, at low temperatures, water shows similar behavior, indicating an absence of hydrogen bonds acting on the water molecule and a shallow water potential in the direction perpendicular to the channels. In addition, we observed multiple tunneling modes (between 0.66 and 14.7 meV) in the INS spectra of beryl due to transitions between the split ground-state of the water protons. Here, we present a study of (i) the effect of pressure on the dynamics of water in beryl, (ii) the dynamics of water in beryl containing alkali metals (which results in changing the orientation of the water molecule in the crystal), and (iii) the dynamics of water in cordierite at low energies. We found a shift in the tunneling and vibrational modes of water in beryl to higher energies at 22 kbar relative to 1 bar. No tunneling modes were observed for water in cordierite and type-II water in beryl. Therefore, we conclude that very small differences in the size and structure of the pores and the orientation of the water molecule in these minerals result in changes in the potential of the water protons and drastic changes in the confined water dynamics.

Harvesting the Electromagnetic Energy Confined Close to a Hot Body

Abstract In the close vicinity of a hot body, at distances smaller than the thermal wavelength, a high electromagnetic energy density exists due to the presence of evanescent fields radiated by the partial charges in thermal motion around its surface. This energy density can surpass the energy density in vacuum by several orders of magnitude. By approaching a photovoltaic (PV) cell with a band gap in the infrared frequency range, this nonradiative energy can be transferred to it by photon tunnelling and surface mode coupling. Here we review the basic ideas and recent progress in near-field energy harvesting.