Dynamics of localized states in N = 4 SUSY QM

A consistent approach is offered for investigating the temporal dynamics of localized states. It is based on exactly solvable quantum mechanical models with multi-well potentials and the associate propagators. The Hamiltonian states with multi-well potentials form an adequate basis for expanding wave packets (WP) of various types and degrees of localization. Special features of WP tunneling have been studied with due regard for all Hamiltonian states with symmetric and asymmetric potentials.     

Correlation between low-temperature tunneling density of states in glasses and the glass transition temperature

The density of states of the low-temperature tunneling levels which contribute to the excess specific heat and other anomalous properties of amorphous materials is shown to be proportional to the reciprocal glass transition temperature. This result agrees with recent experimental observations for a number of glass formers.     

Exact results for anomalous transport in one-dimensional hamiltonian systems

Anomalous transport in one-dimensional translation invariant hamiltonian systems with short range interactions is shown to belong in general to the Kardar-Parisi-Zhang universality class. Exact asymptotic forms for density-density and current-current time correlation functions and their Fourier transforms are given in terms of the Pr?hofer-Spohn scaling functions, obtained from their exact solution for the polynuclear growth model. The exponents of corrections to scaling are found as well, but not so the coefficients. Mode coupling theories developed previously are found to be adequate for weakly nonlinear chains but in need of corrections for strongly anharmonic interparticle potentials. A simple condition is given under which Kardar-Parisi-Zhang behavior does not apply, sound attenuation is only logarithmically superdiffusive, and heat conduction is more strongly superdiffusive than under Kardar-Parisi-Zhang behavior.     

Graphene-based tunnel junction

The tunneling current in a junction formed by graphene half-planes and bilayer graphene with two possible packing types and two possible orientations of the crystal lattice is calculated by the Green’s function technique in the framework of the tight-binding approximation. It is shown that the band structure of graphene oriented toward the junction by the armchair-type edges leads to a power-law dependence of the tunneling current on applied voltage being specific for each specific kind of graphene. The characteristic features of this dependence are determined by the change in the number of transport channels with the growth of the applied voltage. For all junctions under study with zigzag edges oriented toward each other, it is found that the tunneling current exhibits characteristic peaks related to the existence of the localized edge states. The effects induced by the gate voltage are also studied. For the structures with zigzag edges, it is shown that the effect of switching off/on takes place for the junctions. The junctions formed by the graphene armchair edges do not exhibit any pronounced switching phenomena and the growth of the bias voltage results in higher values of the conductivity.     

Peculiarities of two-photon impurity absorption spectra in a quantum molecule with a tunnel-transparent potential barrier

The effect of dissipative tunneling parameters on the spectral dependence of the probability of two-photon impurity absorption in a quantum molecule is theoretically investigated. The effect of the tunnel barrier transparency on two-photon impurity absorption in a quantum molecule is shown to manifest itself as a change in the width of energy levels of the virtual and final states due to variations in such parameters of dissipative tunneling as temperature, photon-mode frequency, and the constant of interaction with a heat bath.     

Effect of Landau Zener tunneling by the varying sweeping rate of external field

We study the effect of Landau--Zener (LZ) tunneling caused by the varying sweeping rate of the external field, and solve the problem about the LZ tunneling rate among many levels. The LZ tunneling rate is essentially changed by the unsteady variation of the time-dependent sweeping field and is different from the steadily varying sweeping field, which makes the particles in lower states transit periodically to upper states within a finite time.     

Thermodynamic properties of small amorphous and crystalline Silica particles at low temperatures

We have measured the low-temperature (K) specific heat and heat release of small amorphous and crystalline SiO₂ particles embedded in Teflon and of Vycor. The temperature and time dependence of these properties have been interpreted in terms of the tunneling model. We found that the particle size influences the density of states of tunneling systems of the composite. The smaller the size of the particles the larger is the density of states of tunneling systems P₀. Quartz grains with dimensions in the micrometer range show similar glass-like properties as vitreous silica. In comparison with bulk vitreous silica, Vycor shows a much larger P₀ in agreement with the behavior we found for small SiO₂ particles. We discuss the implication of our results on the origin of the universal low-temperature properties of glasses. Received 9 April 1998     

Kondo晶格中的超导理论

为解释重费密子超导现象,本文在Kondo晶格中建立了S波和P波超导理论,并在推广的Nambu空间中对f电子和传导电子的杂化作用进行了自洽处理,计算了有关物理量。理论证明:如果认为f电子参与超导,对S波,所得到的超导转变温度与Tachiki等人的结果一致,但比热跃交与他们的不同,本文的结果更合理些;对P波,由Kondo晶格模型描述的重费密子超导系统等效于修正的局域的费密超流体。此外,本文还研究了杂质散射对超导态的影响,并对各种不同的超导态分别得到了出现无能隙超导的条件。 关键词：     

Comparative Effect of an Addition of a Surface Term to Woods-Saxon Potential on Thermodynamics of a Nucleon

In this study, we reveal the difference between Woods-Saxon(WS) and Generalized Symmetric WoodsSaxon(GSWS) potentials in order to describe the physical properties of a nucleon, by means of solving Schr¨odinger equation for the two potentials. The additional term squeezes the WS potential well, which leads an upward shift in the spectrum, resulting in a more realistic picture. The resulting GSWS potential does not merely accommodate extra quasi bound states, but also has modified bound state spectrum. As an application, we apply the formalism to a real problem,an α particle confined in Bohrium-270 nucleus. The thermodynamic functions Helmholtz energy, entropy, internal energy,specific heat of the system are calculated and compared for both wells. The internal energy and the specific heat capacity increase as a result of upward shift in the spectrum. The shift of the Helmholtz free energy is a direct consequence of the shift of the spectrum. The entropy decreases because of a decrement in the number of available states.     

Resonant tunneling of ultracold atoms through vacuum induced potentials

We demonstrate resonant tunneling of ultracold atoms through potentials produced by the interaction of atoms with the vacuum field of a system of cavities. We show the close connection of the transmission characteristics to the resonant states in vacuum induced potentials. Transmission of cold atoms, though sharing some features with tunneling in finite semiconductor superlattices, is strongly dependent on the coherent addition of amplitudes from various wells and barriers.     

Theory of tunneling conductance of STS around magnetic impurity in superconductors

Local density of states of quasiparticles around the magnetic impurity in superconductors are calculated on the basis of a pair potential the spatial dependence of which is determined self-consistently using negative Hubbard model. The spatial dependence of the tunneling conductance observed by Scanning tunneling spectroscopy (STS) strongly depends on the magnitude of the impurity potentials.     

Inter-Well Coupling and Resonant Tunneling Modes of MultipleGraphene Quantum Wells

We investigate the inter-well coupling of multiple graphene quantum well structures consisting of graphene superlattices with different periodic potentials. The general form of the eigenlevel equation for the bound states of the quantum well is expressed in terms of the transfer matrix elements. It is found that the electronic transmission exhibits resonant tunneling peaks at the eigenlevels of the bound states and shifts to the higher energy with increasing the incident angle. If there are N coupled quantum wells, the resonant modes have N-fold splitting. The peaks of resonant tunneling can be controlled by modulating the graphene barriers.     

Observation of quantum coherence in mesoscopic molecular magnets

By applying a transverse magnetic field B( perpendicular) of sufficient strength to the uniaxial molecular magnets Fe8 and Mn12, the tunneling splitting Delta(t) of their S = +/-10 magnetic ground states can be made large compared to perturbations such as hyperfine and dipolar interactions. We present evidence for such a Delta(t) from magnetic specific heat data below 1 K that is consistent with coherent quantum mechanical tunneling in a "mesoscopic" system under such conditions.     

Dynamics of a cold quantum gas in a δ-split one-dimensional potential well

Dynamics of a wave function in a non-symmetrically split (spatially asymmetric) doublewell potential is considered. We study the dependence of the probability of well-to-well transitions on the degree of spatial asymmetry of well sizes and show that the quantum tunneling between the wells is significantly suppressed by this asymmetry. Practically complete suppression occurs at five-ten percent asymmetry. This is close to the threshold of sensitivity of contemporary experimental schemes for creating two-well potentials. We predict the phenomenon of resonance in quantum tunneling of considered states. We have also shown that an incoherently prepared superposition state tunnels in a double-well potential almost in the same way as a perfectly coherent state.     

STM tunneling through a quantum wire with a side-attached impurity

The STM tunneling through a quantum wire (QW) with a side-attached impurity (atom, island) is investigated using a tight-binding model and the non-equilibrium Keldysh Green function method. The impurity can be coupled to one or more QW atoms. The presence of the impurity strongly modifies the local density of states of the wire atoms, thus influences the STM tunneling through all the wire atoms. The transport properties of the impurity itself are also investigated mainly as a function of the wire length and the way it is coupled to the wire. It is shown that the properties of the impurity itself and the way it is coupled to the wire strongly influence the STM tunneling, the density of states and differential conductance.     

Zero-bias tunneling anomaly in a two-dimensional electron system with disorder

The temperature dependence of a zero-bias anomaly in the tunneling conductance of an Al/δ-GaAs tunneling structure with a two-dimensional electron density in the δ-layer of 3.5 × 10¹² cm^?2 has been investigated. It has been shown that the respective drop Δρ(?, T) in the tunneling density of states ρ near the Fermi level E _F of the two-dimensional electron system depends logarithmically on the energy ? within the range of 2.7kT < |?| < ?/τ, where ? is measured with respect to E _F and τ is the momentum relaxation time of two-dimensional electrons. It has been found that the drop depth Δρ(0, T)/ρ is also proportional to ln(kT/?₀) in the temperature range T = 0.1–20 K and saturates below 0.1 K.     

Coherent tunneling of lithium defect pairs in KCl crystals

The tunneling of two lithium ion impurities on next-nearest neighbor sites in potassium chloride are investigated both experimentally and theoretically. The strong dipolar interaction leads to coherent tunneling motion of the two defect ions between degenerate off-center positions. Comparing data of rotary echo experiments for impurity pairs ⁷Li—⁷Li, ⁶Li—⁶Li, and ⁷Li—⁶Li with theory permits a thorough investigation of the isotope effect and of the effect of the interaction on the tunnel states. Our findings confirm the tunneling model with <111> off-center states to be valid even for strongly interacting impurities. Using degenerate perturbation theory in terms of two-particle states, we obtain essentially exact expressions for the tunneling spectrum and the dynamical susceptibility which agree well with the measured data.     

Logarithmically slow expansion of hot bubbles in gases

We predict a logarithmically slow expansion of hot bubbles in gases in the process of cooling. A model problem is first solved, when the temperature has compact support. Then the temperature profile decaying exponentially at large distances is considered. The periphery of the bubble is shown to remain essentially static ("glassy") in the process of cooling until it is taken over by a logarithmically slowly expanding "core." An analytical solution to the problem is obtained by matched asymptotic expansion. This problem gives an example of how logarithmic corrections enter dynamic scaling.     

Thermodynamics of phonon-modulated tunneling centers

In recent years tunneling centers have frequently been used to explain the unusual thermodynamic properties of disordered materials; in these approaches, however, the effect of the tunneling-phonon interaction is neglected. The present study considers the archetype model of phonon-assisted tunneling, which is well known from other areas of tunneling physics (quantum diffusion, etc.). It is shown that the full thermodynamic information can be rigorously extracted from a single Green function. An extended factorization procedure beyond Hartree-Fock is introduced, which is checked by sum rules as well as by exact Goldberger-Adams expansions. The phonon-modulated internal energy and specific heat are calculated for different power-law coupling setups.     

Heat generation properties determined by chemical potentials

We investigate the current-induced heat generation in a quantum dot (QD) coupled to four spin chemical potentials, which originate from the magnetic pumping field applied on the QD. Both resonant and non-resonant electron tunneling process is analyzed. It is found that the heat generation characteristic is mainly determined by the two spin chemical potentials lying nearest to the dot level. In particular, when the difference of this two potentials is less than two phonon energy, the heat generation exhibits quantum properties, unique behavior to nanosystems and absent in macroscopic bulks.