Coulomb blockade of the persistent current in a one-dimensional ballistic Luttinger liquid ring

The effect of an electrostatic energy (in the geometrical capacitance approach) on a persistent current is considered. It is shown that at high temperatures the current amplitude shows periodic dips as a function of the potential difference between a ring and a reservoir. These dips correspond to a lift of the Coulomb blockade. In a minimum of a dips a current is periodic in a magnetic flux with a period at any temperatures. Received: 6 April 1998 / Revised: 5 June 1998 / Accepted: 21 July 1998     

The thermal Green functions in nonextensive quantum statistical mechanics

The thermal Green functions of the quantum-mechanical harmonic oscillator are constructed within the framework of nonextensive statistical mechanics with normalized q -expectation values. For the Tsallis index q greater than unity, these functions are found to be expressed analytically in terms of the Hurwitz zeta function. It is found that influence of the nonextensivity on the time-ordered thermal propagator is relevant only at the “on-shell” states. In particular, the finite-temperature contribution to the thermal propagator becomes enhanced for the strong nonextensivity. Received 30 September 1998     

A phenomenological model of percolating magnetic nanostructures

Transport and magnetotransport properties were analysed systematically in percolating magnetic nanostructures such as Ni-rich and films. These granular magnetic films exhibit giant Hall effect. We identified features which are common and unique to these systems. Among the features are the correlation between a -like temperature dependent resistivity and a particle size distribution having a large fraction of small nanometer sized particles, and the power law dependence between the magnetoresistivity and the room temperature resistivity. Assuming the presence of nanometer sized particles in the percolating conduction channels whose contributions are sensitive to temperature and the external magnetic field, we developed a phenomenological model to explain all the common features. Received 4 November 1998     

Heat transport through a quantum dot with one-dimensional interacting leads under Coulomb blockade regime

The peculiarities of a low temperature heat transfer through a ballistic quantum dot (a double potential barrier) with interacting leads due to a long-range Coulomb interaction (in the geometrical capacitance approach) are considered. It is found that the thermal conductance K shows periodic peaks as a function of the electrostatic potential of a dot at low temperatures. At the peak maximum it is whereas near the minimum it is . Near the peak maximum the dependence K(T) is essentially nonmonotonic at the temperatures correspondent to the level spacing in the quantum dot. Received 20 October 1999 and Received in final form 20 January 2000     

Plateau transitions in fractional quantum Hall liquids

Effects of backward scattering between fractional quantum Hall (FQH) edge modes are studied. Based on the edge-state picture for hierarchical FQH liquids, we discuss the possibility of the transitions between different plateaux of the tunneling conductance G. We find a selection rule for the sequence which begins with a conductance (m: integer, p: even integer) in units of e ²/h. The shot-noise spectrum as well as the scaling behavior of the tunneling current is calculated explicitly. Received 5 October 1999 and Received in final form 19 November 1999     

Influence of hydrogen distribution on magnetic properties of amorphous samples

We have studied the effect of the homogeneity of hydrogen distribution on magnetic properties of hydrogen charged amorphous samples (Metglass 2826MB: Fe₄₀Ni₄₀Mo₄B₁₈). The results suggest that, in high magnetostrictive samples, the induced internal stresses and hence the magnetic anisotropy are related to the hydrogen distribution and not to the total quantity of hydrogen inside the sample. To perform this study, the homogeneity of hydrogen distribution in the sample was improved by using a very low rate of hydrogen charging by means of a pulsed electrolytic current. Furthermore, this pulsed electrolytic current allows us to introduce a high quantity of hydrogen without breaking the sample. Received 7 May 1999 and Received in final form 11 October 1999     

Quasiclassical Hamiltonians for large-spin systems

We extend and apply a previously developed method for a semiclassical treatment of a system with large spin S. A multisite Heisenberg Hamiltonian is transformed into an effective classical Hamilton function which can be treated by standard methods for classical systems. Quantum effects enter in form of multispin interactions in the Hamilton function. The latter is written in the form of an expansion in powers of J/(TS), where J is the coupling constant. Main ingredients of our method are spin coherent states and cumulants. Rules and diagrams are derived for computing cumulants of groups of operators entering the Hamiltonian. The theory is illustrated by calculating the quantum corrections to the free energy of a Heisenberg chain which were previously computed by a Wigner-Kirkwood expansion. Received 5 May 1999 and received in final form 24 September 1999     

Quantum dynamics of a generalized Coleman-Hepp model

Studies on a generalized Coleman-Hepp model are done on the basis of a spin coherent state representation and a transformation property of the model Hamiltonian. Namely, transforming the original model Hamiltonian into a simpler form, we can determine time evolution of the whole system by successive applications of rotation operators in a spinor space. Dynamics of detector spins as well as that of an incident particle are fully discussed. Explicit numerical evaluations are also performed. Relevance of our solution to a generalized Cini model is also briefly mentioned. Received 24 August 1999