Recursion-transfer-matrix Research Articles

Physics of artificial nano-structures on surfaces

Quantum electron transport through nano-structures such as metal atomic wires or molecular bridges is investigated with various theoretical approaches. The difference of the quantization feature between Na and Al atom wires is explained based on the eigenchannel analyses combined with the recursion-transfer matrix calculation. The eigenchannels are calculated self-consistently for Au atom wires at finite bias voltage and the nonlinear conductance is explored in relation to the offset energies of d band channels. As for molecular bridges, we find that a remarkable metalization is caused, if the coupling of the molecule with the metal electrode is enhanced. Internal current distribution within the molecular networks is discussed and exotic properties of the quantum transport is found. In particular, a strong induced loop current is revealed circulating the ring part of the molecule. The direction of the loop current is switched sharply when the electron incident energy sweeps a degenerate molecular level.

Numerical Method for Local Density of States and Current Density Decomposed into Eigenchannels in Multichannel System

Scattering states in a multichannel quantum transport system are generally decomposed into eigenchannels with no interchannel mixing, which are a set of special channels obtained by the unitary transformation of the original channels. We present a numerical method of decomposing the local density of states and the current density into eigenchannels using the recursion-transfer matrix method. The method is applied to electron transport through square prisms and single/double cubic dots between electrodes, and it is shown, along with channel transmissions, how the local density of states and the current density are resolved into the eigenchannels for the systems.

Theoretical Studies on Surface Electronics States. Atom Manipulation and Atomic Contact.

Scanning tunneling microscopy (STM) has made it possible not only to observe atomic structures and electronic states of surfaces with atomic resolutions but also to modify surface structures in atomic scale. To investigate atomic processes and electronic processes induced by the STM tip, a first-principles recursion-transfer matrix (RTM) method has been developed. In this article the RTM method is introduced, and examples of application of the method to atom manipulation and atomic contact are presented. Adiabatic potential surfaces of atom extracted from a silicon surface to an aluminum tip under applied bias voltage are calculated, and decrease of activation barrier is discussed in terms of the changes of electron density distributions around the atom. Current density and tunneling barrier distributions are also clarified in detail, and the formation of atomic contact with approach of a tip is described.

Theory of surface charge-density waves and their STM images

We have studied theoretically the property of the charge-density waves at a surface or interface and their STM images. The self-consistent numerical approach presented here is based on the formalism of the recursion-transfer matrix with the tight-binding Hamiltonian. We show that charge-density waves can be modified under the presence of the surface due to the contact with the normal phase, or the bias voltage of the STM tip. The tunnel current of STM is calculated by a Laudauer-type formula.

Theoretical Study of Current and Barrier Height between Aluminum Tip and Silicon Surface in Scanning Tunneling Microscopy

The first-principles calculations for the electronic structure of the aluminum tip and the silicon surface in scanning tunneling microscopy are performed using the recursion-transfer matrix method, which is an effective method for exploring the microscopic electronic states of a bielectrode system under electric field and current. The atomic-scale current distribution and the potential barrier between the tip and the surface are presented. It is revealed that the opening of a hole in the potential barrier occurs when the tip-sample distance is 10 a.u. at a surface bias of +2.0 V.

Two-dimensional Ising model in random magnetic fields

The statistical mechanics of finite L×L Ising square lattices in a field ±h of random sign is investigated numerically by a modified recursive transfer matrix method for 6<~L<~16. Our results are consistent with the absence of a spontaneous magnetization for h≠0 even in the ground state. The singularities occurring at T=0 in the range 0<~h<~4J, J being the exchange constant, are discussed in terms of a cluster expansion. For nonzero T, less than the critical temperature of the pure two-dimensional Ising model, and h sufficiently small, the system exhibits a nonzero spin-glass order parameter of the Mattis type although there is no magnetization. The ferromagnetic correlation function becomes long ranged for h→0 and is calculated from the domain-wall density.