arXiv subjects

Santanu K. Maiti

Publications and source records attributed to Santanu K. Maiti.

176 records · Page 10Linked to original sources

arXiv2009

Electron transport through honeycomb lattice ribbons with armchair edges

We address electron transport in honeycomb lattice ribbons with armchair edges attached to two semi-infinite one-dimensional metallic electrodes within the tight-binding framework. Here we present numerically the conductance-energy and current-voltage characteristics as functions of the length and width of the ribbons. Our theoretical results predict that for a ribbon with much smaller length and width, so-called a nanoribbon, a gap in the conductance spectrum appears across the energy E=0. While, this gap decreases gradually with the increase of the size of the ribbon, and eventually it almost vanishes. This reveals a transformation from the semiconducting to the conducting material, and it becomes much more clearly visible from our presented current-voltage characteristics.

cond-mat.mes-hall↗

arXiv2009

Persistent current in one-dimensional non-superconducting mesoscopic rings: effects of single hopping impurity, in-plane electric field and foreign atoms

Persistent current in one-dimensional non-superconducting mesoscopic rings threaded by a slowly varying magnetic flux $ϕ$ is studied based on the tight-binding model. The behavior of the persistent current is discussed in three aspects: (a) single hopping impurity, (b) in-plane electric field and (c) in presence of some foreign atoms.

cond-mat.mes-hall↗

arXiv2009

Anomalous quantum transport in a thin film

We present a numerical study of electron transport in a thin film of varying disorder strength with the distance from its surface. A simple tight-binding model is used to describe the system, in which the film is attached to two metallic electrodes and the coupling of this film to the electrodes is illustrated by the Newns-Anderson chemisorption theory. Quite interestingly we observe that, in the smoothly varying disordered film current amplitude increases with the increase of disorder strength in the strong disorder regime, while it decreases in the weak disorder regime. This behavior is completely opposite from a conventional disordered film, where current amplitude always decreases with the increase of disorder strength.

cond-mat.mes-hall↗

arXiv2008

Persistent Current in Metallic Rings and Cylinders

We explore the behavior of persistent current and low-field magnetic response in mesoscopic one-channel rings and multi-channel cylinders within the tight-binding framework. We show that the characteristic properties of persistent current strongly depend on total number of electrons $N_e$, chemical potential $μ$, randomness and total number of channels. The study of low-field magnetic response reveals that only for one-channel rings with fixed $N_e$, sign of the low-field currents can be predicted exactly, even in the presence of disorder. On the other hand, for multi-channel cylinders, sign of the low-field currents cannot be mentioned exactly, even in the perfect systems with fixed $N_e$ as it significantly depends on the choices of $N_e$, $μ$, number of channels, disordered configurations, etc.

cond-mat.mes-hall↗

arXiv2008

Fractional periodic persistent current in a twisted normal metal loop: an exact result

We explore a novel mechanism for control of periodicity in persistent current in a twisted normal metal loop threaded by a magnetic flux $ϕ$. A simple tight-binding model is used to describe the system. Quite interestingly we see that, depending on the number of twist $p$, the persistent current exhibits $ϕ_0/p$ ($ϕ_0=ch/e$, the elementary flux-quantum) periodicity. Such fractional periodicity provides a new finding in the study of persistent current.

cond-mat.mes-hall↗

arXiv2008

A Basic Introduction on Math-Link in Mathematica

Starting from the basic ideas of mathematica, we give a detailed description about the way of linking of external programs with mathematica through proper mathlink commands. This article may be quite helpful for the beginners to start with and write programs in mathematica. In the first part, we illustrate how to use a mathemtica notebook and write a complete program in the notebook. Following with this, we also mention elaborately about the utility of the local and global variables those are very essential for writing a program in mathematica. All the commands needed for doing different mathematical operations can be found with some proper examples in the mathematica book written by Stephen Wolfram \cite{wolfram}. In the rest of this article, we concentrate our study on the most significant issue which is the process of linking of {\em external programs} with mathematica, so-called the mathlink operation. By using proper mathlink commands one can run very tedious jobs efficiently and the operations become extremely fast.

cs.MS↗

arXiv2008

How to Run Mathematica Batch-files in Background ?

Mathematica is a versatile equipment for doing numeric and symbolic computations and it has wide spread applications in all branches of science. Mathematica has a complete consistency to design it at every stage that gives it multilevel capability and helps advanced usage evolve naturally. Mathematica functions work for any precision of number and it can be easily computed with symbols, represented graphically to get the best answer. Mathematica is a robust software development that can be used in any popular operating systems and it can be communicated with external programs by using proper mathlink commands. Sometimes it is quite desirable to run jobs in background of a computer which can take considerable amount of time to finish, and this allows us to do work on other tasks, while keeping the jobs running. Most of us are very familiar to run jobs in background for the programs written in the languages like C, C++, F77, F90, F95, etc. But the way of running jobs, written in a mathematica notebook, in background is quite different from the conventional method. In this article, we explore how to create a mathematica batch-file from a mathematica notebook and run it in background. Here we concentrate our study only for the Unix version, but one can run mathematica programs in background for the Windows version as well by using proper mathematica batch-file.

cs.MS↗

arXiv2008

Parallel Evaluation of Mathematica Programs in Remote Computers Available in Network

Mathematica is a powerful application package for doing mathematics and is used almost in all branches of science. It has widespread applications ranging from quantum computation, statistical analysis, number theory, zoology, astronomy, and many more. Mathematica gives a rich set of programming extensions to its end-user language, and it permits us to write programs in procedural, functional, or logic (rule-based) style, or a mixture of all three. For tasks requiring interfaces to the external environment, mathematica provides mathlink, which allows us to communicate mathematica programs with external programs written in C, C++, F77, F90, F95, Java, or other languages. It has also extensive capabilities for editing graphics, equations, text, etc. In this article, we explore the basic mechanisms of parallelization of a mathematica program by sharing different parts of the program into all other computers available in the network. Doing the parallelization, we can perform large computational operations within a very short period of time, and therefore, the efficiency of the numerical works can be achieved. Parallel computation supports any version of mathematica and it also works as well even if different versions of mathematica are installed in different computers. The whole operation can run under any supported operating system like Unix, Windows, Macintosh, etc. Here we focus our study only for the Unix based operating system, but this method works as well for all other cases.

cs.MS↗

arXiv2008

Ladder network as a mesoscopic switch: An exact result

We investigate the possibilities of a tight binding ladder network as a mesoscopic switching device. Several cases have been discussed in which any one or both the arms of the ladder can assume random, ordered or quasiperiodic distribution of atomic potentials. We show that, for a special choice of the Hamiltonian parameters it is possible to prove exactly the existence of mobility edges in such a system, which plays a central role in the switching action. We also present numerical results for the two-terminal conductance of a general model of a quasiperiodically grown ladder which support the general features of the electron states in such a network. The analysis might be helpful in fabricating mesoscopic or DNA switching devices.

cond-mat.mes-hall↗

arXiv2008

Metal-insulator transition in an aperiodic ladder network: an exact result

We show, in a completely analytical way, that a tight binding ladder network composed of atomic sites with on-site potentials distributed according to the quasiperiodic Aubry model can exhibit a metal-insulator transition at multiple values of the Fermi energy. For specific values of the first and second neighbor electron hopping, the result is obtained exactly. With a more general model, we calculate the two-terminal conductance numerically. The numerical results corroborate the analytical findings and yield a richer variety of spectrum showing multiple mobility edges.

cond-mat.mes-hall↗

arXiv2006

Enhancement of persistent current in mesoscopic rings $&$ cylinders : shortest $&$ next possible shortest higher order hopping

We present a detailed study of persistent current and low-field magnetic susceptibility in single isolated normal metal mesoscopic rings and cylinders in the tight-binding model with higher order hopping integral in the Hamiltonian. Our exact calculations show that order of magnitude enhancement of persistent current takes place even in presence of disorder if we include higher order hopping integral in the Hamiltonian. In strictly one-channel mesoscopic rings the sign of the low-field currents can be predicted exactly even in presence of impurity. We observe that perfect rings with both odd and even number of electrons support only diamagnetic currents. On the other hand in the disordered rings, irrespective of realization of the disordered configurations of the ring, we always get diamagnetic currents with odd number of electrons and paramagnetic currents with even number of electrons. In mesoscopic cylinders the sign of the low-field currents can't be predicted exactly since it strongly depends on the total number of electrons, $N_e$, and also on the disordered configurations of the system. From the variation of persistent current amplitude with system size for constant electron density, we conclude that the enhancement of persistent current due to additional higher order hopping integrals are visible only in the mesoscopic regime.

cond-mat.mes-hall↗

arXiv2006

Persistent currents with long-range hopping in 1D single-isolated-diffusive rings

We show from exact calculations that a simple tight-binding Hamiltonian with diagonal disorder and long-range hopping integrals, falling off as a power $μ$ of the inter-site separation, correctly describes the experimentally observed amplitude (close to the value of an ordered ring) and flux-periodicity ($hc/e$) of persistent currents in single-isolated-diffusive normal metal rings of mesoscopic size. Long-range hopping integrals tend to delocalize the electrons even in the presence of disorder resulting orders of magnitude enhancement of persistent current relative to earliar predictions.

cond-mat.mes-hall↗

arXiv2005

On the role of electron correlation and disorder on persistent currents in isolated one-dimensional rings

To understand the role of electron correlation and disorder on persistent currents in isolated 1D rings threaded by magnetic flux $ϕ$, we study the behavior of persistent currents in aperiodic and ordered binary alloy rings. These systems may be regarded as disordered systems with well-defined long-range order so that we do not have to perform any configuration averaging of the physical quantities. We see that in the absence of interaction, disorder suppresses persistent currents by orders of magnitude and also removes its discontinuity as a function of $ϕ$. As we introduce electron correlation, we get enhancement of the currents in certain disordered rings. Quite interestingly we observe that in some cases, electron correlation produces kink-like structures in the persistent current as a function of $ϕ$. This may be considered as anomalous Aharonov-Bohm oscillations of the persistent current and recent experimental observations support such oscillations. We find that the persistent current converges with the size of the rings.

cond-mat.mes-hall↗

arXiv2004

Strange behavior of persistent currents in small Hubbard rings

We show exactly that small Hubbard rings exhibit unusual kink-like structures giving anomalous oscillations in persistent current. Singular behavior of persistent current disappears in some cases. In half-filled systems mobility gradually drops to zero with interaction, while it converges to some finite value in non-half-filled cases.

cond-mat.mes-hall↗