arXiv subjects

Daniela Dragoman

Publications and source records attributed to Daniela Dragoman.

At least 37 records · Page 2Linked to original sources

arXiv2012

Optical analogues of quantum chirality

We show that the quantum chirality of charge carriers in graphene can be mimicked in optical structures. More precisely, we demonstrate that the particular form of the transmission coefficient at an interface in graphene between regions with different parameters can be retrieved in optics in either isotropic, gyrotropic and electro-optic materials or in complex conjugate materials. Quantitative analogies are found, at least in some parameter range, between optical and quantum parameters for which the transmission coefficient is similar in the optical and quantum cases, and hence the optical fields and quantum wavefunctions propagate in a similar manner.

cond-mat.mes-hall↗

arXiv2012

Geometrical-induced rectification in two-dimensional ballistic nanodevices

The paper demonstrates that a two-dimensional ballistic nanodevice in which the electron gas satisfies either the Schroodinger equation (as in quantum wells in common semiconductor heterostructures) or the Dirac equation (as in graphene) is able to rectify an electric signal if the device has a non-uniform cross section, for instance a taper configuration. No p-n junctions or dissimilar electrodes are necessary for rectification.

cond-mat.mes-hall↗

arXiv2012

Properties of finite Gaussians and the discrete-continuous transition

Weyl's formulation of quantum mechanics opened the possibility of studying the dynamics of quantum systems both in infinite-dimensional and finite-dimensional systems. Based on Weyl's approach, generalized by Schwinger, a self-consistent theoretical framework describing physical systems characterised by a finite-dimensional space of states has been created. The used mathematical formalism is further developed by adding finite-dimensional versions of some notions and results from the continuous case. Discrete versions of the continuous Gaussian functions have been defined by using the Jacobi theta functions. We continue the investigation of the properties of these finite Gaussians by following the analogy with the continuous case. We study the uncertainty relation of finite Gaussian states, the form of the associated Wigner quasi-distribution and the evolution under free-particle and quantum harmonic oscillator Hamiltonians. In all cases, a particular emphasis is put on the recovery of the known continuous-limit results when the dimension $d$ of the system increases.

math-ph↗

arXiv2012

Graphene radio: Detecting radiowaves with a single atom sheet

We present the experimental evidence of RF demodulation by a graphene monolayer embedded in a coplanar structure. The demodulator was tested in the frequency range from 100 MHz to 25 GHz using amplitude modulated input signals. An input power of 0 dBm (1 mW) was used which is the typical power emitted for short range wireless communication systems, such as Bluetooth. The graphene demodulator exhibits good signal response in the frequency range associated to industrial, scientific and medical (ISM) radio band (2.4 GHz).

cond-mat.mes-hall↗

arXiv2011

Berry Phase and Traversal Time in Asymmetric Graphene Structures

The Berry phase and the group-velocity-based traversal time have been calculated for an asymmetric non-contacted or contacted graphene structure, and significant differences have been observed compared to semiconductor heterostructures. These differences are related to the specific, Dirac-like evolution law of charge carriers in graphene, which introduces a new type of asymmetry. When contacted with electrodes, the symmetry of the Dirac equation is broken by the Schrodinger-type electrons in contacts, so that the Berry phase and traversal time behavior in contacted and non-contacted graphene differ significantly.

cond-mat.mes-hall↗

arXiv2011

Time Flow in Graphene and Its Implications on the Cutoff Frequency of Ballistic Graphene Devices

This manuscript deals with time flow in ballistic graphene devices. It is commonly believed that in the ballistic regime the traversal time of carriers in gated graphene at normal incidence is just the ratio of the length of the device and the Fermi velocity. However, we show that the traversal time is much slower if the influence of metallic contacts on graphene is considered. Even the transmission at normal incidence becomes smaller than 1, contradicting yet another common belief. These unexpected effects are due to the transformation of Schrodinger electrons in the metallic contact into Dirac electrons in graphene and vice versa. As a direct consequence of these transformations, the ultimate performance of gated ballistic devices are much lower than expected, in agreement with experimental results.

cond-mat.mes-hall↗

arXiv2010

Kane-Like Electrons in Type II/III Heterostructures versus Dirac-Like Electrons in Graphene

The propagation of charge carriers in graphene is compared to that in type II/III heterostructures for which a two-band Kane model is appropriate. In particular, conditions for a quantitative analogy between these two cases are searched for, and found to be quite restrictive. The analysis in this paper shows that the essential property of graphene is not the spinor character of its wavefunction but the linear dispersion relation, which does not hold in finite-gap two-band Kane-type semiconductors. Therefore, Kane-like and Dirac-like charge carriers behave differently, except in zero-bandgap semiconductor superlattices.

cond-mat.mes-hall↗

arXiv2009

Real-Time Detection of Deoxyribonucleic Acid Bases via their Negative Differential Conductance Signature

In this paper we present a method for the real-time detection of the bases of the deoxyribonucleic acid using their signatures in negative differential conductance measurements. The present methods of electronic detection of deoxyribonucleic acid bases are based on a statistical analysis because the electrical currents of the four bases are weak and do not differ significantly from one base to another. In contrast, we analyze a device that combines the accumulated knowledge in nanopore and scanning tunneling detection, and which is able to provide very distinctive electronic signatures for the four bases.

cond-mat.mes-hall↗

arXiv2008

Special Relativity in Quantum Phase Space

A phase space treatment of special relativity of quantum systems is developed. In this approach a quantum particle remains localized if subject to inertial transformations, the localization occurring in a finite phase space area. Unlike non-relativistic transformations, relativistic transformations generally distort the phase space distribution function, being equivalent to aberrations in optics.

quant-ph↗

arXiv2008

Evidence Against Klein Paradox in Graphene

It is demonstrated that both transmission and reflection coefficients associated to the Klein paradox at a step barrier are positive and less than unity, so that the particle-antiparticle pair creation mechanism commonly linked to this phenomenon is not necessary. Because graphene is a solid-state testing ground for quantum electrodynamics phenomena involving massless Dirac fermions we suggest that the transport characteristic through a p-n graphene junction can decide between the results obtained in this paper and the common Klein paradox theory, which imply negative transmission and higher-than-unity reflection coefficients. Recent experimental evidence supports our findings.

quant-ph↗

arXiv2007

Quantum Electric Circuits Analogous to Ballistic Conductors

The conductance steps in a constricted two-dimensional electron gas and the minimum conductivity in graphene are related to a new uncertainty relation between electric charge and conductance in a quantized electric circuit that mimics the electric transport in mesoscopic systems. This uncertainty relation makes specific use of the discreteness of electric charge. Quantum electric circuits analogous to both constricted two-dimensional electron gas and graphene are introduced. In the latter case a new insight into the origin of minimum conductivity is obtained.

quant-ph↗

arXiv2007

Negative Differential Resistance of Electrons in Graphene Barrier

The graphene is a native two-dimensional crystal material consisting of a single sheet of carbon atoms. In this unique one-atom-thick material, the electron transport is ballistic and is described by a quantum relativistic-like Dirac equation rather than by the Schrodinger equation. As a result, a graphene barrier behaves very differently compared to a common semiconductor barrier. We show that a single graphene barrier acts as a switch with a very high on-off ratio and displays a significant differential negative resistance, which promotes graphene as a key material in nanoelectronics.

quant-ph↗

arXiv2007

Metamaterials for Ballistic Electrons

The paper presents a metamaterial for ballistic electrons, which consists of a quantum barrier formed in a semiconductor with negative effective electron mass. This barrier is the analogue of a metamaterial for electromagnetic waves in media with negative electrical permittivity and magnetic permeability. Besides applications similar to those of optical metamaterials, a nanosized slab of a metamaterial for ballistic electrons, sandwiched between quantum wells of positive effective mass materials, reveals unexpected conduction properties, e.g. single or multiple room temperature negative differential conductance regions at very low voltages and with considerable peak-to-valley ratios, while the traversal time of ballistic electrons can be tuned to larger or smaller values than in the absence of the metamaterial slab. Thus, slow and fast electrons, analogous to slow and fast light, occur in metamaterials for ballistic electrons.

quant-ph↗

arXiv2006

Photon States from Propagating Complex Electromagnetic Fields

A wavefunction for single- and many-photon states is defined by associating photons with different momenta to different spectral and polarization components of the classical, generally complex, electromagnetic field that propagates in a definite direction. By scaling each spectral component of the classical field to the square root of the photon energy, the appropriately normalized photon wavefunction acquires the desired interpretation of probability density amplitude, in contradistinction to the Riemann-Silbertsein wavefunction that can be considered as the amplitude of the photon probability energy density.

quant-ph↗

arXiv2006

On the Quantum-Classical Character of the Quantum Wavefunction of Material Particles

We show that the quantum wavefunction, interpreted as the probability density of finding a single non-localized quantum particle, which evolves according to classical laws of motion, is an intermediate description of a material quantum particle between the quantum and classical realms. Accordingly, classical and quantum mechanics should not be treated separately, a unified description in terms of the Wigner distribution function being possible. Although defined on classical phase space coordinates, the Wigner distribution function accommodates the nonlocalization property of quantum systems, and leads to both the Schrodinger equation for the quantum wavefunction and to the definition of position and momentum operators.

quant-ph↗

arXiv2006

Evolution Law of Quantum Observables from Classical Hamiltonian in Non-Commutative Phase Space

The evolution equations of quantum observables are derived from the classical Hamiltonian equations of motion with the only additional assumption that the phase space is non-commutative. The demonstration of the quantum evolution laws is quite general; it does not rely on any assumption on the operator nature of x and p and is independent of the quantum mechanical formalism.

quant-ph↗

arXiv2006

The Localized Quantum Vacuum Field

A model for the localized quantum vacuum is proposed in which the zero-point energy of the quantum electromagnetic field originates in energy- and momentum-conserving transitions of material systems from their ground state to an unstable state with negative energy. These transitions are accompanied by emissions and re-absorptions of real photons, which generate a localized quantum vacuum in the neighborhood of material systems. The model could help resolve the cosmological paradox associated to the zero-point energy of electromagnetic fields, while reclaiming quantum effects associated with quantum vacuum such as the Casimir effect and the Lamb shift; it also offers a new insight into the Zitterbewegung of material particles.

quant-ph↗

arXiv2004

Momentum Jumps in Quasi-2D Ballistic Systems

It is shown that the depopulation of magnetoelectric subbands of ballistic electrons in quasi-2D systems, due to an increased magnetic field parallel to the 2D electron gas plane, produces a momentum jump of the ballistic electrons in a direction transverse to the magnetic field. The present technological achievements allow the observation of this new phenomenon, which can be used to implement qubit states or electron switches

quant-ph↗