Optical response of an artificial composite nanodimer comprising a semiconductor quantum dot and a metal nanosphere is analyzed theoretically. We show that internal degrees of freedom of the system can manifest bistability and optical hysteresis as functions of the incident field intensity. We argue that these effects can be observed for real-world systems, such as a CdSe quantum dot and an Au nanoparticle hybrid. These properties can be revealed by measuring the optical hysteresis of Rayleigh scattering. We also show that the total dipole moment of the system can be switched abruptly between its two stable states by small changes in the excitation intensity. The latter promises various applications in the field of all-optical processing at the nanoscale, the most basic of them being the volatile optical memory.

The combination of self-assembly and electronic properties as well as its true nanoscale dimensions make DNA a promising candidate for a building block of single molecule electronics. We argue that the intrinsic double helix conformation of the DNA strands provides a possibility to drive the electric current through the DNA by the perpendicular electric (gating) field. The transistor effect in the poly(G)-poly(C) synthetic DNA is demonstrated within a simple model approach. We put forward experimental setups to observe the predicted effect and discuss possible device applications of DNA. In particular, we propose a design of the single molecule analog of the Esaki diode. DOI: 10.1103/PhysRevLett.98.096801 PACS numbers: 85.35.ÿp, 85.30.Mn, 85.30.Tv, 87.14.Gg The controversial question of charge transport in DNA molecules has been attracting a great deal of attention recently (see for an overview). The interest in DNA transport properties is at least twofold: on the one hand, the charge migration is believed to be important for the radiation damage repair [4] and, on the other, DNA double helices are expected to be particularly useful for molecular electronics [3,[5][6][7]. While random base sequences are relevant for biological samples, artificially created periodic DNA molecules [8], such as the poly(A)-poly(T) or poly(G)-poly(C), are probably the best candidates for novel device applications. The electrical transport through dry and wet DNA has been extensively studied both theoretically and experimentally and a variety of results has emerged: DNA has been reported to demonstrate proximity-induced superconducting [9], metallic [10 -13], semiconducting [14 -18], and insulating [19,20] behavior. Contact related effects, the impact of the environment, and the DNA base pair sequence lead to such diversity of results. According to both theory and experiment, the dry poly(G)-poly(C) synthetic DNA is a semiconductor: theoretical ab initio calculations predict a wide-band-gap semiconductor behavior (see, e.g., Ref.[21]) while experimental measurements reveal about 2 V voltage gap at low temperature [14].Many effects useful for molecular device applications have been reported: rectification, the Kondo effect, the Coulomb blockade, etc. (see Ref.[7] for a recent overview). In this contribution, it is demonstrated for the first time that the intrinsic helix conformation of the DNA strands determines the transport properties of gated DNA molecules. In particular, we show that the electric current through the double helix DNA (in the base stacking direction) can be driven by the perpendicular gating field. We put forward new experimental setups to reveal the predicted effect and discuss possible applications of the DNA. In particular, we propose a design of the single molecule analog of the Esaki diode.Two approaches are widely used to describe the DNA: ab initio calculations [21][22][23][24][25][26][27][28] and model-based Hamiltonians [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. The former can pr...

We consider a two-parameter one-dimensional Hamiltonian with uncorrelated diagonal disorder and nonrandom long-range intersite interaction J mn = J / ͉m − n͉ . The model is critical at 1 Ͻ Ͻ 3 / 2 and reveals the localization-delocalization transition with respect to the disorder magnitude. The localization-delocalization transition (LDT) in disordered systems, predicted by Anderson for three dimensions in 1958, 1 (see also Ref.2) still remains a fascinating problem (see Refs. 3-5 for an overview). During the last two decades, remarkable progress has been achieved in understanding the LDT, especially in discovering the nature of wave functions at transition. This progress became possible thanks to the fruitful idea of the multifractality of wave functions at criticality. [6][7][8][9][10] This conjecture was analytically proven for an ensemble of power-law random banded matrices (PRMB), which revealed the LDT with respect to the interaction exponent 11,12 (see Ref. 5 for an overview). Within the framework of the latter model, it was demonstrated, in particular, that (i) the distribution function of the inverse participation ratio (IPR) is scale invariant at transition and (ii) the relative IPR fluctuation (the ratio of the standard deviation to the mean) is of the order of unity at the critical point. 13,14 This finding confirmed the conjecture that was put forward for the first time in Refs. 15 and 16 that distributions of relevant physical magnitudes are universal at criticality (see also . This invariance is a powerful tool to monitor the critical point.In the present paper, we consider a two-parameter tightbinding Hamiltonian on a regular one-dimensional (1D) lattice of size N with nonrandom long-range intersite interaction:where ͉n͘ is the ket vector of a state with on-site energy n . These energies are stochastic variables, uncorrelated for different sites and distributed uniformly around zero within the interval of width ⌬. The hopping integrals are J mn = J / ͉m − n͉ , J nn = 0 with 1 Ͻ ഛ 3 / 2. For definiteness we set J Ͼ 0, then the LDT with respect to disorder magnitude occurs at the upper band edge, provided 1 Ͻ Ͻ 3/2. 20,21 The transition is similar to that within the standard 3D Anderson model. =3/2 represents the marginal case in which all states are expected to be weakly localized. 21To detect the transition we analyze level and wave function statistics. We perform a numerical analysis of size and disorder scaling of the relative fluctuation of both the nearest-level spacing (LS) and the participation number (PN). The latter is defined aswhere n denotes the nth component of the th normalized eigenstate of the Hamiltonian (1). The relative fluctuation of the nearest-level spacing is an invariant parameter at transition, as was conjectured in Ref.17 for the 3D Anderson model and demonstrated later for a variety of other disordered models (see, e.g., Refs. 5 and references therein). The invariance can be used to detect the critical point. We demonstrate that within the present model, the ratio of the...

Abstract.A new type of quantum interference device based on a graphene nanoring in which all edges are of the same type is studied theoretically. The superposition of the electron wavefunction propagating from the source to the drain along the two arms of the nanoring gives rise to interesting interference effects. We show that a side-gate voltage applied across the ring allows for control of the interference pattern at the drain. The electron current between the two leads can therefore be modulated by the side gate. The latter manifests itself as conductance oscillations as a function of the gate voltage. We study quantum nanorings with two edge types (zigzag or armchair) and argue that the armchair type is more advantageous for applications. We demonstrate finally that our proposed device operates as a quantum interference transistor with high on/off ratio.

We perform both analytical and numerical studies of the one-dimensional tight-binding Hamiltonian with stochastic uncorrelated on-site energies and nonfluctuating long-range hopping integrals J mn = J / ͉m − n͉ . It was argued recently ͓A. Rodríguez et al., J. Phys. A 33, L161 ͑2000͔͒ that this model reveals a localizationdelocalization transition with respect to the disorder magnitude provided 1 Ͻ Ͻ 3 / 2. The transition occurs at one of the band edges ͑the upper one for J Ͼ 0 and the lower one for J Ͻ 0͒. The states at the other band edge are always localized, which hints at the existence of a single mobility edge. We analyze the mobility edge and show that, although the number of delocalized states tends to infinity, they form a set of null measure in the thermodynamic limit, i.e., the mobility edge tends to the band edge. The critical magnitude of disorder for the band edge states is computed versus the interaction exponent by making use of the conjecture on the universality of the normalized participation number distribution at the transition.

We study the thermoelectric properties of rectangular graphene rings connected symmetrically or asymmetrically to the leads. A side-gate voltage applied across the ring allows for the precise control of the electric current flowing through the system. The transmission coefficient of the rings manifest Breit-Wigner line shapes and/or Fano line shapes, depending on the connection configuration, the width of nanoribbons forming the ring and the side-gate voltage. We find that the thermopower and the figure of merit are greatly enhanced when the chemical potential is tuned close to resonances. Such enhancement is even more pronounced in the vicinity of Fano-like antiresonances which can be induced by a side-gate voltage independently of the geometry. This opens a possibility to use the proposed device as a tunable thermoelectric generator.

We study theoretically the optical response of graded linear arrays of noble metal nanospheres in which the center-to-center distances and/or the radii of the spheres change linearly along the chain. A strong asymmetry of the system response with respect to the direction of incidence of the incoming light is revealed. We show that for light propagating from smaller to larger spheres the optical signal can be localized in a controlled way at an arbitrary subset of a few neighboring spheres by adjusting the wavelength of the incoming field. This opens new opportunities to control the flow of electromagnetic energy at the nanometer scale.

We conduct a theoretical study of the nonlinear optical response of a two-dimensional semiconductor quantum dot supercrystal subjected to a quasi-resonant continuous wave excitation. A constituent quantum dot is modeled as a three-level ladder-like system (comprising the ground, the one-exciton, and the bi-exction states). To study the stationary response of the supercrystal, we propose an exact linear parametric method of solving the nonlinear steady-state problem, while to address the supercrystal optical dynamics qualitatively, we put forward a novel method to calculate the bifurcation diagram of the system. Analyzing the dynamics, we demonstrate that the supercrystal can exhibit multistability, periodic and aperiodic self-oscillations, and chaotic behavior, depending on parameters of the supercrystal and excitation conditions. The effects originate from the interplay of the intrinsic nonlinearity of quantum dots and the retarded inter-dot dipole-dipole interaction. The latter provides a positive feedback which results in the exotic supercrystal optical dynamics. These peculiarities of the supercrystal optical response open up a possibility for all-optical applications and devices. In particular, an all-optical switch, a tunable generator of THz pulses (in self-oscillating regime), a noise generator (in chaotic regime), and a tunable bistable mirror can be designed. a b c FIG. 1. PbSe rocksalt 2D nanostructures with (a) honeycomb and (b) square lattice symmetry, (c) -CdSe nanostructure with a compressed zincblende and slightly distorted square lattices (scale bars, 50 nm). Insets show the electrodiffractograms in the [111] (a) and [100] (b,c) projections. The figure is from Ref. [7].linearity of the layer is ensured by the fact that two-level emitters are nonlinear systems. The positive feedback originates from the secondary field, which is generated by the emitters themselves; this is the so-called intrinsic feedback, i.e., here a cavity (external feedback) is not required.A two-dimensional (2D) semiconductor quantum dot (SQD) supercrystal represents a limiting case of a thin layer. In this paper, we conduct a theoretical study of the nonlinear optical response of such a system. A single SQD is considered as a point-like system with three consecutive levels of the ground, one-exciton, and bi-arXiv:1910.02553v1 [physics.optics]