Excitonic states of weakly one-dimensional quantum wires

Il Nuovo Cimento D - We report on calculations of excitonic properties of weakly one-dimensional quantum wires where the exciton centre of mass is quantized by the harmonic potentials of electron...     

The bound states of weakly coupled long-range one-dimensional quantum hamiltonians

We study the small λ behavior of the ground state energy, E(λ), of the Hamiltonian $\text{?(}\text{d}{}^2\text{dx}{}^2\text{) + λV(x)}$. In particular, if V(x) ～ ?ax^?2 at infinity and if 69-1, we prove that $\text{(?E(λ))}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= ?[}\text{1}\text{2}\text{λ + aλ}{}^2\text{lnλ] ∫ dxV(x) + O(λ}{}^2\text{)}$.     

Luttinger-liquid behavior in weakly disordered quantum wires

We have measured the temperature dependence of the conductance in long V-groove quantum wires fabricated in GaAs/AlGaAs heterostructures. Our data are consistent with recent theories developed within the framework of the Luttinger-liquid model, in the limit of weakly disordered wires. We show that, for the relatively low level of disorder in our quantum wires, the value of the interaction parameter g congruent with 0.66, which is the expected value for GaAs. However, samples with a higher level of disorder show conductance with stronger temperature dependence, which does not allow their treatment in the framework of perturbation theory. Fitting such data with perturbation-theory models leads inevitably to wrong (lower) values of g.     

Minimal excitation states of electrons in one-dimensional wires

A strategy is proposed to excite particles from a Fermi sea in a noise-free fashion by electromagnetic pulses with realistic parameters. We show that by using quantized pulses of simple form one can suppress the particle-hole pairs which are created by a generic excitation. The resulting many-body states are characterized by one or several particles excited above the Fermi surface accompanied by no disturbance below it. These excitations carry charge which is integer for noninteracting electron gas and fractional for Luttinger liquid. The operator algebra describing these excitations is derived, and a method of their detection which relies on noise measurement is proposed.     

Electronic states in hyperbolic-boundary crescent-shaped quantum wires

A fully two-dimensional study of the electronic sub-bands in crescent-shaped quantum wires is presented. The confinement energies and the wave functions are compared by means of an aspect ratio to those produced by the adiabatic approximation. Guidelines for applying the adiabatic model are provided and the adiabatic quantum number classification scheme is discussed. Non- adiabatic states are determined among the first few sub-bands and a built-in dipole is identified. The energy spectrum is explored as a function of wire dimensions achievable by present-day technology. Wire parameters corresponding to maximized sub-band separations are determined.     

Excitonic and electronic states in ellipsoidal and semiellipsoidal quantum dots

A simple model is assumed to obtain analytical solutions of the Schrödinger equation in prolate spheroidal coordinates for the electron–hole pair confined to an ellipsoidal quantum dot (EQD) or to a semiellipsoidal quantum dot (SEQD). Numerical calculations are carried out to find the excitonic states as well as the electronic states decoupled from holes in such geometries. Their dependence on the inverse of the eccentricity of the ellipsoidal surfaces for different interfocal distances is investigated. The binding energy and the recombination radiation energy are calculated for GaAs and InAs QDs; the same dependences are also investigated. Comparison with previous calculations and experiments shows a good order-of-magnitude agreement. It is demonstrated that some of the available states in an EQD are forbidden in the SEQD and, consequently, some of the photoluminescence lines observed in the former case are suppressed in the latter geometry.     

Analyticity of quantum states in one-dimensional tight-binding model

Analytical complexity of quantum wavefunction whose argument is extended into the complex plane provides an important information about the potentiality of manifesting complex quantum dynamics such as time-irreversibility, dissipation and so on. We examine Pade approximation and some complementary methods to investigate the complex-analytical properties of some quantum states such as impurity states, Anderson-localized states and localized states of Harper model. The impurity states can be characterized by simple poles of the Pade approximation, and the localized states of Anderson model and Harper model can be characterized by an accumulation of poles and zeros of the Pade approximated function along a critical border, which implies a natural boundary (NB). A complementary method based on shifting the expansion-center is used to confirm the existence of the NB numerically, and it is strongly suggested that the both Anderson-localized state and localized states of Harper model have NBs in the complex extension. Moreover, we discuss an interesting relationship between our research and the natural boundary problem of the potential function whose close connection to the localization problem was discovered quite recently by some mathematicians. In addition, we examine the usefulness of the Pade approximation for numerically predicting the existence of NB by means of two typical examples, lacunary power series and random power series.     

Helical liquids and Majorana bound states in quantum wires

We show that the combination of spin-orbit coupling with a Zeeman field or strong interactions may lead to the formation of a helical electron liquid in single-channel quantum wires, with spin and velocity perfectly correlated. We argue that zero-energy Majorana bound states are formed in various situations when such wires are situated in proximity to a conventional s-wave superconductor. This occurs when the external magnetic field, the superconducting gap, or, most simply, the chemical potential vary along the wire. These Majorana states do not require the presence of a vortex in the system. Experimental consequences of the helical liquid and the Majorana states are also discussed.