Tunable optical Aharonov-Bohm effect in a semiconductor quantum ring

By applying an electric field perpendicular to a semiconductor quantum ring we show that it is possible to modify the single particle wave function between quantum dot (QD)-like to ring-like. The constraints on the geometrical parameters of the quantum ring to realize such a transition are derived. With such a perpendicular electric field we are able to tune the Aharanov-Bohm (AB) effect for both single particles and for excitons. The tunability is in both the strength of the AB-effect as well as in its periodicity. We also investigate the strain induce potential inside the self assembled quantum ring and the effect of the strain on the AB effect

Magnetic properties of HO2 thin films

We report on the magnetic and transport studies of hafnium oxide thin films grown by pulsed-laser deposition on sapphire substrates under different oxygen pressures, ranging from 10-7 to 10-1 mbar. Some physical properties of these thin films appear to depend on the oxygen pressure during growth: the film grown at low oxygen pressure (P ~= 10-7 mbar) has a metallic aspect and is conducting, with a positive Hall signal, while those grown under higher oxygen pressures (7 x 10-5 <= P <= 0.4 mbar) are insulating. However, no intrinsic ferromagnetic signal could be attributed to the HfO2 films, irrespective of the oxygen pressure during the deposition.Comment: 1

Self-consistent model for ambipolar tunneling in quantum-well systems

We present a self-consistent approach to describe ambipolar tunneling in asymmetrical double quantum wells under steady-state excitation and extend the results to the case of tunneling from a near-surface quantum well to surface states. The results of the model compare very well with the behavior observed in photoluminescence experiments in $InGaAs/InP$ asymmetric double quantum wells and in near-surface $AlGaAs/GaAs$ single quantum wells.Comment: 10 pages, REVTeX 3.

Carrier relaxation mechanisms in self-assembled (In,Ga)As/GaAs quantum dots: Efficient P -> S Auger relaxation of electrons

We calculate the P-shell--to-S-shell decay lifetime \tau(P->S) of electrons in lens-shaped self-assembled (In,Ga)As/GaAs dots due to Auger electron-hole scattering within an atomistic pseudopotential-based approach. We find that this relaxation mechanism leads to fast decay of \tau(P->S)~1-7 ps for dots of different sizes. Our calculated Auger-type P-shell--to-S-shell decay lifetimes \tau(P->S) compare well to data in (In,Ga)As/GaAs dots, showing that as long as holes are present there is no need for an alternative polaron mechanism.Comment: Version published in Phys. Rev.

Discriminating among Earth composition models using geo-antineutrinos

It has been estimated that the entire Earth generates heat corresponding to about 40 TW (equivalent to 10,000 nuclear power plants) which is considered to originate mainly from the radioactive decay of elements like U, Th and K, deposited in the crust and mantle of the Earth. Radioactivity of these elements produce not only heat but also antineutrinos (called geo-antineutrinos) which can be observed by terrestrial detectors. We investigate the possibility of discriminating among Earth composition models predicting different total radiogenic heat generation, by observing such geo-antineutrinos at Kamioka and Gran Sasso, assuming KamLAND and Borexino (type) detectors, respectively, at these places. By simulating the future geo-antineutrino data as well as reactor antineutrino background contributions, we try to establish to which extent we can discriminate among Earth composition models for given exposures (in units of kt$\cdot$ yr) at these two sites on our planet. We use also information on neutrino mixing parameters coming from solar neutrino data as well as KamLAND reactor antineutrino data, in order to estimate the number of geo-antineutrino induced events.Comment: 24 pages, 10 figures, final version to appear in JHE

Engineering ultralong spin coherence in two-dimensional hole systems at low temperatures

For the realisation of scalable solid-state quantum-bit systems, spins in semiconductor quantum dots are promising candidates. A key requirement for quantum logic operations is a sufficiently long coherence time of the spin system. Recently, hole spins in III-V-based quantum dots were discussed as alternatives to electron spins, since the hole spin, in contrast to the electron spin, is not affected by contact hyperfine interaction with the nuclear spins. Here, we report a breakthrough in the spin coherence times of hole ensembles, confined in so called natural quantum dots, in narrow GaAs/AlGaAs quantum wells at temperatures below 500 mK. Consistently, time-resolved Faraday rotation and resonant spin amplification techniques deliver hole-spin coherence times, which approach in the low magnetic field limit values above 70 ns. The optical initialisation of the hole spin polarisation, as well as the interconnected electron and hole spin dynamics in our samples are well reproduced using a rate equation model.Comment: 16 pages, 6 figure

Production of a0a_0-mesons in pp and pn reactions

We investigate the cross section for the reaction $NN \to NNa_0$ near threshold and at medium energies. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also considered. The results are used to calculate the contribution of the $a_0$ meson to the cross sections and invariant $K \bar K$ mass distributions of the reactions $pp\to pn K^+\bar K^0$ and $pp\to pp K^+K^-$. It is found that the experimental observation of $a_0^+$ mesons in the reaction $pp\to pn K^+\bar K^0$ is much more promising than the observation of $a_0^0$ mesons in the reaction $pp\to pp K^+K^-$.Comment: 26 pages, including 11 eps figures, to be bublished in J. Phys.

Magnetic field-induced exchange effects between Mn ions and free carriers in ZnSe quantum well through the intermediate nonmagnetic barrier studied by photoluminescence

Photoluminescence (PL) of the 50 nm $Zn_{0.9}Be_{0.05}Mn_{0.05}Se$/ $d$ nm $Zn_{0.943}Be_{0.057}Se$/ 2.5 nm $ZnSe$/ 30 nm $Zn_{0.943}Be_{0.057}Se$ structures is investigated as a function of magnetic field ($B$) and thickness ($d$) of intermediate $Zn_{0.943}Be_{0.057}Se$ nonmagnetic barrier between the $Zn_{0.9}Be_{0.05}Mn_{0.05}Se$ semimagnetic barrier and $ZnSe$ quantum well at the temperature 1.2 K. The rate of the shift of different PL bands of the structures under study is estimated in low and high magnetic fields. The causes of the shift rate increase under pass from low to high magnetic fields are interpreted. The peculiarities of the effect of the intermediate barrier on the luminescence properties of the structures are presented. It is shown that deformation of adjacent layers by the barrier plays a crucial role in the formation of these properties, especially in forming the $Mn$ complexes in the $Zn_{0.9}Be_{0.05}Mn_{0.05}Se$ layer. The change of the band gap as well as of the donor and acceptor levels energies under the effect of biaxial compression of the $Zn_{0.9}Be_{0.05}Mn_{0.05}Se$ layer by the $Zn_{0.943}Be_{0.057}Se$ are estimated. It is concluded that the $Zn_{0.943}Be_{0.057}Se$ intermediate barrier also appreciably changes the effect of giant Zeeman splitting of the semimagnetic $Zn_{0.9}Be_{0.05}Mn_{0.05}Se$ barrier energy levels on the movement of the energy levels of $ZnSe$ quantum well in a magnetic field and on polarization of the quantum well exciton emission

Strangeness production in proton-proton and proton-nucleus collisions

In these lectures we discuss the investigation of the strange meson production in proton-proton ($pp$) and in proton-nucleus ($pA$) reactions within an effective Lagrangian model. The kaon production proceeds mainly via the excitations of $N^*$(1650), $N^*$(1710), and $N^*$(1720) resonant intermediate nucleonic states, in the collision of two initial state nucleons. Therefore, the strangeness production is expected to provide information about the resonances lying at higher excitation energies. For beam energies very close to the kaon production threshold the hyperon-proton final state interaction effects are quite important. Thus, these studies provide a check on the models of hyperon-nucleon interactions. The in-medium production of kaons show strong sensitivity to the self energies of the intermediate mesons.Comment: 16 pages, 9 figures, Talk presented in the workshop on Hadron Physics, Puri, India, March 7-17,200