The effective Hamiltonian describing the motion of an exciton in an external non-homogeneous magnetic field is derived. The magnetic field plays the role of an effective potential for the exciton motion, results into an increment of the exciton mass and modifies the exciton kinetic energy operator. In contrast to the homogeneous field case, the exciton in a non-homogeneous magnetic field can also be trapped in the low field region and the field gradient increases the exciton confinement. The trapping energy and wave function of the exciton in a GaAs two-dimensional electron gas for specific circular magnetic field configurations are calculated. The results show than excitons can be trapped by non-homogeneous magnetic fields, and that the trapping energy is strongly correlated with the shape and strength of the non-homogeneous magnetic field profile. 71.35.Ji, 75.70.Cn,

No abstract

No abstract

O composto 5-(4-pyridinyl)-1,3,4-oxadiazole-2-thiol (Hpyt) adsorve espontaneamente sobre ouro formando SAMs ("Self-Assembled Monolayers") que, de acordo com os resultados eletroquímicos e de STM ("Scanning Tunneling Microscopy"), contêm poros através dos quais as moléculas dos complexos [Fe(CN) 6 ] 4-, a dependência da corrente faradáica com o pH da solução eletrolítica permitiu o cálculo do pKa da molécula de Hpyt adsorvida sobre ouro (4,2). Os parâmetros termodinâmicos, H ads and G ads , para o processo de adsorção desta molécula foram estimados em -20,01 e -39,39 kJ mol -1 , respectivamente, utilizando-se o modelo de Langmuir. O processo redox da metaloproteína citocromo c foi estudado utilizando-se a SAM de Hpyt. A constante de velocidade heterogênea de transferência de elétrons foi calculada em 2,29 10 -3 cm s -1 .5-(4-pyridinyl)-1,3,4-oxadiazole-2-thiol (Hpyt) spontaneously adsorbs on gold forming SAMs (self-assembled monolayers) that, based on STM (Scanning Tunneling Microscopy) and electrochemical data, contain pinholes through which [Fe(CN) 6 ] 4-and [Ru(NH 3 ) 6 ] 3+ probe molecules access the underlying gold electrode. For the former molecule, the dependence of the faradaic current on the electrolyte solution pH value allowed the evaluation of the surface pKa as 4.2. The thermodynamic parameters H ads and G ads for the Hpyt adsorption process could be described by the Langmuir model and were calculated as -20.01 and -39.39 kJ mol -1 , respectively. Electrodic redox reaction of cytochrome c metalloprotein was accessed by using the Hpyt SAM with a heterogeneous electron transfer rate constant of 2.29 10 -3 cm s -1 .

The trapping of excitons in a semiconductor quantum well due to a circular symmetric nonhomogeneous magnetic field is studied. The effect of the spin state of the exciton on its trapping energy is analyzed, and the importance of the interaction of the orbital and spin Zeeman effect as compared to the diamagnetic term in the exciton Hamiltonian is emphasized. Magnetic field profiles are considered, which can experimentally be created through the deposition of ferromagnetic disks on top of a semiconductor heterostructure. This setup gives rise to a magnetic dipole type of profile in the xy plane of the exciton motion. We find that the spin direction of the exciton influences its localization by changing the confinement region in the effective potential. The exciton confinement increases with magnetic field intensity, and this is more pronounced when the exciton g-factor is different from zero. The numerical calculations are performed for GaAs/AlxGa1−xAs quantum wells and we show that it open up a new realistic path for experiments designed to probe exciton trapping in semiconductors. 71.35.Ji, 75.70.Cn, 71.70.Ej