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We report a detailed study of ac/dc magnetization and longitudinal/transverse transport properties of La[sub 1.2]Sr[sub 1.8]Mn[sub 2]O[sub 7] single crystals below T[sub c] = 118 K. We find that the resistivity minimum at 40 K is related to the reentrant spin glass phase at the same temperature, accompanied by additional anomalous Hall effects. The carrier concentration from the ordinary Hall effects remains constant during the transition and is close to the nominal doping level (0.4 holes/Mn). The spin glass behavior comes from the competition between ferromagnetic double exchange and antiferromagnetic superexchange interactions, which leads to phase separation, i.e., a mixture of ferromagnetic and antiferromagnetic clusters, representing the canted antiferromagnetic state. [ABSTRACT FROM AUTHOR]

Monolayers of semiconducting van der Waals solids, such as transition metal dichalcogenides, acquire significant electric polarization normal to the layers when placed on a substrate or in a heterogeneous stack. This causes a linear coupling of electrons to electric fields normal to the layers. Irradiation at oblique incidence at frequencies above the gap causes interband transitions due to coupling to both normal and in-plane ac electric fields. The interference between the two processes leads to sizable in-plane photocurrents and valley currents. The direction and magnitude of the currents are controlled by light polarization and are determined by their helical or nonhelical components. The helicity-dependent ballistic current arises due to asymmetric photogeneration. The nonhelical current has a ballistic contribution (dominant in sufficiently clean samples) caused by asymmetric scattering of photoexcited carriers, and a side-jump contribution. A magneto-induced photocurrent is due to the Lorentz force or due to an intrinsic magnetic moment related to Berry curvature. [ABSTRACT FROM AUTHOR]

We develop an analytic approach to two-dimensional (2D) holes in a magnetic field that allows us to gain insight into physics of measuring the parameters of holes, such as cyclotron resonance, Shubnikov-de Haas effect and spin resonance. We derive hole energies, cyclotron masses, and the g factors in the semiclassical regime analytically, as well as analyze numerical results outside the semiclassical range of parameters, qualitatively explaining the experimentally observed magnetic field dependence of the cyclotron mass. In the semiclassical regime with large Landau level indices, and for size quantization energy much bigger than the cyclotron energy, the cyclotron mass coincides with the in-plane effective mass, calculated in the absence of a magnetic field. The hole g factor in a magnetic field perpendicular to the 2D plane is defined not only by the constant of direct coupling of the angular momentum of the holes to the magnetic field, but also by the Luttinger constants defining the effective masses of holes. We find that the g factor for quasi-2D holes with heavy mass in the [001] growth direction in GaAs quantum well is g = 4.05 in the semiclasssical regime. Outside the semiclassical range of parameters, holes behave as a species completely different from electrons. Spectra for size- and magnetic-field-quantized holes are nonequidistant, not fanlike, and exhibit multiple crossings, including crossing in the ground level. We calculate the effect of Dresselhaus terms, which transform some of the crossings into anticrossings, and the effects of the anisotropy of the Luttinger Hamiltonian on the 2D hole spectra. Dresselhaus terms of different symmetries are taken into account, and a regularization procedure is developed for the kz3 Dresselhaus terms. Control of the nonequidistant levels and crossing structure by the magnetic field can be used to control the Landau level mixing in hole systems, and thereby control hole-hole interactions in the magnetic field. [ABSTRACT FROM AUTHOR]

We develop an approach for tuning the spin splitting and g-factor of a quantum dot by coupling it to semi-magnetic quantum dot and tuning the electric field. We show that spin splittings and g-factors of the states of a non-magnetic quantum dot coupled to semimagnetic quantum dot can be enhanced orders of magnitude. Evaluations are made for coupled CdTe/CdMnTe quantum dots. These effects are caused by electric field control of repulsion of spin sublevels in the non-magnetic dot due to tunnel coupling of quantum dots. Electric field control of spin splittings in quantum dots is of potential interest in connection with spin qubit rotations for quantum computation. [ABSTRACT FROM AUTHOR]

Single quantum dot molecules have been fabricated from coupled quantum well structures of (Cd, Mn, Mg) Te alloy materials using a selective interdiffusion technique. Incorporation of Mn ions in one of the quantum dots in the molecule results in pairs of quantum dots with markedly different spin splittings. By comparing the observed magnetic field dependence of the optical polarization in photoluminescence with detailed calculations, we show that the coupling between the dots is quantum mechanical tunnel coupling and that it is tunable. [ABSTRACT FROM AUTHOR]

We demonstrate experimentally single-electron quantum dots using a single-top-gate transistor configuration on a composite quantum well. The data indicate a 15 meV Coulomb charging energy and a 20 meV orbital energy spacing, which imply a quantum dot of 20 nm in diameter. Combining with the inherent advantage of a large electron g* factor in InAs, our demonstration is significant for a solid state implementation of a scalable quantum computing. [ABSTRACT FROM AUTHOR]

We report experimental results on gated Y-branch switches made from InAs ballistic electron waveguides. We demonstrate that gating modifies the electron wave functions as well as their interference pattern, resulting in anticorrelated oscillatory transconductances. Our data provide evidence of steering the electron wave function in a multichannel transistor structure. [ABSTRACT FROM AUTHOR]