We review the spin splitting of subband energies caused by bulk and structure inversion asymmetries in semiconductor III-V and II-VI heterostructures. We present both theoretical and experimental aspects of the problem, and we discuss the spin splitting in the absence of external fields as well as its dependence on magnetic and electric fields. The theoretical description of conduction and valence subbands is based on a multiband k • p formalism. Experimental results are summarized, as obtained by beatings of the Shubnikov-de Haas oscillations, magnetoconductance in antilocalization regime, Raman scattering, spin resonance and cyclotron resonance. This review article is motivated by recent interest in spin properties of heterostructures in view of spintronic applications.

We study the rectification of voltage fluctuations in a system consisting of two Coulomb-coupled quantum dots. The first quantum dot is connected to a reservoir where voltage fluctuations are supplied and the second one is attached to two separate leads via asymmetric and energy-dependent transport barriers. We observe a rectified output current through the second quantum dot depending quadratically on the noise amplitude supplied to the other Coulomb-coupled quantum dot. The current magnitude and direction can be switched by external gates, and maximum output currents are found in the nA region. The rectification delivers output powers in the pW region. Future devices derived from our sample may be applied for energy harvesting on the nanoscale beneficial for autonomous and energy-efficient electronic applications. DOI: 10.1103/PhysRevLett.114.146805 PACS numbers: 73.23.-b, 73.50.Td, 73.61.Ey, 85.30.-z Extracting work from random fluctuations by energy conversion to a unidirectional particle flow is a key enabling technology and has consequently triggered substantial experimental and theoretical work [1][2][3][4]. The exploitation of temperature and fluctuation gradients for energy harvesting has led to new concepts such as Brownian and Büttiker-Landauer motors [5][6][7][8], phonon rectifiers [9,10], and piezoelectric nanogenerators [11][12][13]. Challenging factors in miniaturizing heat engines are an efficient energy conversion and the maintenance of welldefined hot and cold spots [14]. Quantum dot structures are among the smallest possible heat engines conceived thus far. Pioneering work in this field was conducted by, among others, Molenkamp et al., who measured the Seebeck voltage of single quantum dots (QDs) and quantum point contacts (QPCs) [15][16][17]. In recent years, research concerning heat engines based on QDs and QPCs followed [18][19][20][21][22]. Furthermore, Coulomb-coupled systems attracted attention due to their ability to generate currents in unbiased wires via the Coulomb drag [23][24][25]. A striking proposal combining rectifying effects with QDs was recently made by Sánchez et al., who showed that two capacitively coupled QDs connected to electron reservoirs operated in the Coulomb-blockade regime can act as a rectifier that transfers each energy quantum that passes from one to the other QD to the motion of single electrons (i.e., to charge quanta) [26]. Notably, the heat and charge current directions are decoupled in the proposed system. Later, Sothmann et al. investigated a similar design based on open QD systems (with conductances higher than the conductance quantum) exhibiting higher output currents, which makes this proposal more accessible to experimental realization [27,28]. Furthermore, it combines maximum output power as well as maximum efficiency at the same electrostatic configuration, which is in contrast to Coulomb-blockade systems, where maximum efficiency theoretically occurs at zero output power [26].In this Letter, we present a system that converts voltage fluctuation...

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