We demonstrate, through experiment and theory, enhanced high-frequency current oscillations due to magnetically-induced conduction resonances in superlattices. Strong increase in the ac power originates from complex single-electron dynamics, characterized by abrupt resonant transitions between unbound and localized trajectories, which trigger and shape propagating charge domains. Our data demonstrate that external fields can tune the collective behavior of quantum particles by imprinting configurable patterns in the single-particle classical phase space.PACS numbers: 05.45. Mt, 73.21.Cd Understanding the interplay between the properties of individual objects and their collective behavior is of fundamental interest in many fields [1][2][3][4]. It explains, for example, jamming and pattern formation in granular systems [1,[5][6][7], dynamical heterogeneity in phase transitions [3], tunneling dynamics and quantum phases in cold atoms [8,9], and the synchronization of networks and complex adaptive systems [2,10]. Moreover, interactions between particles play a key role in determining the structures formed when the particles come into contact [4]. Consequently, tailoring single-particle dynamics may provide a route to controlling the collective dynamics of many-body systems. This is a major challenge both in fundamental science [11][12][13] and for developing new technologies such as high-frequency electronic devices [14][15][16], whose performance can be greatly enhanced by applied quantizing magnetic fields [17,18].The phase space structure of individual particles, in particular the existence and relative location of regular and chaotic trajectories, critically affects thermalization and diffusion both in classical and quantum systems [19,20]. Therefore, manipulating the single-particle phase space, by generating new chaotic trajectories for example, is a promising strategy in the search for ways to control other collective phenomena.Usually, the transition to chaos in Hamiltonian systems occurs by the gradual destruction of stable orbits, in accordance with the Kolmogorov-Arnold-Moser (KAM) theorem [21]. In far rarer non-KAM chaos, the chaotic orbits become abruptly unbounded when the perturbation frequency attains critical values and map out intricate "stochastic webs" in phase space [19]. Experimental realization of non-KAM classical chaos was recently achieved using a quantum system [22]: a semiconductor superlattice (SL) with a magnetic field, B, tilted relative to an electric field, F, along the SL axis. When the frequency of single-electron Bloch oscillations along the SL axis is commensurate with that for cyclotron motion in the plane of the layers [14,22,23], the orbits map out stochastic webs in phase space, which delocalize the electrons in real space. This delocalization creates multiple resonant peaks in the single-electron drift velocity versus F characteristics, which enhance the measured dc conductivity [22].In this Letter, we show, via experiments and theoretical modeling, that non-KAM single-pa...

Electrons performing Bloch oscillations in an energy band of a dc-biased superlattice in the presence of weak dissipation can potentially generate THz fields at room temperature. The realization of such a Bloch oscillator is a long-standing problem due to the instability of a homogeneous electric field in conditions of negative differential conductivity. We establish the theoretical feasibility of stable THz gain in a long superlattice device in which the bias is quasistatically modulated by microwave fields. The modulation waveforms must have at least two harmonics in their spectra.

High-field and nonlinear effects. PACS. 07.57.Hm -Infrared, submillimeter wave, microwave, and radiowave sources.Abstract. -We show that space-charge instabilities (electric field domains) in semiconductor superlattices are the attribute of absolute negative conductance induced by small constant and large alternating electric fields. We propose the efficient method for suppression of this destructive phenomenon in order to obtain a generation at microwave and THz frequencies in devices operating at room temperature. We theoretically proved that an unbiased superlattice with a moderate doping subjected to a microwave pump field provides a strong gain at third, fifth, seventh, etc. harmonics of the pump frequency in the conditions of suppressed domains.c EDP Sciences

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