Abstract-Sub-cycle control of terahertz high-harmonic generation by dynamical Bloch oscillations

O. Schubert, M. Hohenleutner, F. Langer, B. Urbanek, C. Lange, U. Huttner, D. Golde, T. Meier, M. Kira, S. W. Koch, R. Huber

(Submitted on 13 Apr 2016)

http://arxiv.org/abs/1604.03732

Ultrafast charge transport in strongly biased semiconductors is at the heart of highspeed electronics, electro-optics, and fundamental solid-state physics. Intense light pulses in the terahertz (THz) spectral range have opened fascinating vistas: Since THz photon energies are far below typical electronic interband resonances, a stable electromagnetic waveform may serve as a precisely adjustable bias. Novel quantum phenomena have been anticipated for THz amplitudes reaching atomic field strengths. We exploit controlled THz waveforms with peak fields of 72 MV/cm to drive coherent interband polarization combined with dynamical Bloch oscillations in semiconducting gallium selenide. These dynamics entail the emission of phase-stable high-harmonic transients, covering the entire THz-to-visible spectral domain between 0.1 and 675 THz. Quantum interference of different ionization paths of accelerated charge carriers is controlled via the waveform of the driving field and explained by a quantum theory of inter- and intraband dynamics. Our results pave the way towards all-coherent THz-rate electronics.

Abstract-Excitonic terahertz absorption in semiconductors with effective-mass anisotropies

P. Springer, S. W. Koch, and M. Kira
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-7-C30

A microscopic approach is developed to compute the excitonic properties and the corresponding terahertz response for semiconductors characterized by anisotropic effective masses. The approach is illustrated for the example of germanium, where it is shown that the anisotropic electron mass in the 𝐿 valley leads to two distinct terahertz absorption resonances separated by 0.8 meV. Thus, terahertz absorption spectroscopy can be applied to directly observe the mass anisotropy.

© 2016 Optical Society of America

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Abstract-Coherent cyclotron motion beyond Kohn’s theorem

• T. Maag,
• A. Bayer,
• S. Baierl,
• M. Hohenleutner,
• T. Korn,
• C. Schüller,
• D. Schuh,
• D. Bougeard,
• C. Lange,
• R. Huber,
• M. Mootz,
• J. E. Sipe,
• S. W. Koch
• & M. Kira

http://www.nature.com/nphys/journal/v12/n2/full/nphys3559.html

In solids, the high density of charged particles makes many-body interactions a pervasive principle governing optics and electronics. However, Walter Kohn found in 1961 that the cyclotron resonance of Landau-quantized electrons is independent of the seemingly inescapable Coulomb interaction between electrons. Although this surprising theorem has been exploited in sophisticated quantum phenomena¹, such as ultrastrong light–matter coupling, superradiance and coherent control, the complete absence of nonlinearities excludes many intriguing possibilities, such as quantum-logic protocols. Here, we use intense terahertz pulses to drive the cyclotron response of a two-dimensional electron gas beyond the protective limits of Kohn’s theorem. Anharmonic Landau ladder climbing and distinct terahertz four- and six-wave mixing signatures occur, which our theory links to dynamic Coulomb effects between electrons and the positively charged ion background. This new context for Kohn’s theorem unveils previously inaccessible internal degrees of freedom of Landau electrons, opening up new realms of ultrafast quantum control for electrons.

Abstract-Real-time observation of interfering crystal electrons in high-harmonic generation

• M. Hohenleutner,
• F. Langer,
• O. Schubert,
• M. Knorr,
• U. Huttner,
• S. W. Koch,
• M. Kira
• & R. Huber

http://www.nature.com/nature/journal/v523/n7562/full/nature14652.html

Acceleration and collision of particles has been a key strategy for exploring the texture of matter. Strong light waves can control and recollide electronic wavepackets, generating high-harmonic radiation that encodes the structure and dynamics of atoms and molecules and lays the foundations of attosecond science^1, 2, 3. The recent discovery of high-harmonic generation in bulk solids^4, 5, 6combines the idea of ultrafast acceleration with complex condensed matter systems, and provides hope for compact solid-state attosecond sources^6, 7, 8 and electronics at optical frequencies^3, 5, 9,10. Yet the underlying quantum motion has not so far been observable in real time. Here we study high-harmonic generation in a bulk solid directly in the time domain, and reveal a new kind of strong-field excitation in the crystal. Unlike established atomic sources^{1, 2, 3, 9, 11}, our solid emits high-harmonic radiation as a sequence of subcycle bursts that coincide temporally with the field crests of one polarity of the driving terahertz waveform. We show that these features are characteristic of a non-perturbative quantum interference process that involves electrons from multiple valence bands. These results identify key mechanisms for future solid-state attosecond sources and next-generation light-wave electronics. The new quantum interference process justifies the hope for all-optical band-structure reconstruction and lays the foundation for possible quantum logic operations at optical clock rates.

Abstract-Coherent Terahertz Control of Vertical Transport in Semiconductor Heterostructures

O. Vänskä, I. Tittonen, S. W. Koch, and M. Kira

Phys. Rev. Lett. 114, 116802 – Published 16 March 2015

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.116802

Coherent-control protocols are introduced to selectively transport electrons, excitons, or pure two-particle correlations through semiconductor interfaces. The scheme is tested in a double-quantum-well structure where a sequence of terahertz pulses is applied to induce the vertical excitation transfer between the wells. Using a microscopic theory, it is shown that efficient and highly selective transfer can be realized even in the presence of the unavoidable scattering and dephasing processes.

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Abstract-Magnetic control of Coulomb scattering and terahertz transitions among excitons

J. Bhattacharyya, S. Zybell, F. Eßer, M. Helm, H. Schneider, L. Schneebeli, C. N. Böttge, B. Breddermann, M. Kira, S. W. Koch, A. M. Andrews, and G. Strasser

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.125313

Time-resolved terahertz quenching studies of the magnetoexcitonic photoluminescence from GaAs/AlGaAs quantum wells are performed. A microscopic theory is developed to analyze the experiments. Detailed experiment-theory comparisons reveal a remarkable magnetic-field controllability of the Coulomb and terahertz interactions in the excitonic system.

DOI: http://dx.doi.org/10.1103/PhysRevB.89.125313

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• Published 31 March 2014
• Received 23 September 2013
• Revised 11 March 2014

©2014 American Physical Society

Abstract-Sub-cycle control of terahertz high-harmonic generation by dynamical Bloch oscillations

• O. Schubert,
• M. Hohenleutner,
• F. Langer,
• B. Urbanek,
• C. Lange,
• U. Huttner,
• D. Golde,
• T. Meier,
• M. Kira,
• S. W. Koch
• & R. Huber
• • http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2013.349.html

Ultrafast charge transport in strongly biased semiconductors is at the heart of high-speed electronics, electro-optics and fundamental solid-state physics^{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13}. Intense light pulses in the terahertz spectral range have opened fascinating vistas^{14, 15, 16, 17, 18,19, 20, 21}. Because terahertz photon energies are far below typical electronic interband resonances, a stable electromagnetic waveform may serve as a precisely adjustable bias^{5, 11, 17, 19}. Novel quantum phenomena have been anticipated for terahertz amplitudes, reaching atomic field strengths^8, 9, 10. We exploit controlled (multi-)terahertz waveforms with peak fields of 72 MV cm⁻¹ to drive coherent interband polarization combined with dynamical Bloch oscillations in semiconducting gallium selenide. These dynamics entail the emission of phase-stable high-harmonic transients, covering the entire terahertz-to-visible spectral domain between 0.1 and 675 THz. Quantum interference of different ionization paths of accelerated charge carriers is controlled via the waveform of the driving field and explained by a quantum theory of inter- and intraband dynamics. Our results pave the way towards all-coherent terahertz-rate electronic

Abstract-Magnetic control of Coulomb scattering and terahertz transitions among excitons

J. Bhattacharyya, S. Zybell, F. Eßer, M. Helm, H. Schneider, L. Schneebeli, C. N. Böttge, B. Breddermann, M. Kira, S. W. Koch, A. M. Andrews, G. Strasser

http://arxiv-web3.library.cornell.edu/abs/1309.6426

Time-resolved terahertz quenching studies of the magnetoexcitonic photoluminescence from GaAs/AlGaAs quantum wells are performed. A microscopic theory is developed to analyze the experiments. Detailed experiment-theory comparisons reveal a remarkable magnetic-field controllability of the Coulomb and terahertz interactions in the excitonic system.