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Nanoislands for Terahertz Science and Technology
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Schematic cross-section of an ultrafast photoconductive switch with ErAs nanoislands embedded ind a GaAs matrix. |
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We invite applicants at all levels for our efforts devoted to the exploration of novel photoconductive materials. These materials are suitable for ultrafast optoelectronic transduction as required in time-domain and terahertz spectroscopy. Materials currently under study consist of equidistant layers of self-assembled optically inactive nanoislands embedded in a III-V semiconductor matrix. Their significant potential for generating ultrashort electrical pulses should be combined with the virtues of fiber optics in order to simplify systems generating pulsed Terahertz radiation. Such systems are likely to contribute to the wider proliferation of Terahertz imaging and technology. We are looking for enthusiastic and devoted researchers eager to tackle a promising multi-disciplinary project involving fiber optics, short-pulse lasers, semiconductor fabrication, nanostructuring techniques as well as high frequency simulations. Previous experience with any of these areas is considered advantageous. This work is sponsored by the Germany Ministry of Science and Education through a young investigator award on nanotechnology.
Visit related research topic Nanomaterials for terahertz research and technology
See articles:
Nature Materials 2, 122-126 |
App. Phys. Lett. 82, 3179-3181
Contact person Jurgen Smet
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Zero Resistance States and Microwave Photoconductivity
The observation of vanishing electrical resistance in condensed matter is normally one of the hallmarks of superconductivity or the quantum Hall effect. Recently, zero resistance has however been observed in a surprising, apparently unrelated setting: a two-dimensional electron system exhibiting ultrahigh electron mobilities exposed to quasi-monochromatic millimetre wave radiation as well as a very small perpendicular field. This experimental discovery of microwave induced zero-resistance states in the two-dimensional electron system was first reported near the end of 2002 and has unleashed a flood of over 40 theoretical papers. Nevertheless, its origin remains controversially debated. We are seeking an outstanding candidate preferably at the PhD level in order to investigate the origin of this fascinating phenomenon. The prospective candidate should be keen on working in a team and should be enthusiastic about tackling a challenging research project involving state of the art tools. Previous experience with measurements in a cryogenic environment, clean room processing or microwave equipment are considered an advantage. The research is sponsored by the German Science Foundation.
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| Transport in an ultra-clean two-dimensional electron system subjected to monochromatic microwave radiation becomes dissipationless over extended regions of the applied perpendicular magnetic field. |
Visit related research topic Zero Resistance State
See articles:
Nature 420, 646-650 |
Phys. Rev. Lett. 92, 146801 |
Contact person Jurgen Smet
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Interactions between Electron Spins and Nuclear Spins
Semiconductors are ubiquitous in device electronics, because their charge distributions can be conveniently manipulated with voltages to perform logic operations. Achieving a similar level of control over the spin degrees of freedom of either electrons or nuclei in a solid state device could provide intriguing prospects for both information processing and the study of fundamental solid state physics issues. At the Max-Planck-Institute we wish to contribute to this research field by carrying out experiments specifically geared towards an improved understanding of the microscopic interaction processes that take place between the electron and nuclear spin subsystems in a two-dimensional electron system in order to identify ways of manipulating and controlling the degree of spin polarization . We are seeking outstanding candidates preferably at the PhD level. Young postdoctoral applicants with previous experience in related areas will also be considered. The prospective candidate should be keen on working in a team and should be enthusiastic about tackling a challenging research project involving state of the art tools. Previous experience with transport measurements in a cryogenic and high magnetic field environment, clean room processing and high frequency equipment are considered an advantage. The research is sponsored by the German Ministry of Science and Education.
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| Ideas produced by workers in the spintronics and quantum computing communities have sparked efforts to develop new ways of accomplishing the fundamental task of controlling and measuring the nuclear spin polarization in solid state devices, in view of the dearth of existing techniques for locally manipulating nuclear spins. Particularly appealing is the use of mobile objects like conduction electrons in semiconductors as mediators to both probe and modify nuclear spins. |
See articles:
Nature 415, 281-286 |
Phys. Rev. Lett. 92, 086802
Contact person Jurgen Smet
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Coherence Phenomena in Semiconductor Nanostructures
Knowledge of the phase evolution and its controlled destruction in mesoscopic electron interferometers made from semiconductors is basic to the understanding of nano-structures and is crucial for building coherent systems that might be needed in the future for quantum information processing. We plan to study the phase behavior of electrons in quantum dots when the occupation of the dots is one to a few electrons. Another experiment we intend to concentrate on is 'intentional dephasing' of a coherent system. A detector provides information on the quantum state of the particle in a nearby coherent system and thereby influences it inadvertently. We wish to investigate systems with a variable degree of interaction between the system and the detector. We are seeking an outstanding candidate preferably at the PhD level. Young postdoctoral candidates with previous experience in this general area will be considered also. This work is a close collaboration with the team of M. Heiblum at the Braun Submicron Research Center of the Weizmann Institute of Science in Rehovot, Israel. Both institutes offer state-of-the-art clean room and characterization facilities. The Weizmann Institute also produces world class MBE grown GaAs/AlGaAs heterostructures that are key to this project. Prospective candidates are expected to carry out parts of the project at the Weizmann Institute. They should be keen on working in a team and should be enthusiastic about tackling a challenging research project involving many state of the art tools. Previous experience with transport measurements in a cryogenic environment and clean room processing are considered an advantage. This research is sponsored by the German Israeli Foundation.
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| Examples of complex airbridge devices for the study of coherence, the phase evolution and its controlled destruction. The device on the left enables the study of the phase behavior in quantum dots and was produced in the group of M. Heilblum at the Submicron Research center. The devices on the left were produced at the Max-Planck-Institute. They may operated as Aharonov Bohm geometries with a tunable antidot in the center. |
Visit  Weizmann Institute and
Braun Submicron Center
Contact person Jurgen Smet
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Dielectric Waveguides
Microwave radiation is commonly propagated with the help of metallic waveguides. Such waveguides introduce however increasing losses as the frequency is raised. Moreover they are not flexible and for low temperature applications pose a difficulty as they thermally conduct well. We wish to explore the use of dielectric waveguides instead. The basic concept is borrowed from glasfiber for the transmission of optical light. A core material transparent for microwave and terahertz radiation with a large dielectric constant guides most of the radiation power but is surrounded by a cladding material with a smaller dielectric constant in which the tails of the wave can propagate undisturbed. Suitable materials are based on polyethylene and various types of Teflon, which exhibit very weak absorption in the terahertz frequency range. The applicant is expected to contribute to the development of such broadband waveguides suitable for the frequency range from 75 GHz to 1 THz. Both theoretical simulations for designing coupling units to couple radiation in and out of the waveguide with commercial software as well as experimental realization and testing will be part of the task. The dielectric waveguides will be used in low temperature applications for the investigation of microwave photoconductivity phenomena in low dimensional systems. Previous experience with antenna and other high frequency components and with electromagnetic wave simulation software (HFSS, Microwave Studio) are considered an advantage. Applicants at all levels from engineering or physics disciplines will be considered.
Contact person Jurgen Smet
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Linux, python and labview programming
Who has experience with Linux, the C++ programming language and python, would like to earn some additional money and be part of a vibrating research team? We are searching for a Linux/python enthusiast to improve our measurement software controlling complex scientific experiments and to install computers. Similar opportunities also exist for those familiar with LabView and website programming.
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We welcome applicants, who have mechanical workshop experience or CAD experience and are searching for a short term project. Short term projects may entail the improvement of laboratory infrastructure and the design and/or fabrication of mechanical and precision mechanical components.
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