Nanophysics: 4X25' invited talks

Miriam Blaauboer (Technical University Delft)

Quantum entanglement in solid-state nanostructures

 

Entanglement is a fascinating aspect of quantum mechanics which has recently emerged as a resource for quantum information and quantum computation purposes. In this talk I will try to explain what is meant by this and why and how solid-state physicists currently search f or ways to create, manipulate and detect entangled electrons in solid-state nanostructures.

 

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Benoit Hackens (Université catholique de Louvain)

Imaging Coulomb islands in a quantum Hall interferometer

In the quantum Hall regime near integer filling factors, electrons are thought to be transmitted through edge states confined at the borders of the device. Their spatial separation is at the origin of the absence of scattering, which causes the longitudinal resistance to vanish. In mesoscopic samples, however, edge channels may be sufficiently close to allow electrons to tunnel, or to be transmitted through ‘electron islands'. This gives rise to magnetoresistance oscillations characterized by a flux period different from one flux quantum [1].

We show how to take advantage of these oscillations to spatially map these islands in a quantum ring fabricated from an InGaAs/InAlAs heterostructure. Using the biased tip of a scanning gate microscope

(SGM) operated at low temperature (100 mK), we change the conditions of tunneling between the island and the edge states. Scanning the tip over the quantum ring and changing the magnetic field, we observe a continous change of SGM patterns, related to the evolution and location of the active electron islands. This allows to find the origin of the complex spectrum of magnetoresistance oscillations observed in the quantum Hall regime in our interferometer.

[1] B. Rosenow and B. I. Halperin, PRL 98, 106801 (2007).

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Sara Bals (University of Antwerpen)

 

From microscopy to nanoscopy

Nanosystems that are being investigated within the field of physics, biology and chemistry are becoming more complex from structural and chemical point of view. As a consequence, higher demands are being put to microscopic and nanoscopic characterization techniques as well. New developments within the field of transmission electron microscopy (TEM) allow one to investigate these systems at atomic scale, not only structural, but also chemical and electronical. However, al these techniques only provide a 2 dimensional (2D) projection of a 3 dimensional (3D) object. Therefore, electron tomography has been developed which makes 3D characterization by TEM possible as well. Combining advanced 2D and 3D TEM indeed opens up a wealth of new possibilities concerning nanocharacterization. The morphology, inner structure and composition of nanoparticles, nanotubes can be determined and interfaces in complex oxide multilayers can be investigated atomic column by atomic column. Aberration corrected TEM will enable one to go even further and, for example, also study hybrid soft-hard matter nanocompounds, such as metallized biomolecules. 

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Bert Koopmans (Technical University Eindhoven),

Spinning dynamics! – New trends in Spintronics

 

Spintronics is electronics in which not only the electron charge, but also its quantum mechanical spin is being exploited. The spintronic concept of giant magnetoresistance has been used already for over a decade in magnetic hard disk read heads (Nobel prize for Physics 2007). Since then, novel ideas have continuously been launched and explored at a fundamental level, paving the way towards future applications. In this presentation spintronics will be introduced at a tutorial level, and a number of exciting new developments will be sketched.

Interestingly, all these new developments are related to spin dynamics, and are based on two fundamental physical principles. The first principle is the precession of the electron spin in an externally applied field, mutual exchange fields, or local hyperfine fields. Secondly, an important role is being played by the fundamental law describing the conservation of angular momentum – exchanging angular momentum between internal degrees of freedom or between neighbouring nano-reservoirs. In this perspective, new physical concepts aiming at faster, more clever, and cheaper spintronics will be discussed. Faster devices are being explored at a fundamental level using excitation by femtosecond laser pulses. More clever spintronics results by exploiting the concept of current-induced spin momentum transfer, e.g. aiming at the fascinating magnetic racetrack memory. More cheap spintronics may be achieved by embedding it in organic or plastic materials, which has lead to an intriguing new field of research.

 In the second part of the presentation, intriguing new developments in the field of spintronics will be presented. As to one of the intriguing developments, the rapidly evolving field of organic spintronics will be addressed; aiming for new spin- and magnetic functionality in organic devices. While different prototype devices have been successfully realized, their unexpected behaviour is presently posing scientific puzzles – mixing key concepts of spin polarized transport and charge transport through organic materials. An example of the new scientific discoveries is the so-called organic magnetoresistance (OMAR), characterized by 20 – 30 % of magnetoresistance at room temperature and at relatively small fields (~ 10 mT), in regular OLED like structures without any ferromagnetic materials. In a joint effort by a number of groups at TU/e with complementary expertise, we have gained the first understanding of this surprising effect.

Another exciting recent activity in spintronics bridges developments in ultrafast magnetization dynamics (using femtosecond laser pulses to exploit the ultimate dynamics of ferromagnetic systems) and spin-transfer phenomena (using spin-polarized currents rather than magnetic fields to control switching of magnetic devices). It will be shown how the femtosecond magnetic response can be speeded up by optically transferring spins from one nanoreservoir to the other.