A 'spin ratchet': A new electronic structure for generating spin current

December 16, 2010

A research team from the Institut Català de Nanotecnologia (ICN), in Barcelona, has demonstrated a device that induces electron spin motion without net electric currents, a key step in developing the spin computers of the future. The results are published in the Dec 17 issue of the journal Science. The authors are Marius V. Costache and Sergio O. Valenzuela, an ICREA Professor who is leader of the Physics and Engineering of Nanodevices Group at ICN.

Spintronics is a branch of electronics that aims to use the electron spin rather than its charge to transport and store information. The electron spin comes in two forms, "spin up" or "spin down", and would allow significantly more data to be stored and analyzed than is possible with current electronics. Moreover, spin computers would be able to process vast amounts of information while using less energy and generating much less heat than conventional computers.

Advances in spintronics have already impacted commercial products, enabling a huge increase in storage capacity of magnetic hard disks. However, the devices comprise ferromagnetic multilayers that act as spin filters and require conventional electrical charge currents in order to work. To garner the full potential of spintronics, further fundamental advances are urgently needed.

Researchers working in this field face a key challenge: how to generate and control spins without the simultaneous generation of electric current, and the resultant energy losses? This would enable not just data storage, but calculations to be realized directly using spin states.

As reported in the journal Science, Prof. Valenzuela and Dr. Costache have proposed and experimentally demonstrated a ratchet concept to control the spin motion. In analogy to a ratchet wrench, which provides uniform rotation from oscillatory motion, such ratchets achieve directed spin transport in one direction, in the presence of an oscillating signal. Most important, this signal could be an oscillatory current that results from environmental charge noise; thus future devices based on this concept could function by gathering energy from the environment.

The efficiency of the ratchet can be very high. Reported results show electron polarizations of the order of 50%, but they could easily exceed 90% with device design improvements. The spin ratchet, which relies on a single electron transistor with a superconducting island and normal metal leads, is able to discriminate the electron spin, one electron at a time. The devices can also function in a "diode" regime that resolves spin with nearly 100% efficacy and, given that they work at the single-electron level, they could be utilized to address fundamental questions of quantum mechanics in the solid state or to help prepare the path for ultrapowerful quantum or spin computers.

The main drawback of the devices is that they work at low temperature. However, this does not represent a problem for quantum computing applications as solid state implementations of quantum computers will most likely require similar working conditions. Future research at the ICN will focus on increasing the spin ratchet efficiency and testing different ratchet protocols to implement a working device at room temperature.
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CATALAN INSTITUTE OF NANOTECHNOLOGY (ICN)

The Catalan Institute of Nanotechnology (ICN) is a private foundation created in 2003 and forms part of CERCA, the Network of Research Centers launched by the Catalan Government as a key plank of the long-term strategy to foster the development of a knowledge-based economy. The ICN´s multicultural team of scientists, representing over 20 nationalities, aims to produce cutting-edge science and develop next-generation technologies by investigating the new properties of matter that arise from the fascinating behavior at the nanoscale.

Research is devoted on one side to the study and understanding of fundamental physical phenomena associated to state variables (electrons, spin, phonons, photons, plasmons, etc.), the investigation of new properties derived from tailored nanostructures, and the opening of new routes and fabrication processes for the conception of new nanodevices.

On the other side, researchers also explore the state of aggregation at the nanometric scale, the development of nanoproduction methods, synthesis, analysis, and manipulation of aggregates and structures of nanometric dimension, and the development of techniques for characterizing and manipulating nanostructures.

These lead to commercially relevant studies such as the functionalization of nanoparticles, the encapsulation of active agents, novel drugs and vaccines, new nanodevices and nanosensors, with applications in health, food, energy, environment, etc.

The Institute actively promotes collaboration among scientists from diverse areas of specialization (physics, chemistry, biology, engineering), and trains new generations of scientists, offering studentships, doctoral and post-doctoral positions.

More information:
Institut Catala de Nanotecnologia
Tel: +(34) 93 581 4408, Email: info@icn.cat, Web: www.icn.cat
Communicacion Dept.: Ana de la Osa, ana.delaosa.icn@uab.es
Principal Researcher: ICREA Prof. Dr. Sergio Valenzuela, SOV@icrea.cat

Catalan Institute of Nanoscience and Nanotechnology (ICN2)

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