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Primeur weekly 2013-09-02

Focus

Using one Cloud for Cloud computing today? Perhaps two Clouds? In the future there will be MultiClouds. An interview with Dana Petcu of the West University of Timisoara ...

The Cloud

VMware delivers vCloud Hybrid Service ...

HP and SAP collaborate to deliver HP As-a-Service solution for SAP HANA ...

Dell delivers innovative Cloud and virtualization solutions blending VMware technology with Dell end-to-end offerings ...

New FICO software enables data scientists to transform Big Data into predictive models ...

Smart is the new green in Latin America ...

VMware management solutions demonstrated on stage at VMworld ...

HP and Yorkshire Building Society boost agility for financial services providers ...

IBM closes acquisition of CSL International ...

University of California deploys Huawei's Cloud storage system to support computational astrophysics research ...

Desktop Grids

Neutron stars in the computer Cloud ...

EuroFlash

Video Design brings Dataton WATCHOUT and WATCHPAX to InfoComm India 2013 ...

New UK/USA agreement will use high performance computing to boost economic competitiveness ...

Immanuel Bloch is to receive the Körber Prize 2013 ...

Light on twenty-year-old mystery ...

University of Tübingen physicists create interface between atoms and superconductors ...

USFlash

Allinea tools help Canada close innovation gap ...

Dell furthers commitment to Asia with transformative technology solutions from the data centre to the end device ...

Control scheme dynamically maintains unstable quantum system ...

Hadoop release 2.1.0-beta available ...

Mapping the Earth's magnetosphere to predict and prepare for space-weather events ...

EMC and VMware join forces around software-defined storage and VMware virtual SAN ...

HP and VMware enable customers to unify data centre networks ...

OSC hosts first meeting of the MVAPICH Users Group ...

Vampir takes a bite out of inefficiency as codes run on bigger supercomputers ...

HP helps HoneyBaked Ham of Georgia manage seasonal demand via tenfold performance boost ...

Light on twenty-year-old mystery


29 Aug 2013 Groningen - Groningen scientists have found an explanation for a mystery that has been puzzling the physics community since 1995. In the scientific journalNatureon Thursday 28 August - Advance On-line Publication, they explain why electrons pass through very tiny wires - known as quantum point contacts - less smoothly than expected. The observations of the group led by Prof. C.H. (Caspar) van der Wal of the Zernike Institute for Advanced Materials of the University of Groningen will affect electronics on a nanoscale: "Our thinking about this has been too naïve so far".

The mystery concerns nano wires that are about a hundred atoms wide. As early as 1988, the Dutch physicist Bart van Wees, currently a professor at the Zernike Institute, discovered a remarkable effect in this kind of wire. When he made them wider, the flow did not increase gradually but in a stepwise manner. Professor van der Wal stated: "This could be explained by quantum effects that occurred in the wires. There is a formula that describes precisely how these steps occur."

However, in the first step, with the thinnest wires, a tiny exception in the gradual increase was consistently found. "You see an unexpected peak, after which the conduction increases less quickly than expected for a while. This was already noted in the first publication about this by Bart van Wees, but initially researchers thought the inconsistency was due to tiny defects in the material used."

In 1995 it was shown that this was not so. "The peak was real, which meant that physical processes were occurring that we did not properly understand." Hundreds of publications have appeared about the phenomenon, known as 'Zero Bias Anomaly' (ZBA), but no-one could work out what was causing it.

A few years ago, one of Professor van der Wal's PhD students made a number of this type of quantum wire. "They were intended for a completely different type of research. However, we observed the peak and some other interesting trends." Professor van der Wal decided to set up a separate research project.

A Pakistani PhD student, Javaid Iqbal, created a large number of this type of quantum wire. In addition to the 'ordinary' wires whose width is adaptable, he also made wires whose length could be varied. The wires, notably, are very different from the classic electrical wires from our daily lives - a conducting core surrounded by insulating material, but consist of a semiconductor on which electrodes control the edge of a tiny channel. The electrodes create a 'saddle point potential', a sort of a tiny mountain pass where the electrodes on either side control steep walls.

Professor van der Wal stated: "We saw the peak that everyone else was finding. But when we increased the voltage across the wire, suddenly there was a double peak. Others had also observed this, but they thought it indicated that their wire was no longer functioning properly."

By working under extremely controlled circumstances, a fraction above absolute zero temperature, using extremely pure material and by testing a large number of wires, Professor van der Wal's group has been able to prove that the phenomenon is real. "And we discovered that the appearance of the ZBA was not only dependent on the voltage, but also on the length of the wire."

Professor van der Wal contacted theoretical physicists who had been working on the ZBA for years, particularly a group in Israel who had predicted the existence of a double peak. "But they had not predicted that it also depended on length." Together with colleagues from Germany and Spain, they have found an explanation for the phenomenon. "We now think that electrons get trapped on top of the 'mountain pass' that forms the quantum wire", explained Professor van der Wal.

Electrons that flow through the wire behave like quantum waves. "They bash against the walls, and sometimes reflect from the flanks of the mountain pass. They also sense each other's presence." This results in a complex interaction of various physical phenomena. "We call this 'many body physics'. It is very complex. You cannot describe how all the interactions proceed with a single, simple formula."

However, the final result is that an electron is trapped on top of the mountain pass or, in the words of the physicists, becomes localized. This influences the conductivity of the wires and results in the strange peaks. "And with longer wires two or more electrons can become localized, which results in double or even triple peaks."

"What we now know is that the behaviour of electrons in this type of quantum wire is much more complex than we had thought. That has all kinds of consequences." The characteristics of electrons that pass through such a wire, for example their spin - the precessional motion of electrons, can change in the wire. "That's something you have to take into account." The quantum wires are often used in research, for example when making Quantum Dots - used as bits when building a quantum computer.

As well as the article by Professor van der Wal and his colleagues,Naturewill be publishing another article on ZBA, with many of the same conclusions. "The mystery is thus as good as solved. The last details will result in interesting discussions, though", remarked Professor van der Wal enthusiastically.

The paper titled "Odd and even Kondo effects from emergent localization in quantum point contacts", written by M. J. Iqbal, Roi Levy, E. J. Koop, J. B. Dekker, J. P. de Jong, J. H. M. van der Velde, D. Reuter, A. D. Wieck, R. Aguado, Yigal Meir and C. H. van der Wal appears inNature- DOI:10.1038/nature12491
Source: University of Groningen

Back to Table of contents

Primeur weekly 2013-09-02

Focus

Using one Cloud for Cloud computing today? Perhaps two Clouds? In the future there will be MultiClouds. An interview with Dana Petcu of the West University of Timisoara ...

The Cloud

VMware delivers vCloud Hybrid Service ...

HP and SAP collaborate to deliver HP As-a-Service solution for SAP HANA ...

Dell delivers innovative Cloud and virtualization solutions blending VMware technology with Dell end-to-end offerings ...

New FICO software enables data scientists to transform Big Data into predictive models ...

Smart is the new green in Latin America ...

VMware management solutions demonstrated on stage at VMworld ...

HP and Yorkshire Building Society boost agility for financial services providers ...

IBM closes acquisition of CSL International ...

University of California deploys Huawei's Cloud storage system to support computational astrophysics research ...

Desktop Grids

Neutron stars in the computer Cloud ...

EuroFlash

Video Design brings Dataton WATCHOUT and WATCHPAX to InfoComm India 2013 ...

New UK/USA agreement will use high performance computing to boost economic competitiveness ...

Immanuel Bloch is to receive the Körber Prize 2013 ...

Light on twenty-year-old mystery ...

University of Tübingen physicists create interface between atoms and superconductors ...

USFlash

Allinea tools help Canada close innovation gap ...

Dell furthers commitment to Asia with transformative technology solutions from the data centre to the end device ...

Control scheme dynamically maintains unstable quantum system ...

Hadoop release 2.1.0-beta available ...

Mapping the Earth's magnetosphere to predict and prepare for space-weather events ...

EMC and VMware join forces around software-defined storage and VMware virtual SAN ...

HP and VMware enable customers to unify data centre networks ...

OSC hosts first meeting of the MVAPICH Users Group ...

Vampir takes a bite out of inefficiency as codes run on bigger supercomputers ...

HP helps HoneyBaked Ham of Georgia manage seasonal demand via tenfold performance boost ...