Electrons are not enough: Cuprate superconductors defy convention

Mar. 18, 2013 ? To engineers, it's a tale as old as time: Electrical current is carried through materials by flowing electrons. But physicists at the University of Illinois and the University of Pennsylvania found that for copper-containing superconductors, known as cuprates, electrons are not enough to carry the current.

"The story of electrical conduction in metals is told entirely in terms of electrons. The cuprates show that there is something completely new to be understood beyond what electrons are doing," said Philip Phillips, a professor of physics and of chemistry at the U. of I.

In physics, Luttinger's theorem states that the number of electrons in a material is the same as the number of electrons in all of its atoms added together. Electrons are the sub-atomic particles that carry the current in a conductive material. Much-studied conducting materials, such as metals and semiconductors, hold true to the theorem.

Phillips' group works on the theory behind high-temperature superconductors. In superconductors, current flows freely without resistance. Cuprate superconductors have puzzled physicists with their superconducting ability since their discovery in 1987.

The researchers developed a model outlining the breakdown of Luttinger's theorem that is applicable to cuprate superconductors, since the hypotheses that the theorem is built on are violated at certain energies in these materials. The group tested it and indeed found discrepancies between the measured charge and the number of mobile electrons in cuprate superconductors, defying Luttinger.

"This result is telling us that the physics cannot be described by electrons alone," Phillips said. "This means that the cuprates are even weirder than previously thought: Something other than electrons carries the current."

"Theorists have suspected that something like this was true but no one has been able to prove it," Phillips said. "Electrons are charged. Therefore, if an electron does not contribute to the charge count, then there is a lot of explaining to do."

Now the researchers are exploring possible candidates for current-carriers, particularly a novel kind of excitation called unparticles.

Phillips, U. of I. undergraduate student Kiaran Dave (now a graduate student at MIT) and University of Pennsylvania professor Charles Kane published their findings in the journal Physical Review Letters. The National Science Foundation and the Center for Emergent Superconductivity (through a DOE Energy Frontiers Research Center) supported this work.

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The above story is reprinted from materials provided by University of Illinois at Urbana-Champaign.

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Journal Reference:

1. Jun-Yu Ou, Eric Plum, Jianfa Zhang, Nikolay I. Zheludev. An electromechanically reconfigurable plasmonic metamaterial operating in the near-infrared. Nature Nanotechnology, 2013; DOI: 10.1038/NNANO.2013.25

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

Source: http://feeds.sciencedaily.com/~r/sciencedaily/~3/IphBybyx1Lg/130319091727.htm

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Women emerge as crisis leaders in macho Balkans

Kosovo President Atifete Jahjaga, centre, meets with her staff in Pristina on Friday, March 1 2013. Atifete Jahjaga was elected as Kosovo's first female president by the Kosovo lawmakers on 2011 signaling a change on attitude towards woman in politics. Women in the Balkans are leading a political revolution. Historically given little say in the politics of the conservative region, they are increasingly taking top leadership posts, signaling that the traditional rules are changing as Balkan countries shake off their war pasts and move toward membership in the European Union. (AP Photo / Visar Kryeziu )

Kosovo President Atifete Jahjaga, centre, meets with her staff in Pristina on Friday, March 1 2013. Atifete Jahjaga was elected as Kosovo's first female president by the Kosovo lawmakers on 2011 signaling a change on attitude towards woman in politics. Women in the Balkans are leading a political revolution. Historically given little say in the politics of the conservative region, they are increasingly taking top leadership posts, signaling that the traditional rules are changing as Balkan countries shake off their war pasts and move toward membership in the European Union. (AP Photo / Visar Kryeziu )

Kosovo President Atifete Jahjaga, centre, meets with her staff in Pristina on Friday, March 1 2013. Atifete Jahjaga was elected as Kosovo's first female president by the Kosovo lawmakers on 2011 signaling a change on attitude towards woman in politics. Women in the Balkans are leading a political revolution. Historically given little say in the politics of the conservative region, they are increasingly taking top leadership posts, signaling that the traditional rules are changing as Balkan countries shake off their war pasts and move toward membership in the European Union. (AP Photo / Visar Kryeziu )

BELGRADE, Serbia (AP) ? Women in the Balkans are leading a political revolution.

Historically given little say in the politics of the conservative region, they are increasingly taking top leadership posts, signaling that the traditional rules are changing as Balkan countries shake off their war pasts and move toward membership in the European Union.

During the bloody 1990s, many in the Balkans turned to warrior leaders, mostly male nationalists they thought would protect them from the ethnic conflicts that flattened cities and left over a hundred thousand dead. The new millennium has brought crisis in a different form: economic doldrums, naggingly high unemployment and glaring political corruption.

Encouraged by the EU and influenced by closer ties with the West, more and more it is women who are stepping in to change the old ways of doing business in the macho Balkans. Some see women as less nationalistic and more attuned to the needs of a new era ? diplomacy, consensus, and compromise.

"Women have always been more successful than men, with all due respect," said Duska Latinovic, a nurse from the Serb-controlled part of Bosnia. "Women are ... more sensitive, stronger, emotional, and in these rough times people need more of a heart."

Although overall gender equality standards are still far from those in Western democracies, strongly patriarchal Kosovo and the post-war Serb mini-state in Bosnia have both installed women in their top positions. Male-dominated Serbia and Montenegro have passed laws to increase the numbers of women in leadership positions, part of a slate of efforts to convince the EU they belong in the bloc.

"The power of women in the politics is a soft power," Atifete Jahjaga, the female president of Kosovo told the AP. "It is a positive change that our country and other countries in the region ... are making by giving a chance to women."

The latest political newcomer is the charismatic 43-year-old financial expert Alenka Bratusek, Slovenia's first ever female prime minister. While Slovenia has traditionally been more socially liberal than the rest of the Balkans, Bratusek's election last week was significant because it came at a moment of deep financial and political turmoil in the small Alpine state.

A rising star among veteran Slovenian politicians, Bratusek has been entrusted with consolidating the nation's economy and restoring confidence in state institutions, which have been badly shaken by the EU's broader financial crisis.

"It is important that this happened at a sensitive moment, a period of crisis," sociologist Milica Gaber Antic said. "It's a strong message to other women: 'We women can do it!'"

Many women leaders are already being lauded for steering their countries through the storms.

Croatia's former Prime Minister Jadranka Kosor, took over the premiership in turmoil after her predecessor Ivo Sanader was forced to resign in 2009 in a whirl of corruption scandals, and then wrapped up her country's accession talks with the EU.

In 2011 in Kosovo ? where Parliament members were recently issued notebooks with an assortment of sayings including one saying that "silence is the only treasure a woman possesses" ? the little-known Jahjaga was elected the first ever female president, part of a U.S.-brokered compromise that put to a rest the bickering between political groups dominated by formal rebel fighters and murky business leaders.

Last week in the ethnically Serb mini-state in Bosnia another little-known female politician, Zeljka Cvijanovic, was proposed as the new head of government after the previous Cabinet resigned. That would make her the first ever woman to lead the government in any of the country's many levels of power-sharing, where no ministry in the central government is headed by a woman.

"As a woman, I hope to add a new flair and a new dimension to the institutions of Republika Srpska," she said in an interview.

Women accounted for only 1.6 percent of Serbia's Parliament in 1990, the lowest rate in Europe. But with strongman Slobodan Milosevic ouster in 2000 and the country's efforts to join the EU, the proportion of women has soared to 20 percent. Serbian law now calls for every third candidate on an election list to be a woman ? a rule requested as part of EU reforms.

It isn't always the same story across the region. During the communist rule that followed World War II, authorities promoted women's inclusion in politics as part of the communist agenda of gender equality. At the time women served at top positions in the governments and were granted equal rights, jobs, salaries and education.

Bulgaria, for example, had the highest percentage of working women in the world in the 1970s, and women in top offices include the vice president, the parliament speaker, four ministers, and the mayor of the capital city, Sofia.

But, old habits die hard. Kosovo's Minister for European Integration Vlora Citaku acknowledged that "it is almost impossible to forget even for a moment that I am a woman ? I've been reminded of that every day since I became a minister."

She said that being a woman in the male-dominated politics is "a tough life."

"First of all they ask you are you married? What your dad think of you traveling alone surrounded by all men?," she scoffed. "I mean, it's all these stereotypes ... There are certain duties that a woman must do in order to be 'complete.'"

And in Slovenia, shortly after Bratusek won Parliament's approval, political opponents tweeted that "her mandate will be as long as her skirt."

Bratusek responded simply: "I wish we women were no longer judged only by the length of our skirts."

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Ali Zerdin in Slovenia, Veselin Toshkov in Bulgaria, Sabina Niksic and Irena Knezevic in Bosnia, Alison Mutler in Romania, Monica Scislowska in Poland, Karel Janicek in the Czech Republic, Nebi Qena in Kosovo, Pablo Gorondi in Hungary, Darko Bandic in Croatia, and Predrag Milic in Montenegro contributed to this report.

Associated Press

Source: http://hosted2.ap.org/APDEFAULT/cae69a7523db45408eeb2b3a98c0c9c5/Article_2013-03-04-Balkans-Women%20in%20Power/id-3e18935fe414484c8274f4e985fa720b

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