Coexistence of superconductivity and charge density waves observed
Scanning electron microscopy in combination with EELS electron spectroscopy permits to visualise atomic positions of the individual atoms in the heterostructure: Superconducting regions of YBaCuO are identified by yttrium (blue) and copper (pink), the ferromagnetic layers by manganese (green) and lanthanum (red). Courtesy MPI Stuttgart. © MPI Stuttgart
Physicists at BESSY II studied an artificial structure composed of alternating layers of ferromagnetic and superconducting materials. Charge density waves induced by the interfaces were found to extend deeply into the superconducting regions, indicating new ways to manipulate superconductivity. The results are now being published in Nature Materials.
High-Tc superconductors were discovered 30 years ago: A class of ceramic metal oxide materials was found to pass electrical current without energy losses. In contrast to conventional superconductors that have to be cooled almost to absolute zero, this property appears already at comparably high temperatures. In prototypical yttrium barium copper oxide (YBaCuO), the transition temperature is 92 Kelvin (minus 181 degrees centigrade). Hence, liquid nitrogen suffices as coolant to reach the superconducting phase. The discovery of high-temperature superconductivity has started a quest for applications, which are being implemented now. Until now, however, the microscopic mechanism of high-Tc superconductivity is still matter of debate.
Superconducting and feromagnetic thin layers
A team of scientists lead by Prof. Bernhard Keimer, MPI for Solid State Research, and Dr. Eugen Weschke, HZB, have now investigated an artificial layer system composed of alternating nanolayers of YBaCuO and a ferromagnetic material. The thicknesses of the YBaCuO layers varied between 10 nm and 50 nm.
Tiny collective modulations of valence electrons observed
As interfaces often determine the properties of such heterostructures, physicists were particularly interested in their role for the present system. During his PhD work using resonant x-ray diffraction at BESSY II, Alex Frano could detect tiny collective modulations of valence electrons around Cu atoms in the YBaCuO layer. Data analysis revealed that the resulting charge density wave does not remain located close to the interface but extends across the whole layer. “ This finding is quite a surprise, as previous studies revealed a strong tendency of superconductivity to suppress the formation of charge density waves”, explains Frano.
Charge density wave is stabilized
“Engineering artifical interfaces in heterostructures of ferromagnetic and superconducting layers allowed to stabilize charge density waves even in the presence of superconductivity: YBaCuO remains superconducting, while the charges arrange in a periodic structure”, explains Weschke, “ exploring the details of this coexistence on a microscopic scale is a challenging task for future experiments.” A most exciting perspective of the present results is paving the way to controlling the superconducting state itself.
Publication:
Long-range charge-density-wave proximity effect at cuprate/manganate interfaces, A. Frano, S. Blanco-Canosa, E. Schierle, Y. Lu, M. Wu, M. Bluschke, M. Minola, G. Christiani, H. U. Habermeier, G. Logvenov, Y. Wang, P. A. van Aken, E. Benckiser, E. Weschke, M. Le Tacon & B. Keimer, Nature Materials (2016) doi: 10.1038/nmat4682
- HZB congratulates Peter Hegemann on winning the Nobel PrizeOur warmest congratulations go to Peter Hegemann, Professor of Neuroscience and Experimental Biophysics at Humboldt University in Berlin. Together with Prof. Georg Nagel (Julius Maximilian University of Würzburg) and Prof. Karl Deisseroth (Stanford University, USA), he has been awarded the 2026 Nobel Prize in Physiology or Medicine. We are delighted for him, his team, Humboldt University and the entire Berlin scientific community.
- Science in Berlin: collaborative, diverse, innovative, internationalScience is a key social and economic factor for Berlin. It creates jobs and adds value, attracts talent from all over the world, and enriches city life. To ensure that Berlin remains one of the world’s leading centres of science in the future, science must feature even more prominently on the political agenda. This is what BR50 stands for: over 50 non-university research institutions, including the HZB, are joining forces in this network. Following the election in Berlin, BR50 is now addressing politicians with a position paper, accompanied by the campaign “𝗪𝗶𝗿 𝗳𝗼𝗿𝘀𝗰𝗵𝗲𝗻 𝗳ü𝗿 𝗕𝗲𝗿𝗹𝗶𝗻.”
- Does African Architecture exist?The world’s first Pan-African Architecture Biennale took place this September in Nairobi, Kenya. People from the worlds of architecture, art, academia and politics from 54 African countries and the diaspora had travelled to Nairobi to exchange ideas on traditional and contemporary building methods, materials, experiences and projects. Samira Aden co-organised this biennial as lead curator. We spoke to her about it.