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.

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

arö


You might also be interested in

  • Clean cooking fuel with a great impact for southern Africa
    News
    19.04.2024
    Clean cooking fuel with a great impact for southern Africa
    Burning biomass for cooking causes harmful environmental and health issues. The German-South African GreenQUEST initiative is developing a clean household fuel. It aims to reduce climate-damaging CO2 emissions and to improve access to energy for households in sub-Saharan Africa.

  • A simpler way to inorganic perovskite solar cells
    Science Highlight
    17.04.2024
    A simpler way to inorganic perovskite solar cells
    Inorganic perovskite solar cells made of CsPbI3 are stable over the long term and achieve good efficiencies. A team led by Prof. Antonio Abate has now analysed surfaces and interfaces of CsPbI3 films, produced under different conditions, at BESSY II. The results show that annealing in ambient air does not have an adverse effect on the optoelectronic properties of the semiconductor film, but actually results in fewer defects. This could further simplify the mass production of inorganic perovskite solar cells.
  • Spintronics: A new path to room temperature swirling spin textures
    Science Highlight
    16.04.2024
    Spintronics: A new path to room temperature swirling spin textures
    A team at HZB has investigated a new, simple method at BESSY II that can be used to create stable radial magnetic vortices in magnetic thin films.