• The pressure is off and high temperature

    From ScienceDaily@1:317/3 to All on Thu Jul 8 21:30:34 2021
    The pressure is off and high temperature superconductivity remains
    Development of a new pressure-quench technique demonstrates
    superconductivity in iron selenide crystals sans pressure

    Date:
    July 8, 2021
    Source:
    University of Houston
    Summary:
    Using a new pressure quenching (PQ) technique at high temperatures
    to induce superconductivity in iron selenide (FeSe) crystals,
    superconductivity was achieved -- and sustained -- without pressure.



    FULL STORY ==========================================================================
    In a critical next step toward room-temperature superconductivity at
    ambient pressure, Paul Chu, Founding Director and Chief Scientist at
    the Texas Center for Superconductivity at the University of Houston
    (TcSUH), Liangzi Deng, research assistant professor of physics at TcSUH,
    and their colleagues at TcSUH conceived and developed a pressure-quench
    (PQ) technique that retains the pressure-enhanced and/or -induced high transition temperature (Tc) phase even after the removal of the applied pressure that generates this phase.


    ========================================================================== Pengcheng Dai, professor of physics and astronomy at Rice University
    and his group, and Yanming Ma, Dean of the College of Physics at
    Jilin University, and his group contributed toward successfully
    demonstrating the possibility of the pressure-quench technique in a
    model high temperature superconductor, iron selenide (FeSe). The results
    were published in the journal Proceedings of the National Academy of
    Sciences USA.

    "We derived the pressure-quench method from the formation of the
    human-made diamond by Francis Bundy from graphite in 1955 and other
    metastable compounds," said Chu. "Graphite turns into a diamond when
    subjected to high pressure at high temperatures. Subsequent rapid
    pressure quench, or removal of pressure, leaves the diamond phase intact without pressure." Chu and his team applied this same concept to a superconducting material with promising results.

    "Iron selenide is considered a simple high-temperature superconductor
    with a transition temperature (Tc) for transitioning to a superconductive
    state at 9 Kelvin (K) at ambient pressure," said Chu.

    "When we applied pressure, the Tc increased to ~ 40 K, more than
    quadrupling that at ambient, enabling us to unambiguously distinguish the superconducting PQ phase from the original un-PQ phase. We then tried to
    retain the high- pressure enhanced superconducting phase after removing pressure using the PQ method, and it turns out we can." Dr. Chu and colleagues' achievement brings scientists a step closer to realizing
    the dream of room-temperature superconductivity at ambient pressure,
    recently reported in hydrides only under extremely high pressure.



    ========================================================================== Superconductivity is a phenomenon discovered in 1911 by Heike Kamerlingh
    Onnes by cooling mercury below its transition Tc of 4.2 K, attainable with
    the aid of liquid helium, which is rare and expensive. The phenomenon is profound because of superconductor's ability to exhibit zero resistance
    when electricity moves through a superconducting wire and its expulsion
    of magnetic field generated by a magnet. Subsequently, its vast potential
    in the energy and transportation sectors was immediately recognized.

    To operate a superconducting device, one needs to cool it to below
    its Tc, which requires energy. The higher the Tc, the less energy
    needed. Therefore, raising the Tc with the ultimate goal of room
    temperature of 300 K has been the driving force for scientists in superconductivity research since its discovery.

    In defiance of the then-prevailing belief that Tc could not exceed the
    30's K, Paul Chu , and colleagues discovered superconductivity in a new
    family of compounds at 93 K in 1987, achievable by the mere use of the inexpensive, cost- effective industrial coolant of liquid nitrogen. The
    Tc has continuously been raised since to 164 K by Chu et al. and other subsequent groups of scientists.

    Recently a Tc of 287 K was achieved by Dias et al. of Rochester University
    in carbon-hydrogen-sulfide under 267 gigapascal (GPa).

    In short, the advancement of Tc to room temperature is indeed within
    reach. But for future scientific and technological development of
    hydrides, characterization of materials and fabrication of devices at
    ambient pressures is necessary.

    "Our method allows us to make the material superconducting with higher
    Tc without pressure. It even allows us to retain at ambient the non- superconducting phase that exists only in FeSe above 8 GPa. There is
    no reason that the technique cannot be equally applied to the hydrides
    that have shown signs of superconductivity with a Tc approaching room temperature." The achievement inches the academic community closer
    toward room-temperature superconductivity (RTS) without pressure, which
    would mean ubiquitous practical applications for superconductors from the medical field, through power transmission and storage to transportation,
    with impacts whenever electricity is used.



    ========================================================================== Superconductivity as a means to improve power generation, storage and transmission is not a new idea, but it requires further research and development to become widespread before room temperature superconductivity becomes a reality. The capacity for zero electrical resistance means
    energy can be generated, transmitted and stored with no loss -- an
    enormous low-cost advantage. However, current technology demands that
    the superconducting device be kept at severely low temperatures to retain
    its unique state, which still requires additional energy as an overhead
    cost, not to mention the potential hazard of the accidental failure of
    the cooling system. Hence, an RTS superconductor with no extra pressure
    to sustain its beneficial properties is a necessity to move forward with
    more practical applications.

    The properties of superconductivity are also paving the way for a
    competitor to the famous bullet train seen throughout East Asia: a
    maglev train. Short for "magnetic levitation," the first maglev train
    built in Shanghai in 2004 successfully broadened usage in Japan and
    South Korea and is under consideration for commercial operation in the
    US. At top speeds of 375 miles per hour, cross country flights see a
    quick competitor in the maglev train. A room temperature superconductor
    could help Elon Musk realize his dream of a "hyperloop" to travel at a
    speed of 1000 miles per hour.

    This successful implementation of the PQ technique on room temperature superconductors discussed in Chu and Deng's paper is critical in making superconductors possible for ubiquitous practical applications.

    Now the riddle of RTS at ambient pressure is even closer to being solved.

    ========================================================================== Story Source: Materials provided by University_of_Houston. Original
    written by Nicole Johnson. Note: Content may be edited for style and
    length.


    ========================================================================== Journal Reference:
    1. Liangzi Deng, Trevor Bontke, Rabin Dahal, Yu Xie, Bin Gao, Xue
    Li, Ketao
    Yin, Melissa Gooch, Donald Rolston, Tong Chen, Zheng Wu, Yanming
    Ma, Pengcheng Dai, Ching-Wu Chu. Pressure-induced high-temperature
    superconductivity retained without pressure in FeSe single crystals.

    Proceedings of the National Academy of Sciences, 2021; 118 (28):
    e2108938118 DOI: 10.1073/pnas.2108938118 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2021/07/210708170334.htm

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