November 17th
when: Tuesday 08/12/2020, 12:45
where: Zoom meeting!
speaker: Ranga Dias
Title: New Frontiersin Superconductivity: Superhydrides at High Pressures
abstract:
uperconductivity has been one of the most profound quantum phases in condensed matter physics. Efforts to identify and develop room temperature superconducting materials are an intensive area of research, motivated by both fundamental science and the prospects for applications. More than a century of rigorous research has led physicists to believe that the highest Tcthat can be achieved is 40K for conventional superconductors. However, the recent discovery of superconductivity in hydrogen sulfide at 203K changed the notion of what might be possible for phonon–mediated superconductors. In this talk, I willdiscuss recent developmentson high pressure superconductivityOne of the long-standing challenges in experimental physics is the observation of room-temperature superconductivity.Animportantdiscovery leadingto room-temperature superconductivity is the pressure-driven disproportionation of hydrogen sulfide (H2S) to H3S, with a confirmed transition temperature of 203 kelvin at 155 gigapascals. BothH2Sand CH4readily mix with hydrogen to form guest–host structures at lower pressures, andare of comparablesize at4gigapascals. By introducing methane at low pressures into the H2S + H2precursor mixture for H3S,molecular exchange is allowedwithin a large assemblage of van der Waals solids that are hydrogen-rich with H2inclusions; these guest–host structures become the building blocks of superconducting compounds at extreme conditions. I shall present our most recent results onsuperconductivity in a photochemically transformed carbonaceous sulfur hydride system, starting from elemental precursors, with a maximum superconducting transition temperature of 287.7±1.2 kelvin (about 15 degrees Celsius) achieved at 267±10 gigapascals. Superconductivity is established by the observation of zero resistance, a magnetic susceptibility of up to 190 gigapascals, and reduction of the transition temperature under an external magnetic field of up to 9 tesla, with an upper critical magnetic field of about 62 tesla according to the Ginzburg–Landau model at zero temperature. The Raman spectroscopy is used to probe the chemical and structural transformations before metallization.The discovery achieves the more than a century long quest to find room temperature superconductivity, a phenomenon that was first observed by Kamerlingh Onnes in 1911. Finally, I shall discuss future research directions in probing room temperature superconductivityby introduction of chemical tuning within ourternary system at much lower pressures.