Light tunable superconducting devices using transition metal oxides

超导体和超导器件具有一系列令人着迷的特性，使它们非常适合新的应用。虽然许多金属在低温下是超导的，但低密度半导体通常不是。这限制了可以使用超导材料实现的设备架构。D电子氧化物SrTiO_3是一种特殊材料，因为当电子掺杂时，它在很低的载流子密度下是超导的，同时也是一种高迁移率的半导体。因此，可以在这种材料中研究超导的基本极限，以及创造新器件的可能性。在这种体系中，传统的载流子诱导方法--钛酸锶化学掺杂的一个关键限制是超导电性和电导率在低密度极限下崩溃，这很可能是由于不均匀的掺杂造成的。这项提议将开发一种光致超导设备架构来克服这一问题。我们将利用SrTiO_3在低温下强烈的光导响应作为活性元素，并结合元素超导体的邻近效应。众所周知，光致电子-空穴对在低温下表现出很高的电子迁移率，而空穴的迁移率要低得多。由于空间均匀的照明，我们也已经确定，我们可以保持比化学掺杂更低的电导率密度。光的波长和强度是强大的调谐参数：我们不仅可以连续调谐系统中的电子总数，还可以利用SrTiO_3在禁带附近随波长变化的吸收系数来连续调谐系统的局部三维密度。利用这些技术，这项工作将研究在大范围的载流子密度和迁移率范围内诱导超导关联的极限。这些连续可调的光诱导约瑟夫森结将被用作研究人工系统中二维超导体到绝缘体转变的基础，从而解决关于低密度超导体中相位相干性的基本问题。

Superconductors and superconducting devices have a range of fascinating properties that makes them highly suitable for novel applications. While many metals are superconducting at low temperatures, low density semiconductors typically are not. This limits the device architectures that can be implemented using superconducting materials. The d-electron oxide SrTiO3 is a special material since when electron doped it is superconducting at very low carrier densities, and is simultaneously a high mobility semiconductor. The fundamental limits of superconductivity can therefore be investigated in this material, as well as the possibilities of creating novel devices. A key limitation in chemical doping of SrTiO3, the traditional method of inducing carriers in this system, is that the superconductivity and conductivity collapses in the low density limit, most likely due to inhomogeneous doping. This proposal will develop a light-induced superconducting device architecture to overcome this problem. We will utilize the strong photoconducting response of SrTiO3 at low temperatures as the active element, in combination with the proximity effect with elemental superconductors. It is known that photo-induced electron-hole pairs in SrTiO3 show high electron mobility at low temperatures, with the holes far less mobile. Because of the spatially uniform illumination, it has also been established that we can maintain conductivity to lower densities than for chemical doping. The light wavelength and intensity are powerful tuning parameters: we can continuously tune not only the total number of electrons in the system, but also the local three-dimensional density, exploiting the wavelength dependent absorption co-efficient of SrTiO3 near to the band-gap. Using these techniques this work will investigate the limits of inducing superconducting correlations over a wide range of carrier densities and mobilities. These continuously tunable light-induced Josephson junctions will be used as a foundation for studies of the two-dimensional superconductor-to-insulator transition in artificial systems, allowing fundamental questions about the nature of phase coherence in low density superconductors to be addressed.