Light tunable superconducting devices using transition metal oxides

超导体和超导器件具有一系列迷人的特性，使它们非常适合于新的应用。虽然许多金属在低温下都是超导的，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是一种特殊的材料，因为当电子掺杂时，它在非常低的载流子密度下是超导的，同时是高迁移率半导体。因此，可以在这种材料中研究超导性的基本极限，以及创造新设备的可能性。SrTiO 3的化学掺杂（在该系统中诱导载流子的传统方法）中的关键限制是超导电性和导电性在低密度极限中崩溃，这很可能是由于不均匀掺杂。这项提案将开发一种光诱导超导器件架构来克服这个问题。我们将利用SrTiO 3在低温下的强光电导响应作为活性元素，结合元素超导体的邻近效应。已知SrTiO 3中的光致电子-空穴对在低温下显示出高的电子迁移率，而空穴的移动的要小得多。由于空间上均匀的照射，还已经确定，我们可以将电导率保持到比化学掺杂更低的密度。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在带隙附近的波长依赖性吸收系数来连续调谐局部三维密度。使用这些技术，这项工作将调查的限制，诱导超导相关的载流子密度和迁移率的范围很广。这些连续可调的光致约瑟夫森结将被用作人工系统中二维超导体到绝缘体转变研究的基础，从而解决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.