Leggett mode controlled by light pulses

The discovery of symmetry-broken phases that host multiple order parameters, such as multiband superconductors(1,2), has triggered an enormous interest in condensed matter physics. However, many challenges continue to hinder the fundamental understanding of how to control the collective modes corresponding to these multiple order parameters(3,4). Here we demonstrate that, in full analogy with phonons, Raman-active electronic collective modes can be manipulated by intense light pulses. By tuning a sum-frequency excitation process, we selectively trigger collective excitations that can be ascribed to the relative phase fluctuations between two superconducting order parameters-the so-called Leggett mode-in the multiband superconductor MgB2. The excellent comparison between experiments and theory establishes a general protocol for the advanced control of Raman-active electronic modes in symmetry-broken quantum phases of matter

Magnesium diboride on inner wall of copper tube: A test case for superconducting radio frequency cavities

Superconductor magnesium diboride is considered one of the viable materials to substitute bulk niobium for superconducting radio frequency cavities. Utilizing a MgB_{2} coating on the inner wall of a copper cavity will allow operation at higher temperatures (20–25 K) than Nb cavities due to the high transition temperature of MgB_{2} (39 K) and the high thermal conductivity of Cu. In this paper, we present results of MgB_{2} coating on Cu tubes with similar dimensions to a 3 GHz cavity, as the first step towards coating the actual cavity, using the hybrid physical chemical vapor deposition technique. The results show successful coating of a uniform MgB_{2} layer on the inner wall of the Cu tubes with T_{c} as high as 37 K