Girsh Blumberg

How do chiral superconductors break time-reversal symmetry? – Kerr spectroscopy study

Chiral superconductors are unconventional superconducting materials with distinctive topological properties in which time-reversal symmetry is broken. This class of superconductors is predicted to be ideal for building quantum computers. What causes the asymmetric electric transport in chiral superconductors is currently unknown. The Kerr project further investigates the microscopic mechanism that links superconductivity and chirality. Researchers developed a new generation of instruments that measure the polar Kerr effect in the sub-terahertz frequency range. Measurements in this energy scale enable researchers to study the broken symmetries, the origin of unconventional pairing, the in-gap collective modes, and the structures of the superconducting order parameter.

Result

Recent measurements of the polar Kerr effect (PKE), in which a rotation of polarisation is detected for a beam of light reflected from the surface of a superconductor, have emerged as a key experimental probe of time-reversal symmetry (TRS) breaking. The team is developing a new generation of spectroscopic instrumentation for PKE spectroscopy in the sub-THz frequency range, the energy scale that is comparable with the superconducting (SC) gap magnitude of unconventional superconductors. THz range PKE spectroscopy enables to study the broken symmetries, the origin of unconventional pairing, the in-gap collective modes, and the structures of the SC OPs. The team planned to measure the PKE at sub-THz frequencies and with sub-milli-radian angular resolution from a variety of unconventional superconductors that are cooled to 100 mK, deep into SC state. The aim was to understand the basic mechanisms leading to unconventional superconductivity in these systems in order to find answers to the fundamental questions, and to elucidate the microscopic origin of superconductivity in the new families of unconventional superconductors.

Impact

Superconductivity is a phenomenon of electrical current flow without any loss of energy due to resistance. The field of applications of superconductivity is driven by materials science and is nowadays routinely applied in medical applications of magnetic resonance imaging (MRI), in large-scale magnetic guiding systems such as Large Hadron Collider at CERN, the presently constructed nuclear fusion energy plant ITER, and most recently in quantum computational applications. The proposed research will affect public awareness of modern scientific progress in its relation to energy and climate solution through the outreach and public presentations resulting in increased public scientific literacy and engagement with science and technology. The work keeps Estonian physics at the forefront of science and culture through scientific contacts, and promotes education by engaging students in the research.