• Dogra, Anjana
• Kundu, Hemanta Kumar
• Kaur, Simrandeep
• Narayanan, Rajesh
• Bid, Aveek
• Kumar, Sumit
• Vojta, Thomas

Abstract

We study the superconductor-insulator transition in the quasi-two-dimensional electron gas (q-2DEG) formed at the interface of LaScO$_3$/SrTiO$_3$ heterostructures. Using various tuning parameters such as the gate voltage and the magnetic field, we show an intervening anomalous metallic state apart from the usual superconducting and insulating ground states. Further, by studying the scaling of the magnetoresistivity data, we find a highly unusual two-stage divergence of the dynamical critical exponent. The first increase, at higher temperatures, demonstrates that the system hosts a quantum Griffiths phase caused by disorder-induced rare puddles of superconductivity embedded in a non-superconducting matrix. The second, stronger, increase of the dynamical exponent at lower temperatures indicates that the quantum Griffiths phase is cut-off or cloaked below a crossover temperature scale. We elucidate possible mechanisms that account for the cloaking of the Griffiths phase. Finally, we construct a phase diagram that encapsulates the various phases of the q-2DEG as a function of the applied magnetic field and temperature. We further discuss the various cross-overs and phase transitions in the system by utilizing this phase diagram....

Topics

• impedance spectroscopy
• phase
• phase transition
• two-dimensional
• phase diagram
• superconductivity
• superconductivity