Physics

Prof. Arghya Taraphder
IIT Kharagpur

Abstract:

Quite remarkably, two  insulating oxides SrTiO3 and LaAlO3,  joined together  to form a heterostructure, come up with a highly conductive two-dimensional electron liquid (2DEL) at the hetero-interface. This 2DEL exhibits exciting new phenomena such as finite-momentum triplet superconductivity coexisting with inhomogeneous ferromagnetism, gate-voltage-induced superconductor to insulator and metal to insulator transition, as well as a complex excitation spectrum. We study the role of intrinsic disorder on superconductivity and ferromagnetism at the interface and find that for reasonably strong disorder, the system breaks up into mutually excluded regions of superconductivity and ferromagnetism ruling out an FFLO state [1]. This electronic phase-separation accounts for the unusual coexistence of superconductivity and ferromagnetism observed at the interface. The dynamics of the defects at the interface, such as Oxygen vacancies, are investigated further by a Monte-Carlo method and a clustering of vacancies at low temperatures is found [1]. Such a clustering sheds light on ill-understood phenomena like carrier freeze-out at low temperature and pseudo-gap in the superconducting state. A perpendicular magnetic field drives a phase-transition to topological superconductivity and gapless topological excitations [2] at the core of a vortex, such as Majorana fermions, that are vulnerable to disorder. We also report the observation of a transient superconducting state above nominal Tc implying a 'hidden' superconducting order [3]. A three-band model has been used to describe the hidden superconducting state at the interface[4]. The observations of Lifshitz transition, possible BKT transition and considerable MR are  outlined [5,6].

References:

[1] N. Mohanta, A. Taraphder, J. Phys. Cond. Mat. 26, 025705 (2014); ibid 26, 215703

(2014).

[2] N. Mohanta and A. Taraphder, Europhys. Lett. 108, 60001 (2014).

[3] Shelender Kumar, Gopi Nath Daptary, Pramod Kumar, Anjana Dogra, N. Mohanta, A. Taraphder, R. C. Budhani, arXiv:1411.3103 (2014).

[4] N. Mohanta and A. Taraphder, Phys. Rev. B. 92, 174531 (2015).

[5] G. Daptary, et al. Phys. Rev. B. 94, 085104 (2016).

[6] S. Nandy, N. Mohanta, S. Acharya, A. Taraphder Phys. Rev. B (2016) to appear.