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Quite remarkably, two insulating oxides SrTiO 3 and LaAlO 3 , 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. |