Theory of charge and spin ordering in the nickelates - Physics ...

ates remain
temperature
ds, the key
ort high T c
y, spin oneg
antiferroperties
are
ered cobalhe
presence
0 where the
–localizedatistics
may
The multic
‘‘normal’’
icles, pseurconducting
y correlated
as Ti 3 and
2g hole) and
at possess a
hese comperties
[1];
from which
eracy is ‘‘to
etry of the
ck of both
bital degenkinematical
tly, a fermid
insulatorthe
pseudoormation
of
within just
correlations
lectrons are
ifferent orinteractions
that result in a rich variety of magnetic states in S 1=2
oxides such as RTiO 3 , Na x CoO 2 , Sr 2 CoO 4 , RNiO 3 ,
NaNiO 2 . In contrast, spin correlations in single-band cuprates
are of AF nature exclusively and hence strong.
How to suppress
Mott
the orbital degeneracy and
interfaces
promote
cupratelike physics in other S 1=2 oxides? In this
Letter, we suggest and argue theoretically that this goal
can be achieved in oxide superlattices. Specifically, we
focus on Ni-based superlattices (see Fig. 1) which can be
fabricated using recent advances in oxide heterostructure
technology ([3–5] and references therein). While the proposed
compound has a pseudocubic ABO 3 structure, its
Lots of interesting suggestions!
low-energy electronic states are confined to the NiO 2
planes and, hence, are of a quasi-2D nature. A substrate
induced compression of the NiO 6 octahedra further stabilizes
the x 2 -y 2 orbital. Net effect is a strong enhancement of
(a)
MO 2
LaO
NiO 2
LaO
MO 2
a
c
b
(b)
(c)
(d)
substrate
FIG. 1. (a) Superlattice La 2 NiMO 6 with alternating NiO 2 and
MO 2 planes. MO 2 layers suppress the c-axis hopping resulting in
Chaloupka +
2D electronic structure. Arrows indicate the c-axis compression
of the NiO 6 octahedron Khaliullin, imposed by 2008 tensile epitaxial strain and
supported by Jahn-Teller coupling. (b) ,(c), (d) Strain-induced
stretching of the NiO 2 planes occurs when superlattices with
M Al, Ga, Ti are grown on SrTiO 3 or LaGaO 3 substrates
having large lattice parameter compared to that of LaNiO 3 .
Expected deformations are indicated by arrows.
Al
Ni
Ga
Ni
Ti
Ni
vary d to tune
Mott transition
d