© 2007 Nature Publishing Group
1
Hall data and two-band conduction
The conduction of the LaAlO
3
/SrTiO
3
sample that is deposited at 10
-6
mbar is
completely dominated by oxygen vacancies, with a carrier density n
ox
of the order of
10
17
cm
-2
, as can be directly obtained from the Hall data of Supplementary Figure 1.
The mobility of these carriers increases at low temperatures to about 10
4
cm
2
V
-1
s
-1
.
With this many oxygen vacancies there is no need for a polar discontinuity at the
interface [1,2]. The number of oxygen vacancies can be reduced by depositing the
samples at higher oxygen deposition pressures. When n
ox
drops well below half an
electron per unit cell (of the order of 10
14
cm
-2
), the polar discontinuity is sustained and
interface induced carriers n
int
will contribute to conduction. When two contributions to
conduction (index 1 and 2) are taken into account, the equations for sheet- and Hall
resistance are generally written as
()
()
22
11 2 2
2
11 2 2
1
11 2 2
H
S
nn
R
en n
Ren n
−
µ+ µ
=
µ+ µ
=µ+µ
,
The Hall and sheet resistance data of all our samples can be fitted with this two-band
model [3], where the bands 1 and 2 are likely to be identified as arising from the oxygen
vacancies and the interface respectively.
For the 1.0 and 2.5×10
-3
mbar samples, the sheet resistance is found to be determined by
the interface induced carriers (n
int
µ
int
being larger than n
ox
µ
ox
) despite the fact that
µ
ox
is
much larger than
µ
int
(the latter being of the order of 1 cm
2
V
-1
s
-1
), which is of relevance
to the interpretation of the magnetoresistance data of this manuscript.
However, in the nominator of the expression for R
H
, the squared mobility enters,
making the oxygen vacancies important in the interpretation of R
H
. It is found that n
ox
at
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2
high temperatures is about 10
11
cm
-2
, and that this density is strongly reduced at low
temperatures. This gapping of the carriers is expected since the impurity band becomes
so narrow (few carriers) that it no longer intersects the Fermi level [4]. The low
temperature carrier freeze-out of n
ox
gives rise to the observed upturn in 1/eR
H
in
Supplementary Figure 1.
Concluding, in the samples deposited at relatively high oxygen pressure, the sheet
resistance is determined by the interface induced carriers. The influence of a small
amount of oxygen vacancies only becomes apparent in the measured Hall resistance.
Additionally, for two contributing conduction bands, a small positive contribution to
magnetoresistance is to be expected.
1. Kalabukhov, A., Gunnarsson, R., Borjesson, J., Olsson, E., Claeson, T. & Winkler,
D. Effect of oxygen vacancies in the SrTiO
3
substrate on the electrical properties of
the LaAlO
3
/SrTiO
3
interface. Phys. Rev. B 75, 121404 (2007).
2. Siemons, W., Koster, G., Yamamoto, H., Harrison, W.A., Geballe, T.H., Blank,
D.H.A. & Beasley, M.R. Origin of the unusual transport properties observed at
hetero-interfaces of LaAlO
3
on SrTiO
3
. cond-mat/0603598 (2006).
3. Huijben, M. et al., to be published elsewhere.
4. Tufte, O.N. & Chapman, P.W.
Electron Mobility in Semiconducting Strontium
Titanate. Phys. Rev. 155, 796–802 (1967).
© 2007 Nature Publishing Group
3
Supplementary Figure 1 | Hall coefficient. Temperature dependence of the
inverse Hall resistance of n-type SrTiO
3
-LaAlO
3
conducting interfaces, grown at
various partial oxygen deposition pressures.