Supporting Materials
Structural Characterization
TABLE I Structural characterization of SNO strained films. The film c-axis and thickness is
determined from XRD θ/2θ scans around the (00l)pc reflection. The strain is calculated using the bulk
lattice parameter reported in Ref.1.
Substrate
LSAT
LaAlO3
NdAlO3
YAlO3
Thickness
[nm]
8.9
9.4
10.1
8.4
εxx [%]
as [Å]
cfilm [Å]
Vu.c. [Å3]
1.9
-0.1
-0.9
-2.3
3.868
3.790
3.760
3.709
3.764
3.790
3.829
3.912
56.31
54.43
54.12
53.82
TABLE II Structural characterization of NNO strained films. The film c-axis and thickness is
determined from XRD θ/2θ scans around the (00l)pc reflection. The strain is calculated using the bulk
lattice parameter reported in Ref.2.
Substrate
DyScO3
NdGaO3
LaAlO3
NdAlO3
Thickness
[nm]
11.4
25.9
11.3
12.7
εxx [%]
as [Å]
cfilm [Å]
Vu.c. [Å3]
3.6
1.5
-0.5
-1.3
3.943
3.864
3.790
3.760
3.765
3.797
3.818
3.857
58.55
56.70
54.83
54.52
1
Transport Characterization
The resistivity measurements as a function of temperature were performed in the
range 500 K-4 K using a standard 4-probe configuration. For the measurements
between 4 K and 300 K the sample temperature was controlled in a liquid helium
cryostat, whereas the system was warmed up from RT to 500 K using Peltier
elements. TMI is defined as the temperature at which -∂ln(R)/∂T has a maximum for
the cases of first order MIT, and as the temperature at which it displays a kink for the
other cases. The peak in -∂ln(R)/∂T was fit with a Gaussian function, the standard
deviation of which specifies the temperature width of the MIT.
FIG. 1 Resistivity versus Temperature of NNO films subjected to different levels of strain. The MIT
behavior is consistent with previously reported results.3
2
Computational Methods
Two kinds of DFT simulations were performed in order to investigate the effect of
strain on the bare bandwidth (W) of SNO and NNO, which is believed to be one of
the important control parameters of the MIT transition.
The calculations were performed within generalized gradient approximation4 using
the projector-augmented wave (PAW)5 formalism as implemented in Vienna ab-initio
Simulation Package (VASP).6 Structure relaxations using conjugate-gradient method
were considered as converged when the atomic forces were smaller than
0.005 eV*Å-1. The k-mesh of size 7x7x5 and the plane-wave cutoff energy of 600 eV
were used. Assuming that the f-electrons on RE do not affect the structure relaxation,
we have employed the PAW potentials for Sm and Nd with f-electrons treated as
semi-core states. For the case of NNO the equation of state was obtained by
performing structure relaxation at a set of fixed volumes within bulk Pbnm symmetry.
From these calculations, we extracted the equilibrium lattice constant and the
bandwidth that the system would display as it is subject to the hydrostatic pressure for
which its TMI becomes zero.7 The latter computation was performed only for the NNO
compound. The strain was then calculated with respect to the obtained theoretical
value of the lattice constant. In the second type of calculations, the response of the
film structure to strain was investigated by fixing the in-plane lattice parameter to that
of a cubic substrate and by letting the other degrees of freedom to relax (the volume
was not fixed in these calculations). The c-axis of the Pbnm structure was oriented
normal to the substrate surface.
3
FIG. 2 Results of DFT calculations as a function of strain for SNO. (a) Width of bands distinguished
by the orbital character of the Ni eg-states. (b) Ni-O bond length lNi-O and (c) Ni-O-Ni bond angle 
within the in-plane and out-of-plane directions. The overall behavior is very similar to that reported for
NNO, although slightly higher tendency of the dz2-bandwidth to increase under compressive strain is
observed. The x-axis of the plots goes from positive to negative values in order to be consistent with
Fig. 4 of the main text, simplifying the visualization and comparison of the strain and the tolerance
factor control on the RNOs phase diagram.
4
FIG. 3 Results of DFT calculations as a function of strain for the case of NNO. (a) Width of bands
distinguished by the orbital character of the Ni eg-states. The horizontal dashed green line is given as a
reference and shows the size of the bandwidth of bulk NdNiO 3 at which TMI=0 under the hydrostatic
pressure.7 (b) Ni-O bondlength lNi-O and (c) 
-plane and out-of-plane directions.
Different colors are used between the two panels in order to stress that the relationship with the
bandwidth of the two parameters is intrinsically different.
5
Diffraction Experiment
We studied the magnetic properties of the films through resonant soft x-ray scattering
measurements at the RSXS end station of the REIXS beamline at the Canadian Light
Source (CLS).5 For this experiment we used linearly polarized incoming light
selectively tuned to the Ni L2,3-edge (850-890 eV) and to the R M4,5 edge (1060-1120
eV for R=Sm, 960-1020 eV for R=Nd). By exploiting the substantial enhancement of
the nickelate cross-section in the resonant regime, we investigated the presence of the
(¼ ¼ ¼) Bragg reflection in the temperature range 20 K –300 K. In order to access
the [111]pc direction, the samples were mounted on a wedge-shaped holder inclined at
35°. The rotation axis of the azimuthal angle  coincides with the [111] q vector,
being =0 when the sample [1-10]pc and [111]pc axis lie in the scattering plane. The
diffraction signal was collected either with a multichannel plate or a photodiode,
depending on its intensity.
FIG. 4 Exemplifying diffraction scans measured at T=20K in order to follow the temperature evolution
of the AFM phase. (a), (b), (d) rocking curves about qBragg=(¼ ¼ ¼), with the energy tuned at the Ni L3
resonance and  polarized incident light. The splitting of the peak in Figure 4(b) is due to twinning of
the NdAlO3 substrate. (c) /2 scan about the indicated reflection of the tensively strained NNO film.
6
FIG. 5 Temperature dependence of the (¼ ¼ ¼) reflection as the incident beam energy is tuned to the
R resonance, in (a) R=Sm and in (b) R=Nd. The signal is detected with  polarized incident light. In
Figure 5(a) each symbol is the integrated intensity of a rocking curve about q Bragg. In Figure 5(b) the
signal is probed directly as the sample is cooled with a cryogenic cryostat. In both cases, the curve
evolves as an induced parameter.
References
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2
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Triscone, Adv. Mater. 22, 5517 (2010).
4
J. P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made
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8