Supplementary Information
Gate-tunable quantum oscillations in
ambipolar Cd3As2 thin films
Yanwen Liu1,2, Cheng Zhang1,2, Xiang Yuan1,2, Tang Lei1, Chao Wang3, Domenico
Di Sante4,5, Awadhesh Narayan6,7, Liang He8,9, Silvia Picozzi4, Stefano Sanvito6,
Renchao Che3, Faxian Xiu1,2
1
State Key Laboratory of Surface Physics and Department of Physics, Fudan
University, Shanghai 200433, China
2
Collaborative Innovation Center of Advanced Microstructures, Fudan University,
Shanghai 200433, China
3
Department of Materials Science and Advanced Materials Laboratory, Fudan
University, Shanghai 200433, China
4
Consiglio Nazionale delle Ricerche (CNR-SPIN), Via Vetoio, L'Aquila, Italy
5
Department of Physical and Chemical Sciences, University of L'Aquila, Via Vetoio
10, I-67010 L'Aquila, Italy
6
School of Physics, CRANN and AMBER, Trinity College, Dublin 2, Ireland
7
Department of Physics, University of Illinois at Urbana-Champaign, Illinois, USA
8
National Laboratory of Solid State Microstructures, School of Electronic Science and
Engineering, Nanjing University, Nanjing 210093, China
9
Collaborative Innovation Center of Advanced Microstructures, Nanjing University,
Nanjing 210093, China

Correspondence and requests for materials should be addressed to F. X. and R. C.
(E-mails: faxian@fudan.edu.cn and rcche@fudan.edu.cn)
1
I. Sample descriptions
Several as-grown thin film samples have been measured with ionic gating.
Sample Q1 is the sample described in the main text for positive gate voltages and SdH
oscillations (Fig. 2c, the electron density in Fig. 3e, Fig. 4 and Fig. 5). Sample Q6
shows a systematic hole carrier transport in the main text (Fig. 2d, Fig. 3). The results
of samples Q2~Q5 are summarized in the Supplementary Section VII (Fig. S12-17).
All these samples exhibit the similar transport properties.
II. Hopping conduction
a
b
c
4.12
4.26
Q2 -1.25 V
Q1 -1.5 V
4.10
Q6 -0.6 V
4.10
4.08
log(R)
log(R)
log(R)
4.24
4.08
4.06
4.06
4.20
4.04
4.04
4.22
4.02
0.3
0.4
0.5
0.6
0.7
0.8
T-1/3 (K-1/3)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.3
T-1/3 (K-1/3)
0.4
0.5
0.6
0.7
T-1/3 (K-1/3)
Figure S1| Hopping transport of Cd3As2 thin films at low temperatures under several
gate voltages.
III. Gating effect of Cd3AS2 thin films with solid electrolyte
The gate sweeping process was carried out at 290 K, slightly higher than the
frozen point of solid electrolyte (~280 K). The on-off ratio at 290 K is about 5 (Fig.
S2), while at low temperatures it could increase to about 30 (Fig. S4). We believe that
by reducing the dimensionality, the band gap can be slightly enlarged which results in
the improved on-off ratio.
The carrier density and mobility show negligible temperature dependence below
60 K (Fig. S3a-b). The behavior is similar to that of MoS2 devices encapsulated by
2
0.8
hBN1. It is probably attributed to the reduction of impurity scattering because the
solid electrolyte serves as a top gate.
Figure S2 | Rxx-Vg curve at 290 K of sample Q1 (black one). The sweep rate of gate
voltage is 1 mV/s. The leakage current (blue curve) is negligible and therefore the
electrostatic doping effect is dominated during the experiments.
b
10
0.2
0.7
3500
0.3
0.9
8
6
4
3000
2500
Vg (V)
2000
2
10
100
T (K)
nhall (×1012 cm-2)
10
0
0.5
1.2
μhall (cm2V-1s-1)
nhall (×1012 cm-2)
12
c
Vg (V)
0
0.2
0.5
0.9
0.3
0.7
1.2
10
nhall
3600
μhall
9
3400
8
7
3200
6
3000
5
4
2800
3
2600
2
100
0.0
T (K)
0.2
0.4
0.6
0.8
1.0
1.2
Vg (V)
Figure S3 | Carrier density and mobility obtained from the Hall effect
measurements (sample Q1). a, Temperature-dependent carrier density under
different gate voltages. b, Temperature-dependent mobility under different gate
voltages. Both the carrier density and mobility are nearly temperature independent
below 60 K. c, Gate-dependent carrier density and mobility at 4 K.
3
2400
μhall (cm2V-1s-1)
a
b
14000
Q1
9000
10000
8000
20000
Q6
15000
R (Ω)
R (Ω)
12000
c
Q2
12000
R (Ω)
a
6000
10000
5000
6000
3000
0
4000
0
-2.2
-2.0
-1.8
-1.6
-1.4
-1.2
-1.0
-2.5
-2.0
Vg (V)
-1.5
-1.0
-0.5
Vg (V)
0.0
-2.5
-2.0
-1.5
-1.0
Vg (V)
Figure S4| Resistance at 2 K of the Cd3As2 thin films. a, Id-Vg curve of sample Q1
(in the main text). b, Id-Vg curve of sample Q2. The detailed quantum oscillations are
shown in the Supplementary Section V. When Vg<-2V, the saturation was observed. c,
Id-Vg curve of sample Q6. The ambipolar behavior and the hole-dominated transport
are clearer owing to the increased the area of the gate electrode and the reduced area
of channel.
IV. Two carrier transport of Cd3As2 thin films
With negative gate voltages, hole carriers are electrostatically doped into the thin
films, shifting the Fermi level towards the valence band. Both electrons and holes
contribute to the transport. We note that at the turning points of the Hall slopes
(Fig.S5a-d), the MR curves also show the change of curvature as marked by the
arrows, giving another evidence of the two carrier transport in our Cd3As2 films. With
the two-carrier transport equation, the carrier density and mobility of holes and
electrons could be obtained. Fig. S5c and d show two fitting curves of the Hall data
with red dash lines for sample Q1, and the fitting results are summarized in Fig. S7.
Similar analyses have been applied to sample Q6 (Fig. S8). From the Kohler’s plot2–4
as explained in the main text, we could also identify the two carrier transport
distinctly (see the Kohler’s plots in Fig. S6e-f for sample Q1 and Fig. S9 for sample
Q6).
It is interesting that the Kohler’s plot of MR at 0 V doesn’t fall on a universal
curve at high field (Fig. S6d). However, with the linear Hall slopes at high field (not
4
-0.5
0.0
shown here), it does not show the two carrier transport but exhibits anisotropy of
scattering time at the Fermi surface. The shadowed area marks the regime where the
Kohler’s rule is obeyed at low field. The shadowed area increases as the gate voltage
increasing (Fig. S6c-d), suggesting the reduction of the anisotropy. The results agree
with the observed dipolar pattern in the polar plots in Fig.5c of the main text. The
curves at 4 K deviate from the universal curve because of the quantum oscillations.
With increasing carrier density, the influence from orbit quantization is enhanced,
making the Kohler’s rule break down3,4 (Fig. S6a-b). In the Kohler’s plot of 1.2 V, the
curves have similar trend but a little shift from each other, different from the disorder
in the Kohler’s plot at negative gate voltage (Fig. S6e-f). The violation here doesn’t
explicitly mean the anisotropy of Fermi surface.
a
b
8
4
Vg=-1 V
Vg=-1.5V
30
10
Rxy
Rxy
4
2
0
Rxy (kΩ)
0
Rxx (kΩ)
8
Rxy (Ω)
Rxx (kΩ)
25
20
Rxx
Rxx
-4
-2
6
15
-8
-4
-2
0
2
4
6
8
-8
-8
B (T)
-6
-4
-2
2
4
6
8
1.5
Vg=-1.8 V
Vg=-2 V
14
1.0
1.0
22
0.5
20
13
0.0
18
Rxx (kΩ)
Rxy
Rxy (Ω)
Rxx (Ω)
-4
B (T)
d
24
0
0.5
Rxx
0.0
Rxy
12
-0.5
-0.5
16
Rxy (kΩ)
c
-6
Rxx
11
-1.0
14
-1.0
-8
-6
-4
-2
0
2
4
6
10
8
B (T)
-8
-6
-4
-2
0
B (T)
5
2
4
6
8
-1.5
Figure S5 | Two carrier transport of sample Q1. MR and Hall under 4 K at the gate
voltage of -1 V (a), -1.5 V (b), -1.8 V (c) and -2V (d), respectively. The blue lines are
the Hall data and the black lines are the MR data. The red dash lines in c and d are the
fitting curves of two-carrier model.
a
c
b
0.20
0.5
Vg= 1.2 V
4K
20K
30K
40K
60K
80K
0.05
0.00
0.0
1.0x10-4
2
xx
2
0.5
0.4
Vg=0 V
4K
20K
30K
40K
60K
80K
0.2
0.1
0.0
0
1x10-5
2
2x10-5
2
2
3x10-5
-2
B /Rxx(0) (T Ω )
4x10-5
ΔRxx(B)/Rxx(0)
ΔRxx(B)/Rxx(0)
e
0.6
0.3
2.0x10-5
2
4.0x10-5
2
xx
6.0x10-5
2 -2
0.4
0.3
Vg =0.2 V
4K
20K
30K
40K
60K
80K
0.2
0.1
0.0
8.0x10-5
0
B /R (0) (T Ω )
B /R (0) (T Ω )
d
4K
20K
30K
40K
60K
80K
0.1
0.0
0.0
3.0x10-4
2.0x10-4
2 -2
Vg=0.5 V
0.2
f
0.8
0.6
0.4
Vg=-1.8 V
2K
10K
20K
40K
80K
120K
0.2
0.0
0.0
2
2
5.0x10-7
2 -2
B /Rxx(0) (T Ω )
1x10-5 2x10-5 3x10-5 4x10-5 5x10-5 6x10-5
2 -2
2
2
xx
B /R (0) (T Ω )
ΔRxx(B)/Rxx(0)
0.10
0.3
ΔRxx(B)/Rxx(0)
0.15
ΔRxx(B)/Rxx(0)
ΔRxx(B)/Rxx(0)
0.4
0.6
0.4
Vg=-2 V
2K
10K
20K
40K
80K
120K
0.2
0.0
0.0
5.0x10-7
B2/Rxx(0)2 (T2Ω-2)
Figure S6 | The Kohler’s plots of the MR curves of sample Q1 at the gate voltage
of 1.2 V (a), 0.5 V (b), 0.2 V(c), 0 V (d), -1.8 V (e) and -2 V (f), respectively. If there
is a single type of charge carrier with the same scattering time at the Fermi surface
everywhere, the temperature-dependent Kohler plot of MR curve would overlap each
other. Here the non-overlapping behavior in e and f along with the non-linear Hall
data suggests unambiguously two-carrier transport. The non-overlapping behavior in e
suggests different scattering time at the Fermi surface.
6
1.0x10-6
b
Vg=-1 V
150K
80K
40K
20K
10K
2K
6000
4000
0
120K
80K
40K
20K
10K
2K
2000
Rxy (Ω)
Rxy (Ω)
2000
Vg=-1.5 V
4000
e
10
8
6
4
0
2
-2
-2000
-1
-2000
-4000
0
f
-4000
-8
c
-6
-4
-2
0
2
4
6
8
B (T)
d
2000
Vg=-1.8 V
120K
80K
40K
20K
10K
2K
1500
1000
-6
-4
-2
0
4
6
8
Vg=-2 V
1500
120K
80K
40K
20K
10K
2K
500
0
2
B (T)
1000
Rxy (Ω)
500
Rxy (Ω)
-8
np (×1012 cm-2)
-6000
-8000
1
Vg (V)
-1.8 V:
-2 V:
μ
μ
n
n
15
0.10
10
0.05
5
1
10
μp (m2V-1s-1)
8000
ns (×1012 cm-2)
a
100
T (K)
g
2.5
0
-1.8 V
-2 V
2.0
-500
σn/σp
-500
-1000
-1000
-1500
1.5
1.0
0.5
-1500
-2000
-8
-6
-4
-2
0
B (T)
2
4
6
8
-8
-6
-4
-2
0
2
4
6
8
B (T)
0.0
1
10
100
T (K)
Figure S7 | Temperature- and gate-dependent hall resistance Rxy of ~50 nm-thick
Cd3As2 thin film (sample Q1). a, Rxy under -1 V (gate voltage), indicative of
electron-dominated n-type conductivity. b, Rxy under -1.5 V, showing a nonlinear
behaviour originated from two-carrier transport owing to the gate-induced holes. c,
Rxy under -1.8 V. The Cd3As2 channel undergoes a transition from electron- to holedominated transport as evidenced by the change of slope at B≥3T. d, Rxy under -2 V.
The holes are dominant in Hall resistance. e, Gate-dependent sheet carrier density. It
implies the ambipolar transport. The hole carrier density was extracted from the fits to
the two-carrier transport model. Electron carrier density was obtained from the Hall
effect measurements. The graduated background represents the amount and type of
carriers, blue for holes and red for electrons. f, Temperature-dependent hole mobility
(solid circles) and hole density (open squares) under -1.8 V (red) and -2 V (blue),
obtained from the fits to the two-carrier transport model. g, Temperature-dependent
conductance ratio σn/σp. The dashed line marks σn/σp=1.
7
a
b
1500
Vg (V)
1.2x1013
Vg(V)
1000
p (cm-2)
-0.8
-0.9
-1.05
-1.3
-2.2
Rxy (Ω)
500
-2.2
-1.3
-0.9
-0.8
12
9.0x10
6.0x1012
3.0x1012
1
10
0
100
T (K)
c
800
μp (cm2V-1s-1)
-500
-1000
600
400
Vg (V)
-2.2
-1.3
-0.9
-0.8
200
-1500
0
-8
-6
-4
-2
0
2
4
6
8
1
10
100
T (K)
B (T)
Figure S8 | Two carrier transport of sample Q6. a, Rxy at 2 K under negative gate
voltage. The black dash lines are the fitting curves of two-carrier model. b-c,
Temperature-dependent hole mobility (b) and hole density (c) under negative gate
voltage, obtained from the fits to the two-carrier transport model.
8
b
0.8
Vg = -0.5 V
0.6
2K
10 K
20 K
40 K
60 K
80 K
0.7
Vg = -0.9 V
0.6
△Rxx(B)/Rxx(0)
△Rxx(B)/Rxx(0)
a
0.4
0.2
2K
10 K
20 K
40 K
60 K
80 K
0.5
0.4
0.3
0.2
0.1
0.0
0.0
5.0x10-7
0.0
1.0x10-6
0
d
c
3x10-7
4x10-7
5x10-7
Vg = -2.2 V
0.35
2K
10 K
20 K
40 K
60 K
80 K
△Rxx(B)/Rxx(0)
△Rxx(B)/Rxx(0)
0.40
Vg = -1.3 V
0.3
2x10-7
B2/Rxx(0)2 (T2Ω-2)
B2/Rxx(0)2 (T2Ω-2)
0.4
1x10-7
0.2
0.1
2K
10 K
20 K
40 K
60 K
80 K
0.30
0.25
0.20
0.15
0.10
0.05
0.0
0.00
0.0
2.0x10-7
2
4.0x10-7
2
6.0x10-7
2
8.0x10-7
0.0
2.0x10-7
4.0x10-7
2
-7
-7
6.0x10
8.0x10
2
2 -2
1.0x10-6
B /Rxx(0) (T Ω )
-2
B /Rxx(0) (T Ω )
Figure S9 | The Kohler’s plots of the MR curves of sample Q6 at the gate voltage
of -0.5 V (a), -0.9 V (b), -1.3 V(c), 0 V (d), -2.2 V (e), respectively.
V. SdH oscillations analysis (sample Q2).
Quantum lifetime could be obtained by the Dingle plot (Fig. S10a). With
increasing carrier density, the quantum lifetime becomes smaller (Fig. 4e), suggesting
the enhancement of the scattering process while the Fermi level is lifted into the
conduction band. The cyclotron mobility μSdH consequently decreases from ~8000
cm2V-1s-1 to ~2000 cm2V-1s-1. At the same time, the quantum mobility μQ which is
affected by both large and small angle scattering, could be estimate from μQ~1/Bstart
(Bstart is the magnetic field where the first oscillation could be identified)1,5–7. The
Bstart here increases with increasing gate voltage (Fig. S10b-f), leading to the
decreasing of the μQ from about 3000 cm2V-1s-1 to 1500 cm2V-1s-1, which is
comparable to the results calculated from the SdH oscillations and the measured Hall
mobility (Fig. S10c). The amplitude of SdH oscillations decreases from ~15 to ~2 Ω,
9
indicating the declining of SdH oscillations.
b
0
0.2
0.3
0.5
0.7
0.9
1.2
Ln[△RBsinh(λ)]
3
2
15
0
Vg=0.3 V
4K
8K
15K
30K
60K
-10
1
0.20
10
Bstart
5
-5
0.16
-15
0.10
0.24
0.15
0.20
0.25
-1
0
1/B (T )
e
10
Vg=0.5 V
-5
6K
10K
20K
40K
80K
0.30
Bstart
5
6K
10K
20K
40K
-10
-15
0.35
0.15
0.20
4K
8K
15K
30K
60K
0.25
0.30
1/B (T-1)
1/B (T )
-1
d
c
15
10
△R (Ω)
Vg (V)
4
△R (Ω)
a
f
6
2
4
Bstart
0
Vg=0.7 V
-5
4K
8K
15K
30K
60K
-10
0.10
0.15
0.20
1/B (T-1)
6K
10K
20K
40K
80K
0.25
0.30
Bstart
Bstart
2
△R (Ω)
△R (Ω)
△R (Ω)
5
0
Vg=0.9 V
-2
4K
8K
15K
30K
60K
-4
-6
0.15
0.20
6K
10K
20K
40K
80K
0.25
1
0
Vg=1.2 V
4K
8K
15K
30K
60K
-1
-2
0.10
1/B (T-1)
0.15
6K
10K
20K
40K
80K
0.20
0.25
1/B (T-1)
Figure S10 | SdH oscillations and Dingle plot (sample Q2). a, Dingle plots of ln[△
Rbsin(λ)] versus 1/B under different gate voltage. Lifetimes are obtained from the
linear fit of the data. b-f, Temperature dependent SdH oscillations under the gate
voltage of 0.3 V (b), 0.5 V (c), 0.7 V (d), 0.9 V (e) and 1.2 V (f)
VI. Angular dependent transport measurements.
Angular dependent transport measurements were carried out to probe the nature
of SdH oscillations. The measurement configuration is shown in the inset of Fig. S11,
where the sample normal is tilted away from the magnetic field by an angle θ. Within
a small θ, the oscillations show aligned peaks and valleys, while in the large θ,
oscillations starts to reduce. We believe that the compression of Fermi sphere in the
reduced dimension of Cd3As2 causes such angular dependence of magnetoresistance.
10
60
θ
B
50
△R (Ω)
40
30
Vg=0.9 V
60°
45°
30°
15°
10°
5°
0°
20
10
0
-9
-8
-7
-6
-5
-4
Bcosθ (T)
-3
-2
Figure S11 | Angular dependence of SdH oscillations of sample Q1 at the gate
voltage of 0.9 V. The SdH oscillations are plotted as a function of Bcosθ. The inset
shows the measurement configuration.
VII.
Reproducibility of two-carrier transport from other Cd3As2
thin films.
Except the sample mentioned in the main text, several other thin films were also
measured with the ionic gating. All of them showed the gate-tunable SdH oscillations
and two carrier transport, proving a good reproducibility of our results (Fig. S12-17).
The related parameters obtained from SdH oscillations are summarized in Table SI.
11
a
b
0V
1500
Vg
-1.25V
-1.5V
-1.7V
-1.95V
-2.2V
-2.5V
1.2x104
104
8x103
0.5 V
Rxx (Ω)
Rxx (Ω)
1000
1V
1.5 V
6x103
4x103
2V
500
2.5 V
2.9 V
3.2 V
0
100
0
200
100
200
T (K)
T (K)
Figure S12 | Gate-tunable Rxx-T curves of sample Q2. The results are similar to the
main text results. a, Gate-induced insulator-metal transition was also observed under
positive gate voltage. b, With negative gate voltages the Rxx-T curves show
semiconducting-like feature. Also the curves cross over each other at about 80 K.
12
a
b
6000
Vg=0V
Vg=-1.25V
2000
4000
1000
Rxy (Ω)
Rxy (Ω)
2000
0
0
-2000
T (K)
-1000
1.9
-4000
-2000
10
-6000
-8
-6
-4
-2
0
2
4
6
8
-8
-6
-4
B (T)
c
0
2
4
6
8
20
B (T)
d
Vg=-1.5V
1000
-2
30
Vg=-1.95V
1500
40
60
1000
500
Rxy (Ω)
Rxy (Ω)
500
0
0
-500
-500
-1000
-1000
-1500
-8
-6
-4
-2
0
2
4
6
8
-8
B (T)
-6
-4
-2
0
2
4
6
8
B (T)
Figure S13 | Temperature-dependent hall resistance Rxy of ~50 nm-thick Cd3As2
thin film (sample Q2). a, The linear Rxy under zero gate voltage, indicative of
electron-dominated n-type conductivity. b, Rxy under -1.25 V gate voltage showing a
nonlinear behaviour originated from two-carrier transport owing to the gate-induced
holes. c, Rxy under -1.5 V gate voltage. The Cd3As2 channel undergoes a transition
from electron- to hole- dominated transport as evidenced by the change of slope at
B≥4T. d, Rxy under -1.95 V. The holes are dominant in Hall resistance.
13
a
c
-1.5V
-1.7V
-1.95V
6
σp/σn
5
4
3
2
1
10
20
30
μp (cm2V-1s-1)
d
b
40
50
60
70
80
T (K)
600
500
400
-1.5V
-1.7V
-1.95V
300
0
10
20
e
40
50
60
40
50
60
T (K)
8
np (x1012 cm-2)
30
-1.5V
-1.7V
-1.95V
7
6
5
4
3
0
10
20
30
T (K)
Figure S14 | Temperature- and gate-dependent carrier density and mobility
(sample Q2). a, Gate-dependent sheet carrier density. It implies the ambipolar
transport. The hole carrier density was extracted from the fits to the two-carrier
transport model. Electron carrier density was obtained from the Hall effect
measurements. b, Gate-dependent mobility of holes and electrons. The insets sketch
the positions of the Fermi level. The graduated background in a and b represents the
amount and type of carriers (blue for holes and red for electrons). c-e,
Temperature-dependent conductivity ratio (c), hole mobility (d) and hole density (e),
obtained from the fits to the two-carrier transport model. Dashed lines in c, as guides
to the eye, display the temperature trends of the conductivity ratio.
14
V1=gV
2
0
-2
0
d
20
Q3
Vg=0V
10
△R (Ω)
2
R (Ω)
R (Ω)
4
c
Q2
Vg=0.75V
4
Q2
Vg=0.5V
6
6
0
-2
T (K)
0
-4
-4
-6
0.20
-6
0.10
0.25
0.15
0.20
0.5V
Q2 T=2K
0.20
1/B (T-1)
0.25
Q3
0.9
Vg=0V
0.8
Vg=0.5V
0.7
0.6
0
5
10
15
0.15
20
25
0.20
0.25
1/B (T )
h
7.5
Ln[△R/R·Bsinh(λ)]
0.75V
0.10
-1
g
1.0
△σxx(T)/△σxx(0)
R (Ω)
1V
0.25
1/B (T )
f
1.25V
0.20
-1
Q3
Q2 0.5V
Q2 0.75V
Q3 0V
Q3 0.5V
0.20
7.0
6.5
Vg=0V
6.0
5.5
0.15
0.10
5.0
4.0
0.15
0.18
1/B (T-1)
T (K)
4
6
8
10
15
20
0.05
Vg=0.5V
4.5
2.5
R
e
0.15
0.15
1/B (T )
1/B (T-1)
5Ω
-20
0.10
0.25
-1
1/B (T-1)
0.15
2
xx
K2
K5.2
K4
K6
K8
K01
K51
K02
-2
-6
0.10
2
-10
-4
-8
0.10
Q3
Vg=0.5V
4
△R (Ω)
b
8
).u.a(
a
0.21
0
1
2
3
4
5
6
Landau Index n
8 6 4 2 0 2- 4- 6- 8Figure S15 | SdH oscillations of Cd3As2 thin films. a-b, Temperature-dependent
)T( dleiF citengaM
amplitude of the SdH oscillations at 0.5 and 0.75 V (sample Q2), respectively. c-d,
Temperature-dependent amplitude of SdH oscillations (sample Q3) at 0 and 0.5 V,
respectively. e, Gate-dependent amplitude of the SdH oscillations (Q2) at 2 K. f,
Normalized conductivity amplitude versus temperature for sample Q3 at gate voltage
of 0 and 0.5 V. g, Dingle plot at 2 K of sample Q3 at different gate voltage of 0 and
0.5 V. h, Landau level index n with respect to 1/B of sample Q2 and Q3 under
different gate voltage. Integer indices denote the △Rxx peak positions in 1/B and half
integer indices represent the △Rxx valley positions. The intercepts are close to 0.5.
15
3000
Vg=-1.25V
2000
Rxy (Ω)
b
2K
2.5K
4K
6K
8K
10K
1000
0
Vg=-1.5V
800
2K
10K
20K
30K
40K
60K
400
Rxy (Ω)
a
-1000
0
-400
-2000
-800
-3000
-10 -8
-6
-4
-2
0
2
4
6
8
10
-10 -8
Magnetic Field (T)
Vg=-1.7V
600
d
2K
10K
20K
30K
40K
60K
400
Rxy (Ω)
-4
-2
0
2
4
6
8
10
Magnetic Field (T)
200
600
Vg=-1.95V
2K
10K
20K
30K
40K
60K
400
Rxy (Ω)
c
-6
0
-200
200
0
-200
-400
-400
-600
-10 -8
-6
-4
-2
0
2
4
6
8
-600
10
Magnetic Field (T)
-10 -8
-6
-4
-2
0
2
4
6
8
10
Magnetic Field (T)
Figure S16 | Temperature-dependent Hall resistance Rxy of sample Q4.
Two-carrier transport was also observed in sample Q4. When scanning the gate
voltage to reach the negative range, the hole-dominated transport takes place, showing
a good reproducibility of ionic gating on different MBE-grown samples.
16
6
Q6
△Rxx (Ω)
4
2
0
Vg = 0 V
-2
3K
6K
10 K
20 K
40 K
-4
-6
0.10
0.15
0.20
0.25
2K
4K
8K
15 K
30 K
60 K
0.30
B (T)
Figure S17 | SdH oscillations of Cd3As2 thin films (sample Q6).
VIII.
Band evolution of Cd3As2 thin films
According to our calculation results, at a thickness of ~ 50 nm the bulk Dirac
cone is fully gapped, with bulk gap larger than 20 meV. This gap falls off with
increasing thickness, and is very close to zero for a thin film of thickness ~ 60 nm.
This variation in the bulk gap is in reasonable agreement with our experimental
results. Since Cd3As2 also has an inverted gap, apart from the bulk Dirac point, it also
exhibits surface Dirac crossings when confined in a quantum well geometry. These
surface cones are highlighted in red in Figure S18b and c. Note that in contrast to the
bulk cone, the surface crossing is already gapless for films as thin as ~12 nm. This
behavior is similar to the case of Na3Bi, the other putative three-dimensional Dirac
17
semimetal8.
Figure S18 | Band evolution of Cd3As2 thin films. (a) Brillouin zone for the
P42/nmc unit cell used for the first-principles-derived tight-binding computations.
Band structures for slabs with representative thicknesses (b) 8 nm and (c) 12 nm are
shown, with the bulk bands shaded in blue. The surface bands are highlighted in red.
(d) Variation of the bulk band gap, Ebulk, with increasing thickness of the slab.
Table SI| Estimated parameters from the SdH oscillations at T=2K
sample Vg(V)
FSdH(T)
kf(Å)
mcyc(me) vF(105 m/s) Ef(meV) t(10-13 s) l(nm) μSdH(cm2V-1s-1)
Q2
0.75
29.31
0.0298
0.046
7.5
148
1.57
118
6021
Q3
0
22.96
0.0264
0.030
10
176
0.86
87
4995
Q3
0.5
27.92
0.0291
0.035
9.7
186
1.08
105
5450
18
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19