BiS2 - based superconductivity in F-substituted NdOBiS2

Article (PDF Available) · July 2012with31 Reads
Source: arXiv
Abstract
We have successfully synthesized a new BiS2-based superconductor NdOBiS2 with F-doping. This compound is composed of superconducting BiS2 layers and blocking NdO layers, which indicates that the BiS2 layer is the one of the common superconducting layers like the CuO2 layer of cuprates or Fe-As layer of Fe-based superconductors. We can obtain NdO1-xFxBiS2 with bulk superconductivity by a solid-state reaction under ambient pressure. Therefore, NdO1-xFxBiS2 should be the suitable material to elucidate the mechanism of superconductivity in the BiS2-layer.
1
BiS
2
- based superconductivity in F-substituted NdOBiS
2
Satoshi Demura,
1,2
Yoshikazu Mizuguchi,
1,3
Keita Deguchi,
1,2
Hiroyuki Okazaki,
1
Hiroshi Hara,
1,2
Tohru Watanabe,
1,2
Saleem James Denholme,
1
Masaya Fujioka,
1
Toshinori Ozaki,
1
Hiroshi Fujihisa,
4
Yoshito Gotoh,
4
Osuke Miura,
3
Takahide Yamaguchi,
1
Hiroyuki Takeya,
1
and Yoshihiko Takano
1,2
E-mail : Demura.Satoshi@nims.go.jp
1
National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
2
University of Tsukuba, Graduate School of Pure and Applied Sciences, Tsukuba, Ibaraki
305-8577, Japan
3
Tokyo Metropolitan University, Graduate School of Science and Engineering, Hachioji,
Tokyo 192-0397, Japan
4
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5,
1-1-1, Higashi, Tsukuba 305-8565, Japan.
Abstract
We have successfully synthesized a new BiS
2
-based superconductor NdOBiS
2
with
F-doping. This compound is composed of superconducting BiS
2
layers and blocking NdO
layers, which indicates that the BiS
2
layer is the one of the common superconducting layers
like the CuO
2
layer of cuprates or Fe-As layer of Fe-based superconductors. We can obtain
2
NdO
1-x
F
x
BiS
2
with bulk superconductivity by a solid-state reaction under ambient pressure.
Therefore, NdO
1-x
F
x
BiS
2
should be the suitable material to elucidate the mechanism of
superconductivity in the BiS
2
-layer.
3
Quite recently, Y. Mizuguchi et al. reported superconductivity in the novel BiS
2
-based
superconductor Bi
4
O
4
S
3
with a superconducting transition temperature (T
c
) of 8.6 K [1]. This
material has a layered structure composed of superconducting BiS
2
layers and blocking layers
of Bi
4
O
4
(SO
4
)
1-x
, where x indicates the defects of SO
4
2-
ions at the interlayer sites. The
stacking structure of the superconducting and blocking layer is analogous to those of high-T
c
cuprates [2-5] and Fe-based superconductors [6-14]. In both systems, their T
c
can be enhanced
by changing the blocking layers. In order to enhance the T
c
of the BiS
2
-based superconductor,
the investigation of exchanging the blocking layer will be of great interest.
Soon after the discovery of Bi
4
O
4
S
3
, a new BiS
2
-based superconductor LaO
1-x
F
x
BiS
2
was
reported [15]. This compound consists of the same superconducting layer but with different
blocking layers compared to that of Bi
4
O
4
S
3
. Furthermore, the superconductivity shows a
relatively high T
c
of 10.6 K. This fact suggests that the BiS
2
layer is the common
superconducting layer, and the blocking layer contributes to the enhancement of the T
c
in this
system. LaO
1-x
F
x
BiS
2
shows a small superconducting volume fraction for ambient pressure
but achieves bulk superconductivity under high pressure. This result suggests that high
pressure would promote F substitution. Therefore, chemical pressure for the exchange of La
by Nd possibly induces the promotion of F substitution. Here, we report that a new
BiS
2
-based superconductor NdO
1-x
F
x
BiS
2
(x = 0.1 - 0.7) can be obtained by a solid-state
reaction under ambient pressure.
4
The polycrystalline samples of NdO
1-x
F
x
BiS
2
(x = 0.1 - 0.7) were prepared by a
solid-state reaction. Mixtures of Bi grains, Bi
2
S
3
grains, Nd
2
O
3
powders, Nd
2
S
3
powders, and
NdF
3
powders with nominal compositions of NdO
1-x
F
x
BiS
2
(x = 0.1 - 0.7) were ground,
pelletized, and sealed into an evacuated quartz tube. The tube was heated at 800 °C for 10 h.
The obtained samples were characterized by X-ray diffraction with Cu-K
α
θ
-2
θ
method. The temperature dependence of magnetization was measured by a
superconducting quantum interface device (SQUID) magnetometer with an applied field of 1
Oe. The resistivity measurements were performed using the four-terminal method from 300 to
2 K. In order to investigate an upper critical field of NdO
1-x
F
x
BiS
2
, the temperature
dependence of resistivity between 10 and 2 K was measured under a magnetic field of up to 7
T.
Figure 1(a) shows the X-ray diffraction profile for the powdered samples of
NdO
1-x
F
x
BiS
2
(x = 0.1 - 0.7). With the exception of a few minor peaks relating to impurity
phases, all of the peaks can be characterized to space group P4/nmm. The nominal x
dependence of the lattice constants a and c is summarized in Fig. 1(b) and (c). These lattice
constants were estimated from 2
θ
values and Miller indices. The a lattice constant exhibits
little change with increasing x while the c lattice constant dramatically decreases. The
decrease of the lattice parameter c indicates that F substitutes O since the ionic radius of F is
smaller than that of O.
5
Figure 2(a) shows the temperature dependence of magnetic susceptibility for
NdO
1-x
F
x
BiS
2
(x = 0.1 - 0.7). A superconducting transition is observed for all samples. These
samples with x = 0.1 - 0.6 exhibit a high shielding volume fraction exceeding 90 % (2 K,
ZFC), indicating the appearance of bulk superconductivity in those samples. The x
dependence of T
c
is plotted in Fig. 2(b). The T
c
varies like a bell curve with increasing x. The
NdO
0.7
F
0.3
BiS
2
sample exhibits the optimal T
c
of all samples.
The temperature dependence of the resistivity for NdO
0.7
F
0.3
BiS
2
is shown in Fig. 3.
Resistivity slightly decreases between 300 and 130 K. Below 130 K, resistivity gradually
increases and the superconducting transition appears around 6 K. This behavior, where the
resistivity increases with decreasing temperature is also observed in LaO
1-x
F
x
BiS
2
. The onset
and zero-resistivity temperatures are estimated to be T
c
onset
= 5.6 K and T
c
zero
= 5.2 K,
respectively. Figure 4(a) shows the temperature dependence of the resistivity from 10 to 2 K
under a magnetic field. The T
c
of NdO
0.7
F
0.3
BiS
2
decreases with increasing magnetic field.
The upper critical field (B
c2
) and the irreversibility field (B
irr
) are plotted in Fig. 4(b). The
B
c2
(0) was estimated to be 5.2 T with the data points at 0.4 ~ 2.0 T using the WHH theory,
which gives B
c2
(0) = -0.69T
c
(d B
c2
/dT)|
Tc
[16].
In conclusion, the BiS
2
-based superconductor NdO
1-x
F
x
BiS
2
(x = 0.1 - 0.7) has been
successfully synthesized by a solid-state reaction method. Chemical pressure promotes the F
substitution, which originated from the exchange of La by Nd. As a result, NdO
1-x
F
x
BiS
2
with
6
bulk superconductivity can be obtained under ambient pressure. These results demonstrate
that the BiS
2
layer is the common superconducting layer. Thus, if we synthesize materials with
the stacking structure consisting of the BiS
2
layer and other blocking layers, new
superconductors with the BiS
2
-layer would be discovered.
Acknowledgements
This work was partly supported by a Grant-in-Aid for Scientific Research from the
Ministry of Education, Culture, Sports, Science and Technology (KAKENHI).
7
References
1
Y. Mizuguchi et al., arXiv:1207.3145.
2
J. G. Bednorz and K. Müller, Z. Physik B Condensed Matter 64, 189-193 (1986).
3
M. K. Wu, et al., Phys. Rev. Lett. 58, 908–910 (1987).
4
H. Maeda et al., Jpn. J. Appl. Phys. 27, L209-L210 (1988).
5
A.Schilling et al., Nature 363, 56 - 58 (1993).
6
Y. Kamihara et al., J. Am. Chem. Soc. 130, 3296–3297 (2008).
7
X. H.Chen et al., Nature 453, 761-762 (2008).
8
Z. A. Ren et al., Chinese Phys. Lett. 25, 2215 (2008).
9
M. Rotter, M. Tegel and D. Johrendt, Phys. Rev. Lett. 101, 107006(1-4) (2008).
10
X. C. Wang et al., Solid State Commun. 148, 538–540 (2008).
11
F. C. Hsu et al., 105, 14262–14264 (2008).
12
K. W. Yeh et al., EPL 84, 37002(p1-4) (2008).
13
Y. Mizuguchi et al. Appl. Phys. Lett. 94, 012503(1-3) (2009).
14
J. Guo et al., Phys. Rev. B 82, 180520(1-4) (2010).
15
Y. Mizuguchi et al., arXiv:1207.3567
16
N. R. Werthamer, E. Helfand, and P. C. Hohemberg, Phys. Rev. 147, 295-302 (1966).
8
Figure caption
Fig. 1
(a) X-ray diffraction patterns of NdO
1-x
F
x
BiS
2
(x = 0.1 - 0.7). Filled circles indicate the peaks
of the impurity phases. (b) and (c) show the nominal x dependence of the lattice constants a
and c , respectively.
Fig. 2
(a) The temperature dependence of the magnetic susceptibility for NdO
1-x
F
x
BiS
2
(x = 0.1 -
0.7).
(b) The F concentration dependence of the superconducting transition temperature for
NdO
1-x
F
x
BiS
2
(x = 0.1 - 0.7).
Fig. 3
The temperature dependence of resistivity for NdO
0.7
F
0.3
BiS
2
between 300 and 2 K.
Fig. 4
(a) The temperature dependence of the resistivity from 10 to 2 K under magnetic fields
(b) Magnetic field temperature phase diagram for NdO
0.7
F
0.3
BiS
2
. The dashed lines are liner
fits to the data.
9
Fig. 1(a). S. Demura
5 15 25 35 45 55 65
Intensity (arb. unit)
2
θ
(degree)
x = 0.1
002
003
101
102
004
110
104
114
212
106
117
206
109
005
200
122
220
x = 0.2
x = 0.3
x = 0.4
x = 0.5
(a)
NdO
1-x
F
x
BiS
2
105
x = 0.6
x = 0.7
10
Fig. 1(b). S. Demura
3.96
3.98
4
4.02
4.04
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
NdO
1-x
F
x
BiS
2
a (Å)
(b)
nominal x
11
Fig. 1(c). S. Demura
13.35
13.4
13.45
13.5
13.55
13.6
13.65
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
NdO
1-x
F
x
BiS
2
(c)
c (Å)
nominal x
12
Fig. 2(a) S. Demura
-0.2
-0.15
-0.1
-0.05
0
0 2 4 6 8 10
Temperature (K)
Magnetic susceptibility (emu / cm
3
)
x = 0.7
x = 0.6
x = 0.5
× x = 0.4
x = 0.3
x = 0.2
x = 0.1
H = 1 Oe
NdO
1-x
F
x
BiS
2
(a)
13
Fig. 2(b) S.Demura
5
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
nominal x
T
c
(K)
NdO
1-x
F
x
BiS
2
(b)
14
Fig. 3 S. Demura
0
1
2
3
4
5
6
7
8
0 50 100 150 200 250 300
Resistivity (mcm)
Temperature (K)
NdO
0.7
F
0.3
BiS
2
T
c
5.6 K
15
Fig. 4 S. Demura
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6 8 10
Resistivity (mcm)
Temperature (K)
NdO
0.7
F
0.3
BiS
2
0 T
0.4 T
0.8 T
1.2 T
1.6 T
2.0 T
2.5 T
3.0 T
4.0 T
(a)
16
Fig. 4(b) S. Demura
0
2
4
6
8
10
0 1 2 3 4 5 6 7
B
c2
(T)
Temperature (K)
(b)
NdO
0.7
F
0.3
BiS
2
B
c2
B
irr
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