Superconductivity in the honeycomb-lattice pnictide SrPtAs

Full text of DOI:10.1143/JPSJ.80.055002

Journal of the Physical Society of Japan 80 (2011) 055002
DOI: 10.1143/JPSJ.80.055002
SHORT NOTES
Superconductivity in the Honeycomb-Lattice
Pnictide SrPtAs
Yoshihiro NISHIKUBO1;2,
Kazutaka KUDO1 , and Minoru NOHARA
;2
ꢀ
1;2
1Department of Physics, Faculty of Science, Okayama University,
Okayama 700-8530, Japan
2
Transformative Research Project on Iron Pnictides (TRIP), Japan
Science and Technology Agency (JST), Chiyoda, Tokyo 102-0075, Japan
(Received January 26, 2011; accepted March 17, 2011;
published online May 10, 2011)
Fig. 1. (Color online) Crystal structures of (a) AlB2 (space group
P6=mmm) and (b) SrPtAs (space group P63=mmc).
KEYWORDS: pnictide superconductor, AlB2-type structure,
honeycomb lattice, SrPtAs
Transition-metal pnictides form a fascinating class of
superconductors. Their representatives are iron-based mate-
1
,2)
rials,
ments), AEFe As (AE = alkali earth elements), and AFeAs
which include REFeAsO (RE = rare earth ele-
2
2
(
A = alkali elements). The highest transition temperature
)
3
Tc to date has reached 56 K in Th-substituted GdFeAsO.
Pnictides without iron also exhibit superconductivity, though
Tc is markedly lower than that of the iron-based super-
4
)
conductors. For example, Tc ¼ 3 and 0.7 K in BaNi2P2
5
)
and BaNi As with a ThCr Si -type structure, respectively.
2
2
2
2
6)
T ¼ 5:2 K in SrPt As with a CaBe Ge -type structure.
c
2
2
2
2
These superconducting pnictides share a common crystal
structure with a square lattice of transition-metal elements.
A honeycomb lattice is also an attractive playground
7)
for superconductivity. MgB2 (Tc ¼ 39 K) with an AlB2-
8
,9)
type structure, CaAlSi (Tc ¼ 5:68{7:7 K)
with an AlB2
Fig. 2. Temperature dependence of magnetization divided by applied
field, M=H, of SrPtAs at 30 Oe under zero-field-cooling (ZFC) and field-
cooling (FC) conditions.
10,11)
derivative structure, and CaC6 (Tc ¼ 11:5 K)
with an
intercalated-graphite structure exhibit superconductivity
with a relatively high T owing to a strong electron–phonon
c
9
,12,13)
14,15)
16)
coupling,
and interlayer bands.
soft phonons,
multibands/multigaps,
17)
sealed in an evacuated quartz tube. The ampule was heated
ꢁ
ꢁ
In this paper, we report superconductivity in SrPtAs at 700 C for 3 h and then at 1000 C for 24 h. After furnace
with Tc ¼ 2:4 K. To our knowledge, this is the first super- cooling, the sample was ground, pelletized, wrapped with
ꢁ
conducting pnictide with a honeycomb lattice structure. Ta foil, and heated at 950 C for 2 h in an evacuated quartz
SrPtAs crystallizes in a hexagonal KZnAs-type structure tube. The products were confirmed to be a single phase of
1
8)
with the space group P6 =mmc (#194). This structure is SrPtAs by powder X-ray diffraction. Lattice parameters were
3
ꢀ
8)
ꢀ
derived from the binary AlB -type structure with the space estimated to be a ¼ 4:244 A and c ¼ 8:989 A, consistent
2
1
group P6=mmm (#191). The schematic views of AlB and with the previous report.
2
The magnetization M was
SrPtAs are shown in Fig. 1. In AlB2, boron atoms form measured from 1.7 to 5 K under a magnetic field of 30 Oe
honeycomb layers and aluminum atoms are intercalated with the Magnetic Property Measurement System (Quantum
between them. In SrPtAs, the aluminum sites are occupied Design). The electrical resistivity ꢀ was measured by the
by strontium atoms and the boron sites are occupied by standard DC four-terminal method in the temperature range
either platinum or arsenic atoms so that they alternate in the between 1.8 and 300 K under magnetic fields up to 1000 Oe
honeycomb layer as well as in the c-axis. Thus, the structure using the physical property measurement system (Quantum
can be viewed as an ordered variant of the AlB -type Design).
2
structure.
Figure 2 shows the temperature dependence of mag-
Polycrystalline samples of SrPtAs were synthesized by a netization divided by the applied field, M=H, of SrPtAs at
solid-state reaction. The PtAs2 precursor was first synthe- 30 Oe under zero-field-cooling and field-cooling conditions.
ꢁ
sized by heating Pt powder and As grains at 700 C in M exhibited a diamagnetic behavior below about 2.4 K,
an evacuated quartz tube. Then, Sr, Pt, and PtAs2 powders indicating the occurrence of superconductivity at Tc ¼ 2:4 K.
of stoichiometric amounts were mixed and ground. The The shielding and flux exclusion signals at 1.7 K correspond
resulting powder was placed in an alumina crucible and to 45 and 23% of perfect diamagnetism, respectively. The
data support the appearance of bulk superconductivity at
Tc ¼ 2:4 K in SrPtAs.
ꢀ
E-mail: kudo@science.okayama-u.ac.jp
0
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#2011 The Physical Society of Japan

J. Phys. Soc. Jpn. 80 (2011) 055002
SHORT NOTES
Y. NISHIKUBO et al.
edge, this is the first pnictide superconductor with a
honeycomb lattice. Our result shed light on a novel route
to develop pnictide superconductors.
Acknowledgement Part of this work was performed at the Advanced
Science Research Center, Okayama University.
1)
2)
3)
4)
5)
Y. Kamihara, T. Watanabe, M. Hirano, and H. Hosono: J. Am. Chem.
Soc. 130 (2008) 3296.
For a review see K. Ishida, Y. Nakai, and H. Hosono: J. Phys. Soc. Jpn.
7
8 (2009) 062001.
C. Wang, L. Li, S. Chi, Z. Zhu, Z. Ren, Y. Li, Y. Wang, X. Lin, Y. Luo,
S. Jiang, X. Xu, G. Cao, and Z. Xu: Europhys. Lett. 83 (2008) 67006.
T. Mine, H. Yanagi, T. Kamiya, Y. Kamihara, M. Hirano, and H.
Hosono: Solid State Commun. 147 (2008) 111.
F. Ronning, N. Kurita, E. D. Bauer, B. L. Scott, T. Park, T. Klimczuk,
R. Movshovich, and J. D. Thompson: J. Phys.: Condens. Matter 20
(
2008) 342203.
Fig. 3. (Color online) Temperature dependence of electrical resistivity ꢀ
for SrPtAs. The upper inset shows ꢀ in magnetic fields. The lower inset
shows the temperature dependence of the upper critical field Hc2. The dotted
line indicates a linear extrapolation of the data from 1.85 to 2.08 K.
6) K. Kudo, Y. Nishikubo, and M. Nohara: J. Phys. Soc. Jpn. 79 (2010)
123710.
7) J. Nagamatsu, N. Nakagawa, T. Muranaka, Y. Zenitani, and J.
Akimitsu: Nature 410 (2001) 63.
8
)
M. Imai, K. Nishida, T. Kimura, and H. Abe: Appl. Phys. Lett. 80
2002) 1019.
S. Kuroiwa, H. Sagayama, T. Kakiuchi, H. Sawa, Y. Noda, and J.
(
9
)
Akimitsu: Phys. Rev. B 74 (2006) 014517.
0) T. E. Weller, M. Ellerby, S. S. Saxena, R. P. Smith, and N. T. Skipper:
Nat. Phys. 1 (2005) 39.
Figure 3 shows the temperature dependence of ꢀ for
SrPtAs. ꢀ exhibited a metallic behavior and clearly showed a
superconducting transition at low temperatures. The upper
inset of Fig. 3 shows the resistive transition in detail. The
onset temperature determined from the 10% rule was 2.45 K,
and the 10–90% transition width was about 0.06 K. The
temperature where ꢀ points to zero was 2.37 K.
1
1
1) N. Emery, C. H e´ rold, M. d’Atsuto, V. Garcia, Ch. Bellin, J. F.
Mar eˆ ch e´ , P. Lagrange, and G. Loupias: Phys. Rev. Lett. 95 (2005)
0
87003.
1
1
2) Ch. W a¨ lti, E. Felder, C. Degen, G. Wigger, R. Monnier, B. Delley, and
H. R. Ott: Phys. Rev. B 64 (2001) 172515.
3) S. Kuroiwa, T. Takasaki, T. Ekino, and J. Akimitsu: Phys. Rev. B 76
As shown in the upper inset of Fig. 3, Tc gradually
decreased with increasing external magnetic field. The
temperature dependence of the upper critical field Hc2 was
determined from the midpoint of the resistive transition,
(
2007) 104508.
14) A. Q. R. Baron, H. Uchiyama, Y. Tanaka, S. Tsutsui, D. Ishikawa, S.
Lee, R. Heid, K.-P. Bohnen, S. Tajima, and T. Ishikawa: Phys. Rev.
Lett. 92 (2004) 197004.
1
5) S. Kuroiwa, A. Q. R. Baron, T. Muranaka, R. Heid, K.-P. Bohnen, and
J. Akimitsu: Phys. Rev. B 77 (2008) 140503(R).
as shown in the lower inset of Fig. 3. H ðTÞ exhibited an
c2
upward curvature with a visible change in the slope dH =dT
c2
16) S. Souma, Y. Machida, T. Sato, T. Takahashi, H. Matsui, S.-C. Wang,
H. Ding, A. Kaminski, J. C. Campuzano, S. Sasaki, and K. Kadowaki:
Nature 423 (2003) 65.
near T . Thus, we tentatively estimated H ð0Þ to be 2200 Oe
c
c2
from a linear extrapolation of the data at a lower tempera-
ture part between 1.85 and 2.08 K. The Ginzburg–Landau
1
7) H. Okazaki, R. Yoshida, K. Iwai, K. Noami, T. Muro, T. Nakamura, T.
Wakita, Y. Muraoka, M. Hirai, F. Tomioka, Y. Takano, A. Takenaka,
M. Toyoda, T. Oguchi, and T. Yokoya: Phys. Rev. B 80 (2009) 035420.
8) G. Wenski and A. Mewis: Z. Anorg. Allg. Chem. 535 (1986) 110.
ꢀ
coherence length ꢁ was obtained as 387 A from ꢁ ¼ ½ꢁ0=
0
0
1=2
2
ꢂHc2ð0Þꢂ , where ꢁ0 is the magnetic flux quantum. Here,
1
it is worth noting that the upward curvature of Hc2ðTÞ
suggests a multiband/multigap superconductivity in the
present compound. A similar behavior has been reported in
19) A. Gurevich: Physica C 456 (2007) 160.
2
2
0) A. Gurevich: Phys. Rev. B 67 (2003) 184515.
1) F. Hunte, J. Jaroszynski, A. Gurevich, D. C. Larbalestier, R. Jin, A. S.
Sefat, M. A. McGuire, B. C. Sales, D. K. Christen, and D. Mandrus:
Nature 453 (2008) 903.
1
9,20)
21)
22)
MgB2,
LaFeAsO0:89F0:11
,
and Ba(Fe Co ) As .
x 2 2
1ꢃx
In summary, we observed superconductivity at Tc ¼ 2:4 K
2
2) N. Ni, M. E. Tillman, J.-Q. Yan, A. Kracher, S. T. Hannahs, S. L.
Bud’ko, and P. C. Canfield: Phys. Rev. B 78 (2008) 214515.
in the honeycomb-lattice pnictide SrPtAs. To our knowl-
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#2011 The Physical Society of Japan