Table Of ContentUnusual T variation with hole concentration in Bi Sr La CuO
c 2 2−x x 6+δ
Mu-Yong Choi and J. S. Kim
Department of Physics and Institute of Basic Sciences
Sungkyunkwan University, Suwon 440-746, Korea
0
0 We have investigated the Tc variation with the hole concentration p in the La-doped Bi 2201
0
system,Bi2Sr2−xLaxCuO6+δ. ItisfoundthattheBi2201systemdoesnotfollowthesystematicsin
2
Tc and p observed in other high-Tc cupratesuperconductors (HTSC’s). The Tc vs p characteristics
n are quitesimilar to what observed in Zn-doped HTSC’s. An exceptionally large residual resistivity
a component in the inplane resistivity indicates that strong potential scatterers of charge carriers
J
reside in CuO2 planes and are responsible for the unusual Tc variation with p, as in the Zn-doped
4 systems. However, contrary to the Zn-doped HTSC’s, the strong scatter in the Bi 2201 system is
2 possibly a vacancy in the Cu site.
] PACS numbers: 74.72.Hs, 74.62.Dh, 74.62.Bf, 74.25.Dw
n
o
c
- Many high-Tc cuprate superconductors (HTSC’s) dis- andcarbonateswas adoptedin preparingpolycrystalline
pr play an approximately parabolic dependence of Tc upon samples of Bi2Sr2−xLaxCuO6+δ. The x-ray diffraction
u the hole concentration p with the maximum Tc at p ≈ (XRD) analysis shows all the samples to be single phase
s 0.16. [1,2] (p is defined as the hole concentration per to the threshold of detection. The oxygen content in
t. Cu atom in CuO2 planes. ) This behavior was ob- the sample of x = 0.1 could be varied by annealing the
a
m served first in La2−xSrxCuO4. [1] Then other HTSC’s samesample invacuumfor6 hatdifferenttemperatures
such as YBa2Cu3O7−y [2], Bi2Sr2CaCu2O8+δ [3], and (400oC, 500oC, and then 600oC). S was measured by
d- TlSr2CaCu2O7+δ [1] were also found to show approxi- employing the dc method described in Ref. 10. The
mately the same relation between T and p which scales resistivityρwasmeasuredthroughtheconventionallow-
n c
o only with the maximum Tc, Tc, max. Though not stud- frequency ac four-probe method.
c ied for the full range of p, several other HTSC’s are also Figure 1 showsthe temperature dependences of S and
[ knowntohaveTc, max atp≈0.14∼0.15.[4,5]Therefore ρ of Bi2Sr2−xLaxCuO6+δ (BSLCO) with 0.1 ≤ x ≤ 0.8.
1 one might expect that there possibly exists a universal The temperature and doping dependences of S in Fig.
v relation between Tc and p which all HTSC’s satisfy. [2] 1(a) are typical of HTSC’s. S(290 K) increases with
9 Existence of a universal parabolic relation between T doping x from -15.5 µV/K to 60 µV/K. Correspond-
c
3 and p for all HTSC’s, despite the different combinations ing p determined from the relations between S(290 K)
3
of constituent atoms, the presence of various charge- and p in Ref. 3 varies from 0.286 to 0.073 with doping.
1
carrier reservoir layers, and a variety of inter-plane cou- The ρ measurements in Fig. 1(b) displays that the T of
0 c
0 pling strengths, cannot be common but is believed to BSLCO has its maximum at x ∼ 0.5 or p ∼ 0.22. The
0 be related to a noble nature of high-temperature su- appearance of Tc, max at x ∼ 0.5 agrees with the previ-
/ perconductivity. It is therefore not strange that the ous measurements. [11] T /T against p is plotted
t c c, max
a recent observations in Zn-doped HTSC’s of departure in Figure 2. The T (= 21.5 K) of x = 0.5 is used as
c
m from the universal relation have drawn particular inter- T for solid circles. The dotted curve is of the ‘uni-
c, max
- est. [6–9] Much attention has focused on the function of versal’ relation, Tc/Tc, max = 1- 82.6 (p - 0.16)2, in Ref.
d
Zn. Within a HTSC, Zn substitutes for Cu in the CuO2 1. The relationhas not yet been fully tested in the over-
n
plane and behaves as a nonmagnetic impurity without doped region of p > 0.25. Figure 2 clearly displays that
o
altering the carrier concentration. In this report, we BSLCO does not follow the systematics. Superconduc-
c
: showthatasimilarnon-universalTc-prelationholdsalso tivity inthe underdopedregionis deeply suppressedand
v
i for the La-doped Bi 2201 system, Bi2Sr2−xLaxCuO6+δ, the Tc, max appears at an overdoped hole concentration
X which contains strong disordersin CuO2 planes differing p ∼ 0.22 rather than 0.16 . Besides, the Tc, max of ∼
r from impurities. 21.5 K is also unusually low, which is only 14 the Tc of
a We have obtained the hole concentration p of the Tl2Ba2CuO6+δ, isostuctural of BSLCO. [12] Taking the
samples from the thermopower (S) measurements. The maximum Tc of Tl2Ba2CuO6+δ as Tc, max, BSLCO has
room-temperature thermopower S(290 K) of HTSC’s much lower Tc/Tc, max’s, as represented by open circles
was found to be a universal function of p over the in Figure 2.
whole range of doping, [1,3] which has since been Unusual T variation with p is exposed more dramat-
c
used widely to determine the p of HTSC’s. The ically in the vacuum-annealed sample of x = 0.1 which
superconducting-transition temperature T was deter- superconducts at T ≤ 10 K without vacuum-annealed.
c
mined at half the normal-state resistivity. The con- Vacuum annealing reduces the content of oxygen atoms
ventional solid-state reaction of stoichiometric oxcides interstitial between Bi-O planes and consequently p in
1
CuO2 planes.[13–15]Fig 3(a)showsthat successivevac- planes and a large residual resistivity at an underdoped
uum annealings at 400oC, 500oC, and then 600oC en- hole concentration are closely related to the strong sup-
hance S of Bi2Sr1.9La0.1CuO6+δ from -15.5 µV/K to - pression of high-temperature superconductivity and the
9.3µV/K.Thecorrespondingvariationofpisfrom0.286 more rapid T depression in the underdoped region.
c
to 0.240. We expect from the observed T -p relation of
c
BSLCOinFigure2thatT ofthesampleofx=0.1rises We wish to thank Y. Yun and I. Baek for their assis-
c
with annealing from 10 K to 20 K. The ρ measurements tances with the XRD analysis.
inFigure3(b),however,showthatthesuperconductivity
observedintheas-grownsampledisappearswithanneal-
ing in vacuum. We observed similar behaviors also in
Bi2Sr2CuO6+δ which had been prepared from the nomi-
nalcompositionofBi:Sr:Cu=2:2:1.5. Thesemiconduct-
ing as-grown sample of Bi2Sr2CuO6+δ having p = 0.282
exhibited a superconducting-transition onset at 11.5 K [1] M. R.Presland et al., Physica C 176, 95 (1991).
when vacuum-annealed at 400oC. And yet subsequent [2] J. L. Tallon, C. Bernhard, H. Shaked, R. L. Hitterman,
vacuum annealings at 500oC and 600oC put the sam- and J. D. Jorgensen, Phys.Rev. B 51, 12 911 (1995).
ple back in the semiconducting states. The p’s of the [3] S. D. Obertelli, J. R. Cooper, and J. L. Tallon, Phys.
Bi2Sr2CuO6+δ sample annealed at 400oC, 500oC, and Rev. B 46, 14 928 (1992).
600oC were 0.256, 0.250 and 0.216 respectively, all of [4] M.A.G.Aranda,D.C.Sinclair,andJ.P.Attfield,Phys-
ica C 221, 304 (1994).
which are located in the superconducting region of Fig-
[5] D. C. Sinclair el al., Physica C 176, 95 (1991).
ure 2.
[6] T. Kluge, Y. Koike, A. Fujiwara, M. Kato, T. Noji, and
The T vs p characteristics of as-grownsamples repre-
c Y. Saito, Phys.Rev.B 52, R727 (1995).
sented by the open circles in Figure 2 resemble those of
[7] J.L.Tallon, C.Bernhard,G.V.M.Williams, andJ.W.
Zn-dopedHTSC’sinRef. 6and7. Ithasbeensuggested Loram, Phys. Rev.Lett. 79, 5294 (1997).
that the primary effect of Zn impurities is to produce
[8] Y.Fukuzumi,K.Mizuhashi,K.Takenaka,andS.Uchida,
a large residual resistivity as a nonmagnetic potential Phys. Rev.Lett. 76, 684 (1996).
scatterer in the unitary limit and that the more rapid
[9] C. Bernhard, J. L. Tallon, C. Bucci, D. DeRenz, G.
depression of Tc in the underdoped region is related to Guidi, G. V. M. Williams, and Ch. Niedemayer, Phys.
the large residual resistivity reaching the universal two- Rev. Lett.77, 2304 (1996).
dimensionalresistanceh/4e2≈6.5kΩ/2perCuO2plane [10] W.N.Kang,K.C.Cho,Y.M.Kim,andMu-YongChoi,
at the edge of the underdoped superconducting region. Phys. Rev.B 39, 2763 (1989).
[8] Unlike most HTSC’s, the Bi 2201 superconductor is [11] A.Maeda,M.Hase,I.Tsukada,K.Noda,S.Takebayashi,
found to have an exceptionally large residual resistivity. and K.Uchinokura, Phys.Rev.B 41, 6418 (1990).
[16,17] The corresponding two-dimensional residual re- [12] Y. Shimakawa, Y. Kubo, T. Manako, H. Igarashi, F.
sistance per CuO2 plane ranges from 0.3 kΩ/2 at an Izumi, and H.Asano, Phys. Rev.B 42, 10 165 (1990).
overdoped hole concentration to 10 kΩ/2 at an under- [13] M.Runde,J.L.Routbort,J.N.Mundy,S.J.Rothman,
doped concentration with 50 % uncertainties. [18] The C. L. Wiley, and X.Xu. Phys.Rev.B 46, 3142 (1992).
large residual resistivity indicates that BSLCO contains [14] T. Yasuda, S. Takano, and L. Rinderer, Physica C 208,
strong scatterers of charge carriers in the planes. The 385 (1993).
[15] Y. Shimakawa, Y. Kubo, T. Manako, and H. Igarashi,
strong scatterer in BSLCO is, however, not an impurity
Phys. Rev.B 40, 11 400 (1989).
but most likely a vacancyin the Cu site, since any ofBi,
[16] Yoichi Ando, G. S. Boebinger, A. Passner, N. L. Wang,
Sr, and La can hardly substitute for Cu and disordersin
C. Geibel, and F. Steglich, Phys. Rev. Lett. 77, 2065
the noncopper sites have little effect on superconducting
(1996).
properties but changing the hole concentration. Never-
[17] S.Martin,A.T.Fiory,R.M.Fleming.L.F.Shneemeyer,
theless, a vacancy in the CuO2 plane is expected to act and J. V. Waszczak, Phys. Rev.B 41, 846 (1990).
asanonmagneticpotentialscatterer,justliketheZnim-
[18] Holeconcentrations ofthesamples inRef.16and17 are
purity inthe planes. Vacuum annealingmaycauseextra
estimated from the inplane resistivity at room tempera-
vacanciesinCuO2 planesaswellasexpellingintersititial ture,ρab(300K),andthetemperaturedependenceofρab.
oxygenatoms. Thusthesamearguementintermsofdis- A ρab(300 K) ≈ 5 mΩcm and a semiconductor-like tem-
order in the CuO2 plane can be adopted for an explana- perature dependence at low temperatures of ρab usually
tion of the deeper suppression of Tc in vacuum-annealed appear in a sample with an underdoped hole concentra-
samples. tion.
Although the above discussion does not provide a full
accountfortheoriginofthe nonuniversalT vspcharac-
c
teristics,itmaybeconcludedthatsimilaritybetweenthe
Bi 2201 HTSC with disorders differing from impurities
andotherHTSC’swithZnimpuritiesseemtostrengthen
the arguement that a strong potential scattering in the
2
FIG.2. Tc of Bi2Sr2−xLaxCuO6+δ, normalized to Tc, max,
plotted as a function of the hole concentration p determined
from the S data in Figure 1 and the S-p relations in Ref. 1.
20 0.9 Tc, max = 21.5 K for closed circles and 85 K for open circles.
(a) The error bars show the upper limit of Tc for the sample of
x = 0.8 with p = 0.098. The dotted curve is a plot of the
10 ‘universal’ relation in Ref. 1.
0.7
)
K
V/ 0
mS (
0.5
-10 0
0.3
(a)
0.1
(b)
)
K
1 V / -10 600 oC
0.9
) mS ( 450000 ooCC
m
c 0.8 as grown
W ( 0.1 0.7
r 0.5 -20
00..13 1
(b)
0.01
0 100 200 300
T (K) 600 oC
)
cm 0.1 450000 ooCC
FIG.1. (a)ThethermopowerS and(b)theresistivityρof W (
r
Bi2Sr2−xLaxCuO6+δ as functions of temperature. The num-
as grown
bersnext tothecurvesdenotetheLa contentx in themate-
rials.
0.01
0 100 200 300
T (K)
FIG. 3. (a) S and
1.2 (b) ρ of vacuum-annealed Bi2Sr1.9La0.1CuO6+δ as functions
of temperature. The numbers next to the curves denote the
1.0 annealing temperatures.
0.8
x
a
m
Tc, 0.6
/c
T
0.4
0.2
0.0
0.0 0.1 0.2 0.3
p
3
