E L S E V I E R Physica B !99&200 (1994) 288-290

PHYSICA[

Hall effect studies of the mixed and normal states of Y _xPr Ba2Cu307-a single crystals (0 < x < 1)

C.C. Almasan a'*, S.H. Han a, K. Yoshiara a't, M. Buchgeister a, B.W. Le& '2, L.M. Paulius a'3, D.A. GajewskP, M.B. Maple ''b

"Department of Physics and h~stitute.lbr Pure and Applied Physical Sciences, Universi O' of Cal(lbrnia, San Diego, La Jolla, CA 92093, USA

b Center,Ibr Materials Science, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

A b s t r a c t

Hall effect measurements on single-crystal specimens of Y~-x Pr,, Ba2Cu307-5 (0 < x _< II reveal a "negative Hall anomaly" below T¢, in the superconducting state. The depth a of the negative Hall signal scales with T/T, and the maximum value of A decreases linearly with x and vanishes at x ~ 0.24. These results show that the sign anomaly is not consistent with models that invoke pinning to explain this effect, and suggest that the negative anomaly could have an intrinsic origin. Hall effect measurements in the normal state show that the cotangent of the Hall angle can be described by cot On = A T 2 + B with both A and B increasing linearly with decreasing T,, in agreement with recent reports on Y~ _., Pr., Ba2Cu3OT_ fi thin films.

In this paper, we present Hall effect measurements performed in both the mixed and normal states, as a function of Pr concentration x, on Y t _., Pr, Ba2Cu307 - ~t single crystals. Our principal findings are (1) the depth d of the "'negative Hall anomaly" which occurs in this system for low x values scales with the reduced temper- ature T/Tc, and 12) the maximum values of d decreases linearly with x and vanishes at x ~ 0.24. These res,lts show that the sign anomaly is not consistent with models that invoke pinning to explain this effect, and suggest

* Corresponding author. Permanent address: Material and Electronic Devices i.abora-

tory, Mitsubishi Electric Corp., Sagamihara, Kanagawa, Japan. : Present address: Department of Physics, Hankuk University of Foreign Studies, Yong In Gun, Kyungi Do, Korea 449-791. 3 Present address: Department of Physics, Western Michigan University, Kalamazoo, MI 49008-3899, USA.

that the negative anomaly has an intrinsic origin and is not determined by extrinsic factors such as, for example, inhomogeneities in oxygen content. A fit of the cotangent of the Hall angle cot O~t(T) in the normal state with a T 2 dependence shows that both the slope and the intercept increase lioearly with decreasing To. A more detailed account of this work can be found in Ref. [1].

Measurements of the longitudinal resistivity p.,.~ and Hall resistivity p.,., as a function of temperature T ( 1 0 K <_ T < 270K) and magnetic field H up to 8 T were carried out on eight high-quality single crystals of Yt-.~Pr~Ba2Cu3OT_,~ {0 < x < I) grown by a method described elsewhere [2]. A five-probe contact arrange- ment was used. The Hall voltage V.~r was obtained from the antisymmetric part of the transverse voltage (meas- ured while sweeping the magnetic field at a constant temperaturet und.r magnetic field t t reversal (in our measurements, ttilc and H ±J ).

0921-452694/$07.00 ~ 1994 Elsevier Science B.V. All rights reserved SSDI 0921-4526(93)EOI95-M

C.C. Ahnasan et al. / Physica B 199&200 (1994) ~,~ 8-~90 289

5 ! I u t i i u

T . 8 1 K YBa2C U 3 0 7 . 8

10 c " , ' i l >.~ " , a l l 5

0

t T=92K ~ 87.5F ; > ~ 86K

83K 81K

0 76K

- 5 | | | i | i ! |

0 2 4 6 8 H (T)

Fig. 1. Hall voltage V,.,. versus applied field H data on Y t -x Prx Ba2Cu.~O7 _., for temperatures in the neighborhood of T~. Inset: Hall voltage V.~ r and longitudinal voltage V.~ versus H a t S l K.

Figure 1 shows Hall voltage V.,.,. versus H data in the neighborhood of T~ for the YBazCu3OT_~s crystal. While V~ r is positive for T > T~, it displays a "negative Hall anomaly" a few degrees below T~ which shifts to highe~ fields at lower temperatures. Shown in the inset of Fig. 1 are V.~ r and the longitudinal voltage V~x versus H, meas- ured at 81 K. The negative Hall region occurs where V.~.~ increases rapidly with increasing field. We observed a similar V~ r versus H profile for all the crystals with x<0.15. For x>0.24, only a positive Hall signal was observed. A similar behavior was reported by Jia et al. [3 ] .

Figure 2 contains a plot of the magnitude of the min- imum Hall signal A, obtained from Vx~, versus H curves, versus the reduced temperature TITs. We estimated the Pr content of the single crystals by comparing the Tjs to those of high-quality polycrystalline samples [4]. The result for x = 0 is similar to the one reported by Luo et ai. for epitaxial YBazCu307 films [5]. An interesting feature of the curves for the x = 0, 0.08 and 0.13 crystals is that A is nonzero over the same reduced temperature range (0.88 < T/T~ < i) and that Am~ decreases with increasing x, as shown in the inset. A linear decrease of Am~ with x is observed for x < 0.24, while Am~ = 0 for x>0.24. The close similarity of the profiles and the monotonic evolu- tion of Am~x with x suggest that the negative anomaly has

. . . . . by an i n t i ' i n s i c o r i g i n O.llr~ll"~A i s ~ # H U t I.At~tklA~¢ae~;~AIILllt~..~ ~-.'~tlat'C'v;nc;oittO,~

factors such as inhomogeneities in oxygen content as suggested earlier [6].

Wang and Ting [7] have proposed that the observed negative Hall resistivity in certa-n high T~ superconduc- tor~ can be explained in terms of pinaing forces existing in the samples with the sign of p.,~. simply reflecting that of the velocity component of the vortex parallel to J.

4 4

3

3 ~2

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1

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i - i - i -

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o • ,~"~ t, 0.13

I D a & & & & & ~ l l ~ & & &

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Fig. 2. Magnitude of the minimum Hall signal A, obtv;.ned from P~v versus H curves for Y t_~ Pr~ BazCu3OT-a crystals taken at different temperatures, versus reduced temperature T/T,. The data exhibit a maximum Am,~ which is shown in the inset as a function of x.

Several other mechanisms have also been proposed [8,9]. Recently, Harris et al. [10] reported the observa- tion of opposite Hall signs for vortices perpendicular and parallel to the CuO2 layers of YBa2Cu3Ov-,s single crys- tals. The competition between the two opposing Magnus forces on the vortex cores led them to an explanation of negative Hall anomaly in terms of "'pancake" vortices which lie in the CuO2 planes and are linked by inter- layer segments which reside in between and parallel to the C u a 2 planes. A possible explanation of the suppression of the negative Hall anomaly in the Y1 -~ Pr~BazCu30~ -,i is given in Ref. [1].

Another model for the existence of the negati~,e Hall voltage in the superconducting state relies on the pres- ence of pinning forces. However, this model cannot ex- plain the decrease of the magnitude of the negative Hall voltage with increasing x as argued by Jia et al. [3], since, for low Pr concentrations, the pinning force increases with increasing x [11], which, within the context of this model, would produce an increase in the magnitude of the negative Hall voltage. Furthermore, recently, Bud- hani et al. [12] reported a decrease in the magnitude of the sign anomaly of TI2Ba2Ca2Cu3Oto thin films with increasing defect concentration through heavy-ion ir- radiation.

Anderson [13] recently proposed that the observed linear temperature dependence of px_, and the Hal~ carrier number nn = V/'eltH (V is the unit-cell volume) m ttle normal state can be understood if the transport proper- ties are governed by two scattering times. According to his picture, one transport lifetime r,~ determines the longitudinal resistivity, while both r,, and a transverse

290 C.C. Aimasan et aL / Physica B 199&200 (1994) 288-290

v

8

800

600

400

200

0 0

! - i • i - i • i • | •

.iF++• ,+ °o ~o ~o ~ eo-i0o "0"0 . o o

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_.. " , . = m l l ~ t ; o o ~ • o.0t .~**'~..~|~Wo3o v - 0 0.13 ~ ~ o ~ ' m 0.29"

• 0,42 • 0.51"

i im l I m | i l

1 2 3 4 5 6 7 Ta(104 K 2)

Fig. 3. Cotangent of Hall angle cot(OH) versus T' of Y t -.~ Prx Ba,Cu30~ _,+ at 6 T. Inset: slope A and intercept B ver- sus T~. Note H = 6 T.

scattering lifetime r , determine the Hall carrier number. The transverse scattering rate I/TH is determined by spinon-spinon scattering and should vary as T 2. The cotangent of the Hall angle cot OH = p,,,,/RHH should then be given by

cot Ou = A T 2 + B, (1)

where A is related to the spinon bandwidth (predicted to be sensitive to carrier concentration [ 13]) and B is due to magnetic impurity scattering.

The simultaneous measurements of Px~ and I/RH en- abled us to calculate cot OH(T) for different x values. This quantity is independent of the thickness of the crystal and the current applied in the ab plane. Figure 3 shows a plot of cot OH versus T 2 calculated for a field of 6 T for our Y~ -x Prx Ba2Cu307-6 single crystals. As pre- viously reported [14,15], for the x = 0 crystal, the T 2 dependence is observed in the temperature range 120-200 K. As x increases, the range of the T 2 depend- ence moves towards higher temperatures.

We fitted the results of Fig. 3 with Eq. (1). The inset of Fig. 1 contains a plot of the values obtained for the slope A and the intercept B versus T~ for different x values. Both A and B increase linearly with decreasing T~. This result is in agreement with a previous report for epitaxial

films of Yt -~PrxBa ,CuaOT-6 by Xiong et al. [14] and in contrast to measurements by Jiang et al. of Yt-xPr~Ba2CuaOT-~ single crystals [16] in which only B was found to increase while A was constant with their experimental resolution.

A c k n o w l e d g e m e n t s

We thank R.C. Budhani for helpful discussions. This research was supported by the US Department of Energy under Grant No. DE-FG03-86ER-45230. Work at Los Alamos was performed under the auspices of the US Department of Energy. The characterization of the single crystals was performed with a SQUID magnetometer provided by the Center for Interface and Materials Science and funded by the W.A. Keck Foundation. One of us (MB) acknowledges partial support from Alexan- der-yon Humboldt Foundation.

R e f e r e n c e s

[1] M.B. Maple et al., to appear in J. Superconductivity. [2] L.M. Paul|us, B.E. Lee, M.B. Maple and P.K. Tsai,

Physica C, submitted. 1"3] Y.X. Jia, J.Z. Liu, M.D. Lan and R.N. Shelton, Phys. Rev.

B 47 (i993) 6043. [4] M.B. Maple et al., J. Alloys Compounds 181 (1992) 135. [5] J. Luo et al., Phys. Rev. Lett. 68 (1992) 690. [6] E.C. Jones et al., Physica C, submitted. [7] Z.D. Wang and C.S. Ting, Phys. Rev. Lett. 67 (1991) 3618. [8] T.R. Chien, T.W. Jing, N.P. Ong and Z.Z. Wang, Phys.

Rev. Lett. 66 (1991) 3075. [9] S.J. Hagen et al., Phys. Rev. B 41 (1990) 11630.

[10] J.~.'!. Harris, N.P. Or.g and Y.iF. Yah, Phys. Rev. Left. 71 (1993} 1455.

[i 1] L,M. Paul|us, C.C. Almasan and M.B. Maple, Phys. Rev. B 47 (1993) 11627.

[12] R.C. Budhani, S.H. Liou and Z.X. Ca|, Phys. Rev. Lett. 71 (1993} 621.

[13] P.W. Anderson, Phys. Rev. Lett. 67 (1991) 2992. [14] P. Xiong, G. Xiao and X.D. Wu, Phys. Rev. B 47 (1993)

5516. [15] T.R. Chien, Z.Z. Wang and N.P. Ong, Phys. Rev. Lett. 67

(1991) 2088. [16] W. Jiang, J.L. Peng, S.J. Hagen and R.L. Greene, Phys.

Rev. B 46 (1992) 8694.