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Paraconductivity and phase-relaxation time in YBa2Cu3Ox thin films
Physica B 284 }288 (2000) 985}986
Paraconductivity and phase-relaxation time in YBa Cu O V thin "lms A. Gue!af *, M. Salim , M.S. Raven , K. Bousbahi School of Electrical and Electronic Engineering, The University of Nottingham, Nottingham NG7 2RD, UK University of Sciences and Technology of Oran, BP 1505, Oran El-Mnaouer, Algeria
Abstract We present results of the c-axis coherence length m (0) and the phase-relaxation time q (at 100 K) obtained from the "t A P to paraconductivity data for YBCO thin "lms. The average values for m (0) and q (at 100 K) are 0.183 nm and A P 0.18;10\ s, respectively. We "nd that three of our "lms which are oxygen-de"cient have c-axis coherence lengths ranging from 0.049 to 0.090 nm. The phase-relaxation time decreases with increasing ¹ with mean-slope "!6.15;10\ s K\ and a minima at 81 K. 2000 Elsevier Science B.V. All rights reserved. Keywords: Paraconductivity; Phase-relaxation time; YBa Cu O V
1. Introduction
2. Experimental procedure
In thermodynamic #uctuations, there are two processes: the direct or Aslamazov}Larkin contribution [1] which corresponds to the enhancement of conductivity due to the acceleration of superconducting pairs and the indirect or Maki}Thompson contribution [2,3] which is due to the interaction between the superconducting pairs and the normal state quasiparticles. Measurements in the #uctuation regime are commonly used to probe microscopic parameters such as coherence length and phaserelaxation time in high-temperature superconductors. In this paper, we present measurements of the paraconductivity in a number of epitaxial thin "lms of YBa Cu O V with di!erent ¹ values ranging from 54 to 88.9 K. From the paraconductivity results, the c-axis coherence length m (0), the pair-breaking parameter d"n; /8k ¹q A P and the phase-relaxation time q (at 100 K) are P determined.
The YBCO thin "lms used in this work were grown by in situ o!-axis RF magnetron sputter deposition using a stoichiometric single target. The X-ray di!raction analysis showed that all "lms deposited on LaAlO (1 0 0), MgO(1 0 0) and SrTiO (1 0 0) were c-axis oriented. Stan dard four terminal method was used to measure the DC resistivity of the "lms as a function of temperature.
* Corresponding author. E-mail address: [email protected] (A. Gue!af)
3. Results and discussion A typical plot of the paraconductivity, *p " VV *p*"#*p+2 where *p*", *p+2 are the Lawrence and VV VV VV VV Doniach (LD) [4] and the Maki}Thompson (MT) [5,6] terms, is shown in Fig. 1 for sample Y116SP in the reduced temperature range 0.01(e(0.1. Our results of coherence lengths shown in Table 1 are consistent with data reported in the literature for thin "lms, single crystals and polycrystalline samples of YBa Cu O [5,7]. V The estimation of the value of phase-relaxation time in the literature is of the order of 0.10 ps at 100 K similar to the values of q obtained for some of our "lms. There are, P however, signi"cant di!erences between the values of q obtained from some other samples, for instance, P
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 3 1 9 - 4
986
A. Guewaf et al. / Physica B 284}288 (2000) 985} 986 Table 1 Critical temperature ¹ , coherence length m (0), pair-breaking A parameter d and phase-relaxation time q (at 100 K) for various P "lms
Fig. 1. Paraconductivity *p versus the reduced temperature VV e"ln(¹/¹ )K(¹!¹ )/¹ of sample Y116SP. The results from the "t of the direct (LD) and indirect (MT) contributions and the sum of these two processes (LD#MT) are plotted.
Sample no.
Substrate
¹ (K)
m (0) A (nm)
d
q P (ps)
Y123L Y116SP Y111MP Y129M Y130L Y78MP
LaAlO SrTiO MgO MgO LaAlO MgO
88.9 85 80 74.2 61.9 54
0.410 0.212 0.140 0.088 0.090 0.049
0.21 0.18 0.16 0.13 0.11 0.09
0.14 0.17 0.19 0.23 0.27 0.33
with increasing ¹ with mean-slope equal to !6.15;10\ s K\ and a minima occurring at 81 K.
4. Summary
Fig. 2. Phase-relaxation time q as a function of the critical P temperature ¹ for various YBa Cu O "lms. The solid line V represents a linear "t to the data with mean slope" !6.15;10\ s K\ . The graph presentsa minimum at 81 K.
sample Y78MP, Y129M and Y130L having larger q values. One of the reasons for this is that the MT P contribution to the paraconductivity is too small and therefore the "ts are not so sensitive to changes in q . The P other reason is that the MT process is very sensitive to the quality of the material [7]. This implies that q could P be a function of growth and annealing parameters as reported in Ref. [8]. The samples mentioned above are oxygen de"cient with ¹ 's of 54, 61.9 and 74.2 K, respec tively. In Fig. 2, q is plotted as a function of ¹ for our P ten di!erent "lms. The graph shows that q decreases P
We generally obtained a good "t to the paraconductivity data in the reduced temperature range 0.01(e(0.1. From the paraconductivity results, the c-axis coherence length m (0) and the phase-relaxation time q at 100 A P K were determined. The "ts to our data obtained from ten di!erent "lms give the set of average values m (0)"0.183 nm, q (100 K)"0.18;10\ s which is A P consistent with the data of coherence length and phaserelaxation time reported in the literature.
References [1] L.G. Aslamazov, A.I. Larkin, Fiz. Tverd. Tela (Leningrad) 10 (1968) 1104 [Sov. Phys. Solid State 10 (1968) 875]. [2] K. Maki, Prog. Theor. Phys. 39 (1968) 897. [3] R.S. Thompson, Phys. Rev. B 1 (1970) 327. [4] W.E. Lawrence, S. Doniach, in: E. Kanda (Ed.), Proceedings of the 12th International Conference on Low Temperature Physics, Kyoto, 1970, Keigaku, Tokyo, 1971, p. 361. [5] S. Hikami, A.I. Larkin, Mod. Phys. Lett. B 2 (1988) 693. [6] K. Maki, R.S. Thompson, Phys. Rev. B 39 (1989) 2767. [7] W. Lang, G. Heine, P. Schwab, X.Z. Wang, D. BaK uerle, Phys. Rev. B 49 (1994) 4209. [8] N. Overend, M.A. Howson, J. Phys.: Condens Matter 4 (1992) 9615.
.
Paraconductivity and phase-relaxation time in YBa Cu O V thin "lms A. Gue!af *, M. Salim , M.S. Raven , K. Bousbahi School of Electrical and Electronic Engineering, The University of Nottingham, Nottingham NG7 2RD, UK University of Sciences and Technology of Oran, BP 1505, Oran El-Mnaouer, Algeria
Abstract We present results of the c-axis coherence length m (0) and the phase-relaxation time q (at 100 K) obtained from the "t A P to paraconductivity data for YBCO thin "lms. The average values for m (0) and q (at 100 K) are 0.183 nm and A P 0.18;10\ s, respectively. We "nd that three of our "lms which are oxygen-de"cient have c-axis coherence lengths ranging from 0.049 to 0.090 nm. The phase-relaxation time decreases with increasing ¹ with mean-slope "!6.15;10\ s K\ and a minima at 81 K. 2000 Elsevier Science B.V. All rights reserved. Keywords: Paraconductivity; Phase-relaxation time; YBa Cu O V
1. Introduction
2. Experimental procedure
In thermodynamic #uctuations, there are two processes: the direct or Aslamazov}Larkin contribution [1] which corresponds to the enhancement of conductivity due to the acceleration of superconducting pairs and the indirect or Maki}Thompson contribution [2,3] which is due to the interaction between the superconducting pairs and the normal state quasiparticles. Measurements in the #uctuation regime are commonly used to probe microscopic parameters such as coherence length and phaserelaxation time in high-temperature superconductors. In this paper, we present measurements of the paraconductivity in a number of epitaxial thin "lms of YBa Cu O V with di!erent ¹ values ranging from 54 to 88.9 K. From the paraconductivity results, the c-axis coherence length m (0), the pair-breaking parameter d"n; /8k ¹q A P and the phase-relaxation time q (at 100 K) are P determined.
The YBCO thin "lms used in this work were grown by in situ o!-axis RF magnetron sputter deposition using a stoichiometric single target. The X-ray di!raction analysis showed that all "lms deposited on LaAlO (1 0 0), MgO(1 0 0) and SrTiO (1 0 0) were c-axis oriented. Stan dard four terminal method was used to measure the DC resistivity of the "lms as a function of temperature.
* Corresponding author. E-mail address: [email protected] (A. Gue!af)
3. Results and discussion A typical plot of the paraconductivity, *p " VV *p*"#*p+2 where *p*", *p+2 are the Lawrence and VV VV VV VV Doniach (LD) [4] and the Maki}Thompson (MT) [5,6] terms, is shown in Fig. 1 for sample Y116SP in the reduced temperature range 0.01(e(0.1. Our results of coherence lengths shown in Table 1 are consistent with data reported in the literature for thin "lms, single crystals and polycrystalline samples of YBa Cu O [5,7]. V The estimation of the value of phase-relaxation time in the literature is of the order of 0.10 ps at 100 K similar to the values of q obtained for some of our "lms. There are, P however, signi"cant di!erences between the values of q obtained from some other samples, for instance, P
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 3 1 9 - 4
986
A. Guewaf et al. / Physica B 284}288 (2000) 985} 986 Table 1 Critical temperature ¹ , coherence length m (0), pair-breaking A parameter d and phase-relaxation time q (at 100 K) for various P "lms
Fig. 1. Paraconductivity *p versus the reduced temperature VV e"ln(¹/¹ )K(¹!¹ )/¹ of sample Y116SP. The results from the "t of the direct (LD) and indirect (MT) contributions and the sum of these two processes (LD#MT) are plotted.
Sample no.
Substrate
¹ (K)
m (0) A (nm)
d
q P (ps)
Y123L Y116SP Y111MP Y129M Y130L Y78MP
LaAlO SrTiO MgO MgO LaAlO MgO
88.9 85 80 74.2 61.9 54
0.410 0.212 0.140 0.088 0.090 0.049
0.21 0.18 0.16 0.13 0.11 0.09
0.14 0.17 0.19 0.23 0.27 0.33
with increasing ¹ with mean-slope equal to !6.15;10\ s K\ and a minima occurring at 81 K.
4. Summary
Fig. 2. Phase-relaxation time q as a function of the critical P temperature ¹ for various YBa Cu O "lms. The solid line V represents a linear "t to the data with mean slope" !6.15;10\ s K\ . The graph presentsa minimum at 81 K.
sample Y78MP, Y129M and Y130L having larger q values. One of the reasons for this is that the MT P contribution to the paraconductivity is too small and therefore the "ts are not so sensitive to changes in q . The P other reason is that the MT process is very sensitive to the quality of the material [7]. This implies that q could P be a function of growth and annealing parameters as reported in Ref. [8]. The samples mentioned above are oxygen de"cient with ¹ 's of 54, 61.9 and 74.2 K, respec tively. In Fig. 2, q is plotted as a function of ¹ for our P ten di!erent "lms. The graph shows that q decreases P
We generally obtained a good "t to the paraconductivity data in the reduced temperature range 0.01(e(0.1. From the paraconductivity results, the c-axis coherence length m (0) and the phase-relaxation time q at 100 A P K were determined. The "ts to our data obtained from ten di!erent "lms give the set of average values m (0)"0.183 nm, q (100 K)"0.18;10\ s which is A P consistent with the data of coherence length and phaserelaxation time reported in the literature.
References [1] L.G. Aslamazov, A.I. Larkin, Fiz. Tverd. Tela (Leningrad) 10 (1968) 1104 [Sov. Phys. Solid State 10 (1968) 875]. [2] K. Maki, Prog. Theor. Phys. 39 (1968) 897. [3] R.S. Thompson, Phys. Rev. B 1 (1970) 327. [4] W.E. Lawrence, S. Doniach, in: E. Kanda (Ed.), Proceedings of the 12th International Conference on Low Temperature Physics, Kyoto, 1970, Keigaku, Tokyo, 1971, p. 361. [5] S. Hikami, A.I. Larkin, Mod. Phys. Lett. B 2 (1988) 693. [6] K. Maki, R.S. Thompson, Phys. Rev. B 39 (1989) 2767. [7] W. Lang, G. Heine, P. Schwab, X.Z. Wang, D. BaK uerle, Phys. Rev. B 49 (1994) 4209. [8] N. Overend, M.A. Howson, J. Phys.: Condens Matter 4 (1992) 9615.
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