Probing the current-phase relation in Josephson point-contact junctions between $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 and $$\hbox {Ba}_{0.6}$$ Ba 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 superconductors
Abstract The Josephson effect in point contacts between an “ordinary” superconductor $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 ( $$T_c \approx 6.6 \, {\mathrm {K}}$$ T c ≈ 6.6 K ) and single crystals of the Fe-based superconductor Ba $$_{0.6}$$ 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 ( $$T_c \appro...
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| Format: | Article |
| Language: | English |
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Nature Portfolio
2021-12-01
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| Series: | Scientific Reports |
| Online Access: | https://doi.org/10.1038/s41598-021-00762-0 |
| _version_ | 1819008799520849920 |
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| author | Valeriy A. Stepanov Chengtian Lin Renato S. Gonnelli Mauro Tortello |
| author_facet | Valeriy A. Stepanov Chengtian Lin Renato S. Gonnelli Mauro Tortello |
| author_sort | Valeriy A. Stepanov |
| collection | DOAJ |
| description | Abstract The Josephson effect in point contacts between an “ordinary” superconductor $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 ( $$T_c \approx 6.6 \, {\mathrm {K}}$$ T c ≈ 6.6 K ) and single crystals of the Fe-based superconductor Ba $$_{0.6}$$ 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 ( $$T_c \approx 38.5 \, {\mathrm {K}}$$ T c ≈ 38.5 K ), was investigated. In order to shed light on the order parameter symmetry of Ba $$_{0.6}$$ 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 , the dependence of the Josephson supercurrent $$I_s$$ I s on the temperature and on $$\sin (d\varphi )$$ sin ( d φ ) with $$d = 1, 2$$ d = 1 , 2 was studied. The dependencies of the critical current on temperature $$I_c (T)$$ I c ( T ) and of the amplitudes of the first current steps of the current–voltage characteristic $$i_n^{exp} (\sqrt{P})$$ i n exp ( P ) $$(n = 0, 1, 2)$$ ( n = 0 , 1 , 2 ) on the power of microwave radiation with frequency $$f = (1.5 \div 8)\, {\mathrm {GHz}}$$ f = ( 1.5 ÷ 8 ) GHz were measured. It is shown that the dependencies $$I_c (T)$$ I c ( T ) are close to the well-known Ambegaokar–Baratoff (AB) dependence for tunnel contacts between “ordinary” superconductors and to the dependence calculated by Burmistrova et al. (Phys Rev B 91, 214501 (2015)) for microshorts between an “ordinary” superconductor and a two-band superconductor with $$s \pm$$ s ± order parameter symmetry at certain values of the transparency of boundaries and thickness of the transition layer. It is found that the dependencies $$i_n^{exp} (\sqrt{P})$$ i n exp ( P ) cannot be approximated within the resistively shunted model using the normalized microwave frequencies $$\Omega = 2 \pi f / (2eV_c / \hbar )$$ Ω = 2 π f / ( 2 e V c / ħ ) with characteristic voltages $$V_c = I_c R_N$$ V c = I c R N , $$(R_N$$ ( R N —normal resistance of the contact) found from the low-voltage parts of the current–voltage characteristics. The reasons for this failure are discussed and a method is proposed for accurately determining the value of $$\Omega$$ Ω , which takes into account all the features of the point contact affecting the period of the dependence $$i_n^{exp} (\sqrt{P})$$ i n exp ( P ) . An analysis of the $$I_c (T)$$ I c ( T ) and $$i_n^{exp} (\sqrt{P})$$ i n exp ( P ) dependencies shows that the superconducting current of the Josephson contacts under investigation is proportional to the $$\sin$$ sin of the phase difference $$\varphi$$ φ , $$I_s = I_c sin(\varphi )$$ I s = I c s i n ( φ ) . The implications of these results on the symmetry of the order parameter are also discussed. |
| first_indexed | 2024-12-21T00:46:13Z |
| format | Article |
| id | doaj.art-1c004875b03e49f7bd8f18d849078085 |
| institution | Directory Open Access Journal |
| issn | 2045-2322 |
| language | English |
| last_indexed | 2024-12-21T00:46:13Z |
| publishDate | 2021-12-01 |
| publisher | Nature Portfolio |
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| series | Scientific Reports |
| spelling | doaj.art-1c004875b03e49f7bd8f18d8490780852022-12-21T19:21:30ZengNature PortfolioScientific Reports2045-23222021-12-0111111210.1038/s41598-021-00762-0Probing the current-phase relation in Josephson point-contact junctions between $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 and $$\hbox {Ba}_{0.6}$$ Ba 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 superconductorsValeriy A. Stepanov0Chengtian Lin1Renato S. Gonnelli2Mauro Tortello3P.N. Lebedev Physical Institute of the Russian Academy of SciencesMax-Planck-Institut für FestkörperforschungDipartimento di Scienza Applicata e Tecnologia, Politecnico di TorinoDipartimento di Scienza Applicata e Tecnologia, Politecnico di TorinoAbstract The Josephson effect in point contacts between an “ordinary” superconductor $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 ( $$T_c \approx 6.6 \, {\mathrm {K}}$$ T c ≈ 6.6 K ) and single crystals of the Fe-based superconductor Ba $$_{0.6}$$ 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 ( $$T_c \approx 38.5 \, {\mathrm {K}}$$ T c ≈ 38.5 K ), was investigated. In order to shed light on the order parameter symmetry of Ba $$_{0.6}$$ 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 , the dependence of the Josephson supercurrent $$I_s$$ I s on the temperature and on $$\sin (d\varphi )$$ sin ( d φ ) with $$d = 1, 2$$ d = 1 , 2 was studied. The dependencies of the critical current on temperature $$I_c (T)$$ I c ( T ) and of the amplitudes of the first current steps of the current–voltage characteristic $$i_n^{exp} (\sqrt{P})$$ i n exp ( P ) $$(n = 0, 1, 2)$$ ( n = 0 , 1 , 2 ) on the power of microwave radiation with frequency $$f = (1.5 \div 8)\, {\mathrm {GHz}}$$ f = ( 1.5 ÷ 8 ) GHz were measured. It is shown that the dependencies $$I_c (T)$$ I c ( T ) are close to the well-known Ambegaokar–Baratoff (AB) dependence for tunnel contacts between “ordinary” superconductors and to the dependence calculated by Burmistrova et al. (Phys Rev B 91, 214501 (2015)) for microshorts between an “ordinary” superconductor and a two-band superconductor with $$s \pm$$ s ± order parameter symmetry at certain values of the transparency of boundaries and thickness of the transition layer. It is found that the dependencies $$i_n^{exp} (\sqrt{P})$$ i n exp ( P ) cannot be approximated within the resistively shunted model using the normalized microwave frequencies $$\Omega = 2 \pi f / (2eV_c / \hbar )$$ Ω = 2 π f / ( 2 e V c / ħ ) with characteristic voltages $$V_c = I_c R_N$$ V c = I c R N , $$(R_N$$ ( R N —normal resistance of the contact) found from the low-voltage parts of the current–voltage characteristics. The reasons for this failure are discussed and a method is proposed for accurately determining the value of $$\Omega$$ Ω , which takes into account all the features of the point contact affecting the period of the dependence $$i_n^{exp} (\sqrt{P})$$ i n exp ( P ) . An analysis of the $$I_c (T)$$ I c ( T ) and $$i_n^{exp} (\sqrt{P})$$ i n exp ( P ) dependencies shows that the superconducting current of the Josephson contacts under investigation is proportional to the $$\sin$$ sin of the phase difference $$\varphi$$ φ , $$I_s = I_c sin(\varphi )$$ I s = I c s i n ( φ ) . The implications of these results on the symmetry of the order parameter are also discussed.https://doi.org/10.1038/s41598-021-00762-0 |
| spellingShingle | Valeriy A. Stepanov Chengtian Lin Renato S. Gonnelli Mauro Tortello Probing the current-phase relation in Josephson point-contact junctions between $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 and $$\hbox {Ba}_{0.6}$$ Ba 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 superconductors Scientific Reports |
| title | Probing the current-phase relation in Josephson point-contact junctions between $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 and $$\hbox {Ba}_{0.6}$$ Ba 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 superconductors |
| title_full | Probing the current-phase relation in Josephson point-contact junctions between $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 and $$\hbox {Ba}_{0.6}$$ Ba 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 superconductors |
| title_fullStr | Probing the current-phase relation in Josephson point-contact junctions between $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 and $$\hbox {Ba}_{0.6}$$ Ba 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 superconductors |
| title_full_unstemmed | Probing the current-phase relation in Josephson point-contact junctions between $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 and $$\hbox {Ba}_{0.6}$$ Ba 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 superconductors |
| title_short | Probing the current-phase relation in Josephson point-contact junctions between $$\hbox {Pb}_{0.6}$$ Pb 0.6 In $$_{0.4}$$ 0.4 and $$\hbox {Ba}_{0.6}$$ Ba 0.6 K $$_{0.4}$$ 0.4 (FeAs) $$_2$$ 2 superconductors |
| title_sort | probing the current phase relation in josephson point contact junctions between hbox pb 0 6 pb 0 6 in 0 4 0 4 and hbox ba 0 6 ba 0 6 k 0 4 0 4 feas 2 2 superconductors |
| url | https://doi.org/10.1038/s41598-021-00762-0 |
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