Superconductivity in hole-doped germanium point contacts

We have observed superconductivity in heavy p-doped Ge by measuring of differential resistance dV/dI(V) of Ge–PtIr point contacts. The superconducting features disappear above 6 K or above 1 T, what can be taken as the critical temperature and the critical magnetic field, respectively. The observed dV/dI(V) spectrum with Andreev reflection like features was fitted within one-gap Blonder–Tinkham–Klapwijk model. The extracted superconducting gap demonstrates Bardeen–Cooper–Schrieffer-like behavior with 2Δ/k_BT_c = 10.5 ± 0.5 ratio, which is much higher than expected for conventional superconductors. Magnetic field suppresses Andreev reflection features, but the superconducting gap moderately decreases in magnetic field similarly as it was observed previously for the type II superconductors, including nickel borocarbide and iron-based superconductors. Curiously, we have not yet observed superconductivity in n-doped Ge with a similar dopant concentration.

Key words: p-doped Ge, Andreev reflection spectroscopy, Blonder–Tinkham–Klapwijk model, superconducting gap.

References

1. M. L. Cohen, “Superconductivity in many-valley semi-conductors and in semimetals,” Phys. Rev. 134, A511 (1964). CrossRef Google Scholar

2. J. Wittig, “Zur supraleitung von germanium und silizium unter hohem druck," Z. Phys. 195, 215 (1966). CrossRef Google Scholar

3. K. J. Chang, M. M. Dacorogna, M. L. Cohen, J. M. Mignot, G. Chouteau, and G. Martinez, “Superconductivity in high-pressure metallic phases of Si,” Phys. Rev. Lett. 54, 2375 (1985). CrossRef Google Scholar

4. D. Erskine, P. Y. Yu, K. J. Chang, and M. L. Cohen, “Superconductivity and phase transitions in compressed Si to 45 GPa,” Phys. Rev. Lett. 57, 2741 (1986). CrossRef Google Scholar

5. T. Herrmannsdörfer, R. Skrotzki, V. Heera, O. Ignatchik, M. Uhlarz, A. Mücklich, M. Posselt, B. Schmidt, K.-H. Heinig, W. Skorupa, M. Voelskow, C. Wündisch, M. Helm, and J. Wosnitza, “Superconductivity in thin-film germanium in the temperature regime around 1 K,” Supercond. Sci. Technol. 23, 034007 (2010). CrossRef Google Scholar

6. S. Prucnal, V. Heera, R. Hübner, M. Wang, G. P. Mazur, M. J. Grzybowski, X. Qin, Y. Yuan, M. Voelskow, W. Skorupa, L. Rebohle, M. Helm, M. Sawicki, and S. Zhou, “Superconductivity in single-crystalline, aluminum- and gallium-hyperdoped germanium,” Phys. Rev. Mater. 3, 054802 (2019). CrossRef Google Scholar

7. L. Boeri, J. Kortus, and O. K. Anderson, “Electron–phonon superconductivity in hole-doped diamond: A first-principles study,” J. Phys. Chem. Solids 67, 552 (2006). CrossRef Google Scholar

8. T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, A. Mücklich, M. Posselt, H. Reuther, B. Schmidt, K.-H. Heinig, W. Skorupa, M. Voelskow, C. Wündisch, R. Skrotzki, M. Helm, and J. Wosnitza, “Superconducting state in a gallium-doped germanium layer at low temperatures,” Phys. Rev. Lett. 102, 217003 (2009). CrossRef Google Scholar

9. Y. G. Naidyuk and I. K. Yanson, Point-Contact SpectroScopy (Springer, New York, 2005). CrossRef Google Scholar

10. Y. G. Naidyuk, I. V. Koshkin, and A. A. Lysykh, “Nonlinear effects in electrical conductivity of germanium point-contacts due to electron–phonon interaction,” Fiz. Nizk. Temp. 13, 103 (1987) [Sov. J. Low Temp. Phys. 13, 57 (1987)]. Google Scholar

11. A. Sirohi, S. Gayen, M. Aslam, and G. Sheet, “Mesoscopic superconductivity above 10 K in silicon point contacts,” Appl. Phys. Lett. 113, 242601 (2018). CrossRef Google Scholar

12. A. N. Ionov and I. S. Shlimak, “Effect of electron-electron interaction on low-temperature conduction and Hall constant of heavily doped p-type germanium,” Fizika i Tekhnika Polu-provodnikov 19, 1226 (1985) [in Russian]. Google Scholar

13. G. E. Blonder, M. Tinnkham, and T. M. Klapwijk, “Transition from metallic to tunneling regimes in superconducting micro-constrictions: Excess current, charge imbalance, and supercurrent conversion,” Phys. Rev. B 25, 4515 (1982). CrossRef Google Scholar

14. Y. G. Naidyuk and K. Gloos, “Anatomy of point-contact Andreev reflection spectroscopy from the experimental point of view,” Fiz. Nizk. Temp. 44, 343 (2018) [Low Temp. Phys. 44, 257 (2018)]. CrossRef Google Scholar

15. L. Aggarwal, A. Gaurav, G. S. Thakur, Z. Haque, A. K. Ganguli, and G. Sheet, “Unconventional superconductivity at mesoscopic point contacts on the 3D dirac semimetal Cd3As2,” Nature Mater. 15, 32 (2016). CrossRef Google Scholar

16. Y. G. Naidyuk, O. E. Kvitnitskaya, I. K. Yanson, G. Fuchs, K. Nenkov, A. Waelte, G. Behr, D. Souptel, and S.-L. Drechsler, “Point-contact spectroscopy of the antiferromagnetic super-conductor HoNi2B2C in the normal and superconducting state,” Phys. Rev. B 76, 014520 (2007). CrossRef Google Scholar

17. Y. G. Naidyuk, O. E. Kvitnitskaya, L. V. Tiutrina, I. K. Yanson, G. Behr, G. Fuchs, S.-L. Drechsler, K. Nenkov, and L. Schultz, “Peculiarities of the superconducting gaps and the electron-boson interaction in TmNi2B2C as seen by point-contact spectroscopy,” Phys. Rev. B 84, 094516 (2011). CrossRef Google Scholar

18. Y. G. Naidyuk, O. E. Kvitnitskaya, N. V. Gamayunova, D. L. Bashlakov, L. V. Tyutrina, G. Fuchs, R. Hühne, D. A. Chareev, and A. N. Vasiliev, “Superconducting gaps in FeSe studied by soft point-contact Andreev reflection spectroscopy,” Phys. Rev. B 96, 094517 (2017). CrossRef Google Scholar

19. E. Bustarret, “Superconductivity in doped semiconductors,” Physica C 514, 36 (2015). CrossRef Google Scholar

20. Y. G. Naidyuk, R. Haussler, and H. v. Löhneysen, “Magnetic field dependence of the Andreev reflection structure in the conductivity of S-N point-contacts,” Physica B 218, 122 (1996). CrossRef Google Scholar

21. Y. Miyoshi, Y. Bugoslavsky, and L. F. Cohen, “Andreev reflection spectroscopy of niobium point contacts in a magnetic field,” Phys. Rev. B 72, 012502 (2005). CrossRef Google Scholar

22. C. Liu, X. Song, Q. Li, Y. Ma, and C. Chen, “Superconductivity in shear strained semi-conductors,” Chin. Phys. Lett. 38, 086301 (2021). CrossRef Google Scholar