Galvanomagnetic effects in electron-doped superconducting compounds

1. Galvanomagnetic effects in electron-doped superconducting compounds D. S. Petukhov1, T. B. Charikova1, G. I. Harus1, N. G. Shelushinina1, V. N. Neverov1, O. E. Petukhova1, A. A. Ivanov2 1Institute of Metal Physics UB RAS, Ekaterinburg 2Moscow Engineering Physics Institute, Moscow

2. Topics • Introduction • The aim of the work • Experiment: samples, experimental equipment • Results • Conclusion

3. Introduction There is no universally accepted mechanism of the superconducting state formation in HTSC Properties of the superconductor in the normal state determine its properties in the superconducting state Studies of galvanomagnetic phenomena provide important information about the behavior of carriers in the normal state of HTSC There are questions concerning the physical picture of normal and mixed state of HTSC Clarify the features of the superconducting state in HTSC

4. Introduction Various researchers have found features of the behavior Hall resistivity dependencies on the temperature and magnetic field. YBa2Cu3O7 Nd1.85Ce0.15CuO4+δ Hagen S. J. PRB V.47 P.1064 (1993)

5. Introduction La2-xCexCuO4 Pr2-xCexCuO4 Y. Dagan PRB V.76 P. 024506 (2007) K. Jin PRB V.78 P. 174521 (2008)

6. Introduction • There is a sign change in the mixed state. • A similar anomaly is observed in many materials. • Trend dependence of the Hall resistance does not depend on the sign of the majority charge carriers. • The presence or absence of anomaly depends on the purity of the sample. YBa2Cu3O7 A. Casaca PRB V.59 P. 1538 (1999)

7. Introduction The sign change of the Hall coefficient in the mixed state can be explained: Thermoelectric models Models of Nozieres-Vinen and Bardeen-Stephen Pinning models Two-band/two-gap models

8. Hall coefficient in the normal state NieLuoarXiv:cond-mat/0003074v2, P. 1 (2000)

9. Shubnikov de Haas oscillations Nd2-xCexCuO4+δ M.V. Kartsovnik New Journal of Physics V13, P. 1-18 (2011)

10. ARPES data Armitage N.P. Rev. Mod. Phys. V82, P. 2421 (2010) Armitage N.P.PRL V88, P. 257001 (2002) Matsui H. PRL V94, P. 047005 (2005) Matsui H. PRL V75, P. 224514 (2007) Nd2-xCexCuO4+δ

11. The aim of the work The aim of the work was to investigate magnetic field dependence of the resistivity and Hall effect of electron-doped superconductor in the normal and mixed state, in order to study the dynamics of Abrikosov vortices in the resistive state in the electron-doped cuprate superconductor.

12. Experiment: the samples In the experiments, we used single-crystal films Nd2-xCexCuO4+δ/SrTiO3 (x = 0.15; 0.17; 0.18) with orientation(001).The thicknesses of the films were 1200-2000 Å (x = 0.15), 1000 Å (x = 0.17) and 3100 Å (x = 0.18). The films were subjected to heat treatment (annealing) under various conditions. Optimal doped region(х=0.15): • the optimally annealing in the vacuum(60 min, Т = 780°С, р = 10-2 mmHg); • the non-optimally annealing in the vacuum(40 min, Т = 780°С, р = 10-2 mmHg); • As grown (without annealing); Overdoped region(х=0.17): • the optimally annealing in a vacuum ( Т = 780°С, р = 10-5 mmHg); Overdoped region(х=0.18): • the optimally annealing in a vacuum (35 min, Т = 600°С, р = 10-5 mmHg). Ivanov A.A., Galkin S.G., Kuznetsov A.V. et al., Physica C, V. 180,P. 69 (1991)

13. The measurement equipment Hall effect measurements were carried out with 4-contact method in the solenoid, "Oxford Instruments" (IMP UD RAS) and SQUID-magnetometer MPMS XL firm Quantum Design (IMP UD RAS) in magnetic fields up to 90 kOe at the temperature of Т = (1.7 – 4.2) К .

14. Results: Hall coefficient in the normal state (T=4.2K B=9T) Charikova T. B., Physica C, V. 483 ,P. 113 (2012)

15. Dependences of the Hall coefficient on the magnetic field for optimally annealing Nd2-xCexCuO4+δ x=0.15, 0.17, 0.18

16. The theoretical model We used the Bardeen-Stephen model, which has been adapted to respond to two types of carriers (electrons and holes). Each of the carriers gives a contribution to the conductivity and Hall coefficient: where Re, σe- is the contribution of electrons, and Rh, σh - the contribution of the holes. Bardeen-Stephen model gives an expression for the resistivity and Hall coefficient for one type of carrier in the form: i=e, h. where ρni = 1/eniμiare resistivities in the normal state, Rni = ± 1/eniare Hall coefficients in the normal state, Hc2i are upper magnetic fields, Hp is depinning field, ni, μiare carrier concentrations and mobilities, respectively (for electrons i=e and for holes i=h). Thus, if H<Hp, the samples are in the SC state and Ri, ρi=0; if H>Hc2i, then the samples are in the normal state and Ri=Rni, ρxxi=ρni. In the calculations, the fields Hc2e, Hc2h, Hpare found graphically from the dependence of R(H) and ρxx(H), the mobilities are close in magnitude: μh/μe~1. As a result of the calculations parameters ne, nh, μe, μhwere obtained.

17. Dependences of RH(H) and ρxx(H) for optimally annealingNd1.85Ce0.15CuO4+δ T=4.2К

18. Dependences of RH(H) and ρxx(H) for optimally annealingNd1.83Ce0.17CuO4+δ T=4.2К

19. Dependences of RH(H) and ρxx(H) for optimally annealingNd1.82Ce0.18CuO4+δ T=4.2К

20. The main parameters of the samples Nd2-xCexCuO4+δ(optimally annealing)

21. Dependences of RH(H) and ρxx(H) for optimally annealingNd1.85Ce0.15CuO4+δ T=4.2К

22. Dependences of RH(H) and ρxx(H) for non-optimally annealingNd1.85Ce0.15CuO4+δT=4.2К

23. Dependences of RH(H) and ρxx(H) for as grownNd1.85Ce0.15CuO4+δT=4.2К

24. The main parameters of the samples Nd1.85Ce0.15CuO4+δ

25. Conclusion • The model is based on a simple Drude model for the normal state and semi-phenomenological model for the Bardeen-Stephen mixed state (modified considering the coexistence of electrons and holes) can to qualitatively describe the behavior of the Hall coefficient. • The possibility of such descriptions allows us to consider the relationship of the hole and electron subsystems as one of the important properties inherent in cuprate HTSC.