1. Spin thermopower in the overscreened Kondo model
NanoCTM final network meeting and workshop Poznań, September 2013
Spin thermopower in the overscreened Kondo model
Tomaž Rejec, Rok Žitko, Jernej Mravlje and Anton Ramšak
Department of Physics, University of Ljubljana
Jožef Stefan Institute, Ljubljana

2. Outline
Spin-Seebeck coefficient
Kondo models (fully screened, underscreened, overscreened)
NRG results

3. Spin-Seebeck coefficient
TL=TR  L
V=0  R

4. Spin-Seebeck coefficient
TL=TR  L
V≠0  R

5. Spin-Seebeck coefficient
TL=TR  L
V≠0  R

6. Spin-Seebeck coefficient
TL>TR  L
V=0  R

7. Spin-Seebeck coefficient
TL>TR  L
V=0  R

8. Spin-Seebeck coefficient
TL>TR  L
ed≠0
V=0  R

9. Spin-Seebeck coefficient
TL>TR  L
ed≠0
V≠0  R
Seebeck coefficient

10. Spin-Seebeck coefficient
TL>TR  L
B≠0
V=0  R

11. Spin-Seebeck coefficient
TL>TR  L
B≠0
V=0  R
Spin current!

12. Spin-Seebeck coefficient
TL>TR  L
B≠0
Vs≠0  R
Spin-Seebeck coefficient
Spin voltage:

13. Spin-Seebeck coefficient
For small DT, Vs:
Non-interacting QD:
B>G
B=G
B<G

14. J1=J2 : overscreened Kondo effect
Kondo models
NFL:
J1=J2 : overscreened Kondo effect

15. Kondo models

16. Kondo models
S=1/2; i=1 : fully screened Kondo model
S=1/2; i=1,2 : overscreened Kondo model
S=1; i=1 : underscreened Kondo model

17. Results – fully screened Kondo model
B=TK
B>G
B=G
B<G

18. Results – overscreened Kondo model
NFL FL
conformal filed theory

19. Results – underscreened Kondo model
singular FL

20. Summary
Measuring the spin thermopower at low magentic fields would provide a sensitive test for distinguishing between fully screened, underscreened and overscreened Kondo behaviour
Possible applications: generation of spin current for spintronics applications, sensitive measurement of low magnetic fields