Spin thermopower in the overscreened Kondo model NanoCTM final network meeting and workshop Poznań, 23-27 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

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

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

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

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

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

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

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

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

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

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

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

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

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

Kondo models

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

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

Results – overscreened Kondo model NFL FL conformal filed theory

Results – underscreened Kondo model singular FL

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