Spintronics How spin can act on charge carriers

Spintronics: How spin can act on charge carriers and vice versa Tomas Jungwirth Institute of Physics Prague University of Nottingham

Mott without spin current Mott with spin current I Spintronics I From Wikipedia, the free encyclopedia Spintronics (a pormanteau meaning spin transport electronics). . GMR 1988 MRAM 2006 Dirac without current through magnet Dirac with current through magnet I I I AMR 1857 HD Read-heads 1990‘s I

Mott with antiferromagnets Mott with ferromagnets I I I Dirac with ferromagnets I I Dirac with antiferromagnets I I I

Magnetic-field control of FMs: scales with current Control by current via spin torques: scales with current density Control by photo-carriers via spin torques: sub ps timescales er Las 0. 1 p. J Relativistic spin-orbit torques might work equally well in AFMs plus photocarriers in SCs Electro-static field control via relativistic magnetic anisotropy effects: 1 f. J Should work equally well or better in AFMs: more choices including SCs (or piezo-electric)

Writing by current via spin torques: scales with current density Writing by photo-carriers via spin torques: sub ps timescales er Las 0. 1 p. J Relativistic spin-orbit torques might work equally well in AFMs plus photocarriers in SCs

Optical spin-transfer torque OSTT Pn s M M s Pn M M Němec, Tesařová, Novák, TJ et al. Nature Phys. ’ 12, Nature Photonics ‘ 13, Nature Commun. ‘ 13 Fernandez-Rossier, Nunez, Abofath, Mac. Donald cont-mat/0304492

Optical spin-transfer torque OSTT Pn s s Pn M Němec, Tesařová, Novák, TJ et al. Nature Phys. ’ 12, Nature Photonics ‘ 13, Nature Commun. ‘ 13 Fernandez-Rossier, Nunez, Abofath, Mac. Donald cont-mat/0304492 M

Optical spin-transfer torque OSTT Pn s s Pn M Němec, Tesařová, Novák, TJ et al. Nature Phys. ’ 12, Nature Photonics ‘ 13, Nature Commun. ‘ 13 Fernandez-Rossier, Nunez, Abofath, Mac. Donald cont-mat/0304492 M

Electrical spin-transfer torque Antidamping-like (adiabatic) STT OSTT Pn s M Zhang and Li PRL 2004 Vanhaverbeke et al. PRB 2007, . . .

Electrical spin-transfer torque Field-like (non-adiabatic) STT s Pn Zhang and Li PRL 2004 Vanhaverbeke et al. PRB 2007, . . . M

Electrical spin-transfer torque Antidamping-like STT Field-like STT ~ small in weakly SO-coupled dense-moment metal FMs large in strongly SO-coupled dilute-moment (Ga, Mn)As

Electrical spin-transfer torque: current induced DW motion

Electrical spin-transfer torque: current induced DW motion v. DW =0 j. C “intrinsic” pinning j Antidamping STT Antidamping-like STT Zhang & Li, PRL 93, 127204 (2004) Vanhaverbeke & Viret, PRB 75, 024411 (2007)

Electrical spin-transfer torque: current induced DW motion v. DW < j. C j Antidamping STT Antidamping-like STT Field-like STT Zhang & Li, PRL 93, 127204 (2004) Vanhaverbeke & Viret, PRB 75, 024411 (2007)

Electrical spin-transfer torque: current induced DW motion v. DW > < j. C j Antidamping STT Antidamping-like STT Field-like STT Zhang & Li, PRL 93, 127204 (2004) Vanhaverbeke & Viret, PRB 75, 024411 (2007)

Steady-state carrier spin polarization torque QM averaging in non-equilibrium Electrical spin injection Non-relativistic STT Steady state Optical spin injection External OSTT antidamping-like torque M

Steady-state carrier spin polarization torque QM averaging in non-equilibrium Electrical spin injection Relativistic SOT Internal Steady state Optical spin injection (Ga, Mn)As OSOT M

Steady-state carrier spin polarization torque Linear response: eigenstates of H & non-equilibrium distribution Electrical drift and relaxation: broken inversion symmetry Relativistic SOT Internal Steady state Optical generation and relaxation

Paramagnets Spin-orbit Magnetic field of moving nucleus in electron‘s rest frame Spin-galvanic effect = SOT without acting on Electrical drift and relaxation: broken inversion symmetry Aronov, Lyanda-Geller, JETP ’ 89, Edelstein SSC ’ 90, Ganichev et al. Nature ‘ 02

Paramagnets Spin-orbit Magnetic field of moving nucleus in electron‘s rest frame Spin Hall effect

MRAM switching by in-plane current SHE spin-current non-relativistic STT Ralph, Buhrman, et al. , Science ‘ 12 Hall antidamping STT SHE in Pt acts as the external polarizer

MRAM switching by in-plane current attractive alternative to perp. current STT Conventional perpendicular current STT

MRAM switching by in-plane current attractive alternative to perp. current STT Conventional perpendicular current STT

Competing scenario: In-plane current swithing by relativitic SOT due to broken structural inversion symmetry at Co/Pt? Miron et al. , Nature ‘ 11

Ralph, Buhrman et al. : SHE Miron et al. : SOT -We see antidamping-like torque -We also see antidamping-like torque -SOT is field-like so we exclude it -SOT is field-like but maybe there is some antidamping-like SOT as well - non-relativistic STT in metals is dominated by the antidamping torque

Where could a comparable strength antidamping-like SOT come from?