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Range of materials or model systems 2D models with simple Rashba

Current Nanospin related theory topics in Prague in collaboration with Texas and Warsaw based primarily on Nottingham and Hitachi experimental activities. As. Ga. Mn. Range of materials or model systems 2D models with simple Rashba spin-orbit coupled bands.

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Range of materials or model systems 2D models with simple Rashba

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  1. Current Nanospin related theory topics in Praguein collaboration with Texas and Warsawbased primarily on Nottingham and Hitachi experimental activities

  2. As Ga Mn • Range of materials or model systems • 2D models with simple Rashba • spin-orbit coupled bands • Dilute-moment ferromagnetic • semiconductors: • still simple bands yet strongly • exchange and SO split • dilute moment – tunable, • weak dipolar fields, smaller • STT currents • Systems with complex bands • but room Tc: FeNi, CoFe, CoPt,….

  3. Technical issues • Analytical calculations (Rashba model) • k.p semiphenomenological modelling (typical for semiconductors) • extensive library of home-made routines • spd-tight-binding modelling (half way between phenomenological and ab initio) • home-made codes • Full ab initio heavy numerics (transition metals based structures) • standard full-potential libraries, home-made relativistic ab-initio codes • Conclusions derived from bulk band structures • total energy calculations, Boltzmann and Kubo transport equations • Device specific modeling • Landauer-Buttiker formalism

  4. majority _ _ _ FSO _ FSO I minority e.g. anomalous Hall effect V Extraordinary magnetoresistance (AHE/SHE, AMR, STT) Ordinary magnetoresistance: response in normal metals to external magnetic field via classical Lorentz force Extraordinary magnetoresistance: response to internal magnetization in ferromagnets via quantum-relativistic spin-orbit coupling B _ _ _ _ _ _ _ _ _ _ _ FL + + + + + + + + + + + + + I or anisotropic magnetoresistance V e.g. ordinary (quantum) Hall effect

  5. Intrinsic vs. extrinsic AHE in Rashba 2D systems Solvable analytically skew scattering side jump intrinsic group velocity semicalssical Boltzmann eq. distribution function quantum Kubo formula jump side int. skew sc.

  6. skew scattering term: - absent in 2DEG for two-band occupation - absent in 2DHG for any band occupation • extenting the study to: • 4-band spherical Kohn-Luttinger model spherical K-L model Rashba - full 6(multi)-band model of DMSs - ab initio band structures of metals Proposed experimental setup so far microscopic calculations of intrinsic AHE only in these systems

  7. ky kx Origin of non-crystalline and crystalline AMR in GaMnAs Boltzmann eq. in relax. time approximation 1st order Born approximation 4-band spherical Kohn-Luttinger model SO-coupling – spherical model FM exchange spiitting M 1/k (M) ~(k . s)2 ~Mx . sx ky kx M hot spots for scattering of states moving  M  R(M  I)> R(M || I) ky kx

  8. M current  M  ) ) current [110]  ) full 6-band Hamiltonian: non-crystalline and crystalline AMR spherical model: non-crystalline AMR only theory • explains sign of non-crystalline AMR • consistent with experimentally seen • increasing role of crystalline terms with • increasing compensation • large AMR dominated by crystalline terms • in ultrathin layers not explained by bulk theory exp.

  9. Ga py Mn As Mn px • Ferromagnetism mediated by As p-orbital-like band states: • basic SO coupling related symmetries similar to familiar GaAs, unchanged by MnGa • carriers with strong SO coupling and exchange splitting due to hybridization with MnGa d-orbitals • straightforward means for relating intuitive physical pictures with microscopic calculations • compare with ferro metals: model of scattering of non-SO-coupled non-exchange-split s-state • carriers to localized d-states  difficult to match with ab initio theories with mixed s-d carriers

  10. Strain and doping-depent magnetocrystalline anisotropy macroscopic elastic theory simulations of strains GaMnAs microscopic magneto- crystalline anisotropies

  11. New device functionalities and new opportunity for exploring the rich phenomenology of magnetocrystalline anisotropies in (Ga,Mn)As

  12. Close relatives to GaMnAs with new degrees of freedomn-type DMSs, higher Tc,… III = I + II  Ga = Li + Zn • GaAs and LiZnAs are twin semiconductors • Prediction that Mn-doped are also twin ferromagnetic semiconductors • No limit for Mn-Zn (II-II) substitution • Independent carrier doping by Li-Zn • stoichiometry adjustment Limited confidence in ab initio calc. Reasonable confidence when comparing to GaMnAs bench-mark material

  13. L EF As p-orb. Ga s-orb. As p-orb. Electron mediated Mn-Mn coupling in n-type Li(Zn,Mn)As similar to hole mediated coupling in p-type (Ga,Mn)As Tc~

  14. Family of I-II-V hosts

  15. theoretical exploration of I-II-V’s  I-Mn-V’s  I-(II,Mn)V DMSs • MOCVD growth of the most promising theory candidates • MBE growth to achieve better stoichiometry control for the promising MOCVD materials

  16. MnI formation in mixed (Al,Ga)As and Ga(As,P) higher in (Al,Ga)As and Ga(As,P) than in GaAs smaller interstitial space only in Ga(As,P) Less interstitials in Ga(As,P) more interstitials in (Al,Ga)As

  17. L EF As p-orb. Ga s-orb. As p-orb. n-type AlAs with int. Mnonly electrons can mediate FM coupling for both subst. and int. Mn Comparable Tc to n-type hosts with substitutional Mn moments

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