Searching for Majorana fermions in semiconducting nano -wires

1. Searching for Majorana fermions in semiconducting nano-wires Pedram Roushan Peter O’Malley John Martinis Department of Physics, UC Santa Barbara BorzoyehShojaei Chris Palmstrøm Materials Department , UC Santa Barbara Roman Lutchyn Microsoft Station Q The 8th Capri Spring School on Transport in Nanostructures April 2012, Capri, Italy

2. Theoretical proposals on Majorana fermions Kitaev, Phys.-Usp. (2001) Fu & Kane, PRL (2008) Sau et al., PRL (2010) And more… for a review see: Alicea, arXiv:1202.1293v1

3. Majorana fermions in Josephson junctions Lutchyn et al., PRL (2010) Josephson Current Trivial Topological π 2π 3π 4π Flux (F)

4. Majorana fermions in Josephson junctions Lutchyn et al., PRL (2010) Josephson Current Resonance Amplitude Trivial Topological π 2π 3π 4π Flux (F) Frequency

5. The parameter space

6. The parameter space Non-helical EFermi Spin-orbit splitting

7. The parameter space Non-helical Non-helical EFermi EFermi Spin-orbit splitting

8. Molecular Beam Epitaxy grown quantum wells 50 nm AlSb 5 nm GaSb Cap 5 nm GaSb Cap 5 nm GaSb Cap 50 nm Al0.5Ga0.5Sb 5 nm Al0.5Ga0.5Sb 15 nm InAsQW 15 nm InAs QW 15 nm InAs QW 100 nm AlSb 20 nm AlSb 100 nm AlSb 10 x 2.5 nm GaSb / 2.5 nm AlSb S.L. 10 x 2.5 nm GaSb / 2.5 nm AlSb S.L. 10 x 2.5 nm GaSb / 2.5 nm AlSb S.L. 2000 nm GaSb 2000 nm AlSb 2000 nm AlSb 1000 nm GaSb 1000 nm GaSb S.I. (100) GaAs Substrate 100 nm GaAs 100 nm AlSb 500 nm GaAs 500 nm GaAs 10 nm AlAs S.I. (100) GaAs Substrate S.I. (100) GaAs Substrate

9. Measuring 2DEG parameters: mobility and concentration rsheet= 10 to 150 W/□ μe= 74,000 to 210,000cm2 / V∙s ne = 5x1011 to 3x1012 to cm2 l = 0.9 to 6 mm Iin Iout rxy=Vxy/ I rxx= Vxx/ I n =6 n =8 T = 60 mK

10. Measuring 2DEG parameters: Effective mass m*=0.039me Temperature (K) Theory: D. Shoenberg, Magnetic oscillations in metals. Cambridge university press (1984).

11. Magneto-resistance feasurement: Weak anti-localization Spin-orbit coupling •Rashba(a) • Dresselhaus(g) Lack of inversion symmetry Asymmetric quantum well

12. Measuring 2DEG parameters: Spin-orbit coupling a= 13±1 meV.Å g= 425±6 eV.Å3 Theory: Iordanskii et al., JETP Lett. (1994), Knap et al. PRB (1996), Lyanda-Geller PRL (1998) Experiment: Miller et al. , PRL (2003). Kallaheret al., PRB (2010). …

13. 2DEG Band structure parameters: EFermi kF=0.018 Å-1

14. 2DEG Band structure parameters: EFermi kF=0.018 Å-1

15. 2DEG Band structure parameters: EFermi kF=0.018 Å-1

16. Conclusion and outlook Come to UC Santa Barbara and visit us