magnetic nanostructures f. j. himpsel, dept. of physics, uw-madison limits of data storage...
TRANSCRIPT
Magnetic Nanostructures
F. J. Himpsel, Dept. of Physics, UW-Madison
• Limits of Data Storage
• Magnetoelectronics
• One-Dimensional Structures on Silicon
SSSC Meeting, Irvine, Oct. 4, 2001
All of the information ... accumulated in all the books
in the world can be written … in a cube of material
1/200 inch wide.
Use 125 atoms to store one bit.
Richard Feynman
Caltech, December 29th, 1959
Smaller Bits Less Energy Stored Slower Readout
Use Highly-Parallel Readout
Array of Scanning Probes Array of Shift Registers
( Millipede, IBM Zrich ) ( nm m )
50 nm 10 nm particle
Magnetic Storage Media
600nm
17 Gbits/inch2 commercial
Hundreds of particles per bit
Single particle per bit !
Magnetic ForceMicroscopeImage (IBM)
Giant Magnetoresistance:
Spin-Polarized Tunneling:
Magnetoelectronics
Spin Currents instead of
Charge Currents
Filtering mechanisms
• Interface: Spin-dependent Reflectivity Quantum Well States
• Bulk: Spin-dependent Mean Free Path Magnetic Doping
Parallel Spin Filters Resistance Low
Opposing Spin Filters Resistance High
GMR and Spin - Dependent Scattering
High Resolution Photoemission
States near the Fermi level
determine magneto-transport
( 3.5 kT = 90 meV )
-10
-8
-6
-4
-2
0
2
4
XK
Ni
En
erg
y R
ela
tiv
e t
o E
F [
eV
]
0.7 0.9 1.1
k|| along [011] [Å-1 ]
Why Silicon ? Couple Nano- to MicroelectronicsUtilize Silicon Technology
Storage Media: 1 Particle (Atom) per BitAtomically Precise Tracks
Step Arrays as Templates: 2 - 80 nm
1 Kink in 20 000 Atoms
Emulate Lithography: CaF2 Masks Selective Deposition
Atomic Wires: Exotic Electrons in 1D
One-Dimensional Structures on Silicon
Si(111) 77
Control the step spacing
in units of
2.3 nm = 7 atom rows
Step Step
x - Derivative of the STM Topography
“Illumination from the Left Casting Shadows”
Hole Holon + Spinon
EF
Photoelectron
Spin - Charge Separation
in a One-Dimensional Metal
Zacher, Arrigoni, Hanke, and Schrieffer, PRB 57, 6379 (1998)
Spinon
Holon
EF =
Crossing at EF
Si(557)-Au
• Splitting persists at EF
• Electron count is even
Not spin charge separation
EFermi
Two degenerate orbitals ?
Bonding
Antibonding
E2E1
Tailoring the Electronic Structure
Electron count even,
two bands, metallic
Electron count odd,
one band, “gap”
stepped flat