stm differential conductance of a pair of magnetic adatoms
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STM Differential Conductance of a Pair of Magnetic Adatoms. Outline Review of one-impurity results Setup of two-impurity problem Two-impurity results. Brian Lane, Kevin Ingersent, U. of Florida. Thanks Charles Taylor and the UF HPC staff. - PowerPoint PPT PresentationTRANSCRIPT
STM Differential Conductance of a Pair of Magnetic Adatoms
Brian Lane, Kevin Ingersent, U. of Florida
Outline Review of one-impurity results Setup of two-impurity problem Two-impurity results
Thanks
Charles Taylor and the UF HPC staff.
Brent Nelson and the UF Physics Computer Support staff.
Supported by NSF Grant DMR-0312939
Investigate competition between Kondo screening and magnetic ordering, which occurs in systems such as heavy fermions, small magnetic devices, and quantum dots. This competition can be studied using scanning tunneling microscopy (STM).
W. Chen, et al, Phys. Rev. B 60, 12 (1999)
Motivation for Study
Review of the one-impurity problem
impurity
STM tip
tc
td
Vd = hybridization between impurity and conduction electrons
td = matrix element for tunneling into discrete impurity state
tc = matrix element for tunneling into continuous surface state
Vd
non-magnetic metal
One-Impurity STM Results
Energies measured in units of ½-bandwidth D.DOS: (E) ~ (E+D)½
Fano line shape develops due to interference between tunneling paths.
G(V) vs. VVd = 0.18
-10-8-10-6-10-4 10-8 10-6 10-4
0.2
0.4
0.6
5.0
0.0
G(V) vs. V
eV/D
G(V
) (a
rb. u
nits
)
One-Impurity STM Results
STM with two impurities
impurity 1
STM tip
tc
td
Impurities are identical and separated by a distance R.
No direct tunneling between impurities.
STM tip is directly over one of the impurities (no direct tunneling into the other).
Now we have a Kondo effect and an RKKY interaction.
Vd
impurity 2
Vd
R
non-magnetic surface
IRKKY(R) (arb. units) vs. kFR
FM
AFM
|IRKKY|/TK(1-imp) measures the competition between the two effects.
4
sin 2 2 cos 2~
F F F
RKKY
F
k R k R k RI
k R
2-imp T*chi & d-spectral functionT vs. T/D
T
T/D
(E) ~ (E+D)½, Vd = 0.18
Effective TK is dropping as R decreases for the FM cases.
Impurity Spectral Density vs. /D
/D
Two-Impurity Thermodynamic and Spectral Results
10-15 10-10 10-5 10.0
0.1
0.2
0.3
0.4
10-510-10 1-10-5 -10-10-1
Two-Impurity STM ConductanceG(V) vs. V
td/tc = 0.1
eV/D
G(V
) (a
rb. u
nits
)
-10-5 -10-10 10-10 10-5
0.2
0.0
0.4
Two-Impurity STM ConductanceG(V) vs. V
td/tc = 0.4
eV/D
G(V
) (a
rb. u
nits
)
-10-5 -10-10 10-10 10-5
0.4
0.0
0.2
0.6
0.8
1.0
Conclusions The competition between Kondo screening and the RKKY
interaction is clearly revealed in the STM spectrum. For FM RKKY, the effective TK drops and the lowest
energy scale of the STM line shape decreases with R. For AFM RKKY, the STM spectrum remains featureless.
Future Work Include direct-exchange interaction between impurities. Vary tip position and tunnel from tip into both impurities. Compare with predictions from other methods (e.g.,
DMRG for R=0). Compare more closely with experiment.
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