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Pauli spin susceptibility in 2D electronsystem of (111) Si MOSFET.
Cryoconference 2010
Kapustin Aleksandra,b, A.A. Shashkina, V.T. Dolgopolova,M. Goiranb, H. Rakotob and Z.D. Kvonc
a Institute of Solid State Physics, Russian Academy of Science, Chernogolovka, Moscow region, 142432 Russia.
b Laboratoire National des Champs Magnetique Pulsees,31400 Toulouse,France.c Institute of Semiconductor Physics, Russian Academy of Science, Siberian branch, Novosibirsk, Russia.
Si MOSFETs and regime of strongelectron-electron interaction.
Ec≫E
F
Si
rs= 1/a
B(πn
s)1/2
Interaction parameter:
strong interaction limit:
in 2D systems
Si(111) and Si(100): comparison
Si(100) Si(111)
mc=(m
xm
y)1/2
gv (theory)
y
x
0.19me
0.358me
2 6
Si(111): higher values EC/E
F ,than in Si(100),
are expected at the same electron concentration.
Si(111)
Results of our previous experiments with Si(111): valleydegeneracy g
v=2 and growth of effective electron mass.
Si(111)
Si(100)
similar growth of mass in Si(111),as in Si(100),vs. parameter r
s,
characterizing interaction
T=0.03K 0.12 0.2 0.3 0.38 0.47 0.55 0.62 0.75
Δν =4 gv=2 in our Si(111)
small B fields:
Si(111)
Si MOSFET in parallel magnetic field B||: another way
to probe interaction effects.
ρ(B)/ρ(B=0)=f(ξ)
Si(111) MOSFET
ξ is the degree ofspin polarization
initial regions of MR curvesfor different concentrations n
s
Bsat
=Bp- field of full spin polarization
small B fields: M=χBχ-Pauli spin susceptibilityξ=χB/μ
Bn
s=Δ
z/2E
F(B=0)
magnetoresistance(MR) in B||
Corresponding MR theory: V.T. Dolgopolov, A. GoldJETP Letters vol. 71, p.42 (2000) χ∝gm is determined by
interaction effects
Measuring Pauli spin susceptibility in a Si(111) MOSFET
ξ = B/Bχ
ρ /ρ(0) is a universal function f(ξ)
Bχ ∝1/χ
if ξ(B) is linear up to ξ=1,then B(ξ=1)=B
χ
small B fields:
i.e. Bχ is a full spin poralization
determined fromPauli spin susceptibility
used for Bχnormalization
field,
Si(111)
Si(111)
1.Bχ(n
s) corresponds to growing χ
Bχ , calculated using,
mass values,measured in B ┴
dashed line:
2. MR saturation occurs earlier, than expected from χ , measured in weak B fields
Bsat
<Bχ
Si(111)
Sharp increase of χ ,measured in weak B fields,and nonlinear ξ(B) dependence in large B fields.
ξ(B)- is nonlinear (sharp bend)
Possible explanation of Bsat
<Bχ and nonlinear ξ(B)
:
filling of the upper subbands, separated by a gap Δ from the lower subbands.
Bsat
<Bχ
Si(111)
gives experimental evidence that in our Si(111)there is a valley splitting of Δ≈20K,which can explain g
v=2 seen in these samples.
Experimental results
1. In Si(111) Pauli spin susceptibility χ∝ gm growswith a decrease in electron concentration n
s due to interactions
This agrees with our earlier measurements of effectiveelectron mass m in these samples.
2.Full spin polarization is reached earlier, than expected from measurements of χ in small B. It may be explained by in-plane magnetic field induced filling of the upper subbands,corresponding to 2 (of total 6) valleys, which are emptyin B=0.
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