Spectrum of 2D semimetal based on HgTe quantum well in QHE mode

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Spectrum of 2D semimetal based on HgTe quantum
well in QHE mode

• D.A. Kozlov, Z.D. Kvon,
• N.N. Mikhailov, S.A. Dvoretskiy, V.T.
  Dolgopolov, E.V. Deviatov,
• J.C. Portal

Yekaterinburg - 2012
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Inverted spectrum in volume HgTe
Normal spectrum (GaAs, CdTe)
Inverted spectrum (HgTe)
Jls
EC s (l0) J1/2 j1/2
EC p (l1) J3/2
EV p (l1) J3/2
?g gt 0
?g ? - 0.35 ??
J3/2 j3/2 j1/2
EV s (l0) J1/2
J1/2 j1/2
EV p (l1) J1/2
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Spectrum of HgTe QW for different widths of QW

• Heterostructure

w (??)
2D Bands position vs QW depth
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First realization of 2D semimetal
T 0.2K
Grown heterostructure 20.5nm (013)-oriented
HgTe QW
First transport measurements
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Fitting magnetotransport using classical Drude
model for two-components gas
Eoverlap EFN EFP
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Gated sample 2DEG, 2DHG and 2D-semimetal
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Universal semimetal realization regardless of
quantum well orientation
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Cyclotron resonanceeffective mass dependence
We obtain 0.18m0 for holes and 0.0240.032m0 for
electrons. Effective mass is higher in semimetal
compared to 2DEG
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(112)- and (100)-oriented QWs spectrum
calculations
(112)
(100)
(112)- and (013)-oriented QWs have about 5meV
overlap energy and 2 holes valleys (100)-oriented
QW have about 1meV overlap energy and four holes
valleys
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QHE in semimetal
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Very simplified Landau levels picture
The only reliable parameter in this charts are
overlap energies about 5meV and 1.25meV for
(013)- and (100)-oriented QWs correspondingly. All
other parameters are invented from common reasons
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Experimental Landau maps
In both types of quantum wells we have
well-pronounced QHE regime. Main difference
between QWs is different overlap energy (less in
(100)-QW) and greater asymmetry between electron
and holes in (100)-QW
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Experimental Landau maps

1. Spin gaps are greater than cyclotron gaps
2. We could not observe valley degeneration in both
   QWs in transport
3. Landau levels in (013)-QW are more soft
   compared to (100)-QW

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Charge neutrality point in magnetic field and
edge states
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Capacity measurements
Csample CgCqw /(Cg Cqw)
?g geometrical capacity of insulator CQW q2
D quantum well capacity D density of states
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Capacity measurements

1. Capacity increase in semimetal state compared to
   2DEG state
2. Huge equivalent serial resistance at v 0
   compared to rxx in transport measurements

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Conclusions and questions

1. 2D semimetal with different energies of overlap
   has been investigated in QHE mode. They have both
   many common and different features.
2. Behaviour of resistivity tensor in QHE mode is
   determined by differential filling factor v ve
   vh
3. Landau levels chart are modified by fine energy
   tuning which strength depends from overlap energy
   between Ec and Ev

1. What is really happening on the edges?
2. Why are we not seeing valley degeneracy?
3. Why are we not seeing more peculiarities
   concerned with landau levels crossing?
4. and more, more and more questions