Transcript Infrared Spectroscopy at High Magnetic Field

Infrared Spectroscopy
at
High Magnetic Field
Li-Chun “Richard” Tung & Yong-Jie Wang
National High Magnetic Laboratory at FSU
How to create high magnetic field
• SC magnet up to 20T
Resistive Magnet up to 35T
from NHMFL report
Hybrid Magnet up to 45T
taken from NHMFL; “Why a hybrid Magnet system?”
Even higher field
• Pulse field facility up to 100T (NHMFL-LANL)
• Sing-turn magnet up to 220T
Destructive method
collapsing the magnet coil or magnet itself;
up to 1000T
Why do we need high magnetic
field
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Couple to the spins
Destroy or settle the correlation
Resonance phenomena
Localize the electrons lB(nm)=25.6/(B1/2)
Reduce the screening effect
Break the time reversal symmetry
At high magnetic field,
they fly…….
Systems can be studied by IR
spectroscopy
by Dr. D. N. Basov (UCSD)
Outline
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Fourier Transform IR spectroscopy
New IR-active modes in CdMnTe QW
MW-ZRE in 2D electron gas system
Carbon nanotubes
MgB2 two gap superconductor
Graphene
IR facilities available at NHMFL-FSU
Fourier Transform IR
spectroscopy
wikipedia
Interferogram
1
[1  cos(kx)];
2
1
J (k ) T (k )  2 Fc [ I ( x)  I (0)]
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I k ( x)  J (k ) T (k )
A typical spectrum
Magneto-IR transmission
Putting the spectrum in the
context
New IR-active modes in CdMnTe
QW
In collaboration with
Grzegorz Karczewski
Institute of Physics, Polish Academy of
Science
Motivation
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Large and tunable g-factor
Strong electron-phonon interaction
Strong exchange interaction
Full spin polarized state
Giant and tunable g-factor
Teran et. al. (2002)
Spin-Flip Resonance
Karczewski and Wang (2002)
Sample
• ne=0-2•1011 cm-2; mobility ~ 104 cm2/Vs
Feature of the new modes
Summary of the new modes
CR vanishes above optical
phonon frequency
A LO-phonon assisted CR?
Ruling out intra-Mn transition
• The intra-Mn transitions from Mn:3d5 are
either too high (> 1000cm-1) or too low
(~2cm-1; splitting due to spin-orbital
couplings)
• Even for the intra-Mn transitions, their
energies should still be magnetic-field
dependent.
• The intensity of 125cm-1 does not
increase with Mn concentration
accordingly. From 0.84% to 3.9%, the
intensity at the same field are roughly the
same.
Are M1 and M2 originate from TO
and LO phonon frequency?
A Magnetic Phonon mode?
The 125 cm-1 absorption line exists at B=0T.
It’s behavior resembles that of
the spin-dependent phonon mode.
Though the magnetic ordering is now induced by
applying magnetic field.
MW-ZRE in 2D electron gas
system
In collaboration with
Chiangli Yang and Rui-Rui Du
Physics and astronomy, Rice University
Horst Stormer
Physics, Columbia University
Microwave induced ZRE
Zudov et. al. (2003)
Multi-photon Process
Zudov et. al. (2006)
Motivation
• With the helps of BWO and FIR laser, we
can extend the frequency range to several
THz.
• IR spectroscopy to observe the absorption
of the photons
MW-ZRE effect can be observed
at high frequencies
In the future
• Increase the intensity by using FIR Laser
and setting the BWO at a much closer
position.
New transmission/transport probe
• Capable of measuring both simultaneously
at 300mK up to 31T.
• IR frequency range from 10cm-1 to
10,000cm-1.
MgB2 : two gap superconductor
In collaboration with
Xiaoxing Xi
Physics, Pennsylvania State University
MgB2
TC ~ 39K
Two gaps:
2-D sigma-band gap ~ 7.2 meV
3-D pi-band gap ~ 24 meV
Hc2 ~ 25T
Ortolani et. al. (2005)
Preliminary data
Carbon nanotubes
In collaboration with
Sonal Brown, Jinbo Cao and Jan Musfeldt
Chemistry, University of Tennessee
Mini-gap in Carbon nanotubes
Akima et. al. (2006)
Ouyang et. al. (2001)
Bucket paper (tubes in random
shape, size, and orientation)
Aligned Carbon nanotubes
Graphene
In collaboration with
Erik Henriksen, Zhigang Jiang , Philip Kim
and Horst Stormer
Physics, Columbia University
Massless Dirac Fermion in
Graphene
NHMFL reports (2006)
Transport properties of graphene
Zhang et. al. (2005)
About graphene
• En  sgn( n)c~ 2eB n
• Unique Dirac point
• Change of selection rule
• Room temperature quantum Hall effect
Gusynin et. al. (2006)
What can IR spectroscopy do?
• Optical investigation can survey over
individual Landau level transitions
• Exploring low energy transitions
Gusynin et. al. (2006)
Some results
• B1/2 dependence
• -1 -> 2 (-2 -> 1) LL transition
• single piece graphene
• with device
• doped Si substrate
• 100 cm-1 to 3000 cm-1
• possible excitonic gap
Sadowski et. al. (2006)
IR facilities available at NHMFLFSU
• FT-IR interferometers and FIR lasers
• IR transmission up to 35T in both of
Faraday and Voigt configuration down to
3He temperature
• IR reflection up to 31T in Faraday
configuration
and more …