Infrared Spectroscopy Infrared Spectroscopy at at High Magnetic Field High Magnetic Field

Li-Chun “Richard” Tung & Yong-Jie WangLi-Chun “Richard” Tung & Yong-Jie Wang

National High Magnetic Laboratory at FSUNational High Magnetic Laboratory at FSU

How to create high magnetic fieldHow to create high magnetic field

• SC magnet up to 20TSC magnet up to 20T

Resistive Magnet up to 35TResistive Magnet up to 35T

from NHMFL report

Hybrid Magnet up to 45THybrid Magnet up to 45T

taken from NHMFL; “Why a hybrid Magnet system?”

Even higher fieldEven higher field

• Pulse field facility up to 100T (NHMFL-LANL)Pulse field facility up to 100T (NHMFL-LANL)• Sing-turn magnet up to 220TSing-turn magnet up to 220T

Destructive methodDestructive method

collapsing the magnet coil or magnet itself;collapsing the magnet coil or magnet itself;

up to 1000Tup to 1000T

Why do we need high magnetic fieldWhy do we need high magnetic field

• Couple to the spinsCouple to the spins• Destroy or settle the correlationDestroy or settle the correlation• Resonance phenomenaResonance phenomena

• Localize the electrons Localize the electrons llBB(nm)=25.6/(B(nm)=25.6/(B1/21/2))

• Reduce the screening effectReduce the screening effect• Break the time reversal symmetryBreak the time reversal symmetry

At high magnetic field,At high magnetic field, they fly……. they fly…….

Systems can be studied by IR Systems can be studied by IR spectroscopyspectroscopy

by Dr. D. N. Basov (UCSD)

OutlineOutline

• Fourier Transform IR spectroscopyFourier Transform IR spectroscopy• New IR-active modes in CdMnTe QWNew IR-active modes in CdMnTe QW• MW-ZRE in 2D electron gas systemMW-ZRE in 2D electron gas system• Carbon nanotubesCarbon nanotubes

• MgBMgB22 two gap superconductor two gap superconductor

• Graphene Graphene • IR facilities available at NHMFL-FSUIR facilities available at NHMFL-FSU

Fourier Transform IR spectroscopyFourier Transform IR spectroscopy

wikipedia

InterferogramInterferogram

)]0(2

1)([2)()(

)];cos(1[2

1)()()(

IxIFkTkJ

kxkTkJxI

c

k

A typical spectrumA typical spectrum

Magneto-IR transmissionMagneto-IR transmission

Putting the spectrum in the contextPutting the spectrum in the context

New IR-active modes in CdMnTe QWNew IR-active modes in CdMnTe QW

In collaboration withIn collaboration with

Grzegorz KarczewskiGrzegorz Karczewski

Institute of Physics, Polish Academy of ScienceInstitute of Physics, Polish Academy of Science

MotivationMotivation

• Large and tunable g-factorLarge and tunable g-factor• Strong electron-phonon interactionStrong electron-phonon interaction• Strong exchange interactionStrong exchange interaction• Full spin polarized state Full spin polarized state

Giant and tunable g-factorGiant and tunable g-factor

Teran et. al. (2002)

Spin-Flip ResonanceSpin-Flip Resonance

Karczewski and Wang (2002)

SampleSample

• nnee=0-2=0-2•10•101111 cm cm-2-2; mobility ~ 10; mobility ~ 1044 cm cm22/Vs/Vs

Feature of the new modesFeature of the new modes

Summary of the new modesSummary of the new modes

CR vanishes above optical phonon CR vanishes above optical phonon frequencyfrequency

A LO-phonon assisted CR?A LO-phonon assisted CR?

Ruling out intra-Mn transitionRuling out intra-Mn transition

• The intra-Mn transitions from Mn:3dThe intra-Mn transitions from Mn:3d55 are are either too high (> 1000cmeither too high (> 1000cm-1-1) or too low ) or too low (~2cm(~2cm-1-1; splitting due to spin-orbital ; splitting due to spin-orbital couplings)couplings)

• Even for the intra-Mn transitions, their Even for the intra-Mn transitions, their energies should still be magnetic-field energies should still be magnetic-field dependent.dependent.

• The intensity of 125cmThe intensity of 125cm-1-1 does not increase does not increase with Mn concentration accordingly. From with Mn concentration accordingly. From 0.84% to 3.9%, the intensity at the same 0.84% to 3.9%, the intensity at the same field are roughly the same.field are roughly the same.

Are M1 and M2 originate from TO Are M1 and M2 originate from TO and LO phonon frequency?and LO phonon frequency?

A Magnetic Phonon mode?A Magnetic Phonon mode?

The 125 cm-1 absorption line exists at B=0T.

It’s behavior resembles that of the It’s behavior resembles that of the spin-dependent phonon mode.spin-dependent phonon mode.

Though the magnetic ordering is now induced by applying magnetic field.

MW-ZRE in 2D electron gas systemMW-ZRE in 2D electron gas system

In collaboration withIn collaboration with

Chiangli Yang and Rui-Rui DuChiangli Yang and Rui-Rui Du

Physics and astronomy, Rice UniversityPhysics and astronomy, Rice University

Horst StormerHorst Stormer

Physics, Columbia UniversityPhysics, Columbia University

Microwave induced ZREMicrowave induced ZRE

Zudov et. al. (2003)

Multi-photon ProcessMulti-photon Process

Zudov et. al. (2006)

Motivation Motivation

• With the helps of BWO and FIR laser, we can With the helps of BWO and FIR laser, we can extend the frequency range to several THz.extend the frequency range to several THz.

• IR spectroscopy to observe the absorption of IR spectroscopy to observe the absorption of the photonsthe photons

MW-ZRE effect can be observed at MW-ZRE effect can be observed at high frequencieshigh frequencies

In the futureIn the future

• Increase the intensity by using FIR Laser and Increase the intensity by using FIR Laser and setting the BWO at a much closer position.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.

MgBMgB22 : two gap superconductor : two gap superconductor

In collaboration withIn collaboration with

Xiaoxing XiXiaoxing Xi

Physics, Pennsylvania State UniversityPhysics, Pennsylvania State University

MgBMgB22

TC ~ 39K

Two gaps:2-D sigma-band gap ~ 7.2 meV3-D pi-band gap ~ 24 meV

Hc2 ~ 25T

Ortolani et. al. (2005)

Preliminary dataPreliminary data

Carbon nanotubesCarbon nanotubes

In collaboration withIn collaboration with

Sonal Brown, Jinbo Cao and Jan MusfeldtSonal Brown, Jinbo Cao and Jan Musfeldt

Chemistry, University of TennesseeChemistry, University of Tennessee

Mini-gap in Carbon nanotubesMini-gap in Carbon nanotubes

Ouyang et. al. (2001)

Akima et. al. (2006)

Bucket paper (tubes in random Bucket paper (tubes in random shape, size, and orientation)shape, size, and orientation)

Aligned Carbon nanotubes Aligned Carbon nanotubes

GrapheneGraphene

In collaboration withIn collaboration with

Erik Henriksen, Zhigang Jiang , Philip Kim and Erik Henriksen, Zhigang Jiang , Philip Kim and Horst StormerHorst Stormer

Physics, Columbia UniversityPhysics, Columbia University

Massless Dirac Fermion in GrapheneMassless Dirac Fermion in Graphene

NHMFL reports (2006)

Transport properties of grapheneTransport properties of graphene

Zhang et. al. (2005)

About grapheneAbout graphene

• • Unique Dirac pointUnique Dirac point• Change of selection ruleChange of selection rule• Room temperature quantum Hall effectRoom temperature quantum Hall effect

nBecnEn 2~)sgn(

Gusynin et. al. (2006)

What can IR spectroscopy do?What can IR spectroscopy do?

• Optical investigation can survey over individual Optical investigation can survey over individual Landau level transitionsLandau level transitions

• Exploring low energy transitionsExploring low energy transitions

Gusynin et. al. (2006)

Some resultsSome results

Sadowski et. al. (2006)

• 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

IR facilities available at NHMFL-FSUIR facilities available at NHMFL-FSU

• FT-IR interferometers and FIR lasers FT-IR interferometers and FIR lasers • IR transmission up to 35T in both of Faraday IR transmission up to 35T in both of Faraday

and Voigt configuration down to and Voigt configuration down to 33He He temperaturetemperature

• IR reflection up to 31T in Faraday IR reflection up to 31T in Faraday configurationconfiguration

and more …