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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.

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Infrared Spectroscopy at High Magnetic Field

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  1. Infrared Spectroscopy at High Magnetic Field Li-Chun “Richard” Tung & Yong-Jie Wang National High Magnetic Laboratory at FSU

  2. How to create high magnetic field • SC magnet up to 20T

  3. Resistive Magnet up to 35T from NHMFL report

  4. Hybrid Magnet up to 45T taken from NHMFL; “Why a hybrid Magnet system?”

  5. 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

  6. Why do we need high magnetic field • 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

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

  8. Systems can be studied by IR spectroscopy by Dr. D. N. Basov (UCSD)

  9. Outline • 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

  10. Fourier Transform IR spectroscopy wikipedia

  11. Interferogram

  12. A typical spectrum

  13. Magneto-IR transmission

  14. Putting the spectrum in the context

  15. New IR-active modes in CdMnTe QW In collaboration with Grzegorz Karczewski Institute of Physics, Polish Academy of Science

  16. Motivation • Large and tunable g-factor • Strong electron-phonon interaction • Strong exchange interaction • Full spin polarized state

  17. Giant and tunable g-factor Teran et. al. (2002)

  18. Spin-Flip Resonance Karczewski and Wang (2002)

  19. Sample • ne=0-2•1011 cm-2; mobility ~ 104 cm2/Vs

  20. Feature of the new modes

  21. Summary of the new modes

  22. CR vanishes above optical phonon frequency

  23. A LO-phonon assisted CR?

  24. 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.

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

  26. A Magnetic Phonon mode? The 125 cm-1 absorption line exists at B=0T.

  27. It’s behavior resembles that of the spin-dependent phonon mode. Though the magnetic ordering is now induced by applying magnetic field.

  28. 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

  29. Microwave induced ZRE Zudov et. al. (2003)

  30. Multi-photon Process Zudov et. al. (2006)

  31. 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

  32. MW-ZRE effect can be observed at high frequencies

  33. 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.

  34. MgB2 : two gap superconductor In collaboration with Xiaoxing Xi Physics, Pennsylvania State University

  35. 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)

  36. Preliminary data

  37. Carbon nanotubes In collaboration with Sonal Brown, Jinbo Cao and Jan Musfeldt Chemistry, University of Tennessee

  38. Mini-gap in Carbon nanotubes Akima et. al. (2006) Ouyang et. al. (2001)

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

  40. Aligned Carbon nanotubes

  41. Graphene In collaboration with Erik Henriksen, Zhigang Jiang , Philip Kim and Horst Stormer Physics, Columbia University

  42. Massless Dirac Fermion in Graphene NHMFL reports (2006)

  43. Transport properties of graphene Zhang et. al. (2005)

  44. About graphene • Unique Dirac point • Change of selection rule • Room temperature quantum Hall effect Gusynin et. al. (2006)

  45. What can IR spectroscopy do? • Optical investigation can survey over individual Landau level transitions • Exploring low energy transitions Gusynin et. al. (2006)

  46. 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)

  47. IR facilities available at NHMFL-FSU • 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 …

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