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Department of Physics

Ahn, Keun Hyuk

Contact Info
Title: Associate Professor
Email: kenahn@njit.edu
Office: 483 Tiernan Hall
Phone: 973-596-5227
Dept: Physics
Webpage: http://web.njit.edu/~kenahn/

About Me

Community Outreach ProgramJuly-August 2007 American Chemical Society Project SEED

Title: Studying materials with computersParticipants: High-school students

Site: New Jersey Institute of TechnologyPurpose: Providing high school students with research experience

Program website

Education

1994-2000 The Johns Hopkins University;Ph. D. in PhysicsThesis: Theory of colossal magnetoresistive perovskite manganites.  Advisor: Prof. A. J. Millis (now at Columbia University)

1992-1994 Seoul National University, South Korea;M. S. in PhysicsThesis: The three-flavor MSW effect and its application to the cosmologically decoupled neutrinos.  Advisor: Prof. J. E. Kim

1988-1992 Seoul National University, South Korea;B. S. in PhysicsThesis: On the linearity of the transformation in special relativity

Honors and Professional Service

  • Graduation with honors, Seoul National University, Seoul, South Korea, 1992
  • Honor prize, Seoul National University, Seoul, South Korea, 1988
  • Invited speaker at 2005 Magnetism and Magentic Materials Conference
  • Invited speaker at 2005 American Physical Society March Meeting
  • Referee for Phys. Rev. Lett., Appl. Phys. Lett. and Phys. Rev. B (5 papers per year since 1999).
  • Reviewer of proposals for Department of Energy
  • Providing comments for Phys. Rev. Focus (http://focus.aps.org/story/v15/st15).

Course Website

Current course (Fall 2009)

Physics 105 Section 001 (Mon 4-5:25 /Thr 10-11:25) and Section 003 (Mon 4-5:25/Thr 11:30-12:55)

 

Pervious courses

Spring 2009: Physics 105 Section 006 and 008

Fall 2008: Physics 105 Section 011

Spring 2008: Physics 105 Section 006

Fall 2007: Physics 105 Section 013

Spring 2007: Physics 105 Section 006

 

Courses I Teach

GENERAL PHYSICS
INDEPENDENT STUDY
DOCT DISSERTATION & RES
DOCT DISSERTATION & RES

Research Interests

Theoretical Condensed Matter Physics (Theoretical physics about materials in solid states) 

Research Topics

  • Colossal magnetoresistive manganites
  • Symmetry-based atomic scale theory of lattice distortions
  • Multiphase coexistence in manganites
  • Ultrafast optical response of materials
  • Ultrafast dynamics of non-equilibrium systems
  • Spin current transport
  • X-ray spectroscopy of strongly correlated materials

 


Selected Publications

Publications in Nature / Phys. Rev. Lett. / Phys. Rev. B / Appl. Phy. Lett.

21. Dynamics and spectral weights of shake-up valence excitations in transition metal K-edge resonant inelastic x-ray scattering.  K. H. Ahn, A. J. Fedro, and M. van Veenendaal, Phys. Rev. B 79, 045103 (2009).

 

20. Infrared-active excitations related to Ho3+ ligand-field splitting at the commensurate-incommensurate magnetic phase transition in HoMn2O5A. A. Sirenko, S. M. O¡¯Malley, K. H. Ahn, S. Park, G. L. Carr, and S-W. Cheong, Phys. Rev. B 78, 174405 (2008).

 

19. Epitaxial checkerboard arrangement of nanorods in ZnMnGaO4 films studied by x-ray diffraction.  S. M. O´Malley, P. L. Bonanno, K. H. Ahn, A. A. Sirenko, A. Kazimirov, S. Park, and S-W. Cheong, Phys. Rev. B 78, 165424 (2008).

 

18. Nematic domains and resistivity in an itinerant metamagnet coupled to phonons.  H. Doh, Y. B. Kim, and K. H. Ahn, Phys. Rev. Lett. 98, 126407 (2007).

 

17. Observation of strain and temperature induced changes in the band structure of thin La0.8MaO3-d films.  T. A. Tyson, Q. Qing, M. A. DeLeon, C. Dubourdieu, L. Fratila, Y. Q. Cai, and K. H. Ahn, Appl. Phys. Lett. 90, 101915 (2007)

 

16. Electronic properties of structural twin and antiphase boundaries in materials with strong electron-lattice couplings.  K. H. Ahn, T. Lookman, A. Saxena and A. R. Bishop, Phys. Rev. B 71, 212102 (2005).

15. Coherent optical and acoustic phonon generation correlated to charge ordering phase transition in La1-xCaxMnO3.  D. Lim, V. K. Thorsm©ªlle, R. D. Averitt, Q. X. Jia, K. H. Ahn, M. J. Graf , S. A. Trugman and A. J. Taylor, Phys. Rev. B 71, 134403 (2005).

 

14. Strain-induced metal-insulator phase coexistence in perovskite manganites.  K. H. Ahn, T. Lookman and A. R. Bishop, Nature 428, 401 (2004). [pdf file]. (Number of citations >150)  [Featured as ¡°News & Views¡± in Nature Materials 3, 207 (2004) [pdf file] by N. Mathur and P. Littlewood, and in the Los Alamos News Bulletin. Invited for 2005 APS March Meeting and 2005 Magnetism and Magentic Materials Conference.]

 

13. Ultrafast quasiparticle relaxation dynamics in normal metals and heavy fermion materials.  K. H. Ahn, M. J. Graf, S. A. Trugman, J. Demsar, R. D. Averitt, J. L. Sarrao and A. J. Taylor, Phys. Rev. B 69, 045114 (2004). [Included in Virtual Journal of Ultrafast Science 3, Issue 2 (2004)]

 

12. Strain selection of charge and orbital ordering patterns in half-doped manganites.  M. J. Calderón, A. J. Millis and K. H. Ahn, Phys. Rev. B 68 - Rapid Comm., 100401 (2003).

 

11. Atomic scale lattice distortions and domain wall profiles.  K. H. Ahn, T. Lookman, A. Saxena and A. R. Bishop, Phys. Rev. B 68, 092101 (2003).

 

10. Elasticity-driven nanoscale electronic structure in superconductors.  J.-X. Zhu, K. H. Ahn, Z. Nussinov, T. Lookman, A. V. Balatsky and A. R. Bishop, Phys. Rev. Lett. 91, 057004 (2003). 

9. Quasiparticle relaxation dynamics in heavy fermion compounds.  J. Demsar, R. D. Averitt, K. H. Ahn, M. J. Graf, S. A. Trugman, V. V. Kabanov, J. L. Sarrao and A. J. Taylor, Phys. Rev. Lett. 91, 027401 (2003).  [Included in Virtual Journal of Ultrafast Science 2, Issue 8 (2003)]

 

8. Superconductivity in magnetically ordered CeTe1.82.  M. H. Jung, A. Alsmadi, H. C. Kim, Y. Bang, K. H. Ahn, K. Umeo, A. H. Lacerda, H. Nakotte, H. C. Ri and T. Takabatake, Phys. Rev. B 67, 212504 (2003).

 

7. Ground state properties of ferromagnetic metal/conjugated polymer interfaces.  S. J. Xie, K. H. Ahn, D. L. Smith, A. R. Bishop and A. Saxena, Phys. Rev. B 67, 125202 (2003).

 

6. Effects of the uniaxial strain in LaMnO3.  K. H. Ahn and A. J. Millis, Phys. Rev. B 64, 115103 (2001).

 

5. Effects of magnetic ordering on the anisotropy and temperature dependence of the optical conductivity in LaMnO3: a tight binding approach.  K. H. Ahn and A. J. Millis, Phys. Rev. B 61, 13545 (2000). (Number of citations > 30)

 

4. Optical conductivity of manganites: Crossover from Jahn-Teller small polaron to coherent transport in the ferromagnetic state.  M. Quijada, J. Černe, J. R. Simpson, H. D. Drew, K. H. Ahn, A. J. Millis, R. Shreekala, R. Ramesh, M. Rajeswari and T. Venkatesan, Phys. Rev. B 58, 16093 (1998). (Number of citations > 110)

 

3. Interplay of charge and orbital ordering in manganese perovskites.  K. H. Ahn and A. J. Millis, Phys. Rev. B 58, 3697 (1998). (Number of citations > 30)

 

2. Magnetic properties and colossal magnetoresistance of La(Ca)MnO3 materials doped with Fe.  K. H. Ahn, X. W. Wu, K. Liu and C. L. Chien, Phys. Rev. B 54, 15299 (1996). (Number of citations > 160)

 

1. Charge ordering and magnetoresistance in Nd1-xCaxMnO3 due to reduced double exchange.  K. Liu, X. W. Wu, K. H. Ahn, T. Sulchek, C. L. Chien and J. Q. Xiao, Phys. Rev. B 54, 3007 (1996). (Number of citations > 70)

Full list of publications