Y. C. Chang’s Research Group [▼cv.html ]


Welcome to my website. 

I am an emeritus professor of the Physics Dept., University of Illinois at Urbana-Champaign (UIUC),

and an emeritus research fellow at the Research Center for Applied Sciences, Academia Sinica.

Currently, I am an adjunct professor at Dept. of Physics, National Cheng Kung University, Tainan, Taiwan.

I received a bachelor's degree in physics from National Cheng-Kung University in Taiwan in 1974

and a Ph.D. in physics from the California Institute of Technology in 1980.

I joined the Department of Physics, UIUC in 1980 as a visiting assistant professor and became a full professor in 1991.

In 2005 I joined Research Center for Applied Sciences, Academia Sinica as a director (till 2012) and a distinguished research fellow (till 2022).

Our current research interests include

  1. Exploring intriguing physical phenomena related to excitons interacting with surrounding free carriers

from the strongly correlated phase (in low density) to the Fermi-liquid phase (in high density).

  1. Development of a highly efficient geometry-adapted Green-function method for computing

the light scattering effects from three-dimensional micro- and nano-structures for applications in nanophotonics.


Research areas:

Developing novel theoretical methods for investigating electronic, optical, and transport properties of semiconductors

and low-dimensional systems such as quantum wells, nanostructures and layered materials.

Exploring intriguing physical phenomena related to excitons interacting with surrounding free carriers from

the strongly correlated phase (in low density) to the Fermi-liquid phase (in high density). [R1, R2, R3, R4, R7]

Our research topics include:

  • exciton condensation, AC Stark phenomena;

  • magnetic multilayers and giant magnetoresistance;

  • photonic crystals and cavities, nanophotonics, and biosensing via plasmonic nanostructures [R5]

  • optical metrology of semiconductor thin films, gratings and nano/microstructures

  • quantum transport properties, single-photon generators, and spintronics [R6]

  • device modeling on infrared detectors, semiconductor lasers and modulators, and resonant tunneling diodes.



Representative papers

The representative publications (click the R to link):

R1 Y. C. Chang*, S. Shiau, M. Combescot, Phys. Rev. B 98, 235203 (2018). ▲36

R2 E. Liu, J. van Baren, Z. Lu, T. Taniguchi, K. Watanabe, D. Smirnov, Y. C. Chang*, C. H. Lui*, Nature Communications 12, 6131 (2021). ▲20

R3 E. Liu, E. Barré, J. van Baren, M. Wilson, T. Taniguchi, K. Watanabe, Y. Cui, N. M. Gabor, T. F. Heinz, Y. C. Chang*, C. H. Lui*, Nature 594, 46 (2021). ▲45

R4 M. M. Altaiary, E. Liu, C.-T. Liang, F.-C. Hsiao, J. van Baren, M.Willson, A. Shi, T. Taniguchi, K. Watanabe, N. M. Gabor, Y.-C. Chang*, C. H. Lui*, Nano Letters22, 1829 (2022). ▲7

R5 C.H. Chien, S. H. Wu, T. H. B. Ngo, Y. C. Chang*, Phys. Rev. Applied (Letter) 11, 051001 (2019). ▲9

R6 D. M.-T. Kuo, and Y. C. Chang*, Phys. Rev. Lett. 99, 086803 (2007). ▲39

R7 I. E. Perakis and Y. C. Chang*, Phys. Rev. B 47, 6573-6584 (1993). ▲12

R8 Y. C. Chang*, Phys. Rev. B 37, 8215 (1988). ▲130

R9 S.-F. Ren, H. Chu, and Y. C. Chang*, Phys. Rev. Lett. 59, 1841-4 (1987). ▲58

R10 Band Mixing in Semiconductor Superlattices, J. N. Schulman and Y. C. Chang, Phys. Rev. B 31, 2056 (1985). ▲264

R11 Theory of Line Shapes of Exciton Resonances in Semiconductor Superlattices, H. Chu and Y. C. Chang*, Phys. Rev. B 39, 10861-71 (1989). ▲72

R12 Y. C. Chang*, J. N. Schulman, G. Bastard, Y. Guldner, M. Voos, Phys. Rev. B 31, 2557 (1985). ▲126


Research achievements

I have made contributions to theoretical explanations and predictions for phenomena related to electronic materials

important to the industry. An important early contribution was the finding of the band-mixing effect [R10] in the excitation spectra

of semiconductor quantum wells and superlattices and the development of a new theoretical technique to calculate

the optical signal of complicated lineshapes of Fano resonances related to discrete excitonic states coupled with continua

from other subband-to-subband transitions in semiconductor quantum wells [R11]

We developed the effective bond-orbital models (EBOM) for low-dimensional semiconductors, which becomes a popular technique

for modeling the electronic structures and optoelectronic properties in heterostructures and nanostructures today [R8]

We have elucidated the electronic and acoustic properties of artificially structured materials and the behavior of optical phonons

in superlattices and pointed out the angular anisotropy and interface modes of vibrational states in semiconductor superlattices [R9]

In 1985, we pointed out the existence of quasi-interface states in HgTe-CdTe superlattices due to the sign reversal

of effective mass from HgTe to CdTe across the interface that was later identified as the topologically protected state [R12]


Preliminary results of ongoing research

Currently, we are developing a semi-empirical pseudopotential model (SEPM) for two-dimensional (2D) materials with planar basis functions.

The semi-empirical pseudopotentials (SEPs) are parametrized model potentials that mimic the self-consistent local potentials obtained from

the first-principles calculations based on density functional theory (DFT).

It allows us to describe the electronic properties of 2D materials accurately while reducing computational effort.

The SEPM has been successfully applied to graphene and armchair graphene nanoribbons [doi.org/10.3390/nano13142066].

The SEPM can be conveniently applied to moiré superlattices made of twisted bilayer transitional metal dichalcogenides (TMDCs).

Examples for best-fit SEPs for monolayer WSe2 are shown here [▼SEP.html ]


Recent publications (2019-2023) [▼ recentpubs.html ]


Highly cited papers [▼highlycited.html ]


Group Members

  • Shiue-Yuan Shiau, Research Center for Applied Sciences, Academia Sinica, Taipei, 115, Taiwan. E-mail:  shiau.sean@gmail.com

  • Raj Kumar Paudel, Research Center for Applied Sciences, Academia Sinica, Taipei, 115, Taiwan. E-mail:  rajupdl6@gate.sinica.edu.tw


Collaborators

  • Monique Combescot and François Dubin, Sorbonne Université, CNRS, Institut des NanoSciences de Paris, 75005-Paris, France.

  • Chun Hung Lui − Department of Physics and Astronomy, University of California, Riverside, California 92521, United States; Email: joshua.lui@ucr.edu

  • H.-C. Hsu, Department of Photonics, National Cheng Kung University, Tainan 701, Taiwan; E-mail: hsuhc@mail.ncku.edu.tw

  • Chi Chen, Research Center for Applied Sciences, Academia Sinica, Taipei, 115, Taiwan; E-mail: chenchi@gate.sinica.edu.tw

  • Chung-Yuan Ren, Department of Physics, National Kaohsiung Normal University, Kaohsiung 824, Taiwan; E-mail: cyren@nknu.edu.tw

  • Fu-Chen Hsiao, Department of Electrical and Computer Engineering, NC State University, Raleigh, NC 27606, United States; E-mail: fhsiao3@illinois.edu 

  • C.-H. Chien, Institute of Lighting and Energy Photonics National Yang Ming Chiao Tung University, Tainan 711, Taiwan; E-mail: pokky@gmail.com