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Nai-Chang Yeh

Professor of Physics, California Institute of Technology
Fletcher Jones Foundation Co-Director, Kavli Nanoscience Institute

Ph.D., Massachusetts Institute of Technology
B.Sc., National Taiwan University

Condensed matter experiments: correlated electronic systems, including high-temperature superconducting cuprates and iron-based compounds and novel magnetic oxides; spintronics; topological materials, including topological insulators and superconductors; physics and devices of low-dimensional systems such as graphene, carbon nanotubes and silicon nano-pillars; development and applications of scanning probe microscopy; nano-science and nano-technology; low-temperature phases of helium; development of superconducting cavity-stabilized oscillators.

Group Photo

From left to right, front row: Slobodan, Prof. Yeh, Jenelyn, Peter; back row: Marcus, Cameron, Andrew, Nils, and Kevin

Recent research highlights

Local quasiparticle density of states and Fourier transformed local density of states in YBa2Cu3O7-δ (Y-123).

Local density of states in Y-123 at H = 5T. Fourier transformed local density of states in Y-123 at H = 5T.

Left image: The LDOS modulations of Y-123 at H = 5T and 6 K over a (22 x 29) nm2 area, showing patterns associated with density-wave modulations and vortices (circled objects) for ω = (a) -9 meV ~ -Δ', (b) -23 meV ~ -ΔSC, (c) -33 meV ~ -VCO and (d) -53 meV. We note that the vortex contrasts are the most apparent at |ω| <~ ΔSC and become nearly invisible for |ω| >>VCO. The vanishing contrast at high energies may be due to the onset of Cu-O optical phonons (~ 50 meV for the cuprates) so that both the collective modes and quasiparticles become scattered inelastically. Right image: FT studies of the conductance maps of Y-123: |F(k,ω)| at H = 5T and ω = -12 meV. We identify three sets of ω- independent wave-vectors in addition to the reciprocal lattice constants and the (π,π) resonance: QPDW and QCDW along (π,0)/(0,π) and QSDW along (π,π), which are circled for clarity. For more information on the measurements in the hole-type cuprate Y-123, please see arxiv:0906.1776 and arxiv:0808.3016 [Europhys. Lett. 87, 37005 (2009)]. For more information on the vortex-state measurements in the infinite-layer electron-type cuprate La0.1Sr0.9CuO2 (La-112), please see arxiv:0809.0541 [Europhys. Lett. 85, 17004 (2009)]. For a recent review on unconventional low-energy excitations in cuprate superconductors, please see Int. J. Mod. Phys. B 23, 4543 - 4577 (2009).

Observation of Fermi-energy dependent unitary impurity resonances in a strong topological insulator Bi2Se3 with scanning tunneling spectroscopy.

Please see arxiv:arXiv:1201.5618 [Solid State Comm. 152, 747 (2012)] for more information.

Measurement of a sign-changing two-gap superconducting phase in electron-doped Ba(Fe1-xCox)2As2 single crystals using scanning tunneling spectroscopy.

Please see arxiv:1007.5086 [Phys. Rev. Lett. 106, 087004 (2011)] for more information.

Strain-induced pseudo-magnetic fields and charging effects in CVD-grown graphene.

Please see arxiv:1009.0081 [Surface Science 605, 16491656 (2011)] for more information.

Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganite La0.7Ca0.3MnO3.

Please see arxiv:1004.1448 [Phys. Rev. B 82, 13441 (2010)] for more information.

Conference Information:

June 23 -- June 27, 2014
The 8th Joint Meeting of Chinese Physicists Worldwide (OCPA8) (
The 8th Joint Meeting of Chinese Physicists Worldwide (Official Conference Poster).

Contact Information:

Professor Nai-Chang Yeh
120 Bridge
California Institute of Technology
MC 149-33
Pasadena, CA 91125
(626) 395-4313

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