Research Staff Member, IBM Research
Distinguished Research Chair Professor, National Taiwan University
Honorary Chair Professor, National Tsing Hua University
IBM T. J. Watson Research Center
Route 134, 1101 Kitchawan Road
Yorktown Heights, NY 10598 U.S.A.
Dr. Tsuei received his B.S. in 1960 from the National Taiwan University and both his M.S. (1963) and Ph.D. (1966) from the California Institute of Technology. After seven years on the faculty of Caltech, Dr. Tsuei joined IBM Thomas J. Watson Research Center in 1973 as a Research Staff Member and held several research manager positions in the Physical Sciences Department during the period of 1974 to 1993. Since 1993, he has returned to the position of Research Staff Member to devote his full time to the experiments of phase-sensitive tests of pairing symmetry in various superconductors and to the theoretical study of the microscopic mechanism responsible for high-temperature superconductivity in cuprates.
In the early stage of his career, he focused his effort on the study of electrical and magnetic properties of bulk non-crystalline conducting systems. He and his co-workers demonstrated the phenomena of collective flux pinning in amorphous superconductors and the existence of ferromagnetism in bulk glassy metallic alloys obtained with the technique of quenching from the liquid state. He also invented an in-situ process for making a multi-filamentary superconducting composite wire (known as a Tsuei wire). These inhomogeneous superconductors have been used as a model system for studying the superconducting proximity effect and percolation phenomena.
His recent research interests include: tricrystal experiments for the phase-sensitive determination of pairing symmetry in cuprate superconductors, half flux quantum states in d-wave Π-SQUIDs and large-scale arrays of Π-loops, quantum-dot arrays for simulating strongly correlated systems, and the microscopic pairing mechanism of high-temperature superconductivity.
Honors and Awards
- Distinguished Research Chair Professor, Department of Physics, National Taiwan University, 2007.
- Honorary Chair Professor, Department of Physics, National Tsing Hua University, since 2006.
- Elected Fellow of the American Association for the Advancement of Science, 2001.
- Asian American Dynamic Achievement Award, Organization of Chinese Americans, 2000.
- IBM Corporate Award, June 2000.
- Oliver E. Buckley Condensed Matter Physics Prize of the American Physical Society, for his work on pairing symmetry in high-temperature superconductors; co-recipient, 1998.
- Bodo von Borries Lectureship, University of Tuebingen, Germany, 1998.
- Invited Professor, Universit� Paris-Sud (Orsay, France), 1996 and 1997.
- Elected to the Academia Sinica (Academy of Sciences in Taiwan), 1996.
- IBM Innovation Achievement Award, 1995.
- Max Planck Research Prize, Max Planck Society and Alexander von Humboldt Foundation of Germany, 1992.
- Elected Fellow, American Physical Society, 1974.
- “Half-Integer Flux Quantization in Unconventional Superconductors”, C. C. Tsuei and J. R. Kirtley. Invited paper submitted for a book entitled "100 Years of Superconductivity", edited by H. Rogalla and P. Kes, for the celebration of the discovery of superconductivity by Kamerlingh Onnes in 1911.
- “Low Loss Superconducting Titanium Nitride Coplanar Waveguide Resonators”, Michael R. Vissers, Jiansong Gao, David S. Wisbey, Dustin A. Hite, Chang C. Tsuei, Antomio D. Corcoles, Matthias Steffen, David P. Pappas. To be published in Applied Physics Letters in 2011.
- “Ab initio Understanding of the Pseudogap in Cuprate High Temperature Superconductors via the Fluctuating Bond Model”, R. A. Nistor, G. J. Martyna, D. M. Newns, C. C. Tsuei and M. H. Mueser. To be published in Phys. Rev. B in 2011.
- “Integer and half-integer flux-quantum transitions in a niobium/iron-pnictide loop”, C. –T. Chen, C. C. Tsuei, M. B. Ketchen, Z. –A. Ren and Z. X. Zhao. Nature Physics 6, 260 (2010).
- C. C. Tsuei, “Ductile superconducting copper-base alloys,” Science 180, 57-58 (1973).
- C. C. Tsuei and H. Lilienthal, “Magnetization distribution in an amorphous ferromagnet,” Phys. Rev. B 13, 4899-4906 (1976).
- P. H. Kes and C. C. Tsuei, “Collective flux-pinning phenomena in amorphous superconductors,” Phys. Rev. Lett. 47, 1930-1934 (1981).
- C. C. Tsuei, D. M. Newns, C. C. Chi, and P. C. Pattnaik, “Anomalous isotope effect and van Hove singularity in superconducting Cu oxides,” Phys. Rev. Lett. 65, 2724-2727 (1990).
- C. C. Tsuei, J. R. Kirtley, C. C. Chi, Lock-See Yu-Jahnes, A. Gupta, T. Shaw, J. Z. Sun, and M. B. Ketchen, “Pairing symmetry and flux quantization in a tricrystal superconducting ring of YBa2Cu3O7-δ,” Phys. Rev. Lett. 73, 593-596 (1994).
- J. R. Kirtley, C. C. Tsuei, J. Z. Sun, C. C. Chi, Lock-See Yu-Jahnes, A. Gupta, M. Rupp, and M. B. Ketchen, “Symmetry of the order parameter in the high-Tc superconductor YBa2Cu3O7-δ,” Nature 373, 225-228 (1995).
- C. C. Tsuei, J. R. Kirtley, M. Rupp, J. Z. Sun, A. Gupta, M. B. Ketchen, C. A. Wang, Z. F. Ren, J. H. Wang, and M. Bhushan, “Pairing symmetry in single-layer tetragonal Tl2Ba2CuO6+δ superconductors,” Science 271, 329-332 (1996).
- C. C. Tsuei, J. R. Kirtley, Z. F. Ren, J. H. Wang, H. Raffy, and Z. Z. Li, “Pure dx2-y2 order parameter symmetry in the tetragonal superconductor Tl2Ba2CuO6+δ,” Nature 387, 481-483 (1997).
- J. R. Kirtley, C. C. Tsuei, and K. A. Moler, “Temperature dependence of the half-integer magnetic flux quantum,” Science 285, 1373-1375 (1999).
- C. C. Tsuei and J. R. Kirtley, “Pairing symmetry in cuprate superconductors,” Rev. Mod. Phys. 72, 969-1016 (2000).
- Hans Hilgenkamp, Ariando, Henk-Jan H. Smilde, Dave H. A. Blank, Guus Rujnders, Horst Rogalla, John R. Kirtley, and Chang C. Tsuei, “Ordering and manipulation of the magnetic moments in large-scale Π-loop arrays,” Nature 422, 50-53 (2003).
- C. C. Tsuei, J. R. Kirtley, G. Hammerl, J. Mannhart, H. Raffy, and Z. Z. Li, “Robust dx2-y2 pairing symmetry in hole-doped cuprate superconductors,” Phys. Rev. Lett. 93, 187004 1-4 (2004).
- J. R. Kirtley, C. C. Tsuei, Ariando, C. J. M. Verwijs, S. Harkema, H. Hilgenkamp, “Angle-resolved phase sensitive determination of the in-plane gap in YBa2Cu3O7-δ,” Nature Physics 2, 190-194 (2006).
- D. M. Newns and C. C. Tsuei, “Fluctuating Cu-O-Cu bond model of high-temperature superconductivity,” Nature Physics 3, 184-191 (2007).
- “Integer and half-integer flux-quantum transitions in a niobium/iron-pnictide loop”, C. –T. Chen, C. C. Tsuei, M. B. Ketchen, Z. –A. Ren and Z. X. Zhao. Nature Physics 6, 260 (2010).
- Phase-sensitive Determination of Pairing Symmetry in Cuprate Superconductors
An unambiguous determination of the pairing symmetry in cuprate superconductors represents an important step towards understanding the origin of high-temperature superconductivity. Before the advent of phase-sensitive pairing symmetry tests , the symmetry of pair wavefunctions in cuprates was a topic of intense debate for many years.
To definitively determine the order parameter symmetry, Tsuei designed and implemented a novel experiment  based on two macroscopic quantum phenomena: Josephson pair tunneling and fluxoid quantization. The experiment involves a c-axis epitaxial film consisting of three cuprate crystals with specially-chosen crystallographic directions. The three linear interfaces between the three crystals, which intersect at the tricrystal point, form grain boundary Josephson junctions. The tricrystal geometry was chosen by design such that for a dx2-y2-wave superconductor, there are an odd number of sign changes in the component of the pair wavefunction normal to the grain boundaries, and hence a net phase shift of Π in a superconducting loop circling the tricrystal meeting point. Based on the considerations of free energy and flux quantization , it has been shown that the magnetic flux threading through such a loop (termed Π-loop) is quantized in half-integral multiples of the flux quantum Φ0.
Tsuei and his co-workers Kirtley et al., using a high-resolution scanning SQUID microscope, made the first direct observation of the half-flux quantum effect in YBa2Cu3O7 (YBCO) in 1994 . The presence of a spontaneously generated half-flux quantum in the 3-junction ring centered at the tricrystal meeting point and the fact that there is no magnetic flux in the other three rings (as shown in the following figure) represent the first definitive evidence for dx2-y2-wave pairing symmetry in a cuprate superconductor. The original tricrystal experiment  was repeated and confirmed by Sugimoto et al. in 2002.
The tricrystal magnetometry method used in these pairing symmetry tests has the advantage over other phase-sensitive measurement techniques in that it is non-invasive, provides an in-situ diagnostic of sample inhomogeneity and flux trapping, and measures the quantized magnetic flux of the tricrystal samples in their ground state with no need for an externally applied transport current during the measurement. More details of the tricrystal pairing symmetry experiments can be found in a review article .
Tsuei, Kirtley, and co-workers, in a series of tricrystal experiments, have used the half-flux quantum effect as an unambiguous signature of the dx2-y2 order parameter symmetry in several optimally hole-doped and electron-doped cuprate superconductors [2-10]. These phase-sensitive pairing symmetry tests have also ruled out twinning, bi-layers, extended s-wave (including the g-wave) pairing, and magnetic spin-flip scattering as possible explanations for the observed half-integer flux quantum effect.
In the past, conventional (phase-insensitive) experiments have reported numerous conflicting results regarding the doping dependence of the gap symmetry in various high-temperature superconductors. Tsuei et al. have carried out a series of phase-sensitive tests using tricrystal experiments to provide evidence for dx2-y2 pairing symmetry in three different cuprate systems with doping levels ranging from underdoped, through optimal doping, to the overdoped regimes .
The data points shown in the figure above depict the doping range of the phase diagram tested with the tricrystal experiments, and the d-wave pair state was found in all cases studied. The solid curve is Tc as a function of doping concentration p (holes per CuO2 plane), as calculated with the well-established empirical formula of Presland et al. (1991).
The results of this work  clearly show that the dx2-y2 pair state is robust against a wide range of doping variations. Equally important, this work also rules out doping-induced time reversal symmetry broken pair states with (dx2-y2 + is) or (dx2-y2 + idxy) symmetry. In addition, another tricrystal experiment, in which we investigated the temperature dependence of the half-flux quantum effect, indicates that there is no change in the d-wave pairing symmetry of YBCO over the temperature range of 0.2K to 91K, the Tc of YBCO . The observation of d-wave pairing symmetry in cuprate superconductors having large variations in doping concentration and temperature emphasize the importance of the common origin of the robust d-wave pairing symmetry.
A novel tetracrystal Π/4-rotated wedge experiment by Tsuei et al.  has produced strong model-independent pair tunneling evidence for pure dx2-y2 order parameter symmetry in tetragonal single-layer Tl2Ba2CuO6+δ. The tetracrystal configuration was used for the realization of an all d-wave SQUID with a built-in Π-phase shift in the superconducting loop (hence the name Π-SQUID) . Using a ramp-type edge Josephson junction technique developed by Hilgenkamp et al. , the fabrication of periodic arrays of of 2x104 half-fluxons integrated on a single chip was demonstrated . The realization of Π-SQUIDs and Π-arrays has laid the foundation for developing d-wave superconductive electronics, including large-scale integrated quantum devices and circuits for potential applications in quantum computation.
As a consequence of the Cu-O chains in the crystal structure of YBCO, an admixed d+s pair state is allowed based on group theory. To determine the location of the nodes in the gap function of a (d+s)-wave superconductor such as YBCO, Kirtley, Tsuei and their co-workers  have recently carried out an angle-resolved phase-sensitive determination of the momentum dependence of the in-plane energy gap in YBCO by observing the presence and absence of the half-flux quantum effect in a series of 2-YBCO/Nb junction rings as a function of the junction angles with respect to the YBCO crystallographic axis. In this experiment, each ring contains two YBCO/Nb ramp-type edge junctions with the angle of one junction normal fixed relative to the YBCO a-axis, while the other junction angle is varied in intervals as small as half a degree from ring to ring. The magnetic flux state of these rings is monitored with a scanning SQUID microscope, and the results are displayed in the following figure.
The location of the transition between rings of no spontaneous flux and those of a half-flux quantum leads to the conclusion that the s to d gap ratio in optimally doped YBCO is less than 0.1, and that any imaginary component to the dx2-y2-wave gap, if present, is insignificantly small.
The establishment of dx2-y2–wave pairing symmetry has important implications for understanding high-temperature superconductivity. Spin-singlet pairing with dx2-y2 symmetry represents a well-defined prerequisite in all theoretical models of the high-Tc mechanism in cuprate superconductors. Recent studies on the low-energy quasiparticle excitations near the nodes of the d-wave energy gap have led to the prediction and confirmation of new effects in low-temperature properties such as specific heat and thermal conductivity. These studies have produced strong supporting evidence for d-wave pairing symmetry. Furthermore, they suggest that, in the context of the Fermi liquid framework, a generic BCS formalism can serve as a starting point for a viable description of the superconducting state in cuprate superconductors.
- Origin of High-Temperature Superconductivity in Cuprates
Building on the insight gained from this knowledge of d-wave pairing symmetry, Newns and Tsuei have developed a microscopic model of high temperature superconductivity . This model is based on the observation that the charge carrier motion along the in-plane Cu-O-Cu bond, by crystal symmetry, must be non-linearly modulated by the vibration of the intervening oxygen (red spheres), as shown in the figure below. We call this model the "Fluctuating Bond Model" (FBM) because the bond strength is a function of the square of the oxygen vibration amplitude (anharmonic effect).
Such bond fluctuations enable d-wave pairing mediated by an anharmonic two-(local) phonon process. This new pairing mechanism, decoupled from the large on-site Coulomb repulsion, is qualitatively different from the conventional one-phonon BCS pairing interaction. The excitation responsible for the electron-electron interaction is dressed at long wavelengths to become a quadrupolar (d-wave symmetry) charge fluctation (dCDW). Anomalous scattering by such dCDW fluctuations - tending to eliminate the Fermi surface at the antinodal points - is related to the d-wave pseudogap, and to a possible low-temperature dCDW state . Our fluctuating bond model provides a natural explanation of several key features of high-temperature superconductors, such as the doping dependence of the isotope shift in Tc shown in the following figure.
Our fluctuating bond model also provides a natural explanation of another key feature of high-temperature superconductors, which is the C4v symmetry breaking probed with a low-temperature STM shown in the figure below.
 C. C. Tsuei and J. R. Kirtley, “Pairing Symmetry in Cuprate Superconductors,” Rev. Mod. Phys. 92, 969 (2000).
 C. C. Tsuei, J. R. Kirtley, C. C. Chi, Lock-See Yu-Jahnes, A. Gupta, T. Shaw, J. Z. Sun, and M. B. Ketchen, “Pairing Symmetry and Flux Quantization in a Tricrystal Superconducting Ring of YBa2Cu3O7-δ,” Phys. Rev. Lett. 73, 593 (1994).
 J. R. Kirtley, C. C. Tsuei, J. Z. Sun, C. C. Chi, Lock-See Yu-Jahnes, A. Gupta, M. Rupp, and M. B. Ketchen, “Symmetry of the Order Parameter in the High-Tc Superconductor YBa2Cu3O7-δ,” Nature 373, 225 (1995).
 C. C. Tsuei, J. R. Kirtley, M. Rupp, J. Z. Sun, Lock-See Yu-Jahnes, C. C. Chi, A. Gupta, M. B. Ketchen, “Flux quantization in tricrystal cuprate rings – a new probe of pairing symmetry,” J. Phys. Chem. Solids 56, 1787 (1995).
 J. R. Kirtley, C. C. Tsuei, M. Rupp, J. Z. Sun, L. S. Yu-Jahnes, A. Gupta, M. B. Ketchen, K. A. Moler, M. Bhushan, “Direct imaging of integer and half integer Josephson vortices in high Tc grain boundaries,” Phys. Rev. Lett. 76, 1336 (1996).
 J. R. Kirtley, C. C. Tsuei, H. Raffy, Z. Z. Li, A. Gupta, J. Z. Sun, and S. Megtert, “Half-integer flux quantum effect in tricrystal Bi2Sri2CaCu2O8+δ,” Europhys. Lett. 36, 707 (1996).
 C. C. Tsuei, J. R. Kirtley, M. Rupp, J. Z. Sun, A. Gupta, M. B. Ketchen, C. A. Wang, Z. F. Ren, J. H. Wang, M. Bhushan, “Pairing Symmetry in Single-Layer Tetragonal Tl2Ba2CuO6+δ Superconductors,” Science 271, 329 (1996).
 C. C. Tsuei, J. R. Kirtley, Z. F. Ren, J. H. Wang, H. Raffy, and Z. Z. Li, “Pure dx2-y2 order parameter symmetry in the tetragonal superconductor Tl2Ba2CuO6+δ,” Nature 387, 481 (1997).
 J. R. Kirtley, C. C. Tsuei, and K. A. Moler, “Temperature Dependence of the Half-Integer Magnetic Flux Quantum,” Science 285, 1373 (1999).
 C. C. Tsuei and J. R. Kirtley, “Phase-Sensitive Evidence for d-Wave Pairing Symmetry in Electron-doped Cuprate Superconductors,” Phys. Rev. Lett. 85, 182 (2000).
 C. C. Tsuei, J. R. Kirtley, G. Hammer, J. Mannhart, H. Raffy, and Z. Z. Li, “Robust dx2-y2 pairing symmetry in high-temperature superconductors,” Phys. Rev. Lett. 93, 187004 (2004).
 R. R. Schulz, B. Chesca, B. Goetz, C. W. Schneider, A. Schmehl, H. Bielefeldt, H. Hilgenkamp, J. Mannhart, and C. C. Tsuei, “Design and realization of an all d-wave Π-superconducting quantum interference device,” Appl. Phys. Lett. 76, 912 (2000).
 H. Hilgenkamp, Ariando, H.-J. H. Smilde, D. H. A. Blank, G. Rijnders, H. Rogalla, J. R. Kirtley, C. C. Tsuei, “Ordering and manipulation of the magnetic moments in Large-scale superconducting Π-loop arrays”, Nature 422, 50 (2003).
 J. R. Kirtley, C. C. Tsuei, A. Ariando, C. J. M. Verwijs, S. Harkema and H. Hilgenkamp, ”Angle-resolved phase-sensitive determination of the in-plane gap symmetry in YBa2Cu3O7-δ”, Nature Physics 2, 190 (2006).
 D. M. Newns and C. C. Tsuei, “Fluctuating Cu-O-Cu bond model of high-temperature superconductivity,” Nature Physics 3, 184-191 (2007).