We use analytical approaches (mainly mathematical techniques under the name of Quantum Field Theory) to understand different models of strongly correlated electrons (see highlights below). Currently we are exploring various new techniques to describe plausible non-fermi liquid states of strongly correlated electrons. In particular, we are trying to generalize the so-called bosonization techniques and exclusion statistics to describe non-fermi liquids at dimensions larger than one.

Result Highlights

Kondo Effect in Quantum Dots

In collaboration with Prof. P.A. Lee at M.I.T., we predicted the existence and experimental manifestations of the Kondo effect in Quantum Dots in 1988[1]. This prediction was verified in 1998 and has become an area of active research in recent years.

Key publications:
[1] On-site Coulomb repulsion and resonant tunneling", T.K. Ng and P.A. Lee, Phys. Rev. Lett. 61, 1768(1988).

End State in Quantum Spin Chains

In 1994, I made another theoretical prediction - the existence of topological spin excitations at the end-points of one-dimensional quantum antiferromagnetic spin chains[1]. This prediction was verified by numerical DMRG method in 1995[2].

Key publications:
[1] "Edge states in antiferromagnetic quantum spin chains", T.K. Ng, Phys. Rev. B50, 555(1994).
[2] "Edge states in open antiferromagnetic Heisenberg chains", S.J. Qin, T.K. Ng and Z.B. Su, Phys. Rev. B52, 12844(1995).

Spontaneous Vortex State in Magnetic Superconductors

In collaboration with Dr. C.M. Varma at Bell Labs, Lucent Technology, we predicted the existence of a Spontaneous Vortex State in the magnetic superconductor ErNi2B2C in 1997[1,2]. This new state of matter was verified in 2001 in neutron scattering experiment.

Key publications:
[1] "Spontaneous Vortex Phase observed?", T.K. Ng and C.M. Varma, Phys. Rev. Lett. 78, 330(1997).
[2] "Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors", T.K. Ng and C.M. Varma, Phys. Rev. Lett. 78, 3745(1997).

Topological Spin Excitation in Quantum Antiferromagnets at Two Dimensions

In 1999, I predicted the existence of fermionic, S=1/2, topological spin excitations in disordered quantum antiferromagets at two dimensions[1] and identified them with spinons proposed earlier by P.W. Anderson.

Key publications:
[1] "Topological spin excitations of Heisenberg antiferromagnets in two dimensions", T.K. Ng, Phys. Rev. Lett. 82, 3504(1999).

Marginal Fermi-liquid Superconductor

In collaboration with Dr. Y.L. Liu, we studied the properties of a marginal fermi-liquid superconductor in 1999[1] and showed that some of the properties of our model coincide well with properties of high-temperature superconductors in the pseudo-gap phase.

Key publications:
[1] "A model of marginal Fermi liquid superconductor at two dimensions", Y.L. Liu and T.K. Ng, Phys. Rev. Lett. 83, 5539(1999).