arXiv subjects

T. K. Ng

Publications and source records attributed to T. K. Ng.

24 records · Page 2Linked to original sources

arXiv1999

A model of marginal Fermi liquid superconductor at two dimensions

In this paper we study a model of s-wave marginal Fermi liquid superconductor at two dimensions. Besides the usual Bardeen-Cooper-Schrieffer(BCS) point attractive interaction, the fermions in our system also interact {\em via} a long range repulsive interaction $v(q)=g_{D}/q^2$. We find that although superconductivity is not destroyed by the long-ranged repulsion interaction (demonstrated by the existence of Meissner effect), nevertheless the BCS pairing function $Δ_{BCS}$ is strongly suppressed resulting in power-law correlation $<Δ_{BCS}(\vec{x})Δ_{BCS}(0)>\sim|\vec{x}|^{-2γ}$. This observation is explained within a general picture of marginal Fermi liquid.

cond-mat.supr-con↗

arXiv1999

Bosonization theory of fermions interacting via a confining potential

We study in this paper the properties of a gas of fermions interacting {\em via} a scalar potential $v(q)=4π{e}^2/q^2$ for $q<Λ<<k_F$ at dimensions larger than one, where $Λ$ is a high momentum cutoff and $k_F$ is the fermi wave vector. In particular, we shall consider the $e^2\to\infty$ limit where the potential becomes confining. Within a bosonization approximation, effective Hamiltonians describing the low energy physics of the system are constructed, where we show that the system can be described as a fermi liquid formed by chargeless quasi-particles which has vanishing wavefunction overlap with the bare fermions in the system.

cond-mat.str-el↗

arXiv1999

Supersymmetric Mean-Field Theory of t-J Model

The supersymmetric formulation of t-J model is studied in this paper at the mean-field level where $δ$-T phase diagram is computed. We find that slave-fermion-like spiral phase is stable at low doping concentration, and the slave-boson-like d-wave fermionic spin pairing state becomes energetically favourable when $δ\geq$ 0.23. An improvement in free energy using Gutzwiller's method lowers the transition doping concentration to 0.06. We also point out the existence of new branches of excitations in the supersymmetric theory.

cond-mat.supr-con↗

arXiv1998

Supersymmetry in models with strong on-site Coulomb repulsion - application to t-J model

A supersymmetric way of imposing the constraint of no double occupancy in models with strong on-site Coulomb repulsion is presented in this paper. In this formulation the physical operators in the constrainted Hilbert space are invariant under local unitary transformations mixing boson and fermion representations. As an illustration the formulation is applied to the $t-J$ model. The model is studied in the mean-field level in the J=0 limit where we show how both the slave-boson and slave-fermion formulations are included naturally in the present approach and how further results beyond both approaches are obtained.

cond-mat↗

arXiv1997

Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors

The flux-line lattice in the compound $ErNi_2B_2C$, which has a tendency to ferromagnetic order in the a-b plane is studied with external magnetic field direction close to the c-axis. We show the existence of an instability where the direction of flux-lines spontaneously tilts away from that of the applied field near the onset of ferromagnetic order. The enhanced fluctuations in the flux lattice and the square flux lattice recently observed are explained and further experiments suggested.

cond-mat.supr-con↗

arXiv1996

Spontaneous vortex phase discovered?

It is argued that a spontaneous vortex phase may exist in the recently discovered compound $ErNi_2B_2C$ at temperature below 2.3K. The consequences of this proposal are discussed. In particular the magnetic response of the system are studied both above and below 2.3K and further experiments proposed.

cond-mat↗