arXiv subjects

Zhao-bin Su

Publications and source records attributed to Zhao-bin Su.

8 recordsLinked to original sources

arXiv2001

Metal-insulator crossover in superconducting cuprates in strong magnetic fields

The metal-insulator crossover of the in-plane resistivity upon temperature decrease, recently observed in several classes of cuprate superconductors, when a strong magnetic field suppresses the superconductivity, is explained using the $U(1)\times SU(2)$ Chern-Simons gauge field theory. The origin of this crossover is the same as that for a similar phenomenon observed in heavily underdoped cuprates without magnetic field. It is due to the interplay between the diffusive motion of the charge carriers and the ``peculiar'' localization effect due to short-range antiferromagnetic order. We also calculate the in-plane transverse magnetoresistance which is in a fairly good agreement with available experimental data.

cond-mat.supr-con↗

arXiv2000

Probing superconducting phase fluctuations from the current noise spectrum of pseudogaped metal-superconductor tunnel junctions

We study the current noise spectra of a tunnel junction of a metal with strong pairing phase fluctuation and a superconductor. It is shown that there is a characteristic peak in the noise spectrum at the intrinsic Josephson frequency $ω_J=2eV$ when $ω_J$ is smaller than the pairing gap but larger than the pairing scattering rate. In the presence of an AC voltage, the tunnelling current noise shows a series of characteristic peaks with increasing DC voltage. Experimental observation of these peaks will give direct evidence of the pair fluctuation in the normal state of high-$T_c$ superconductors and from the half width of the peaks the pair decay rate can be estimated.

cond-mat.str-el↗

arXiv1999

Semiclassical theory of excitonic polaritons in a planar semiconductor microcavity

We present a comprehensive theoretical description of quantum well exciton-polaritons imbedded in a planar semiconductor microcavity. The exact non-local dielectric response of the quantum well exciton is treated in detail. The 4-spinor structure of the hole subband in the quantum well is considered, including the pronounced band mixing effect. The scheme is self-contained and can be used to treat different semiclassical aspects of the microcavity properties. As an example, we analyze the "selection" rules for the exciton-cavity mode coupling for different excitons.

cond-mat.mes-hall↗

arXiv1999

Pseudogap phase in the U(1) gauge theory with incoherent spinon pairs

The pseudogap effect of underdoped high-$T_c$ superconductors is studied in the U(1) gauge theory of the t-J model including the spinon pairing fluctuation. The gauge fluctuation breaks the long range correlation between the spinon pairs. The pairing fluctuation, however, suppresses significantly the low-lying gauge fluctuations and leads to a stable but phase incoherent spin gap phase which is responsible for the pseudogap effects. This quantum disordered spin gap phase emerges below a characteristic temperature $T^{*}$ which is determined by the effective potential for the spinon pairing gap amplitude. The resistivity is suppressed by the phase fluctuation below $% T^{*}$, consistent with experiments.

cond-mat.str-el↗

arXiv1998

Phenomenological Understanding of a Transport Regime with Reflection Symmetry in the Quantum Hall System in a Composite Fermion Picture

In this paper, we present a phenomenological picture based on the composite fermion theory, in responding to the recent discovery by Shahar et al. of a new transport regime near the transition from a $ν=1$ quantum Hall liquid to a Hall insulator(ref[8]). In this picture, the seemingly unexpected reflection symmetry in the longitudinal resistivity $ρ_{xx}$ can be understood clearly as due to the symmetry of the gapful excitations which dominate $σ_{xx}$ across the transition, and the abrupt change in $σ_{xy}$ at the transition. The parameter $α$ in the linear fit of $ν_0(T)$ in ref[8] is also given a simple physical meaning and the effective mass can be calculated from $α$, which gives a reasonable value of several electron band mass. When taking into account the result of network model, the almost invariant Hall resistivity $ρ_{xy}$ across the transition is also well-understood.

cond-mat.mes-hall↗

arXiv1997

A mean field theory for the spin ladder system

In the present paper, we propose a mean field approach for spin ladders based upon the Jordan-Wigner transformation along an elaborately ordered path. We show on the mean field level that ladders with even number legs open a energy gap in their low energy excitation with a magnitude close to the corresponding experimental values, whereas the low energy excitation of the odd-number-leg ladders are gapless. It supports the validity of our approach. We then calculate the gap size and the excitation spectra of 2-leg-ladder system. Our result is in good agreement with both the experimental data and the numerical results.

cond-mat.str-el↗

arXiv1997

$U(1)\times SU(2)$ gauge theory of underdoped cuprate superconductors

The $U(1)\times SU(2)$ Chern-Simons gauge theory is applied to study the 2-D $t-J$ model describing the normal state of underdoped cuprate superconductors. The U(1) field produces a flux phase for holons converting them into Dirac-like fermions, while the SU(2) field, due to the coupling to holons gives rise to a gap for spinons. An effective low-energy action involving holons, spinons and a self-generated U(1) gauge field is derived. The Fermi surface and electron spectral function obtained are consistent with photoemission experiments. The theory predicts a minimal gap proportional to doping concentration. It also explains anomalous transport properties including linear $T$ dependence of the in-plane resistivity.

cond-mat.str-el↗

arXiv1997

The Fermi surface of underdoped high-T_c superconducting cuprates

The coexistence of $π$-flux state and d-wave RVB state is considered in this paper within the slave boson approach. A critical value of doping concentration $δ_c$ is found, below which the coexisting $π$-flux and d-wave RVB state is favored in energy. The pseudo Fermi surface of spinons and the physical electron spectral function are calculated. A clear Fermi-level crossing is found along the (0,0) to ($π$, $π$) direction, but no such crossing is detected along the ($π$, 0) to ($π$, $π$) direction. Also, an energy gap of d-wave symmetry appears at the Fermi level in our calculation. The above results are in agreement with the angle-resolved photoemission experiments which indicate at a d-wave pseudo-gap and a half-pocket-like Fermi surface in underdoped cuprates.

cond-mat.str-el↗