arXiv subjects

Jung Hoon Han

Publications and source records attributed to Jung Hoon Han.

119 records · Page 7Linked to original sources

arXiv2003

A New Mean-Field Theory of the Kondo Resonance at Finite Bias

We introduce a new slave-boson mean-field treatment of the Kondo effect in a quantum dot attached to the leads, when the bias voltage across the leads is finite. The model employs two slave boson and two pseudo-fermion operators to express the localized electron. The solution of the mean-field equations gives in general two resonance peaks pinned to the chemical potential of each lead. The Kondo temperature is shown to scale as $min(\tstar, (\tstar)^2/V)$, where $\tstar$ is the Kondo temperature at equilibrium, and $V$ is the chemical potential difference of the leads.

cond-mat.str-el↗

arXiv2002

Low-Frequency Optical Conductivity in Inhomogeneous d-wave Superconductors

Motivated by the recent optical conductivity experiments on Bi_2Sr_2CaCu_2O_{8+delta} films, we examine the possible origin of low-frequency dissipation in the superconducting state. In the presence of spatial inhomogeneity of the local phase stiffness rho_s, it is shown that some spectral weight is removed from omega=0 to finite frequencies and contribute to dissipation. A case where both rho_s and the local normal fluid density are inhomogeneous is also considered. We find an enhanced dissipation at low frequency if the two variations are anti-correlated.

cond-mat.supr-con↗

arXiv2002

Signature of Spin Collective Mode in Local Tunneling Spectra of a d-wave Superconductor

We consider the influence of magnetic excitations on the local density of states in the d-wave superconductor. The magnetic susceptibility is calculated within the renormalized $t-t'-J$ model and its influence on the quasiparticle self-energy is considered using a minimal model originally proposed by Polkovnikov {\it et al.}[cond-mat/0203176]. We find the local density of states possess periodic components both along $(π,0)$ and $(π,π)$ directions with the associated wavevectors changing in magnitude as the quasiparticle energy is varied. Comparison with the STM experiment reveals that the calculated LDOS modulation is inconsistent with the measured data.

cond-mat.supr-con↗

arXiv2001

Pairing in the spin sector

The nanometer-scale gap inhomogeneity revealed by recent STM images of BSCCO surface suggests that the ``gap coherence length'' is of that order. Thus a robust pairing gap can develop despite the poorly screened Coulomb interaction. This can be taken as an evidence that the pairing in high $T_c$ materials occurs primarily in the neutral (spin) sector. We provide theoretical support for this point of view.

cond-mat.supr-con↗

arXiv2001

Staggered currents in the mixed state

The current pattern in the mixed state of high-$T_{c}$ superconductors is studied in the U(1) mean field theory of the t-J model. Our findings are the following. 1) In the absence of antiferromagnetism a robust staggered current pattern exists in the core of vortices if the doping is not too high. 2) At a fixed doping and with increasing magnetic field, the size of the staggered current core expands, and eventually percolates. 3) The polarity of the staggered current is pinned by the direction of the magnetic field. 4) Vortex cores locally modify the hole density - in a staggered (non-staggered) core, the excess charge is slightly negative (positive). 5) Gutzwiller projection does not wash out the staggered current. Finally we present two experimental predictions concerning neutron scattering and STM spectra that capture the signature of the staggered current induced by the vortices.

cond-mat.supr-con↗

arXiv2000

Staggered Currents in the Vortex Core

We study the electronic structure of the vortex core in the cuprates using the U(1) slave-boson mean-field wavefunctions and their Gutzwiller projection. We conclude that there exists local orbital antiferromagnetic order in the core near optimal doping. We compare the results with that of BCS theory and analyze the spatial dependence of the local tunneling density of states.

cond-mat.supr-con↗

arXiv2000

The Superfluid Density in the D-density-wave Scenario

Recently Chakravarty, Laughlin, Morr and Nayak made an interesting proposal that the cuprate superconductors possess a hidden ``d-density wave'' order. We study the implication of this proposal for the superfluid density ρ_s. We find that it predicts a temperature gradient |dρ_s/dT|_{T=0} that is strongly doping dependent near the critical doping (\approx 5%) at which the superconducting transition temperature vanishes.

cond-mat.supr-con↗

arXiv2000

Numerical Test of Disk Trial Wave function for Half-Filled Landau Level

The analyticity of the lowest Landau level wave functions and the relation between filling factor and the total angular momentum severely limits the possible forms of trial wave functions of a disk of electrons subject to a strong perpendicular magnetic field. For N, the number of electrons, up to 12 we have tested these disk trial wave functions for the half filled Landau level using Monte Carlo and exact diagonalization methods. The agreement between the results for the occupation numbers and ground state energies obtained from these two methods is excellent. We have also compared the profile of the occupation number near the edge with that obtained from a field-theoretical method. The results give qualitatively identical edge profiles. Experimental consequences are briefly discussed.

cond-mat.mes-hall↗

arXiv2000

Antiferromagnetism, Stripes, and Superconductivity in the t-J Model with Coulomb Interaction

We study mean-field phases of the t-J model with long-range Coulomb interaction. In the order of increasing doping density we find a classical antiferromagnet, charge and spin stripes, and a uniform d-wave superconductor, at the realistic doping parameters. Both in-phase and anti-phase stripes exist as metastable configurations, but the in-phase stripes have a slightly lower energy. The dependence of the stripe width and the inter-stripe spacing on the doping is examined. Effects of fluctuations around the mean-field states are discussed.

cond-mat.supr-con↗

arXiv2000

The Structure of a Vortex in the t-J Model

We study the single-vortex solution of the t-J model within resonating-valence-bond (RVB) mean-field theory. We find two types of vortex cores, insulating and metallic, depending on the parameters of the model. The pairing order parameter near both cores have $d_{x^2 -y^2}+iηd_{xy}$ symmetry. For some range of $t/J$ the calculated tunneling spectrum of the metallic vortex core agrees qualitatively with the STM tunneling data for BSCCO.

cond-mat.supr-con↗

arXiv1998

Ground State Wavefunctions of General Filling Factors in the Lowest Landau Level

We present a set of explicit trial wavefunctions for the filling factors ν=n/(2n\pm 1) and ν=1/2 in the symmetric gauge. We show that the zeroes of the wavefunction, except those dictated by the Fermi statistics, are detached from the particles. The evolution of zeroes as the filling factor is varied is examined. We show that the wavefunction at half-filling exhibits a 2k_F-like oscillation in its occupation number profile. The center-of-mass motion of the ground state droplet is described in terms of the intra-Landau- level excitations of composite fermions.

cond-mat.mes-hall↗