arXiv subjects

K. -K. Voo

Publications and source records attributed to K. -K. Voo.

3 recordsLinked to original sources

arXiv2003

Temperature Effect and Fermi Surface Investigation in the Scanning Tunneling Microscopy of Bi$_2$Sr$_2$CaCu$_2$O$_8$

Based on a Fermi liquid picture, the temperature effect on the impurity-induced spatial modulation of local density of states (LDOS) is investigated for the d-wave superconductor Bi$_2$Sr$_2$CaCu$_2$O$_8$, in the context of scanning tunneling microscopy (STM). It is found that stripe-like structure exists even in the normal state due to a local-nesting mechanism, which is different from the octet scattering mechanism proposed by McElroy $et al$. {[Nature {\bf 422}, 592 (2003)]} in the d-wave superconducting ($d$SC) state. The normal-state spectra, when Fourier-transformed into the reciprocal space, can reveal the information of the entire Fermi surface at a single measuring bias, in contrast to the point-wise tracing proposed by McElroy $et al$. This may serve as another way to check the reality of Landau quasiparticles in the normal state. We have also re-visited the spectra in the $d$SC state and pointed out that, due to the Umklapp symmetry of the lattice, there should exist additional peaks in the reciprocal space, but experimentally yet to be found.

cond-mat.supr-con↗

arXiv2001

Spin Excitation in d-wave Superconductors : A Fermi Liquid Picture

A detailed study of the Inelastic Neutron Scattering (INS) spectra of the high-$T_c$ cuprates based on the Fermi liquid (FL) picture is given. We focus on the issue of the transformation between the commensurate and incommensurate (IC) excitation driven by frequency or $temperature$. For La$_{2-x}$Sr$_x$CuO$_4$ (LSCO), the condition of small $Δ(0)/v_F a$ (where $a$ is the lattice constant, and henceforth will be set to 1) can simultaneously reproduces the always existing IC peaks in the superconducting (SC) and normal state, and the always fixed location at temperature or frequency change. For YBa$_2$Cu$_3$O$_{6+x}$ (YBCO), a moderate $Δ(0)/v_F a$ and proximity of the van Hove singularity (vHS) at ${\bar M}=(0,π)$ to the Fermi level can reproduce the frequency- and temperature-driven shifting IC peaks in the SC state, and the vanishing of the IC peak in the normal state. The commensurate peak is found to be more appropriately described as a random phase approximation (RPA) effect. We address the conditional peak shifting behavior to a refined consideration on the nesting effect which is previously overlook. As a result, both the data on LSCO and the recent data on YBCO (on YBa$_2$Cu$_3$O$_{6.7}$ by Arai $et$ $al.$ and YBa$_2$Cu$_3$O$_{6.85}$ by Bourges $et$ $al.$) can be reasonably reconciled within a FL picture. We also point out that the one-dimensional-like data by Mook $et$ $al.$ on a detwinned and more underdoped sample YBa$_2$Cu$_3$O$_{6.6}$ could be due to a gap anisotropy effect discussed by Rendell and Carbotte, and we proceed to suggest a way of clarifying it.

cond-mat.supr-con↗

arXiv1999

Commensurate and Incommensurate Spin Fluctuations in YBa_2Cu_3O_{6+y}

We present an interpretation of the recent neutron data on the commensurate and incommensurate spin fluctuations found in YBa_2d$Cu_3O_{6+y} based on a special configuration of the electronic dispersion and intervention from the d_{x^2-y^2}-wave superconducting phase. The observed switch over between the commensurate and incommensurate fluctuation spectra at the change of frequency or temperature is naturally accounted within this scenario.

cond-mat.supr-con↗