arXiv subjects

Yong Baek Kim

Publications and source records attributed to Yong Baek Kim.

At least 235 records · Page 13Linked to original sources

arXiv2003

Critical Current of the Spin-Triplet Superconducting Phase in Sr$_2$RuO$_4$

There have been two different proposals for the spin-triplet order parameter of the superconducting phase in Sr$_2$RuO$_4$; an $f$-wave order parameter and the multigap model where some of the bands have the line node. In an effort to propose an experiment that can distinguish two cases, we study the behavior of the supercurrent and compute the critical current for these order parameters when the sample is a thin film with the thickness $d \ll ξ$ where $ξ$ is the coherence length. It is found that the supercurrent behaves very differently in two models. This will serve as a sharp test for the identification of the correct order parameter.

cond-mat.supr-con↗

arXiv2003

Statistics of spinons in the spin-liquid phase of Cs2CuCl4

Motivated by a recent experiment on Cs2CuCl4, we study the spin dynamics of the spin-liquid phase of the spin-1/2 frustrated Heisenberg antiferromagnet on the anisotropic triangular lattice. There have been two different proposals for the spin-liquid phase of Cs2CuCl4. These spin-liquid states support different statistics of spinons; the bosonic Sp(N) large-N mean field theory predicts bosonic spinons while the SU(2) slave-boson mean field theory leads to fermionic spinons. We compute the dynamical spin structure factor for both types of spin-liquid state at zero and finite temperatures. While at zero temperature both theories agree with experiment on a qualitative level, they show substantial differences in the temperature dependence of the dynamical spin structure factor.

cond-mat.str-el↗

arXiv2002

Effect of Ring Exchange on Orbital Antiferromagnet

We study the effect of four-particle ring exchange process on orbital antiferromagnetic state that occurs in some correlated electron systems in two dimensions. The primary question is whether the ring exchange process enhances or suppresses the orbital antiferromagnetic ordering. Using the fact that the orbital antiferromagnetic state arises in the large-N limit of the SU(N) generalization of the t-J model, we consider the large-N limit of the t-J-$K$ model where $K$ represents the four-particle ring exchange term. The phase diagrams in the large-N mean field theory are obtained for the half-filling and finite hole concentrations at zero temperature. It is found that the ring exchange in general favors dimerized states or the inhomogeneous orbital antiferromagnetic state, and suppresses the homogeneous orbital antiferromagnetic state. We compare our results with other related models of strongly correlated systems with ring exchange processes.

cond-mat.str-el↗

arXiv2002

On the residual resistivity near a two dimensional metamagnetic quantum critical point

The behavior of the residual (impurity-dominated) resistivity is computed for a material near a two dimensional quantum critical point characterized by a divergent $q=0$ susceptibility. A singular renormalization of the amplitude for back-scattering of an electron off of a single impurity is found. When the correlation length of the quantum critical point exceeds the mean free path, the singular renormalization is found to convert the familiar `Altshuler-Aronov' logarithmic correction to the conductivity into a squared-logarithmic form. Impurities can induce unconventional Friedel oscillations, which may be observable in scanning tunnelling microscope experiments. Possible connections to the metamagnetic quantum critical end point recently proposed for the material $Sr_{3}Ru_{2}O_{7}$ are discussed.

cond-mat.str-el↗

arXiv2002

Pseudogap Kondo Physics from Charge Fluctuations in a Quantum Dot

We consider charge fluctuations in a quantum dot coupled to an interacting one-dimensional electron liquid. We find the behavior of this system to be similar to the multichannel pseudogap Kondo model. By tuning the coupling between the dot and the one-dimensional electron liquid, one can access the quantum critical point and the various fixed points which arise. The differential capacitance is computed and is shown to contain detailed information about the system.

cond-mat.str-el↗

arXiv2002

Pairing Instability in a Nematic Fermi Liquid

Nematic Fermi liquid arises when the system of interacting fermions spontaneously breaks the rotational symmetry while the translational symmetry is preserved. We consider a Nematic Fermi liquid of fermions with two distinct quantum numbers. Two quantum numbers represent the spin degrees of freedom or the layer degrees of freedom of the bilayer system. There are two director modes in this system: the in-phase and out-of-phase modes. We find that the out-of-phase (in-phase) mode mediates an attractive (repulsive) interaction between fermions with different quantum numbers. Pairing instability occurs under certain conditions when the in-phase mode is gapped due to a lattice potential. Implications to the stripe phase of Cuprates and the quantum Hall effect of two dimensional electron systems are discussed.

cond-mat.str-el↗

arXiv2002

"Quasiparticle Charge" in Superconductors: Effect of Mott Physics or Hidden Order Parameter ?

The renormalization factor, dubbed ``quasiparticle charge'' Z_e, of the coupling between the supercurrent and quasiparticles was analyzed in the context of high temperature cuprates in a recent paper by Ioffe and Millis. They observed that Z_e in cuprates deviates from the BCS value (Z_e=1), which was interpreted as the proximity effect near a Mott insulator. Here we show that the deviation from Z_e=1 can occur, in general, even in the absence of quasiparticle interactions, when the superconducting order coexists with another order parameter with the same internal symmetry. As an example, we compute the coefficient of the linear temperature dependence of the superfluid density when the d-wave superconducting state coexists with the orbital antiferromagnetic state (d-density wave), and find that Z_e varies from 1/\sqrt{2} to 1.

cond-mat.supr-con↗

arXiv2001

Fractionalization patterns in strongly correlated electron systems: Spin-charge separation and beyond

We discuss possible patterns of electron fractionalization in strongly interacting electron systems. A popular possibility is one in which the charge of the electron has been liberated from its Fermi statistics. Such a fractionalized phase contains in it the seed of superconductivity. Another possibility occurs when the spin of the electron, rather than its charge, is liberated from its Fermi statistics. Such a phase contains in it the seed of magnetism, rather than superconductivity. We consider models in which both of these phases occur and study possible phase transitions between them. We describe other fractionalized phases, distinct from these, in which fractions of the electron themselves fractionalize, and discuss the topological characterization of such phases. These ideas are illustrated with specific models of p-wave superconductors, Kondo lattices, and coexistence between d-wave superconductivity and antiferromagnetism.

cond-mat.str-el↗

arXiv2001

Specific heat anomaly in the d-density wave state and emergence of incommensurate orbital antiferromagnetic order

We study the effect of finite chemical potential on the d-density wave state that has been proposed to explain the pseudogap phenomena in underdoped cuprates. We find that the specific heat anomaly at the transition temperature, below which the d-density wave state forms, gets weaker when finite chemical potential is introduced. This provides a useful ground for the proper interpretation of the specific heat measurement in regard to the existence of the d-density wave state below the pseudogap temperature. Further increase of the chemical potential leads to an incommensurate orbital antiferromagnetic state before the system eventually turns into the normal state. This is an inhomogeneous state characterized by novel charge ordering and an analog of the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in superconductivity.

cond-mat.str-el↗

arXiv2000

Bilayer Quantum Hall States at $ν=1$ and Coulomb Drag

We consider a number of strongly-correlated quantum Hall states which are likely to be realized in bilayer quantum Hall systems at total Landau level filling fraction ${ν_T}=1$. One state, the $(3,3,-1)$ state, can occur as an instability of a compressible state in the large $d/l_B$ limit, where $d$ and $l_B$ are the interlayer distance and magnetic length, respectively. This state has a hierarchical descendent which is interlayer coherent. Another interlayer coherent state, which is expected in the small $d/l_B$ limit is the well-known Halperin $(1,1,1)$ state. Using the concept of composite fermion pairing, we discuss the wavefunctions which describe these states. We construct a phase diagram using the Chern-Simons Landau-Ginzburg theory and discuss the transitions between the various phases. We propose that the longitudinal and Hall drag resistivities can be used together with interlayer tunneling to experimentally distinguish these different quantum Hall states. Our work indicates the bilayer ${ν_T}=1$ quantum Hall phase diagram to be considerably richer than that assumed so far in the literature.

cond-mat.mes-hall↗

arXiv2000

Bi-layer Paired Quantum Hall States and Coulomb Drag

We consider three states which are likely to be realized in bi-layer quantum Hall systems at total Landau level filling fraction ${ν_T}=1$. Two of these states may be understood as paired states. One can occur as an instability of a compressible state in the large $d/l_B$ limit, where $d$ and $l_B$ are the interlayer distance and magnetic length. The other is the $(1,1,1)$ state, which is expected in the small $d/l_B$ limit. We propose that the longitudinal and Hall drag resistivities can be used to distinguish these different quantum Hall states. The drag resistivities may be computed in a straightforward manner using the paired state formulation.

cond-mat.mes-hall↗

arXiv2000

Quantum-disordered slave-boson theory of underdoped cuprates

We study the stability of the spin gap phase in the U(1) slave-boson theory of the t-J model in connection to the underdoped cuprates. We approach the spin gap phase from the superconducting state and consider the quantum phase transition of the slave-bosons at zero temperature by introducing vortices in the boson superfluid. At finite temperatures, the properties of the bosons are different from those of the strange metal phase and lead to modified gauge field fluctuations. As a result, the spin gap phase can be stabilized in the quantum critical and quantum disordered regime of the boson system. We also show that the regime of quantum disordered bosons with the paired fermions can be regarded as the strong coupling version of the recently proposed nodal liquid theory.

cond-mat.str-el↗

arXiv2000

Spin waves in a two dimensional p-wave superconductor: Sr$_2$RuO$_4$

We study spin excitations in a two dimensional p-wave superconductor with ${\vec Δ} = {\hat d}({\hat k}_1 \pm i {\hat k}_2)$ symmetry in the context of the newly discovered superconducting Sr$_2$RuO$_4$. The polarization and spectrum of spin wave excitations are identified and their experimental consequences are discussed.

cond-mat.supr-con↗

arXiv2000

Collective modes and sound propagation in a p-wave superconductor: Sr$_2$RuO$_4$

There are five distinct collective modes in the recently discovered p-wave superconductor Sr$_2$RuO$_4$; phase and amplitude modes of the order parameter, clapping mode (real and imaginary), and spin wave. The first two modes also exist in the ordinary s-wave superconductors, while the clapping mode with the energy $\sqrt{2} Δ(T)$ is unique to Sr$_2$RuO$_4$ and couples to the sound wave. Here we report a theoretical study of the sound propagation in a two dimensional p-wave superconductor. We identified the clapping mode and study its effects on the longitudinal and transverse sound velocities in the superconducting state. In contrast to the case of $^3$He, there is no resonance absorption associated with the collective mode, since in metals $ω/(v_F |{\bf q}|) \ll 1$, where $v_F$ is the Fermi velocity, {\bf q} is the wave vector, and $ω$ is the frequency of the sound wave. However, the velocity change in the collisionless limit gets modified by the contribution from the coupling to the clapping mode. We compute this contribution and comment on the visibility of the effect. In the diffusive limit, the contribution from the collective mode turns out to be negligible. The behaviors of the sound velocity change and the attenuation coefficient near $T_c$ in the diffusive limit are calculated and compared with the existing experimental data wherever it is possible. We also present the results for the attenuation coefficients in both of the collisionless and diffusive limits at finite temperatures.

cond-mat.supr-con↗

arXiv2000

Chern-Simons versus dipolar composite fermions at finite wavevector

It was recently shown that dipolar composite fermions emerged from the lowest-Landau-level formulation of the quantum Hall effect give rise to similar results as those of the Chern-Simons gauge theory in the long wavelength and low energy limit. We ask whether this correspondence is still valid at finite wavevectors where the excitations do not necessarily look like dipolar quasiparticles. In particular, q=2k_F density-density response function of the compressible state at ν=1/2 is evaluated in the low energy limit within the framework of the lowest-Landau-level theory. The imaginary parts of the density-density response functions at q=2k_F of two theories have the same \sqrtω dependence. However, the coefficient of the \sqrtω term in the case of the lowest-Landau-level theory is not universal and can be much smaller than the corresponding coefficient in the Chern-Simons theory. We also discuss possible connection between these results and the recent experiment on phonon-mediated drag in the double-layer ν=1/2 system.

cond-mat.mes-hall↗

arXiv2000

Half-quantum vortex and d-soliton in Sr$_2$RuO$_4$

Assuming that the superconductivity in Sr$_2$RuO$_4$ is described by a planar p-wave order parameter, we consider possible topological defects in Sr$_2$RuO$_4$. In particular, it is shown that both of the ${\hat d}$-soliton and half-quantum vortex can be created in the presence of the magnetic field parallel to the $a$-$b$ plane. We discuss how one can detect the ${\hat d}$-soliton and half-quantum vortex experimentally.

cond-mat.supr-con↗

arXiv2000

Phonon-mediated drag at $ν=1/2$: A test of the Chern-Simons composite fermion theory

We report on a study of the phonon-mediated frictional drag between two-dimensional electron layers at the Landau level filling factor $ν=1/2$ predicted by Chern-Simons composite-fermion theory. Frictional drag between widely spaced layers is dominated by the phonon-mediated interaction and is altered from its zero-field form because of the large composite-fermion effective mass and, less strongly, by magnetic local-field effects. We find that the reduced drag resistance $ρ(T)/T^2$ peaks at a larger temperature and has a different density dependence than at zero field. We compare these results with recent experimental findings.

cond-mat.mes-hall↗

arXiv1999

Orthogonality Catastrophe and Spontaneous Symmetry Breaking in Double-layer Fermi-liquid-like States

The double-layer electron system with total filling factor $ν=1/2$ can be regarded as two separate Fermi-liquid-like states with $ν=1/4$ when the layer separation is sufficiently large and there is no tunneling. The weak tunneling in this state suffers an orthogonality catastrophe and it becomes irrelevant. Using the symmetric and antisymmetric combinations of layer indices as the pseudospin degrees of freedom, we show that there exists the first order transition from the above pseudospin unpolarized state to the pseudospin polarized Fermi-liquid-like state with $ν=1/2$ as the tunneling strength becomes sufficiently large.

cond-mat.mes-hall↗