arXiv subjects

Chyh-Hong Chern

Publications and source records attributed to Chyh-Hong Chern.

At least 19 recordsLinked to original sources

arXiv2022

Preservation of the harmonic overtones in the violin family beyond Stradivari

Three hundred years ago, Antonio Stradivari enjoyed the golden period of the violin making in the human history. Luthiers and researchers endeavor to study his legendary legacy. Unfortunately, a consensus that the present progress has reached his level remains lacking. Most of the instruments suffer from low sounding power and enigmatic deficit of harmonic overtones. In fact, there is significant energy dissipation in the acoustic couplings in the violin family, completely unaware to luthiers and researchers. The current acoustic mechanism is inefficient in resonance of the wooden plates and hence is the low rate of mechanical energy conversion to the desired sound. We propose a new method for the amelioration of the acoustic couplings to enhance the preservation of the overtone components up to 161% of the pristine and to reduce the instrumental dissipation intensity up to 3.8 dB off (73% off). It results in the tremendously improved sound projection, the shorter reaction time, the longer reverberation time, and consequently the enrichment of the timbre complexity. Our physical method is applicable to the violin family of all sizes and ages, including the Stradivari, and extendable to all string instruments.

physics.class-ph↗

arXiv2018

Theory of Superconductivity in Strongly Correlated Electron Systems

In the correlated electron system with the pseudogap, there are full-gapped domains and Fermi-arced domains coexisting. Those domains are created by the quantum-fluctuated antiferromagnetic fluctuations that generate the short-ranged attractive potential to produce the Fermi arcs and the superconductivity. In the full-gapped domains, s-wave or (d_{x^2-y^2}\pm id_{xy})-wave symmetry of the electron pairs is favored. In the Fermi-arced domains, only d_{x^2-y^2}-wave symmetry of pairs is stable. Superconductivity of different pairing symmetry coexists in different domains, as well. Different from the Cooper pairs, the correlated electrons pair up in the \emph{real} space with an energy gap. Gapless states, on the contrary, hinder the development of superconductivity.

cond-mat.str-el↗

arXiv2018

Lattice Theoretical Approach in Strongly Correlated Electron Systems

The effective lattice models in strongly correlated electron systems are \emph{derived} in particular for the cuprate superconductors, that incorporate the quantum fluctuations of the spin Berry's phase and the antiferromagnetic fluctuation. Consistent with the field-theoretical approach, the density modulation, the weak ferromagnetism, and the superconductivity are reproduced. We discussed the pros and cons of the effective-model approach and demonstrate that both positive and negative Hubbard model are the effective models subject to the occurrence of the quantum fluctuations of the correlation degrees of freedom.

cond-mat.str-el↗

arXiv2017

Fluctuations in Strongly Correlated Electron Systems

High transition temperature superconductors in cuprates exhibit the charge-density-wave fluctuations and the ferromagnetic time-reversal-symmetry-breaking fluctuation in the polar Kerr rotation experiments. We demonstrate that they share the same root of origin, and the underlying mechanism also leads to the pseudogap formation. The pseudogap formation, the charge-density-wave fluctuation, and the time-reversal-symmetry-breaking fluctuation are the consequent phenomena of the correlation. They are the basic notions in strongly correlated electron systems.

cond-mat.str-el↗

arXiv2016

Non-relativistic fermionic energy gap in the non-abelian gauge systems

We demonstrate that the non-relativistic fermions open the energy gap when the SU(N) gauge bosons, mediating the interaction between fermions, acquire the mass. Surprisingly, even though there is the SU(N) gauge symmetry, there is always one fermionic energy gap which is not degenerate to the rest of the $N-1$ fermions for $N \ge 3$ in the fundamental representation.

cond-mat.str-el↗

arXiv2015

Deconfinement of electric charges in hydrogen-bonded ferroelectrics

In addition to the gauge charges, a new charge degree of freedom is found in the deconfined phase in the lattice Ising gauge theory. While applying to the hydrogen-bonded ferroelectrics, the new charge is essentially the electric charge, leading to the divergent dielectric susceptibility. The new degree of freedom paves an experimentally accessible way to identify the deconfined phase in the lattice Ising gauge theory.

cond-mat.str-el↗

arXiv2014

Pseudogap Formation and Quantum Phase Transition in Strongly-Correlated Electron Systems

Pseudogap formation is an ubiquitous phenomena in strongly-correlated superconductors, for example cuprates, heavy-fermion superconductors, and iron pnictides. As the system is cooled, an energy gap opens in the excitation spectrum before entering the superconducting phase. The origin of formation and the relevancy to the superconductivity remains unclear, which is the most challenging problem in condensed matter physics. Here, using the cuprate as a model, we demonstrate that the formation of pseudogap is due to a massive gauge interaction between electrons, where the mass of the gauge boson, determining the interaction length scale, is the consequence of the remnant antiferromagnetic fluctuation inherited from the parent compounds. Extracting from experimental data, we predict that there is a quantum phase transition belonging to the 2D XY universality class at the critical doping where pseudogap transition vanishes.

cond-mat.str-el↗

arXiv2014

Gauge Field and Confinement-Deconfinement Transition in Hydrogen-Bonded Ferroelectrics

Quantum melting of ferroelectric moment in the frustrated hydrogen-bonded system with "ice rule" is studied theoretically by using the quantum Monte Carlo simulation. The large number of nearly degenerate configurations are described as the gauge degrees of freedom, i.e., the model is mapped to a lattice gauge theory which shows the confinement-deconfinment transition (CDT). The dipole-dipole interaction $J_2$, on the other hand, explicitly breaks the gauge symmetry leading to the ferroelectric transition (FT) at finite temperature $T$. It is found that the crossover from FT to CDT manifests itself in the reduced correlation length of the polarization $ξ_{\text{FT}} \sim Δ(K-K_c)^{-ν}$ with $Δ\propto \sqrt{J_2}$ while $K_c$ and $ν$ remains finite in the limit $J_2 \to 0$. In contrast, the Currie-Weiss-like law for the susceptibility $χ$ and the spontaneous polarization behaves smoothly and the length scale $ξ_{\text{CDT}}$, related to the molecular symmetry and volume for CDT, does not reduce in this limit.

cond-mat.str-el↗

arXiv2011

Spin structure factor and thermodynamics in the antiferromagnetic quantum Ising model in the pyrochlore lattice

We numerically compute the temperature dependence of spin structure factor and thermodynamic quantities in the antiferromagnetic quantum Ising model in the pyrochlore lattice. This model exhibits spin disorder ground state with exponentially-decayed spin correlation. We reproduce the temperature dependence of the pinch point structure in the neutron scattering experiment and correct entropy obtained from the measurement of the specific heat.

cond-mat.stat-mech↗

arXiv2011

Deconfined Fractionally Charged Excitation in Any Dimensions

An exact incompressible quantum liquid is constructed at the filling factor $1/m^2$ in square lattice. It supports deconfined fractionally charged excitation. At the filling factor $1/m^2$, the excitation has fractional charge $\pm e/m^2$, where $e$ is the electric charge. This model can be easily generalized to the integer lattice in any $D$ dimensions, where the charge of excitations becomes $\pm e/m^D$.

cond-mat.str-el↗

arXiv2011

Spin Distribution in Diffraction Pattern of Two-dimensional Electron Gas with Spin-orbit Coupling

Spin distribution in the diffraction pattern of two-dimensional electron gas by a split gate and a quantum point contact is computed in the presence of the spin-orbit coupling. After diffracted, the component of spin perpendicular to the two-dimensional plane can be generated up to 0.42 $\hbar$. The non-trivial spin distribution is the consequence of a pure spin current in the transverse direction generated by the diffraction. The direction of the spin current can be controlled by tuning the chemical potential.

cond-mat.mes-hall↗

arXiv2010

Disorder from disorder and confinement in the quantum Ising model in the pyrochlore lattice

At zero temperature, the classical antiferromagnetic Ising model on the pyrochlore lattice is a spin disorder phase of the critical spin correlation. It is a deconfined phase in that the binding energy of the monopole-anti-monopole pair is independent of their distance of separation. We show that turning on a transverse magnetic field turns it into the cooperative paramagnet, and the spin correlation becomes exponential decay. Furthermore, it introduces the quantum confinement (of magnetic monopoles), where the binding energy of the pair is proportional to their distance of separation. This disorder state undergoes adiabatic transition to the paramagnetic state in the large field limit. The effective Hamiltonian (without magnetic monopoles) in small field is the Ising Hamiltonian plus ring exchange interaction.

cond-mat.str-el↗

arXiv2010

Non-magnetic Stern-Gerlach Experiment from Electron Diffraction

Using the wave nature of the electrons, we demonstrate that a transverse spin current can be generated simply by the diffraction through a single slit in the spin-orbital coupling system of the two-dimensional electron gas. The diffracted electron picks up the transverse momentum. The up spin electron goes one way and the down spin electron goes the other, producing the coherent spin current. In the system of spin-orbital coupling $\sim10^{-13}$ eV$\cdot$m, the \emph{out-of-plane} component of the spin of the electron can be generated up to 0.42 $\hbar$. Based on this effect, a novel device of grating to distill spin is designed. Two first diffraction peaks of electron carry different spins, duplicating the non-magnetic version of Stern-Gerlach experiment. The direction of the spin current can be controlled by the gate voltage with low energy cost.

cond-mat.mes-hall↗

arXiv2010

Featureless Mott Insulators

A family of the pair hopping models exhibiting the incompressible quantum liquid at fractional filling $1/m^D$ is constructed in $D$ dimensional lattice. Except in one dimension, the lattice is the generalized edge-shared triangular lattice, for example the triangular lattice in two dimensions and tetrahedral lattice in three dimensions. They obey the new symmetry, conservation of the center-of-mass position proposed by Seidel et al..\cite{Seidel2005} The uniqueness of the ground state is proved rigorously in the open boundary condition. The finiteness of the excitation energy is calculated by the single mode approximation.

cond-mat.str-el↗

arXiv2009

On the valence bond solid in the presence of Dzyaloshinskii-Moriya interaction

We examine the stability of the valence bond solid (VBS) phase against the Dzyaloshinskii-Moriya (DM) interaction in the bipartite lattice. Despite the VBS is vulnerable against the antiferromagnetic interaction, for example in the Q-J model proposed by Sandvik, where the quantum phase transition occurs at $J^*/Q = 0.04$, we found that on the contrary the VBS is very stable against the DM interaction. The quantum phase transition does not occur until D/Q goes to infinity, where D is the strength of the DM interaction. The VBS in the ALKT model and the Haldane gap system also exhibit the same property.

cond-mat.str-el↗

arXiv2009

Modulation of superconductivity by spin canting in a hybrid antiferromagnet/superconductor oxide

The proximity effect of a C-type antiferromagnet (C-AFM) with the spin canting at low temperature is investigated in the hybrid Nd0.35Sr0.65MnO3(NSCO)/YBa2Cu3O7(YBCO) oxide system through magnetic and transport measurements. It is found that the onset of a spin-canted state destroys partially the superconducting order parameter. Interestingly, due to the instability of this spin-canted state, zero-resistivity recovers at the offset of spin canting. Our result demonstrates clearly the high sensitivity of superconducting order parameter to a modulation of internal field.

cond-mat.supr-con↗

arXiv2008

Modelling the Berezinskii-Kosterlitz-Thouless Transition in the NiGa_2S_4

In the two-dimensional superfluidity, the proliferation of the vortices and the anti-vortices results in a new class of phase transition, Berezinskii-Kosterlitz-Thouless (BKT) transition. This class of the phase transitions is also anticipated in the two-dimensional magnetic systems. However, its existence in the real magnetic systems still remains mysterious. Here we propose a phenomenological model to illustrate that the novel spin-freezing transition recently uncovered in the NMR experiment on the NiGa_2S_4 compound is the BKT-type. The novel spin-freezing state observed in the NiGa_2S_4 possesses the power-law decayed spin correlation.

cond-mat.str-el↗

arXiv2008

Spin Anisotropy in ZnCu_3(OH)_6Cl_2

The spin anisotropic exchange interaction is suggested to contribute significantly to the abnormal upturn of the magnetic susceptibility in the ZnCu$_3$(OH)$_6$Cl$_2$. The saturation of the magnetic susceptibility below 300 mK observed in the muon spin resonance ($μ$SR) experiment is the quantum effect of the spin flipping process.

cond-mat.str-el↗