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C. D. Hu

Publications and source records attributed to C. D. Hu.

16 recordsLinked to original sources
arXiv2025

The Quantum Channels of the Compton Scattering of an Entangled Pair of Photons

Using the Compton scattering of an entangled pair of photons as an example, we demonstrate the process of deriving the Kraus operators corresponding to the interaction from the underlying fundamental theory, quantum electrodynamics. The normalization of the final density matrix of the entangled photons after the interaction is crucial to obtaining the correct correlations. The reduced density matrix of the photon, which does not participate in the interaction directly, remains unchanged. It indicates that quantum effects, using an entangled pair of photons for quantum sensing, can only be observed via the correlations or superposition of the complete entangled pair of photons.

quant-ph↗
arXiv2021

Natural Negative-Refractive-Index Materials

Our calculation shows that negative refractive index (NRI), which was known to exist only in metamaterials in the past, can be found in Dirac semimetals (DSM). Electrons in DSM have zero effective mass and hence the system carries no nominal energy scale. Therefore, unlike those of ordinary materials, the electromagnetic responses of the electrons in DSM will not be overwhelmed by the physical effects related to electron mass. NRI is induced by the combination of the quantum effect of vacuum polarization and its finite temperature correction which is proportional to $T^4$ at low temperature. It is a phenomenon of resonance between the incident light and the unique structure of Dirac cones, which allows numerous states to participate in electron-hole pair production excited by the incident light with similar dispersion relation to that of Dirac cones. NRI phenomenon of DSM manifests in an extensive range of photon frequency and wave number and can be observed around giga Hertz range at temperature slightly higher than room temperature.

cond-mat.other↗
arXiv2012

Analytical methods of asymmetry double sine-Gordon equation in infinite one-dimensional system

Traditionally, Double Sine-Gordon Equation (DSGE) is seen as a nonintegrable equation. That means we cannot find general solutions in asymmetry DSGE. In this paper, we develop analytical method to solve this equation by Mobius transformation. And finally, this can reduce the problem to find roots of polynomial of four degree in one element. We have known this can be solved by square formally because its degree less than five. Although complexity as a solution, but in this sense, we can say we formally solve this nonintegrable equation.

math-ph↗
arXiv2012

A study of solutions of the combined sine cosine Gordon equation

We have studied the solutions of the combined sine-cosine-Gordon Equation found by Wazwaz (App. Math. Comp. 177, 755 (2006)) using the variable separated ODE method. These solutions can be transformed into a new form. We have derived the relation between the phase of the combined sine-cosine-Gordon equation and the parameter in these solutions. Its applications in physical systems are also discussed

math-ph↗
arXiv2012

Solitons and spin transport in an antiferromagnetic spin chain

We study the spin transport on a S=1/2 antiferromagnetic chain with external fields which provids a phase angle. The equation of motion becomes the sine-Gordon equation after Jordan-Wigner transformation and bosonization. Soliton solutions of the sine-Gordon equations for a system of finite length are found and the quantum fluctuations are calculated. The spin is transported as the soliton solutions evolves with the adiabatical variation of the phase angle in the phase space. We observe that the spin is transported by ΔS=1, as the phase angle changes by the period of 2π when the quantum fluctuation enables the system makes transition between two solutions. This quantum spin transport is not affected by disturbance of environment.

cond-mat.str-el↗
arXiv2010

Nonmagnetic impurity perturbation to the quasi-two-dimensional quantum helimagnet LiCu2O2

A complete phase diagram of Zn substituted quantum quasi-two-dimensional helimagnet LiCu2O2 has been presented. Helical ordering transition temperature (T_h) of the original LiCu2O2 follows finite size scaling for less than ~ 5.5% Zn substitution, which implies the existence of finite helimagnetic domains with domain boundaries formed with nearly isolated spins. Higher Zn substitution > 5.5% quenches the long-range helical ordering and introduces an intriguing Zn level dependent magnetic phase transition with slight thermal hysteresis and a universal quadratic field dependence for T_c (Zn > 0.055,H). The magnetic coupling constants of nearest-neighbor (nn) J1 and next-nearest-neighbor (nnn) J2 (alpha=J2/J1) are extracted from high temperature series expansion (HTSE) fitting and N=16 finite chain exact diagonalization simulation. We have also provided evidence of direct correlation between long-range helical spin ordering and the magnitude of electric polarization in this spin driven multiferroic material.

cond-mat.str-el↗
arXiv2010

Long Range orders in multiferroics

We proposed that in multiferroics there exists a third long range order besides the electric polarization and magnetic order. This long range order reduces the symmetry of the spatial part of the wave functions of electrons. Thus the cancellation in the spin current" model can be avoided. As a result, the expectation value of electric polarization will be larger by an order of magnitude. We have derived a new form of electric polarization \vec{P} -\vec{Q}\times(\vec{s_i}\times\vec{s_{j+1}}) where \vec{Q} is the wave vector of this long range order

cond-mat.str-el↗
arXiv2010

Quantum critical surface of the zigzag spin chain under magnetic field: Application to superconducting quantum dots

We analyze the exact ground state of XXZ zigzag spin chain with applied magnetic field and find the quantum critical surface. Using the theorem of positive semi-definite matrix, we can prove that the ground states for a specific region, are fully polarized state and one magnon states. With Bethe ansatz, we argue that this is the quantum critical surface in all cases. A first in the literature, we derive the analytical expression of quantum critical surface for superconducting quantum dots array in the presence of gate voltage.

cond-mat.str-el↗
arXiv2009

Solution of the asymmetric double sine-Gordon equation

We present solutions of asymmetric double sine-Gordon equation (DSGE) of an infinite system based on Mobius transformation and numerical exercise. This method is able to give the forms of the solutions for all the region on the ϕ-ηparameter plane where ϕis an additional phase and ηis the ratio of the magnitudes of two sine terms. We are able to show how the deconfinement occurs near ϕ=(1/2+n)πand ϕ=n pi. and also find the solution for all values of ϕ. We predict different kind of solutions and transitions among them in different parts of the parameter space of this equation.

cond-mat.str-el↗
arXiv2008

Quantum spin pump on a finite antiferromagnetic chain through bulk states

We studied the possibility of the spin pump in a S=1/2 antiferromagnetic chain. The spin chain is mapped into a fermion system and bosonization is utilized to transform the equation of motion to a sine-Gordon equation. The sine-Gordon equation on a finite chain with different boundary conditions is solved. Among numerous solutions, the static soliton is compatible with the original physical system. By varying adiabatically a angle in the phase space composed of applied electric and magnetic fields, the spin states change between the Neel state and dimer state and a quantized spin is transported by the bulk state from one end of the system to the other.

cond-mat.str-el↗
arXiv2008

Relationship between ferroelectricity and Dzyaloshinskii-Moriya interaction in multiferroics and the effect of bond-bending

We studied the microscopic mechanism of multiferroics, in particular with the "spin current" model (Hosho Katsura, Naoto Nagaosa and Aleander V. Balatsky, Phys. Rev. Lett. 95, 057205 (2005)). Starting from a system with helical spin configuration, we solved for the forms of the electron wave functions and analyzed their characteristics. The relation between ferroelectricity and Dzyaloshinskii-Moriya interaction (I. Dzyaloshinskii, J. Phys. Chem. Solids 4, 241 (1958) and T. Moriya, Phys. Rev. 120, 91 (1960)) is clearly established. There is also a simple relation between the electric polarization and the wave vector of magnetic orders. Finally, we show that the bond-bending exists in transition metal oxides can enhance ferroelectricity.

cond-mat.str-el↗
arXiv2008

Quantum spin pumping at fractionally quantized magnetization state for a system with competing exchange interactions

We study the quantum spin pumping of an antiferromagnetic spin-1/2 chain with competing exchange interactions. We show that spatially periodic potential modulated in space and time acts as a quantum spin pump. In our model system, an applied electric field causes a spin gap to its critical ground state by introducing bond-alternation exchange interactions. We study quantum spin pumping at different quantized magnetization states and also explain physically the presence and absence of quantum spin pumping at different fractionally quantized magnetization states.

cond-mat.str-el↗
arXiv2006

The magnetic orders induced ferroelectricity

We studied the ferroelectricity of magnetic oxides in which its emergence coincides with the onset of a second incommensurate magnetic order. We solved for the wave function of e_{g} electrons in the presence of magnetic orders. The coupling between the magnetic and electric orders is provided by the spin-orbit interaction. It was found that the net electric dipole moment of the system came from the bond between the transition metal and oxygen atoms. The anisotropy of d-orbitals also played an important role. Finally, the form of the coupling leads us to the conclusion that it is an improper ferroelectricity.

cond-mat.str-el↗
arXiv2005

A study on the coexistence of BEC and BCS states

We pointed out in this work that in dealing with the BEC-BCS crossover problem, the dynamic effect of is not negligible. Accordingly, an equation of motion approach was devised to calculate the Green$^{\prime}$s functions. Based on our result, we concluded that instead of crossover, BCS states and Bose-Einstein condensation always coexist.

cond-mat.supr-con↗