arXiv subjects

Tianxing Ma

Publications and source records attributed to Tianxing Ma.

At least 109 records · Page 6Linked to original sources

arXiv2010

Spontaneous symmetry breakings in two-dimensional kagome lattice

We study spontaneous symmetry breakings for fermions (spinless and spinful) on a two-dimensional kagome lattice with nearest-neighbor repulsive interactions in weak coupling limit, and focus in particular on topological Mott insulator instability. It is found that at $\frac{1}{3}$-filling where there is a quadratic band crossing at $Γ$-point, in agreement with Ref. 1, the instabilities are infinitesimal and topological phases are dynamically generated. At $\frac{2}{3}$-filling where there are two inequivalent Dirac points, the instabilities are finite, and no topological phase is favored at this filling without breaking the lattice translational symmetry. A ferromagnetic quantum anomalous Hall state with infinitesimal instability is further proposed at half-filling of the bottom flat band.

cond-mat.mtrl-sci↗

arXiv2010

Reduced fidelity in Kitaev honeycomb model

We study the reduced fidelity and reduced fidelity susceptibility in the Kitaev honeycomb model. It is shown that the reduced fidelity susceptibility of two nearest site manifest itself a peak at the quantum phase transition point, although the one-site reduced fidelity susceptibility vanishes. Our results directly reveal that the reduced fidelity susceptibility can be used to characterize the quantum phase transition in the Kitaev honeycomb model, and thus suggest that the reduced fidelity susceptibility is an accurate marker of the topological phase transition when it is properly chosen, despite of its local nature.

cond-mat.str-el↗

arXiv2010

Classical spins in topological insulators

Following the recent theoretical proposal and experiment on quantum spin Hall effect in HgTe/CdTe quantum wells, we consider a single magnetic impurity localized in the bulk of the system, which we treat as a classical spin. It is shown that there are always localized excited states in the bulk energy gap for arbitrarily strong impurity strength in inverted region, while the localized excited states vanish for very strong impurity strength in normal region. Similar conclusion also applies to three-dimensional topological insulators. This distinct difference serves as another novel criterion for the conventional and topological insulating phases when the time-reversal symmetry is broken, and can be easily experimentally observed through the STM and/or ARPES experiments.

cond-mat.mtrl-sci↗

arXiv2008

Extra Current and Integer Quantum Hall Conductance in the Spin-Orbit Coupling System

We study the extra term of particle current in a 2D k-cubic Rashba spin-orbit coupling system and the integer quantization of the Hall conductance in this system. We provide a correct formula of charge current in this system and the careful consideration of extra currents provides a stronger theoretical basis for the theory of the quantum Hall effect which has not been considered before. The non-trivial extra contribution to the particle current density and local conductivity, which originates from the cubic dependence on the momentum operator in the Hamiltonian, will have no effect on the integer quantization of the Hall conductance. The extension of Noether's theorem for the 2D k-cubic Rashba system is also addressed. The two methods reach to exactly the same results.

cond-mat.mes-hall↗

arXiv2008

NMR relaxation rate and static spin susceptibility in graphene

The NMR relaxation rate and the static spin susceptibility in graphene are studied within a tight-binding description. At half filling, the NMR relaxation rate follows a power law as $T^2$ on the particle-hole symmetric side, while with a finite chemical potential $μ$ and next-nearest neighbor $t'$, the $(μ+3t')^2$ terms dominate at low excess charge $δ$. The static spin susceptibility is linearly dependent on temperature $T$ at half filling when $t'=0$, while with a finite $μ$ and $t'$, it should be dominated by $(μ+3t')$ terms in low energy regime. These unusual phenomena are direct results of the low energy excitations of graphene, which behave as massless Dirac fermions. Furthermore, when $δ$ is high enough, there is a pronounced crossover which divides the temperature dependence of the NMR relaxation rate and the static spin susceptibility into two temperature regimes: the NMR relaxation rate and the static spin susceptibility increase dramatically as temperature increases in the low temperature regime, and after the crossover, both decrease as temperature increases at high temperatures. This crossover is due to the well-known logarithmic Van Hove singularity in the density of states, and its position dependence of temperature is sensitive to $δ$.

cond-mat.str-el↗

arXiv2007

Resonant spin polarization in a two-dimensional hole gas: Effect of the Luttinger term, structural inversion asymmetry and Zeeman splitting

The electric-field-induced resonant spin polarization of a two-dimensional hole gas described by Luttinger Hamiltonian with structural inversion asymmetry and Zeeman splitting in a perpendicular magnetic field was studied. The spin polarization arising from splitting between the light and the heavy hole bands shows a resonant peak at a certain magnetic field. Especially, the competition between the Luttinger term and the structural inversion asymmetry leads to a rich resonant peaks structure, and the required magnetic field for the resonance may be effectively reduced by enlarging the effective width of the quantum well. Furthermore, the Zeeman splitting tends to move the resonant spin polarization to a relative high magnetic field and destroy these rich resonant spin phenomena. Finally, both the height and the weight of the resonant peak increase as the temperature decreases. It is believed that such resonant spin phenomena can be verified in the sample of a two-dimensional hole gas, and it may provide an efficient way to control spin polarization by an external electric field.

cond-mat.mes-hall↗

arXiv2007

Spin accumulation from the non-Abelian Aharonov-Bohm effect

Recently, it has been shown that the spin-orbit coupling (SOC) of the Dresselhaus type in $[110]$ quantum wells can be mathematically removed by a non-Abelian gauge transformation. In the presence of an additional uniform magnetic field, such a non-Abelian gauge flux leads to a spin accumulation at the edges of the sample, where the relative sign of the spin accumulation between the edges can be tuned by the sign of the Dresselhaus SOC constant. Our prediction can be tested by Kerr measurements within the available experimental sensitivities.

cond-mat.mes-hall↗

arXiv2006

Theory of superconductivity in doped cuprates

Within the t-t'-J model, the physical properties of doped cuprates in the superconducting-state are discussed based on the kinetic energy driven superconducting mechanism. We show that the superconducting-state in cuprate superconductors is controlled by both superconducting gap parameter and single particle coherence, and then quantitatively reproduce some main features found in the experiments on cuprate superconductors, including the doping dependence of the superconducting gap parameter and superconducting transition temperature, the electron spectral function at [π,0] point, the charge asymmetry of superconductivity in the hole and electron doping, and the doping and energy dependence of the incommensurate magnetic scattering at both low and high energies and commensurate [π,π] resonance at intermediate energy. We also show that the incommensurate magnetic excitations at high energy have energies greater than the superconducting gap energy, and are present at the superconducting transition temperature.

cond-mat.supr-con↗

arXiv2006

Sign changes and resonance of intrinsic spin Hall effect in two-dimensional hole gas

The intrinsic spin Hall conductance shows rich sign changes by applying a perpendicular magnetic field in a two-dimensional hole gas. Especially, a notable sign changes can be achieved by adjusting the characteristic length of the Rashba coupling and hole density at moderate magnetic fields. This sign issue may be easily realized in experiments. The oscillations of the intrinsic spin Hall conductance as a function of 1/$B$ is nothing else but Shubnikov-de Haas oscillations, and the additional beatings can be quantitatively related to the value of the spin-orbit coupling parameter. The Zeeman splitting is too small to introduce effective degeneracy between different Landau levels in a two-dimensional hole gas, and the resonant intrinsic spin Hall conductance appears in high hole density and strong magnetic field due to the transition between mostly spin-$-{1/2}$ holes and spin-3/2 holes is confirmed. Two likely ways to establish intrinsic spin Hall effect in experiments and a possible application are suggested.

cond-mat.mes-hall↗

arXiv2006

Spin Hall Conductance of the Two Dimensional Hole Gas in a Perpendicular Magnetic Field

The charge and spin Hall conductance of the two-dimensional hole gas within the Luttinger model with and without inversion symmetry breaking terms in a perpendicular magnetic field are studied, and two key phenomena are predicted. The sign of the spin Hall conductance is modulated periodically by the external magnetic field, which means a possible application in the future. Furthermore, a resonant spin Hall conductance in the two-dimensional hole gas with a certain hole density at a typical magnetic field is indicated, which implies a likely way to firmly establish the intrinsic spin Hall effect. The charge Hall conductance is unaffected by the spin-orbit coupling.

cond-mat.mes-hall↗

arXiv2006

The magnetic nature of superconductivity in doped cuprates

Within the kinetic energy driven superconducting mechanism, the magnetic nature of cuprate superconductors is discussed. It is shown that the superconducting state is controlled by both charge carrier gap function and quasiparticle coherent weight. This quasiparticle coherent weight grows linearly with the hole doping concentration in the underdoped and optimally doped regimes, and then decreases with doping in the overdoped regime, which leads to that the maximal superconducting transition temperature occurs around the optimal doping, and then decreases in both underdoped and overdoped regimes. Within this framework, we calculate the dynamical spin structure factor of cuprate superconductors, and reproduce all main features of inelastic neutron scattering experiments, including the energy dependence of the incommensurate magnetic scattering at both low and high energies and commensurate resonance at intermediate energy.

cond-mat.supr-con↗

arXiv2005

Enhancement of superconducting transition temperature by the additional second neighbor hopping t' in the t-J model

Within the kinetic energy driven superconducting mechanism, the effect of the additional second neighbor hopping t' on the superconducting state of the t-J model is discussed. It is shown that t' plays an important role in enhancing the superconducting transition temperature of the t-J model. It is also shown that the superconducting-state of cuprate superconductors is the conventional Bardeen-Cooper-Schrieffer like, so that the basic Bardeen-Cooper-Schrieffer formalism is still valid in quantitatively reproducing the doping dependence of the superconducting gap parameter and superconducting transition temperature, and electron spectral function at $(π,0)$ point, although the pairing mechanism is driven by the kinetic energy by exchanging dressed spin excitations.

cond-mat.supr-con↗

arXiv2005

The charge asymmetry in superconductivity of hole- and electron-doped cuprates

Within the t-t'-J model, the charge asymmetry in superconductivity of hole- and electron-doped cuprates is studied based on the kinetic energy driven superconducting mechanism. It is shown that superconductivity appears over a narrow range of doping in electron-doped cuprates, and the superconducting transition temperature displays the same kind of the doping controlled behavior that is observed in the hole-doped case. However, the maximum achievable superconducting transition temperature in the optimal doping in electron-doped cuprates is much lower than that of the hole-doped case due to the electron-hole asymmetry.

cond-mat.supr-con↗

arXiv2005

Doping dependence of charge dynamics in electron-doped cuprates

Within the t-t'-J model, the doping dependence of charge dynamics in electron-doped cuprates is studied. The conductivity spectrum shows a pseudogap structure with a low-energy peak appearing at $ω\sim 0$ and an rather sharp midinfrared peak appearing around $ω\sim 0.3\mid t\mid$, and the resistivity exhibits a crossover from the high temperature metallic-like to low temperature insulating-like behavior in the relatively low doped regime, and a metallic-like behavior in the relatively high doped regime, in qualitative agreement with experiments. Our results also show that these unusual behaviors of the charge dynamics is intriguingly related to the magnetic correlation in the system.

cond-mat.str-el↗

arXiv2004

Interplay between single particle coherence and kinetic energy driven superconductivity in doped cuprates

Within the kinetic energy driven superconducting mechanism, the interplay between the single particle coherence and superconducting instability in doped cuprates is studied. The superconducting transition temperature increases with increasing doping in the underdoped regime, and reaches a maximum in the optimal doping, then decreases in the overdoped regime, however, the values of this superconducting transition temperature in the whole superconducting range are suppressed to low temperature due to the single particle coherence. Within this superconducting mechanism, we calculate the dynamical spin structure factor of cuprate superconductors, and reproduce all main features of inelastic neutron scattering experiments in the superconducting-state.

cond-mat.supr-con↗

arXiv2004

Unusual heat transport in underdoped cuprates

Within the t-J model, the heat transport of the underdoped cuprates is studied based on the fermion-spin theory. It is shown that at low temperatures the energy dependence of the thermal conductivity spectrum consists of two bands. The higher-energy band shows a weak peak, while the low-energy peak is located at a finite energy. This high-energy broad band is severely suppressed with increasing temperatures, and vanishes at higher temperature. It is also shown that the temperature dependence of the thermal conductivity increases monotonously with increasing temperatures, in agreement with experiments.

cond-mat.str-el↗

arXiv2004

A gauge invariant dressed holon and spinon description of the normal-state of underdoped cuprates

A partial charge-spin separation fermion-spin theory is developed to study the normal-state properties of the underdoped cuprates. In this approach, the physical electron is decoupled as a gauge invariant dressed holon and spinon, with the dressed holon behaving like a spinful fermion, and represents the charge degree of freedom together with the phase part of the spin degree of freedom, while the dressed spinon is a hard-core boson, and representing the amplitude part of the spin degree of freedom. The electron local constraint for single occupancy is satisfied. Within this approach, the charge and spin dynamics of the underdoped cuprates are studied based on the t-t'-J model. It is shown that the charge dynamics is mainly governed by the scattering from the dressed holons due to the dressed spinon fluctuation, while the scattering from the dressed spinons due to the dressed holon fluctuation dominates the spin dynamics.

cond-mat.str-el↗

arXiv2003

Unusual charge transport and spin response of doped bilayer triangular antiferromagnets

Within the t-J model, the charge transport and spin response of the doped bilayer triangular antiferromagnet are studied by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in the electronic structure, the qualitative behaviors of the physical properties are the same as in the single layer case. The conductivity spectrum shows the low-energy peak and unusual midinfrared band, the temperature dependent resistivity is characterized by the nonlinearity metallic-like behavior in the higher temperature range, and the deviation from the metallic-like behavior in the lower temperature range, and the commensurate neutron scattering peak near the half-filling is split into six incommensurate peaks in the underdoped regime, with the incommensurability increases with the hole concentration at lower dopings, and saturates at higher dopings.

cond-mat.str-el↗