arXiv subjects

Xian-Ru Hu

Publications and source records attributed to Xian-Ru Hu.

35 records · Page 2Linked to original sources

arXiv2019

Thermodynamics of charged AdS black holes in rainbow gravity

In this paper, the thermodynamic property of charged AdS black holes is studied in rainbow gravity. By the Heisenberg Uncertainty Principle and the modified dispersion relation, we obtain deformed temperature. Moreover, in rainbow gravity we calculate the heat capacity in a fixed charge and discuss the thermal stability. We also obtain a similar behaviour with the liquid-gas system in extending phase space (including $P$ and $r$) and study its critical behavior with the pressure given by the cosmological constant and with a fixed black hole charge $Q$. Furthermore, we study the Gibbs function and find its characteristic swallow tail behavior, which indicates the phase transition. We also find there is a special value about the mass of test particle which would lead the black hole to zero temperature and a diverging heat capacity with a fixed charge.

gr-qc↗

arXiv2017

Hawking radiation-quasinormal modes correspondence for large AdS black holes

It is well-known that the non-strictly thermal character of the Hawking radiation spectrum generates a natural correspondence between Hawking radiation and black hole quasinormal modes. This main issue has been analyzed in the framework of Schwarzschild black holes, Kerr black holes and nonextremal Reissner-Nordstrom black holes. In this paper, by introducing the effective temperature, we reanalysis the non-strictly thermal character of large AdS black holes. The results show that the effective mass corresponding to the effective temperature is approximatively the average one in any dimension. And the other effective quantities can also be obtained. Based on the known forms of frequency in quasinormal modes, we reanalysis the asymptotic frequencies of the large AdS black hole in three and five dimensions. Then we get the formulas of the Bekenstein-Hawking entropy and the horizon's area quantization with functions of the quantum "overtone" number $n$.

gr-qc↗

arXiv2016

First-principle study on compensated half metallic double perovskite compound $Ba_2PrVO_6$

The first-principle study on double perovskite compound Ba$_2$PrVO$_6$ has been presented in this paper. By analysing band structures and integrated density of states, it is found that Ba$_2$PrVO$_6$ is ferromagnetic metallic within LSDA and compensated half metallic whithin LSDA+U. According to the total and partial density of states, the anti-ferromagnetism of Ba$_2$PrVO$_6$ is originated from the spin down state Pr$^{4+}$ ($4f_{-2}$) and the spin up hybridized state between the partially filled $t_{2g}$ state of V and the partially filled triple-degeneration state $4f_{-1}$, $4f_{+1}$, $4f_{+3}$ of Pr. We have investigated the magnetic evaluation of Ba$_2$PrVO$_6$ through fixed spin moment calculations, and the results indicate that the compensated half-metallic state is the ground state. The thermodynamic properties of Ba$_2$PrVO$_6$ are also studied by employing the quasi-harmonic Debye model.

cond-mat.mtrl-sci↗

arXiv2015

A first-principle study of half-Heusler alloys CKMg and SiKMg

The structural, electronic, and magnetic properties of half-Heusler alloys CKMg and SiKMg are studied by using first-principle density functional theory. The calculations reveal the SiKMg alloy is a half-metallic ferromagnet with the magnetic moment of 1 $μ_B$ per formula unit at equilibrium lattice constant. The magnetic moment mainly originates from the strong spin-polarization of $p$ electrons of Si atom and partial involvement of $d$ electrons of K atom. The half-metallic gap is 0.105 eV. The robustness of half-metallic against the lattice constants for SiKMg is also calculated. CKMg alloy is nearly half-metallic with a spin polarization of 99.99 \%\ at equilibrium lattice constant, but it is a good half-metallic alloy when a low pressure is applied. This shows CKMg is a very promising spintronic functional material.

cond-mat.mtrl-sci↗

arXiv2015

Half-metallic ferromagnetism in the RbSe and CsTe compounds with CsCl structure: A first-principles study

We investigate the electronic structures and magnetic properties of RbSe and CsTe compounds in CsCl, RS and ZB structures by using first-principles calculation. It is shown that these two compounds exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 $μ_B$ per formula in all the three structures. Total energy calculations indicate the CsCl phase is more stable than the other two phases. We investigate these two compounds with CsCl structure in detail. The ferromagnetism results mainly from the spin-polarization of p states of anion Se (Te) for the two compounds. The half-metallicities of RbSe and CsTe compounds can be preserved up to 2.5\% and 0.8\% compression of lattice constants with respect to their equilibrium lattices, respectively.

cond-mat.mtrl-sci↗

arXiv2015

First-principle study on bulk and (1 1 1) surface of MP (M=K and Rb) in rocksalt structure

The electronic and magnetic properties of bulk and (1 1 1) surfaces for MP (M=K ans Rb) in rocksalt structure have been investigated by employing first-principle calculations. The results reveal that the compounds are half-metallic ferromagnets at the equilibrium lattice constants with large half-metallic band gaps of 0.46 and 0.74 eV. The (111) surfaces of KP and RbP keep their bulk half-metallic property. We study the stabilities of the bulk compounds and their (1 1 1) surfaces as well.

cond-mat.mtrl-sci↗

arXiv2015

$Ab$ $intito$ study on some new spin-gapless semiconductors: The Zr-based quanternary Heusler alloys

Employing $ab$ $intito$ electronic structure calculations, we have investigated electronic and magnetic properties of the Zr-based quanternary Heusler alloys: ZrCoVIn, ZrFeVGe, ZrCoFeP, ZrCoCrBe and ZrFeCrZ (Z=In and Ga). Our $ab$ $intito$ calculation results show that all the alloys are (or nearly) spin-gapless semiconductors. All the alloys have large band gaps, indicating the stability of them at room temperature. The Slater-Pauling behaviours of these alloys are discussed as well. The values of Curie temperature of all the alloys are estimated. And it is found that the values of the Curie temperature for all our calculated quanternary Heusler alloys are higher than that of room temperature.

cond-mat.mtrl-sci↗

arXiv2015

A first-principle study on some quanternary Heusler alloys with 4d and 3d transition metal elements

In this letter, we investigate the magnetic properties, electronic structures, Slater-Pauling behaviours of some quanternary Heusler alloys with 4d and 3d transition metal elements. The energy levels of the minority-spin electronic band structures for all our calculated alloys are discussed. We have summaried 21 quanternary Heusler alloys. Our calculations indicate that the half metals ZrCoCrSi, ZrCoCrIn, ZrCoFeSi, ZrFeVAl, ZrFeVGa and NbFeCrAl have large spin-flip gaps.

cond-mat.mtrl-sci↗

arXiv2014

Generalized Holographic Equipartition for Friedmann-Robertson-Walker Universes

The novel idea that spatial expansion of our universe can be regarded as the consequence of the emergence of space was proposed by Padmanabhan. By using of the basic law governing the emergence, which Padmanabhan called holographic equipartition, he also arrives at the Friedmann equation in a flat universe. When generalized to other gravity theories, the holographic equipartition need to be generalized with an expression of $f(ΔN,N_{sur})$. In this paper, we give general expressions of $f(ΔN,N_{sur})$ for generalized holographic equipartition which can be used to derive the Friedmann equations of the Friedmann-Robertson-Walker universe with any spatial curvature in higher (n+1)-dimensional Einstein gravity, Gauss-Bonnet gravity and more general Lovelock gravity. The results support the viability of the perspective of holographic equipartition.

gr-qc↗

arXiv2014

Emergence of space and the general dynamic equation of Friedmann-Robertson-Walker universe

A novel idea that the cosmic acceleration can be understood from the perspective that spacetime dynamics is an emergent phenomena was proposed by T. Padmanabhan. The Friedmann equations of FRW universe can be derived from different gravity theories with different modifications of Padmanabhan's proposal. In this paper, a unified formula is proposed, in which those modifications can be treated as special cases when the formula is applied to different universe radii. Furthermore, the dynamic equations of FRW universe in the $ f(R) $ theory and deformed Ho{ř}ava-Lifshitz theory are investigated. The results show the validity of our proposed formula.

gr-qc↗

arXiv2012

First-principles study on the magnetic properties of six potential half-metallic ferromagnets: alkaline-earth (Ca, Sr) doped XC (X=Si, Ge, Sn)

Six half-metallic ferromagnets X0.75Y0.25C (X=Si, Ge, Sn and Y =Ca and Sr) with zinc-blende structure, resulting from alkaline-earth (Ca, Sr) substitution for X, are predicted based on the density functional theory. The calculated total magnetic moments of these ferromagnets are all integer 2.00μB per supercell, which are one of important characters of half-metallic ferromagnets. Our calculations indicate that X0.75Y0.25C have wide spin gap and potentially have high Curie temperature. Alkaline-earth doping results in the spin-polarization and half-metallicity of these compounds. It is confirmed that the p-d exchange coupling is responsible for the ferromagnetism of X0.75Y0.25C except Sn0.75Ca0.25C.

cond-mat.mtrl-sci↗

arXiv2011

Half-metallic properties for the Ti2YZ (Y=Fe,Co,Ni,Z=Al,Ga,In) Hesuler alloys: A first-principles study

Using the full-potential local orbital minimum-basis method,the Ti2-based full-Heusler alloys are studied. The results show that these compounds exhibit a half-metallic behavior, however, in contrast to the conventional full-Heusler alloys,the full-Heusler alloys show a Slater-Pauling behavior and the total spin magnetic moment per unit cell(Mt) following the rule Mt=Zt-18. The origin of the gap in these half-metallic alloys are well understood. It is found that the half-metallic properties of Ti2-based compounds are insensitive to the lattice distortion and a fully spin polarization can be obtained within a wide range of lattice parameters. This is favorable in practical application.

cond-mat.mtrl-sci↗

arXiv2011

The Klein-Gordon equation in Machian model

The non-local Machian model is regarded as an alternative theory of gravitation which states that all particles in the Universe as a 'gravitationally entangled' statistical ensemble. It is shown that the Klein-Gordon equation can be derived within this Machian model of the universe. The crucial point of the derivation is the activity of the Machian energy background field which causing a fluctuation about the average momentum of a particle, the non-locality problem in quantum theory is addressed in this framework.

gr-qc↗

arXiv2011

Thermodynamical properties of interacting holographic dark energy model with apparent horizon

We have investigated the thermodynamical properties of the universe with dark energy. It is demonstrated that in a universe with spacial curvature the natural choice for IR cutoff could be the apparent horizon radius. We shown that any interaction of pressureless dark matter with holographic dark energy, whose infrared cutoff is set by the apparent horizon radius, implying a constant effective equation of state of dark component in a universe. In addition we found that for the static observer in space, the comoving distance has a faster expansion than the apparent horizon radius with any spatial curvature. We also verify that in some conditions the modified first law of thermodynamics could return to the classic form at apparent horizon for a universe filled with dark energy and dark matter. Besides, the generalized second law of thermodynamics is discussed in a region enclosed by the apparent horizon.

hep-th↗

arXiv2011

The Friedmann equation in modified entropy-area relation from entropy force

According to the formal holographic principle, a modification to the assumption of holographic principle in Verlinder's investigation of entropy force is obtained. A more precise relation between entropy and area in the holographic system is proposed. With the entropy corrections to the area-relation, we derivate Newton's laws and Einstein equation with a static spherically symmetric holographic screen. Furthermore we derived the correction terms to the modified Friedmann equation of the FRW universe starting from the holographic principle and the Debye model.

hep-th↗

arXiv2010

Observational Constraints on Phantom Crossing DGP Gravity

We study the observational constraints on the Phantom Crossing DGP model. We demonstrate that the crossing of the phantom divide does not occur within the framework of the original Dvali-Gabadadze-Porrati (DGP) model or the DGP model developed by Dvali and Turner. By extending their model in the framework of an extra dimension scenario, we study a model that realizes crossing of the phantom divide. We investigate the cosmological constraints obtained from the recent observational data of Type Ia Supernovae, Cosmic Microwave Background anisotropies, and Baryon Acoustic Oscillations. The best fit values of the parameters with 1$σ$ (68%) errors for the Phantom Crossing DGP model are $Ω_{m,0}=0.27^{+0.02}_{-0.02}$, $β=0.54^{+0.24}_{-0.30}$. We find that the Phantom Crossing DGP model is more compatible with the observations than the original DGP model or the DGP model developed by Dvali and Turner. Our model can realize late-time acceleration of the universe, similar to that of $Λ$CDM model, without dark energy due to the effect of DGP gravity. In our model, crossing of the phantom divide occurs at a redshift of $z \sim 0.2$.

astro-ph.CO↗

arXiv2010

The modified wave function of test particle approaching holographic screen from entropy force

In this note we generalize entropy based on the quantum mechanical probability density distribution. Motivated by J. Munkhammar and the uncertainty of entropy we modified the origin wave function of the test particle. The corrected one acting on the quantum particle is subject to the uncertainty principle. Considering the uncertain relation, the corrected probability of the particle for measurement on holographic screen has been proposed. We also derivate the speed of information transfer described by wave function. Our quantum approach to entropy stress the information in a physical system is directly associated with its quantum mechanical entropy defined by the equality of the partition function.

hep-th↗