arXiv subjects

J. P. Hu

Publications and source records attributed to J. P. Hu.

At least 19 recordsLinked to original sources

arXiv2025

The Hubble Tension resolved by the DESI Baryon Acoustic Oscillations Measurements

The $Λ$ cold dark matter ($Λ$CDM) cosmological model provides a good description of a wide range of astrophysical and cosmological observations. However, severe challenges to the phenomenological $Λ$CDM model have emerged recently, including the Hubble constant tension and the significant deviation from the $Λ$CDM model reported by the Dark Energy Spectroscopic Instrument (DESI) collaboration. Despite many explanations for the two challenges have been proposed, the origins of them are still intriguing mysteries. Here, we investigate the DESI Baryon Acoustic Oscillations (BAOs) measurements to interpret the Hubble constant tension. Employing a non-parametric method, we find that the dark energy equation of state $w(z)$ evolves with redshift from DESI BAO data and type Ia supernovae. From the Friedmann equations, the Hubble constant ($H_0$) is derived from $w(z)$ model-independently. We find that the values of $H_0$ show a descending trend as a function of redshift, and can effectively resolve the Hubble constant tension. Our study finds that the two unexpected challenges to the $Λ$CDM model can be understood in one physical framework, e.g., dynamical dark energy.

astro-ph.CO↗

arXiv2025

Measuring Hubble constant using localized and unlocalized fast radio bursts

The Hubble constant ($H_0$) is one of the most important parameters in the standard $\rm ΛCDM$ model. The measurements given by the main two methods show a gap larger than $4σ$, which is known as Hubble tension. Fast radio bursts (FRBs) are extragalactic pulses with durations of milliseconds. They can be used as cosmological probes. We constrain $H_0$ using localized and nonlocalized FRBs. We first used 108 localized FRBs to constrain $H_0$ using the probability distributions of \DMhost and \DMIGM from the IllustrisTNG simulation. Then, we used a Monte Carlo sampling to calculate the pseudo-redshift distributions of 527 nonlocalized FRBs from CHIME observations. The 108 localized FRBs yield a constraint of $H_0=69.40_{-1.97}^{+2.14}$ ${\rm km\ s^{-1} Mpc^{-1}}$, which lies between the early- and late-time values. The constraint of $H_{0}$ from nonlocalized FRBs yields $H_0=68.81_{-0.68}^{+0.68}$ ${\rm km\ s^{-1} Mpc^{-1}}$. This result indicates that the uncertainty on the constraint of $H_0$ drops to $\sim1\%$ when the number of localized FRBs is increased to $\sim500$. These uncertainties only include the statistical error. The systematic errors are also discussed and play a dominant role in the current sample.

astro-ph.CO↗

arXiv2025

Uncorrelated estimations of $H_0$ redshift evolution from DESI baryon acoustic oscillation observations

The Dark Energy Spectroscopic Instrument (DESI) collaboration recently released the first year data of baryon acoustic oscillations (BAOs). Based on the five different tracers, the cosmological constraint shows a hint of deviation from the standard $Λ$CDM model. In this letter, we combine the DESI BAOs with other cosmic probes to constrain the evolution of Hubble constant as a function of redshift in the flat $Λ$CDM model. The non-parametric method is used to estimate the value of Hubble constant at different redshift bins. The correlation among different bins are removed by diagonalizing the covariance matrix. The joint data sample demonstrate a decreasing trend of Hubble constant with a significance of $6.4 σ$, which can naturally resolve the Hubble tension. To avoid statistical effects caused by the binning methods, we tested other three different binning methods and also found a decreasing trend. It may be due to dynamical dark energy or modified gravity.

astro-ph.CO↗

arXiv2024

Hints of new physics for the Hubble tension: violation of cosmological principle

Discrepancy between the measurements of Hubble constant $H_{0}$ from the cosmic microwave background (CMB) and the local distance ladder is the most serious challenge to the standard $Λ$CDM model. Recent researches point out that it might be related with the violation of cosmological principle. Here, we investigate the impact of dipole-monopole correction on the constraints of $H_{0}$ utilizing the dipole fitting method based on the $Λ$CDM model and cosmography method. Our results show that the dipole-monopole correction can reduce the constraints of $H_{0}$ from a larger value consistent with SH0ES results to a smaller value consistent with Planck results. This finding can effectively alleviate the Hubble tension. Through making redshift tomography and model-independent analyses, we confirm that our findings are independent of redshift and cosmological model. In addition, the theoretical prediction of $H(z)/(1+z)$ reconstructed by the constraints of $Λ$CDM model with the dipole correction is in agreement with BAOs measurements including 5 DESI BAOs within 1$σ$ range except datapoint at z = 0.51. Our research suggests that the Hubble tension originates from new physics beyond the standard $Λ$CDM model, which might lead to a violation of the cosmological principle.

astro-ph.CO↗

arXiv2023

Charge-density wave transition in magnetic topological semimetal EuAl$_4$

The interplay among topology, charge-density wave (CDW), and magnetism can give rise to a plethora of exotic quantum phenomena. Recently, a group of magnetic topological semimetals with tetragonal lattices and CDW order were found to exhibit anomalous magnetic instability, helical spin ordering, and the presence of skyrmions. However, the underlying mechanism responsible for these observations remains unclear. Here, we conducted a comprehensive investigation into the impact of CDW on the topological and magnetic properties of EuAl$_4$ using optical spectroscopy and the first-principles calculations. Through optical spectroscopy, we observed a partial gap (60~meV) on the Fermi surface and an enhanced mid-infrared absorption around 0.4~eV after the CDW transition. Magneto-optical spectroscopy and the first-principles calculations proved that, by affecting the band structure, the CDW order frustrates the antiferromagnetic interactions but strengthened the ferromagnetic ones, which can destabilize the magnetism. With lower symmetry in the CDW ordered state, carriers from the Weyl bands will mediate the anisotropic magnetic interactions promoting the formation of chiral spin textures. Conversely, without the CDW order, the counterpart EuGa$_4$ shows robust collinear antiferromagnetic order. Our findings uncover the pivotal role played by CDW order in arousing intricate magnetism in topological materials and provide valuable insights into controlling topological and magnetic properties through the manipulation of CDW orders.

cond-mat.supr-con↗

arXiv2023

Testing the cosmological principle with the Pantheon+ sample and the region-fitting method

The cosmological principle is fundamental to the standard cosmological model. It assumes that the Universe is homogeneous and isotropic on very large scales. As the basic assumption, it must stand the test of various observations. In this work, using the region fitting (RF) method, we mapped the all-sky distribution of cosmological parameters ($Ω_{m}$ and $H_{0}$) and find that the distribution significantly deviates from isotropy. A local matter underdensity region exists toward (${308.4^{\circ}}$$_{-48.7}^{+47.6}$, ${-18.2^{\circ}}$$_{-28.8}^{+21.1}$) as well as a preferred direction of the cosmic anisotropy (${313.4^{\circ}}$$_{-18.2}^{+19.6}$, ${-16.8^{\circ}}$$_{-10.7}^{+11.1}$) in galactic coordinates. Similar directions may imply that local matter density might be responsible for the anisotropy of the accelerated expansion of the Universe. Results of statistical isotropy analyses including Isotropy and Isotropy with real-data positions (RP) show high confidence levels. For the local matter underdensity, the statistical significances are 2.78$σ$ (isotropy) and 2.34$σ$ (isotropy RP). For the cosmic anisotropy, the statistical significances are 3.96$σ$ (isotropy) and 3.15$σ$ (isotropy RP). The comparison of these two kinds of statistical isotropy analyses suggests that inhomogeneous spatial distribution of real sample can increase the deviation from isotropy. The similar results and findings are also found from reanalyses of the low-redshift sample (lp+) and the lower screening angle ($θ_\mathrm{max}$ = 60$^{\circ}$), but with a slight decrease in statistical significance. Overall, our results provide clear indications for a possible cosmic anisotropy. This possibility must be taken seriously. Further testing is needed to better understand this signal.

astro-ph.CO↗

arXiv2023

Evidence of a decreasing trend for the Hubble constant

The current discrepancy between the Hubble constant $H_0$ derived from the local distance ladder and from the cosmic microwave background is one of the most crucial issues in cosmology, as it possibly indicates unknown systematics or new physics. Here we present a novel non-parametric method to estimate Hubble constant as a function of redshift. We establish independent estimates of the evolution of Hubble constant by diagonalizing the covariance matrix. From type Ia supernovae and the observed Hubble parameter data, a decreasing trend of Hubble constant with a significance of 5.6$σ$ confidence level is found. At low redshift, its value is dramatically consistent with that measured from the local distance ladder, and it drops to the value measured from the cosmic microwave background at high redshift. Our results can relieve the Hubble tension, and prefer the late-time solutions of it, especially the new physics.

astro-ph.CO↗

arXiv2022

$E_{\mathrm{iso}}$-$E_{\mathrm{p}}$ correlation of gamma ray bursts: calibration and cosmological applications

Gamma-ray bursts (GRBs) are the most explosive phenomena and can be used to study the expansion of Universe. In this paper, we compile a long GRB sample for the $E_{\mathrm{iso}}$-$E_{\mathrm{p}}$ correlation from Swift and Fermi observations. The sample contains 221 long GRBs with redshifts from 0.03 to 8.20. From the analysis of data in different redshift intervals, we find no statistically significant evidence for the redshift evolution of this correlation. Then we calibrate the correlation in six sub-samples and use the calibrated one to constrain cosmological parameters. Employing a piece-wise approach, we study the redshift evolution of dark energy equation of state (EOS), and find that the EOS tends to be oscillating at low redshift, but consistent with $-1$ at high redshift. It hints a dynamical dark energy at $2σ$ confidence level at low redshift.

astro-ph.HE↗

arXiv2022

High-redshift cosmography: Application and comparison with different methods

Cosmography is used in cosmological data processing in order to constrain the kinematics of the universe in a model-independent way. In this paper, we first investigate the effect of the ultraviolet (UV) and X-ray relation of a quasar on cosmological constraints. By fitting the quasar relation and cosmographic parameters simultaneously, we find that the 4$σ$ deviation from the cosmological constant cold dark matter ($Λ$CDM) model disappears. Next, utilizing the Pantheon sample and 31 long gamma-ray bursts (LGRBs), we make a comparison among the different cosmographic expansions ($z$-redshift, $y$-redshift, $E(y)$, $\log(1+z)$, $\log(1+z)+k_{ij}$, and Pad$\rm \acute{e}$ approximations) with the third-order and fourth-order expansions. The expansion order can significantly affect the results, especially for the $y$-redshift method. Through analysis from the same sample, the lower-order expansion is preferable, except the $y$-redshift and $E(y)$ methods. For the $y$-redshift and $E(y)$ methods, despite adopting the same parameterization of $y=z/(1+z)$, the performance of the latter is better than that of the former. Logarithmic polynomials, $\log(1+z)$ and $\log(1+z) + k_{ij}$, perform significantly better than $z$-redshift, $y$-redshift, and $E(y)$ methods, but worse than Pad$\rm \acute{e}$ approximations. Finally, we comprehensively analyze the results obtained from different samples. We find that the Pad$\rm \acute{e}_{(2,1)}$ method is suitable for both low and high redshift cases. The Pad$\rm \acute{e}_{(2,2)}$ method performs well in a high-redshift situation. For the $y$-redshift and $E(y)$ methods, the only constraint on the first two parameters ($q_{0}$ and $j_{0}$) is reliable.

astro-ph.CO↗

arXiv2021

A density-wave-like transition in the polycrystalline V3Sb2 sample with bilayer kagome lattice

Recently, transition-metal-based kagome metals have aroused much research interest as a novel platform to explore exotic topological quantum phenomena. Here we report on the synthesis, structure, and physical properties of a bilayer kagome lattice compound V3Sb2. The polycrystalline V3Sb2 samples were synthesized by conventional solid-state-reaction method in a sealed quartz tube at temperatures below 850 Celsius degree. Measurements of magnetic susceptibility and resistivity revealed consistently a density-wave-like transition at Tdw ~ 160 K with a large thermal hysteresis, even though some sample-dependent behaviors are observed presumably due to the different preparation conditions. Upon cooling through Tdw, no strong anomaly in lattice parameters and no indication of symmetry lowering were detected in powder x-ray diffraction measurements. This transition can be suppressed completely by applying hydrostatic pressures of about 1.8 GPa, around which no sign of superconductivity is observed down to 1.5 K. Specific-heat measurements reveal a relatively large Sommerfeld coefficient γ = 18.5 mJ/mol-K2, confirming the metallic ground state with moderate electronic correlations. Density functional theory calculations indicate that V3Sb2 shows a non-trivial topological crystalline property. Thus, our study makes V3Sb2 a new candidate of metallic kagome compound to study the interplay between density-wave-order, nontrivial band topology, and possible superconductivity.

cond-mat.str-el↗

arXiv2021

Measuring cosmological parameters with a luminosity-time correlation of gamma-ray bursts

Gamma-ray bursts (GRBs), as a possible probe to extend the Hubble diagram to high redshifts, have attracted much attention recently. In this paper, we select two samples of GRBs that have a plateau phase in X-ray afterglow. One is short GRBs with plateau phases dominated by magnetic dipole (MD) radiations. The other is long GRBs with gravitational-wave (GW) dominated plateau phases. These GRBs can be well standardized using the correlation between the plateau luminosity $L_0$ and the end time of plateau $t_b$. The so-called circularity problem is mitigated by using the observational Hubble parameter data and Gaussian process method. The calibrated \ltb ~correlations are also used to constrain $Λ$CDM and $w(z)$ = $w_{0}$ models. Combining the MD-LGRBs sample from Wang et al. (2021) and the MD-SGRBs sample, we find $Ω_{m} = 0.33_{-0.09}^{+0.06}$ and $Ω_Λ$ = $1.06_{-0.34}^{+0.15}$ excluding systematic uncertainties in the nonflat $Λ$CDM model. Adding type Ia supernovae from Pantheon sample, the best-fitting results are $w_{0}$ = $-1.11_{-0.15}^{+0.11}$ and $Ω_{m}$ = $0.34_{-0.04}^{+0.05}$ in the $w=w_0$ model. These results are in agreement with the $Λ$CDM model. Our result supports that selection of GRBs from the same physical mechanism is crucial for cosmological purposes.

astro-ph.CO↗

arXiv2021

Standardized long gamma-ray bursts as a cosmic distance indicator

Gamma-ray bursts (GRBs) are the most luminous explosions and can be detectable out to the edge of Universe. It has long been thought they can extend the Hubble diagram to very high redshifts. Several correlations between temporal or spectral properties and GRB luminosities have been proposed to make GRBs cosmological tools. However, those correlations cannot be properly standardized. In this paper, we select a long GRB sample with X-ray plateau phases produced by electromagnetic dipole emissions from central new-born magnetars. A tight correlation is found between the plateau luminosity and the end time of the plateau in X-ray afterglows out to the redshift $z=5.91$. We standardize these long GRBs X-ray light curves to a universal behavior by this correlation for the first time, with a luminosity dispersion of 0.5 dex. The derived distance-redshift relation of GRBs is in agreement with the standard $Λ$CDM model both at low and high redshifts. The evidence of accelerating universe from this GRB sample is $3σ$, which is the highest statistical significance from GRBs to date.

astro-ph.HE↗

arXiv2021

Observation of the Critical State to Multiple-Type Dirac Semimetal Phases in KMgBi

Dirac semimetals (DSMs) are classified into different phases based on the types of the Dirac fermions. Tuning the transition among different types of the Dirac fermions in one system remains challenging. Recently, KMgBi was predicted to be located at a critical state that various types of Dirac fermions can be induced owing to the existence of a flat band. Here, we carried out systematic studies on the electronic structure of KMgBi single crystal by combining angle-resolve photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS). The flat band was clearly observed near the Fermi level. We also revealed a small bandgap of ~ 20 meV between the flat band and the conduction band. These results demonstrate the critical state of KMgBi that transitions among various types of Dirac fermions can be tuned in one system.

cond-mat.mtrl-sci↗

arXiv2020

Testing cosmic anisotropy with Pantheon sample and quasars at high redshifts

In this paper, we investigate the cosmic anisotropy from the SN-Q sample, consisting of the Pantheon sample and quasars, by employing the hemisphere comparison (HC) method and the dipole fitting (DF) method. Compared to the Pantheon sample, the new sample has a larger redshift range, a more homogeneous distribution, and a larger sample size. For the HC method, we find that the maximum anisotropy level is $AL_{max}=0.142\pm0.026$ in the direction ($l$, $b$) = $({316.08^{\circ}}^{+27.41}_{-129.48}$, ${4.53^{\circ}}^{+26.29}_{-64.06})$. The magnitude of anisotropy is $A$ = ($-$8.46 $^{+4.34}_{-5.51}$)$\times$$10^{-4}$ and the corresponding preferred direction points toward $(l$, $b)$ = ($29.31^{\circ}$$^{+30.59}_{-30.54}$, $71.40^{\circ}$$^{+9.79}_{-9.72}$) for the quasar sample from the DF method. The combined SN and quasar sample is consistent with the isotropy hypothesis. The distribution of the dataset might impact the preferred direction from the dipole results. The result is weakly dependent on the redshift from the redshift tomography analysis. There is no evidence of cosmic anisotropy in the SN-Q sample. Though some results obtained from the quasar sample are not consistent with the standard cosmological model, we still do not find any distinct evidence of cosmic anisotropy in the SN-Q sample.

astro-ph.CO↗

arXiv2020

Orbital selectivity of layer resolved tunneling on iron superconductor Ba0.6K0.4Fe2As2

We use scanning tunneling microscopy/spectroscopy (STM/S) to elucidate the Cooper pairing of the iron pnictide superconductor Ba0.6K0.4Fe2As2. By a cold-cleaving technique, we obtain atomically resolved termination surfaces with different layer identities. Remarkably, we observe that the low-energy tunneling spectrum related to superconductivity has an unprecedented dependence on the layer-identity. By cross-referencing with the angle-revolved photoemission results and the tunneling data of LiFeAs, we find that tunneling on each termination surface probes superconductivity through selecting distinct Fe-3d orbitals. These findings imply the real-space orbital features of the Cooper pairing in the iron pnictide superconductors, and propose a new and general concept that, for complex multi-orbital material, tunneling on different terminating layers can feature orbital selectivity.

cond-mat.supr-con↗

arXiv2020

Momentum dependent $d_{xz/yz}$ band splitting in LaFeAsO

We performed angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of the nematic phase in LaFeAsO. Degeneracy breaking between the dxz and dyz hole bands near the Γ and M point is observed in the nematic phase. Different temperature dependent band splitting behaviors are observed at the Γ and M points. The energy of the band splitting near the M point decreases as the temperature decreases while it has little temperature dependence near the Γ point. The nematic nature of the band shift near the M point is confirmed through a detwin experiment using a piezo device. Since a momentum dependent splitting behavior has been observed in other iron based superconductors, our observation confirms that the behavior is a universal one among iron based superconductors.

cond-mat.supr-con↗

arXiv2018

Evidence of Interfacial Topological Superconductivity on the Topological Semimetal Tungsten Carbide Induced by Metal Deposition

Interfaces between materials with different electronic ground states have become powerful platforms for creating and controlling novel quantum states of matter, in which inversion symmetry breaking and other effects at the interface may introduce additional electronic states. Among the emergent phenomena, superconductivity is of particular interest. In this work, by depositing metal films on a newly identified topological semimetal tungsten carbide (WC) single crystal, we have obtained interfacial topological superconductivity evidenced from soft point contact spectroscopy. This very robust phenomenon has been demonstrated for a wide range of Metal/WC interfaces, involving both non-magnetic and ferromagnetic films, and the superconducting transition temperatures is surprisingly insensitive to the magnetism of thin films, suggesting a spin-triplet pairing superconducting state. The results offer an opportunity to implement topological superconductivity using convenient thin film coating method.

cond-mat.supr-con↗

arXiv2018

Evidence for triplet superconductivity near an antiferromagnetic instability in CrAs

Superconductivity was recently observed in CrAs as the helimagnetic order is suppressed by applying pressure, suggesting possible unconventional superconductivity. To reveal the nature of the superconducting order parameter of CrAs, here we report the angular dependence of the upper critical field under pressure. Upon rotating the field by 360 degrees in the $bc$-plane, six maxima are observed in the upper critical field, where the oscillations have both six-fold and two-fold symmetric components. Our analysis suggests the presence of an unconventional odd-parity spin triplet state.

cond-mat.supr-con↗