arXiv subjects

H. Cheng

Publications and source records attributed to H. Cheng.

9 recordsLinked to original sources

arXiv2024

Anomalous shot noise in a bad metal beta-tantalum

We investigate the electronic shot noise produced by nanowires of $\beta$-Ta, an archetypal ``bad" metal with resistivity near the Ioffe-Regel localization limit. The Fano factor characterizing the shot noise exhibits a strong dependence on temperature and is suppressed compared to the expectations for quasiparticle diffusion, but hopping transport is ruled out by the analysis of scaling with the nanowire length. These anomalous behaviors closely resemble those of strange metal nanowires, suggesting that $\beta$-Ta may host a correlated electron liquid. This material provides an accessible platform for exploring exotic electronic states of matter.

cond-mat.str-el↗

arXiv2021

Intrinsic Spin Susceptibility and Pseudogap-like Behavior in Infinite-Layer LaNiO2

The recent discovery of superconductivity in doped infinite-layer nickelates has stimulated intensive interest, especially for similarities and differences compared to that in cuprate superconductors. In contrast to cuprates, although earlier magnetization measurement reveals a Curie-Weiss-like behavior in undoped infinite-layer nickelates, there is no magnetic ordering observed by elastic neutron scattering down to liquid helium temperature. Until now, the nature of the magnetic ground state in undoped infinite-layer nickelates was still elusive. Here, we perform a nuclear magnetic resonance (NMR) experiment through 139La nuclei to study the intrinsic spin susceptibility of infinite-layer LaNiO2. First, the signature for magnetic ordering or freezing is absent in the 139La NMR spectrum down to 0.24 K, which unambiguously confirms a paramagnetic ground state in LaNiO2. Second, a pseudogap-like behavior instead of Curie-Weiss-like behavior is observed in both the temperature-dependent Knight shift and nuclear spin-lattice relaxation rate (1/T1), which is widely observed in both underdoped cuprates and iron-based superconductors. Furthermore, the scaling behavior between the Knight shift and 1/T1T has also been discussed. Finally, the present results imply a considerable exchange interaction in infinite-layer nickelates, which sets a strong constraint for the proposed theoretical models.

cond-mat.supr-con↗

arXiv2019

Analytical and numerical studies of central galactic outflows powered by tidal disruption events -- a model for the Fermi bubbles?

Capture and tidal disruption of stars by the supermassive black hole in the Galactic center (GC) should occur regularly. The energy released and dissipated by this processes will affect both the ambient environment of the GC and the Galactic halo. A single star of super-Eddington eruption generates a subsonic out ow with an energy release of more than $10^{52}$ erg, which still is not high enough to push shock heated gas into the halo. Only routine tidal disruption of stars near the GC can provide enough cumulative energy to form and maintain large scale structures like the Fermi Bubbles. The average rate of disruption events is expected to be $10^{-4}$ ~ $10^{-5}$ yr$^{-1}$, providing the average power of energy release from the GC into the halo of dW/dt ~ 3*10$^{41}$ erg/s, which is needed to support the Fermi Bubbles. The GC black hole is surrounded by molecular clouds in the disk, but their overall mass and filling factor is too low to stall the shocks from tidal disruption events significantly. The de facto continuous energy injection on timescales of Myr will lead to the propagation of strong shocks in a density stratified Galactic halo and thus create elongated bubble-like features, which are symmetric to the Galactic midplane.

astro-ph.HE↗

arXiv2019

A spin dynamics study in layered van der Waals single crystal, Cr$_2$Ge$_2$Te$_6$

We study the magnetisation dynamics of a bulk single crystal Cr$_2$Ge$_2$Te$_6$ (CGT), by means of broadband ferromagnetic resonance (FMR), for temperatures from 60 K down to 2 K. We determine the Kittel relations of the fundamental FMR mode as a function of frequency and static magnetic field for the magnetocrystalline easy - and hard - axis. The uniaxial magnetocrystalline anisotropy constant is extracted and compared with the saturation magnetisation, when normalised with their low temperature values. The ratios show a clear temperature dependence when plotted in the logarithmic scale, which departs from the predicted Callen-Callen power law fit of a straight line, where the scaling exponent \textit{n}, $K_{u}(T) \propto [M_s(T)/M_s(2$ K$)]^n$, contradicts the expected value of 3 for uniaxial anisotropy. Additionally, the spectroscopic g-factor for both the magnetic easy - and hard - axis exhibits a temperature dependence, with an inversion between 20 K and 30 K, suggesting an influence by orbital angular momentum. Finally, we qualitatively discuss the observation of multi-domain resonance phenomena in the FMR spectras, at magnetic fields below the saturation magnetisation.

cond-mat.mtrl-sci↗

arXiv2015

Wave-function Visualization of Core-induced Interaction of Non-hydrogenic Rydberg Atom in Electric Field

We have investigated the wave-function feature of Rydberg sodium in a uniform electric field and found that the core-induced interaction of non-hydrogenic atom in electric field can be directly visualized in the wave-function. As is well known, the hydrogen atom in electric field can be separated in parabolic coordinates (\eta, \xi), whose eigen-function can show a clear pattern towards negative and positive directions corresponding to the so-called red and blue states without ambiguity, respectively. It can be served as a complete orthogonal basis set to study the core-induced interaction of non-hydrogenic atom in electric field. Owing to complete different patterns of the probability distribution for red and blue states, the interaction can be visualized in the wave-function directly via superposition. Moreover, the constructive and destructive interferences between red and blue states are also observed in the wave-function, explicitly explaining the experimental measurement for the spectral oscillator strength.

physics.atom-ph↗

arXiv2014

5G Wireless Backhaul Networks: Challenges and Research Advance

5G networks are expected to achieve gigabit-level throughput in future cellular networks. However, it is a great challenge to treat 5G wireless backhaul traffic in an effective way. In this article, we analyze the wireless backhaul traffic in two typical network architectures adopting small cell and millimeter wave commmunication technologies. Furthermore, the energy efficiency of wireless backhaul networks is compared for different network architectures and frequency bands. Numerical comparison results provide some guidelines for deploying future 5G wireless backhaul networks in economical and highly energy-efficient ways.

cs.NI↗

arXiv2002

Ballistic Magnetoresitance over 4000% at Room Temperature in Ni-Ni Electrodeposited Nanocontacts

This paper reports ballistic magnetoresistance values over 4000% measured in electrodeposited Ni-Ni nanocontacts with T geometry previously developed . Over the time, after several magnetic field cycles, the ballistic magnetoresistance relaxed to a 400%. While that the magnetoreistance of a contact could rise indefinitely; relaxtion and reproducibility are, however, the main issue. We find that the tip ending radius conforming the contacts appears not to play the main role.

cond-mat↗

arXiv2002

Sufficiently Small $\barθ$ in $SU(3)^3 \times S_3$ Unification Model

Since CP violation in weak decays is successfully described by the KM mechanism, the strong CP problem cannot easily be accommodated. This leads us to reconsider the issue. If the axion and massless up quark are abandoned, we must extend the standard model. Extension to $SU(3)^3 \times S_3$ unification leads to the following situation: {\it if} CP is a high-energy symmetry and the appropriate symmetry-breaking hierarchy of scales is in place, then the $\barθ$ parameter of the QCD sub-theory is guaranteed to be sufficiently small. We find $\barθ < 10^{-11}$ while the empirical limit from the neutron electric dipole moment requires only that $\barθ < 1.3 \times 10^{-10}$.

hep-ph↗

arXiv2001

Hindered rotation of H2 adsorbed interstitially in nanotube bundles

A theoretical study on the rotational dynamics of H2 molecules trapped in the interstitial channels (ICs) of a carbon nanotube bundle is presented. The potential used in this study is modeled as a sum of atom-atom (C-H) van der Waals interactions and electrostatic interactions of the molecule with the surrounding nanotubes.The rotational energy spectra is calculated using a product wave function, where the coupling between translational and rotational modes is treated in a mean-field manner . Molecular dynamics (MD) simulation study was performed for estimating the hydrogen rotational barrier. Both theoretical calculations and simulation results reveal the existence of a large rotational barrier (~ 40 meV). The consequences of this rotational barrier for the rotational energy levels are worked out in detail.

cond-mat.mtrl-sci↗