arXiv subjects

C. H. Li

Publications and source records attributed to C. H. Li.

82 records · Page 5Linked to original sources

arXiv2012

Measurements of the mass and width of the eta_c using psi' -> gamma eta_c

The mass and width of the lowest lying S-wave spin singlet charmonium state, the eta_c, are measured using a data sample of 1.06x10^8 psi' decays collected with the BESIII detector at the BEPCII storage ring. We use a model that incorporates interference between the signal reaction, psi' -> gamma eta_c, and a non-resonant radiative background to successfully describe the line shape of the eta_c. We measure the eta_c mass to be 2984.3 +- 0.6 +- 0.6 MeV/c^2 and the total width to be 32.0 +- 1.2 +- 1.0 MeV, where the first errors are statistical and the second are systematic.

hep-ex↗

arXiv2012

First observation of $η(1405)$ decays into $f_{0}(980)π^0$

The decays $J/ψ\rightarrow γπ^+π^-π^0$ and $J/ψ\rightarrow γπ^0π^0π^0$ are analyzed using a sample of 225 million $\jpsi$ events collected with the BESIII detector. The decay of $η(1405)\ar f_{0}(980)π^0$ with a large isospin violation is observed for the first time. The width of the $f_{0}(980)$ observed in the dipion mass spectra is anomalously narrower than the world average. Decay rates for three-pion decays of the $η'$ are also measured precisely.

hep-ex↗

arXiv2011

Comment: "Electrical injection and detection of spin accumulation in silicon at 500 K with magnetic metal / silicon dioxide contacts" [Nature Commun. 2:245 doi:10.1038/ncomms125 (2011)]

In a recent publication, we demonstrated electrical spin injection and detection in n-type silicon at temperatures up to 500K using ferromagnetic metal / SiO2 tunnel barrier contacts in a three-terminal geometry (Nature Commun. 2:245 doi:10.1038/ncomms125 (2011)). In comparing our measured spin-voltage signal with the value predicted by theory, we followed the analysis of Tran et al, (Phys. Rev. Lett. 102, 036601 (2009)), and inadvertently propagated an error found therein. As they note in a recent erratum (arXiv:0810.4770v2), the correct expression for the spin resistance area product from the theory for a sample with a spin diffusion length LSD much less than the contact width or channel thickness (our experimental situation) is given by the product {gamma}^2 {rho} LSD, where {gamma} is the tunneling spin polarization, and {rho} is the resistivity of the semiconductor transport channel. With this correction, our measured spin voltages are much larger than those predicted by theory, rather than in good agreement as we stated. We emphasize that the basic conclusions of our paper are the same - the systematic decrease in electron spin lifetime with increasing electron density demonstrates spin accumulation in the Si channel rather than in interface states. We further show that the measured spin lifetimes are essentially independent of the tunnel barrier material (SiO2, Al2O3, MgO) or the magnetic metal used (Fe, CoFe, NiFe), demonstrating clear correlation of the measured spin lifetime with the character of the Si, and little correlation with the tunnel barrier / interface or magnetic metal.

cond-mat.mtrl-sci↗

arXiv2011

Antiferromagnetic order and superlattice structure in nonsuperconducting and superconducting RbyFe(1.6+x)Se2

Neutron diffraction has been used to study the lattice and magnetic structures of the insulating and superconducting Rb$_y$Fe$_{1.6+x}$Se$_2$. For the insulating Rb$_{y}$Fe$_{1.6+x}$Se$_2$, neutron polarization analysis and single crystal neutron diffraction unambiguously confirm the earlier proposed $\sqrt{5}\times\sqrt{5}$ block antiferromagnetic structure. For superconducting samples ($T_c=30$ K), we find that in addition to the tetragonal $\sqrt{5}\times\sqrt{5}$ superlattice structure transition at 513 K, the material develops a separate $\sqrt{2}\times \sqrt{2}$ superlattice structure at a lower temperature of 480 K. These results suggest that superconducting Rb$_{y}$Fe$_{1.6+x}$Se$_2$ is phase separated with coexisting $\sqrt{2}\times \sqrt{2}$ and $\sqrt{5}\times\sqrt{5}$ superlattice structures.

cond-mat.supr-con↗

arXiv2010

Infrared study of the charge-ordered multiferroic LuFe(2)O(4)

The reflectivity of a large LuFe(2)O(4) single crystal has been measured with the radiation field either perpendicular or parallel to the c axis of its rhombohedral structure, from 10 to 500K, and from 7 to 16000 cm-1. The transition between the two-dimensional and the three-dimensional charge order at T_(CO) = 320 K is found to change dramatically the phonon spectrum in both polarizations. The number of the observed modes above and below T_(CO), according to a factor-group analysis, is in good agreement with a transition from the rhombohedral space group R{bar 3}m to the monoclinic C2/m. In the sub-THz region a peak becomes evident at low temperature, whose origin is discussed in relation with previous experiments.

cond-mat.str-el↗

arXiv2009

Electrical spin injection into Si(001) through a SiO2 tunnel barrier

We demonstrate spin polarized tunneling from Fe through a SiO2 tunnel barrier into a Si n-i-p heterostructure. Transport measurements indicate that single step tunneling is the dominant transport mechanism. The circular polarization, Pcirc, of the electroluminescence (EL) shows that the tunneling spin polarization reflects Fe majority spin. Pcirc tracks the Fe magnetization, confirming that the spin-polarized electrons radiatively recombining in the Si originate from the Fe. A rate equation analysis provides a lower bound of 30% for the electron spin polarization in the Si at 5 K.

cond-mat.mtrl-sci↗

arXiv2005

Electrical Spin Pumping of Quantum Dots at Room Temperature

We report electrical control of the spin polarization of InAs/GaAs self-assembled quantum dots (QDs) at room temperature. This is achieved by electrical injection of spin-polarized electrons from an Fe Schottky contact. The circular polarization of the QD electroluminescence shows that a 5% electron spin polarization is obtained in the InAs QDs at 300 K, which is remarkably insensitive to temperature. This is attributed to suppression of the spin relaxation mechanisms in the QDs due to reduced dimensionality. These results demonstrate that practical regimes of spin-based operation are clearly attainable in solid state semiconductor devices.

cond-mat.mtrl-sci↗

arXiv2003

Epitaxial Growth of the Diluted Magnetic Semiconductors CryGe1-y and CryMnxGe1-x-y

We report the epitaxial growth of CryGe1-y and CryMnxGe1-x-y(001) thin films on GaAs(001), describe the structural and transport properties, and compare the measured magnetic properties with those predicted by theory. The samples are strongly p-type, and hole densities increase with Cr concentration. The CryGe1-y system remains paramagnetic for the growth conditions and low Cr concentrations employed (y < 0.04), consistent with density functional theory predictions. Addition of Cr into the ferromagnetic semiconductor MnxGe1-x host systematically reduces the Curie temperature and total magnetization.

cond-mat.mtrl-sci↗

arXiv2003

Analysis of the Transport Process Providing Spin Injection through an Fe/AlGaAs Schottky Barrier

Electron spin polarizations of 32% are obtained in a GaAs quantum well via electrical injection through a reverse-biased Fe/AlGaAs Schottky contact. An analysis of the transport data using the Rowell criteria demonstrates that single step tunneling is the dominant transport mechanism. The current-voltage data show a clear zero-bias anomaly and phonon signatures corresponding to the GaAs-like and AlAs-like longitudinal-optical phonon modes of the AlGaAs barrier, providing further evidence for tunneling. These results provide experimental confirmation of several theoretical analyses indicating that tunneling enables significant spin injection from a metal into a semiconductor.

cond-mat.mtrl-sci↗

arXiv2002

Cascade production from antikaon induced reactions on lambda and sigma

Using a gauged flavor SU(3) invariant hadronic Lagrangian, we study $Ξ$ production from $\bar K$ induced reactions on $Λ$ and $Σ$ in a coupled-channel approach. Including the four channels of $\bar KΛ$, $\bar KΣ$, $πΞ$, and $ηΞ$, we solve the Bethe-Salpeter equation in the $K$-matrix approximation by neglecting the off-shell contribution in the intermediate states. For the transition potential which drives the higher-order contribution, we consider all allowed Born diagrams in the $s$, $t$, and $u$ channels. With coupling constants determined from the SU(3) symmetry with empirical input, we find that the cross sections for the reactions $\bar KΛ\toπΞ$, $\bar KΣ\toπΞ$, $\bar KΛ\toηΞ$, and $\bar KΣ\toηΞ$ all have values of a few mb. In contrast to the results from the lowest-order Born approximation, the magnitude of these cross sections is less sensitive to the values of the cut-off parameters in the form factors. From the transition matrix in the coupled-channel approach, we have further evaluated the cross sections for the elastic process $\bar KΛ\to\bar KΛ$, $\bar KΣ\to\bar KΣ$, $πΞ\toπΞ$, and $ηΞ\toηΞ$ as well as for the inelastic processes $\bar KΛ\to\bar KΣ$ and $πΞ\toηΞ$. Implications of the reactions studied here in $Ξ$ production from relativistic heavy ion collisions are discussed.

nucl-th↗