arXiv subjects

X. Lu

Publications and source records attributed to X. Lu.

99 records · Page 6Linked to original sources

arXiv2013

CeIrIn5: Superconductivity on a Magnetic Instability

We report the doping-induced antiferromagnetic state and Fermi liquid state that are connected by a superconducting region in a series of CeIrIn$_{5-x}$Hg$_x$, CeIrIn$_{5-x}$Sn$_x$ and CeIr$_{1-x}$Pt$_x$In$_5$ single crystals. Measurements of the specific heat $C(T)$ and electrical resistivity $ρ(T)$ demonstrate that hole doping via Hg/In substitution gives rise to an antiferromagnetic ground state, but substitutions of In by Sn or Ir by Pt (electron doping) favor a paramagnetic Fermi liquid state. A cone-like non-Fermi liquid region is observed near CeIrIn$_5$, showing a diverging effective mass on the slightly Hg-doped side. The obtained temperature-doping phase diagram suggests that CeIrIn$_5$ is in proximity to an antiferromagnetic quantum critical point, and heavy fermion superconductivity in this compound is mediated by magnetic quantum fluctuations rather than by valence fluctuations.

cond-mat.str-el↗

arXiv2012

Beam-helicity asymmetry arising from deeply virtual Compton scattering measured with kinematically complete event reconstruction

The beam-helicity asymmetry in exclusive electroproduction of real photons by the longitudinally polarized HERA positron beam scattering off an unpolarized hydrogen target is measured at HERMES. The asymmetry arises from deeply virtual Compton scattering and its interference with the Bethe--Heitler process. Azimuthal amplitudes of the beam-helicity asymmetry are extracted from a data sample consisting of $ep\rightarrow epγ$ events with detection of all particles in the final state including the recoiling proton. The installation of a recoil detector, while reducing the acceptance of the experiment, allows the elimination of background from $ep\rightarrow eNπγ$ events, which was estimated to contribute an average of about 12% to the signal in previous HERMES publications. The removal of this background from the present data sample is shown to increase the magnitude of the leading asymmetry amplitude by 0.054 +/- 0.016 to -0.328 +/- 0.027 (stat.) +/- 0.045 (syst.).

hep-ex↗

arXiv2012

Electronic tuning and uniform superconductivity in CeCoIn5

We report a globally reversible effect of electronic tuning on the magnetic phase diagram in CeCoIn_{5} driven by electron (Pt and Sn) and hole (Cd, Hg) doping. Consequently, we are able to extract the superconducting pair breaking component for hole and electron dopants with pressure and co-doping studies, respectively. We find that these nominally non-magnetic dopants have a remarkably weak pair breaking effect for a d-wave superconductor. The pair breaking is weaker for hole dopants, which induce magnetic moments, than for electron dopants. Furthermore, both Pt and Sn doping have a similar effect on superconductivity despite being on different dopant sites, arguing against the notion that superconductivity lives predominantly in the CeIn_{3} planes of these materials. In addition, we shed qualitative understanding on the doping dependence with density functional theory calculations.

cond-mat.supr-con↗

arXiv2012

Enhancement of Betatron radiation from laser-driven Ar clustering gas

Bright betatron x-ray has been generated using an Ar clustering gas jet target irradiated with a 3 TW ultra-high contrast laser. The measured emission flux with photon energy > 2.4 keV reaches 2\times10^8 photons/shot. It is ten-fold enhancement comparing to the emission flux produced by using gas target in the same laser parameters. Observation shows that much larger electron beam charge and divergence angle lead to this improvement. Simulations point to the existence of cluster in gas results in the increasing of electron injection and much larger wiggling amplitude in wake-field, enriching the betatron x-ray photons.

physics.plasm-ph↗

arXiv2012

Temperature dependence of in-plane correlation lengths in exchange biased Co/FeF2

We have measured resonant soft x-ray diffuse magnetic scattering as a function of temperature in a positively exchange biased Co/FeF2 bilayer and analyzed the data in the distorted wave Born approximation to obtain in-plane charge and magnetic correlation lengths associated with the Co and FeF2 layers and estimate interfacial roughness. Tuning to the Fe and Co L3 edges reveals significantly different temperature trends in these quantities in the antiferromagnetic and ferromagnetic layers, respectively. While the magnetic correlation length of the uncompensated interfacial spins in FeF2 layer increase as temperature decreases, these quantities remain unchanged in the Co layer. Our results indicate that uncompensated Fe spins order within a range of few hundred nanometers in otherwise randomly distributed uncompensated magnetic moments, giving rise to spin clusters in the antiferromagnet whose size increase as the temperature decrease.

cond-mat.mtrl-sci↗

arXiv2011

Textured Superconducting State in the Heavy Fermion CeRhIn5

Anisotropic, spatially textured electronic states often emerge when the symmetry of the underlying crystalline structure is lowered. However, the possibility recently has been raised that novel electronic quantum states with real-space texture could arise in strongly correlated systems even without changing the underlying crystalline structure. Here we report evidence for such texture in the superconducting quantum fluid that is induced by pressure in the heavy-fermion compound CeRhIn5. When long-range antiferromagnetic order coexists with unconventional superconductivity, there is a significant temperature difference between resistively- and thermodynamically-determined transitions into the superconducting state, but this difference disappears in the absence of magnetism. Anisotropic transport behaviour near the superconducting transition in the coexisting phase signals the emergence of textured superconducting planes that are nucleated preferentially along the {100} planes and that appear without a change in crystal symmetry. We show that CeRhIn5 is not unique in exhibiting a difference between resistive and bulk superconducting transition temperatures, indicating that textured superconductivity may be a general consequence of coexisting orders.

cond-mat.str-el↗

arXiv2011

Strong terahertz radiation from relativistic laser interaction with solid density plasmas

We report a plasma-based strong THz source generated by using intense femtosecond laser pulses to irradiate solid targets at relativistic intensity >10^18W/cm2. Energies up to 50 microJ/sr per THz pulse is observed in the specular direction when the laser pulses are incident onto a copper foil at 67.5 degree. The source appears to be linearly polarized. The temporal, spectral properties of the THz are measured by a single shot, electro-optic sampling method with a chirped laser pulse. The THz radiation is attributed to the self-organized transient fast electron currents formed along the target surface. Such a strong THz source allows potential applications in THz nonlinear physics.

physics.optics↗

arXiv2010

Superconducting order parameter in nonmagnetic borocarbides RNi$_{2}$B$_{2}$C (R=Y, Lu) probed by point-contact Andreev reflection spectroscopy

We report on the measurements of the superconducting order parameter in the nonmagnetic borocarbides LuNi$_2$B$_2$C and YNi$_2$B$_2$C. Andreev conductance spectra are obtained from nanoscale metallic junctions on single crystal surfaces prepared along three major crystallographic orientations: [001], [110], and [100]. The gap values extracted by the single-gap Blonder-Tinkham-Klapwijk model follow the BCS predictions as a function of temperature and magnetic field and exhibit a small anisotropy. These observations are robust and reproducible among all the measurements on two different sets of LuNi$_2$B$_2$C crystals and one set of YNi$_2$B$_2$C crystals. We suggest possible explanations for the small gap anisotropy based on the recent detailed gap measurements by angle-resolved photoemission spectroscopy and the tunneling cone effect. Our results provide a consistent picture of the superconducting gap structure in these materials, addressing the controversy particularly in the reported results of point-contact Andreev reflection spectroscopy.

cond-mat.supr-con↗

arXiv2009

A GRB Follow-up System at the Xinglong Observatory and Detection of the High-Redshift GRB 060927

A gamma-ray burst (GRB) optical photometric follow-up system at the Xinglong Observatory of National Astronomical Observatories of China (NAOC) has been constructed. It uses the 0.8-m Tsinghua-NAOC Telescope (TNT) and the 1-m EST telescope, and can automatically respond to GRB Coordinates Network (GCN)alerts. Both telescopes slew relatively fast, being able to point to a new target field within about 1 min upon a request. Whenever available, the 2.16-m NAOC telescope is also used. In 2006, the system responded to 15 GRBs and detected seven early afterglows. In 2007, six GRBs have been detected among 18 follow-up observations. TNT observations of the second most distant GRB 060927 (z=5.5) are shown, which started as early as 91s after the GRB trigger. The afterglow was detected in the combined image of first 19x20s unfiltered exposures. This GRB follow-up system has joined the East-Asia GRB Follow-up Observation Network (EAFON).

astro-ph.HE↗