arXiv subjects

Y. Liu

Publications and source records attributed to Y. Liu.

At least 397 records · Page 22Linked to original sources

arXiv2015

Enhanced superconductivity at the interface of W/Sr$_{2}$RuO$_{4}$ point contact

Differential resistance measurements are conducted for point contacts (PCs) between tungsten tip approaching along the $c$ axis direction and the $ab$ plane of Sr$_{2}$RuO$_{4}$ single crystal. Three key features are found. Firstly, within 0.2 mV there is a dome like conductance enhancement due to Andreev reflection at the normal-superconducting interface. By pushing the W tip further, the conductance enhancement increases from 3\% to more than 20\%, much larger than that was previously reported, probably due to the pressure exerted by the tip. Secondly, there are also superconducting like features at bias higher than 0.2 mV which persists up to 6.2 K, resembling the enhanced superconductivity under uniaxial pressure for bulk Sr$_{2}$RuO$_{4}$ crystals but more pronounced here. Third, the logarithmic background can be fitted with the Altshuler-Aronov theory of tunneling into quasi two dimensional electron system, consistent with the highly anisotropic electronic system in Sr$_{2}$RuO$_{4}$.

cond-mat.supr-con↗

arXiv2014

Antiferromagnetic spinor condensates in a two-dimensional optical lattice

We experimentally demonstrate that spin dynamics and the phase diagram of spinor condensates can be conveniently tuned by a two-dimensional optical lattice. Spin population oscillations and a lattice-tuned separatrix in phase space are observed in every lattice where a substantial superfluid fraction exists. In a sufficiently deep lattice, we observe a phase transition from a longitudinal polar phase to a broken-axisymmetry phase in steady states of lattice-confined spinor condensates. The steady states are found to depend sigmoidally on the lattice depth and exponentially on the magnetic field. We also introduce a phenomenological model that semi-quantitatively describes our data without adjustable parameters.

cond-mat.quant-gas↗

arXiv2014

Perfect charge compensation in WTe2 for the extraordinary magnetoresistance: From bulk to monolayer

The electronic structure of WTe2 bulk and layers are investigated by using the first principles calculations. The perfect electron-hole (n-p) charge compensation and high carrier mobilities are found in WTe2 bulk, which may result in the large and non-saturating magnetoresistance (MR) observed very recently in the experiment [Ali et al., Nature 514, 205 (2014)]. The monolayer and bilayer of WTe2 preserve the semimetallic property, with the equal hole and electron carrier concentrations. Moreover, the very high carrier mobilities are also found in WTe2 monolayer, indicating that the WTe2 monolayer would have the same extraordinary MR effect as the bulk, which could have promising applications in nanostructured magnetic devices.

cond-mat.mes-hall↗

arXiv2014

Observation of a new charged charmoniumlike state in B -> J/psi K pi decays

We present the results of an amplitude analysis of anti-B0 -> J/psi K- pi+ decays. A new charged charmoniumlike state Zc(4200)+ decaying to J/psi pi+ is observed with a significance of 6.2 sigma. The mass and width of the Zc(4200)+ are 4196 +31-29 +17-13 MeV/c^2 and 370 +70-70 +70-132 MeV, respectively; the preferred assignment of the quantum numbers is J^P = 1^+. In addition, we find evidence for Zc(4430)+ -> J/psi pi+. The analysis is based on a 711 fb^-1 data sample collected by the Belle detector at the asymmetric-energy e+ e- collider KEKB.

hep-ex↗

arXiv2014

Magnetic field induced enlargement of the regime of critical fluctuations in the classical superconductor V3Si from high-resolution specific heat experiments

We report high-resolution specific heat data on a high-quality single crystal of the classical superconductor V3Si, which reveal tiny lambda-shape anomalies appearing superimposed onto the BCS specific heat jump at the superconducting transition in magnetic fields of 2 T and higher. The appearance of these anomalies is accompanied by a magnetic-field-induced broadening of the superconducting transition. We demonstrate, using scaling relations predicted by the fluctuation models of the 3d-XY and the 3d-Lowest-Landau-Level (3d-LLL) universality class, that the effect of critical fluctuations becomes experimentally observable due to of a magnetic field-induced enlargement of the regime of critical fluctuations. The scaling indicates that a reduction of the effective dimensionality due to the confinement of quasiparticles into low Landau levels is responsible for this effect.

cond-mat.supr-con↗

arXiv2014

Microwave spectroscopic studies of the bilayer electron solid states at low Landau filling in a wide quantum well

At the low Landau filling factor $(ν)$ termination of the fractional quantum Hall effect (FQHE) series, two-dimensional electron systems (2DESs) exhibit an insulating phase that is understood as a form of pinned Wigner solid. Here we use microwave spectroscopy to probe the transition to the insulator for a wide quantum well (WQW) sample that can support single-layer or bilayer states depending on its overall carrier density, $n$. We find the insulator exhibits a resonance, which is characteristic of a bilayer solid. The resonance also reveals a pair of transitions within the solid, which are not accessible to dc transport measurements. As $n$ is biased deeper into the bilayer solid regime, the resonance grows in specific intensity, and the transitions within the insulator disappear. These behaviors are suggestive of a picture of the insulating phase as an emulsion of liquid and solid components.

cond-mat.mes-hall↗

arXiv2014

STEREO-Wind Radio Positioning of an Unusually Slow Drifting Event

On 13 March 2010 an unusually long duration event was observed by radio spectrographs onboard the STEREO-B and Wind spacecraft. The event started at about 13:00 UT and ended at approximately 06:00 UT on 14 March. The event presents itself as slow drifting, quasi-continuous emission in a very narrow frequency interval, with an apparent frequency drift from about 625 kHz to approximately 425 kHz. Using the Leblanc, Dulk, and Bougeret (1998) interplanetary density model we determined that the drift velocities of the radio source are $\approx$33km s$^{-1}$ and $\approx$52km s$^{-1}$ for 0.2 and 0.5 times the densities of Leblanc model, respectively with a normalization density of 7.2cm$^{-3}$ at 1AU and assuming harmonic emission. A joint analysis of the radio direction finding data, coronograph white-light observations and modeling revealed that the radio sources appear to be localized in regions of interaction with relatively high density and slow solar wind speed.

astro-ph.SR↗

arXiv2014

Measurement of the inclusive semileptonic branching fraction $\mathcal{B}(B_s^0 \rightarrow X^- \ell^+ ν_\ell)$ at Belle

We report a measurement of the inclusive semileptonic $B_s^0$ branching fraction in a $121~fb^{-1}$ data sample collected near the $Υ(5S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. Events containing $B_s^0$ pairs are selected by reconstructing a tag side $D_s^+$ and identifying a signal side lepton $\ell^+$ ($\ell = e, μ$) that is required to have the same-sign charge to ensure that both originate from different $B_s^0$ mesons. The $B_s^0 \rightarrow X^- \ell^+ ν_\ell$ branching fraction is extracted from the ratio of the measured yields of $D_s^+$ mesons and $D_s^+ \ell^+$ pairs and the known production and branching fractions. The inclusive semileptonic branching fraction is measured to be $[9.6 \pm 0.4\text{(stat)} \pm 0.7\text{(syst)}]~\%$.

hep-ex↗

arXiv2014

Momentum resolved spin dynamics of bulk and surface excited states in the topological insulator $\mathrm{Bi_{2}Se_{3}}$

The prospective of optically inducing a spin polarized current for spintronic devices has generated a vast interest in the out-of-equilibrium electronic and spin structure of topological insulators (TIs). In this Letter we prove that only by measuring the spin intensity signal over several order of magnitude in spin, time and angle resolved photoemission spectroscopy (STAR-PES) experiments is it possible to comprehensively describe the optically excited electronic states in TIs materials. The experiments performed on $\mathrm{Bi_{2}Se_{3}}$ reveal the existence of a Surface-Resonance-State in the 2nd bulk band gap interpreted on the basis of fully relativistic ab-initio spin resolved photoemission calculations. Remarkably, the spin dependent relaxation of the hot carriers is well reproduced by a spin dynamics model considering two non-interacting electronic systems, derived from the excited surface and bulk states, with different electronic temperatures.

cond-mat.mtrl-sci↗

arXiv2014

Coherent keV backscattering from plasma-wave boosted relativistic electron mirrors

A new parameter regime of laser wakefield acceleration driven by sub-petawatt femotsecond lasers is proposed, which enables the generation of relativistic electron mirrors further accelerated by the plasma wave. Integrated particle-in-cell simulation including the mirror formation and Thomson scattering demonstrates that efficient coherent backscattering up to keV photon energy can be obtained with moderate driver laser intensities and high density gas targets.

physics.plasm-ph↗

arXiv2014

Measurement of the Branching Fraction Br(Lambda_c+ -> p K- pi+)

We present the first model-independent measurement of the absolute branching fraction of the Lambda_c+ -> p K- pi+ decay using a data sample of 978 fb^-1 collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. The number of Lambda_c+ baryons is determined by reconstructing the recoiling D(*)- anti-p pi+ system in events of the type e+e- -> D(*)- anti-p pi+ Lambda_c+. The branching fraction is measured to be Br(Lambda_c+ -> p K- pi+) = (6.84 +- 0.24^{+0.21}_{-0.27})%, where the first and second uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2014

The coolest 'stars' are free-floating planets

We show that the coolest known object that is probably formed in a star-like mode is a free-floating planet. We discovered recently that the free-floating planetary mass object OTS,44 (M9.5, ~12 Jupiter masses, age ~2 Myr) has significant accretion and a substantial disk. This demonstrates that the processes that characterize the canonical star-like mode of formation apply to isolated objects down to a few Jupiter masses. We detected in VLT/SINFONI spectra that OTS44 has strong, broad, and variable Paschen beta emission. This is the first evidence for active accretion of a free-floating planet. The object allows us to study accretion and disk physics at the extreme and can be seen as free-floating analog of accreting planets that orbit stars. Our analysis of OTS44 shows that the mass-accretion rate decreases continuously from stars of several solar masses down to free-floating planets. We determined, furthermore, the disk mass (10 Earth masses) and further disk properties of OTS44 through modeling its SED including Herschel far-IR data. We find that objects between 14 and 0.01 solar masses have the same ratio of the disk-to-central-mass of about 1%. Our results suggest that OTS44 is formed like a star and that the increasing number of young free-floating planets and ultra-cool T and Y field dwarfs are the low-mass extension of the stellar population.

astro-ph.SR↗

arXiv2014

Coexistence of superconductivity and charge-density-wave domain in $1T$-Fe$_x$Ta$_{1-x}$SSe

A series of $1T$-Fe$_x$Ta$_{1-x}$SSe (0 $\leq x \leq$ 0.1) single crystals was fabricated via the chemical-vapor-transport (CVT) method and investigated by structure, transport, and magnetic measurements along with the density-functional-theory (DFT) calculations. The superconductivity (SC) in parent $1T$-TaSSe can be gradually suppressed by Fe-substitution ($x\leq0.03$), accompanied by the disappearance of charge-density-wave (CDW). DFT calculations show that the Fe-substitution effectively inhibits the CDW superstructure and thereby the CDW domains are destroyed. With further increasing $x$ ($x>0.03$), the disorder-induced scattering increases, and the system enters into the possible Anderson localization (AL) state. Our results prove the SC develops in the CDW phase and coexists with the CDW domain in $1T$-TaSSe system.

cond-mat.supr-con↗

arXiv2014

Automatic data analysis for Sky Brightness Monitor

The Sky Brightness Monitor (SBM) is an important instrument to measure the brightness level for the sky condition, which is a critical parameter for judging a site for solar coronal observations. In this paper we present an automatic method for the processing of SBM data in large quantity, which can separate the regions of the Sun and the nearby sky as well as recognize the regions of the supporting arms in the field of view. These processes are implemented on the data acquired by more than one SBM instruments during our site survey project in western China. An analysis applying the result from our processes has been done for the assessment of the scattered-light levels by the instrument. Those results are considerably significant for further investigations and studies, notably to derive a series of the other important atmospheric parameters such as extinctions, aerosol content and precipitable water vapor content for candidate sites. Our processes also provide a possible way for full-disk solar telescopes to track the Sun without an extra guiding system.

astro-ph.SR↗

arXiv2014

Contrasting H-mode behaviour with deuterium fuelling and nitrogen seeding in the all-carbon and metallic versions of JET

The former all-carbon wall on JET has been replaced with beryllium in the main torus and tungsten in the divertor to mimic the surface materials envisaged for ITER. Comparisons are presented between Type I H-mode characteristics in each design by examining respective scans over deuterium fuelling and impurity seeding, required to ameliorate exhaust loads both in JET at full capability and in ITER.

physics.plasm-ph↗

arXiv2014

CuSe-based layered compound Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$ as a quasi-two-dimensional metal

We have investigated the physical properties of a new layered oxyselenide Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$, which crystallizes in an unusual intergrowth structure with Cu$_{2}$Se$_{2}$ and Bi$_{2}$YO$_{4}$ layers. Electric transport measurement indicates that Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$ behaves metallic. Thermal transport and Hall measurements show that the type of the carriers is hole-like and it may be a potential thermoelectric material at high temperatures. First principle calculations are in agreement with experimental results and show that Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$ is a quasi-2D metal. Further theoretical investigation suggests the ground states of the Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$-type can be tuned by designing the blocking layers, which will enrich the physical properties of these compounds.

cond-mat.mtrl-sci↗

arXiv2014

Electronic Structures of Black Phosphorus Studied by Angle-resolved Photoemission Spectroscopy

Electronic structures of single crystalline black phosphorus were studied by state-of-art angleresolved photoemission spectroscopy. Through high resolution photon energy dependence measurements, the band dispersions along out-of-plane and in-plane directions are experimentally determined. The electrons were found to be more localized in the ab-plane than that is predicted in calculations. Beside the kz-dispersive bulk bands, resonant surface state is also observed in the momentum space. Our finds strongly suggest that more details need to be considered to fully understand the electronic properties of black phosphorus theoretically.

cond-mat.mtrl-sci↗

arXiv2014

Effect of polarization fatigue on the Rayleigh coefficients of ferroelectric lead zirconate titanate thin films: experimental evidence and implications

The effect of polarization fatigue on the Rayleigh coefficients of ferroelectric lead zirconate titanate (PZT) thin film was systematically investigated. It was found that electrical fatigue strongly affects the Rayleigh behaviour of the PZT film. Both the reversible and irreversible Rayleigh coefficients decrease with increasing the number of switching cycles. This phenomenon is attributed to the growth of an interfacial degraded layer between the electrode and the film during electrical cycling. The methodology used in this work could serve as an alternative non-destructive way for evaluating the fatigue endurance and degradation in dielectric properties of ferroelectric thin-film devices during applications.

cond-mat.mtrl-sci↗