arXiv subjects

C. H. Wang

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

At least 37 records · Page 2Linked to original sources

arXiv2009

Field-induced coupled superconductivity and spin density wave order in the Heavy Fermion compound CeCoIn5

The high field superconducting state in CeCoIn5 has been studied by transverse field muon spin rotation measurements with an applied field parallel to the crystallographic c-axis close to the upper critical field Hc2 = 4.97 T. At magnetic fields >= 4.8 T the muon Knight shift is enhanced and the superconducting transition changes from second order towards first order as predicted for Pauli-limited superconductors. The field and temperature dependence of the transverse muon spin relaxation rate sigma reveal paramagnetic spin fluctuations in the field regime from 2 T < H < 4.8 T. In the normal state close to Hc2 correlated spin fluctuations as described by the self consistent renormalization theory are observed. The results support the formation of a mode-coupled superconducting and antiferromagnetically ordered phase in CeCoIn5 for H directed parallel to the c-axis.

cond-mat.str-el↗

arXiv2009

Simple Behavior of Primary Cross Sections for Low Mass Particles in p-pbar Collisions at y=0 and sqrt(s)=1.8 TeV

A set of inclusive cross sections at zero rapidity is presented for p-pbar interactions at center of mass energy sqrt(s)=1.8 TeV. Six particle cross sections are corrected for secondary contributions from decays of higher mass resonances in order to produce a set of primary cross sections. The primary cross sections per spin state are well described by d(sigma^p)/dy|_(y=0)= 0.721*(pi*lambdabar_(pi)^2)*exp(-m/T), where m is the particle rest mass, T=hbar*c/r_h, and r_h=0.97 fm. The deuterium production cross section is also described if r_h is replaced by r_A=r_h*A^(1/3). The same exponential in m and T describes primary charm fractions in e+e- collisions at least up to the J/Psi mass. There is no significant evidence for strangeness or charm suppression if only primary production of light hadrons is considered. There is evidence that the primary cross section for each particle may have the same value for pp and pbar-p collisions and that it may have nearly constant values between sqrt(s)=63 GeV and sqrt(s)=1800 GeV. Fits to the final state transverse momenta of the particles using a gas model favor a temperature T=132 MeV, a chemical potential mu=129 MeV, and a transverse flow of the gas with beta_f=0.27.

hep-ex↗

arXiv2009

Inelastic Neutron Scattering Studies of the Intermediate Valence Compound CePd3

Inelastic neutron scattering measurements on a CePd3 single crystal show a magnetic response at 300 K that is independent of momentum transfer with a Lorentzian quasielastic energy spectrum with a half width of 23 meV. This is in agreement with the Anderson impurity model (AIM), that predicts local moment relaxational behavior in this temperature regime. The 7 K magnetic response has an inelastic Lorentzian spectrum, with characteristic energy of 53 meV and half width 32 meV at the (h, 1/2, 0) zone boundary. Such an inelastic spectrum is expected for the AIM at low temperature. Unlike the Q-independence of the impurity model, a variation of intensity with momentum transfer, including intensity maxima at the zone boundary, is observed in the data. However, this variation is only of order 20 percent, which is much smaller than that predicted by the Anderson lattice model (ALM). The large shifts in spectral weight expected for the ALM as Q varies from zone boundary to zone center are not observed in the experimental spectra.

cond-mat.str-el↗

arXiv2009

Reply to "Comment on `Low-temperature phonon thermal conductivity of single-crystalline Nd$_2$CuO$_4$: Effects of sample size and surface roughness' " by Sun et al

In their comment \cite{Sun} on our study of phonon heat transport in Nd$_2$CuO$_4$ \cite{Li}, Sun and Ando estimate that the phonon mean free path at low temperature is roughly half the width of the single crystal used in our study, from which they argue that phonon scattering cannot be dominated by sample boundaries. Here we show that their use of specific heat data on Nd$_2$CuO$_4$, which contains a large magnetic contribution at low temperature that is difficult to reliably extract, leads to an underestimate of the mean free path by a factor two compared to an estimate based on the specific heat data of the non-magnetic isostructural analog Pr$_2$CuO$_4$. This removes the apparent contradiction raised by Sun and Ando.

cond-mat.supr-con↗

arXiv2009

Giant Anisotropy of Magnetoresistance and "Spin Valve" effect in Antiferromagnetic $Nd_{2-x}Ce_xCuO_{4}$

We have studied anisotropic magnetoresistance (MR) and magnetization with rotating magnetic field (B) within $CuO_2$ plane in lightly doped AF $Nd_{2-x}Ce_xCuO_{4}$. \emph{A giant anisotropy} in MR is observed at low temperature below 5 K. The c-axis resistivity can be tuned about one order of magnitude just by changing B direction within $CuO_2$ plane and a scaling behavior between out-of-plane and in-plane MR is found. A "Spin valve" effect is proposed to understand the giant anisotropy of out-of-plane MR and the evolution of scaling parameters with the external field. It is found that the field-induced spin-flop transition of Nd$^{3+}$ layer under high magnetic field is the key to understand the giant anisotropy. These results suggest that a novel entanglement between charge and spin dominates the underlying physics.

cond-mat.supr-con↗

arXiv2007

Spinning particles in scalar-tensor gravity

We develop a new model of a spinning particle in Brans-Dicke spacetime using a metric-compatible connection with torsion. The particle's spin vector is shown to be Fermi-parallel (by the Levi-Civita connection) along its worldline (an autoparallel of the metric-compatible connection) when neglecting spin-curvature coupling.

gr-qc↗

arXiv2007

Low-temperature phonon thermal conductivity of cuprate single crystals

The effect of sample size and surface roughness on the phonon thermal conductivity $κ_p$ of Nd$_2$CuO$_4$ single crystals was studied down to 50 mK. At 0.5 K, $κ_p$ is proportional to $\sqrt{A}$, where $A$ is the cross-sectional area of the sample. This demonstrates that $κ_p$ is dominated by boundary scattering below 0.5 K or so. However, the expected $T^3$ dependence of $κ_p$ is not observed down to 50 mK. Upon roughing the surfaces, the $T^3$ dependence is restored, showing that departures from $T^3$ are due to specular reflection of phonons off the mirror-like sample surfaces. We propose an empirical power law fit, to $κ_p \sim T^α$ (where $α< 3$) in cuprate single crystals. Using this method, we show that recent thermal conductivity studies of Zn doping in YBa$_2$Cu$_3$O$_y$ re-affirm the universal heat conductivity of d-wave quasiparticles at $T \to 0$.

cond-mat.supr-con↗

arXiv2007

Measurement of charmless $B$ Decays to $ηK^*$ and $ηρ$

We report measurements of branching fractions and CP asymmetries for $B \to ηK^*$ and $B \to ηρ$ decays. These results are obtained from a $414 {\rm fb}^{-1}$ data sample collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We measure the following branching fractions: ${\mathcal B}(B^0 \to ηK^{*0}) = (15.2 \pm 1.2 \pm 1.0)\times 10^{-6}$ and ${\mathcal B}(B^+\toηK^{*+}) = (19.3^{+2.0}_{-1.9}\pm 1.5)\times 10^{-6}$, where the first error is statistical and the second systematic. We also find a $2.7σ$ excess in the $B^+\toηρ^+$ mode and measure $\mathcal B(B^+\toηρ^+)= (4.1^{+1.4}_{-1.3}\pm 0.4)\times 10^{-6} <6.5 \times 10^{-6}$ at 90% confidence level. For $B^0 \to ηρ^0$ decays, we determine the upper limit $\mathcal B(B^0\toηρ^0) < 1.9 \times 10^{-6}$ at 90% confidence level. The partial rate asymmetries are ${\mathcal A_{CP}}(ηK^{*0}) = 0.17 \pm 0.08 \pm 0.01$, ${\mathcal A_{CP}}(ηK^{*+}) = 0.03 \pm 0.10 \pm 0.01$, and ${\mathcal A_{CP}}(ηρ^+) = -0.04^{+0.34}_{-0.32}\pm 0.01$.

hep-ex↗

arXiv2007

Magnetic field induced spin-flop transition in Na$_x$CoO$_2$ (0.5$<$x$<$0.55)

The isothermal magnetoresistance (MR) with magnetic field (H) parallel to and perpendicular to ab plane is systematically studied on the single crystal Na$_{0.52}$CoO$_2$ with charge ordering at $\sim 50$ K and an in-plane ferromagnetism below 25 K. The isothermal MR behavior with H $\parallel$ ab plane and H $\perp$ ab plane is quite different. When H $\parallel$ ab plane, the MR is always negative and the in-plane ferromagnetic behavior is enhanced. While the MR with H $\perp$ ab plane changes from negative to positive with decreasing temperature or increasing H, and the in-plane ferromagnetic behavior is suppressed. A striking feature is that the MR with H $\perp$ ab plane shows a hysteresis behavior below 25 K, which is absent for the case of H $\parallel$ ab plane. These results provide strong evidence for a spin-flop transition of small moments of Co$^{3.5-δ}$ sites induced by H $\perp$ ab plane, leading to a metamagnetic transition for small moments of Co$^{3.5-δ}$ sites. These complex magnetism suggests an unconventional superconductivity in Na$_x$CoO$_2$ system because the Na$_x$CoO$_2$ around x=0.5 is considered to be the parent compound of superconductivity.

cond-mat.str-el↗

arXiv2006

Measurement of charmless $B$ Decays to $ηK^*$ and $ηρ$

We report branching fractions and CP asymmetries for $B \to ηK^*$ and $B \to ηρ$ decays. These results are obtained from a $414 {\rm fb}^{-1}$ data sample collected at the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. The branching fractions, in parts per million, of $ηK^{*0}$, $ηK^{*+}$, $ηρ^0$, and $ηρ^+$ are $15.9\pm 1.2 \pm 0.9$, $19.7^{+2.0}_{-1.9} \pm 1.4$, $0.84^{+0.56}_{-0.51} \pm 0.18$, and $4.1^{+1.4}_{-1.3} \pm 0.34$, respectively. We find no evidence for CP asymmetries in these modes.

hep-ex↗

arXiv2006

Anisotropic Magnetoresistance in Charge-Ordering $Na_{0.34}(H_3O)_{0.15}CoO_2$:Strong Spin-Charge Coupling and Spin Ordering

Angular-dependent in-plane magnetoresistance (AMR) for single crystal $Na_{0.34}(H_3O)_{0.15}CoO_2$ with charge ordering is studied systematically. The anisotropic magnetoresistance shows a twofold symmetry at high temperature with rotating H in the Co-O plane, while a sixfold symmetry below a certain temperature ($T_ρ$). At $T_ρ$, the symmetry of AMR changes from twofold to fourfold with rotating magnetic field (H) in the plane consisting of the current and c-axis. The variation of AMR symmetry with temperature arises from the subtle changes of the spin structure. These results give a direct evidence for the itinerant electrons directly coupled to the localized spins.

cond-mat.str-el↗

arXiv2006

Giant isotope effect and spin state transition induced by oxygen isotope exchange in ($Pr_{1-x}Sm_x)_{0.7}Ca_{0.3}CoO_3$

We systematically investigate effect of oxygen isotope in $(Pr_{1-x}Sm_x)_{0.7}Ca_{0.3}CoO_3$ which shows a crossover with x from ferromagnetic metal to the insulator with spin-state transition. A striking feature is that effect of oxygen isotope on the ferromagnetic transition is negligible in the metallic phase, while replacing $^{16}O$ with $^{18}O$ leads to a giant up-shift of the spin-state transition temperature ($T_s$) in the insulating phase, especially $T_s$ shifts from 36 to 54 K with isotope component $α_S=-4.7$ for the sample with x=0.175. A metal-insulator transition is induced by oxygen isotope exchange in the sample x=0.172 being close to the insulating phase. The contrasting behaviors observed in the two phases can be well explained by occurrence of static Jahn-Teller distortions in the insulating phase, while absence of them in the metallic phase.

cond-mat.str-el↗

arXiv2006

Magnetic and transport properties in Gd$_{1-x}$Sr$_x$CoO$_{3}$ ($x$= 0.10-0.70)

Magnetic and transport properties of polycrystalline Gd$_{1-x}$Sr$_x$CoO$_{3}$ ($x$= 0.10-0.70) are investigated systemically. Cluster-glass magnetism for $x \leq$ 0.45 and long-range ferromagnetic order in higher doping level are observed. Transport measurements indicate insulator-like behaviors for the samples with $x \leq$ 0.30, and an insulator-metal (IM) transition around $x$ = 0.35, and metallic behaviors for higher $x$ samples. In contrast to La$_{1-x}$Sr$_{x}$COO$_{3}$, the striking feature is that the system reenters insulator-like state for $x \geq$ 0.60, and the long-range ferromagnetic order and IM transition take place in samples with higher Sr content. It could be attributed to the enhancement of low-spin state stability for the trivalent Co ions due to the small radius of Gd$^{3+}$ ion.

cond-mat.str-el↗

arXiv2005

Charge ordering in charge-compensated $Na_{0.41}CoO_2$ by oxonium ions

Charge ordering behavior is observed in the crystal prepared through the immersion of the $Na_{0.41}CoO_2$ crystal in distilled water. Discovery of the charge ordering in the crystal with Na content less than 0.5 indicates that the immersion in water brings about the reduction of the $Na_{0.41}CoO_2$. The formal valence of Co changes from +3.59 estimated from the Na content to +3.5, the same as that in $Na_{0.5}CoO_2$. The charge compensation is confirmed to arise from the intercalation of the oxonium ions as occurred in the superconducting sodium cobalt oxide bilayer-hydrate.\cite{takada1} The charge ordering is the same as that observed in $Na_{0.5}CoO_2$. It suggests that the Co valence of +3.5 is necessary for the charge ordering.

cond-mat.mtrl-sci↗

arXiv2005

In-plane ferromagnetism in charge-ordering $Na_{0.55}CoO_2$

The magnetic and transport properties are systematically studied on the single crystal $Na_{0.55}CoO_2$ with charge ordering and divergency in resistivity below 50 K. A long-range ferromagnetic ordering is observed in susceptibility below 20 K with the magnetic field parallel to Co-O plane, while a negligible behavior is observed with the field perpendicular to the Co-O plane. It definitely gives a direct evidence for the existence of in-plane ferromagnetism below 20 K. The observed magnetoresistance (MR) of 30 % at the field of 6 T at low temperatures indicates an unexpectedly strong spin-charge coupling in triangle lattice systems.

cond-mat.str-el↗

arXiv2005

Influence of doping level on the Hall coefficient and on the thermoelectric power in $Nd_{2-x}Ce_xCuO_4$

Hall coefficient $R_H$ and thermoelectric power TEP are studied systematically in the single crystals $Nd_{2-x}Ce_xCuO_{4+δ}$ (NCCO) with different x from underdoped to overdoped regime. With increasing doping level, both $R_H$ and TEP decrease and change their sign from negative to positive. A striking feature is that the temperature dependence of the Hall angle follows a $T^4$ behavior in the underdoped regime, while a $T^2$ in the overdoped regime. These behaviors are closely related to the evolution of Fermi surface with doping level observed by ARPES.

cond-mat.str-el↗

arXiv2005

Doping evolution of chemical potential, spin-correlation gap, and charge dynamics in Nd$_{2-x}$Ce$_x$CuO$_4$

We report optical reflectivity study on Nd$_{2-x}$Ce$_x$CuO$_4$ over a broad doping range 0$\leq x\leq$0.20. The study reveals a systematic shift of chemical potential with doping. A pronounced peak structure specific to the electron-doped cuprate is observed in optical scattering rate based on the extended Drude model analysis. The energy scale of the peak could be very different from that of the peak in conductivity spectrum. We clarify that the "hot spots" gap probed in photoemission experiments correlates directly with the sharp suppression feature in scattering rate rather than conductivity spectra. The gap is associated with the short-range antiferromagnetic correlation, and disappears in a manner of fading away with increasing doping and temperature. In the heavily overdoped region, a dominant $ω^2$-dependence of the scattering rate is identified up to very high energy.

cond-mat.supr-con↗

arXiv2005

Ballistic magnon transport and phonon scattering in the antiferromagnet Nd$_2$CuO$_4$

The thermal conductivity of the antiferromagnet Nd$_2$CuO$_4$ was measured down to 50 mK. Using the spin-flop transition to switch on and off the acoustic Nd magnons, we can reliably separate the magnon and phonon contributions to heat transport. We find that magnons travel ballistically below 0.5 K, with a thermal conductivity growing as $T^3$, from which we extract their velocity. We show that the rate of scattering of acoustic magnons by phonons grows as $T^3$, and the scattering of phonons by magnons peaks at twice the average Nd magnon frequency.

cond-mat.supr-con↗