High-TcT_\mathrm{c} superconductivity in undoped ThFeAsN

Unlike the widely studied ReFeAsO series, the newly discovered iron-based superconductor ThFeAsN exhibits a remarkably high critical temperature of 30 K, without chemical doping or external pressure. Here we investigate in detail its magnetic and superconducting properties via muon-spin rotation/relaxation ($\mu$SR) and nuclear magnetic resonance (NMR) techniques and show that ThFeAsN exhibits strong magnetic fluctuations, suppressed below 35 K, but no magnetic order. This contrasts strongly with the ReFeAsO series, where stoichiometric parent materials order antiferromagnetically and superconductivity appears only upon doping. The ThFeAsN case indicates that Fermi-surface modifications due to structural distortions and correlation effects are as important as doping in inducing superconductivity. The direct competition between antiferromagnetism and superconductivity, which in ThFeAsN (as in LiFeAs) occurs at already zero doping, may indicate a significant deviation of the $s$-wave superconducting gap in this compound from the standard $s^{\pm}$ scenario.Comment: 6 pages, 5 figure

Bulk Rotational Symmetry Breaking in Kondo Insulator SmB6

Kondo insulator samarium hexaboride (SmB6) has been intensely studied in recent years as a potential candidate of a strongly correlated topological insulator. One of the most exciting phenomena observed in SmB6 is the clear quantum oscillations appearing in magnetic torque at a low temperature despite the insulating behavior in resistance. These quantum oscillations show multiple frequencies and varied effective masses. The origin of quantum oscillation is, however, still under debate with evidence of both two-dimensional Fermi surfaces and three-dimensional Fermi surfaces. Here, we carry out angle-resolved torque magnetometry measurements in a magnetic field up to 45 T and a temperature range down to 40 mK. With the magnetic field rotated in the (010) plane, the quantum oscillation frequency of the strongest oscillation branch shows a four-fold rotational symmetry. However, in the angular dependence of the amplitude of the same branch, this four-fold symmetry is broken and, instead, a twofold symmetry shows up, which is consistent with the prediction of a two-dimensional Lifshitz-Kosevich model. No deviation of Lifshitz-Kosevich behavior is observed down to 40 mK. Our results suggest the existence of multiple light-mass surface states in SmB6, with their mobility significantly depending on the surface disorder level.Comment: 15 pages, 9 figure

Computational fluid dynamics combustion analysis evaluation

This study involves the development of numerical modelling in spray combustion. These modelling efforts are mainly motivated to improve the computational efficiency in the stochastic particle tracking method as well as to incorporate the physical submodels of turbulence, combustion, vaporization, and dense spray effects. The present mathematical formulation and numerical methodologies can be casted in any time-marching pressure correction methodologies (PCM) such as FDNS code and MAST code. A sequence of validation cases involving steady burning sprays and transient evaporating sprays will be included

Nonclassicality of quantum excitation of classical coherent field in photon loss channel

We investigate the nonclassicality of photon-added coherent states in the photon loss channel by exploring the entanglement potential and negative Wigner distribution. The total negative probability defined by the absolute value of the integral of the Wigner function over the negative distribution region reduces with the increase of decay time. The total negative probability and the entanglement potential of pure photon-added coherent states exhibit the similar dependence on the beam intensity. The reduce of the total negative probability is consistent with the behavior of entanglement potential for the dissipative single-photon-added coherent state at short decay times.Comment: 5 pages, 5 figures, RevTex4, submitte

Mean parity of single quantum excitation of some optical fields in thermal environments

The mean parity (the Wigner function at the origin) of excited binomial states, excited coherent states and excited thermal states in thermal channel is investigated in details. It is found that the single-photon excited binomial state and the single-photon excited coherent state exhibit certain similarity in the aspect of their mean parity in the thermal channel. We show the negative mean parity can be regarded as an indicator of nonclassicality of single-photon excitation of optical fields with a little coherence, especially for the single-photon excited thermal states.Comment: 4 pages, 4 figures, RevTex4; PACS numbers: 42.50.Dv, 03.65.Yz, 05.40.Ca; Three typo errors have been correcte

Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)2_2(ClO4_4)2_2

Cu(pz)$_2$(ClO$_4$)$_2$ (with pz denoting pyrazine C$_4$H$_4$N$_2$) is a two-dimensional spin-1/2 square-lattice antiferromagnet with $T_{\mathrm{N}}$ = 4.24 K. Due to a persisting focus on the low-temperature magnetic properties, its room-temperature structural and physical properties caught no attention up to now. Here we report a study of the structural features of Cu(pz)$_2$(ClO$_4$)$_2$ in the paramagnetic phase, up to 330 K. By employing magnetization, specific heat, $^{35}$Cl nuclear magnetic resonance, and neutron diffraction measurements, we provide evidence of a second-order phase transition at $T^{\star}$ = 294 K, not reported before. The absence of a magnetic ordering across $T^{\star}$ in the magnetization data, yet the presence of a sizable anomaly in the specific heat, suggest a structural order-to-disorder type transition. NMR and neutron-diffraction data corroborate our conjecture, by revealing subtle angular distortions of the pyrazine rings and of ClO$^-_4$ counteranion tetrahedra, shown to adopt a configuration of higher symmetry above the transition temperature.Comment: 10 pages, 12 figure

Dependence of quantum correlations of twin beams on pump finesse of optical parametric oscillator

The dependence of quantum correlation of twin beams on the pump finesse of an optical parametric oscillator is studied with a semi-classical analysis. It is found that the phase-sum correlation of the output signal and idler beams from an optical parametric oscillator operating above threshold depends on the finesse of the pump field when the spurious pump phase noise generated inside the optical cavity and the excess noise of the input pump field are involved in the Langevin equations. The theoretical calculations can explain the previously experimental results, quantitatively.Comment: 27 pages, 8 figure

Extraction of Plumes in Turbulent Thermal Convection

We present a scheme to extract information about plumes, a prominent coherent structure in turbulent thermal convection, from simultaneous local velocity and temperature measurements. Using this scheme, we study the temperature dependence of the plume velocity and understand the results using the equations of motion. We further obtain the average local heat flux in the vertical direction at the cell center. Our result shows that heat is not mainly transported through the central region but instead through the regions near the sidewalls of the convection cell.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

Nodeless superconductivity in the noncentrosymmetric Mo3_3Rh2_2N superconductor: a μ\muSR study

The noncentrosymmetric superconductor Mo$_3$Rh$_2$N, with $T_c = 4.6$ K, adopts a $\beta$-Mn-type structure (space group $P$4$_1$32), similar to that of Mo$_3$Al$_2$C. Its bulk superconductivity was characterized by magnetization and heat-capacity measurements, while its microscopic electronic properties were investigated by means of muon-spin rotation and relaxation ($\mu$SR). The low-temperature superfluid density, measured via transverse-field (TF)-$\mu$SR, evidences a fully-gapped superconducting state with $\Delta_0 = 1.73 k_\mathrm{B}T_c$, very close to 1.76 $k_\mathrm{B}T_c$ - the BCS gap value for the weak coupling case, and a magnetic penetration depth $\lambda_0 = 586$ nm. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined by zero-field (ZF)-$\mu$SR measurements, hints at a preserved time-reversal symmetry in the superconducting state. Both TF-and ZF-$\mu$SR results evidence a spin-singlet pairing in Mo$_3$Rh$_2$N.Comment: 5 figures and 5 pages. Accepted for publication as a Rapid Communication in Phys. Rev.