Insulator to superfluid transition in coupled photonic cavities in two dimensions

A system of coupled photonic cavities on a two-dimensional square lattice is systematically investigated using the stochastic series expansion quantum Monte Carlo method. The ground state phase diagram contains insulating phases with integer polariton densities surrounded by a superfluid phase. The finite-size scaling of the superfluid density is used to determine the phase boundaries accurately. We find that the critical behavior is that of the generic, density-driven Mott-superfluid transition with dynamic exponent z=2, with no special multicritical points with z=1 at the tips of the insulating-phase lobes (as exist in the case of the Bose-Hubbard model). This demonstrates a limitation of the description of polaritons as structureless bosons.First author draf

Staggered magnetism in LiV2_2O4_4 at low temperatures probed by the muon Knight shift

We report on the muon Knight shift measurement in single crystals of LiV2O4. Contrary to what is anticipated for the heavy-fermion state based on the Kondo mechanism, the presence of inhomogeneous local magnetic moments is demonstrated by the broad distribution of the Knight shift at temperatures well below the presumed "Kondo temperature" ($T^*\simeq 30$ K). Moreover, a significant fraction ($\simeq10$ %) of the specimen gives rise to a second component which is virtually non-magnetic. These observations strongly suggest that the anomalous properties of LiV2O4 originates from frustration of local magnetic moments.Comment: 11 pages, 5 figures, sbmitted to J. Phys.: Cond. Mat

Direct evaporative cooling of 41K into a Bose-Einstein condensate

We have investigated the collisional properties of 41K atoms at ultracold temperature. To show the possibility to use 41K as a coolant, a Bose-Einstein condensate of 41K atoms in the stretched state (F=2, m_F=2) was created for the first time by direct evaporation in a magnetic trap. An upper bound of three body loss coefficient for atoms in the condensate was determined to be 4(2) 10^{-29} cm -6 s-1. A Feshbach resonance in the F=1, m_F=-1 state was observed at 51.42(5) G, which is in good agreement with theoretical prediction.Comment: 4 pages, 4 figure

Incommensurate Matrix Product State for Quantum Spin Systems

We introduce a matrix product state (MPS) with an incommensurate periodicity by applying the spin-rotation operator of each site to a uniform MPS in the thermodynamic limit. The spin rotations decrease the variational energy with accompanying translational symmetry breaking and the rotational symmetry breaking in the spin space even if the Hamiltonian has the both symmetries. The optimized pitch of rotational operator reflects the commensurate/incommensurate properties of spin-spin correlation functions in the $S=1/2$ Heisenberg chain and the $S=1/2$ ferro-antiferro zigzag chain.Comment: 6 pages, 5 figure

Ground state of spin-1 Bose-Einstein condensates with spin-orbit coupling in a Zeeman field

We systematically investigate the weakly trapped spin-1 Bose-Einstein condensates with spin-orbit coupling in an external Zeeman field. We find that the mean-field ground state favors either a magnetized standing wave phase or plane wave phase when the strength of Zeeman field is below a critical value related to the strength of spin-orbit coupling. Zeeman field can induce the phase transition between standing wave and plane wave phases, and we determine the phase boundary analytically and numerically. The magnetization of these two phases responds to the external magnetic field in a very unique manner, the linear Zeeman effect magnetizes the standing wave phase along the direction of the magnetic field, but the quadratic one demagnetizes the plane wave phase. When the strength of Zeeman field surpasses the critical value, the system is completely polarized to a ferromagnetic state or polar state with zero momentum

Proton Spin Relaxation Induced by Quantum Tunneling in Fe8 Molecular Nanomagnet

The spin-lattice relaxation rate $T_{1}^{-1}$ and NMR spectra of $^1$H in single crystal molecular magnets of Fe8 have been measured down to 15 mK. The relaxation rate $T_1^{-1}$ shows a strong temperature dependence down to 400 mK. The relaxation is well explained in terms of the thermal transition of the iron state between the discreet energy levels of the total spin S=10. The relaxation time $T_1$ becomes temperature independent below 300 mK and is longer than 100 s. In this temperature region stepwise recovery of the $^1$H-NMR signal after saturation was observed depending on the return field of the sweep field. This phenomenon is attributed to resonant quantum tunneling at the fields where levels cross and is discussed in terms of the Landau-Zener transition.Comment: 13 pages, 5 figure

Collisional stability of localized Yb(3P2{}^3\mathrm{P}_2) atoms immersed in a Fermi sea of Li

We establish an experimental method for a detailed investigation of inelastic collisional properties between ytterbium (Yb) in the metastable ${}^3\mathrm{P}_2$ state and ground state lithium (Li). By combining an optical lattice and a direct excitation to the ${}^3\mathrm{P}_2$ state we achieve high selectivity on the collisional partners. Using this method we determine inelastic loss coefficients in collisions between $^{174}$Yb(${}^3\mathrm{P}_2$) with magnetic sublevels of $m_J=0$ and $-2$ and ground state $^6$Li to be $(4.4\pm0.3)\times10^{-11}~\mathrm{cm}^3/\mathrm{s}$ and $(4.7\pm0.8)\times10^{-11}~\mathrm{cm}^3/\mathrm{s}$, respectively. Absence of spin changing processes in Yb(${}^3\mathrm{P}_2$)-Li inelastic collisions at low magnetic fields is confirmed by inelastic loss measurements on the $m_J=0$ state. We also demonstrate that our method allows us to look into loss processes in few-body systems separately.Comment: 12 pages, 7 figure

Benchmarking acid and base dopants with respect to enabling the ice V to XIII and ice VI to XV hydrogen-ordering phase transitions

Doping the hydrogen-disordered phases of ice V, VI and XII with hydrochloric acid (HCl) has led to the discovery of their hydrogen-ordered counterparts ices XIII, XV and XIV. Yet, the mechanistic details of the hydrogen-ordering phase transitions are still not fully understood. This includes in particular the role of the acid dopant and the defect dynamics that it creates within the ices. Here we investigate the effects of several acid and base dopants on the hydrogen ordering of ices V and VI with calorimetry and X-ray diffraction. HCl is found to be most effective for both phases which is attributed to a favourable combination of high solubility and strong acid properties which create mobile H3O+ defects that enable the hydrogen-ordering processes. Hydrofluoric acid (HF) is the second most effective dopant highlighting that the acid strengths of HCl and HF are much more similar in ice than they are in liquid water. Surprisingly, hydrobromic acid doping facilitates hydrogen ordering in ice VI whereas only a very small effect is observed for ice V. Conversely, lithium hydroxide (LiOH) doping achieves a performance comparable to HF-doping in ice V but it is ineffective in the case of ice VI. Sodium hydroxide, potassium hydroxide (as previously shown) and perchloric acid doping are ineffective for both phases. These findings highlight the need for future computational studies but also raise the question why LiOH-doping achieves hydrogen-ordering of ice V whereas potassium hydroxide doping is most effective for the 'ordinary' ice Ih.Comment: 18 pages, 7 figures, 1 tabl

Improved high-temperature resistant matrix resins

A study was performed with the objective of developing matrix resins that exhibit improved thermo-oxidative stability over state-of-the-art high temperature resins for use at temperatures up to 644 K (700 F) and air pressures up to 0.7 MPa (100 psia). The work was based upon a TRW discovered family of polyimides currently licensed to and marketed by Ethyl Corporation as EYMYD(R) resins. The approach investigated to provide improved thermo-oxidative properties was to use halogenated derivatives of the diamine, 2, 2-bis (4-(4-aminophenoxy)phenyl) hexafluoropropane (4-BDAF). Polyimide neat resins and Celion(R) 12,000 composites prepared from fluorine substituted 4-BDAF demonstrated unexpectedly lower glass transition temperatures (Tg) and thermo-oxidative stabilities than the baseline 4-BDAF/PMDA polymer

The Kinematics of the Outer Halo of M87

Radial velocities are presented for a new sample of globular clusters in the outer halo of M87 at a distance of 300 to 540 arcsec (24 to 43 kpc) from the center of this galaxy. These are used to augment our previously published data and an analysis of the rotation and velocity dispersion of the M87 globular cluster system is carried out. The rotation is $\sim300$ \kms at R = 32 kpc, at which point the velocity dispersion is also still quite high, $\sim450$ \kms. The high rotation is interesting. The outer halo of M87 is, as was found in our previous kinematic analysis, very massive.Comment: Accepted for publication in the AJ. 13 pages with 3 figure