The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation (BEC) and superfluidity, which have been tested experimentally in a variety of different systems. When bosons are interacting, disorder can destroy condensation leading to a so-called Bose glass. This phase has been very elusive to experiments due to the absence of any broken symmetry and of a finite energy gap in the spectrum.Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (Br-doped dichloro-tetrakis-thiourea-Nickel, DTN).The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand-canonical ensemble; Br-doping introduces disorder in the hoppings and interaction strengths, leading to localization of the bosons into a Bose glass down to zero field, where it acquires the nature of an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the BEC (corresponding to a magnetically ordered phase) is marked by a novel, universal exponent governing the scaling on the critical temperature with the applied field, in excellent agreement arXiv:1109.4403v2 [cond-mat.str-el] 21 Sep 2011 2 with theoretical predictions. Our study represents the first, quantitative account of the universal features of disordered bosons in the grand-canonical ensemble.PACS numbers: 03.75. Lm, 71.23.Ft, 68.65.Cd, 72.15.Rn Introduction. Disorder can have a very strong impact on quantum fluids. Due to their wave-like nature, quantum particles are subject to destructive interference when scattering against disordered potentials. This leads to their quantum localization (or Anderson localization), which prevents e.g.electrons from conducting electrical currents in strongly disordered metals [1], and non-interacting bosons from condensing into a zero-momentum state [2]. Yet interacting bosons represent a matter wave with arbitrarily strong non-linearity, whose localization properties in a random environment cannot be deduced from the standard theory of Anderson localization. For strongly interacting bosons it is known that Anderson localization manifests itself in the Bose glass: in this phase the collective modes of the system -and not the individual particles -are Anderson-localized over arbitrarily large regions, leading to a gapless energy spectrum, and a finite compressibility of the fluid [3, 4]. Moreover nonlinear bosonic matter waves can undergo a localization-delocalization quantum phase transition in any spatial dimension when the interaction strength is varied [3, 4]; the transition brings the system from a non-interacting Anderson insulator to an interacting superfluid condensate, or from a superfluid to a Bose glass. Such a transition is relevant for a large variety of physical systems, including superfluid helium in porous media [6], Cooper pairs in disordered superconductors [7], and cold atoms in random optical potenti...

At a very low temperature of 9mK, electrons in the 2nd Landau level of an extremely high mobility two-dimensional electron system exhibit a very complex electronic behavior. With varying filling factor, quantum liquids of different origins compete with several insulating phases leading to an irregular pattern in the transport parameters. We observe a fully developed ν = 2 + 2/5 state separated from the even-denominator ν = 2 + 1/2 state by an insulating phase and a ν = 2 + 2/7 and ν = 2 + 1/5 state surrounded by such phases. A developing plateau at ν = 2 + 3/8 points to the existence of other even-denominator states.Low-temperature electron correlation in the lowest Landau level (LL) of a two-dimensional electron system (2DES) separates largely into two regions. At very low filling factor, ν ≤ 1/5, an insulating phase exists, which has now quite convincingly been determined to be a pinned electron solid [1,2,3]. At higher filling factor 1 > ν >∼ 1/5 the multiple sequences of fractional quantum Hall effect (FQHE) liquids [4,5, 6,7] dominate, which show the characteristic vanishing magneto resistance, R xx , and quantized Hall resistance, R xy , at many odd-denominator rational fractional fillings ν = p/q [8].Altogether about fifty such FQHE states have been observed in this region. Their multiple sequences can largely be described within the composite fermion (CF) model [9,10, 11,12], with the exact origin of some higher order states still being argued. The electrical behavior between FQHE states carries no particularly strong transport signature, being thought of as arising largely from the conduction of excited quasiparticles of the neighboring FQHE states, with CF liquids occurring at some even-denominator fractions.At high LL's a very different pattern seems to emerge. There charge density wave (CDW) or liquid crystal like states dominate, often referred to as electronic stripe and bubble phases [13,14,15]. Characteristically these states are pinned to the lattice, immobilizing the electrons of this LL, which leads to transport properties identical to those of the neighboring integer quantum Hall effect (IQHE) states. FQHE states are absent in these high LL's, except for the recent observation of two FQHE features in the third LL, at elevated temperatures [16]. Of course, high LL fillings typically occur at lower magnetic fields and hence at poorer resolution of potential FQHE features. However, very general theoretical arguments [17,18] based on an increasing extent of the wavefunction with increasing LL index, hence the increasing importance of exchange and the diminishing applicability of point-like interactions, clearly support this trend.It is in the 2nd LL where electron liquids and electron solids collide. The larger extent of the wavefunction as compared to the lowest LL and its additional zero allows for a much broader range of electron correlations to be favorable, leading to an ever changing competition between multiple electronic phases as the filling factor is varied and as the temperature is low...

We have investigated the influence of impurities on the possible supersolid transition by systematically enriching isotopically-pure 4 He (< 1 ppb of 3 He) with 3 He. The onset of nonclassical rotational inertia is broadened and shifts monotonically to higher temperature with increasing 3 He concentration, suggesting that the phenomenon is correlated to the condensation of 3 He atoms onto the dislocation network in solid 4 He.