Bose Glass State Research Articles

Moving binary Bose-Einstein condensates in a weak random potential

We study the behavior of moving Bose-Bose mixtures in a weak disordered potential in the realm of the Bogoliubov-Huang-Meng theory. Corrections due to the quantum fluctuations, disorder effects and the relative motion of two fluids to the glassy fraction, the condensed depletion, the anomalous density, and the equation of state of each species are obtained analytically for small velocity. We show that the intriguing interplay of the relative motion and the disorder potential could not only change the stability condition, but destroy also the localization process in the two condensates preventing the formation of a Bose glass state. Unexpectedly, we find that the quantum fluctuations reduce with the velocity of the two fluids. The obtained theoretical predictions are checked by our numerical results.

First-principles study of an S=1 quasi one-dimensional quantum molecular magnetic material

We use density functional theory to study the structural, magnetic and electronic structure of the organo-metallic quantum magnet $\mathrm{NiCl_2-4SC(NH_2)_2}$ (DTN). Recent work has demonstrated the quasi-1D nature of the molecular crystal and its quantum phase transitions at low temperatures. This includes a magneto-electric coupling and, when doped with Br, the presence of an exotic Bose-glass state. We systematically show that, by using the generalized gradient approximation (GGA) with inclusion of a van der Waals term to account for weak inter-molecular forces and by introducing a Hubbard $U$ term to the total energy, our calculations reproduce the magnetic anisotropy, the inter-molecular exchange coupling strength and the magneto-electric effect in DTN, which were observed in previous experiments. Further analysis into the electronic structure gives insight into the underlying magnetic interactions, including what mechanisms may be causing the ME effect. Using this computationally efficient model, we predict what effect applying an electric field might have on the magnetic properties of this quantum magnet.

Anomalous frequency dependence of magneto-electric effect in doped DTN

The anomalous frequency dependence observed for the magneto-electric effect in the Bose glass state of dichloro-tetrakis-thoiurea-nickel doped with bromine is analyzed in terms of the hierarchical droplet model of spin glasses. In this model low energy barriers must be overcome before accessing higher energy states leading to scaling laws for the spin correlation functions and an associated frequency dependence for transition rates.

Effects of the Lee-Huang-Yang quantum corrections on a disordered dipolar Bose gas

We study the behavior of a quantum dipolar Bose condensate with the Lee-Huang-Yang quantum corrections at zero temperature in the presence of weak disorder potential. We solve the underlying nonlocal Gross-Pitaevskii equation using a perturbative theory. The role of both the Lee-Huang-Yang term and the disorder potential on the condensed fraction, the equation of state, the compressibility and the superfluid density is deeply analyzed. Surprisingly, we find that the Lee-Huang-Yang quantum corrections not only arrest the dipolar implosion but also lead to reduce the condensate fluctuations due to the disorder effects prohibiting the formation of a Bose glass state. We show that the superfluid density exhibits unconventional behavior.

Localization-Delocalization Transition in Disordered One-Dimensional Exciton-Polariton System

The transition from the delocalized to the localized state has been investigated in a quasi-onedimensional exciton-polariton system excited nonresonantly in GaAs-based microcavity wire with disordered potential. The photoexcited polariton condensate has been found to spread along the wire with а velocity exceeding 1 μm/ps. The propagation along the wire is provided by high energy polaritons. The LP localization length decreases with decreasing blue shift of LPs in the excited spot. The polariton condensate returns to the Bose glass state when the blue shift of the LP resonance at the excitation spot decreases below the critical level that depends on the potential disorder.

Localization-delocalization transition in disordered one-dimensional exciton-polariton system

AbstractThe transition from the delocalized to the localized state has been investigated in a quasi-onedimensional exciton-polariton system excited nonresonantly in GaAs-based microcavity wire with disordered potential. The photoexcited polariton condensate has been found to spread along the wire with а velocity exceeding 1 μm/ps. The propagation along the wire is provided by high energy polaritons. The LP localization length decreases with decreasing blue shift of LPs in the excited spot. The polariton condensate returns to the Bose glass state when the blue shift of the LP resonance at the excitation spot decreases below the critical level that depends on the potential disorder.

Effect of Nanorod Alignment on Flux Pinning State in BaHfO3 Doped SmBa2Cu3 Oy Films

The effect of the microstructure on the flux pinning state in BaHfO 3 (BHO) nanorods doped SmBa 2 Cu 3 O y (SmBCO) films was investigated using high field magnets with a rotator stage. Films with aligned nanorods showed the strong flux pining along c-axis, which disappears at high magnetic fields. This behavior corresponds to the existence of the Bose glass state in the film, which is also supported by the behaviors of the activation energy and the critical exponent of the liquid-glass transition estimated from the transport properties. Moreover, the field dependencies of the flux pinning force are explained by the flux pinning models for the correlated nanorods and the random pinning centers in the films with the aligned and the firework nanorods structures. The strong relationship is confirmed between the structure of the nanorods and the pinning properties in the BHO doped SmBCO films.

Thermodynamic evidence for the Bose glass transition in twinnedYBa2Cu3O7−δcrystals

We used a micromechanical torsional oscillator to measure the magnetic response of a twinned YBa$_2$Cu$_3$O$_{7-\delta}$ single crystal disk near the Bose glass transition. We observe an anomaly in the temperature dependence of the magnetization consistent with the appearance of a magnetic shielding perpendicular to the correlated pinning of the twin boundaries. This effect is related to the thermodynamic transition from the vortex liquid phase to a Bose glass state.

Irreversibility Fields and Critical Current Densities in Strongly Pinned YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> Films With Artificial Pinning Centers

We propose a microscopic approach to derive angular dependent critical current density J c (θ) of YBCO films with c-axis correlated nanorods, based on the energy gain by pinning. Results are in good agreement with experimental ones. Irreversibility fields and J c in YBa 2 Cu 3 O 7-x thin films containing segmented BaSnO 3 nanorods are systematically changed by selection of nanorod length and its spacing, and the variations are explained by the “harmonic oscillator” approach based on the Bose glass state. Analysis of pinning energies and J c indicates that stacked BSO nanorod segments in line behave as single columnar with a smaller diameter pin for B|| c, in contrast, as nanoparticle pins for B||ab.

Irreversibility fields and critical current densities in strongly pinned YBa2Cu3O7-x films with BaSnO3 nanorods: The influence of segmented BaSnO3 nanorods

We report irreversibility fields Birr and critical current densities Jc in YBa2Cu3O7-x thin films containing segmented BaSnO3 nanorods. Birr and Jc are systematically changed by selection of nanorod length and its spacing, and the variations are explained by the “harmonic oscillator” approach based on the Bose glass state. Analysis of pinning energies and Jc indicates that segmented nanorods behave as single columnar pin for B || c, in contrast, as nanoparticle pins for B || ab. The present results may help to further investigate anisotropy tuning of pinning structures.

Magnetic susceptibility investigation of Bose-glass state in Ni0.85Cd0.15Cl2-4SC(NH2)2 at ultra-low temperatures

We report measurements of the AC susceptibility of a site-diluted quantum magnet Ni0.85Cd0.15Cl2-4SC(NH2)2 (15% Cd-doped dichloro-tetrakis-thiourea-Nickel, or Cd-DTN) down to 10 mK Below a crossover temperature Tcr ≍ 100 ∼ 200mK, we find that the critical fields Hc for Bose-Einstein condensation obey the scaling relation |Hc(T)–Hc(0)| ∼ Tα, with a novel and universal scaling exponent α ≍ 0.9, which is in agreement with numerical results from a theoretical model. Our findings provide strong evidence of the existence of a Bose glass phase in Cd-DTN, and they display a quantitative signature of the transition between a Bose glass and a Bose Einstein condensate.

Phase Transition of Interacting Disordered Bosons in One Dimension

Interacting bosons generically form a superfluid state. In the presence of disorder it can get converted into a compressible Bose glass state. Here we study such a transition in one dimension at moderate interaction using bosonization and renormalization group techniques. We derive the two-loop scaling equations and discuss the phase diagram. We find that the correlation functions at the transition are characterized by universal exponents in a finite region around the fixed point.

Bose-glass state in one-dimensional random antiferromagnets

One-dimensional random antiferromagnets ${({\text{CH}}_{3})}_{2}{\text{CHNH}}_{3}\text{Cu}{({\text{Cl}}_{x}{\text{Br}}_{1\ensuremath{-}x})}_{3}$ [abbreviated as $\text{IPA-Cu}{({\text{Cl}}_{x}{\text{Br}}_{1\ensuremath{-}x})}_{3}$] show three magnetic phases: Cl rich, intermediate, and Br rich. In this study, to confirm the presence of a gapped or gapless state in addition to a Bose-glass (BG) state of spin triplets at two magnetic phase boundaries, magnetic susceptibility, specific heat, and magnetization were measured. Contrary to our proposed model, the results suggest a gapless state and a BG state at the Br-rich phase boundary, and a spin-gap state at the Cl-rich phase boundary. From the viewpoints of the universality class, the BG state may be interpreted as a result of Anderson localization. Therefore, $\text{IPA-Cu}{({\text{Cl}}_{x}{\text{Br}}_{1\ensuremath{-}x})}_{3}$ are intriguing compounds for studying the BG state because of good one dimensionality.

Disordered States inIPA−Cu(ClxBr1−x)3Induced by Bond Randomness

The mixtures of two spin-gap compounds IPA-Cu(ClxBr1-x)3 are studied by electron paramagnetic resonance and magnetization processes [M(H)]. From electron paramagnetic resonance spectra, the symmetry of the spin-gap state breaks down, even for x=0.99. From M(H) curves for x=0.95 and 0.92, however, spin gaps survive below mu0Hc1=10+/-1 T, and the M(H) slopes bend at mu0Hc3=40+/-1 T, below the saturation field Hc2. Such a curvature suggests an exotic phase transition: Bose-Einstein condensation of spin triplets occurs at Hc1 <H <Hc3 and a Bose-glass state may be realized at Hc3 <H <Hc2, successively. As a result, the possibility of fine-tuning the density of bosons by H provides a tool for determining the role of the interactions.

Critical current of type-II superconductors in a broken Bose glass state

The tilt modulus of a defective Abrikosov vortex lattice pinned by material line defects is computed using the boson analogy. It tends to infinity at long wavelength, which yields a Bose glass state that is robust to the addition of weak point-pinning centers and which implies a restoring force per vortex line for rigid translations about mechanical equilibrium that is independent of magnetic field. It also indicates that the Bose glass state breaks into pieces along the direction of the correlated pinning centers if the latter have finite length. The critical current is predicted to crossover from two-dimensional to three-dimensional behavior as a function of sample thickness along the correlated pinning centers in such case. That crossover notably can occur at a film thickness that is much larger than that expected from point pins of comparable strength. The above is compared to the dependence on thickness shown by the critical current in certain films of high-temperature superconductors currently being developed for wire technology.

Introduction of c-axis-correlated 1D pinning centers and vortex Bose glass in Ba–Nb–O-dopedErBa2Cu3Oy films

We report the effectiveness of barium niobate as a needle-type vortex pinningcenter, as well as a change in the vortex state in Ba–Nb–O (BNO)-dopedErBa2Cu3Oy thin films.BNO doping was effective for improving critical current properties for a magnetic field direction parallelto the c axis of a matrix film and induced the generation of columnar defectswith diameters of 5–25 nm. The irreversibility lines were also changedby the BNO doping and were similar to those of heavy-ion-irradiatedYBa2Cu3Oy crystals in which the vortex Bose glass state was induced. It is suggested that thecharacteristic field relevant to crossover from the Bose glass to collective pinned glass dependson the BNO doping level. There is a possibility that Ba-based perovskite-type oxides promotethe formation of nanorods universally and these nanorods play the role of one-dimensionalc-axis-correlated pinning centers.

Nano-engineering of pinning centres in bulk Y-123 – The realisation of a Bose glass state

So far, nano-sized defects generated by irradiation techniques are the most powerful approach to very strong pinning capability. In the present study, chemical attempts have been alternatively investigated to introduce with a melt texturing process the following different types of nano-sized pinning defects: (a) nano-scale correlation of lattice defects, (b) nano-sized particles or needles of a secondary phase, and (c) extended structures with correlated nano-sized defects. A periodic array of nano-scale twin boundaries has been formed inside melt-processed YBa2Cu3O7−δ (YBCO) with Ru additions. The pinning efficiency of the resulting material is strongly modified in the presence of such disorder. The arrangement of the regular twin boundary along the c-axis has a strong influence on irreversibility line and critical current density. The behavior of the irreversibility line indicates correlated disorder which was attributed to the formation of arrays of nanotwins. The field tilt angle below which pinning by the twin boundary is effective is found to be approximately 40°.

Bose glass state in bulk(Nd,Eu,Gd)Ba2Cu3Oxwith a high irreversibility field

$(\mathrm{Nd},\mathrm{Eu},\mathrm{Gd}){\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ (NEG123) bulk shows the high irreversibility properties. In order to clarify the origin of high irreversibility fields, the transport properties of NEG123 bulk with the high irreversibility field were investigated against high magnetic fields, temperatures, and field angles. We found that a dip in the angular dependent resistivity appears at $B∕∕c$, originated to the correlated disorder along the $c$ axis. In addition, the Bose glass phase was observed around $B∕∕c$ by the detailed analysis of the glass transition temperature and exponent. Therefore the Bose glass state plays an important role for realization of the high irreversibility field. It is suggested that new effective pinning centers correlated along the $c$ axis are responsible for the high irreversibility field.

Vortex solid state inYBa2Cu3O7−δtwinned crystals

We report on the scaling of transport properties around the vortex melting in YBa$_2$Cu$_3$O$_{7- \delta}$ oriented-twin single crystals in applied magnetic fields between 1T and 18T. We find that for all the measured field range the linear resistivity scales as $\rho (t,\theta) \sim t^{sy} {\cal F}_{\pm} (\sin(\theta)t^{-sx})$, with $t=|T-T_{BG}|$ and $\theta$ the angle between de planar defects and the magnetic field. The scaling is valid only for angles where the transition temperature $T_{BG} (\theta)$ shows a cusp. The critical exponents $sx$ and $sy$ are in agreement with the values predicted by Lidmar and Wallin only at magnetic fields below 4T. A change in the value of $sx$ from $sx = 1 \pm 0.2$ to $sx = 3 \pm 0.2$ at around $H^{cr} \approx $ 4T when the magnetic field is increased, is responsible for changes in the shape of the $T_{BG} (\theta)$ curve and in the dependence of the linear dissipation on temperature and angle. The results strongly suggest the existence of a different vortex glassy phase in twinned crystals compared to the Bose-glass state found in samples with linear defects.

Signature of the matching field in Bose-glass melting of untwinnedYBa2Cu3O7−δsingle crystals

We map out the phase boundary separating the Bose-glass and vortex-liquid phases in an irradiated twin-free YBa_2Cu_3O_(7-δ) single crystal. We take the phase boundary to be the temperature T_g and magnetic field H at which the crystal begins to screen a small ac magnetic field, h_(ac). There is a significant change in slope dT_g/dH of the phase boundary at the matching field B_Φ (≃0.5 T) indicating that interstitial vortices significantly weaken pinning in the Bose-glass state. There is also a pronounced peak in the slope dT_g/dH just below B_Φ at higher h_(ac). Both features disappear when the field is tilted away from the columns.