697 research outputs found
Holographic dissipative space-time supersolids
Driving a system out of equilibrium enriches the paradigm of spontaneous
symmetry breaking, which could then take place not only in space but also in
time. The interplay between temporal and spatial symmetries, as well as
symmetries from other internal degrees of freedom, can give rise to novel
nonequilibrium phases of matter. In this study, we investigate a
driven-dissipative superfluid model using holographic methods and reveal the
existence of a space-time supersolid (STS) phase which concomitantly breaks the
time translation, spatial translation, and the internal U(1) symmetry. The
holographic methods naturally include finite temperature effects, which enables
us to explore the complex phase diagram of this model and observe a cascade of
out-of-equilibrium phase transitions from the STS phase to a synchronized
superfluid phase, and finally to a normal fluid phase, by increasing the
temperature.Comment: 9 pages, 7 figure
Dynamical evolution of spinodal decomposition in holographic superfluids
We study the nonlinear dynamical evolution of spinodal decomposition in a
first-order superfluid phase transition using a simple holographic model in the
probe limit. We first confirm the linear stability analysis based on
quasinormal modes and verify the existence of a critical length scale related
to a gradient instability -- negative speed of sound squared -- of the
superfluid sound mode, which is a consequence of a negative thermodynamic
charge susceptibility. We present a comparison between our case and the
standard Cahn-Hilliard equation for spinodal instability, in which a critical
length scale can be also derived based on a diffusive instability. We then
perform several numerical tests which include the nonlinear time evolution
directly from an unstable state and fast quenches from a stable to an unstable
state in the spinodal region. Our numerical results provide a real time
description of spinodal decomposition and phase separation in one and two
spatial dimensions. We reveal the existence of four different stages in the
dynamical evolution, and characterize their main properties. Finally, we
investigate the strength of dynamical heterogeneity using the spatial variance
of the local chemical potential and we correlate the latter to other features
of the dynamical evolution.Comment: 19 pages, 13 figure
The Reaction of Allyl Isothiocyanate with Hydroxyl/Water and β-Cyclodextrin Using Ultraviolet Spectrometry
Metodom ultraljubičaste spektrofotometrije istražena je reakcija alil izotiocijanata (AITC) s hidroksilom/vodom i β-ciklodekstrinom (β-CD) u mediju različite kiselosti odnosno lužnatosti. Mjereni su kinetički parametri reakcije. Utvrđeno je da se, nakon što AITC prijeđe u tioureu, apsorpcijski pik pomakne s 240 na 226 nm i da molarna apsorpcija poraste 16 puta. Reakcija se može okarakterizirati kao pseudoreakcija prvog reda jer je konstantna koncentracija hidroksila. β-CD može inhibirati reakciju AITC s hidroksilom/vodom, tj. hidrolizu AITC. Izračunati su konstanta nastajanja (Ka) i termodinamički parametri kompleksne reakcije. S povećanjem temperature smanjuje se Ka. Rezultati pokusa pokazuju da proces uključuje egzotermnu reakciju koju pokreće entalpija praćena negativnom entropijom.The reaction of allyl isothiocyanate (AITC) with hydroxyl/water and β-cyclodextrin (β-CD) in different acidic-alkaline media has been investigated by ultraviolet spectrometry. The kinetic parameters of the reaction were measured. It was found that after AITC translating into thiourea, the absorption peak shifted from 240 to 226 nm and the molar absorptivity increased about 16 times. The reaction can be seen as a pseudo first order reaction because the concentration of hydroxyl was constant. β-CD can inhibit the reaction of AITC with hydroxyl/water, i.e. the hydrolysis of AITC. The formation constant (Ka) and thermodynamic parameters of the complex reaction were calculated. Ka decreased with the increase of temperature. The experimental results indicated that the inclusive process was an exothermic and enthalpy-driven process accompanied with a negative entropic contribution
Correlated states in twisted double bilayer graphene
Electron-electron interactions play an important role in graphene and related
systems and can induce exotic quantum states, especially in a stacked bilayer
with a small twist angle. For bilayer graphene where the two layers are twisted
by a "magic angle", flat band and strong many-body effects lead to correlated
insulating states and superconductivity. In contrast to monolayer graphene, the
band structure of untwisted bilayer graphene can be further tuned by a
displacement field, providing an extra degree of freedom to control the flat
band that should appear when two bilayers are stacked on top of each other.
Here, we report the discovery and characterization of such displacement-field
tunable electronic phases in twisted double bilayer graphene. We observe
insulating states at a half-filled conduction band in an intermediate range of
displacement fields. Furthermore, the resistance gap in the correlated
insulator increases with respect to the in-plane magnetic fields and we find
that the g factor according to spin Zeeman effect is ~2, indicating spin
polarization at half filling. These results establish the twisted double
bilayer graphene as an easily tunable platform for exploring quantum many-body
states
Experimental observation of magnetic bobbers for a new concept of magnetic solid-state memory
The use of chiral skyrmions, which are nanoscale vortex-like spin textures,
as movable data bit carriers forms the basis of a recently proposed concept for
magnetic solid-state memory. In this concept, skyrmions are considered to be
unique localized spin textures, which are used to encode data through the
quantization of different distances between identical skyrmions on a guiding
nanostripe. However, the conservation of distances between highly mobile and
interacting skyrmions is difficult to implement in practice. Here, we report
the direct observation of another type of theoretically-predicted localized
magnetic state, which is referred to as a chiral bobber (ChB), using
quantitative off-axis electron holography. We show that ChBs can coexist
together with skyrmions. Our results suggest a novel approach for data
encoding, whereby a stream of binary data representing a sequence of ones and
zeros can be encoded via a sequence of skyrmions and bobbers. The need to
maintain defined distances between data bit carriers is then not required. The
proposed concept of data encoding promises to expedite the realization of a new
generation of magnetic solid-state memory
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