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"condensed matter"
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Mechanics of elastomeric molecular composites
A classic paradigm of soft and extensible polymer materials is the difficulty of combining reversible elasticity with high fracture toughness, in particular for moduli above 1 MPa. Our recent discovery of multiple network acrylic elastomers opened a pathway to obtain precisely such a combination. We show here that they can be seen as true molecular composites with a well–cross-linked network acting as a percolating filler embedded in an extensible matrix, so that the stress–strain curves of a family of molecular composite materials made with different volume fractions of the same cross-linked network can be renormalized into a master curve. For low volume fractions (<3%) of cross-linked network, we demonstrate with mechanoluminescence experiments that the elastomer undergoes a strong localized softening due to scission of covalent bonds followed by a stable necking process, a phenomenon never observed before in elastomers. The quantification of the emitted luminescence shows that the damage in the material occurs in two steps, with a first step where random bond breakage occurs in the material accompanied by a moderate level of dissipated energy and a second step where a moderate level of more localized bond scission leads to a much larger level of dissipated energy. This combined use of mechanical macroscopic testing and molecular bond scission data provides unprecedented insight on how tough soft materials can damage and fail.
Journal Article
Broad spectral tuning of ultra-low-loss polaritons in a van der Waals crystal by intercalation
Phonon polaritons—light coupled to lattice vibrations—in polar van der Waals crystals are promising candidates for controlling the flow of energy on the nanoscale due to their strong field confinement, anisotropic propagation and ultra-long lifetime in the picosecond range
1
–
5
. However, the lack of tunability of their narrow and material-specific spectral range—the Reststrahlen band—severely limits their technological implementation. Here, we demonstrate that intercalation of Na atoms in the van der Waals semiconductor α-V
2
O
5
enables a broad spectral shift of Reststrahlen bands, and that the phonon polaritons excited show ultra-low losses (lifetime of 4 ± 1 ps), similar to phonon polaritons in a non-intercalated crystal (lifetime of 6 ± 1 ps). We expect our intercalation method to be applicable to other van der Waals crystals, opening the door for the use of phonon polaritons in broad spectral bands in the mid-infrared domain.
The spectral range of long-lived and confined phonon polaritons in a polar van der Waals crystal is shown to be tunable by intercalation of Na atoms, expanding their potential for nanophotonic applications in the mid-infrared domain.
Journal Article
Graphene bilayers with a twist
Near a magic twist angle, bilayer graphene transforms from a weakly correlated Fermi liquid to a strongly correlated two-dimensional electron system with properties that are extraordinarily sensitive to carrier density and to controllable environmental factors such as the proximity of nearby gates and twist-angle variation. Among other phenomena, magic-angle twisted bilayer graphene hosts superconductivity, interaction-induced insulating states, magnetism, electronic nematicity, linear-in-temperature low-temperature resistivity and quantized anomalous Hall states. We highlight some key research results in this field, point to important questions that remain open and comment on the place of magic-angle twisted bilayer graphene in the strongly correlated quantum matter world.
Magic-angle twisted bilayer graphene plays host to many interesting phenomena, including superconductivity. This Review highlights key research results in the field, points toward important open questions, and comments on the place of magic-angle twisted bilayer graphene in the strongly correlated quantum matter world.
Journal Article
Dynamical heterogeneities in glasses, colloids, and granular media
\"Most of the solid materials we use in everyday life, from plastics to cosmetic gels exist under a non-crystalline, amorphous form: they are glasses. Yet, we are still seeking a fundamental explanation as to what glasses really are and to why they form. In this book, we survey the most recent theoretical and experimental research dealing with glassy physics, from molecular to colloidal glasses and granular media. Leading experts in this field present broad and original perspectives on one of the deepest mysteries of condensed matter physics, with an emphasis on the key role played by heterogeneities in the dynamics of glassiness\"-- Provided by publisher.
Book
Room-temperature stabilization of antiferromagnetic skyrmions in synthetic antiferromagnets
Room-temperature skyrmions in ferromagnetic films and multilayers show promise for encoding information bits in new computing technologies. Despite recent progress, ferromagnetic order generates dipolar fields that prevent ultrasmall skyrmion sizes, and allows a transverse deflection of moving skyrmions that hinders their efficient manipulation. Antiferromagnetic skyrmions shall lift these limitations. Here we demonstrate that room-temperature antiferromagnetic skyrmions can be stabilized in synthetic antiferromagnets (SAFs), in which perpendicular magnetic anisotropy, antiferromagnetic coupling and chiral order can be adjusted concurrently. Utilizing interlayer electronic coupling to an adjacent bias layer, we demonstrate that spin-spiral states obtained in a SAF with vanishing perpendicular magnetic anisotropy can be turned into isolated antiferromagnetic skyrmions. We also provide model-based estimates of skyrmion size and stability, showing that room-temperature antiferromagnetic skyrmions below 10 nm in radius can be anticipated in further optimized SAFs. Antiferromagnetic skyrmions in SAFs may thus solve major issues associated with ferromagnetic skyrmions for low-power spintronic devices.
Antiferromagnetic skyrmions—which have distinct advantages over skyrmions found in other magnetic systems—are observed at room temperature in synthetic antiferromagnets. These results hold promise for low-power spintronic devices.
Journal Article
Superconductivity in a quintuple-layer square-planar nickelate
Since the discovery of high-temperature superconductivity in copper oxide materials
1
, there have been sustained efforts to both understand the origins of this phase and discover new cuprate-like superconducting materials
2
. One prime materials platform has been the rare-earth nickelates and, indeed, superconductivity was recently discovered in the doped compound Nd
0.8
Sr
0.2
NiO
2
(ref.
3
). Undoped NdNiO
2
belongs to a series of layered square-planar nickelates with chemical formula Nd
n
+1
Ni
n
O
2
n
+2
and is known as the ‘infinite-layer’ (
n
=
∞
) nickelate. Here we report the synthesis of the quintuple-layer (
n
= 5) member of this series, Nd
6
Ni
5
O
12
, in which optimal cuprate-like electron filling (
d
8.8
) is achieved without chemical doping. We observe a superconducting transition beginning at ~13 K. Electronic structure calculations, in tandem with magnetoresistive and spectroscopic measurements, suggest that Nd
6
Ni
5
O
12
interpolates between cuprate-like and infinite-layer nickelate-like behaviour. In engineering a distinct superconducting nickelate, we identify the square-planar nickelates as a new family of superconductors that can be tuned via both doping and dimensionality.
The authors report a superconducting transition beginning at 13 K in films of the quintuple-layer nickelate Nd
6
Ni
5
O
12
.
Journal Article