Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Graphene and other two-dimensional materials, such as transition metal dichalcogenides, have rapidly established themselves as intriguing building blocks for optoelectronic applications, with a strong focus on various photodetection platforms The versatility of these material systems enables their application in areas including ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges These detectors can be integrated with other photonic components based on the same material, as well as with silicon photonic and electronic technologies Here, we provide an overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of different two-dimensional crystals or of two-dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides

http://www-g.eng.cam.ac.uk/nms/publications/pdf/nnano.2014.215.pdf

Photodetectors based on graphene, other two-dimensional materials and hybrid systems

Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a catalyst in fuel and dye-sensitized solar cells. Chemically functionalized graphene can also improve storage and diffusion of ionic species and electric charge in batteries and supercapacitors. Two-dimensional crystals provide optoelectronic and photocatalytic properties complementing those of graphene, enabling the realization of ultrathin-film photovoltaic devices or systems for hydrogen production. Here, we review the use of graphene and related materials for energy conversion and storage, outlining the roadmap for future applications.

Graphene, related two-dimensional crystals, and hybrid systems for energy conversion and storage

Physical Review B

Annual review of condensed matter physics

We present theoretical results on the interplay of magnetic and superconducting orders in diffusive ferromagnet-superconductor-ferromagnet trilayers The induced triplet superconducting correlations throughout the trilayer lead to an induced spin magnetization We include self-consistency of the order parameter in the superconducting layer at arbitrary temperatures, arbitrary interface transparency, and any relative orientation of the exchange fields in the two ferromagnets We propose to use the torque on the trilayer in an external magnetic field as a probe of the presence of triplet correlations in the superconducting phase

/pdf/interplay-of-magnetic-and-superconducting-proximity-effects-1bc1gijcfd.pdf

Interplay of magnetic and superconducting proximity effects in ferromagnet-superconductor-ferromagnet trilayers.

We report complementary studies of the critical temperature and the critical current in ferromagnet (Ni) - superconductor (Nb) multilayers. The observed oscillatory behavior of both quantities upon variation of the thickness of the ferromagnetic layer is found to be in good agreement with theory. The length scale of oscillations is identical for both quantities and is set by the magnetic length corresponding to an exchange field of 200 meV in Ni. The consistency between the behavior of the two quantities provides strong evidence for periodic pi phase shifts in these devices.

Observation of Periodic pi-Phase Shifts in Ferromagnet-Superconductor Multilayers

The Riccati formulation of the quasiclassical theory of nonequilibrium superconductors is developed for spin-dependent scattering near magnetic interfaces. We derive boundary conditions for the Riccati distribution functions at a spin-active interface. The boundary conditions are formulated in terms of an interface $S$-matrix describing the reflection and transmission of the normal-state conduction electrons by the interface. The $S$-matrix describes the effects of spin filtering and spin mixing (spin rotation) by a ferromagnetic interface. The boundary conditions for the Riccati equations are applicable to a wide range of nonequilibrium transport properties of hybrid systems of superconducting and magnetic materials. As an application we calculate the spin and charge conductance of a normal metal-ferromagnet-superconductor (NFS) point contact; the spin mixing angle that parameterizes the $S$-matrix is determined from experimental measurements of the peak in the subgap differential conductance of the NFS point contact. We also use the new boundary conditions to derive the effects of spin mixing on the phase-modulated thermal conductance of a superconducting-ferromagnetic-superconducting (SFS) point contact. For high-transparency (metallic ferromagnet) ``$\ensuremath{\pi}$'' junctions, the phase modulation of the thermal conductance is dramatically different from that of nonmagnetic, ``0'' junctions. For low-transparency (insulating ferromagnet) SFS tunnel junctions with weak spin-mixing resonant transmission of quasiparticles with energies just above the gap edge leads to an increase of the thermal conductance, compared to the normal-state conductance at ${T}_{c}$, over a broad temperature range when the superconducting phase bias is $\ensuremath{\phi}\ensuremath{\gtrsim}\ensuremath{\pi}∕2$.

Nonequilibrium superconductivity near spin-active interfaces

We present calculations of the thermal and electric linear response in graphene, including disorder in the 
self-consistent t-matrix approximation. For strong impurity scattering, near the unitary limit, the formation of 
a band of impurity states near the Fermi level leads to that Mott’s relation holds at low temperature. For higher 
temperatures, there are strong deviations due to the linear density of states. The low-temperature thermopower 
is proportional to the inverse of the impurity potential and the inverse of the impurity density. Information 
about impurity scattering in graphene can be extracted from the thermopower, either measured directly or 
extracted via Mott’s relation from the electron-density dependence of the electric conductivity.

Impurity scattering and Mott's formula in graphene

We present a theory for quasiparticle heat transport through superconducting weak links. The thermal conductance depends on the phase difference ($\ensuremath{\phi}$) of the superconducting leads. Branch-conversion processes, low-energy Andreev bound states near the contact, and the suppression of the local density of states near the gap edge are related to phase-sensitive transport processes. Theoretical results for the influence of junction transparency, temperature, and disorder, on the conductance, are reported. For high-transmission weak links, $D\ensuremath{\rightarrow}1$, the formation of an Andreev bound state leads to suppression of the density of states for the continuum excitations, and thus, to a reduction in the conductance for $\ensuremath{\phi}\ensuremath{\simeq}\ensuremath{\pi}$. For low-transmission ($D\ensuremath{\ll}1$) barriers resonant scattering leads to an increase in the thermal conductance as $T$ drops below ${T}_{c}$ (for phase differences near $\ensuremath{\phi}=\ensuremath{\pi}$).

Tomas Löfwander

Papers

Interplay of magnetic and superconducting proximity effects in ferromagnet-superconductor-ferromagnet trilayers.

Observation of Periodic pi-Phase Shifts in Ferromagnet-Superconductor Multilayers

Nonequilibrium superconductivity near spin-active interfaces

Impurity scattering and Mott's formula in graphene

Phase modulated thermal conductance of Josephson weak links.