Condensed Matter Perspective Research Articles

Study of spin polarization in graphene-based unconventional superconductor junctions

In this paper, we study spin polarization in ferromagnetic-unconventional superconductor graphene junction, where we consider three different Cooper pairing states: one unconventional dx2-y2-wave and two time-reversal symmetry broken dx2-y2+is and dx2-y2+idxy . In the absence of Fermi wave mismatch (FWM), a high-spin polarization is achievable if we increase the exchange field of ferromagnet close to the Fermi energy values in the ferromagnetic region. In the presence of FWM, the angle between the normal to the interface and the x-axis of superconducting crystal, i. e. β plays a crucial role in spin polarization. For β=π/8, the polarization is totally negative especially in the sub-gap region when modified conventional Andreev reflection (MCAR) governs, and it is completely positive when modified specular Andreev reflection (MSAR) dominates on the tunneling junction. If we rotate β from β=π/8 to β=π/4, the spin polarization shows three different behaviors for the mentioned Cooper pairing states. Therefore, not only is it possible to discriminate MCAR from MSAR which is significant especially from a condensed-matter perspective but also one can find high spin polarization by tuning the junction parameters which is important in spintronic applications.

Hydrodynamic transport in strongly coupled disordered quantum field theories

We compute direct current thermoelectric transport coefficients in strongly coupled quantum field theories without long lived quasiparticles, at finite temperature and charge density, and disordered on long wavelengths compared to the length scale of local thermalization. Many previous transport computations in strongly coupled systems are interpretable hydrodynamically, despite formally going beyond the hydrodynamic regime. This includes momentum relaxation times previously derived by the memory matrix formalism, and non-perturbative holographic results; in the latter case, this is subject to some important subtleties. Our formalism may extend some memory matrix computations to higher orders in the perturbative disorder strength, as well as give valuable insight into non-perturbative regimes. Strongly coupled metals with quantum critical contributions to transport generically transition between coherent and incoherent metals as disorder strength is increased at fixed temperature, analogous to mean field holographic treatments of disorder. From a condensed matter perspective, our theory generalizes the resistor network approximation, and associated variational techniques, to strongly interacting systems where momentum is long lived.

Proteins Fibrils from a Polymer Physics Perspective

Protein fibrils resulting from assembly of proteins or peptides into long, insoluble, highly ordered fibrillar structures are emerging as one of the fastest growing scientific areas, since interest in these systems spans disciplines as broad and diverse as medicine, biology, soft condensed matter, nanotechnology, and materials science. Since the discovery of the implication of protein amyloid fibrils in neurodegenerative diseases, to their more recent applications in high-performance materials, the understanding of these intriguing macromolecular assemblies has been steadily widening and deepening. Thus, the precise characterization of structural, physical, and mechanical properties of protein fibrils is the first critical step toward our understanding of these systems not only in the context of biology and medicine but also in nanotechnology and advanced biomaterials applications. In this Perspective we wish to discuss how polymer and colloidal science concepts can be efficiently used to unravel very useful information on the mechanisms of formation, structure, and physical properties of protein fibrils and want to show, through available examples, how a soft condensed matter perspective can shed light into these fascinating systems.

The Casimir effect from a condensed matter perspective

The Casimir effect, a key observable realization of vacuum fluctuations, is usually taught in graduate courses on quantum field theory. The growing importance of Casimir forces in microelectromechanical systems motivates this subject as a topic for graduate many-body physics courses. To this end, we revisit the Casimir effect using methods common in condensed matter physics. We recover previously derived results and explore the implications of the analogies implicit in this treatment.

Soft condensed matter perspective on moisture transport in cooking meat

AbstractWe have viewed cooking meat from the perspective of soft condensed physics and posed that the moisture transport during cooking can be described by Flory‐Rehner theory of swelling/shrinking polymer gels. This theory contains the essential physics to describe the transport of liquid moisture due to the denaturation and shrinkage of the heated protein matrix. The validity of our hypothesis is shown by a numerical model, which comprises a linearization of the Flory‐Rehner theory augmented with Darcy's law for porous media flow, applied to the simulation of cooking experiments performed on a rectangular piece of beef. Reasonably, comparable results are obtained from simulations and experiments. Further analysis of simulations resolves yet another unexplained phenomena observed during heating of meat. Literature review suggests that Flory‐Rehner is applicable to cooking of other gel‐like foods. © 2007 American Institute of Chemical Engineers AIChE J, 2007

A quantum field theory of simplicial geometry and the emergence of spacetime

We present the case for a fundamentally discrete quantum spacetime and for Group Field Theories as a candidate consistent description of it, briefly reviewing the key properties of the GFT formalism. We then argue that the outstanding problem of the emergence of a continuum spacetime and of General Relativity from fundamentally discrete quantum structures should be tackled from a condensed matter perspective and using purely QFT methods, adapted to the GFT context. We outline the picture of continuum spacetime as a condensed phase of a GFT and a research programme aimed at realizing this picture in concrete terms.

21] Analysis of diffuse scattering and relation to molecular motion

This chapter discusses the features of diffuse scattering from macromolecules. Diffuse studies are important because they provide the only way to distinguish among different models for correlated movement. This chapter uses interchangeably the terms movement and displacement, reflecting the mixing of space and time averages in an X-ray scattering experiment. Despite this ambiguity, much of the disorder in macromolecular crystals is dynamic. Even if the interconversion of conformations within crystallized molecules does not occur on fast time scales, diffuse scattering studies still reveal the conformational flexibility of the molecules, which is crucial to understanding their biological function. Any variation in the periodicity of the electron density of a crystal, not just the disorder introduced by atomic displacements, gives rise to diffuse scattering. The chapter presents a survey of what the diffuse scattering looks like from various kinds of crystal disorder. For example, both mosaicity and substitution disorder produce diffuse scattering. Although all imperfections are interesting from a condensed-matter perspective, displacement disorder is most relevant to the biological behavior of molecules. This is the focus of this chapter.