다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

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Spintronics: Fundamentals and applications

The proximity effect at superconductor-ferromagnet interfaces produces damped oscillatory behavior of the Cooper pair wave function within the ferromagnetic medium. This is analogous to the inhomogeneous superconductivity, predicted long ago by Fulde and Ferrell (P. Fulde and R. A. Ferrell, 1964, ``Superconductivity in a strong spin-exchange field,'' Phys. Rev. 135, A550--A563), and by Larkin and Ovchinnikov (A. I. Larkin and Y. N. Ovchinnikov, 1964, ``Inhomogeneous state of superconductors,'' Zh. Eksp. Teor. Fiz. 47, 1136--1146 [Sov. Phys. JETP 20, 762--769 (1965)]), and sought by condensed-matter experimentalists ever since. This article offers a qualitative analysis of the proximity effect in the presence of an exchange field and then provides a description of the properties of superconductor-ferromagnet heterostructures. Special attention is paid to the striking nonmonotonic dependence of the critical temperature of multilayers and bilayers on the ferromagnetic layer thickness as well as to the conditions under which ``$\ensuremath{\pi}$'' Josephson junctions are realized. Recent progress in the preparation of high-quality hybrid systems has permitted the observation of many interesting experimental effects, which are also discussed. Finally, the author analyzes the phenomenon of domain-wall superconductivity and the influence of superconductivity on the magnetic structure in superconductor-ferromagnet bilayers.

Proximity effects in superconductor-ferromagnet heterostructures

This review considers unusual effects in superconductor-ferromagnet structures, in particular, the triplet component of the condensate generated in those systems. This component is odd in frequency and even in momentum, which makes it insensitive to nonmagnetic impurities. If the exchange field is not homogeneous in the system, the triplet component is not destroyed even by a strong exchange field and can penetrate the ferromagnet over long distances. Some other effects considered here and caused by the proximity effect are enhancement of the Josephson current due to the presence of the ferromagnet, induction of a magnetic moment in superconductors resulting in a screening of the magnetic moment, and formation of periodic magnetic structures due to the influence of the superconductor. Finally, theoretical predictions are compared with existing experiments.

https://arxiv.org/pdf/cond-mat/0506047.pdf

Odd triplet superconductivity and related phenomena in superconductor-ferromagnet structures

Within a time span of 15 years, acoustic metamaterials have emerged from academic curiosity to become an active field driven by scientific discoveries and diverse application potentials. This review traces the development of acoustic metamaterials from the initial findings of mass density and bulk modulus frequency dispersions in locally resonant structures to the diverse functionalities afforded by the perspective of negative constitutive parameter values, and their implications for acoustic wave behaviors. We survey the more recent developments, which include compact phase manipulation structures, superabsorption, and actively controllable metamaterials as well as the new directions on acoustic wave transport in moving fluid, elastic, and mechanical metamaterials, graphene-inspired metamaterials, and structures whose characteristics are best delineated by non-Hermitian Hamiltonians. Many of the novel acoustic metamaterial structures have transcended the original definition of metamaterials as arising from the collective manifestations of constituent resonating units, but they continue to extend wave manipulation functionalities beyond those found in nature.

/pdf/acoustic-metamaterials-from-local-resonances-to-broad-4s4297ihw6.pdf

Acoustic metamaterials: From local resonances to broad horizons.

We theoretically investigate microwave transmission through a zero-index metamaterial loaded with dielectric defects. The metamaterial is impedance matched to free space, with the permittivity and permeability tending towards zero over a given frequency range. By simply varying the radii and permittivities of the defects, total transmission or reflection of the impinging electromagnetic wave can be achieved. The proposed defect structure can offer advances in shielding or cloaking technologies without restricting the object's viewpoint. Active control of the observed exotic transmission and reflection signatures can occur by incorporating tunable refractive index materials such as liquid crystals and ${\mathrm{BaSrTiO}}_{3}$.

https://dr.ntu.edu.sg/bitstream/10220/7157/1/cuong.pdf

Total transmission and total reflection by zero index metamaterials with defects

In conventional materials, strong absorption usually requires that the material have either high loss or a large thickness-to-wavelength ratio ($d/\ensuremath{\lambda}\ensuremath{\gg}1$). We find the situation to be vastly different for bilayer structures composed of a metallic substrate and an anisotropic epsilon-near-zero (ENZ) metamaterial, where the permittivity in the direction perpendicular to its surface, ${\ensuremath{\epsilon}}_{z}$, vanishes. Remarkably, perfect absorption can occur in situations where the metamaterial is arbitrarily thin ($d/\ensuremath{\lambda}\ensuremath{\ll}1$) and arbitrarily low loss. Our numerical and analytical solutions reveal that under the conditions ${\ensuremath{\epsilon}}_{z}\ensuremath{\rightarrow}0$ and $\ensuremath{\mathfrak{I}}({\ensuremath{\epsilon}}_{z})\ensuremath{\gg}\ensuremath{\mathfrak{R}}({\ensuremath{\epsilon}}_{z})$, at perfect absorption there is a linear relationship between the thickness and the loss, which means the thickness of the absorber can be pushed to zero by reducing the material loss to zero. This counterintuitive behavior is explained in terms of coherent perfect absorption (or stimulated absorption) via critical coupling to a fast wave propagating along the ENZ layer.

Coherent perfect absorption in epsilon-near-zero metamaterials

We study triplet pairing correlations in clean ferromagnet ($F$)/superconductor ($S$) nanojunctions, via fully self-consistent solution of the Bogoliubov--de Gennes equations. We consider FSF trilayers, with $S$ being an $s$-wave superconductor, and an arbitrary angle $\ensuremath{\alpha}$ between the magnetizations of the two $F$ layers. We find that contrary to some previous expectations, triplet correlations, odd in time, are induced in both the $S$ and $F$ layers in the clean limit. We investigate their behavior as a function of time, position, and $\ensuremath{\alpha}$. The triplet amplitudes are largest at times on the order of the inverse Debye frequency, and at that time scale they are long-ranged in both $S$ and $F$. The zero temperature condensation energy is found to be lowest when the magnetizations are antiparallel.

Odd triplet pairing in clean superconductor/ferromagnet heterostructures.

We study proximity effects at ferromagnet-superconductor interfaces by self-consistent numerical solution of the Bogoliubov--de Gennes equations for the continuum, without any approximations. Our procedures allow us to study systems with long superconducting coherence lengths. We obtain results for the pair potential, the pair amplitude, and the local density of states. We use these results to extract the relevant proximity lengths. We find that the superconducting correlations in the ferromagnet exhibit a damped oscillatory behavior that is reflected in both the pair amplitude and the local density of states. The characteristic length scale of these oscillations is approximately inversely proportional to the exchange field, and is independent of the superconducting coherence length in the range studied. We find the superconducting coherence length to be nearly independent of the ferromagnetic polarization.

Proximity effects at ferromagnet-superconductor interfaces

The superconducting transition temperature ${T}_{c}$ of a ferromagnet (F)--superconductor (S)--ferromagnet trilayer depends on the mutual orientation of the magnetic moments of the F layers. This effect has been previously observed in F/S/F systems as a ${T}_{c}$ difference between parallel and antiparallel configurations of the F layers. Here we report measurements of ${T}_{c}$ in $\mathrm{CuNi}/\mathrm{Nb}/\mathrm{CuNi}$ trilayers as a function of the angle between the magnetic moments of the CuNi ferromagnets. The observed angular dependence of ${T}_{c}$ is in qualitative agreement with a F/S proximity theory that accounts for the odd triplet component of the condensate predicted to arise for noncollinear orientation of the magnetic moments of the F layers.

Klaus Halterman

Papers

Total transmission and total reflection by zero index metamaterials with defects

Coherent perfect absorption in epsilon-near-zero metamaterials

Odd triplet pairing in clean superconductor/ferromagnet heterostructures.

Proximity effects at ferromagnet-superconductor interfaces

Angular dependence of the superconducting transition temperature in ferromagnet-superconductor-ferromagnet trilayers.