May 2012 Volume 11, Issue 5

Insight

Editorial

Open access p353
doi:10.1038/nmat3328
Open-access journals are publishing at a pace that is not much faster than some recently launched subscription-based journals. The swiftest and surest route to full open-access publishing is then for funders, institutions and publishers to agree on the conditions for self-archiving in publicly accessible repositories.
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Commentary

Nanoferronics is a winning combination pp354 - 357
Manuel Bibes
doi:10.1038/nmat3318
Progress in controlling different ferroic orders such as ferromagnetism and ferroelectricity on the nanoscale could offer unprecedented possibilities for electronic applications.
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Research Highlights

Beaten to action | Honey, I shrunk the mask | Close to the edge | Optimized for the clinic | Picking holes

News and Views

Editorial

Spintronics p367
Fabio Pulizzi
doi:10.1038/nmat3327
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Commentary

New moves of the spintronics tango pp368 - 371
Jairo Sinova and Igor Žutić
doi:10.1038/nmat3304
The ability of spintronics to re-energize itself in directions that germinate new subfields has made it one of the most fertile grounds for basic research aimed at future applications. A brief overview of the connections between five emerging subfields suggests exciting things to come.
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Reviews

Current-induced torques in magnetic materials pp372 - 381
Arne Brataas, Andrew D. Kent and Hideo Ohno
doi:10.1038/nmat3311
Spin-transfer torque is the rotation that a spin-polarized current induces on the magnetization of the solid it flows through. The way in which currents generate torques in a wide variety of magnetic materials and structures is discussed in this Review, as well as recent state-of-the-art demonstrations of current-induced-torque devices that show great promise for enhancing the functionality of semiconductor devices.
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Spin Hall effect devices pp382 - 390
Tomas Jungwirth, Jörg Wunderlich and Kamil Olejník
doi:10.1038/nmat3279
The spin Hall effect is a relativistic spin–orbit coupling phenomenon, which can be used to electrically generate or detect spin currents in non-magnetic systems. This Review discusses the experiments that have established the basic physical understanding of the effect, and the role that several of the spin Hall devices have had in the demonstration of spintronic functionalities and physical phenomena.
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Spin caloritronics pp391 - 399
Gerrit E. W. Bauer, Eiji Saitoh and Bart J. van Wees
doi:10.1038/nmat3301
Spin caloritronics focuses on the interaction of electron spins with heat currents. This Review describes newly discovered physical effects that have re-invigorated the field by stimulating further research into understanding the fundamentals of spin–phonon interactions, and providing new avenues to explore to improve current thermoelectric technology.
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Silicon spintronics pp400 - 408
Ron Jansen
doi:10.1038/nmat3293
Control of the electron spin as well as its charge is predicted to lead to efficient electronic devices, with potentially new functionalities. Injecting and manipulating spin-polarized carriers in silicon is a natural step towards integrating spintronics with current technology. This Review describes the first encouraging results as well as the open questions and challenges that still remain.
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Progress Article

Spintronics and pseudospintronics in graphene and topological insulators pp409 - 416
Dmytro Pesin and Allan H. MacDonald
doi:10.1038/nmat3305
Graphene and topological insulator two-dimensional electron systems are described by massless Dirac equations. Although the two systems have similar Hamiltonians, they are polar opposites in terms of spin-orbit coupling strength. The status of efforts to achieve long spin-relaxation times in weakly spin–orbit-coupled graphene, and large current-induced spin-polarizations in strongly spin–orbit-coupled topological insulator surface states are reviewed in this Progress Article.
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Letters

Josephson supercurrent through a topological insulator surface state pp417 - 421
M. Veldhorst, M. Snelder, M. Hoek, T. Gang, V. K. Guduru, X. L. Wang, U. Zeitler, W. G. van der Wiel, A. A. Golubov, H. Hilgenkamp and A. Brinkman
doi:10.1038/nmat3255
The observation of a superconductive current flowing through a topological insulator is considered the first step towards the observation of the elusive Majorana fermions. This is now achieved in a superconductor/topological insulator/superconductor junction in which direct evidence of Josephson supercurrents is reported.
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Copper ion liquid-like thermoelectrics pp422 - 425
Huili Liu, Xun Shi, Fangfang Xu, Linlin Zhang, Wenqing Zhang, Lidong Chen, Qiang Li, Ctirad Uher, Tristan Day and G. Jeffrey Snyder
doi:10.1038/nmat3273
A common route to obtain efficient thermoelectrics is to optimize the ratio between electrical and thermal conductivity. Typically, materials with a complex, glass-like phonon structure and therefore a very low thermal conductivity are studied. Now, a route showing that solid ions in a liquid-like state can have a low enough thermal conductivity to compete with the best existing thermoelectrics is proposed.
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Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves pp426 - 431
Shulin Sun, Qiong He, Shiyi Xiao, Qin Xu, Xin Li and Lei Zhou
doi:10.1038/nmat3292
Electromagnetic waves propagating on the surface of materials are used in a variety of applications such as on-chip photonics. The demonstration now of a nearly 100% efficient coupling of these surface waves to freely propagating waves promises to improve photonic applications such as surface–plasmon couplers, antireflection coatings and many more.
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A super-oscillatory lens optical microscope for subwavelength imaging pp432 - 435
Edward T. F. Rogers, Jari Lindberg, Tapashree Roy, Salvatore Savo, John E. Chad, Mark R. Dennis and Nikolay I. Zheludev
doi:10.1038/nmat3280
The maximum imaging resolution in classical optics is limited to approximately the wavelength of light used, and subwavelength resolution can only be achieved by advanced imaging schemes. The appeal of the super-oscillatory lens optical microscope described here is that it enables subwavelength imaging with, in principle, unlimited resolution using a modified conventional microscope.
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Articles

Liquid–liquid transition without macroscopic phase separation in a water–glycerol mixture pp436 - 443
Ken-ichiro Murata and Hajime Tanaka
doi:10.1038/nmat3271
The plausible existence of a liquid–liquid transition (LLT) pre-empted by crystallization in supercooled water has long been debated. So far, indications of such a ‘hidden’ LLT have been found in nanoconfined water and in the amorphous polymorphism of ice. Now, the finding of an isocompositional LLT in a water–glycerol mixture where glycerol prevents water crystallization suggests a new link to an elusive LLT in pure water.
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See also: News and Views by Angell

Controlling the Curie temperature in (Ga,Mn)As through location of the Fermi level within the impurity band pp444 - 449
M. Dobrowolska, K. Tivakornsasithorn, X. Liu, J. K. Furdyna, M. Berciu, K. M. Yu and W. Walukiewicz
doi:10.1038/nmat3250
Although (Ga,Mn)As is considered the model ferromagnetic semiconductor, the electronic structure of the charges — holes in this case — and its connection with the Curie temperature (T_C) are still unclear. Experiments now provide a direct link between T_C and the existence of an impurity band for the holes. Clarifying this issue is essential to designing other materials with potentially higher T_C.
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See also: News and Views by Samarth

Infrared metamaterial phase holograms pp450 - 454
Stéphane Larouche, Yu-Ju Tsai, Talmage Tyler, Nan M. Jokerst and David R. Smith
doi:10.1038/nmat3278
Metamaterials have enabled many different photonic technologies. Now, the realization of holographic information storage promises new types of applications, in particular when combined with other metamaterials functionality.
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Sparsity-based single-shot subwavelength coherent diffractive imaging pp455 - 459
A. Szameit, Y. Shechtman, E. Osherovich, E. Bullkich, P. Sidorenko, H. Dana, S. Steiner, E. B. Kley, S. Gazit, T. Cohen-Hyams, S. Shoham, M. Zibulevsky, I. Yavneh, Y. C. Eldar, O. Cohen and M. Segev
doi:10.1038/nmat3289
Coherent diffractive imaging is a powerful numerical technique that can reconstruct and enhance images. The demonstration of this technique with subwavelength resolution now exhibits the possibility of new applications such as single-shot imaging of ultrafast events with ultrahigh resolution.
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A silica sol–gel design strategy for nanostructured metallic materials pp460 - 467
Scott C. Warren, Matthew R. Perkins, Ashley M. Adams, Marleen Kamperman, Andrew A. Burns, Hitesh Arora, Erik Herz, Teeraporn Suteewong, Hiroaki Sai, Zihui Li, Jörg Werner, Juho Song, Ulrike Werner-Zwanziger, Josef W. Zwanziger, Michael Grätzel, Francis J. DiSalvo and Ulrich Wiesner
doi:10.1038/nmat3274
Although materials used in electrochemical devices for energy applications would benefit from the precise structural control that can be achieved by using silica sol–gel chemistry, such synthetic approaches typically result in insulating porous materials. Now, a simple approach based on a multifunctional sol–gel precursor allows the synthesis of porous nanocomposites with metallic percolation networks exhibiting high electrical conductivity.
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Polyvalent choline phosphate as a universal biomembrane adhesive pp468 - 476
Xifei Yu, Zonghua Liu, Johan Janzen, Irina Chafeeva, Sonja Horte, Wei Chen, Rajesh K. Kainthan, Jayachandran N. Kizhakkedathu and Donald E. Brooks
doi:10.1038/nmat3272
The headgroup of phospholipids in eukaryotic cell membranes contains phosphatidyl choline (PC). Now, branched polyglycerols decorated with the 'PC-inverse' choline phosphate (CP) are shown to behave as 'universal' biomembrane adhesives, binding electrostatically to cell membranes and to PC-containing liposomes. Binding can be reversed by exposure to PC-containing polymers. These adhesives may find use as tissue sealants and as drug-delivery vehicles.
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See also: News and Views by Frey