546 50 & 100 YEARS AGO NEWS &VIEWS assistance which can be assistance whichcanbe A strikinginstance ofthe 100 YEARSAGO From show thisfraction intheirblood. who served ascontrols didnot twenty othernormalnew-borns were severely malformed, whereas of two full-termnew-borns who haemoglobin fraction intheblood able todiscover theembryonic … [W]ewere, for thefirst time, in thebloodofsmallembryos in thechromatographic column) embryonic, fraction (thelowest new-borns, butalsothethird, in thecord bloodoffull-term fractions known tobepresent not onlythetwo haemoglobin Thus, we were abletoseparate of afour montholdembryo ... fractions from thehaemolysate to separate thethree distinct modifications, we were able and Prins, withsomeminor procedure describedby Huisman the column chromatographic of intra-uterine life ...By using of foetuses uptofive months reported tobepresent intheblood embryonic haemoglobinwas the existence ofathird normal, In previous communications, 50 YEARSAGO were received by theliners for helpsentout…The messages at once hadwireless messages bridge atthetimeofaccident, and thecaptain,whowas onthe wireless telegraphy installation, The Ambrose lightship, New York. a.m.,175 at 5.30 mileseastofthe collision occurred inadensefog early morningofJanuary23.The of thesteamship afforded inthecaseofcollision and dangers ofnavigation was in overcoming thedifficulties rendered by wireless telegraphy the White Starliner From calamity. the meansofaverting aterrible Wireless telegraphy hasthusbeen and longitudeofthecollision ... Republic a wireless message tothe the rescue were abletotransmit The steamshipsproceeding to Lorraine Republic Nature Nature asking for the latitude askingfor the latitude , andthe 31January1959. 28January1909. is equipped with a isequippedwitha

Republic Florida Lucania with the withthe in the inthe Baltic ...... , Jan Zaanen The pnictidecode CONDENSED-MATTER PHYSICS superconducting state. superconducting pairs,bind condense which inCooper into a quasielectrons,between the causing to these to leads aweak attractivemetal) interaction phonons (atomic lattice vibrations inthe lowat temperatures very exchange the of ‘quasielectrons’. According theory, to BCS liquid’ behaves like agasof non-interacting strongly interact, and resulting the ‘Fermi magic causes electrons the to ‘forget’ that they tively, renders simple. things very Aquantum of quantum weirdness, counter-intui- which, despite grip inthe being their of influence the such asaluminium isremarkably featureless, electronin these worlds? moreeven mysterious over years the cause of superconductivity their hasbecome form quantum surprisingly rich worlds. But the successful, showing that electrons can insolids ensuing research spectacularly hasbeen effort subsequently found. been In some ways, the tion temperatures as150kelvin ashigh have ductivity cuprates inthe in1986,and transi- changedthis of supercon- with discovery the to explainseemed phenomenon the but infull, of superconductivitytheory proposed in1957 TheBardeen–Cooper–Schriefferscale. (BCS) that shows quantum on amacroscopic effects is afamous example of such ‘quantum matter’ superconducts that matter electron The ness? particles compare. superconductors elucidatethat further how two the families of ofobservations two features pnictides inthe 565 and Zabolotnyy In issue, two this studies (Yuan tides share main the properties of cuprates. compellingalso reasons to that believe pnic- pounds containing copper oxide). There are high- deciphering 22-year-old the behind mystery that instrumental pnictides the willbe in of excitement the it hasshifted: isnow hoped stalled above nosuperconductivity which isattained), transition temperature, petuating frenzy? Thequest —this for ahigher pnictides. Butthese what caused —and isper- an army of physicists and chemists to study made from iron-based compounds prompted discovery About ayear ago, announcement the of the of superconductivity observed athightemperatures. pnictides, could actasaRosetta stoneindecoding thetwo-decade mystery Hopes are thattheemergent family ofiron-based superconductors, the superconducting) state of metals ordinary © 2009MacmillanP But incuprates, conspires chemistry questionThe key is:how much isgoing on What happens zillions when of quantum T 2 c at ameagre 56kelvin, and focus the superconductivity in cuprates in superconductivity

form 1 of a new family of superconductors superconductors of family new a of

a macroscopic quantum whole- ublisher et al. et s Limit 5 T on page 569)report

The normal (non- c (the temperature (the ed. Allrightsr et al. et 2 4 . on page 3 (com- eserv ed

ity: the best superconducting best the cupratesity: are found Fermi-liquid states are badfor superconductiv- overtakes busythe highway —and Fermi-liquid the state with force full —causing the electrons to forget levels of doping quantum the weirdness hits tion of stop-and-go isobserved traffic and at low levels of doping aquantum incarna- ing can clear way the on ‘quantum the highway’, cuprates to insulating. become Chemicaldop- ‘traffic’ jams completely, causing undoped motions to such an extent that electron the quantum motions, but can other’s hindereach highway. Theelectrons are subject to perpetual like aquantized form of on dense traffic abusy Metaphorically, the cuprate electron world is against might the of quantum this simplicity. to look inwrong directions. ared herring allalong,been causing theorists superconductivity, two-dimensionality has systemsif both doshare of secret the high- three-dimensional. Theimplication is that, superconductivity materials inthese can be structure layeredthe of pnictides, the crystal conclusion despite that changes view: this on ademanding experiment with asimple temperatures.high But Yuan prerequisitenecessary for superconductivity at were two-dimensional, and that wasa this such quantum-highway asthe behaviour, that superconducting electronic properties, oxide planes. Thisledresearchers to believe electrons can move freely only copper- in the studies.in their Yuan high- systems one out can find what really matters in different. isthat Thehope by comparing both physics, inother regards can quite be they share of gross quantum-highway the aspects But even though pnictides and cuprates might traffic is on the verge of coming to astandstill magnetism —astrong signthat electron the insulate, doshow they amuscular antiferro- over, although pnictides undoped donot quite ditions of to those copper and oxygen pnictidethe layers create similar jamming con- and iron the and arsenic atoms that constitute much to explained high too be theory, by BCS iour. transition Theobserved temperatures are might well share ‘quantum this highway’ behav- electronthe to starts gather traffic speed at intermediate dopings, at point the at which But quantized the both stop-and-go and the In cuprates, the one invariably that finds the isthatThe belief electrons the inpnictides T et al. et c superconductivity. what Thisisexactly 4 7 and Zabolotnyy . NATURE | Vol 457 et al. et et al. et | 29 January2009 5 try to address try 4 now report 6 . At high 2 . More- 3 . T 8 c .

NATURE|Vol 457|29 January 2009 NEWS & VIEWS

To appreciate the results of Zabolotnyy and 1. Kamihara, Y., Watanabe, T., Hirano, M. & Hosono, H. 7. Cooper, R. A. et al. Science doi:10.1126/science.1165015 colleagues5, one has to dig a bit deeper into the J. Am. Chem. Soc. 130, 3296–3297 (2008). (2008). weird side of the quantum world. The quan- 2. Grant, P. M. Nature 453, 1000–1001 (2008). 8. Kivelson, S. A. & Yao, H. Nature Mater. 7, 927–928 3. Nature Phys. 2, 133 (2006). (2008). tity that matters most in the Fermi liquid is the 4. Yuan, H. Q. et al. Nature 457, 565–568 (2009). 9. Damascelli, A., Hussain, Z. & Shen, Z.-X. Rev. Mod. Phys. Fermi surface — a boundary in the abstract 5. Zabolotnyy, V. B. et al. Nature 457, 569–572 (2009). 75, 473–541 (2003). space of quasielectron quantum numbers that 6. Zaanen, J. Science 315, 1372–1373 (2007). 10. Zaanen, J. Nature 448, 1000–1001 (2007). at absolute zero temperature separates the unoccupied states from the occupied ones. Photoemission experiments, which meas- ure the energy of electrons emitted from the PLANT GENOMICS metals when these are subjected to electro– magnetic radiation, show sharp Fermi surfaces in cuprates in the Fermi-liquid regime at high Sorghum in sequence levels of doping. At low levels of doping, where Takuji Sasaki and Baltazar A. Antonio the electrons are in the stop-and-go regime and so are far from forming quasielectrons, these The drought tolerance of sorghum is just one of the features that make measurements show that there are still fuzzy it a valuable crop plant. There is much for agronomists to learn from the remnants of these Fermi surfaces9. Although not at all understood, these remnants can be complete genome sequence of this type of grass. taken as a signal that the quantum weirdness is already in action in an attempt to simplify It is almost four years since the genome and Solanaceae (tomato and potato) families, the electron traffic flow in the direction of the sequence of the rice plant, Oryza sativa, was will be completed in the next few years. Fermi-liquid state. completed1. Rice is the world’s most important Worldwide annual production of sorghum Moreover, the observed, simple rounded- crop, and the availability of an accurate, com- is about 60 million tonnes, less than that of square shape of the single cuprate Fermi surface plete, map-based sequence of a cereal genome the other major cereal crops. It is nonetheless seems to be in accord with the predictions of the prompted ground-breaking studies of the a staple for both humans and livestock, and naive LDA (local density approximation) elec- genetic underpinning of valuable agricultural is also a potential source of biofuel. Sorghum tronic-band-structure theory of metals, which traits, both in rice itself and in other cereals. originates from tropical Africa, which makes completely ignores the quantum highways. But The genomes of more than ten plant species it highly tolerant to drought and well adapted the Fermi surfaces in pnictides are more com- have since been completely sequenced, to to arid countries in northeast Africa, where plex, and there is much more to investigate. which can now be added that of a second it is mainly grown, as well as to dry areas in According to the LDA, it is a semimetal-like cereal species, Sorghum bicolor, as reported by the United States and India. Most notably, affair of circle-shaped pockets of electrons Paterson et al. on page 551 of this issue2. This sorghum provides an example of a plant that and electron holes. Using high-resolution constitutes another milestone in plant biol- carries out the C4 type of photosynthesis. This photoemission data, Zabolotnyy et al.5 man- ogy, but it won’t, of course, mean that the photosynthetic pathway, found in many plants age to observe the pockets, but instead of the sequencing machines will now lie idle: among growing in conditions of high temperature predicted circles, these look like design wheels commercially important crop plants, the and light intensity, and low water availability, and aircraft propellers. Does this scrambling genomes of other members of the grass family is considered to be more efficient in fixing car- of the LDA Fermi surfaces in the pnictides tell Poaceae (which includes maize, wheat and bon dioxide than the C3 route that is found, us about a close victory of quantum weirdness barley, as well as rice and sorghum), in addition for instance, in rice and wheat. Research into over electron jamming4, or is there an alterna- to representatives of the Fabaceae (soybean) the genomic basis of sorghum’s adaptation tive, more conventional explanation? It is too early to tell. At present, it is not at all certain whether pnictides code for cuprates or just for themselves. But there is yet another excellent reason to believe in the ‘pnictide code’. Temperature is the mortal enemy of quantum physics. Therefore, one anticipates that when

quantum weirdness is in a tight battle with the QUIRK/PHOTOLIBRARY.COM P. quantum highway, the influence of tempera- ture might be disproportionate. This is such a difficult problem that, according to some, the mathematics of string theory is needed to understand it10. But we already know what this means empirically: at temperatures well above

Tc one finds cuprates in a ‘bad metal’ state, in which the electron matter shows extreme forms of dissipation in stark contrast to the very small friction that characterizes the Fermi-liquid state7. There are indications that the pnictide metals can be as ‘bad’ as the cuprates, and I am impatiently waiting for a concerted effort that will nail this down. ■ Jan Zaanen is at the Instituut Lorentz for Theoretical Physics, Leiden University, PO Box In the field — sorghum 9504, 2300 RA Leiden, the Netherlands. under cultivation. e-mail: [email protected]

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