SODIUM DA HYDROGEN, SUPERCONDUCTOR A KAN TAKARDA

Superconductor yana ɗaukar wutar lantarki ba tare da tsayayya ko kaɗan ba, ƙasa da wani zafi mai muhimmanci (critical temperature), Tc. Ga abubuwa masu yawan hydrogen, lambobin tarihi suna da ban mamaki: H₃S da LaH₁₀ suna zama superconductors sama da kelvin 200. Amma suna yin hakan ne kawai idan aka matse su a kusan megabar ɗaya, kusan ninki miliyan na matsin yanayi. Ƙalubalen shi ne samun irin wannan aiki a ƙaramin matsi.

Hydrogen yana taimakawa saboda yana da sauƙi: ƙwayoyinsa suna girgiza a mitoci masu girma sosai, kuma waɗannan girgizar na iya haɗa electrons zuwa nau’i-nau’in da ke ɗaukar wutar superconductivity. A cikin yawancin mafi kyawun hydrides, hydrogen ba ya ƙara samar da ƙwayoyin H₂. Sinadaran da hydrogen ke zama biyu-biyu a cikinsu an daɗe ana ɗaukarsu marasa kyau, saboda ƙarfin haɗin da ke cikin kowane nau’i yana janye electrons ɗinsa daga aiki.

Sinadarin da aka samu ta hanyar bincike

Tianran Chen, na Jami’ar Tennessee, da Taner Yildirim, na Cibiyar Binciken Neutron ta NIST, sun riga sun nuna sodium hexahydride, NaH6, a cikin binciken kwamfuta na tsari fiye da 100,000 masu yawan hydrogen. Wani bincike mai zaman kansa shi ma ya yi hasashen Tc mai girma gare shi. A nan sun yi nazarinsa sosai — gaba ɗaya ta hanyar lissafi:

algoridim na juyin halitta (evolutionary algorithm) don nemo tsarin lu’ulu’u mafi dacewa a kowane matsi;
lissafin injiniyancin quantum na electrons, girgizar ƙwayoyi da haɗinsu, wanda ke ba da Tc ta hanyar wata dabara ta yau da kullum;
molecular dynamics a kelvin 300, don duba cewa tsarin suna riƙe da juna lokacin da ƙwayoyi ke girgiza.

Ba a ƙera ko auna wani samfuri ba.

Lu’ulu’u biyu, halaye biyu

Lissafin sun bayyana yanayi mai cunkoso: a gigapascal 50, tsari 15 daban-daban suna daidaitacce, mafi yawansu ’yan’uwan kusa ne na manyan siffofi biyu. A duka biyun, hydrogen yana zaune cikin nau’i-nau’i da aka ɗan miƙa.

Siffar cube an yi hasashen za ta zama superconductor har zuwa kelvin 230 a gigapascal 50 — kusan −43 °C a rabin megabar — kuma har yanzu kelvin 215 a gigapascal 200.
Siffar rhombohedral tana zama daidaitacciya har ƙasa zuwa gigapascal 10, inda Tc da aka yi hasashe kelvin 34 ne. Idan aka matse ta, Tc yana hawa da sauri: kelvin 99 a gigapascal 50, 157 a 90, kusan kelvin 1.6 a kowane gigapascal.

Akwai wata matsala da marubutan suka bayyana. A gigapascal 50, siffar cube ta kelvin 230 ba ita ce tsarin da ya fi daidaito ba: tana ɗan sama da makamashin da ake buƙata don ta farfashe zuwa sodium hydride mai sauƙi da hydrogen. Tana zama daidaitacciya daga wannan farfashewa ne kawai sama da gigapascal 60, kuma siffofin biyu suna musanya wuri kusa da gigapascal 114. A molecular dynamics a kelvin 300, siffar cube tana zama cikakkiya — a tsawon wasu ’yan kashi ɗaya cikin tiriliyan na daƙiƙa.

Hydrogen biyu-biyu da ke taimakawa

Abin da ya fi ban mamaki shi ne tsarin aikin. Nau’i-nau’in ba sa hana superconductivity. Kowace girgiza da ke haɗuwa sosai da electrons ita ce wadda za ta bayyana a Raman spectroscopy, wata dabarar dakin gwaje-gwaje ta gama-gari; sauran kusan ba sa haɗuwa ko kaɗan. Da suka duba wasu hydrides 102 a gigapascal 200, marubutan sun sami tsari iri ɗaya: girgizar da ke aiki a Raman suna haɗuwa kusan sau 40 fiye da sauran a matsakaici.

A cikin siffar rhombohedral, matsi yana karkatar da nau’i-nau’in hydrogen, daga digiri 4 a gigapascal 10 zuwa digiri 21 a 90. Yayin da suke karkata, manyan girgizar suna ƙara haɗuwa — tare da hawan Tc, yayin da tsarin electrons kusan ba ya canzawa. Wani samfurin lissafi mai sauƙi ya dace da wannan yanayin, ko da yake marubutan sun jaddada cewa fassara ce, ba hujja ba.

Daga allon kwamfuta zuwa dakin gwaje-gwaje

Waɗannan hasashe ne. Zafin da aka lissafa ya dogara ga wani ma’auni na yau da kullum amma mai daidaitawa, kuma gigapascal 50 har yanzu kusan matsin yanayi rabin miliyan ne. Idan aka tabbatar, NaH6 zai nuna cewa fuskantar nau’i-nau’in hydrogen sabuwar hanya ce ta tsara superconductors na hydride. Kalma ta gaba ta masu gwaji ce.