利用光使电子发生扭曲,从而在奇异材料中产生不对称的图案

时间:2020-03-18 20:01 来源:seo 作者:杏鑫 点击量:

利用光使电子发生扭曲,从而在奇异材料中产生不对称的图案

偏振光法可以在层状材料中产生和测量非对称态。

Some+molecules%2c+including+most+of+the+ones+in+living+organisms%2c+have+shapes+that+can+exist+in+two+different+mirror-image+versions.+The+right-+and+left-handed+versions+can+sometimes+have+different+properties%2c+such+that+only+one+of+them+carries+out+the+molecule%26rsquo%3bs+functions.+Now%2c+a+team+of+physicists+has+found+that+a+similarly+asymmetrical+pattern+can+be+induced+and+measured+at+will+in+certain+exotic+materials%2c+using+a+special+kind+of+light+beam+to+stimulate+the+material.%0aIn+this+case%2c+the+phenomenon+of+%26ldquo%3bhandedness%2c%26rdquo%3b+known+as+chirality%2c+occurs+not+in+the+structure+of+the+molecules+themselves%2c+but+in+a+kind+of+patterning+in+the+density+of+electrons+within+the+material.+The+researchers+found+that+this+asymmetric+patterning+can+be+induced+by+shining+a+circularly+polarized+mid-infrared+light+at+an+unusual+material%2c+a+form+of+transition-metal+dichalcogenide+semimetal+called+TiSe2%2c+or+titanium+diselenide.%0aThe+new+findings%2c+which+could+open+up+new+areas+of+research+in+the+optical+control+of+quantum+materials%2c+are+described+today+in+the+journal+Nature+in+a+paper+by+MIT+postdocs+Suyang+Xu+and+Qiong+Ma%2c+professors+Nuh+Gedik+and+Pablo+Jarillo-Herrero%2c+and+15+colleagues+at+MIT+and+other+universities+in+the+U.S.%2c+China%2c+Taiwan%2c+Japan%2c+and+Singapore.%0aThe+team+found+that+while+titanium+diselenide+at+room+temperature+has+no+chirality+to+it%2c+as+its+temperature+decreases+it+reaches+a+critical+point+where+the+balance+of+right-handed+and+left-handed+electronic+configurations+gets+thrown+off+and+one+type+begins+to+dominate.+They+found+that+this+effect+could+be+controlled+and+enhanced+by+shining+circularly+polarized+mid-infrared+light+at+the+material%2c+and+that+the+handedness+of+the+light+(whether+the+polarization+rotates+clockwise+or+counterclockwise)+determines+the+chirality+of+the+resulting+patterning+of+electron+distribution.%0a%26ldquo%3bIt%26rsquo%3bs+an+unconventional+material%2c+one+that+we+don%26rsquo%3bt+fully+understand%2c%26rdquo%3b+says+Jarillo-Herrero.+The+material+naturally+structures+itself+into+%26ldquo%3bloosely+stacked+two-dimensional+layers+on+top+of+each+other%2c%26rdquo%3b+sort+of+like+a+sheaf+of+papers%2c+he+says.%0aWithin+those+layers%2c+the+distribution+of+electrons+forms+a+%26ldquo%3bcharge+density+wave+function%2c%26rdquo%3b+a+set+of+ripple-like+stripes+of+alternating+regions+where+the+electrons+are+more+densely+or+less+densely+packed.+These+stripes+can+then+form+helical+patterns%2c+like+the+structure+of+a+DNA+molecule+or+a+spiral+staircase%2c+which+twist+either+to+the+right+or+to+the+left.%0aOrdinarily%2c+the+material+would+contain+equal+amounts+of+the+right-+and+left-handed+versions+of+these+charge+density+waves%2c+and+the+effects+of+handedness+would+cancel+out+in+most+measurements.+But+under+the+influence+of+the+polarized+light%2c+Ma+says%2c+%26ldquo%3bwe+found+that+we+can+make+the+material+mostly+prefer+one+of+these+chiralities.+And+then+we+can+probe+its+chirality+using+another+light+beam.%26rdquo%3b+It%26rsquo%3bs+similar+to+the+way+a+magnetic+field+can+induce+a+magnetic+orientation+in+a+metal+where+ordinarily+its+molecules+are+randomly+oriented+and+thus+have+no+net+magnetic+effect.%0aBut+inducing+such+an+effect+in+the+chirality+with+light+within+a+solid+material+is+something+%26ldquo%3bnobody+ever+did+before%2c%26rdquo%3b+Gedik+explains.%26nbsp%3b%0aAfter+inducing+the+particular+directionality+using+the+circularly+polarized+light%2c+%26ldquo%3bwe+can+detect+what+kind+of+chirality+there+is+in+the+material+from+the+direction+of+the+optically+generated+electric+current%2c%26rdquo%3b+Xu+adds.+Then%2c+that+direction+can+be+switched+to+the+other+orientation+if+an+oppositely+polarized+light+source+shines+on+the+material.%0aGedik+says+that+although+some+previous+experiments+had+suggested+that+such+chiral+phases+were+possible+in+this+material%2c+%26ldquo%3bthere+were+conflicting+experiments%2c%26rdquo%3b+so+it+had+been+unclear+until+now+whether+the+effect+was+real.+Though+it%26rsquo%3bs+too+early+in+this+work+to+predict+what+practical+applications+such+a+system+might+have%2c+the+ability+to+control+electronic+behavior+of+a+material+with+just+a+light+beam%2c+he+says%2c+could+have+significant+potential.%0aWhile+this+study+was+carried+out+with+one+specific+material%2c+the+researchers+say+the+same+principles+may+work+with+other+materials+as+well.+The+material+they+used%2c+titanium+diselenide%2c+is+widely+studied+for+potential+uses+in+quantum+devices%2c+and+further+research+on+it+may+also+offer+insights+into+the+behavior+of+superconducting+materials.%0aGedik+says+that+this+way+of+inducing+changes+in+the+electronic+state+of+the+material+is+a+new+tool+that+could+potentially+be+applied+more+broadly.+%26ldquo%3bThis+interaction+with+light+is+a+phenomenon+which+will+be+very+useful+in+other+materials+as+well%2c+not+just+chiral+material%2c+but+I+suspect+in+affecting+other+kinds+of+orders+as+well%2c%26rdquo%3b+he+says.%0aAnd%2c+while+chirality+is+well-known+and+widespread+in+biological+molecules+and+in+some+magnetic+phenomena%2c+%26ldquo%3bthis+is+the+first+time+we%26rsquo%3bve+shown+that+this+is+happening+in+the+electronic+properties+of+a+solid%2c%26rdquo%3b+Jarillo-Herrero+says.%0a%26ldquo%3bThe+authors+found+two+new+things%2c%26rdquo%3b+says+Jasper+van+Wezel%2c+a+professor+at+the+University+of+Amsterdam%2c+who+was+not+part+of+the+research+team.+He+said+the+new+findings+are+%26ldquo%3ba+new+way+of+testing+whether+or+not+a+material+is+chiral%2c+and+a+way+of+enhancing+the+overall+chirality+in+a+big+piece+of+material.+Both+breakthroughs+are+significant.+The+first+as+an+addition+to+the+experimental+toolbox+of+materials+scientists%2c+the+second+as+a+way+of+engineering+materials+with+desirable+properties+in+terms+of+their+interaction+with+light.%26rdquo%3b%0aReference%3a+%26ldquo%3bSpontaneous+gyrotropic+electronic+order+in+a+transition-metal+dichalcogenide%26rdquo%3b+by+Su-Yang+Xu%2c+Qiong+Ma%2c+Yang+Gao%2c+Anshul+Kogar%2c+Alfred+Zong%2c+Andr%26eacute%3bs+M.+Mier+Valpia%2c+Thao+H.+Dinh%2c+Shin-Ming+Huang%2c+Bahadur+Singh%2c+Chuang-Han+Hsu%2c+Tay-Rong+Chang%2c+Jacob+P.+C.+Ruff%2c+Kenji+Watanabe%2c+Takashi+Taniguchi%2c+Hsin+Lin%2c+Goran+Karapetrov%2c+Di+Xiao%2c+Pablo+Jarillo-Herrero+and+Nuh+Gedik%2c+26+February+2020%2c+Nature.%0aDOI%3a+10.1038%2fs41586-020-2011-8%0aThe+research+was+supported+by+the+U.S.+Department+of+Energy%2c+the+Gordon+and+Betty+Moore+Foundation%2c+and+the+National+Science+Foundation.+The+team+included+researchers+at+MIT%2c+Carnegie+Mellon+University%2c+Drexel+University%3b+National+Sun+Yat-Sen+University%2c+National+Cheng+Kung+University%2c+and+Academia+Sinica+in+Taiwan%3b+Shenzen+University+in+China%2c+Northeastern+University%2c+the+National+University+of+Singapore%2c+Cornell+University%2c+and+the+National+Institute+for+Materials+Science+in+Japan.

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