| Original language | English (US) |
|---|---|
| Article number | 8654239 |
| Pages (from-to) | 159-160 |
| Number of pages | 2 |
| Journal | IEEE Transactions on Energy Conversion |
| Volume | 34 |
| Issue number | 1 |
| DOIs | |
| State | Published - Mar 2019 |
Bibliographical note
Funding Information:ductors. Providedt hat the crystal is homogeneouwsi th re-spectt o the occurencoef superconductiviatnyd the effect of antiferromagneotircd eringis to elevatet he resistivity,t he incompleteneossf superconductivictayn be ascribedt o the proximityo f the sheet resistance to its criticalv aluef or superconductor-insulatrtaonr si-tion. In disordere2dD superconductoar st ransitionto insulatinsgt ateh asb eeno bservedfo r granulaor r amorphous films when the resistancep er unit area (sheet resistancee)x ceedsth e critical value of ,~h/4e 2 = 6.5 k~ \[13\S].u chb ehaviorw as also observedfo r the oxide superconductboyr reducingo xygenc ontentto increase the extento f disorder\[ 14,15\]. Recentlyt his superconductor-insulattroarn sitionis remarkeda s a universapl ropertyo f 2D superconductor basedo n the dualityo f the Cooper pairs and vor- tices\[16\I]n. one caset he Cooperp airsc ondensien to an uniqueq uantumst atew ith localizedv ortex( super-conductinsgt ate)w hile in the otherc aset he vortices condensae nd the Cooperp airslocalize. In the latter caset hes upercurrenist suppresseadn dthe insulating behaviore merges.T heree xistsa direct competition betweenth ec ondensatioonf the Cooperp airsa ndthe vorticesa t a crossoverr egion. Simple consideration showst hatthis regionl ocatesa t the sheetr esistance of .,~h /4e ~. Assuming that the electronicp ropertieso f the presentc ompoundasr e dominatemd ainlyb y the 2D BEDT-TTF moleculela yers,w e estimatedth e sheet resistanceosf the presenst erieso f compoundasr ound the temperaturreeg iono f interestA. lthought heabso-lute valueso f the sheetr esistancaer ed eterminewdi th someu ncertaintdyu eto the size and shapeli mitations of grownc rystalst,h ee stimatevda luesf or the K-, Rb-and Tl-salts are 4-t-2k ~, 16-4-5k ~ and 7-4-3k ~, re-spectivelyI.n Fig.l, Fig.3(a)a ndF ig.5(a)t hev alueo f sheetr esistanceasr ei ndicatefdo r eachm easuremeantt the right axis. Taking into accountt he experimental errora ndthe influencoe f the interlayecro uplingo n the actuatl hresholdva lue,w e concludeth att heestimated valuesa rec loset o the criticasl heetr esistancaen dt hese systema rec onsideretdo be closet o thei nsulatinsgt ate. By applyingm agnetifci eld this superconductoinr-s u-latort ransitionis enhanced\[16In\] .F ig. 3(a), the resistivity increasein high magnetifcie ld above1 T seems to be acceleratebde low 0.5 K. This behavioirs remi-niscento f the magnetifci eld induceds uperconductor-insulatort ransition\[14,15O\]n. the other hand there is no antiferromagnetic-tlirkaen sitionin NH4-salta nd the resistivityis kept low aroundt hesuperconducting transitionT. hus,the sharps uperconductitnrga nsition is observed. We note that the superconductivity-lrikeesi stivity decreasree portehde reh asn otb eenf oundin someo ther sampleso f K-salt\[17,18\T].h is may be understooidn termso f the variationo f the sheetr esistancien the vicinityo f its criticalv alue.We also noticet he report by Mori et al. that somec rystalso f NH4-saltd id not shows uperconductivditoyw nt o 0.6 K\[6,9\T].h e criterion of the occurencoef superconductivwitays related to its residuarle sistancrea tio.If ther esiduarle sistance ratio exceeded10 0 it showeds uperconductivitTyh. is criterionis understoobdy the sheetr esistancper oblem: to observet he superconductivitthye sheetr esistance mustn ot exceedth e criticalv alue. In summaryth, es uperconductivity-rliekseis tivitdye - creasesa re observedin c~-(BEDT-TTF)~MHg(SCN)4 (M=K, Rb, Tl) below0 .3 K, 0.5 K, 0.1 K, respectively. We presenta model ascribingt he incompleteneosfs superconductivtitoy the proximityo f the sheetr esis-tancet o its criticalv aluef or superconductor-insulator transitionc,a usedb y the elevatedre sistancdeu eto an antiferromagnetic-slipkien ordering. M.V.K. acknowledgetsh e supportf rom the Japan Societyf or the Promotiono f Science. This work was supportedin part by a Grant for InternationaJol int Researchfr omthe New Energya nd ResearchD evelop
