▁thermal ▁conduct ivity ▁at ▁low ▁temper atures , ▁which ▁is ▁instead ▁domin ated ▁by ▁ph on ons . ▁The ▁decrease ▁in ▁electron ▁concentration ▁reduced ▁the ▁rate ▁of ▁electron - phon on ▁scatter ing . ▁ ▁Some ▁research ▁claims ▁that ▁it ▁may ▁be ▁a ▁topological ▁ins ulator . ▁Other ▁research ers ▁found ▁no ▁evidence ▁of ▁topological ▁surface ▁states . ▁ ▁The ▁increasing ▁elect rical ▁resistance ▁with ▁a ▁reduction ▁in ▁temperature ▁indicates ▁that ▁the ▁material ▁behav es ▁as ▁an ▁ins ulator ; ▁however , ▁recent ▁measurements ▁reve al ▁a ▁F erm i ▁surface ▁( an ▁abstract ▁boundary ▁of ▁electrons ▁in ▁momentum ▁space ) ▁characteristic ▁of ▁a ▁good ▁metal , ▁indicating ▁a ▁more ▁ex otic ▁dual ▁metal - ins ulating ▁ground ▁state . ▁The ▁elect rical ▁resist ivity ▁at ▁temper atures ▁below ▁ 4 K ▁displays ▁a ▁distinct ▁plate au , ▁which ▁is ▁thought ▁to ▁be ▁the ▁co ex istence ▁of ▁an ▁ins ulating ▁state ▁( bul k ) ▁and ▁a ▁conduct ing ▁state ▁( sur face ). ▁ ▁At ▁temper atures ▁approaching ▁absolute ▁zero , ▁the ▁quantum ▁oscill ations ▁of ▁the ▁material ▁grow ▁as ▁the ▁temperature ▁decl ines , ▁a ▁behavior ▁that ▁contradict s ▁both ▁the ▁F erm i ▁analysis ▁and ▁the ▁rules ▁that ▁govern ▁conventional ▁met als . ▁While ▁it ▁has ▁been ▁argued ▁that ▁quantum ▁oscill ations ▁on ▁samples ▁grown ▁from ▁al umin ium ▁flux ▁may ▁arise ▁from ▁al umin um ▁inclus ions , ▁such ▁an ▁explanation ▁is ▁ex cluded ▁for ▁samples ▁grown ▁by ▁the ▁image ▁furn ace ▁method ▁rather ▁than ▁by ▁the ▁flux