National;
LaboratoG;
for;
Condensed;
Matter;
Physics,;
Institute;
of;
Physics,;
Chinese;
Academy;
of;
Sciences,;
Beijing;
100190,;
China;
of;
Micro-;
and;
Nanosciences,;
Aalto;
University,;
PO;
Box;
13500,;
FI-00076;
Aalto,;
Finland;
Innovation;
Center;
of;
Quantum;
Matter,;
Beijing;
100190,;
China;