1. Department of Materials Science and EngineeringNational Tsing Hua University Hsinchu 30013 Taiwan
2. Department of PhysicsNational Sun Yat‐Sen University Kaohsiung 80424 Taiwan
3. Frontier Research Center on Fundamental and Applied Sciences of MattersNational Tsing Hua University Hsinchu 30013 Taiwan
4. Physics DivisionThe National Center for Theoretical Science Hsinchu 30013 Taiwan