Department of Applied Physics, Stanford University, Stanford, California 94305, USA.
Phys Rev Lett. 2013 May 24;110(21):216601. doi: 10.1103/PhysRevLett.110.216601. Epub 2013 May 22.
The fate of the low-temperature conductance at the charge-neutrality (Dirac) point in a single sheet of graphene on boron nitride is investigated down to 20 mK. As the temperature is lowered, the peak resistivity diverges with a power-law behavior and becomes as high as several megohms per square at the lowest temperature, in contrast with the commonly observed saturation of the conductivity. As a perpendicular magnetic field is applied, our device remains insulating and directly transitions to the broken-valley-symmetry, ν=0 quantum Hall state, indicating that the insulating behavior we observe at zero magnetic field is a result of broken valley symmetry. Finally we discuss the possible origins of this effect.
在氮化硼单原子层石墨烯的电荷中性（狄拉克）点，低温电导率的命运被研究到 20mK。随着温度的降低，峰值电阻率呈幂律发散，在最低温度下高达几兆欧姆每平方，与通常观察到的电导率饱和形成对比。当施加垂直磁场时，我们的器件仍然保持绝缘，并直接进入破谷对称，ν=0 量子霍尔态，这表明我们在零磁场下观察到的绝缘行为是破谷对称的结果。最后，我们讨论了这种效应的可能起源。
