Direct measurements of inelastic scattering exponents of monolayer epitaxial graphene on SiC

Wei-Chen Lin^1,2,3, Cheng-Hsueh Yang^1,4, Yanfei Yang¹, Ching-Chen Yeh⁵, Pin-Chi Liao⁵, Chun-Wei Chang⁵, Randolph E. Elmquist¹, Chi-Te Liang^4,5,6,7,8*

¹Physical Measurement Laboratory, PhysicalNational Institute of Standards and Technology (NIST), Gaithersburg, Maryland, USA
²Taiwan International Graduate Program (TIGP), Academia Sinica, Taipei, Taiwan
³Department of Engineering and System Science, Department of EnNational Tsing Hua University, Hsinchu, Taiwan
⁴Graduate Institute of Applied Physics, Graduate InsNational Taiwan University, Taipei, Taiwan
⁵Department of Physics, National Taiwan University, Taipei, Taiwan
⁶Centre for Quantum Science and Engineering (CQSE), National Taiwan University, Taipei, Taiwan
⁷Taiwan Consortium of Emergent Crystalline Materials (TCECM), Taipei, Taiwan
⁸Taiwan Semiconductor Research Institute (TSRI), Hsinchu, Taiwan

* Presenter:Chi-Te Liang, email:ctliang@phys.ntu.edu.tw

The scaling theory of localization provides a comprehensive framework for understanding the transition between the localized and the extended states near the quantum Hall (QH) regime. Prior studies or measurements of the inelastic scattering exponent p in two dimensions, which plays a crucial role in quantum dephasing, mostly extract a magnetic-field-independent p spanning a wide range (1 ≦ p ≦ 4) or determine p indirectly through the relationp=2κγ. Here κ and γ are the critical exponent and the universal exponent, respectively. Therefore, it is highly desirable to measure p at different magnetic fields directly. Here we study two different types of graphene devices over a wide range of magnetic fields in both the low and high current regimes. The latter allows us to determine p directly through the current-heating model. We show that p ≈ 2 using current-heating studies in all cases. At high fields, these results are in excellent agreement with that determined from p=2κγ in the low current regime. However, with low currents, a vastly different inelastic scattering exponent p’ ≈ 1 is found in our analysis of weak localization (WL) in the low-field region. Such an unexpected discrepancy may be explained as follows. In the WL analysis, the electron and phonon systems are in thermal equilibrium so that we probe p’ ≈ 1. In contrast, in the high current regime where there is a substantial difference between the electron effective temperature and the lattice (phonon) temperature, we extract the exponent p ≈ 2. Our new experimental results further add mysteries to the seemly well-understood QH systems and quantum dephasing in two dimensions.

Keywords: Graphene, Inelastic scattering, Two-dimensional, exponent, Critical exponent