A recent study on graphene has uncovered that two key parameters describing electron behavior—energy-loss and quantum-coherence exponents—do not always behave the same way, especially when controlled by a gate voltage. Scientists have shown that these exponents, known as the inelastic scattering exponent and the dephasing exponent, can change independently under different conditions. This finding challenges a long-held assumption that the two exponents should be equivalent in describing electron interactions in materials like graphene. The research was conducted using gated epitaxial graphene, a type of graphene grown on silicon carbide and modified with a gate to control the density of electrons. A team of scientists from multiple institutions, led by Dr. Wei-Chen Lin at National Taiwan University, used two distinct methods to measure the exponents. They applied current-heating measurements to determine the inelastic scattering exponent, which describes how electrons lose energy through scattering events. Meanwhile, they used weak-localization analysis to measure the dephasing exponent, which relates to the loss of quantum coherence, or the ability of electrons to maintain their wave-like properties. At zero gate voltage, the two exponents were already different: the inelastic scattering exponent was approximately 2, while the dephasing exponent was around 1. As the gate voltage was increased, the inelastic scattering exponent rose to about 3, while the dephasing exponent dropped to approximately 0.75. This divergence suggests that energy relaxation and the loss of quantum phase coherence are governed by different microscopic processes. The results imply that these two phenomena should not be assumed to be linked in all situations. The study, published in the journal Carbon, offers a new framework for separately analyzing energy relaxation and quantum coherence in graphene and other two-dimensional materials. Understanding these processes is crucial for advancing technologies that depend on maintaining long-lived quantum states, such as quantum computing and ultra-sensitive electronic devices. "Distinguishing these processes is important for understanding low-temperature quantum transport and for developing devices that rely on long-lived electronic coherence," said Chi-Te Liang, a physics professor at National Taiwan University and a corresponding author of the study.