Ultrasensitive Calorimetric Measurements of the Electronic Heat Capacity of Graphene

• Published in: Nano letters 2021-06, Vol.21 (12), p.5330-5337
• Main Authors: Aamir, Mohammed Ali, Moore, John N, Lu, Xiaobo, Seifert, Paul, Englund, Dirk, Fong, Kin Chung, Efetov, Dmitri K
• Format: Article
• Language: English
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.1c01553

Heat capacity is an invaluable quantity in condensed matter physics and yet has been completely inaccessible in two-dimensional (2D) van der Waals (vdW) materials, owing to their ultrafast thermal relaxation times and the lack of suitable nanoscale thermometers. Here, we demonstrate a novel thermal relaxation calorimetry scheme that allows the first measurements of the electronic heat capacity of graphene. It is enabled by combining a radio frequency Johnson noise thermometer, which can measure the electronic temperature with a sensitivity of ∼20 mK/Hz1/2, and a photomixed optical heater that modulates T e with a frequency of up to Ω = 0.2 THz. This allows record sensitive measurements of the electronic heat capacity C e < 10 –19 J/K and the fastest measurement of electronic thermal relaxation time τ e < 10 –12 s yet achieved by a calorimeter. These features advance heat capacity metrology into the realm of nanoscale and low-dimensional systems and provide an avenue for the investigation of their thermodynamic quantities.