Ultrasensitive Calorimetric Measurements of the Electronic Heat Capacity of Graphene

Abstract

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/Hz 1/2 , 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 lowdimensional systems and provide an avenue for the investigation of their thermodynamic quantities.

Thermal self-oscillations in monolayer graphene coupled to a superconducting microwave cavity

“…Here C G is the electronic heat capacity of graphene, Σ is the material constant describing cooling of the graphene electrons via phonons, A is the area of the flake, T 0 is the bath temperature and P diss is the part of the incoming microwave pumping power P in , which penetrates through the resonator and is absorbed in graphene. The heat capacity of graphene is known [39]…”

Theory of the effective Seebeck coefficient for photoexcited 2D materials: the case of graphene

“…[18][19][20][21][22] Moreover, local and ultra-fast measurement of the electronic temperature has also been recently demonstrated. [44] Hence, it is becoming experimentally feasible to measure the thermoelectric signal generated by heating the same spot on a graphene sample, in the presence or absence of a concurrent photoexcited density, extracting valuable information on the local electronic relaxation processes. The theory described in this work is the first one that can consistently treat both cases on equal footing.…”

Thermal self-oscillations in monolayer graphene coupled to a superconducting microwave cavity

“…Here C G is the electronic heat capacity of graphene, Σ is the material constant describing cooling of the graphene electrons via phonons, A is the area of the flake, T 0 is the bath temperature and P diss is the part of the incoming microwave pumping power P in , which penetrates through the resonator and is absorbed in graphene. The heat capacity of graphene is known [50] C…”