Thermodynamic probe of the bulk gap in the quantum spin Hall insulator 1T'-WTe₂

Single-layer 1T'-phase WTe₂ has recently drawn great interest as a candidate material for hosting an intrinsic quantum spin Hall insulator state at low temperature, a highly attractive property for numerous studies and applications. Such a state requires topologically-protected helical edge states coincident with a bulk band gap. Initial calculations of the 1T'-WTe₂ electronic structure predicted semimetallic bands, however, several studies have shown simultaneous experimental evidence of edge states and a bulk gap in photoemission, tunneling spectroscopy, and electron transport. The nature of this gap, however, is not fully resolved, with disagreements between predicted gaps from first-principles calculations and spectroscopic measurements in various conditions. Here, we probe the thermodynamic properties of fully-encapsulated single-layer 1T'-WTe₂ using low-temperature capacitance to illuminate the discussion of this gap and its single-particle or interaction-driven origin.