  We propose a tubal van der Waals heterostructure by rolling up the graphene
and MoS2 atomic layers into a tubal form. We illustrate that the interlayer
space for the tubal van der Waals heterostructure can be varied in a specific
range, which is determined by the competition between the interlayer van der
Waals force and the mechanical properties of the atomic layers. The variability
of the interlayer space can be utilized to efficiently tune mechanical
properties of the tubal van der Waals heterostructure. More specifically, we
demonstrate that the Poisson's ratio of the tubal van der Waals heterostructure
can be manipulated by a factor of two by varying the interlayer space from 1.44
to 4.44. Our work promotes a new member with tunable Poisson's ratio to the van
der Waals heterostructure family.
