Pressure-induced gap modulation and topological transitions in twisted bilayer and twisted double bilayer graphene

Abstract

We study the electronic and topological properties of fully relaxed twisted bilayer (TBG) and double bilayer (TDBG) graphene under perpendicular pressure. An approach has been proposed to obtain the equilibrium in-plane structural deformation and out-of-plane corrugation in moiré superlattices under pressure. We find that the in-plane relaxation becomes much stronger under higher pressure, while the corrugation height in each layer is maintained. The comparison between band structures of relaxed and rigid structures demonstrates that not only the gaps on the electron and hole sides (∆e and ∆ h) are significantly underestimated without relaxation but also the detailed dispersions of the middle bands of rigid structures are rather different from those of relaxed systems. ∆e and ∆ h in TBG reach maximum values around critical pressures with narrowest middle bands. Topological transitions occur in TDBG under pressure with the middle valence and conduction bands in one valley touching and their Chern numbers transferred to each other. The pressure can also tune the gap at the neutrality point of TDBG, which becomes closed for a pressure range and reopened under higher pressure. The behavior of electronic structure of supertlattices under pressure is sensitive to the twist angle θ with the critical pressures generally increase with θ.

Magic angle and plasmon mode engineering in twisted trilayer graphene with pressure

“…( 3). It has been proven that the vertical compression has a negligible influence on the intralayer interactions, whereas significantly modify the interlayer hoppings [15,18]. Therefore, we only modify the interlayer hopping term V ppσ as [18]:…”

“…Interestingly, for twisted bilayer graphene with a moderate twist angle that shows relatively weak correlation under ambient pressure, an appropriate hydrostatic pressure induces robust insulating phases and superconductivity with higher T c than that in zero-pressure magic-angle case [13,14]. Theoretically, vertical pressure can be used to achieve the ultraflat bands in twisted bilayer graphene with arbitrary twist angle [15][16][17][18][19]. Consequently, when studying the strong correlation, we can reduce the impact of structural inhomogeneity by using a moiré pattern with a short wavelength.…”

Tailoring the Band Structure of Twisted Double Bilayer Graphene with Pressure

“… 38 , 39 In TBG the pressure changes the width of the low-energy bands 40 , 41 and it can drive the system through a superconducting phase transition. 5 On the basis of theoretical calculations on TDBG, the pressure is expected to have similarly drastic effects on the electronic properties; 20 , 32 thus it gives an ideal control knob for in situ band-structure and topology engineering of TDBG.…”

New method of transport measurements on van der Waals heterostructures under pressure

“…1), the interlayer coupling can be tuned, which strongly influences the electronic structure and thereby the physical properties of these heterostructures. The potential interest of tuning this parameter is demonstrated in various theoretical works [13,[36][37][38][39][40][41][42][43], however, several technological challenges are to be solved for the realization of transport measurements on nanodevices under pressure.…”