Twisted multilayer nodal superconductors

Abstract

Twisted bilayers of nodal superconductors were recently proposed as a promising platform to host superconducting phases that spontaneously break time-reversal symmetry. Here we extend this analysis to twisted multilayers, focusing on two high-symmetry stackings with alternating (±θ) and constant (θ) twist angles. In analogy to alternating-twist multilayer graphene, the former can be mapped to twisted bilayers with renormalized interlayer couplings, along with a remnant gapless monolayer when the number of layers L is odd. In contrast, the latter exhibits physics beyond twisted bilayers, including the occurrence of "magic angles" characterized by cubic band crossings when L mod 4 = 3. Due to their power-law divergent density of states, such multilayers are highly susceptible to secondary instabilities. Within a BCS mean-field theory, defined in the continuum and on a lattice, we find that both stackings host chiral topological superconductivity in extended regions of their phase diagrams.

Customizing topological phases in the twisted bilayer superconductors with even-parity pairings

“…Note that the amplitude of interlayer tunneling will attenuate rapidly in real space. [7,[9][10][11][12][23][24][25][26] Since the interlayer coupling is a minor perturbation to the superconducting order parameter, we assume that the pairing amplitudes in each layer are still uniform for a twisted system.…”

“…[6] However, due to the rarity of odd-parity superconductivity pairing, whose Cooper pairs are composed of two-electron couplings belonging to different orbits with the same spin orientation, [1] this is a serious obstacle from an experimental perspective. Inspired by the research on twisted bilayer cuprates [7][8][9][10][11][12] and spin-singlet topological superconductor, [13][14][15] we investigate the topological properties of a twisted bilayer with different even-parity pairings, i.e., the d-wave and s ± -wave pairings. The d-wave pairing is common in cuprate high-temperature superconductors, [16] and the s ± -wave pairing is considered to play a dominant role in iron-based high-temperature superconductors.…”

2D High-Temperature Superconductor Integration in Contact Printed Circuit Boards

“…The Bi 2 Sr 2 CaCu 2 O 8+ x (BSCCO) cuprate having the d -wave pairing symmetry and displaying superconductivity even when being a monolayer , is an ideal candidate for building highly functional quantum devices. Twisted van der Waals (vdW) heterostructures composed of BSCCO layers were predicted − to break time-reversal symmetry at certain twist angles, a phenomenon that was demonstrated experimentally . As such, BSCCO twisted heterostructures could potentially lead to topological states and Majorana modes .…”

Encapsulating High‐Temperature Superconducting Twisted van der Waals Heterostructures Blocks Detrimental Effects of Disorder

“…The emergence of the topological states in the twisted vdW heterostructures of HTSC BSCCO layers with the d ‐wave superconducting order parameter was suggested. [ 25–30 ] The twist angle close to 45° was found to result in a time‐reversal symmetry (TRS) broken chiral superconducting $${d_{{x^2} - {y^2}}}\; \pm \;i{d_{xy}}$$ phase, which was also reported at the intermediate twist angles and was attributed to the unconventional sign structure of the d ‐wave order parameter. [ 26,31 ] Strong support for this theoretical proposal came from the experimental detection of some new interfacial superconductivity, [ 23 ] manifesting as a dominant second harmonic of the Josephson current close to 45° angle.…”

“…The emergence of the topological states in the twisted vdW heterostructures of HTSC BSCCO layers with the d-wave superconducting order parameter was suggested. [25][26][27][28][29][30] The twist angle close to 45° was found to result in a time-reversal symmetry (TRS) broken chiral superconducting…”