Superconductivity in hexagonal BC monolayer-based films

Yinchang Zhao; Xuerong Nie; Shuming Zeng; Shengliang Wang; Geng Li; Zhenhong Dai; Yifan Yin; Chao Lian; Jun Ni

doi:10.1103/PhysRevB.111.174524

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Superconductivity in hexagonal BC monolayer-based films

Yinchang Zhao, Xuerong Nie, Shuming Zeng, Shengliang Wang, Geng Li, Zhenhong Dai, Yifan Yin, Chao Lian, Jun Ni

DOI 10.1103/PhysRevB.111.174524 · Physical Review B

T1

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Abstract

A key goal in the study of superconductivity is the pursuit of high−Tc superconductors. Due to the metallization of σ−bonding electrons, which typically leads to strong electron-phonon coupling, two-dimensional materials based on hexagonal BC monolayers have been suggested as promising candidates for achieving high−Tc superconductivity. However, compared with graphene, the free-standing BC monolayer faces dynamical instability due to the absence of one π electron. In this work, to elucidate the origin of superconductivity in the BC monolayer, we initially stabilized the system by applying feasible biaxial tensile strain, followed by exploring potential electron doping to uncover more superconducting phases, and ultimately provided a complete superconducting phase diagram for the free-standing BC monolayer through systematical ab initio anisotropic Migdal-Eliashberg theory calculations. Our findings indicate that the structural phases between relative tensile strains εr1=(2.2+0.72ne+1.9ne2−3.56ne3+1.57ne4)% and εr2=(7.1−9.6ne+17.2ne2−17.35ne3+6.7ne4)%, with ne as electron doping density ranging from zero to one electron per unit cell, are dynamically stable and exhibit a three-gap superconducting nature with the critical temperatures Tc from 76 to 122K and the maximum superconducting gaps ΔMax of 19–35 meV. We demonstrated such high−Tc three-gap superconductivity is closely associated with the Fermi surface which exhibits an anomalously strong electron-phonon coupling and comprises two distinct σ Fermi sheets formed by combined s+px,y states and one π Fermi sheet dominated by the C−pz orbitals. Moreover, as an account of strong interaction with the σ−bonding electrons, the in-plane B-C stretching modes govern the strong electron-lattice coupling. Motivated by the route of emergent superconductivity in the strained and doped BC monolayer, we designed 35 two-dimensional materials based on the BC monolayer through atom adsorption, sandwich structuring, and hydrogenation of the adsorption systems, and proved that there are 17 dynamically stable superconductors, e.g., adatoms-BC systems BCLi, BCNa, BCK, BCCu, and BCAg, sandwich structures B2C2Li, B2C2Na, B2C2K, and B2C2Cu, and hydrogenated adatoms-BC systems BCLiH and BCCuH. Ab initio anisotropic Migdal-Eliashberg theory calculations demonstrate that all of the 17 newly searched two-dimensional superconductors have strong electron-phonon coupling and high−Tc multigap superconductivity with the Tc ranging from 33.5 to 118K. Further analysis shows that the decorations from adatoms, hydrogenation, or sandwich structuring provide tensile strain and electron doping simultaneously to the BC layer while adjusting interatomic forces, which, thereby drives the system into a superconducting phase. Theses results pave the way for design of two-dimensional high−Tc multigap superconductors.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
BC Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	76	Pressure not reported	unknown
BC Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	122	Pressure not reported	unknown
BCLi Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
BCLi Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
BCNa Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
BCNa Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
BCK Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
BCK Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
BCCu Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
BCCu Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
BCAg Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
BCAg Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
B2C2Li Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
B2C2Li Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
B2C2Na Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
B2C2Na Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
B2C2K Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
B2C2K Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
B2C2Cu Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
B2C2Cu Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
BCLiH Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
BCLiH Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
BCCuH Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	33.5	Pressure not reported	unknown
BCCuH Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	118	Pressure not reported	unknown
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	39	Pressure not reported	unknown
H3S Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	203	150 GPa	unknown