Type-II Ising Superconductivity and Anomalous Metallic State in Macro-Size Ambient-Stable Ultrathin Crystalline Films

Abstract

Recent emergence of two-dimensional (2D) crystalline superconductors has provided a promising platform to investigate novel quantum physics and potential applications. To reveal essential quantum phenomena therein, ultralow temperature transport investigation on high-quality ultrathin superconducting films is critically required, although it has been quite challenging experimentally. Here, we report a systematic transport study on the ultrathin crystalline PdTe 2 films grown by molecular beam epitaxy (MBE). Interestingly, a new type of Ising superconductivity in 2D centrosymmetric materials is revealed by the detection of large inplane critical field more than 7 times the Pauli limit. Remarkably, in a perpendicular magnetic field, we provide solid evidence of an anomalous metallic state characterized by the resistance saturation at low temperatures with high-quality filters. The robust superconductivity with intriguing quantum phenomena in the macro-size ambient-stable ultrathin PdTe 2 films remains almost the same for 20 months, showing great potentials in electronic and spintronic applications.

Ising pairing in atomically thin superconductors

“…In fact, there exists not just one type-II Ising superconductor. In ultrathin PdTe 2 grown by MBE, Liu et al [22] observed largely enhanced B c2,∥ , exceeding B p by a factor of 6-8 (Fig. 2d).…”

“…Black: spinorbit coupling (SOC) related systems[45,47], Blue: Type-I Ising superconducting materials[5, 12, 14- 16, 18, 74]. Red: Type-II Ising superconducting materials[21,22]. Orange: "beyond" Ising-type superconductivity[50][51][52]72].…”

Recent Advances in 2D Superconductors

“…Very recently, anomalous metallic state was also observed in MBE‐grown PdTe 2 thin films under a perpendicular magnetic field; the detection was convincing since more than 99.999% of high‐frequency noise power was reduced by the high‐quality filter. [ 125 ] In conclusion, the quantum metallic state has brought wide interest and whether the quantum metallic state is an intrinsic state has fundamental importance for us to understand the quantum material and quantum phase transitions.…”

“…Similar type‐II Ising superconductivity was also discovered in the centrosymmetric MBE‐grown ultrathin PdTe 2 films very recently, where the in‐plane critical field is more than 7 times of the Pauli limit. [ 125 ] In the type‐II Ising superconductors, the Ising‐like pairing occurs between the carriers around Γ‐point with their spins aligned perpendicular to the plane rather than the K and K′ points observed in 2H‐type MoS 2 and NbSe 2 , and more type‐II Ising superconductors are expected in the future discovery. [ 254 ]…”

Disorder effects on quantum transport and quantum phase transition in low-dimensional superconducting and topological systems

“…Since stronger inversion symmetry breaking attribute to the missing up-turn feature, a pentalayer stanene should experience a weaker Rashba effect, giving rise to an apparent enhancement of B c;== at low T. This indicates a broader range of inversion symmetry materials host such pairing mechanisms. Recent experiment in ultra-thin crystalline PdTe2 films also demonstrates clear feature of type-II Ising pairing with in-plane critical field more than 7 times the Pauli limit [67].…”