More Like this

1. Interface-induced superconductivity in magnetic topological insulators

   https://doi.org/10.1126/science.adk1270  

   Yi, Hemian; Zhao, Yi-Fan; Chan, Ying-Ting; Cai, Jiaqi; Mei, Ruobing; Wu, Xianxin; Yan, Zi-Jie; Zhou, Ling-Jie; Zhang, Ruoxi; Wang, Zihao; et al (February 2024, Science)

   The interface between two different materials can show unexpected quantum phenomena. In this study, we used molecular beam epitaxy to synthesize heterostructures formed by stacking together two magnetic materials, a ferromagnetic topological insulator (TI) and an antiferromagnetic iron chalcogenide (FeTe). We observed emergent interface-induced superconductivity in these heterostructures and demonstrated the co-occurrence of superconductivity, ferromagnetism, and topological band structure in the magnetic TI layer—the three essential ingredients of chiral topological superconductivity (TSC). The unusual coexistence of ferromagnetism and superconductivity is accompanied by a high upper critical magnetic field that exceeds the Pauli paramagnetic limit for conventional superconductors at low temperatures. These magnetic TI/FeTe heterostructures with robust superconductivity and atomically sharp interfaces provide an ideal wafer-scale platform for the exploration of chiral TSC and Majorana physics. 

   more » « less
2. Unconventional superconducting phase diagram of monolayer ${\mathrm{WTe}}_2$

   https://doi.org/10.1103/PhysRevResearch.7.013224  

   Song, Tiancheng; Jia, Yanyu; Yu, Guo; Tang, Yue; Uzan, Ayelet J; Zheng, Zhaoyi Joy; Guan, Haosen; Onyszczak, Michael; Singha, Ratnadwip; Gui, Xin; et al (February 2025, Physical Review Research)

   The existence of a quantum critical point (QCP) and fluctuations around it are believed to be important for understanding the phase diagram in unconventional superconductors such as cuprates, iron pnictides, and heavy fermion superconductors. However, the QCP is usually buried deep within the superconducting dome and is difficult to investigate. The connection between quantum critical fluctuations and superconductivity remains an outstanding problem in condensed matter. Here combining both electrical transport and Nernst experiments, we explicitly demonstrate the onset of superconductivity at an unconventional QCP in gate-tuned monolayer tungsten ditelluride $\left({\mathrm{WTe}}_2\right)$, with features incompatible with the conventional Bardeen-Cooper-Schrieffer scenario. The results lead to a superconducting phase diagram that is distinguished from other known superconductors. Two distinct gate-tuned quantum phase transitions are observed at the ends of the superconducting dome. We find that quantum fluctuations around the QCP of the underdoped regime are essential for understanding how the monolayer superconductivity is established. The unconventional phase diagram we report here illustrates a previously unknown relation between superconductivity and QCP. Published by the American Physical Society2025 

   more » « less
3. Signatures of a spin-active interface and a locally enhanced Zeeman field in a superconductor-chiral material heterostructure

   https://doi.org/10.1126/sciadv.ado4875  

   Chen, Cliff; Tran, Jason; McFadden, Anthony; Simmonds, Raymond; Saito, Keisuke; Chu, En-De; Morales, Daniel; Suezaki, Varrick; Hou, Yasen; Aumentado, Joe; et al (August 2024, Science Advances)

   A localized Zeeman field, intensified at heterostructure interfaces, could play a crucial role in a broad area including spintronics and unconventional superconductors. Conventionally, the generation of a local Zeeman field is achieved through magnetic exchange coupling with a magnetic material. However, magnetic elements often introduce defects, which could weaken or destroy superconductivity. Alternatively, the coupling between a superconductor with strong spin-orbit coupling and a nonmagnetic chiral material could serve as a promising approach to generate a spin-active interface. Here, we leverage an interface superconductor, namely, induced superconductivity in noble metal surface states, to probe the spin-active interface. Our results unveil an enhanced interface Zeeman field, which selectively closes the surface superconducting gap while preserving the bulk superconducting pairing. The chiral material, i.e., trigonal tellurium, also induces Andreev bound states (ABS) exhibiting spin polarization. The field dependence of ABS manifests a substantially enhanced interface Landég-factor (g_eff~ 12), thereby corroborating the enhanced interface Zeeman energy. 

   more » « less
4. Two-fold symmetric superconductivity in few-layer NbSe2

   https://doi.org/10.1038/s41567-021-01219-x  

   Hamill, Alex; Heischmidt, Brett; Sohn, Egon; Shaffer, Daniel; Tsai, Kan-Ting; Zhang, Xi; Xi, Xiaoxiang; Suslov, Alexey; Berger, Helmuth; Forró, László; et al (April 2021, Nature Physics)

   null (Ed.)

   The strong Ising spin–orbit coupling in certain two-dimensional transition metal dichalcogenides can profoundly affect the superconducting state in few-layer samples. For example, in NbSe2, this effect combines with the reduced dimensionality to stabilize the superconducting state against magnetic fields up to ~35 T, and could lead to topological superconductivity. Here we report a two-fold rotational symmetry of the superconducting state in few-layer NbSe2 under in-plane external magnetic fields, in contrast to the three-fold symmetry of the lattice. Both the magnetoresistance and critical field exhibit this two-fold symmetry, and it also manifests deep inside the superconducting state in NbSe2/CrBr3 superconductor-magnet tunnel junctions. In both cases, the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute the behaviour to the mixing between two closely competing pairing instabilities, namely the conventional s-wave instability typical of bulk NbSe2 and an unconventional d- or p-wave channel that emerges in few-layer NbSe2. Our results demonstrate the unconventional character of the pairing interaction in few-layer transition metal dichalcogenides and highlight the exotic superconductivity in this family of two-dimensional materials. 

   more » « less
5. Possible strain-induced enhancement of the superconducting onset transition temperature in infinite-layer nickelates

   https://doi.org/10.1038/s42005-023-01464-x  

   Ren, Xiaolin; Li, Jiarui; Chen, Wei-Chih; Gao, Qiang; Sanchez, Joshua J.; Hales, Jordyn; Luo, Hailan; Rodolakis, Fanny; McChesney, Jessica L.; Xiang, Tao; et al (November 2023, Communications Physics)

   Abstract The mechanism of unconventional superconductivity in correlated materials remains a great challenge in condensed matter physics. The recent discovery of superconductivity in infinite-layer nickelates, as an analog to high-T_ccuprates, has opened a new route to tackle this challenge. By growing 8 nm Pr_0.8Sr_0.2NiO₂films on the (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.7substrate, we successfully raise the superconducting onset transition temperatureT_cin the widely studied SrTiO₃-substrated nickelates from 9 K into 15 K, which indicates compressive strain is an efficient protocol to further enhance superconductivity in infinite-layer nickelates. Additionally, the x-ray absorption spectroscopy, combined with the first-principles and many-body simulations, suggest a crucial role of the hybridization between Ni and O orbitals in the unconventional pairing. These results also suggest the increase ofT_cbe driven by the change of charge-transfer nature that would narrow the origin of general unconventional superconductivity in correlated materials to the covalence of transition metals and ligands. 

   more » « less