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. Monolayer Superconductivity and Tunable Topological Electronic Structure at the Fe(Te,Se)/Bi ₂ Te ₃ Interface

   https://doi.org/10.1002/adma.202210940  

   Moore, Robert_G; Lu, Qiangsheng; Jeon, Hoyeon; Yao, Xiong; Smith, Tyler; Pai, Yun‐Yi; Chilcote, Michael; Miao, Hu; Okamoto, Satoshi; Li, An‐Ping; et al (April 2023, Advanced Materials)

   Abstract The interface between 2D topological Dirac states and ans‐wave superconductor is expected to support Majorana‐bound states (MBS) that can be used for quantum computing applications. Realizing these novel states of matter and their applications requires control over superconductivity and spin‐orbit coupling to achieve spin‐momentum‐locked topological interface states (TIS) which are simultaneously superconducting. While signatures of MBS have been observed in the magnetic vortex cores of bulk FeTe_0.55Se_0.45, inhomogeneity and disorder from doping make these signatures unclear and inconsistent between vortices. Here superconductivity is reported in monolayer (ML) FeTe_1–ySe_y(Fe(Te,Se)) grown on Bi₂Te₃by molecular beam epitaxy (MBE). Spin and angle‐resolved photoemission spectroscopy (SARPES) directly resolve the interfacial spin and electronic structure of Fe(Te,Se)/Bi₂Te₃heterostructures. Fory = 0.25, the Fe(Te,Se) electronic structure is found to overlap with the Bi₂Te₃TIS and the desired spin‐momentum locking is not observed. In contrast, fory = 0.1, reduced inhomogeneity measured by scanning tunneling microscopy (STM) and a smaller Fe(Te,Se) Fermi surface with clear spin‐momentum locking in the topological states are found. Hence, it is demonstrated that the Fe(Te,Se)/Bi₂Te₃system is a highly tunable platform for realizing MBS where reduced doping can improve characteristics important for Majorana interrogation and potential applications. 

   more » « less
3. Imaging quantum spin Hall edges in monolayer WTe ₂

   https://doi.org/10.1126/sciadv.aat8799  

   Shi, Yanmeng; Kahn, Joshua; Niu, Ben; Fei, Zaiyao; Sun, Bosong; Cai, Xinghan; Francisco, Brian A.; Wu, Di; Shen, Zhi-Xun; Xu, Xiaodong; et al (February 2019, Science Advances)

   A two-dimensional (2D) topological insulator exhibits the quantum spin Hall (QSH) effect, in which topologically protected conducting channels exist at the sample edges. Experimental signatures of the QSH effect have recently been reported in an atomically thin material, monolayer WTe 2 . Here, we directly image the local conductivity of monolayer WTe 2 using microwave impedance microscopy, establishing beyond doubt that conduction is indeed strongly localized to the physical edges at temperatures up to 77 K and above. The edge conductivity shows no gap as a function of gate voltage, and is suppressed by magnetic field as expected. We observe additional conducting features which can be explained by edge states following boundaries between topologically trivial and nontrivial regions. These observations will be critical for interpreting and improving the properties of devices incorporating WTe 2 . Meanwhile, they reveal the robustness of the QSH channels and the potential to engineer them in the monolayer material platform. 

   more » « less
4. Crossover from Conventional to Unconventional Superconductivity in 2M-WS ₂

   https://doi.org/10.1021/acs.nanolett.4c05257  

   Samarawickrama, Piumi; McBride, Joseph; Gautam, Sabin; Fu, ZhuangEn; Watanabe, Kenji; Taniguchi, Takashi; Wang, Wenyong; Tang, Jinke; Ackerman, John; Leonard, Brian M; et al (December 2024, Nano Letters)

   Leveraging the reciprocal-space proximity effect between superconducting bulk and topological surface states (TSSs) offers a promising way to topological superconductivity. However, elucidating the mutual influence of bulk and TSSs on topological superconductivity remains a challenge. Here, we report pioneering transport evidence of a thickness-dependent transition from conventional to unconventional superconductivity in 2M-phase WS2 (2M-WS2). As the sample thickness reduces, we see clear changes in key superconducting metrics, including critical temperature, critical current, and carrier density. Notably, while thick 2M-WS2 samples show conventional superconductivity, with an in-plane (IP) upper critical field constrained by the Pauli limit, samples under 20 nm exhibit a pronounced IP critical field enhancement, inversely correlated with 2D carrier density. This marks a distinct crossover to unconventional superconductivity with strong spin-orbit-parity coupling. Our findings underscore the crucial role of sample thickness in accessing topological states in 2D topological superconductors, offering pivotal insights into future studies of topological superconductivity. 

   more » « less
5. 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