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1. Orphan high field superconductivity in non-superconducting uranium ditelluride

   https://doi.org/10.1038/s41467-024-47090-1  

   Frank, Corey E.; Lewin, Sylvia K.; Saucedo Salas, Gicela; Czajka, Peter; Hayes, Ian M.; Yoon, Hyeok; Metz, Tristin; Paglione, Johnpierre; Singleton, John; Butch, Nicholas P. (April 2024, Nature Communications)

   Abstract Reentrant superconductivity is an uncommon phenomenon in which the destructive effects of magnetic field on superconductivity are mitigated, allowing a zero-resistance state to survive under conditions that would otherwise destroy it. Typically, the reentrant superconducting region derives from a zero-field parent superconducting phase. Here, we show that in UTe₂crystals extreme applied magnetic fields give rise to an unprecedented high-field superconductor that lacks a zero-field antecedent. This high-field orphan superconductivity exists at angles offset between 29^oand 42^ofrom the crystallographicbtocaxes with applied fields between 37 T and 52 T. The stability of field-induced orphan superconductivity presented in this work defies both empirical precedent and theoretical explanation and demonstrates that high-field superconductivity can exist in an otherwise non-superconducting material. 

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2. Tuning magnetic confinement of spin-triplet superconductivity

   https://doi.org/10.1038/s41535-020-00270-w  

   Lin, Wen-Chen; Campbell, Daniel J.; Ran, Sheng; Liu, I-Lin; Kim, Hyunsoo; Nevidomskyy, Andriy H.; Graf, David; Butch, Nicholas P.; Paglione, Johnpierre (December 2020, npj Quantum Materials)

   null (Ed.)

   Abstract Electrical magnetoresistance and tunnel diode oscillator measurements were performed under external magnetic fields up to 41 T applied along the crystallographic b axis (hard axis) of UTe 2 as a function of temperature and applied pressures up to 18.8 kbar. In this work, we track the field-induced first-order transition between superconducting and magnetic field-polarized phases as a function of applied pressure, showing suppression of the transition with increasing pressure until the demise of superconductivity near 16 kbar and the appearance of a pressure-induced ferromagnetic-like ground state that is distinct from the field-polarized phase and stable at zero field. Together with evidence for the evolution of a second superconducting phase and its upper critical field with pressure, we examine the confinement of superconductivity by two orthogonal magnetic phases and the implications for understanding the boundaries of triplet superconductivity. 

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3. Correlation between scale-invariant normal-state resistivity and superconductivity in an electron-doped cuprate

   https://doi.org/10.1126/sciadv.aav6753  

   Sarkar, Tarapada; Mandal, P. R.; Poniatowski, N. R.; Chan, M. K.; Greene, Richard L. (May 2019, Science Advances)

   An understanding of the normal state in the high-temperature superconducting cuprates is crucial to the ultimate understanding of the long-standing problem of the origin of the superconductivity itself. This so-called “strange metal” state is thought to be associated with a quantum critical point (QCP) hidden beneath the superconductivity. In electron-doped cuprates—in contrast to hole-doped cuprates—it is possible to access the normal state at very low temperatures and low magnetic fields to study this putative QCP and to probe the T ➔ 0 K state of these materials. We report measurements of the low-temperature normal-state magnetoresistance (MR) of the n-type cuprate system La 2− x Ce x CuO 4 and find that it is characterized by a linear-in-field behavior, which follows a scaling relation with applied field and temperature, for doping ( x ) above the putative QCP ( x = 0.14). The magnitude of the unconventional linear MR decreases as T c decreases and goes to zero at the end of the superconducting dome ( x ~ 0.175) above which a conventional quadratic MR is found. These results show that there is a strong correlation between the quantum critical excitations of the strange metal state and the high- T c superconductivity. 

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4. Anomalous superconductivity in twisted MoTe ₂ nanojunctions

   https://doi.org/10.1126/sciadv.adq5712  

   Jia, Yanyu; Song, Tiancheng; Zheng, Zhaoyi Joy; Cheng, Guangming; Uzan, Ayelet J; Yu, Guo; Tang, Yue; Pollak, Connor J; Yuan, Fang; Onyszczak, Michael; et al (January 2025, Science Advances)

   Introducing superconductivity in topological materials can lead to innovative electronic phases and device functionalities. Here, we present a unique strategy for quantum engineering of superconducting junctions in moiré materials through direct, on-chip, and fully encapsulated 2D crystal growth. We achieve robust and designable superconductivity in Pd-metalized twisted bilayer molybdenum ditelluride (MoTe₂) and observe anomalous superconducting effects in high-quality junctions across ~20 moiré cells. Unexpectedly, the junction develops enhanced, instead of weakened, superconducting behaviors, exhibiting fluctuations to a higher critical magnetic field compared to its adjacent Pd₇MoTe₂superconductor. In addition, the critical current further exhibits a notable V-shaped minimum at zero magnetic field. These features are unexpected in conventional Josephson junctions and absent in junctions of natural bilayer MoTe₂created using the same approach. We discuss implications of these observations, including the possible formation of mixed even- and odd-parity superconductivity at the moiré junctions. Our results also demonstrate a pathway to engineer and investigate superconductivity in fractional Chern insulators. 

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5. Tuning the Fermi liquid crossover in Sr2RuO4 with uniaxial stress

   https://doi.org/10.1038/s41535-022-00519-6  

   Chronister, A; Zingl, M; Pustogow, A; Luo, Yongkang; Sokolov, D A; Jerzembeck, F; Kikugawa, N; Hicks, C W; Mravlje, J; Bauer, E D; et al (December 2022, npj Quantum Materials)

   Abstract We perform nuclear magnetic resonance (NMR) measurements of the oxygen-17 Knight shifts for Sr₂RuO₄, while subjected to uniaxial stress applied along [100] direction. The resulting strain is associated with a strong variation of the temperature and magnetic field dependence of the inferred magnetic response. A quasiparticle description based on density-functional theory calculations, supplemented by many-body renormalizations, is found to reproduce our experimental results, and highlights the key role of a van-Hove singularity. The Fermi-liquid coherence scale is shown to be tunable by strain, and driven to low values as the associated Lifshitz transition is approached. 

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