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The interplay between superconductivity and charge or spin order is a key focus in condensed matter physics, with kagome lattice systems providing unique insights. The kagome superconductor LaRu 3 Si 2 ( T c  ≃ 6.5 K) features a characteristic kagome band structure and a hierarchy of charge order transitions at T co,I  ≃ 400 K and T co,II  ≃ 80 K, along with an additional transition at T * ≃ 35 K associated with electronic and magnetic responses. Using magnetotransport under pressure up to 40 GPa, we find T c peaks at 9 K (2 GPa)—the highest among kagome superconductors—remains nearly constant up to 12 GPa, and then decreases to 2 K at 40 GPa, forming a dome-shaped phase diagram. Similarly, both the resistivity anomaly at T * and the magnetoresistance exhibit a dome-shaped pressure dependence. Moreover, above 12 GPa, X-ray diffraction reveals that the charge order evolves from long-range to short-range, coinciding with the suppression of T c . These observations indicate that superconductivity in LaRu 3 Si 2 is closely linked to the charge-ordered state and the electronic responses at T co,II and T *. The authors study kagome superconductor LaRu3Si2 under pressure up to 40 GPa. They find a superconducting dome as a function of pressure, with Tc reaching its maximum when the coexisting charge order remains long-range.

Understanding how time-reversal symmetry (TRS) breaks in quantum materials is key to uncovering new states of matter and advancing quantum technologies. However, unraveling the interplay between TRS breaking, charge order, and superconductivity in kagome metals continues to be a compelling challenge. Here, we investigate the kagome metal Cs(V 1− x Nb x ) 3 Sb 5 with x  = 0.07 using muon spin rotation ( μ SR), alternating current (AC) magnetic susceptibility, and scanning tunneling microscopy (STM), under combined tuning by chemical doping, hydrostatic pressure, magnetic field, and depth from the surface. We find that TRS breaking in the bulk emerges below 40 K—lower than the charge order onset at 58 K—while near the surface, TRS breaking onsets at 58 K and is twice as strong. Niobium doping raises the superconducting critical temperature from 2.5 K to 4.4 K. Under pressure, both the critical temperature and superfluid density double, with TRS-breaking superconductivity appearing above 0.85 GPa. These findings reveal a depth-tunable TRS-breaking state and unconventional superconducting behavior in kagome systems. Kagome systems are a rich playground to explore the interplay between superconductivity and charge order. Here, the authors present a comprehensive muon spin rotation analysis, coupled with scanning tunnelling microscopy, under various tuning parameters including chemical doping, depth and hydrostatic pressure to investigate time-reversal symmetry-breaking in Nb-doped CsV 3 Sb 5 .

The cuprate superconductor La 2− x Ba x CuO 4 (LBCO) near x  = 0.125 is a striking example of intertwined electronic orders, where 3D superconductivity is anomalously suppressed, allowing spin and charge stripe order to develop. Understanding this interplay remains a key challenge in cuprates, highlighting the necessity of external tuning for deeper insight. While in-plane uniaxial stress enhances superconductivity and suppresses stripe order, the effects of c -axis compression remains largely unexplored. Here, we use muon spin rotation ( μ SR) and AC susceptibility with an in situ piezoelectric stress device to investigate the spin-stripe order and superconductivity in LBCO-0.115 under c -axis compression. The measurements reveal a gradual suppression of the superconducting transition temperature ( T c ) with increasing c -axis stress, in stark contrast to the strong enhancement observed under in-plane stress. We further show that while in-plane stress rapidly reduces both the magnetic volume fraction ( V m ) and the spin-stripe ordering temperature ( T so ), c -axis compression has no effect, with V m and T so exhibiting an almost unchanged behavior up to the highest applied stress of 0.21 GPa. These findings demonstrate a strong anisotropy in stress response. Unconventional superconductivity in the cuprates involves a complex interplay of competing charge and spin orders, making it challenging to elucidate the underlying mechanisms. Here, the authors apply uniaxial pressure to tune LBCO, and using muon spin rotation and AC susceptibility, reveal a gradual suppression of T c under c -axis stress–contrasting with its strong enhancement under in plane stress–and show that c axis compression leaves spin stripe order intact while in plane stress strongly suppresses it.

Optimization of unconventional superconductivity involves a balance of interaction strengths. Precise determination of correlation strength across different material families is therefore important. Here, we present a combined X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) study of infinite-layer PrNiO 2 and SrCuO 2 that enables fair comparison of their interaction strengths. For both compounds, we study the orbital and magnetic excitations and extract their dispersions along high-symmetry directions. Using a single-band Hubbard model and including physically plausible assumptions about higher-order exchange interactions, we estimate the correlation factor U / t for both compounds. A key finding is that despite the prediction of a smaller Coulomb repulsion U , PrNiO 2 exhibits a correlation strength U / t that is 20% stronger than that of its isostructural cuprate counterpart SrCuO 2 . This indicates that moderation of the correlation strength may further optimize superconductivity in nickelates. Optimization of unconventional superconductivity requires precise determination of correlation strengths across material families. Here, the authors use X-ray absorption spectroscopy and resonant inelastic X-ray scattering to reveal that PrNiO 2 exhibits a 20% stronger correlation strength U/t than in the isostructural cuprate SrCuO 2 , suggesting potential for enhanced superconductivity in nickelates through correlation strength moderation.

The interplay between superconductivity and charge or spin order is a key focus in condensed matter physics, with kagome lattice systems providing unique insights. The kagome superconductor LaRu Si (T  ≃ 6.5 K) features a characteristic kagome band structure and a hierarchy of charge order transitions at T  ≃ 400 K and T  ≃ 80 K, along with an additional transition at T* ≃ 35 K associated with electronic and magnetic responses. Using magnetotransport under pressure up to 40 GPa, we find T peaks at 9 K (2 GPa)-the highest among kagome superconductors-remains nearly constant up to 12 GPa, and then decreases to 2 K at 40 GPa, forming a dome-shaped phase diagram. Similarly, both the resistivity anomaly at T* and the magnetoresistance exhibit a dome-shaped pressure dependence. Moreover, above 12 GPa, X-ray diffraction reveals that the charge order evolves from long-range to short-range, coinciding with the suppression of T . These observations indicate that superconductivity in LaRu Si is closely linked to the charge-ordered state and the electronic responses at T and T*.

Understanding how time-reversal symmetry (TRS) breaks in quantum materials is key to uncovering new states of matter and advancing quantum technologies. However, unraveling the interplay between TRS breaking, charge order, and superconductivity in kagome metals continues to be a compelling challenge. Here, we investigate the kagome metal Cs(V Nb ) Sb with  = 0.07 using muon spin rotation ( SR), alternating current (AC) magnetic susceptibility, and scanning tunneling microscopy (STM), under combined tuning by chemical doping, hydrostatic pressure, magnetic field, and depth from the surface. We find that TRS breaking in the bulk emerges below 40 K-lower than the charge order onset at 58 K-while near the surface, TRS breaking onsets at 58 K and is twice as strong. Niobium doping raises the superconducting critical temperature from 2.5 K to 4.4 K. Under pressure, both the critical temperature and superfluid density double, with TRS-breaking superconductivity appearing above 0.85 GPa. These findings reveal a depth-tunable TRS-breaking state and unconventional superconducting behavior in kagome systems.

The cuprate superconductor La Ba CuO (LBCO) near  = 0.125 is a striking example of intertwined electronic orders, where 3D superconductivity is anomalously suppressed, allowing spin and charge stripe order to develop. Understanding this interplay remains a key challenge in cuprates, highlighting the necessity of external tuning for deeper insight. While in-plane uniaxial stress enhances superconductivity and suppresses stripe order, the effects of -axis compression remains largely unexplored. Here, we use muon spin rotation ( SR) and AC susceptibility with an in situ piezoelectric stress device to investigate the spin-stripe order and superconductivity in LBCO-0.115 under -axis compression. The measurements reveal a gradual suppression of the superconducting transition temperature ( ) with increasing -axis stress, in stark contrast to the strong enhancement observed under in-plane stress. We further show that while in-plane stress rapidly reduces both the magnetic volume fraction ( ) and the spin-stripe ordering temperature ( ), -axis compression has no effect, with and exhibiting an almost unchanged behavior up to the highest applied stress of 0.21 GPa. These findings demonstrate a strong anisotropy in stress response.

Superconductivity in cuprates emerges out of a complex normal state that hosts density waves, pseudogap physics, and strange metal properties. Here, we access this normal state by synchronizing free-electron laser x-rays with high-magnetic-field pulses up to 44 T. We observe a linear increase in charge order amplitude and correlation length that persists far above the vortex melting transition. This behavior is incompatible with standard phase competition between charge order and superconductivity. By means of conventional hard x-ray diffraction and magnetostriction, we show that applied fields also enhance monoclinic lattice distortions. However, this magnetoelastic response is weaker and an epiphenomenon of the stripe order enhancement. Combined with recent observations of field-linear spin freezing, our results point to a direct coupling between magnetic field and the spin component of stripe order in the high-field normal state -- a mechanism independent of superconductivity suppression that has so far remained hidden from scattering probes.