Rui Wang

Geometric frustration drives exotic quantum phases and transitions in condensed matter. One-dimensional frustrated magnets with inherent controllability are particularly promising for studying fundamental quantum physics, yet experimentally tunable systems remain scarce. Here, using first-principles calculations and confined structure search, we predict a novel one-dimensional platform: confined FeS nanotubes with twisted-triangular geometry. These nanotubes exhibit a triple-well energy landscape, hosting two ferroelectric and one paraelectric phases, exhibiting collinear antiferromagnetic and 120\ifmmode^\circ\else\textdegree\fi{} noncollinear (NCL) orders, respectively. Application of axial strains tunes magnetic interactions and frustration, driving transitions from antiferromagnetic to NCL, and then to a double-cell NCL phase. The phase diagram can be described by a model with two dimensionless parameters. Large-scale tensor network simulations reveal starkly distinct chirality responses and magnetization plateaus under different magnitudes of magnetic fields for each phase, directly linking these behaviors to tunable frustration. Therefore, the multiferroic FeS nanotube provides a versatile platform for exploring electrically tunable quantum states, phase transitions, and field-induced phenomena associated with evolving magnetic frustration. This Letter establishes a general strategy combining first-principles prediction, confined structure search, and tensor networks for discovering and understanding frustrated low-dimensional quantum phenomena.

Excitonic insulators host the condensates of bound electron–hole pairs, offering a platform for studying correlated bosonic quantum states and for next-generation device applications. However, how macroscopic coherence emerges from locally collapsed pairing remains elusive. Here, using scanning tunnelling spectroscopy, we report the impurity-induced pair breaking in the excitonic insulator Ta₂Pd₃Te₅. Individual Te vacancies generate a pair of spectral peaks within the excitonic gap. Their energies depend sensitively on the defect configurations and are continuously tunable using tip electric field, indicating controllable impurity scatterings. Spectral mapping shows spatially anisotropic and electronically coupled electron–hole components of the subgap states. These observations, together with mean-field modelling, suggest an excitonic pair-breaking origin. In the strongly electron–hole-imbalanced region, a secondary pair-breaking effect, manifesting an additional pair of subgap states with distinctly lower energies, emerges and displays the interplay of pairing breakings with different excitonic order parameters. Our findings demonstrate the spectroscopic fingerprint of local excitonic depairing at the atomic level, offering a crucial clue to the critical behaviour across excitonic condensation.

Strong correlation, when combined with dissipation in open systems, can lead to a variety of exotic quantum phenomena. Here, we study nontrivial interplays between non-Fermi liquid behaviors emerging from strong correlation and non-Hermiticity arising from open systems. We propose a practical physical setup that realizes a non-Hermitian multichannel Kondo model. We identify a weak-coupling local moment fixed point and a strong-coupling non-Fermi liquid fixed point under PT symmetry, both are enriched by the non-Hermitian effect. Remarkably, universal unconventional Kondo conductance behaviors are found for both cases, which are distinct from all previously studied Kondo systems. Particularly, we show that an anomalous upturn of conductance could take place with increasing the temperature, originating from the interplay between non-Fermi liquid and non-Hermiticity. Our results identify a novel class of transport phenomena unrecognized before, driven by intertwined effects of correlation and dissipation.

Spinons are elementary excitations at the core of frustrated quantum magnets. Although it is well-established that a pair of spinons can emerge from a magnon via deconfinement, controlled manipulation of individual spinons and direct observation of their deconfinement remain elusive. We propose an artificial gauge field scenario that enables the engineering of specific excited states in quantum spin models. This generates spatially localized individual spinons with high controllability. By applying time-dependent gauge fields, we realize adiabatic braiding of these spinons, as well as their dynamical evolution in a controllable manner. These results not only provide the first direct visualization of individual spinons localized in the bulk, but also point to new possibilities to simulate their confinement process. Finally, we demonstrate the feasibility of our scenario in Rydberg atoms, which suggests an experimentally viable direction--gauge field engineering of correlated phenomena in excited states.

Quantum impurities can host exotic many-body states that serve as sensitive probes of bath correlations. However, quantitative and non-perturbative methods for determining impurity thermodynamics in such settings remain scarce. Here, we introduce an impurity renormalization group approach that merges the tensor-network representation with the numerical renormalization group cutoff scheme. This method overcomes conventional limitations by treating bath correlations and impurity interactions on an equal footing. Applying our approach to the finite-temperature quantum critical regime of quantum spin systems, we uncover striking impurity-induced phenomena. In a coupled Heisenberg ladder, the impurity triggers a fractionalization of the local magnetic moment. Moreover, the derivative of the impurity susceptibility develops cusps that mark the crossover into the quantum critical regime. We also observe an exotic evolution of the spin correlation function driven by the interplay between bath correlations and the impurity. Our results demonstrate that this method can efficiently solve correlated systems with defects, opening new pathways to discovering novel impurity physics beyond those in non-interacting thermal baths.

Excitonic insulators host the condensates of bound electron-hole pairs, offering a platform for studying correlated bosonic quantum states. Yet, how macroscopic coherence emerges from locally collapsed pairing remains elusive. Here, using scanning tunnelling spectroscopy, we report the impurity-induced pair breaking in an excitonic insulator Ta2Pd3Te5. Individual Te vacancies are found to generate a pair of spectral peaks within the excitonic gap. Their energies depend sensitively on the defect configurations and are continuously tunable by tip electric field, indicating controllable impurity scatterings. Spectral mapping shows spatially anisotropic and electronically coupled electron-hole components of the subgap states. These observations, together with mean-field modelling, suggest an excitonic pair-breaking origin. In the strongly electron-hole imbalanced region, a secondary pair-breaking effect, manifesting as an additional pair of subgap states with distinctly lower energies, can emerge, presenting the interplay of pairing breakings with different excitonic order parameters. Our findings demonstrate the spectroscopic 'fingerprint' of local excitonic depairing at the atomic level, offering a crucial clue to the critical behavior across excitonic condensation.

Spinons are elementary excitations at the core of frustrated quantum magnets. Although it is well established that a pair of spinons can emerge from a magnon via deconfinement, controlled manipulation of individual spinons and direct observation of their deconfinement remain elusive. We propose an artificial gauge field scenario that enables the engineering of specific excited states in quantum spin models. This generates spatially localized individual spinons with high controllability. By applying time-dependent gauge fields, we realize adiabatic braiding of these spinons, as well as their dynamical evolution in a controllable manner. These results not only provide the first direct visualization of individual spinons localized in the bulk, but also point to new possibilities to simulate their confinement process. Finally, we demonstrate the feasibility of our scenario in Rydberg atoms, which suggests an experimentally viable direction-gauge-field engineering of correlated phenomena in excited states.