Physical Review B

The $p$-$n$ junction is at the heart of the first great technological revolution. Here, the authors fabricate and characterize such a junction made entirely out of cuprates superconductors thin films. They observe a charge transfer between $n$-type Pr${}_{1.85}$Ce${}_{0.15}$CuO${}_4$ and $p$-type La${}_{1.85}$Sr${}_{0.15}$CuO${}_4$, from which a Mott insulating layer emerges at the atomically sharp interface. They first assess the quality of the structure through x-ray diffraction and scanning transmission electron microscopy and then they explore the nature of the insulating interface arising from strong electron correlations with various electrical transport experiments.

CrAs undergoes a first-order helimagnetic transition accompanied by a huge lattice distortion whose microscopic mechanism remains unresolved. Here, the authors demonstrate through stress-strain measurements that the helimagnetic transition in CrAs is substantially more sensitive to uniaxial stress than to hydrostatic pressure. First-principles calculations reveal that this strong response originates from an entanglement between anisotropic strain and orbital-dependent correlations, showing that local correlations can drive nonlinear elastic responses in strongly correlated systems.

Here, the authors combine first-principles dynamical mean-field theory (DMFT), epitaxial materials design, angle-resolved photoemission spectroscopy, and scanning tunneling microscopy/spectroscopy to show that superconductivity in monolayer FeSe/SrTiO${}_3$ is maximized at a magic FeSe${}_4$ tetrahedral angle. They demonstrate that strong electronic correlations, captured by DMFT, substantially enhance electron-phonon coupling within the FeSe layer and produce a superconducting dome. These findings reveal the microscopic origin of enhanced superconductivity and suggest a route for engineering higher-temperature superconductors.

Elucidating the origin of the pseudogap remains a central challenge in copper oxide high‑$T_c$ superconductors. By investigating the magnetotransport properties of Bi‑2212 and Bi‑2223 single crystals, the authors demonstrate here that the pseudogap and superconducting fluctuations are distinct phenomena. Their results strongly suggest that the pseudogap arises from preformed Cooper pairing in the BCS–BEC crossover regime, imposing stringent constraints on theoretical descriptions of high‑$T_c$ cuprates beyond the conventional BCS paradigm.

Zinc telluride (ZnTe) is widely used to generate and detect terahertz radiation with 800-nm laser pulses, yet its dielectric response at typical THz generation intensities remains unclear. Here, the authors show that two-photon absorption creates a transient free-carrier plasma strongly coupled to the lattice, modifying the THz dielectric function and markedly enhancing the 1.55-THz phonon resonance. These findings refine the physical description of THz generation in ZnTe and identify excitation-induced constraints on efficiency and bandwidth.

Two-dimensional moiré materials feature widely tunable electronic structures. When these materials are illuminated by light, they exhibit optical gyrotropy in the form of circular dichroism and birefringence. Here, the authors show that this gyrotropy naturally decomposes into an intrinsic contribution due to interlayer electronic coupling and an extrinsic contribution due to the twisted embedding of the material in physical space. The authors conduct a general symmetry analysis applicable to moiré materials and identify regimes in which the intrinsic, and in which the extrinsic contributions dominate the gyrotropy. Finally, they apply the analysis to twisted bilayer graphene and twisted MoTe${}_2$.

Here, the authors demonstrate how, in single nanomagnets and pairs of dipolar-coupled nanomagnets, the orientation of the applied electric current affects the threshold current density for field-free, all-electrical magnetization switching. Extending this approach to artificial spin ices, it is demonstrated how dipolar interactions influence the nanomagnet switching and enable selective control of their magnetization. These results provide a pathway toward programmable manipulation of dipolar-coupled nanomagnetic devices.

Understanding the properties of helium in diamond is crucial for geological dating and possible quantum applications. Here, the authors determine the lattice location of ion-implanted short-lived ${}^6$He in single-crystal diamond at temperatures from 30°C to 800°C using the β${}^{-}$ emission channeling technique. ${}^6$He preferentially occupies tetrahedral interstitial sites. From the temperature dependence of the interstitial fraction, the migration energy of He is estimated at 1.63–2.89 eV, implying unbound interstitial helium is unstable in diamond over geological timescales, an important insight to be considered in He-based dating methods.

The Lieb-Schultz-Mattis (LSM) theorem powerfully constrains the low-energy behavior of quantum many-body systems. In spin systems with spin rotation and conventional (Euclidean) lattice translation symmetries, it forbids a unique, gapped, symmetric ground state at half-odd-integer spin per unit cell. Here, the authors generalize this theorem to hyperbolic lattices — synthetic structures that emulate negatively curved space. Unlike Euclidean lattice translations, hyperbolic translations are noncommutative. By adapting a flux-threading argument, the authors derive LSM constraints on gapped phases of hyperbolic quantum matter.

The authors introduce here a general electromagnetic multipole expansion, in which the scattering current density is expanded instead of the scattered field. The multipole moments obtained represent simple current configurations and can easily be calculated for an arbitrary multipole order and for scatterers of arbitrary sizes and shapes. They are connected to the conventional field-based moments by simple linear relations, providing a rigorous basis for intuitive design and analysis of complex scattering systems, such as electromagnetic anapoles and chiral structures.

The authors introduce here many-body Euler numbers as a counterpart to many-body Chern numbers to diagnose the spontaneous breaking of time reversal symmetry in (fractional) Chern insulators. In addition, a classification scheme to realize different topological phases in interacting systems using symmetry indicators is laid out.

The carrier mobility in many materials is dominated by scattering of the carriers with phonons. It is often calculated using only linear, one-electron–one-phonon interaction. Here, the authors present a first-principles calculation of the mobility including the nonlinear, long-range electron-phonon interaction, for the representative halide perovskite CsPbI${}_3$. It is shown that the temperature dependence of the carrier mobility decreases by about 10% due to the one-electron–two-phonon interaction, which is attributed to the strong anharmonicity and low phonon frequencies present in halide perovskites.

Vestigial orders are partially melted versions of ordered states stabilized by fluctuations of the order parameter. Observed in several quantum materials, their theoretical description has often relied on a large-$N$ approximation that suffers from ambiguities due to multiple interfering channels. Here, the authors uncover the structural reasons for the ambiguities and from them derive a large-$N$ prescription that removes the ambiguities, yielding unequivocal physical results. This prescription is then applied to multicomponent density wave and superconducting instabilities, where they find exotic vestigial phases describing spin-quadrupolar, charge-4$e$ superconducting, and altermagnetic orders.

Rapid advances in nonlinear Hall transport provide new probes of quantum geometry, but transverse signals generally mix Hall and non-Hall contributions that are difficult to disentangle. Here, the authors introduce a unified experimental protocol that exchanges current and voltage directions to identify antisymmetric Hall and symmetric non-Hall responses. Measurements across representative quantum materials validate the method in both linear and nonlinear regimes.

Disorder strongly modifies the collective electronic state of one-dimensional Josephson junction arrays. However, identifying types of disorder and understanding their link to collective behavior remain challenging. Here, the authors find three classes of fabrication-induced structural disorder and investigate their effects on critical-voltage scaling of arrays in the insulating state. While the scaling remains remarkably robust against some fabrication-induced variations, arrays containing nanoscale gaps exhibit significantly different behavior, demonstrating that the nature of disorder influences the collective state of the system.

The interacting electron-phonon problem has long been studied within the linear coupling approximation, which can break down in the strong-coupling limit. Here, the authors develop an $ab$ $initio$ theory that enables the calculation of the full nonlinear electron-phonon coupling matrix. With this development, the authors demonstrate the critical role of nonlinear couplings in electron-phonon physics by analyzing its impact on the small hole polaron in lithium fluoride.

Ferromagnetic quantum critical points can be masked by emerging modulated magnetic order. Here, the authors use neutron diffraction to show that the example of NbFe${}_2$ provides the first case, where the masking modulated order is a longitudinal spin-density wave. The latter has a large-wavelength incommensurate modulation of its low average moment and is formed from ferrimagnetic building blocks with antiparallel ferromagnetic sheets. The findings can serve as a test case for magnetic quantum order-by-disorder models.