Superconducting nickelates appear to be difficult to synthesize. Since the chemical reduction of $AB{\mathrm{O}}_3$ [rare earth ($A$), transition metal ($B$)] with ${\mathrm{CaH}}_2$ may result in both $AB{\mathrm{O}}_2$ and $AB{\mathrm{O}}_2\mathrm{H}$, we calculate the topotactic H binding energy by density functional theory (DFT). We find intercalating H to be energetically favorable for ${\mathrm{LaNiO}}_2$ but not for Sr-doped ${\mathrm{NdNiO}}_2$. This has dramatic consequences for the electronic structure as determined by $\mathrm{DFT}+\mathrm{dynamical}$ mean field theory: that of $3d^9$ ${\mathrm{LaNiO}}_2$ is similar to (doped) cuprates, $3d^8$ ${\mathrm{LaNiO}}_2\mathrm{H}$ is a two-orbital Mott insulator. Topotactic H might hence explain why some nickelates are superconducting and others are not.

Using the density functional theory combined with dynamical mean-field theory, we have performed systematic study of the electronic structure and its band topology properties of ${\mathrm{Ce}}_3{\mathrm{Pt}}_3{\mathrm{Bi}}_4$ and ${\mathrm{Ce}}_3{\mathrm{Pd}}_3{\mathrm{Bi}}_4$. At high temperatures ($\sim 290\mathrm{K}$), the electronic structures of both compounds resemble the open-core $4f$ density functional calculation results. For ${\mathrm{Ce}}_3{\mathrm{Pt}}_3{\mathrm{Bi}}_4$, clear hybridization gap can be observed below 72 K, and its coherent momentum-resolved spectral function below 18 K exhibits an topologically trivial indirect gap of $\sim 6\mathrm{meV}$ and resembles density functional band structure with itinerant $4f$ state. For ${\mathrm{Ce}}_3{\mathrm{Pd}}_3{\mathrm{Bi}}_4$, no clear hybridization gap can be observed down to 4 K, and its momentum-resolved spectral function resembles electron-doped open-core $4f$ density functional calculations. The band nodal points of ${\mathrm{Ce}}_3{\mathrm{Pd}}_3{\mathrm{Bi}}_4$ at 4 K are protected by the gliding-mirror symmetry and form ringlike structure. Therefore, the ${\mathrm{Ce}}_3{\mathrm{Pt}}_3{\mathrm{Bi}}_4$ compound is topologically trivial Kondo insulator while the ${\mathrm{Ce}}_3{\mathrm{Pd}}_3{\mathrm{Bi}}_4$ compound is topological nodal-line semimetal.

Berry phase, the geometric phase accumulated over a closed loop in parameter space during an adiabatic cyclic evolution, has been demonstrated to play an important role in many quantum systems since its discovery. In gapped Bernal bilayer graphene, the Berry phase can be continuously tuned from zero to $2\pi$, which offers a unique opportunity to explore the tunable Berry phase on physical phenomena. Here, we report experimental observation of Berry-phase-induced valley splitting and crossing in movable bilayer-graphene $p\text{−}n$ junction resonators. In our experiment, the resonators are generated by combining the electric field of a scanning tunneling microscope tip with the gap of bilayer graphene. A perpendicular magnetic field changes the Berry phase of the confined bound states in the resonators from zero to $2\pi$ continuously and leads to the Berry phase difference for the two inequivalent valleys in the bilayer graphene. As a consequence, we observe giant valley splitting and unusual valley crossing of the lowest bound states. Our results indicate that the bilayer-graphene resonators can be used to manipulate the valley degree of freedom in valleytronics.

A prime category of superconducting materials in which to look for spin-triplet pairing and topological superconductivity are superconductors without inversion symmetry. It is predicted that the broken parity symmetry gives rise to an admixture of spin-triplet and spin-singlet pairing states. However, experimental confirmation of pairing mixing in any material remains elusive. In this work, we perform a phase-sensitive experiment to examine the pairing state of noncentrosymmetric superconductor $\alpha$-BiPd. The Little-Parks effect observed in mesoscopic polycrystalline $\alpha$-BiPd rings reveals the presence of half-integer magnetic flux quantization, which provides a decisive evidence for the spin-triplet pairing state. We find both half-quantum fluxes and integer-quantum fluxes of different proportions, consistent with the scenario of an admixture of singlet-triplet pairing.

The magnetic moment of rare earth elements originates from electrons in the partially filled $4f$ orbitals. Accessing this moment electrically by scanning tunneling spectroscopy is hampered by shielding of outerlying orbitals. Here, we show that we can detect the magnetic moment of an individual Ce atom adsorbed on a ${\mathrm{Cu}}_2\mathrm{N}$ ultrathin film on Cu(100) by using a sensor tip that has its apex functionalized with a Kondo screened spin system. We calibrate the sensor tip by deliberately coupling it to a well characterized Fe atom. Subsequently, we use the splitting of the tip’s Kondo resonance when approaching a spectroscopically dark Ce atom to sense its magnetic moment.

Spin-1 antiferromagnets are abundant in nature, but few theories exist to understand their properties and behavior when geometric frustration is present. Here we study the $S=1$ kagome compound ${\mathrm{Na}}_2{\mathrm{Ti}}_3{\mathrm{Cl}}_8$ using a combination of density functional theory, exact diagonalization, and density matrix renormalization group approaches to achieve a first principles supported explanation of its exotic magnetic phases. We find that the effective magnetic Hamiltonian includes essential non-Heisenberg terms that do not stem from spin-orbit coupling, and both trimerized and spin-nematic magnetic phases are relevant. The experimentally observed structural transition to a breathing kagome phase is driven by spin-lattice coupling, which favors the trimerized magnetic phase against the quadrupolar one. We thus show that lattice effects can be necessary to understand the magnetism in frustrated magnetic compounds and surmise that ${\mathrm{Na}}_2{\mathrm{Ti}}_3{\mathrm{Cl}}_8$ is a compound that cannot be understood from only electronic or only lattice Hamiltonians, very much like ${\text{VO}}_2$.

The antiferromagnetic (AFM) compound ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ is suggested to be the first realization of an AFM topological insulator. We report on inelastic neutron scattering studies of the magnetic interactions in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ that possess ferromagnetic triangular layers with AFM interlayer coupling. The spin waves display a large spin gap and pairwise exchange interactions within the triangular layer are long ranged and frustrated by large next-nearest neighbor AFM exchange. The degree of frustration suggests proximity to a variety of magnetic phases, potentially including skyrmion phases, which could be accessed in chemically tuned compounds or upon the application of symmetry-breaking fields.

The phonon linewidth of isotopically controlled hexagonal boron nitride ($h$-BN) single crystals has been determined by Raman scattering. The scattering by isotopic mass disorder induces a phonon broadening that is largest for boron 11 fractions around 0.65. Lowest-order perturbation theory does not suffice to explain the dependence of the isotopic broadening on isotopic composition. A multiple-scattering theory based on the coherent potential approximation provides a good quantitative account of the phonon shift and broadening with isotopic composition observed in the experiments. Isotopic-disorder scattering is shown to have a prominent role in limiting the optical-phonon lifetime in $h$-BN

The evolution of the charge carrier concentrations and mobilities are examined across the charge-density-wave (CDW) transition in ${\mathrm{TiSe}}_2$. Combined quantum oscillation and magnetotransport measurements show that a small electron pocket dominates the electronic properties at low temperatures while an electron and hole pocket contribute at room temperature. At the CDW transition, an abrupt Fermi surface reconstruction and a minimum in the electron and hole mobilities are extracted from two-band and Kohler analysis of magnetotransport measurements. The minimum in the mobilities is associated with the overseen role of scattering from the softening CDW mode. With the carrier concentrations and dynamics dominated by the CDW and the associated bosonic mode, our results highlight ${\mathrm{TiSe}}_2$ as a prototypical system to study the Fermi surface reconstruction at a density-wave transition.

We study the nonequilibrium interaction of two isotropic chemically active particles taking into account the exact near-field chemical interactions as well as hydrodynamic interactions. We identify regions in the parameter space wherein the dynamical system describing the two particles can have a fixed point—a phenomenon that cannot be captured under the far-field approximation. We find that, due to near-field effects, the particles may reach a stable equilibrium at a nonzero gap size or make a complex that can dissociate in the presence of sufficiently strong noise. We explicitly show that the near-field effects originate from a self-generated neighbor-reflected chemical gradient, similar to interactions of a self-propelling phoretic particle and a flat substrate.

Metastatic cancer cells detect the direction of lymphatic flow by self-communication: they secrete and detect a chemical which, due to the flow, returns to the cell surface anisotropically. The secretion rate is low, meaning detection noise may play an important role, but the sensory precision of this mechanism has not been explored. Here we derive the precision of flow sensing for two ubiquitous detection methods: absorption vs reversible binding to surface receptors. We find that binding is more precise due to the fact that absorption distorts the signal that the cell aims to detect. Comparing to experiments, our results suggest that the cancer cells operate remarkably close to the physical detection limit. Our prediction that cells should bind the chemical reversibly, not absorb it, is supported by endocytosis data for this ligand-receptor pair.

A general thermodynamic framework is presented for open quantum systems in fixed contact with a thermal reservoir. The first and second law are obtained for arbitrary system-reservoir coupling strengths, and including both factorized and correlated initial conditions. The thermodynamic properties are adapted to the generally strong coupling regime, approaching the ones defined for equilibrium, and their standard weak-coupling counterparts as appropriate limits. Moreover, they can be inferred from measurements involving only system observables. Finally, a thermodynamic signature of non-Markovianity is formulated in the form of a negative entropy production rate.

The formation and decay of dark matter (DM) bound states deplete the thermal relic density during the chemical decoupling process, allowing for larger DM masses. While so far the bound state formation (BSF) has been described via the emission of an on-shell mediator, we point out that this particular process does not have to be the dominant one in general. If the mediator is coupled in a direct way to any relativistic species present in the early Universe, we demonstrate that BSF can much more efficiently occur through particle scattering. Consequently, DM can be heavier than previously expected.

Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of $2.40\sigma$ and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions.

The ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ reaction is one of the most crucial reactions in nuclear astrophysics. The $E2$ external capture to the ${}^{16}\mathrm{O}$ ground state (GS) has not been emphasized in previous analyses but may make a significant contribution to the ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ cross section depending on the value of the GS asymptotic normalization coefficient (ANC). In the present work, we determine this ANC to be $337\pm 45{\mathrm{fm}}^{-1/2}$ through the ${}^{12}\mathrm{C}({}^{11}\mathrm{B},{}^7\mathrm{Li}){}^{16}\mathrm{O}$ reaction using a high-precision magnetic spectrograph. This sheds light on the existing large discrepancy of more than 2 orders of magnitude between the previously reported ANC values. Based on the new ANC, we experimentally constrain the GS external capture and show that through interference with the high energy tail of the $2^{+}$ subthreshold state, a substantial enhancement in the GS $S_{E2}(300)$ factor can be obtained ($70\pm 7\mathrm{keV}\mathrm{b}$) compared to that of a recent review (45 keV b), resulting in an increase of the total $S$ factor from 140 to 162 keV b, which is now in good agreement with the value obtained by reproducing supernova nucleosynthesis calculations with the solar-system abundances. This work emphasizes that the external capture contribution for the ground state transition cannot be neglected in future analyses of the ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ reaction.

We demonstrate the possibility of realizing Young’s double-slit interference in a hydrogen atom via ab initio simulations. By exposing the hydrogen atom to a high-frequency intensive laser pulse, the bound state distorts into a dichotomic Kramers-Henneberger state whose photoelectron momentum distribution imprints a double-slit interference structure. The dichotomic hydrogen atom presents molecular peculiarities, such as charge-resonance enhanced ionization, electron spin flipping due to the non-Abelian Berry phase. In return, the photoelectron momentum distribution carrying the double-slit interference structure provides unambiguous evidence on the existence of Kramers-Henneberger states, and thus the adiabatic stabilization.

Out of equilibrium systems under the influence of enough energy injection exhibit complex spatiotemporal behaviors. Based on a liquid crystal light valve experiment with translational optical feedback, we observe propagation, spatiotemporal intermittency, and defect turbulence of striped waves. A prototype model of pattern formation with translational coupling shows the same phenomenology. Close to the spatial instability, a local amplitude equation is derived. This amplitude equation allows us to reveal the origin and bifurcation diagram of the observed complex spatiotemporal dynamics. Experimental observations have a qualitative agreement with theoretical findings.

Motivated by the recent observation of an anomalous Hall effect in twisted bilayer graphene, we use a lowest Landau level model to understand the origin of the underlying symmetry-broken correlated state. This effective model is rooted in the occurrence of Chern bands which arise due to the coupling between the graphene device and its encapsulating substrate. Our model exhibits a phase transition from a spin-valley polarized insulator to a partial or fully valley unpolarized metal as the bandwidth is increased relative to the interaction strength, consistent with experimental observations. In sharp contrast to standard quantum Hall ferromagnetism, the Chern number structure of the flat bands precludes an instability to an intervalley coherent phase, but allows for an excitonic vortex lattice at large interaction anisotropy.

Chirality-induced spin transport phenomena are investigated at room temperature without magnetic fields in a monoaxial chiral dichalcogenide ${\mathrm{CrNb}}_3{\mathrm{S}}_6$. We found that spin polarization occurs in these chiral bulk crystals under a charge current flowing along the principal $c$ axis. Such phenomena are detected as an inverse spin Hall signal which is induced on the detection electrode that absorbs polarized spin from the chiral crystal. The inverse response is observed when applying the charge current into the detection electrode. The signal sign reverses in the device with the opposite chirality. Furthermore, the spin signals are found over micrometer length scales in a nonlocal configuration. Such a robust generation and protection of the spin-polarized state is discussed based on a one-dimensional model with an antisymmetric spin-orbit coupling.