Time-resolved charge transport measurement for one-dimensional edge states is a powerful means for investigating nonequilibrium charge dynamics and underlying interaction effects therein. Here, we report a versatile on-chip time-resolved transport measurement scheme that does not require a quantum point contact and is therefore applicable to narrow-gap systems. We apply the technique to noninverted $\mathrm{In}\mathrm{As}/{\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{Sb}$ composite quantum wells, where its ambipolar character enables us to demonstrate the scheme in both the electron and hole regimes separately using a single device. Time-resolved measurements in the quantum Hall regimes clearly exhibit the chirality of each carrier, with pulsed charge waveforms observed only for one magnetic field direction opposite for electrons and holes. Waveform analysis in the time domain reveals reduced group velocity and broadening of edge magnetoplasmon pulses in both the electron and hole regimes, suggesting the influence of charge puddles in the bulk. Our time-resolved measurement scheme, applicable to various systems, will pave the way for investigations of dynamical properties of exotic topological edge states.

In this paper, we use a Ginzburg-Landau approach to show that a suitably strong electric field can drive a phase transition from a superconductor to a normal metal. The transition is induced by taking into account corrections to the permittivity due to the superconductive gap and persists even when screening effects are considered. We test the model against recent experimental observations in which a strong electric field has been observed to control the supercurrent in superconducting thin films. We find excellent agreement with the experimental data and are able to explain several observed features. We additionally suggest a way to test our theoretical proposal via superconductor-superconductor electron tunneling.

We numerically demonstrate and characterize the emergence of distinct dynamical regimes of a finite-temperature bosonic superfluid in an elongated Josephson junction generated by a thin Gaussian barrier over the entire temperature range where a well-formed condensate can be clearly identified. Although the dissipation arising from the coupling of the superfluid to the dynamical thermal cloud increases with increasing temperature as expected, the importance of this mechanism is found to depend on two physical parameters associated (i) with the initial chemical potential difference, compared to some characteristic value, and (ii) the ratio of the thermal energy to the barrier amplitude. The former determines whether the superfluid Josephson dynamics are dominated by gradually damped plasmalike oscillations (for relatively small initial population imbalances), or whether dissipation at early times is instead dominated by vortex- and sound-induced dissipation (for larger initial imbalances). The latter defines the effect of the thermal cloud on the condensate dynamics, with a reversal of roles, i.e., the condensate being driven by the oscillating thermal cloud, being observed when the thermal particles acquire enough energy to overcome the barrier. Our findings are within current experimental reach in ultracold superfluid junctions.

We use a combination of symmetry analysis, phenomenological modeling, and first-principles density functional theory to explore the interplay between the magnetic ground state and the detailed atomic structure in the hexagonal rare-earth manganites. We find that the magnetic ordering is sensitive to a breathing mode distortion of the Mn and O ions in the $ab$ plane, which is described by the ${\mathrm{K}}_1$ mode of the high-symmetry structure. Our density functional calculations of the magnetic interactions indicate that this mode particularly affects the single-ion anisotropy and the interplanar symmetric exchanges. By extracting the parameters of a magnetic model Hamiltonian from our first-principles results, we develop a phase diagram to describe the magnetic structure as a function of the anisotropy and exchange interactions. This in turn allows us to explain the dependence of the magnetic ground state on the identity of the rare-earth ion and on the ${\mathrm{K}}_1$ mode.

Weyl semimetals are phases of matter with gapless electronic excitations that are protected by topology and symmetry. Their properties depend on the dimensions of the systems. It has been theoretically demonstrated that five-dimensional (5D) Weyl semimetals emerge as novel phases during the topological phase transition in analogy to the three-dimensional case. However, experimental observation of such a phenomenon remains a great challenge because the tunable 5D system is extremely hard to construct in real space. Here, we construct 5D electric circuit platforms in fully real space and experimentally observe topological phase transitions in five dimensions. Not only are Yang monopoles and linked Weyl surfaces observed experimentally, but various phase transitions in five dimensions are also proved, such as the phase transitions from a normal insulator to a Hopf link of two Weyl surfaces and then to a 5D topological insulator. The demonstrated topological phase transitions in five dimensions leverage the concept of higher-dimensional Weyl physics to control electrical signals in the engineered circuits.

We study theoretically a junction composed of a $\mathcal{PT}$-symmetric non-Hermitian superconductor (PTS) placed between two conventional superconductors. We show that due to non-Hermitian electron-electron interaction in the PTS region and the combination of symmetries, only discrete values of phases of the conventional superconductors yield solutions for Andreev bound states. Remarkably, in the case of phases 0 and $\pi$, we obtain Andreev bound states that are growing and decaying in time. For $\pi /2$ and $3\pi /2$, there is a Majorana zero mode penetrating through the junction in only one direction forming a quasiparticle supercurrent.

We study a Fermi gas with strong, tunable interactions dispersively coupled to a high-finesse cavity. Upon probing the system along the cavity axis, we observe a strong optomechanical Kerr nonlinearity originating from the density response of the gas to the intracavity field and measure it as a function of interaction strength. We find that the zero-frequency density response function of the Fermi gas increases by a factor of two from the Bardeen-Cooper-Schrieffer to the Bose-Einstein condensate regime. The results are in quantitative agreement with a theory based on operator-product expansion, expressing the density response in terms of universal functions of the interactions, the contact, and the internal energy of the gas. This provides an example of a driven-dissipative, strongly correlated system with a strong nonlinear response, opening up perspectives for the sensing of weak perturbations or inducing long-range interactions in Fermi gases.

We analyze the electronic structure of topological surface states in the family of magnetic topological insulators ${\mathrm{MnBi}}_{2n}{\mathrm{Te}}_{3n+1}$. We show that, at natural-cleavage surfaces, the Dirac cone warping changes its symmetry from hexagonal to trigonal at the magnetic ordering temperature. In particular, an energy splitting develops between the surface states of the same band index but opposite surface momenta upon formation of the long-range magnetic order. As a consequence, measurements of such energy splittings constitute a simple protocol to detect the magnetic ordering via the surface electronic structure, alternative to the detection of the surface magnetic gap. Interestingly, while the latter signals a nonzero surface magnetization, the trigonal warping predicted here is, in addition, sensitive to the direction of the surface magnetic flux. Our results may be particularly useful when the Dirac point is buried in the projection of the bulk states, caused by certain terminations of the crystal or in hole-doped systems, since in both situations the surface magnetic gap itself is not accessible in photoemission experiments.

Strange metals exhibit a variety of anomalous magnetotransport properties, the most striking of which is a resistivity that increases linearly with magnetic field $B$ over a broad temperature and field range. The ubiquity of this behavior across a spectrum of correlated metals—both single- and multiband, with either dominant spin and/or charge fluctuations, of varying levels of disorder or inhomogeneity, and in proximity to a quantum critical point or phase—obligates the search for a fundamental underlying principle that is independent of the specifics of any material. Strongly anisotropic (momentum-dependent) scattering can generate $B$-linear magnetoresistance but only at intermediate field strengths. At high enough fields, the magnetoresistance must eventually saturate. Here, we consider the ultimate limit of such anisotropy, a region or regions on the Fermi surface that impede all orbital (cyclotron) motion through them, but whose imposition can be modelled nonetheless through a modified Boltzmann theoretical treatment. Application of the proposed theorem suggests that the realization of quadratic-to-linear magnetoresistance requires the presence of a bounded sector on the Fermi surface possibly separating two distinct types of carriers. While this bounded sector may have different origins or manifestations, we expect its existence to account for the anomalous magnetotransport found in a wide range of correlated materials.

Optimally doped ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ (YBCO) has a high critical temperature, at 92 K. It is largely believed that Cooper pairs form in YBCO and other cuprates because of spin fluctuations, but the issue and the detailed mechanism are far from settled. In the present work, we employ a state-of-the-art first-principles ability to compute both the low- and high-energy spin fluctuations in optimally doped YBCO. We benchmark our results against recent inelastic neutron scattering and resonant inelastic x-ray scattering measurements. Further, we use strain as an external parameter to modulate the spin fluctuations and superconductivity. We disentangle the roles of barium-apical oxygen hybridization, interlayer coupling, and orbital symmetries by applying an idealized strain, and also a strain with a fully relaxed structure. We show that shortening the distance between Cu layers is conducive to enhanced Fermi surface nesting, which increases spin fluctuations and drives up $T_c$. However, when the structure is fully relaxed, electrons flow to the $d_{z^2}$ orbital as a consequence of a shortened Ba-O bond, which is detrimental for superconductivity.

Metalorganic chemical vapor deposition (MOCVD) has not been often used for studying exciton-polariton condensation and developing polaritonic devices, although it is a powerful mass productive method for practical applications. Here, we demonstrate that the MOCVD-grown GaAs-based microcavity can realize the nonequilibrium condensation of exciton-polariton. We obtained the Rabi splitting values of 10.1 meV in the angle-resolved reflectance spectrum from the MOCVD-grown microcavity. And, we also measured the angle-resolved photoluminescence depending on pumping power to observe condensation behaviors. Furthermore, we found that the occupancy distributions of polaritons are in a nonequilibrium state by fitting Bose-Einstein distributions. To realize the strong coupling and exciton-polariton condensation, we reduced the linewidth broadening of photoluminescence from quantum wells by optimizing growth conditions and designs.

The relaxor ferroelectric transition in ${\mathrm{Cd}}_2{\mathrm{Nb}}_2{\mathrm{O}}_7$ is thought to be described by the unusual condensation of two $\mathrm{\Gamma }$-centered phonon modes, ${\mathrm{\Gamma }}_4^{-}$ and ${\mathrm{\Gamma }}_5^{-}$. However, their respective roles have proven to be ambiguous, with disagreement between ab initio studies, which favor ${\mathrm{\Gamma }}_4^{-}$ as the primary mode, and global crystal refinements, which point to ${\mathrm{\Gamma }}_5^{-}$ instead. Here, we resolve this issue by demonstrating from x-ray pair distribution function measurements that locally, ${\mathrm{\Gamma }}_4^{-}$ dominates, but globally, ${\mathrm{\Gamma }}_5^{-}$ dominates. This behavior is consistent with the near degeneracy of the energy surfaces associated with these two distortion modes found in our own ab initio simulations. Our first-principles calculations also show that these energy surfaces are almost isotropic, providing an explanation for the numerous structural transitions found in ${\mathrm{Cd}}_2{\mathrm{Nb}}_2{\mathrm{O}}_7$, as well as its relaxor behavior. Our results point to several candidate descriptions of the local structure, some of which demonstrate two-in/two-out behavior for Nb displacements within a given Nb tetrahedron. Although this suggests the possibility of a charge analog of spin ice in ${\mathrm{Cd}}_2{\mathrm{Nb}}_2{\mathrm{O}}_7$, our results are more consistent with a Heisenberg-like description for dipolar fluctuations rather than an Ising one. We hope this encourages future experimental investigations of the Nb and Cd dipolar fluctuations, along with their associated mode dynamics.

We present a joint experimental and theoretical study of the driven Su-Schrieffer-Heeger model implemented by arrays of evanescently coupled plasmonic waveguides. Floquet theory predicts that this system hosts for suitable driving frequencies a topologically protected edge state that has no counterpart in static systems, the so-called anomalous Floquet topological $\pi$ mode. By using real- and Fourier-space leakage radiation microscopy in combination with edge and bulk excitation, we unequivocally identify the anomalous Floquet topological $\pi$ mode and study its frequency dependence.

Non-Hermitian quantum systems can exhibit spectral degeneracies known as exceptional points, where two or more eigenvectors coalesce, leading to a nondiagonalizable Jordan block. It is known that symmetries can enhance the abundance of exceptional points in noninteracting systems. Here we investigate the fate of such symmetry protected exceptional points in the presence of a symmetry preserving interaction between fermions and find that (i) exceptional points are stable in the presence of the interaction. Their propagation through the parameter space leads to the formation of characteristic exceptional “fans.” In addition, (ii) we identify a new source for exceptional points which are only present due to the interaction. These points emerge from diagonalizable degeneracies in the noninteracting case. Beyond their creation and stability, (iii) we also find that exceptional points can annihilate each other if they meet in parameter space with compatible many-body states forming a third order exceptional point at the endpoint. These phenomena are well captured by an “exceptional perturbation theory” starting from a noninteracting Hamiltonian.

Quantum link models have attracted a lot of attention in recent times as a generalization of Wilson's lattice gauge theories, and are particularly suitable for realization on quantum simulators and computers. These models are known to host new phases of matter and act as a bridge between particle and condensed matter physics. In this paper, we study the Abelian $\text{U}\left(1\right)$ lattice gauge theory in $(3+1)\mathrm{D}$ tubes using large-scale exact diagonalization. We are then able to motivate the phase diagram of the model with finite-size scaling techniques, and in particular propose the existence of a Coulomb phase. Furthermore, we introduce models involving fermionic quantum links, which generalize the gauge degrees of freedom to be of fermionic nature. We prove that while the spectra remain identical between the bosonic and the fermionic versions of the $\text{U}\left(1\right)$-symmetric quantum link models in $(2+1)\mathrm{D}$, they are different in $(3+1)\mathrm{D}$. We discuss the prospects of realizing the magnetic field interactions as correlated hopping in quantum simulator experiments.

A pyrite system ${\mathrm{NiS}}_{2-x}{\mathrm{Se}}_x$ exhibits a bandwidth controlled Mott transition via (S,Se) substitutions in a two-step process: the antiferromagnetic insulator (AFI) to antiferromagnetic metal (AFM) transition at $x\sim 0.45$ followed by the AFM to paramagnetic metal (PMM) transition at $x\sim 1.0$. Among a few other Mott systems which exhibit similar two-step transitions, $\mathrm{Ni}{(\mathrm{S},\mathrm{Se})}_2$ is of particular interest because a large intermediate AFM region in the phase diagram would provide unique opportunities to study the interplay between the spin and charge order. Muon spin relaxation ($\mu \mathrm{SR}$) measurements on ${\mathrm{NiS}}_{2-x}{\mathrm{Se}}_x$ have been carried out on seven different Se concentrations from $x=0$ to 1.0. The results on quantum evolution demonstrate significantly random spin correlations in the AFM region associated with a rapid reduction of the average local static Ni moment size with increasing $x$, yet without signatures of macroscopic phase separation as confirmed by nearly full volume fraction participating in the static muon relaxation process up to $x\sim$ 0.9 at low temperatures. The observed time spectra in the AFM region indicate Lorentzian distribution of static internal field expected for a spatially dilute spin structure. No signature of dynamic critical behavior was observed in thermal phase transitions. The previous neutron scattering studies found sharp magnetic Bragg peaks with a slower reduction of the average ordered moment size in the AFM region. By comparing and combining the muon and neutron results, here we propose a picture where the spin order is maintained by the percolation of “nonmetallic” localized and dangling Ni moments surrounded by S, while the charge transition from AFI to AFM is caused by the percolation of the conducting paths generated by the Ni-Se-Ni bonds. This model of interpenetrating charge and spin percolation captures the behavior of experimental results on (a) Se concentration for the insulator to metal transition, (b) Se concentration for the AFM to PMM transition, (c) variation of Hall effect in the AFM region due to conducting Ni charges on the backbone of the percolating charge network, (d) evolution of the neutron Bragg intensity, (e) evolution of the muon static local fields, and (f) spatial variation of the local conductance observed by STM.

It is well established that the ground-state electron configuration of the octahedral ${\mathrm{Co}}^{3+}$ ion is $t_{2\mathrm{g}}^6{e}_{\mathrm{g}}^0$, which corresponds to a low-spin (LS) state. However, we theoretically demonstrate that the octahedral ${\mathrm{Co}}^{3+}$ ion in ${\mathrm{Co}}_3{\mathrm{S}}_4$ prefers a high-spin (HS) state with the $t_{2\mathrm{g}}^4{e}_{\mathrm{g}}^2$ configuration, resulting in unusual magnetism. The density-functional theory plus $U$ calculation and ligand-field theory show that weak crystal-field splitting associated with ${\mathrm{S}}^{2-}$ induces a spin crossover from the LS to HS state of the octahedral ${\mathrm{Co}}^{3+}$ ion along with a weak Jahn-Teller-like elongation, and as a result, a ferromagnetic (FM) metal phase is energetically stabilized. Nevertheless, this phase is significantly more stable than the antiferromagnetic (AFM) phase experimentally reported at low temperature. Furthermore, phonon calculations suggest that the FM metal phase is possibly one of the ${\mathrm{Co}}_3{\mathrm{S}}_4$ polymorphs, appearing in the certain experimental growth environment, but it is not expected to appear due to a temperature-dependent transition from the AFM phase. In addition, the Lyons, Kaplan, Dwight, and Menyuk theory shows that this phase is further expected to undergo a phase transition to the frustrated magnetic state. We believe that our work provides insight into magnetism of cobalt compounds and also paves the way to achieve the HS ${\mathrm{Co}}^{3+}$ by design.

In some Dirac systems with time-reversal ($\mathcal{T}$) and glide ($\mathcal{G}$) symmetries, multihelicoid surface states (MHSSs) appear, as discussed in various systems such as electronic and photonic ones. However, the topological nature and the conditions for the appearance of the MHSSs have not been understood. Here we show that MHSSs result from bulk-surface correspondence for the $Z_2$ monopole charge $\mathcal{Q}$, which cannot be defined as a local quantity associated with the Dirac point, unlike the $Z$ monopole charge characterizing Weyl points. The previously known formula of $\mathcal{Q}$ turns out to be non-gauge-invariant and thus cannot characterize the MHSSs. This shortcoming of the definition of $\mathcal{Q}$ is amended by redefining $\mathcal{Q}$ as a global topological invariant in $k$-space. Surprisingly, the newly defined $\mathcal{Q}$, characterizing $\mathcal{GT}$ invariant gapless systems, is equal to the $\mathcal{G}$-protected $Z_2$ topological invariant $\nu$, which is nontrivial only in $\mathcal{T}$-breaking gapped systems. This global definition of $\mathcal{Q}$ automatically guarantees the appearance of MHSSs even when the Dirac point splits into Weyl points or a nodal ring by lowering the symmetry, as long as the $\mathcal{GT}$ symmetry is preserved. $\mathcal{Q}$ can be simplified to symmetry-based indicators when two vertical $\mathcal{G}\mathrm{s}$ are preserved, and filling-enforced topological crystalline insulators are diagnosed in several cases when a $\mathcal{T}$-breaking perturbation is induced. Material candidate ${\mathrm{Li}}_2{\mathrm{B}}_4{\mathrm{O}}_7$ together with a list of space groups preserving MHSSs are also proposed.

The bismuth-based half-Heusler materials host a nontrivial topological band structure, unconventional superconductivity, and large spin-orbit coupling in a system with very low electron density. In particular, the inversion of $p$-orbital-derived bands with an effective angular momentum $j$ of up to 3/2 is thought to play a central role in anomalous Cooper pairing in the cubic half-Heusler semimetal YPtBi, which is thought to be the first “high-spin” superconductor. Here, we report an extensive study of the angular dependence of quantum oscillations (QOs) in the electrical conductivity of YPtBi, revealing an anomalous Shubnikov–de Haas effect consistent with the presence of a coherent $j=3/2$ Fermi surface. The QO signal in YPtBi manifests an extreme anisotropy upon rotation of the magnetic field from the [100] to [110] crystallographic direction, where the QO amplitude vanishes. This radical anisotropy for such a highly isotropic system cannot be explained by trivial scenarios involving changes in effective mass or impurity scattering, but rather is naturally explained by the warping feature of the $j=3/2$ Fermi surface of YPtBi, providing direct proof of active high angular momentum quasiparticles in the half-Heusler compounds.

In confined nanoscale structures, such as nanopores or nanotubes, the polar characteristic of water can be evident; while in bulk or droplet form, it is masked by the statistical molecular arrangements dictated by free energy minimization. In this paper, we show that, under an applied electric field, the polar character of water molecules enables the formation of macroscopic scale columns of water vapor penetrating through a silicone oil bath. These columns are up to 60 μm in length and tens of microns in cross-sectional dimension. We have directly visualized such columns by using water-soluble fluorescent molecules dispersed in silicone oil. The polar nature of columns is evidenced by the measured giant electrorheological effect that correlates with the application of an electric field. We present a phenomenological theory to support our observations and show that the experimental data are consistent with a state of highly aligned water molecular dipoles within each column.