The square Bi layers in $A{\mathrm{MnBi}}_2$ ($A=$ Sr, Ca) host Dirac fermions which coexist with antiferromagnetic order on the Mn sublattice below $T_{\mathrm{N}}=290$ K (Sr) and 265 K (Ca). We have measured the spin-wave dispersion in these materials by triple-axis neutron spectroscopy. The spectra show pronounced spin gaps of $10.2\left(2\right)\mathrm{meV}$ (Sr) and $8.3\left(8\right)\mathrm{meV}$ (Ca) and extend to a maximum energy transfer of 61–63 meV. The observed spectra can be accurately reproduced by linear spin-wave theory from a Heisenberg effective spin Hamiltonian. Detailed global fits of the full magnon dispersion are used to determine the in-plane and interlayer exchange parameters as well as well as the magnetocrystalline anisotropy constant. To within experimental error we find no evidence that the magnetic dynamics are influenced by the Dirac fermions.

$L{1}_0-\mathrm{FePt}/\mathrm{NiO}/A1-\mathrm{FePt}$ trilayers have been grown on MgO(001) substrate, in which the top FePt layer is of $A1$ structure, and the bottom FePt layer is of $L{1}_0$ structure with 001 preferred orientation and strong perpendicular anisotropy. This structure gives rise to a ${90}^{\circ }$ spin alignment configuration of the two ferromagnetic layers across the NiO spacer. To further manipulate the spin configurations of the trilayer structure, we performed an in-plane field cooling (FC). The subsequent hysteresis measurements for the top FePt layer show unambiguous angular dependence of remanent magnetization relative to the direction of the field during FC; i.e., in-plane anisotropy is induced. Taking into account the spin-flop configuration predicted in previous theoretical study, the coupling at the lower interface makes the Ni spins cant out of the $\left(\overline{1}\overline{1}1\right)$ easy plane, and difficult to rotate around the axis perpendicular to the film plane. Correspondingly, the induced anisotropy after FC is considered to result from the realignment of Ni spins and enhancement of the coupling at the upper interface. The magnetic domain imaging results for the bottom perpendicular magnetized FePt layer strongly support this consideration; some of the stripe domains tend to be along the direction of the applied field during FC with reduced stripe width.

Quantum channels can describe all transformations allowed by quantum mechanics. We adapt two existing works [S. Lloyd and L. Viola, Phys. Rev. A 65, 010101 (2001) and E. Andersson and D. K. L. Oi, Phys. Rev. A 77, 052104 (2008)] to superconducting circuits, featuring a single qubit ancilla with quantum nondemolition readout and adaptive control. This construction is efficient in both ancilla dimension and circuit depth. We point out various applications of quantum channel construction, including system stabilization and quantum error correction, Markovian and exotic channel simulation, implementation of generalized quantum measurements, and more general quantum instruments. Efficient construction of arbitrary quantum channels opens up exciting new possibilities for quantum control, quantum sensing, and information processing tasks.

We study the transmission of a disordered waveguide subjected to a finite bias field. The statistical distribution of transmission is analytically shown to take a universal form. It depends on a single parameter, the system length expressed in a rescaled metrics, which encapsulates all the microscopic features of the medium and the bias field. Excellent agreement with numerics is found for various models of disorder and bias field. For white-noise disorder and a linear bias field, we demonstrate the algebraic nature of the decay of the transmission with distance, irrespective of the value of the bias field. It contrasts with the expansion of a wave packet, which features a delocalization transition for large bias field. The difference is attributed to the different boundary conditions for the transmission and expansion schemes. The observability of these effects in conductance measurements for electrons or ultracold atoms is discussed, taking into account key features, such as finite-range disorder correlations, nonlinear bias fields, and finite temperatures.

Crystal structure prediction methods and first-principles calculations have been used to explore low-energy structures of carbon monoxide (CO). Contrary to the standard wisdom, the most stable structure of CO at ambient pressure was found to be a polymeric structure of $Pna{2}_1$ symmetry rather than a molecular solid. This phase is formed from six-membered (four carbon + two oxygen) rings connected by C=C double bonds with two double-bonded oxygen atoms attached to each ring. Interestingly, the polymeric $Pna{2}_1$ phase of CO has a much higher energy density than trinitrotoluene (TNT). On compression to about 7 GPa, $Pna{2}_1$ is found to transform into another chainlike phase of $Cc$ symmetry which has similar ring units to $Pna{2}_1$. On compression to 12 GPa, it is energetically favorable for CO to polymerize into a purely single bonded $Cmca$ phase, which is stable over a wide pressure range and transforms into the previously known $Cmcm$ phase at around 100 GPa. Thermodynamic stability of these structures was verified using calculations with different density functionals, including hybrid and van der Waals corrected functionals.

We report formation of magnetic textures in the ferromagnetic (FM) phase of $\mathrm{L}{\mathrm{a}}_{1-x}\mathrm{S}{\mathrm{r}}_x\mathrm{Mn}{\mathrm{O}}_3$ for $x=0.125$; these textures are magnetic bubbles, magnetic stripe domains, and forced FM states. In situ Lorentz microscopy (LM) observations show that magnetic bubbles exist in the FM insulating phase accompanying the formation of the charge/orbital ordering (CO/OO). Furthermore, stable magnetic bubbles still exist in an intermediate temperature region between the CO/OO ($T_{\mathrm{CO}}=155\mathrm{K}$) and FM ($T_{\mathrm{C}}=190\mathrm{K}$) transition temperatures. These magnetic bubbles are believed to originate from the magnetocrystalline anisotropy and the dipole-dipole interaction in the FM phase. Based on in situ LM observations as a function of both temperature and the strength of the external magnetic field applied, a magnetic field–temperature phase diagram is constructed, exhibiting the stabilizing regions of the magnetic bubbles in the FM phase of $\mathrm{L}{\mathrm{a}}_{0.875}\mathrm{S}{\mathrm{r}}_{0.125}\mathrm{Mn}{\mathrm{O}}_3$.

We image the motion of superconducting vortices in niobium film covered with a regular array of thin permalloy strips. By altering the magnetization orientation in the strips using a small in-plane magnetic field, we can tune the strength of interactions between vortices and the strip edges, enabling acceleration or retardation of the superconducting vortices in the sample and consequently introducing strong tunable anisotropy into the vortex dynamics. We discuss our observations in terms of the attraction/repulsion between point magnetic charges carried by vortices and lines of magnetic charges at the strip edges and derive analytical formulas for the vortex-magnetic strips coupling. Our approach demonstrates the analogy between the vortex motion regulated by the magnetic strip array and electric carrier flow in gated semiconducting devices. Scaling down the geometrical features of the proposed design may enable controlled manipulation of single vortices, paving the way for Abrikosov vortex microcircuits and memories.

We present structural, magnetic, electrical, thermal transport, Hall coefficient, and pressure-dependent resistivity measurements on $\mathrm{C}{\mathrm{u}}_x\mathrm{ZrT}{\mathrm{e}}_{2-y}$ compounds with $x=0.05$, 0.1, 0.15, 0.2, and 0.3, and $y$ varied between $0\le y\le 0.8$. In order to calculate the ground state, ab initio calculations of the electronic structure of these materials were performed. Our results show that copper intercalation in $\mathrm{ZrT}{\mathrm{e}}_2$ induces superconductivity in the $\mathrm{ZrT}{\mathrm{e}}_2$ system. For the $\mathrm{C}{\mathrm{u}}_{0.3}\mathrm{ZrT}{\mathrm{e}}_{1.2}$ sample, Hall and Seebeck coefficient measurements show that the system is predominantly negatively charged with carrier density close to ${10}^{19}\mathrm{c}{\mathrm{m}}^{-3}$. The temperature dependence of the Hall coefficient, the Seebeck coefficient, and the lower critical field indicates that this material presents multiband character. Pressure-dependent resistivity vs temperature measurements reveal that while the normal-state resistivity decreases with increasing applied pressure, the superconducting transition temperature is completely insensitive to the applied pressure (for pressure in the range 0–1.3 GPa). This suggests that the Fermi gas is intrinsically degenerate under very high pressure, and therefore does not change much with varying external pressure. Finally the band structure calculation shows a dispersion curve containing a bulk three-dimensional Dirac conelike feature at the L point in the Brillouin zone, which is gapless in the absence of spin-orbit coupling, but develops a gap when this coupling is considered. Altogether, the results indicate that the superconducting compound $\mathrm{C}{\mathrm{u}}_x\mathrm{ZrT}{\mathrm{e}}_{2-y}$ presents a signature of multiband behavior and may possibly be a new example of a topological superconductor.

A previously unreported Pb-based perovskite ${\mathrm{PbMoO}}_3$ is obtained by high-pressure and high-temperature synthesis. This material crystallizes in the $Pm\overline{3}m$ cubic structure at room temperature, making it distinct from typical Pb-based perovskite oxides with a structural distortion. ${\mathrm{PbMoO}}_3$ exhibits a metallic behavior down to 0.1 K with an unusual $T$-sublinear dependence of the electrical resistivity. Moreover, a large specific heat is observed at low temperatures accompanied by a peak in $C_P/T^3$ around 10 K, in marked contrast to the isostructural metallic system ${\mathrm{SrMoO}}_3$. These transport and thermal properties for ${\mathrm{PbMoO}}_3$, taking into account anomalously large Pb atomic displacements detected through diffraction experiments, are attributed to a low-energy vibrational mode, associated with incoherent off-centering of lone-pair ${\mathrm{Pb}}^{2+}$ cations. We discuss the unusual behavior of the electrical resistivity in terms of a polaronlike conduction, mediated by the strong coupling between conduction electrons and optical phonons of the local low-energy vibrational mode.

Neutron diffraction measurements conducted under applied magnetic fields evidence the ordered structure of ${\mathrm{PrIr}}_2{\mathrm{Zn}}_{20}$ below approximately 0.1 K. A two-channel (orbital) Kondo effect is expected to act within the non-Kramers doublet ground state of the Pr $4f$ electrons of this material in cubic symmetry. Antiferromagnetic reflections are clearly induced under the influence of applied magnetic fields, which are characterized by the propagation vector $\mathit{q}=(1/2,1/2,1/2)$. This result indicates antiferromagnetic-type ordering of the Pr $f$-electron multipoles. The ${\mathrm{\Gamma }}_3$-type quadrupole, $O_2^2$, is the dominant order parameter deduced from the observed magnetic structure factor. We also discuss the entanglement of various finite-magnitude multipoles up to third rank, which are relevant to the low-energy crystalline-electric-field split levels in this material.

Spatially indirect excitons in semiconducting double quantum wells have been shown to exhibit rich collective many-body behavior that results from the nature of the extended dipole-dipole interactions between particles. For many spectroscopic studies of the emission from a system of such indirect excitons, it is crucial to separate the single-particle properties of the excitons from the many-body effects arising from their mutual interactions. In particular, knowledge of the relation between the emission energy of indirect excitons and their radiative lifetime could be highly beneficial for control, manipulation, and analysis of such systems. Here we study a simple analytic approximate relation between the radiative lifetime of indirect excitons and their emission energy. We show, both numerically and experimentally, the validity and the limits of this approximate relation. This relation between the emission energy and the lifetime of indirect excitons can be used to tune and determine their lifetime and their resulting dynamics without the need of directly measuring it, and as a tool for design of indirect exciton based devices.

Plasmonic gratings constitute a paradigmatic instance of the wide range of applications enabled by plasmonics. While subwavelength metal gratings find applications in optical biosensing and photovoltaics, atomically thin gratings achieved by periodically doping a graphene monolayer perform as metasurfaces for the control of terahertz radiation. In this paper we show how these two instances of plasmonic gratings inherit their spectral properties from an underlying slab with translational symmetry. We develop an analytical formalism to accurately derive the mode spectrum of the gratings that provides a great physical insight.

The entanglement entropy generated by quantum transport, similar to any physical observable quantity, is a stochastic variable that has its distribution and can fluctuate. The fundamental question is how to define the entanglement entropy operator which allows one to discuss entanglement entropy fluctuation. By introducing the entanglement entropy operator, we develop a theoretical framework to calculate the entanglement entropy fluctuation as well as its higher order cumulants generated by electronic transport in open systems. The distribution of entanglement entropy generated by opening or closing a quantum point contact (QPC) is solved exactly. When the transmission coefficient of QPC is one-half, the entanglement entropy is maximized and fluctuationless. We also establish a general relation between the generated entanglement entropy fluctuation and charge fluctuation. We apply our theory to electronic transport through a quantum dot and study the generated entanglement entropy in the transient regime. Universal behavior is found for the cumulants of entanglement entropy at short times.

The magnetic structure in the strongly correlated ruthenate $\mathrm{S}{\mathrm{r}}_4\mathrm{R}{\mathrm{u}}_3{\mathrm{O}}_{10}$ has been debated for a long time and still remains elusive. Here, we perform a systematically planar Hall effect study on a single-crystalline $\mathrm{S}{\mathrm{r}}_4\mathrm{R}{\mathrm{u}}_3{\mathrm{O}}_{10}$ nanostripe with a thickness of less than 100 nm. Large sharp switching behavior is observed in the planar Hall resistance, unambiguously indicating a strong anisotropic in-plane ferromagnetic order in the nanostripe, which is in contrast to the bulk system. Temperature-dependent evolution of the in-plane magnetism reveals that the in-plane spin order transforms from a single-domain state below a Curie temperature $T_C$ into a multidomain state below a critical temperature $T_M$, probably due to the inherent strong spin-orbit coupling driven reconfiguration of spins between the $c$ axis and the $ab$ plane.

We consider a modified setup for measuring the Aharonov-Casher phase which consists of a Josephson vortex trapped in an annular topological superconducting junction. The junction encloses both electric charge and magnetic flux. We discover a deviation from the Aharonov-Casher prediction whose origin we identify in an additive universal topological phase that remarkably depends only on the parity of the number of vortices enclosed by the junction. We show that this phase is $\pm 2\pi$ times the topological spin of the Josephson vortex and is proportional to the Chern number. The presence of this phase can be measured through its effect on the junction's voltage characteristics, thus revealing the topological properties of the Josephson vortex and the superconducting state.

We have implemented recently developed multiple-projector pseudopotentials into the plane-wave-based auxiliary-field quantum Monte Carlo (pw-AFQMC) method. Multiple-projector pseudopotentials can yield smaller plane-wave cutoffs while maintaining or improving transferability. This reduces the computational cost of pw-AFQMC, increasing its reach to larger and more complicated systems. We discuss the use of nonlocal pseudopotentials in the separable Kleinman-Bylander form, and the implementation in pw-AFQMC of the multiple-projector optimized norm-conserving pseudopotential ONCVPSP of Hamann. The accuracy of the method is first demonstrated by equation-of-state calculations of the ionic insulator NaCl and more strongly correlated metal Cu. The method is then applied to calibrate the accuracy of density-functional theory (DFT) predictions of the phase stability of recently discovered high temperature and pressure superconducting sulfur hydride systems. We find that DFT results are in good agreement with pw-AFQMC, due to the near cancellation of electron-electron correlation effects between different structures.

${\mathrm{YbInCu}}_4$ undergoes a first-order structural phase transition near $T_v=40$ K associated with an abrupt change of Yb valence state. We perform an ultrafast pump-probe measurement on ${\mathrm{YbInCu}}_4$ and find that the expected heavy-fermion properties arising from the $c-f$ hybridization exist only in a limited temperature range above $T_v$. Below $T_v$, the compound behaves as a normal metal though a prominent hybridization energy gap is still present in the infrared measurement. We elaborate that those seemingly controversial phenomena could be well explained by assuming that the Fermi level suddenly shifts up and moves away from the flat $f$-electron band as well as the indirect hybridization energy gap in the intermediate valence state below $T_v$.

A planar metal-dielectric multilayer structure containing a waveguide layer doped with azo-dye molecules exhibits a sharp Fano resonance that can be shifted by pump light irradiation owing to a photoinduced change of the refractive index of the waveguide layer by photoisomerization of the azo-dye molecules. Azo-dye-containing materials are polarization sensitive and the photoinduced shift of the Fano resonance is expected to depend on the pump polarization. Previous pump-probe attenuated-total-reflection measurements performed with a normal incidence of pump light exhibited intriguingly no dependence on the pump polarization. In this work, we extend our measurements to an oblique incidence, to optimize the overlap between the pump and probe polarizations, and we demonstrate a strong dependence on the pump polarization. To analyze the experimental results for both the normal and oblique pump conditions, we introduce phenomenological equations, based on the angular hole burning model of the photoisomerization of the azo-dye molecules. The equations allow us to describe the dependence of the refractive index changes in the waveguide layer on the pump angle and polarization. Using the equations, we could obtain good theoretical fits to the experimental data. The results of fitting suggest that the overlap between the pump and probe polarizations plays an important role in determining the amount of the photoinduced shift of the Fano resonance.

The crystal and magnetic structures of stoichiometric $\mathrm{ZnC}{\mathrm{r}}_2\mathrm{S}{\mathrm{e}}_4$ have been investigated using synchrotron x-ray and neutron powder diffraction, muon spin relaxation $\left(\mu \mathrm{SR}\right)$, and inelastic neutron scattering. Synchrotron x-ray diffraction shows a spin-lattice distortion from the cubic $Fd\overline{3}m$ spinel to a tetragonal $I{4}_1/amd$ lattice below $T_N=21\mathrm{K}$, where powder neutron diffraction confirms the formation of a helical magnetic structure with magnetic moment of $3.04\left(3\right){\mu }_{\mathrm{B}}$ at 1.5 K, close to that expected for high-spin $\mathrm{C}{\mathrm{r}}^{3+}$. $\mu \mathrm{SR}$ measurements show prominent local spin correlations that are established at temperatures considerably higher $(<100\mathrm{K})$ than the onset of long-range magnetic order. The stretched exponential nature of the relaxation in the local spin-correlation regime suggests a wide distribution of depolarizing fields. Below $T_N$, unusually fast $(>100\mu {\mathrm{s}}^{-1})$ muon relaxation rates are suggestive of rapid site hopping of the muons in static field. Inelastic neutron scattering measurements show a gapless mode at an incommensurate propagation vector of $k=\left[000.4648\right(2\left)\right]$ in the low-temperature magnetic ordered phase that extends to 0.8 meV. The dispersion is modeled by a two-parameter Hamiltonian, containing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions with a $J_{nnn}/J_{nn}=-0.337$.