We study the emergence of odd-frequency superconducting pairing in ${\mathrm{UPt}}_3$. Starting from a tight-binding model accounting for the nonsymmorphic crystal symmetry of ${\mathrm{UPt}}_3$ and assuming an order parameter in the $E_{2u}$ representation, we demonstrate that odd-frequency pairing arises very generally, as soon as intersublattice hopping or spin-orbit coupling is present. We also show that in the low temperature superconducting $B$ phase, the presence of a chiral order parameter together with spin-orbit coupling, leads to additional odd-frequency pair amplitudes not present in the $A$ or $C$ phases. Furthermore, we show that a finite Kerr rotation in the $B$ phase is only present if odd-$\omega$ pairing also exists.

We demonstrate experimentally that composite fermions in monolayer graphene display weak antilocalization. Our experiments deal with fractional quantum Hall (FQH) states in high-mobility, suspended graphene Corbino disks in the vicinity of $\nu =1/2$. We find a strong temperature dependence of conductivity $\sigma$ away from half filling, which is consistent with the expected electron-electron interaction-induced gaps in the FQH state. At half filling, however, the temperature dependence of conductivity $\sigma \left(T\right)$ becomes quite weak, as anticipated for a Fermi sea of composite fermions, and we find a logarithmic dependence of $\sigma$ on $T$. The sign of this quantum correction coincides with the weak antilocalization of graphene composite fermions, indigenous to chiral Dirac particles.

Correlated many-body problems ubiquitously appear in various fields of physics such as condensed matter, nuclear, and statistical physics. However, due to the interplay of the large number of degrees of freedom, it is generically impossible to treat these problems from first principles. Thus the construction of a proper model, namely, effective Hamiltonian, is essential. Here, we propose a simple supervised learning algorithm for constructing Hamiltonians from given energy or entanglement spectra. We apply the proposed scheme to the Hubbard model at the half-filling, and compare the obtained effective low-energy spin model with several analytic results based on the high-order perturbation theory, which have been inconsistent with each other. We also show that our approach can be used to construct the entanglement Hamiltonian of a quantum many-body state from its entanglement spectrum as well. We exemplify this using the ground states of the $S=1/2$ two-leg Heisenberg ladders. We observe a qualitative difference between the entanglement Hamiltonians of the two phases (the Haldane and the rung singlet phase) of the model due to the different origin of the entanglement. In the Haldane phase, we find that the entanglement Hamiltonian is nonlocal by nature, and the locality can be restored by introducing the anisotropy and turning the ground state into the large-$D$ phase. Possible applications to the model construction from experimental data and to various problems of strongly correlated systems are discussed.

The optical properties and thermal dynamics of conical single silicon nanotips are experimentally and theoretically investigated. The spectral and spatial dependencies of their optical extinction are quantitatively measured by spatial modulation spectroscopy (SMS). A nonuniform optical extinction along the tip axis and an enhanced near-infrared absorption, as compared to bulk crystalline silicon, are evidenced. This information is a key input for computing the thermal response of single silicon nanotips under ultrafast laser illumination, which is investigated by laser assisted atom probe tomography (La-APT) used as a highly sensitive temperature probe. A combination of these two experimental techniques and comparison with modeling also permits us to elucidate the impact of thermal effects on the laser assisted field evaporation process. Extension of this coupled approach opens up future perspectives for the quantitative study of the optical and thermal properties of a wide class of individual nano-objects, in particular elongated ones such as nanotubes, nanowires, and nanocones, which constitute promising nanosources for electron and/or ion emission.

Using sum-frequency generation (SFG) spectroscopy, we have investigated ferroelectric orientational ordering of ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{D}}_2\mathrm{O}$ crystalline-ice films grown on Pt(111) at 140 K. The $\mathrm{Im}{\chi }^{\left(2\right)}$ SFG spectrum of the hydrogen-bonded OH (OD) stretching band of ${\mathrm{H}}_2\mathrm{O}$ (${\mathrm{D}}_2\mathrm{O}$) ice film shows a couple of peaks whose signs are all negative, indicating net-H-down (net-D-down) ferroelectric orientational ordering of ${\mathrm{H}}_2\mathrm{O}$ (${\mathrm{D}}_2\mathrm{O}$) molecules with protons (deuterons) preferentially pointing toward the Pt substrate. The spectral features are analyzed in terms of the orientational ordering and OH (OD) vibrational excitons derived from intermolecular couplings. The quantitative analysis of the SFG peak intensity demonstrates the layer-dependent strong ferroelectric orientational ordering. Temperature dependence of the SFG intensity indicates that the ferroelectric orientational ordering decays via second-order type ferroelectric-paraelectric transition at critical temperatures of $T_c=163$ and 167 K for ${\mathrm{H}}_2\mathrm{O}$ (50 bilayers thickness) and ${\mathrm{D}}_2\mathrm{O}$ (64 bilayers thickness) ice films, respectively, which are more than twice as large as that of ferroelectric bulk ice XI ($T_c\sim 72\mathrm{K}$ for ${\mathrm{H}}_2\mathrm{O}, T_c\sim 76\mathrm{K}$ for ${\mathrm{D}}_2\mathrm{O}$). The isotope shift of $T_c$ for the high-$T_c$ ferroelectric ice films on Pt(111) is only about 4 K, which is in stark contrast to a large isotope shift of $T_c$, approximately several tens of Kelvin, of typical high-$T_c$ hydrogen-bonded ferroelectrics. The interadsorbate and adsorbate-substrate interactions at the ice/Pt interface and nuclear quantum effects in the hydrogen-bond network of ice film are responsible for the observed thermal stability of ferroelectric orientational ordering and its isotope effect.

There has been a recent surge of interest in dualities relating theories of Chern-Simons gauge fields coupled to either bosons or fermions within the condensed matter community, particularly in the context of topological insulators and the half-filled Landau level. Here, we study the application of one such duality to the long-standing problem of quantum Hall interplateaux transitions. The key motivating experimental observations are the anomalously large value of the correlation length exponent $\nu \approx 2.3$ and that $\nu$ is observed to be superuniversal, i.e., the same in the vicinity of distinct critical points [Sondhi et al., Rev. Mod. Phys. 69, 315 (1997)]. Duality motivates effective descriptions for a fractional quantum Hall plateau transition involving a Chern-Simons field with $\mathrm{U}\left(N_c\right)$ gauge group coupled to $N_f=1$ fermion. We study one class of theories in a controlled limit where $N_f\gg N_c$ and calculate $\nu$ to leading nontrivial order in the absence of disorder. Although these theories do not yield an anomalously large exponent $\nu$ within the large $N_f\gg N_c$ expansion, they do offer a new parameter space of theories that is apparently different from prior works involving Abelian Chern-Simons gauge fields [Wen and Wu, Phys. Rev. Lett. 70, 1501 (1993); Chen et al., Phys. Rev. B 48, 13749 (1993)].

We present a model compound for the $S=2$ antiferromagnetic (AF) spin chain composed of the salt ($o$-MePy-$\mathrm{V}){\mathrm{FeCl}}_4$. Ab initio molecular-orbital calculations indicate the formation of a partially stacked two-dimensional (2D) spin model comprising five types of exchange interactions between $S=1/2$ and $S=5/2$ spins, which locate on verdazyl radical and Fe ion, respectively. The magnetic properties of the synthesized crystals indicate that the dominant interaction between the $S=1/2$ and $S=5/2$ spins stabilizes an $S=2$ spin in the low-temperature region, and an effective $S=2$ AF chain is formed for $T\ll 10$ K and $H<4$ T. We explain the magnetization curve and electron-spin-resonance modes quantitatively based on the $S=2$ AF chain. At higher fields above quantitatively 4 T, the magnetization curve assumes two-thirds of the full saturation value for fields between 4 and 20 T, and approaches saturation at $\sim 40$ T. The spin model in the high-field region can be considered as a quasi-2D $S=1/2$ honeycomb lattice under an effective internal field caused by the fully polarized $S=5/2$ spin.

A transverse magnetic field $\mathrm{\Gamma }$ is known to induce antiferromagnetic three-sublattice order of the Ising spins ${\sigma }^z$ in the triangular lattice Ising antiferromagnet at low enough temperature. This low-temperature order is known to melt on heating in a two-step manner, with a power-law ordered intermediate temperature phase characterized by power-law correlations at the three-sublattice wave vector $\mathbf{Q}$: $\langle {\sigma }^z\left(\vec{R}\right){\sigma }^z\left(0\right)\rangle \sim cos(\mathbf{Q}·\vec{R})/{\left|\vec{R}\right|}^{\eta \left(T\right)}$ with the temperature-dependent power-law exponent $\eta \left(T\right)\in (1/9,1/4)$. Here, we use a quantum cluster algorithm to study the ferromagnetic easy-axis susceptibility ${\chi }_u\left(L\right)$ of an $L\times L$ sample in this power-law ordered phase. Our numerical results are consistent with a recent prediction of a singular $L$ dependence ${\chi }_u\left(L\right)\sim L^{2-9\eta }$ when $\eta \left(T\right)$ is in the range $(1/9,2/9)$. This finite-size result implies, via standard scaling arguments, that the ferromagnetic susceptibility ${\chi }_u\left(B\right)$ to a uniform field $B$ along the easy axis is singular at intermediate temperatures in the small $B$ limit, ${\chi }_u\left(B\right)\sim {\left|B\right|}^{-\frac{4-18\eta }{4-9\eta }}$ for $\eta \left(T\right)\in (1/9,2/9)$, although there is no ferromagnetic long-range order in the low temperature state. Additionally we establish similar two-step melting behavior (via a study of the order parameter susceptibility ${\chi }_{\mathbf{Q}}$) in the case of the ferrimagnetic three-sublattice ordered phase which is stabilized by ferromagnetic next-neighbor couplings ($J_2$) and confirm that the ferromagnetic susceptibility obeys the predicted singular form in the associated power-law ordered phase.

The growth of up to ten-monolayer-thick Fe films on a Au(001) surface was investigated during deposition at room temperature and during annealing, using low-energy electron diffraction and x-ray photoemission spectroscopy, as well as locally with low-energy electron microscopy and photoemission electron microscopy. The growth proceeds with a submonolayer of Au segregating on the surface of Fe, which is in agreement with previous studies. Annealing was found to be critical for the presence of Au on the Fe surface. Our study identifies a spatially inhomogeneous Au segregation mechanism which proceeds by the formation of cracks in the Fe film, starting at the annealing temperature of $190{}^{\circ }\mathrm{C}$, through which Au diffuses towards the surface. As a result, a system with a nonuniform surface electronic structure is obtained. This study shows the necessity to employ spatially resolved techniques to fully understand the growth modes of the layered epitaxial systems.

Silicene and germanene, as graphenelike materials with observable spin-orbit couplings and two distinctive valleys, have potential applications in future low-dissipation spintronics and valleytronics. We here propose a magnetic system of silicene or germanene intercalated between two ferromagetic (FM) dielectric layers, and find that the system with a proximity-induced asymmetric magnetic field supports an attractive phenomenon named the valley-locked spin-dependent Seebeck effect (VL-SSE) driven by a thermal gradient. The VL-SSE indicates that the carries from only one valley could be thermally excited, with opposite spin polarization counterpropagating along the thermal gradient direction, while nearly no carrier from the other insulating valley is excited due to the relatively wide band gap. It is also illustrated that the VL-SSE here does not survive in the usual FM or anti-FM systems, and can be destroyed by the overlarge temperature broadening. Moreover, we prove that the signal for VL-SSE can be weakened gradually with the enhancement of the local interlayer electric field, and be strengthened lineally by increasing the source-drain temperature difference in a caloritronic field effect transistor. Further calculations indicate that the VL-SSE is robust against many perturbations, including the global and local Fermi levels as well as the magnetic strength. These findings about the valley-locked thermospin effect provide a nontrivial and convenient dimension to control the quantum numbers of spin and valley and are expected to be applied in future spin-valley logic circuits and energy-saving devices.

In this article, we propose a concise theoretical framework based on mixed-field susceptibilities to describe the decay of magnetic dipoles induced by nonmagnetic nanostructures. This approach is first illustrated in simple cases in which analytical expressions of the decay rate can be obtained. We then show that a more refined numerical implementation of this formalism involving a volume discretization and the computation of a generalized propagator can predict the dynamics of magnetic dipoles in the vicinity of nanostructures of arbitrary geometries. We finally demonstrate the versatility of this numerical method by coupling it to an evolutionary optimization algorithm. In this way we predict a structure geometry which maximally promotes the decay of magnetic transitions with respect to electric emitters.

We generalize the concept of parity-time symmetric structures with the goal to create meta-atoms exhibiting extraordinary abilities to overcome the presumed limitations in the scattering of overall lossless particles, such as nonzero forward scattering and the equality of scattering and extinction powers for all lossless particles. Although the forward scattering amplitude and the extinction cross section of our proposed meta-atoms vanish, they scatter incident energy into other directions, with controllable directionality. These meta-atoms possess extreme electromagnetic properties not achievable for passive scatterers. As an example, we study meta-atoms consisting of two or three small dipole scatterers. We consider possible microwave realizations in the form of short dipole antennas loaded by lumped elements. The proposed meta-atom empowers extraordinary response of a shadow-free scatterer and theoretically enables most unusual material properties when used as a building block of an artificial medium.

We enquire into the quasi many-body localization in topologically ordered states of matter, revolving around the case of Kitaev toric code on the ladder geometry, where different types of anyonic defects carry different masses induced by environmental errors. Our study verifies that the presence of anyons generates a complex energy landscape solely through braiding statistics, which suffices to suppress the diffusion of defects in such clean, multicomponent anyonic liquid. This nonergodic dynamics suggests a promising scenario for investigation of quasi many-body localization. Computing standard diagnostics evidences that a typical initial inhomogeneity of anyons gives birth to a glassy dynamics with an exponentially diverging time scale of the full relaxation. Our results unveil how self-generated disorder ameliorates the vulnerability of topological order away from equilibrium. This setting provides a new platform which paves the way toward impeding logical errors by self-localization of anyons in a generic, high energy state, originated exclusively in their exotic statistics.

The properties of magnon modes localized on a ferromagnetic skyrmion are studied. Mode eigenfrequencies display three types of asymptotic behavior for large skyrmion radius $R_s$, namely, ${\omega }_0\propto R_s^{-2}$ for the breathing mode and ${\omega }_{-\left|\mu \right|}\propto R_s^{-1}$ and ${\omega }_{\left|\mu \right|}\propto R_s^{-3}$ for modes with negative and positive azimuthal quantum numbers, respectively. A number of properties of the magnon eigenfunctions are determined. This enables us to demonstrate that the skyrmion dynamics for a traveling-wave ansatz obeys the massless Thiele equation.

We present a time-resolved angle-resolved photoelectron spectroscopy study of ${\mathrm{IrTe}}_2$, which undergoes two first-order structural and charge-ordered phase transitions on cooling below 270 K and below 180 K. The possibility of inducing a phase transition by photoexcitation with near-infrared femtosecond pulses is investigated in the charge-ordered phases. We observe changes of the spectral function occurring within a few hundreds of femtoseconds and persisting up to several picoseconds, which we interpret as a partial photoinduced phase transition (PIPT). The necessary time for photoinducing these spectral changes increases with increasing photoexcitation density and reaches time scales longer than the rise time of the transient electronic temperature. We conclude that the PIPT is driven by a transient increase of the lattice temperature following the energy transfer from the electrons. However, the photoinduced changes of the spectral function are small, which indicates that the low-temperature phase is particularly robust against photoexcitation. We suggest that the system might be trapped in an out-of-equilibrium state, for which only a partial structural transition is achieved.

The Chebyshev expansion offers a numerically efficient and easy-implement algorithm for evaluating dynamic correlation functions using matrix product states (MPS). In this approach, each recursively generated Chebyshev vector is approximately represented by an MPS. However, the recurrence relations of Chebyshev polynomials are broken by the approximation, leading to an error which is accumulated with the increase of the order of expansion. Here we propose a reorthonormalization approach to remove this error introduced in the loss of orthogonality of the Chebyshev polynomials. Our approach, as illustrated by comparison with the exact results for the one-dimensional XY and Heisenberg models, improves significantly the accuracy in the calculation of dynamical correlation functions.

We use cellular dynamical mean-field theory with extended unit cells to study the ground state of the two-dimensional repulsive Hubbard model at finite doping. We calculate the energy of states where $d$-wave superconductivity coexists with spatially nonuniform magnetic and charge order and find that they are energetically favored in a large doping region as compared to the uniform solution. We also study the spatial form of the density and the superconducting and magnetic order parameters at different doping values.

Optically pumped NMR (OPNMR) of the NMR-active ${}^{69/71}\mathrm{Ga}$ species has been shown to be a unique method to probe electronic energy bands in GaAs, with sensitivity to the light hole–to–conduction band transition. This transition is often obscured in other optical measurements such as magnetoabsorption. Using OPNMR, we exploit the hyperfine interaction between conduction band electrons (and their spin states) and nuclear spins, which are detected through phase-sensitive radio-frequency (NMR) spectroscopy. Measurements were made over a range of external magnetic fields ($B_0$) in two different labs with separate experimental setups to obtain the magnetic field dependence of the light hole–to–conduction band transition energy. In addition, $k·p$ theory was used to interpret the experimental results, mapping out this specific transition's magnetic field dependence in an AlGaAs/GaAs quantum well. The combination of theory and experiment point to a mixing of valence bands at a field of approximately $B_0=4.7$ T, swapping the dominant character of the absorption transition and, thus, explaining the magnetic field dependence. Lastly, the experimental dependence of the light hole–to–conduction band transition energy on $B_0$ is found to be less steep compared to the calculated trend, indicating that inclusion of additional effects may be necessary to accurately model the spin-split band structure. The additional insight gained by ${}^{69/71}\mathrm{Ga}$ OPNMR about the light hole states will facilitate future testing of more complex band structure models.

We numerically study the electrical and thermoelectric transport properties in phosphorene in the presence of both a magnetic field and disorder. The quantized Hall conductivity is similar to that of a conventional two-dimensional electron gas, but the positions of all the Hall plateaus shift to the left due to the spectral asymmetry, in agreement with the experimental observations. The thermoelectric conductivity and Nernst signal exhibit remarkable anisotropy, and the thermopower is nearly isotropic. When a bias voltage is applied between top and bottom layers of phosphorene, both thermopower and Nernst signal are enhanced and their peak values become large.

Confinement at the helical edge of a topological insulator is possible in the presence of proximity-induced magnetic (F) or superconducting (S) order. The interplay of both phenomena leads to the formation of localized Majorana bound states (MBS) or likewise (under certain resonance conditions) the formation of ordinary Andreev bound states (ABS). We investigate the properties of bound states in junctions composed of alternating regions of F or S barriers. Interestingly, the direction of magnetization in F regions and the relative superconducting phase between S regions can be exploited to hybridize MBS or ABS at will. We show that the local properties of MBS translate into a particular nonlocal superconducting pairing amplitude. Remarkably, the symmetry of the pairing amplitude contains information about the nature of the bound state that it stems from. Hence this symmetry can in principle be used to distinguish MBS from ABS, owing to the strong connection between local density of states and nonlocal pairing in our setup.