Tellegen and moving metasurfaces are two promising classes of nonreciprocal bianisotropic metasurfaces that offer extended functionalities for electromagnetic wave manipulation. However, in order to realize these metasurfaces, ferrite-based unit cells have been utilized that need to be biased by an external magnetic field. Inspired by recent works on magnet-free non-bianisotropic nonreciprocal building blocks, we introduce designs for magnet-free Tellegen and moving metasurfaces.

We develop a scheme for the computation of the full-counting statistics of transport described by Markovian master equations with an arbitrary time dependence. It is based on a hierarchy of generalized density operators, where the trace of each operator yields one cumulant. This direct relation offers a better numerical efficiency than the equivalent number-resolved master equation. The proposed method is particularly useful for conductors with an elaborate time dependence stemming, e.g., from pulses or combinations of slow and fast parameter switching. As a test bench for the evaluation of the numerical stability, we consider time-independent problems for which the full-counting statistics can be computed by other means. As applications, we study cumulants of higher order for two time-dependent transport problems of recent interest, namely steady-state coherent transfer by adiabatic passage (CTAP) and Landau-Zener-Stückelberg-Majorana (LZSM) interference in an open double quantum dot.

We observe an induced switchable magnetic moment of $1.6\pm 0.40{\mu }_{\mathrm{B}}/\mathrm{Fe}$ for the nominally antiferromagnetic $\mathrm{LaFe}{\mathrm{O}}_3$ extending two to four interface layers into the non–charge transfer system $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3\text{/}\mathrm{LaFe}{\mathrm{O}}_3\text{/}\mathrm{SrTi}{\mathrm{O}}_3\left(111\right)$. Simultaneously a mismatch of oxygen octahedra rotations at the interface implies an atomic reconstruction of reduced symmetry at the interface, reaching two to five layers into $\mathrm{LaFe}{\mathrm{O}}_3$. Density functional theory of a structure with atomic reconstruction and different correlation strength shows a ferrimagnetic state with a net Fe moment at the interface. Together these results suggest that engineered oxygen octahedra rotations, affecting the local symmetry, affect electron correlations and can be used to promote magnetic properties.

Many-body localization (MBL) in a one-dimensional Fermi Hubbard model with random on-site interactions is studied. While for this model all single-particle states are trivially delocalized, it is shown that for sufficiently strong disordered interactions the model is many-body localized. It is therefore argued that MBL does not necessarily rely on localization of the single-particle spectrum. This model provides a convenient platform to study pure MBL phenomenology, since Anderson localization in this model does not exist. By examining various forms of the interaction term, a dramatic effect of symmetries on charge transport is demonstrated. A possible realization in a cold atom experiment is proposed.

A linear-response method to the density functional theory is used to derive lattice dynamics, the transport spectral function, and the electron-phonon coupling (EPC) constant of $\mathrm{T}{\mathrm{i}}_2\mathrm{AlC}$, a member of the very large class of nanolaminated conducting ceramics named MAX phases (where $M$ is a transition metal, $A$ is an element from groups IIIA to VIA, and $X$ is carbon and/or nitrogen). By coupling ab initio calculations with the semiclassical Boltzmann transport theory for electron-phonon scattering, the experimentally observed anisotropic electrical transport properties of $\mathrm{T}{\mathrm{i}}_2\mathrm{AlC}$ are rationalized. Our results indicate that in $\mathrm{T}{\mathrm{i}}_2\mathrm{AlC}$, because of the weak dependence of the EPC constant ${\lambda }_{\mathrm{tr},\alpha }$ $(\alpha =xx$ and $zz)$ on the crystallographic direction, the anisotropy of $\rho \left(T\right)$ results from the anisotropy of the Fermi surface. These conclusions, in contrast with those obtained on $\mathrm{T}{\mathrm{i}}_3\mathrm{Si}{\mathrm{C}}_2$ (another member of the MAX phases family) using a similar approach, establish a correlation between the nanolaminated structure of the MAX phases and the origin of the anisotropy of their transport properties.

Because of its role as a model system with tunable quantum fluctuations and quenched disorder, and the desire for optical control and readout of its states, we have used high-resolution optical absorption spectroscopy to measure the crystal-field excitations for ${\mathrm{Ho}}^{3+}$ ions in ${\mathrm{LiHo}}_x{\mathrm{Y}}_{1-x}{\mathrm{F}}_4$ from the terahertz to visible regimes. We show that many of the excitations yield very narrow lines visibly split even by the nuclear hyperfine interaction, making ${\mathrm{Ho}}^{3+}$ in ${\mathrm{LiHo}}_x{\mathrm{Y}}_{1-x}{\mathrm{F}}_4$ a candidate host for optically addressable electronuclear qubits with quality factors as high as $Q=4.7\times {10}^5$, where the higher-lying levels are electronic singlets. Optical transitions in the easily accessible near- and mid-infrared are narrow enough to allow readout of the ground-state electronuclear qubits responsible for the interesting magnetism of ${\mathrm{LiHo}}_x{\mathrm{Y}}_{1-x}{\mathrm{F}}_4$. While many of the higher-lying states have been observed previously, we also report here detailed spectra of terahertz excitations. The strengths of the electric and magnetic dipole crystal-field transition lines of five of the lowest excited spin-orbit manifolds of dilute ${\mathrm{LiYF}}_4$:${\mathrm{Ho}}^{3+}$ were calculated and compared with measurement. The magnitude of the nuclear hyperfine coupling was used to assign the correct upper and lower states to transition lines.

Motivated by recent experiments, we present here a systematic ab initio study of the length dependence of the thermal conductance of single-molecule junctions. We make use of a combination of density functional theory with nonequilibrium Green's function techniques to investigate the length dependence of the phonon transport in single-alkane chains, contacted with gold electrodes via both thiol and amine anchoring groups. Additionally, we study the effect of the substitution of the hydrogen atoms in the alkane chains by heavier fluorine atoms to form polytetrafluoroethylenes. Our results demonstrate that (i) the room-temperature thermal conductance is fairly length independent for chains with more than 5 methylene units and (ii) the efficiency of the thermal transport is strongly influenced by the strength of the phononic metal-molecule coupling. Our study sheds light on the phonon transport in molecular junctions, and it provides clear guidelines for the design of molecular junctions for thermal management.

We study the electric-field tunable electronic properties of phosphorene thin films, using the framework of density functional theory. We show that phosphorene thin films offer a versatile material platform to study two-dimensional Dirac fermions on application of a transverse electric field. Increasing the strength of the transverse electric field beyond a certain critical value in phosphorene thin films leads to the formation of two symmetry protected gapless Dirac fermions states with anisotropic energy dispersion. The spin-orbit coupling splits each of these Dirac states into two spin-polarized Dirac cones which are also protected by nonsymmorphic crystal symmetries. Our study shows that the position as well as the carrier velocity of the spin-polarized Dirac cone states can be controlled by the strength of the external electric field.

We develop a generalized tight-binding model to investigate the Coulomb excitations in monolayer silicene. The atomic interactions, spin-orbit coupling, magnetic and electric fields, as well as the Coulomb interactions are simultaneously included in our calculations. The magnetic field induces interband plasmons with discrete frequency dispersions restricted to quantized energy states. An intraband plasmon, with a higher intensity and continuous dispersion relation, exists in the presence of free carriers. This mode is dramatically transformed into an interband plasma excitation when the magnetic field is increased, leading to abrupt changes in the value of the plasma frequency and its intensity. Specifically, an electric field may separate the spin and valley polarizations and create additional plasmon modes, a unique feature arising from the buckled structure and the existence of noteworthy spin-orbit coupling.

First-principles methods are employed to determine the structural, mechanical, and thermodynamic reasons for the experimentally reported cubic WN phase. The defect-free rocksalt phase is both mechanically and thermodynamically unstable, with a negative single crystal shear modulus $C_{44}=-86\mathrm{GPa}$ and a positive enthalpy of formation per formula unit $H_f=0.623\mathrm{eV}$ with respect to molecular nitrogen and metallic W. In contrast, WN in the NbO phase is stable, with $C_{44}=175\mathrm{GPa}$ and $H_f=-0.839\mathrm{eV}$. A charge distribution analysis reveals that the application of shear strain along [100] in rocksalt WN results in an increased overlap of the $t_{2g}$ orbitals which causes electron migration from the expanded to the shortened W-W $\langle 110\rangle$ bond axes, yielding a negative shear modulus due to an energy reduction associated with new bonding states 8.1–8.7 eV below the Fermi level. A corresponding shear strain in WN in the NbO phase results in an energy increase and a positive shear modulus. The mechanical stability transition from the NaCl to the NbO phase is explored using supercell calculations of the NaCl structure containing $C_v=0\%-25\%$ cation and anion vacancies, while keeping the N-to-W ratio constant at unity. The structure is mechanically unstable for $C_v<5\%$. At this critical vacancy concentration, the isotropic elastic modulus $E$ of cubic WN is zero, but increases steeply to $E=445\mathrm{GPa}$ for $C_v=10\%$, and then less steeply to $E=561\mathrm{GPa}$ for $C_v=25\%$. Correspondingly, the hardness estimated using Tian's model increases from 0 to 15 to 26 GPa as $C_v$ increases from 5% to 10% to 25%, indicating that a relatively small vacancy concentration stabilizes the cubic WN phase and that the large variations in reported mechanical properties of WN can be attributed to relatively small changes in $C_v$.

Superdipolar glass properties of polar nanoregions (PNRs) in relaxor ferroelectric $\mathrm{PbM}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}{\mathrm{O}}_3$ (PMN) are compared to those of ferromagnetic nanoparticles (FNPs) in the superspin glass ${\left[\mathrm{C}{\mathrm{o}}_{80}\mathrm{F}{\mathrm{e}}_{20}\left(0.9\mathrm{nm}\right)/\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3\left(3\mathrm{nm}\right)\right]}_{10}$. Both the dynamic critical properties at $T>T_g$ and nonergodicity phenomena at $T<T_g$ are comparable, but this does not apply to their polydispersivity at $T\le T_g$. Due to the quenched random size and position distribution of the FNP, the superspin glass exhibits standard Cole-Cole broadening of the spectrum of relaxation frequencies at all temperatures. Contrastingly, the relaxation spectrum of the PNRs in PMN is subject to a crossover from Lacroix-Béné to Cole-Davidson statistics on cooling toward $T_g$. Surprisingly, it becomes replaced by relaxation and creeplike domain-wall dynamics below $T_g$ as a consequence of volume percolation of the PNR at $T_g$ and formation of a ferroelectric microdomain state under the simultaneous control by quenched random electric fields and the softening ferroelectric $F_{1u}$ lattice mode.

Variable-temperature neutron scattering measurements, reverse Monte Carlo analysis, and direct Monte Carlo simulation are used to characterize magnetic order in the metal-organic framework (MOF) $\mathrm{Tb}{\left(\mathrm{HCOO}\right)}_3$ over the temperature range 100 to $1.6 \mathrm{K}=T_{\mathrm{N}}$. The magnetic transition at $T_{\mathrm{N}}$ is shown to involve one-dimensional ferromagnetic ordering to a partially ordered state related to the triangular Ising antiferromagnet and distinct from the canonical partially disordered antiferromagnet model. In this phase, the direction of magnetization of ferromagnetic chains tends to alternate between neighboring chains but this alternation is frustrated and is not itself ordered. We suggest the existence of low-dimensional magnetic order in $\mathrm{Tb}{\left(\mathrm{HCOO}\right)}_3$ is stabilized by the contrasting strength of inter- and intrachain magnetic coupling, itself a consequence of the underlying MOF architecture. Our results demonstrate how MOFs may provide an attractive if as yet underexplored platform for the realization and investigation of low-dimensional physics.

We report ${}^{125}\mathrm{Te}$ nuclear magnetic resonance and ${}^{181}\mathrm{Ta}$ nuclear quadrupole resonance studies on single-crystal ${\mathrm{Ta}}_4{\mathrm{Pd}}_3{\mathrm{Te}}_{16}$, which has a quasi-one-dimensional structure and superconducts below $T_c=4.3$ K. ${}^{181}\mathrm{Ta}$ with spin $I=7/2$ is sensitive to quadrupole interactions, while ${}^{125}\mathrm{Te}$ with spin $I=1/2$ can only relax by magnetic interactions. By comparing the spin-lattice relaxation rate ($1/T_1$) of ${}^{181}\mathrm{Ta}$ and ${}^{125}\mathrm{Te}$, we found that electric-field-gradient (EFG) fluctuations develop below 80 K. The EFG fluctuations are enhanced with decreasing temperature due to the fluctuations of a charge density wave that sets in at $T_{\mathrm{CDW}}=20$ K, below which the spectra are broadened and $1/T_{1}T$ drops sharply. In the superconducting state, $1/T_1$ shows a Hebel-Slichter coherence peak just below $T_c$ for ${}^{125}\mathrm{Te}$, indicating that ${\mathrm{Ta}}_4{\mathrm{Pd}}_3{\mathrm{Te}}_{16}$ is a full-gap superconductor without nodes in the gap function. The coherence peak is absent in the $1/T_1$ of ${}^{181}\mathrm{Ta}$ due to the strong EFG fluctuations.

We present a nonequilibrium Green's-functional approach to study the dynamics following a quench in weakly interacting Bose-Hubbard model (BHM). The technique is based on the self-consistent solution of a set of equations which represents a particular case of the most general set of Hedin's equations for the interacting single-particle Green's function. We use the ladder approximation as a skeleton diagram for the two-particle scattering amplitude useful, through the self-energy in the Dyson equation, for finding the interacting single-particle Green's function. This scheme is then implemented numerically by a parallelized code. We exploit this approach to study the correlation propagation after a quench in the interaction parameter, for one and two dimensions. In particular, we show how our approach is able to recover the crossover from the ballistic to the diffusive regime by increasing the boson-boson interaction. Finally we also discuss the role of a thermal initial state on the dynamics both for one- and two-dimensional BHMs, finding that, surprisingly, at high temperature a ballistic evolution is restored.

Injection of a spin current into the surface or interface states of a topological insulator (TI) induces a charge current (inverse Edelstein effect or IEE) and, inversely, a charge current flowing at the surface or interface states of a TI generates a nonzero spin density (Edelstein Effect or EE) from which a spin current can be ejected into an adjacent layer. The parameters characterizing the efficiency of these conversions between spin and charge currents have been derived in recent experiments. By using a spinor distribution function for a momentum-spin locked TI, we determine a number of spin transport properties of TI-based heterostructure and find that the spin to charge conversion in IEE is controlled by the relaxation of an out-of equilibrium distribution in the TI states while the charge to spin conversion in EE depends on the electron transmission rate at the interface of the TI.

Perovskites containing barium metal at the $A$ site often take up unusual hexagonal structures having more than one type of possible sites for the $B$ cation to occupy. This opens up various different $B\text{−}B$- or $B$-O-$B$-type connectivities and consequent physical properties which are naturally missing in cubic perovskites. ${\mathrm{BaRuO}}_3$ is one such system where doping of Ru $\left(4d^4\right)$ by other transition metals $\left(M^{n+}\right)$ creates similar conditions, giving rise to various $M$-Ru interactions. Interestingly, the $6H$ hexagonal structure of doped barium ruthenate triple perovskite $\left({\mathrm{Ba}}_{3}M{\mathrm{Ru}}_2{\mathrm{O}}_9\right)$ seems to possess some internal checks because within the structure $M$ ion always occupies the $2a$ site and Ru goes to the $4f$ site, allowing only $M$-O-Ru ${180}^{\circ }$ and Ru-O-Ru ${90}^{\circ }$ interactions to occur. The only exception is observed in the case of the Fe dopant, which allows us to study almost the full ${\mathrm{Ba}}_3{\mathrm{Fe}}_{1-x}{\mathrm{Ru}}_{2+x}{\mathrm{O}}_9$ series of compounds with wide ranges of $x$ because here Fe ions have the ability to freely go to the $4f$ sites and Ru readily takes up the $2a$ positions. Therefore, here one has the opportunity to probe the evolution of electronic and magnetic properties as a function of doping by going from ${\mathrm{BaRuO}}_3$ (paramagnetic metal) to ${\mathrm{BaFeO}}_3$ (ferromagnetic insulator). Our detailed experimental and theoretical results show that the series does exhibit a percolative metal-insulator transition with an accompanying but not coincidental magnetic transition as a function of $x$.

We determine the band structure and spin texture of ${\mathrm{WTe}}_2$ by spin- and angle-resolved photoemission spectroscopy (SARPES). With the support of first-principles calculations, we reveal the existence of spin polarization of both the Fermi arc surface states and bulk Fermi pockets. Our results support ${\mathrm{WTe}}_2$ to be a type-II Weyl semimetal candidate and provide important information to understand its extremely large and nonsaturating magnetoresistance.

We study non-Fermi-liquid states that arise at the quantum critical points associated with the spin density wave (SDW) and charge density wave (CDW) transitions in metals with twofold rotational symmetry. We use the dimensional regularization scheme, where a one-dimensional Fermi surface is embedded in $(3-\epsilon )$-dimensional momentum space. In three dimensions, quasilocal marginal Fermi liquids arise both at the SDW and CDW critical points: the speed of the collective mode along the ordering wave vector is logarithmically renormalized to zero compared to that of Fermi velocity. Below three dimensions, however, the SDW and CDW critical points exhibit drastically different behaviors. At the SDW critical point, a stable anisotropic non-Fermi-liquid state is realized for small $\epsilon$, where not only time but also different spatial coordinates develop distinct anomalous dimensions. The non-Fermi liquid exhibits an emergent algebraic nesting as the patches of Fermi surface are deformed into a universal power-law shape near the hot spots. Due to the anisotropic scaling, the energy of incoherent spin fluctuations disperse with different power laws in different momentum directions. At the CDW critical point, on the other hand, the perturbative expansion breaks down immediately below three dimensions as the interaction renormalizes the speed of charge fluctuations to zero within a finite renormalization group scale through a two-loop effect. The difference originates from the fact that the vertex correction antiscreens the coupling at the SDW critical point whereas it screens at the CDW critical point.

Recently, singlet-triplet measurements in double dots have emerged as a powerful tool in quantum information processing. In parallel, quantum dot arrays are being envisaged as analog quantum simulators of many-body models. Thus motivated, we explore the potential of the above singlet-triplet measurements for probing and exploiting the ground state of a Heisenberg spin chain in such a quantum simulator. We formulate an efficient protocol to discriminate the achieved many-body ground state with other likely states. Moreover, the transition between quantum phases, arising from the addition of frustrations in a $J_1-J_2$ model, can be systematically explored using the same set of measurements. We show that the proposed measurements have an application in producing long distance heralded entanglement between well separated quantum dots. Relevant noise sources, such as nonzero temperatures and nuclear spin interactions, are considered.

We numerically investigate the distribution of Drude weights $D$ of many-body states in disordered one-dimensional interacting electron systems across the transition to a many-body localized phase. Drude weights are proportional to the spectral curvatures induced by magnetic fluxes in mesoscopic rings. They offer a method to relate the transition to the many-body localized phase to transport properties. In the delocalized regime, we find that the Drude weight distribution at a fixed disorder configuration agrees well with the random-matrix-theory prediction $P\left(D\right)\propto {({\gamma }^2+D^2)}^{-3/2}$, although the distribution width $\gamma$ strongly fluctuates between disorder realizations. A crossover is observed towards a distribution with different large-$D$ asymptotics deep in the many-body localized phase, which however differs from the commonly expected Cauchy distribution. We show that the average distribution width $〈\gamma 〉$, rescaled by $L\mathrm{\Delta },\mathrm{\Delta }$ being the average level spacing in the middle of the spectrum and $L$ the systems size, is an efficient probe of the many-body localization transition, as it increases (vanishes) exponentially in the delocalized (localized) phase.