Orbital-selective phenomena in mutliorbital systems have received much attention due to their uniqueness as well as possible connections to other phenomena. As orbital-selectiveness is mostly related to the crystal structure, finding a new control parameter other than structure would be of significant importance. Here we report discovery of an orbital-selective doping effect in ${\mathrm{Sr}}_2{\mathrm{Ru}}_{1-x}{\mathrm{Ir}}_x{\mathrm{O}}_4$ (SRIO). Our systematic electronic structure study of SRIO reveals an anomalous orbital-selective doping effect and concomitant Lifshitz transitions (LTs) in the $\gamma$ band. With the help of a tight-binding calculation, we find that the orbital-selective doping effect is due to variation in the spin-orbit coupling (SOC) strength. Our findings not only elucidate the mechanism of LTs in the $\gamma$ band in SRIO but may also open new avenues for novel SOC-controlled orbital-selective phenomena.

We study how impurities influence the current-induced dynamics of magnetic skyrmions moving in a racetrack geometry. For this, we solve numerically the generalized Landau-Lifshitz-Gilbert equation extended by the current-induced spin transfer torque. In particular, we investigate two classes of impurities, nonconducting and magnetic impurities. The first are magnetically rigid objects and yield to an inhomogeneous current density over the racetrack, which we determine separately by solving the fundamental electrostatic equations. In contrast, magnetic impurities leave the applied current density homogeneous throughout the stripe. Depending on the parameters, we observe four different scenarios of skyrmion motions in the presence of disorder, the skyrmion decay, the pinning, the creation of additional skyrmions, and ordinary skyrmion passage. We calculate and discuss phase diagrams in the dependence of the impurity concentration and radii of the impurities.

We numerically investigate non-Abelian braiding dynamics of vortices in two-dimensional topological superconductors, such as $s$-wave superconductors with Rashba spin-orbit coupling. Majorana zero modes (MZMs) hosted by the vortices constitute a topological qubit, which offers a fundamental building block of topological quantum computation. As the MZMs are protected by ${\mathbb{Z}}_2$ invariant, however, the Majorana qubit and quantum gate operations may be sensitive to intrinsic decoherence caused by MZM hybridization. Numerically simulating the time-dependent Bogoliubov–de Gennes equation without assuming a priori existence of MZMs, we examine quantum noises on the unitary operators of non-Abelian braiding dynamics due to interactions with neighboring MZMs and other quasiparticle states. We demonstrate that after the interchange of two vortices, the lowest vortex-bound states accumulate the geometric phase $\pi /2$, and errors stemming from dynamical phases are negligibly small, irrespective of interactions of MZMs. Furthermore, we numerically simulate the braiding dynamics of four vortices in two-dimensional topological superconductors, and discuss an optimal braiding condition for realizing the high performance of non-Abelian statistics and quantum gate operations of Majorana-based qubits.

Classical meta-absorber designs usually have a tradeoff between bandwidth, efficiency, and thickness. Here, we introduce the concept of a nonlocal acoustic metasurface absorber by using a bridge structure connecting resonating unit cells to improve the performances of the meta-absorber. By utilizing the coupling effect between the adjacent unit cells, ultrabroadband sound absorption is achieved with deep-wavelength thickness. The physical mechanism of the nonlocal acoustic metasurface absorber is investigated and uncovered by developing analytical models. We theoretically and numerically study the nonlocal metasurface with a connecting bridge and the traditional metasurface without a bridge. The nonlocality can introduce three specific effects: the optimization of effective acoustic impedances, the shift of Fabry-Perot resonant frequencies, and the enhancement of the coupling effects between adjacent unit cells. These effects contribute to improve the bandwidth and the efficiency of the acoustic meta-absorber. We numerically and experimentally achieve an average absorption coefficient larger than 0.9 within the ultrabroadband bandwidth extending from about 600 to 2600 Hz, with a metasurface of 6.8 cm, viz., λ/9 for the lowest frequency. Our finding demonstrates the advantage of nonlocal acoustic metasurface to conceive a subwavelength sound meta-absorber.

The $5d$-based $\mathrm{Sr}\mathrm{Ir}{\mathrm{O}}_3$ represents a prototype example of nonmagnetic correlated metal which mainly originates from a combined effect of spin-orbit coupling, lattice dimensionality, and crystal structure. Therefore tuning of these parameters results in diverse physical properties in this material. Here, we study the structural, magnetic, and electrical transport behavior in epitaxial $\mathrm{Sr}\mathrm{Ir}{\mathrm{O}}_3$ film ($\sim 40\mathrm{nm}$) grown on $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrate. As opposed to bulk material, the $\mathrm{Sr}\mathrm{Ir}{\mathrm{O}}_3$ film exhibits a ferromagnetic ordering at low temperature below $\sim 20\mathrm{K}$. The electrical transport data indicate an insulating behavior where the nature of charge transport follows Mott's variable-range-hopping model. A positive magnetoresistance is recorded at 2 K which has a correlation with the magnetic moment. We further observe a nonlinear Hall effect at low temperature $(<20\mathrm{K})$ which arises due to an anomalous component of the Hall effect. An anisotropic behavior of both magnetoresistance and the Hall effect has been evidenced at low temperature, which, coupled with the anomalous Hall effect, indicates the development of ferromagnetic ordering. We believe that an enhanced (local) structural distortion caused by lattice strain at low temperatures induces ferromagnetic ordering, thus showing that structural instability plays a vital role in tuning the physical properties in $\mathrm{Sr}\mathrm{Ir}{\mathrm{O}}_3$.

We determined the crystal structure of ${\mathrm{Cs}}_2{\mathrm{LiRuCl}}_6$, which was synthesized in this work, and investigated its magnetic properties. ${\mathrm{Cs}}_2{\mathrm{LiRuCl}}_6$ has a hexagonal structure composed of linear chains of face-sharing ${\mathrm{RuCl}}_6$ and ${\mathrm{LiCl}}_6$ octahedra. In two thirds of the structural chains, ${\mathrm{Ru}}^{3+}$ and ${\mathrm{Li}}^{+}$ sites are almost ordered, while in the other chains their sites are disordered. This situation is analogous to the ground state of the antiferromagnetic Ising model on a triangular lattice. Using electron paramagnetic resonance, we evaluated the $g$ factors of ${\mathrm{Ru}}^{3+}$ with effective spin-$\frac{1}{2}$ as $g_c=2.72$ and $g_{ab}=1.50$ for magnetic fields $H$ parallel and perpendicular to the $c$ axis, respectively. Magnetization curves for $H\parallel c$ and $H\perp c$ are highly anisotropic. However, these magnetization curves approximately coincide when normalized by the $g$ factors. It was found from the magnetization and specific heat results that ${\mathrm{Cs}}_2{\mathrm{LiRuCl}}_6$ can be described as a coupled one-dimensional $S=1/2$ Heisenberg-like antiferromagnet with $J/k_{\mathrm{B}}\simeq 3.7$ K. Three-dimensional ordering occurs at $T_{\mathrm{N}}=0.48$ K. A magnetic phase diagram for $H\parallel c$ is also presented.

We uncover a systematic structure in the single-particle phase diagram of the quasiperiodic Aubry-André-Harper (AAH) model with power-law hoppings ($\sim \frac{1}{r^{\sigma }}$) when the quasiperiodicity parameter is chosen to be a member of the metallic mean family of irrational Diophantine numbers. In addition to the fully delocalized and localized phases, we find a coexistence of multifractal (localized) states with the delocalized states for $\sigma <1$ ($\sigma >1$). The fraction of delocalized eigenstates in these phases can be obtained from a general sequence, which is a manifestation of a mathematical property of the metallic mean family. The entanglement entropy of the noninteracting many-body ground states respects the area law if the Fermi level belongs in the localized regime while logarithmically violating it if the Fermi level belongs in the delocalized or multifractal regimes. The prefactor of the logarithmically violating term is significantly larger in the delocalized phase in comparison to that in the multifractal phase. Entanglement entropy shows the area law even in the delocalized regime for special filling fractions, which are related to the metallic means.

The ground state at 4/11 filling factor is very well understood, Mukherjee et al. [Phys. Rev. Lett. 112, 016801 (2014)] in terms of the 1/3-filled second effective Landau level of the composite fermions whose correlations resemble that of electrons in the ground state of a two-body Haldane pseudo-potential of relative angular momentum 3, $V_3$. We here propose a closed-form ground-state wave function for $V_3$ at 1/3 filling factor. We successfully compare it with the exact wave function for systems with a few electrons by calculating their mutual overlap, pair-correlation function, and entanglement spectra. By numerical exact diagonalization for a few electron systems, we find a window of nonzero $V_3$ is essential together with $V_1$ for being 4/11 state incompressible. The constructed wave function for the 4/11 state using this proposed wave function has satisfactorily high overlap with previously studied composite-fermion-diagonalized ground-state wave function.

This work investigates the Ni-F distance dependence of the crystal-field (CF) transitions of ${\mathrm{Ni}}^{2+}$ in $\mathrm{KNi}{\mathrm{F}}_3$ by high-pressure spectroscopy. All peaks shift to higher energy with pressure according to trends foreseen by the Tanabe-Sugano diagram. At ambient conditions, we obtain Racah and CF splitting parameters of $B=0.118\mathrm{eV}, 10Dq=0.908\mathrm{eV}$; $C/B=4.4$ ($10Dq/B=7.7$). $B$ and $10Dq$ vary with pressure as $\frac{\partial B}{\partial P}=–0.11\mathrm{meV}\mathrm{G}{\mathrm{Pa}}^{–1}$ and $\frac{\partial 10Dq}{\partial P}=24\mathrm{meV}\mathrm{G}{\mathrm{Pa}}^{–1}$. Similar to $\mathrm{KCo}{\mathrm{F}}_3$, the slight decrease of $B$ with pressure reflects the strong ionic character of the Ni-F bond and its high stability against compression. We have correlated the measured pressure dependence of $10Dq$ with the Ni-F bond distance, showing that it follows a potential law as $10Dq=C{R}^{–n}$ with an exponent $n=6.6\pm 0.5$, thus providing experimental data for checking the suitability of theoretical models aiming to explain the slight deviations of observed $R$ dependencies of $10Dq$ from the CF theory ($n=5$). We have applied the experimental $10Dq$($R$) relationship to determine the real Ni-F bond distances in fluoroperovskites $AB{\mathrm{F}}_3:{\mathrm{Ni}}^{2+}$ from the spectroscopically measured $10Dq$ as an alternative method for determining bond distances, $R_{\mathrm{Ni}-\mathrm{F}}$, in impurity systems. We show that the so-obtained $R_{\mathrm{Ni}-\mathrm{F}}$ deviates from the bond distance of the host site, $R_{B-\mathrm{F}}$, proportionally to the difference $R_{B-\mathrm{F}}-R_0$, with $R_0$ being the sum of ionic radii $R_{{\mathrm{F}}^{-}}+R_{{\mathrm{Ni}}^{2+}}$. The behavior is compared to that found for ${\mathrm{Mn}}^{2+}$ along the fluoroperovskite series $AB{\mathrm{F}}_3:{\mathrm{Mn}}^{2+}$. Finally, weak UV peaks observed below the charge-transfer band gap ($E_{\mathrm{g}}\le 10\mathrm{eV}$) in the absorption spectrum, the assignment of which still remains controversial, have been assigned to single and double excitation transitions. The assignment was unveiled on the basis of their energy and pressure shift.

Controlling the intrinsic anomalous Hall conductivity (AHC) induced by Berry curvature is of significance in potential applications. Half-Heusler antiferromagnet GdPtBi provides an excellent platform to design and control the AHC, owing to its simple band structure near the Fermi level. Here, we systematically study the pressure-dependent magnetotransport properties of GdPtBi, in which the AHC can be continuously tuned by applying hydrostatic pressure. While the band structure and magnetism of GdPtBi bear minor changes below 2 GPa, the AHC decreases progressively with increasing pressure, and eventually vanishes at $P=1.5\mathrm{GPa}$. The chiral anomaly effect and electronic structure calculations further manifest that the Weyl nodes persist in this pressure range under magnetic field. Further analysis indicates that the disappearance of AHC in GdPtBi originates from the shift of the Fermi level relative to the Weyl nodes or the change of the canted spin structure of Gd ions in finite magnetic field under pressure. Our results show that pressure is an effective way to tune the anomalous Hall effect in magnetic topological semimetals.

We investigate a quantum phase transition between a Néel phase and a valence bond solid (VBS) phase, each of which breaks a different ${\mathbb{Z}}_2$ symmetry, in a spin-$1/2$ two-leg XXZ ladder with a four-spin interaction. The model can be viewed as a one-dimensional variant of the celebrated $J\text{−}Q$ model on a square lattice. By means of variational uniform matrix product state calculations and an effective field theory, we determine the phase diagram of the model and present evidence that the Néel-VBS transition is continuous and belongs to the Gaussian universality class with the central charge $c=1$. In particular, the critical exponents $\beta ,\eta ,$ and, $\nu$ are found to satisfy the constraints expected for a Gaussian transition within numerical accuracy. These exponents do not detectably change along the phase boundary while they are in general allowed to do so for the Gaussian class.

Analog physics has successfully tackled the problems of gauge theories, event horizons, Big Bang and Universe expansion, and many others. Here, we suggest a photonic model system for a “time machine” based on the paraxial beam approximation. We demonstrate how the closed timelike curves and the well-known grandfather paradox can be studied experimentally in this system. We show how Novikov's self-consistency principle is realized in quantum mechanics owing to Heisenberg's uncertainty principle.

We performed systematic first-principles calculations to explore the possibility of manipulating Dzyaloshinskii-Moriya interactions (DMIs) in heavy metal/ferromagnetic metal bilayers with ferroelectric (FE) polarization of a $\mathrm{PbTi}{\mathrm{O}}_3$ (PTO) substrate. Significantly, both the sign and magnitude of the DMI can be tailored by the FE polarization reversal in PTO. Moreover, the DMIs of Ir/Co/PTO and Ir/Fe/PTO can achieve large values ($\left|d\right|>10\mathrm{meV}$) under the influence of an upward electric polarization of PTO. Our findings provided useful strategies for enhancing and tailoring DMIs in complex heterostructures and paved the way for the development of DMI-based devices with ultralow power consumption.

We consider two-dimensional $q$-state quantum clock models with quantum fluctuations connecting states with all-to-all clock transitions with different choices for the matrix elements. We study the quantum phase transitions in these models using quantum Monte Carlo simulations and finite-size scaling, with the aim of characterizing the crossover from emergent U(1) symmetry at the transition (for $q\ge 4$) to $Z_q$ symmetry of the ordered state. We also study classical three-dimensional clock models with spatial anisotropy corresponding to the space-time anisotropy of the quantum systems. The U(1) to $Z_q$ symmetry crossover in all these systems is governed by a so-called dangerously irrelevant operator. We specifically study $q=5$ and $q=6$ models with different forms of the quantum fluctuations and different anisotropies in the classical models. In all cases, we find the expected classical XY critical exponents and scaling dimensions $y_q$ of the clock fields. However, the initial weak violation of the U(1) symmetry in the ordered phase, characterized by a $Z_q$ symmetric order parameter ${\varphi }_q$, scales in an unexpected way. As a function of the system size (length) $L$, close to the critical temperature ${\varphi }_q\propto L^p$, where the known value of the exponent is $p=2$ in the classical isotropic clock model. In contrast, for strongly anisotropic classical models and the quantum models, we find $p=3$. For weakly anisotropic classical models, we observe a crossover from $p=2$ to $p=3$ scaling. The exponent $p$ directly impacts the exponent ${\nu }^{\prime }$ governing the divergence of the U(1) to $Z_q$ crossover length scale ${\xi }^{\prime }$ in the thermodynamic limit, according to the relationship ${\nu }^{\prime }=\nu (1+|y_q|/p)$, where $\nu$ is the conventional correlation length exponent. We present a phenomenological argument for $p=3$ based on an anomalous renormalization of the clock field in the presence of anisotropy, possibly as a consequence of topological (vortex) line defects. Thus, our study points to an intriguing interplay between conventional and dangerously irrelevant perturbations, which may also affect other quantum systems with emergent symmetries.

We present the pressure-temperature phase diagram ${\mathrm{La}}_5{\mathrm{Co}}_2{\mathrm{Ge}}_3$ up to $\sim 5$ GPa, which was constructed from magnetization, resistivity, and specific heat measurements. At ambient pressure, ${\mathrm{La}}_5{\mathrm{Co}}_2{\mathrm{Ge}}_3$ is an itinerant ferromagnet with a Curie temperature $T_{\text{C}}\sim$ 4 K. Upon increasing pressure up to $\sim 1.7$ GPa, $T_{\text{C}}$ is suppressed down to $\sim 3$ K. Upon further increasing pressure, our results suggest that ${\mathrm{La}}_5{\mathrm{Co}}_2{\mathrm{Ge}}_3$ enters a different low-temperature ground state. The corresponding transition temperature $T^{*}$ has a nonmonotonic pressure dependence up to $\sim 5$ GPa. Our results demonstrate that the ferromagnetic quantum critical point in ${\mathrm{La}}_5{\mathrm{Co}}_2{\mathrm{Ge}}_3$ is avoided by the appearance of a different, likely magnetically ordered, state that has an antiferromagnetic component.

We combine transport, angle-resolved photoemission spectroscopy, and scanning tunneling spectroscopy to investigate several low-energy manifestations of the Hund's coupling in a canonical FeSC family Li(Fe,Co)As. We determine the doping dependence of the coherent-incoherent crossover temperature and the quasiparticle effective mass enhancement in the normal state. Our tunneling spectroscopy result in the superconducting state supports the idea that superconductivity emerging from Hund's metal state displays a universal maximal superconducting gap vs transition temperature ($2{\mathrm{\Delta }}_{\max }/k_B{T}_c$) value, which is independent of doping level and $T_c$.