We studied the phase diagram of ${\mathrm{Sr}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ by means of heat capacity and magnetocaloric effect measurements at temperatures as low as 0.06 K and fields up to 12 T. We confirm the presence of a new quantum critical point at 7.5 T which is characterized by a strong non-Fermi-liquid behavior of the electronic specific heat coefficient $\mathrm{\Delta }C/T\sim -logT$ over more than a decade in temperature, placing strong constraints on theories of its criticality. In particular logarithmic corrections are found when the dimension $d$ is equal to the dynamic critical exponent $z$, in contrast to the conclusion of a two-dimensional metamagnetic quantum critical end point, recently proposed. Moreover, we achieved a clear determination of the new second thermodynamic phase adjoining the first one at lower temperatures. Its thermodynamic features differ significantly from those of the dominant phase and characteristics expected of classical equilibrium phase transitions are not observed, indicating fundamental differences in the phase formation.

We identify the low energy effective Hamiltonian that is expected to describe the low temperature properties of the frustrated magnet ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_7{\mathrm{O}}_{28}$. Motivated by the fact that this effective Hamiltonian has $S=3/2$ effective moments as its degrees of freedom, we use semiclassical spin-wave theory to study the $T=0$ physics of this effective model and argue that singular spin-wave fluctuations destabilize the spiral order favored by the exchange couplings of this effective Hamiltonian. We also use a combination of classical Monte-Carlo simulations and molecular dynamics, as well as analytical approximations, to study the physics at low, nonzero temperatures. The results of these nonzero temperature calculations capture the liquidlike structure factors observed in the temperature range accessed by recent experiments. Additionally, at still lower temperatures, they predict that a transition to nematic order in the bond energies reflects itself in the spin channel in the form of a crossover to a regime with large but finite correlation length for spiral spin correlations and a corresponding slowing down of spin dynamics.

Polar metals, which possess ferroelectriclike polar structure and conductivity simultaneously, have attracted wide interest since the first solid example, $\mathrm{LiOs}{\mathrm{O}}_3$ (below 140 K), was discovered. However, the lack of room-temperature polar metals hinders further research and applications. Thus abundant properties of polar metals are unexplored. Here, with first-principles calculations, we report that the polar metal phase can be stabilized in the strain-engineered $\mathrm{BaTi}{\mathrm{O}}_3$ with electron doping. The mechanism relates to the competition between the shifting of the $t_{2g}$ energy levels and the narrowing of their bandwidth. Surprisingly, it is predicted that the ferroelectric-to-paraelectric transition temperature can be increased by electron doping when the strain is large enough, which holds potential for room-temperature polar metals. Our results indicate that strain engineering is a promising way to achieve $\mathrm{BaTi}{\mathrm{O}}_3$-based polar metals, and they should have practical significance for obtaining easily accessible, ecofriendly, and potential room-temperature polar metals.

We consider a thin normal metal sandwiched between two ferromagnetic insulators. At the interfaces, the exchange coupling causes electrons within the metal to interact with magnons in the insulators. This electron-magnon interaction induces electron-electron interactions, which in turn can result in $p$-wave superconductivity. We solve the gap equation numerically and estimate the critical temperature. In yttrium iron garnet (YIG)-Au-YIG trilayers, superconductivity sets in at temperatures somewhere in the interval between 1 and 10 K. EuO-Au-EuO trilayers require a lower temperature, in the range from 0.01 to 1 K.

Entanglement entropy provides a powerful characterization of two-dimensional gapped topological phases of quantum matter, intimately tied to their description by topological quantum field theories (TQFTs). Fracton topological orders are three-dimensional gapped topologically ordered states of matter that lack a TQFT description. We show that three-dimensional fracton phases are nevertheless characterized, at least partially, by universal structure in the entanglement entropy of their ground-state wave functions. We explicitly compute the entanglement entropy for two archetypal fracton models, the “X-cube model” and “Haah's code,” and demonstrate the existence of a nonlocal contribution that scales linearly in subsystem size. We show via Schrieffer-Wolff transformations that this piece of the entanglement entropy of fracton models is robust against arbitrary local perturbations of the Hamiltonian. Finally, we argue that these results may be extended to characterize localization-protected fracton topological order in excited states of disordered fracton models.

In this paper, we present the construction of tensor network states (TNS) for some of the degenerate ground states of three-dimensional (3D) stabilizer codes. We then use the TNS formalism to obtain the entanglement spectrum and entropy of these ground states for some special cuts. In particular, we work out examples of the 3D toric code, the X-cube model, and the Haah code. The latter two models belong to the category of “fracton” models proposed recently, while the first one belongs to the conventional topological phases. We mention the cases for which the entanglement entropy and spectrum can be calculated exactly: For these, the constructed TNS is a singular value decomposition (SVD) of the ground states with respect to particular entanglement cuts. Apart from the area law, the entanglement entropies also have constant and linear corrections for the fracton models, while the entanglement entropies for the toric code models only have constant corrections. For the cuts we consider, the entanglement spectra of these three models are completely flat. We also conjecture that the negative linear correction to the area law is a signature of extensive ground-state degeneracy. Moreover, the transfer matrices of these TNSs can be constructed. We show that the transfer matrices are projectors whose eigenvalues are either 1 or 0. The number of nonzero eigenvalues is tightly related to the ground-state degeneracy.

Landau free-energy expansion parameters for $0.64\mathrm{Pb}\left(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}\right){\mathrm{O}}_3-0.36\mathrm{PbTi}{\mathrm{O}}_3$ single crystal were determined from the temperature-dependent polarization-electric field ($P-E$) hysteresis loops along ${\left[001\right]}_C$, the temperature-dependent dielectric constant ${\varepsilon }_{11}$, and the electric-field-induced tetragonal-rhombohedral phase-transition temperature. Using these obtained parameters, the phase-transition behavior, polarization, dielectric, and piezoelectric constants can all be calculated, which showed good agreement with experimental results. An orthorhombic-to-tetragonal phase transition was predicted to be around $-15{}^{\circ }\mathrm{C}$, near which coexisting orthorhombic phase and tetragonal phase were confirmed by experiments. Based on our calculations, we concluded that the commonly observed monoclinic phase around the orthorhombic-to-tetragonal phase-transition temperature was an adaptive structure due to the coexistence of tetragonal and orthorhombic phases. Additionally, large shear piezoelectric responses exist near room temperature due to the instability caused by the competition between the coexisting tetragonal and orthorhombic phases.

The phonon dispersion in terbium iron borate ${\mathrm{TbFe}}_3{\left({\mathrm{BO}}_3\right)}_4$ has been measured by inelastic neutron scattering in a temperature range $180<T<350$ K through the displacive structural transition at $T_{\mathrm{S}}=192.5$ K and studied by ab initio calculations. Significant, but not complete, softening of the transverse acoustic (TA) branch has been observed at the corner of the Brillouin zone ($\mathrm{\Lambda }$ point) at temperatures $T⪆T_{\mathrm{S}}$, in full agreement with theoretical calculations. The TA soft mode undergoes considerable broadening at the $\mathrm{\Lambda }$ point near the transition temperature that can be attributed to the anharmonic interference between transverse acoustic and optical modes.

The magnetic structure of ${\mathrm{Ca}}_2{\mathrm{MnReO}}_6$ double perovskite is investigated by neutron powder diffraction and bulk magnetization, showing dominant noncollinear Mn magnetic moments $\left[4.35\left(7\right){\mu }_B\right]$ that are orthogonally aligned with the small Re moments $\left[0.22\left(4\right){\mu }_B\right]$. Ab initio electronic structure calculations show that the strong spin-orbit coupling for Re $5d$ electrons combined with a relatively modest on-site Coulomb repulsion ($U_{\mathrm{eff}}^{Re}\gtrsim 0.6$ eV) is sufficient to render this material insulating. This is a rare example of spin-orbit-assisted Mott insulator outside the realm of iridates, with remarkable magnetic properties.

In multiband systems, such as iron-based superconductors, the superconducting states with locking and antilocking of the interband phase differences are usually considered as mutually exclusive. For example, a dirty two-band system with interband impurity scattering undergoes a sharp crossover between the $s_{\pm }$ state (which favors phase antilocking) and the $s_{++}$ state (which favors phase locking). We discuss here that the situation can be much more complex in the presence of an external field or superconducting currents. In an external applied magnetic field, dirty two-band superconductors do not feature a sharp $s_{\pm }\to s_{++}$ crossover but rather a washed-out crossover to a finite region in the parameter space where both $s_{\pm }$ and $s_{++}$ states can coexist for example as a lattice or a microemulsion of inclusions of different states. The current-carrying regions such as the regions near vortex cores can exhibit an $s_{\pm }$ state while it is the $s_{++}$ state that is favored in the bulk. This coexistence of both states can even be realized in the Meissner state at the domain's boundaries featuring Meissner currents. We demonstrate that there is a magnetic-field-driven crossover between the pure $s_{\pm }$ and the $s_{++}$ states.

We predict a novel current-phase relation in multiterminal Andreev interferometers that emerges from an interplay between long-range quantum coherence and nonequilibrium effects. Under nonzero bias $V$ the current-phase relation $I_S\left(\varphi \right)$ resembles that of a ${\varphi }_0$ junction differing from the latter due to a nonzero average $I_0\left(V\right)={〈I_S\left(\varphi \right)〉}_{\varphi }$. The flux-dependent thermopower $\mathcal{S}\left(\mathrm{\Phi }\right)$ of the system has a similar form to that of the current-phase relation and in certain limits it can reduce to an either odd or even function of $\mathrm{\Phi }$ in agreement with a number of experimental observations.

We discuss the impact of concomitant substitution of Fe by Mn and La by Y in optimally F-doped ${\mathrm{LaFeAsO}}_{0.89}{\mathrm{F}}_{0.11}$. Mn has a known poisoning effect on superconductivity which is particularly strong in the La1111 system, where 0.2% of Mn were reported to completely suppress superconductivity. Through isovalent substitution of La by the much smaller Y we are able to inflict chemical pressure on the structure, which we show is stabilizing the superconducting state, resulting in a drastically larger amount of Mn needed to completely quench superconductivity. Interestingly, we find that the lattice parameter $\mathit{c}$ changes significantly even for small amounts of Mn substitution within a series, which is unexpected taking only the differences between ionic radii into account. We discuss our findings in the light of electron localization caused by small amounts of paramagnetic Mn impurities in ${\mathrm{La}}_{1-y}{\mathrm{Y}}_y{\mathrm{Fe}}_{1-x}{\mathrm{Mn}}_x{\mathrm{AsO}}_{0.89}{\mathrm{F}}_{0.11}$ also indicated by resistivity and Mößbauer measurements.

Magnetotransport experiments on Weyl semimetals are essential for investigating the intriguing topological and low-energy properties of Weyl nodes. If the transport direction is perpendicular to the applied magnetic field, experiments have shown a large positive magnetoresistance. In this work we present a theoretical scattering matrix approach to transversal magnetotransport in a Weyl node. Our numerical method confirms and goes beyond the existing perturbative analytical approach by treating disorder exactly. It is formulated in real space and is applicable to mesoscopic samples as well as in the bulk limit. In particular, we study the case of clean and strongly disordered samples.

We develop a procedure which systematically generates all conserved operators in the disordered models of interacting fermions. Among these operators, we identify and count the independent and local integrals of motion (LIOM), which represent the hallmark of the many-body localization (MBL). The method is tested first on the prototype disordered chain of interacting spinless fermions. As expected for full MBL, we find for large enough disorder $N_M=2^M-1$ independent and quasilocal LIOM with support on $M$ consecutive sites. On the other hand, the study of the disordered Hubbard chain reveals that $3^M-1<N_M\lesssim 4^M/2$, which is less than required for full MBL but much more than in the case of spinless fermions.

The critical behavior of dc magnetization in the uranium ferromagnet URhAl with the hexagonal ZrNiAl-type crystal structure has been studied around the ferromagnetic transition temperature $T_{\mathrm{C}}$. The critical exponent $\beta$ for the temperature dependence of the spontaneous magnetization below $T_{\mathrm{C}},\gamma$ for the magnetic susceptibility, and $\delta$ for the magnetic isotherm at $T_{\mathrm{C}}$, have been obtained with a modified Arrott plot, a Kouvel-Fisher plot, the critical isotherm analysis, and the scaling analysis. We have determined the critical exponents as $\beta =0.287\pm 0.005, \gamma =1.47\pm 0.02$, and $\delta =6.08\pm 0.04$ by the scaling analysis and the critical isotherm analysis. These critical exponents satisfy the Widom scaling law $\delta =1+\gamma /\beta$. URhAl has strong uniaxial magnetic anisotropy, similar to its isostructural UCoAl that has been regarded as a three-dimensional (3D) Ising system in previous studies. However, the universality class of the critical phenomenon in URhAl does not belong to the 3D Ising model ($\beta =0.325, \gamma =1.241$, and $\delta =4.82$) with short-range exchange interactions between magnetic moments. The determined exponents can be explained with the results of the renormalization group approach for a two-dimensional (2D) Ising system coupled with long-range interactions decaying as $J\left(r\right)\sim r^{-(d+\sigma )}$ with $\sigma =1.44$. We suggest that the strong hybridization between the uranium $5f$ and rhodium $4d$ electrons in the U-${\mathrm{Rh}}_{\mathrm{I}}$ layer in the hexagonal crystal structure is a source of the low-dimensional magnetic property. The present result is contrary to current understandings of the physical properties in a series of isostructural UTX uranium ferromagnets (T: transition metals, X: $p$-block elements) based on the 3D Ising model.

Motivated by the recent observation that exponentially long coherence times can be achieved for edge spins in models with strong zero modes, we study the impact of level crossings in finite-length spin chains on the dynamics of the edge spins. Focusing on the $XY$ spin-$1/2$ chain with a transverse or longitudinal magnetic field, two models relevant to understanding recent experimental results on cobalt adatoms, we show that the edge spins can remain coherent for an infinite time even for a finite-length chain if the magnetic field is tuned to a value at which there is a level crossing. Furthermore, we show that the edge spins remain coherent for any initial state for the integrable case of a transverse field because all states have level crossings at the same value of the field, while the coherence time is increasingly large for lower temperatures in the case of a longitudinal field, which is nonintegrable.

We report the crystal structure and physical properties of $\mathrm{S}{\mathrm{r}}_{2-x}\mathrm{L}{\mathrm{a}}_x\mathrm{Ir}{\mathrm{O}}_4$ synthesized by mechanical alloying. The magnetic transition temperature $T_{\mathrm{N}}$ and electrical resistivity decreased with increasing La doping, consistent with previous studies involving single-crystalline samples. We also identified the relationship between $T_{\mathrm{N}}$ and tetragonal distortion ($c/a$) in this system. This result suggests that the magnetism of the Sr214 system is strongly correlated with its crystal structure. Zero-field muon spin rotation/relaxation studies revealed that short-range antiferromagnetic ordering is realized in $\mathrm{S}{\mathrm{r}}_{1.9}\mathrm{L}{\mathrm{a}}_{0.1}\mathrm{Ir}{\mathrm{O}}_4$; also, the spin-glass state is stabilized in the low-temperature region. The Ir moment estimated from the longitudinal field μSR results is $0.045{\mu }_{\mathrm{B}}$, ten times smaller than that of $\mathrm{S}{\mathrm{r}}_2\mathrm{Ir}{\mathrm{O}}_4$ ($\sim 0.4{\mu }_{\mathrm{B}}$), indicating that electrons are introduced into the Ir atoms.

We study the Kondo screening of a magnetic impurity in a two-dimensional superconductor with Rashba spin-orbit coupling (SOC). It is found that the Rashba interaction generates a Kondo screening channel, in which the local moment is screened by the exchange coupling with conduction electrons in different spin and orbital states. The Kondo temperature associated with this process is determined by the interplay between the Rashba SOC and superconducting energy gap. As a result, the quantum phase transition between the magnetic doublet and Kondo singlet ground states is significantly affected by increasing Rashba SOC in such a system. This result uncovers that the Rashba SOC plays an instructive role and provides a screening channel for the Kondo effect, which is expected to be observed in future experiments.

The trapping of delocalized electrons at ultrathin layers of NaCl on Ag(100) is investigated in real time using two-photon photoemission. Above 79 K, electrons localize to deep trap states assigned to low-coordinated sites on the NaCl surface. Below 79 K, these low-coordinated trap states serve as precursors for a new deep trap state at increased binding energies. The observation that the emerging trap state requires a localized precursor state suggests that a dynamic polarization of the NaCl lattice may be required for its formation. This behavior is consistent with the expectations for the formation of a interfacial (electron) small polaron which is theoretically unstable in bulk NaCl. The alkali-halide/noble-metal interface shows the sequential population of multiple metastable deep trap states in two dimensions in real time.

We study the scenario of quenching an interaction-free Fermi sea on a one-dimensional lattice ring by suddenly changing the potential of a site. From the point-of-view of the conventional Friedel oscillation, which is a static or equilibrium problem, it is of interest what temporal and spatial oscillations the local sudden quench will induce. Numerically, the primary observation is that for a generic site, the local particle density switches between two plateaus periodically in time. Making use of the proximity of the realistic model to an exactly solvable model and employing the Abel regularization to assign a definite value to a divergent series, we obtain an analytical formula for the heights of the plateaus, which turns out to be very accurate for sites not too close to the quench site. The unexpect relevance and the incredible accuracy of the Abel regularization are yet to be understood. Eventually, when the contribution of the defect mode is also taken into account, the plateaus for those sites close to or on the quench site can also be accurately predicted. We have also studied the infinite lattice case. In this case, ensuing the quench, the out-going wave fronts leave behind a stable density oscillation pattern. Because of some interesting single-particle property, this dynamically generated Friedel oscillation differs from its conventional static counterpart only by the defect mode.