We consider second-order phase transitions in which the order parameter is a replicated overlap matrix. We focus on a tricritical point that occurs in a variety of mean-field models and that, more generically, describes higher-order liquid-liquid or liquid-glass transitions. We show that the static replicated theory implies slowing down with a logarithmic decay in time. The dynamical equations turn out to be those predicted by schematic mode-coupling theory for supercooled viscous liquids at a $A_3$ singularity, where the parameter exponent is $\lambda =1$. We obtain a quantitative expression for the parameter $\mu$ of the logarithmic decay in terms of cumulants of the overlap, which are physically observable in experiments or numerical simulations.

Altermagnetism is a subclass of antiferromagnetism that features spin-polarized electron bands of a nonrelativistic origin despite the absence of net magnetization in the material. We here theoretically study spin pumping from an altermagnetic insulator into a normal metal. The symmetry properties of the lattice and spin order of the altermagnet alter the magnon dispersion compared to a conventional square lattice antiferromagnet. We find that for a homogeneous magnetic field, the spin pumping current is the same as that of a regular antiferromagnet. If, however, the magnetic field becomes spatially dependent, we predict that the altermagnetic order will leave a unique fingerprint on the spin pumping behavior when the orientation of the spatial modulation does not align with the high-symmetry paths of magnon degeneracy in the altermagnet. This demonstrates that altermagnets can be used for terahertz spin pumping purposes with novel behavior, distinguishing them from their regular antiferromagnet counterparts.

The quantum mechanics of superconducting circuits is derived by starting from a classical Hamiltonian dynamical system describing a dissipationless circuit, usually made of capacitive and inductive elements. However, standard approaches to circuit quantization treat fluxes and charges, which end up as the canonically conjugate degrees of freedom on phase space, asymmetrically. By combining intuition from topological graph theory with a recent symplectic geometry approach to circuit quantization, we present a theory of circuit quantization that treats charges and fluxes on a manifestly symmetric footing. For planar circuits, known circuit dualities are a natural canonical transformation on the classical phase space. We discuss the extent to which such circuit dualities generalize to nonplanar circuits.

We examine a dielectric medium supporting a magnetic current in connection with optical properties and energy propagation. The dispersion relations, propagating modes, and some optical effects are examined for isotropic and anisotropic magnetic conductivity tensors, with the latter ones implying nonreciprocal permittivities. The eigenvalues of the effective permittivity are carried out and associated with the optical symmetries (uniaxial, biaxial) and the subjacent crystal systems. Aspects of electromagnetic energy transport for such systems are also discussed, with the group and energy velocities being presented and carried out for all the particular cases addressed. Our results suggest that a dielectric supporting magnetic current breaks the usual equivalence between group velocity and energy velocity that holds in a nonabsorbing medium, while establishing the equivalence between them in an effective absorbing scenario, two unexpected behaviors.

The piezoelectricity of group-IV monochalcogenides ($\mathit{MX}\mathrm{s}$, with $M=\mathrm{Ge},\mathrm{Sn}$ and $X=\mathrm{S},\mathrm{Se}$) has attracted much attention due to their substantially higher piezoelectric coefficients compared to other 2D materials. However, with increasing layer number, their piezoelectricity rapidly disappears due to the antiferroelectric stacking order, severely limiting their practical applications. Using first-principles calculations, we investigated the piezoelectricity of $\mathit{MX}\mathrm{s}$ with the ferroelectric AA stacking configuration, which has recently been stabilized in experiments. We found that AA-stacked $\mathit{MX}\mathrm{s}$ have a ferroelectric ground state with the smallest lattice constant among other stacking configurations, resulting in a giant piezoelectric coefficient, which is the first demonstration of a strategy where the piezoelectric coefficients can increase with the number of layers. This can be attributed to a strong negative correlation between the lattice constant along the armchair direction and the piezoelectric coefficient, and spontaneous compressive strain stabilized in ferroelectric AA stacking configuration.

Recently, the Floquet ${\mathrm{Na}}_3\mathrm{Bi}$-type material has been proposed as an ideal platform for realizing various phases, i.e., the spin-degenerate Dirac semimetal (DSM) can be turned into the Weyl semimetal (WSM), and even to the Weyl half-metal (WHM). Instead of the conventional electrical methods, we use the RKKY interaction to characterize the topological phase transitions in this paper. It is found that detecting the Ising term $J_I$ is feasible for distinguishing the phase transition of DSM/WSM, since the emergence of $J_I$ is induced by the broken spin degeneracy. For the case with impurities deposited on $z$ axis (the line connecting the Weyl points), the Heisenberg term $J_H$ coexists with $J_I$ in the WSM, while $J_H$ is filtered out and only $J_I$ survives in the WHM. This magnetic filtering effect is a reflection of the fully spin-polarized property (one spin band is in the WSM phase while the other is gapped) of the WHM, and it can act a signal to capture the phase transition of WSM/WHM. This signal can not be disturbed unless the direction of the impurities greatly deviates from $z$ axis. Interestingly, as the impurities are moved into the $x\text{−}y$ plane, there arises another signal (a dip structure for $J_H$ at the phase boundary), which can also identify the phase transition of WSM/WHM. Furthermore, we have verified that all magnetic signals are robust to the term that breaks the electron-hole symmetry. Besides characterizing the phase transitions, our results also suggest that the Floquet DSMs are power platforms for controlling the magnetic interaction.

We study how time-dependent energy fluctuations impact the dynamical quantum phase transitions (DQPTs) following a noisy ramped quench of the transverse magnetic field in a quantum Ising chain. By numerically solving the stochastic Schrödinger equation of the mode-decoupled fermionic Hamiltonian of the problem, we identify two generic scenarios: Depending on the amplitude of the noise and the rate of the ramp, the expected periodic sequence of noiseless DQPTs may either be uniformly shifted in time or else replaced by a disarray of closely spaced DQPTs. Guided by an exact noise master equation, we trace the phenomenon to the interplay between noise-induced excitations which accumulate during the quench and the near-adiabatic dynamics of the massive modes of the system. Our analysis generalizes to any one-dimensional fermionic two-band model subject to a noisy quench.

We propose a Floquet period-doubling time-crystal model based on a disordered interacting long-range spin chain where the periodic swapping of nearby spin couples is applied. This protocol can be applied to systems with any local spin magnitude $s$ and in principle also to systems with nonspin (fermionic or bosonic) local Hilbert space. We explicitly consider the cases $s=1/2$ and $s=1$, using analytical and numerical methods to show that the time-crystal behavior appears in a range of parameters. In particular, we study the persistence of period-doubling oscillations in time and the time-crystal properties of the Floquet spectrum (quasienergy $\pi$-spectral pairing and long-range correlations of the Floquet states), and introduce a quantity (the local imbalance) to assess what initial states give rise to a period-doubling dynamics. We also consider the quasienergy average level-spacing ratio, and find that the interval of parameters where the system dose not thermalize and persistent period doubling is possible corresponds to the one where the Floquet spectrum shows time-crystal properties.

The influence of an external static electric field on spin wave (SW) dynamics leads to an additional topological phase called the Aharonov-Casher (AC) phase. It is manifested as a shift in dispersion and the group velocity direction of the spin wave under the electric field. Within a linear approximation, the AC effect can be considered by including the Dzyaloshinskii-Moriya-like interaction between neighboring spins, which is proportional to the applied electric field. In this paper, we use these findings to examine the possibility of the electric field control of the refraction of coherently propagating SWs. This is done by studying the propagation SWs across the boundary between two regions of a homogeneous ferromagnetic film under the influence of different external electric fields. We have derived an analytical expression for a magnetic Snell's law and performed micromagnetic simulations to demonstrate how the AC phase shift can control SW refraction. This effect enables us to quantify the topological AC phase action. It presents a promising approach for guiding and manipulating the phase and energy flow of SWs using an external electric field, opening a way to control magnonic devices.

Inspired by the first boron-carbon (B-C) clathrate ${\mathrm{SrB}}_3{\mathrm{C}}_3$ and the ternary borohydride ${\mathrm{KB}}_2{\mathrm{H}}_8$ [Miao et al., Phys. Rev. B 104, L100504 (2021)], we have performed first-principles density functional theory calculations of the electronic and phonon band structures for B-C compounds ${\mathrm{MB}}_2{\mathrm{C}}_8$ ($M$ = Na, K, Rb, Cs). Our calculations reveal that these materials are dynamically stable and can potentially exhibit superconductivity at ambient pressure. However, only the K, Rb, and Cs compounds exhibit thermodynamic stability below 50 GPa, while ${\mathrm{NaB}}_2{\mathrm{C}}_8$ remains thermodynamically unstable at all pressures considered. Based on the Allen and Dynes modified McMillan equation, we predict the superconducting transition temperature $T_c$ of these compounds to be over 65 K at ambient pressure, with $T_c$ decreasing under higher pressures. Remarkably, we find ${\mathrm{CsB}}_2{\mathrm{C}}_8$ possesses the highest predicted $T_c$ of 68.76 K. Our findings demonstrate the possibility of high temperature superconductivity in cubic ${\mathrm{MB}}_2{\mathrm{C}}_8$ at ambient pressure, expanding the B-C clathrate superconductor family. These results provide valuable insights to guide the identification of new atmospheric pressure superconductors.

Obeying non-Abelian statistics, Majorana fermions holds a promise to implement fault-tolerant quantum computing. It was found that Majorana fermions can be simulated by the zero-energy excitation in a nanowire with strong spin-orbit coupling interacting with an $s$-wave superconductor under a magnetic field. However, the signal of Majorana fermion in that system is obscured by the disorder in the nanowire and the confinement potential at the wire end. Thus, more controllable platforms are desired to simulate Majorana fermions. We here propose an alternative scheme to simulate the Majorana fermions in a trapped-ion system. Our dimerized-ion configuration permits us to generate the Majorana modes not only at zero energy but also at the nonzero ones, which enlarge the family of Majorana modes and supply another qubit carrier for quantum computing. We also investigate the controllability of the Majorana modes by Floquet engineering. It is found that a widely tunable number of Majorana modes are created on demand by applying a periodic driving on the trapped-ion system. Enriching the platforms for simulating Majorana fermions, our result would open another avenue for realizing fault-tolerant quantum computing.

In many Ce-based superconductors, superconducting (SC) phases emerge or can be tuned in proximity to the antiferromagnetic (AFM) quantum critical point (QCP), but so far the explicit phase evolution near the QCP lacks theoretical understanding. Here, by combing the density functional theory plus dynamical mean-field theory $(\mathrm{DFT}+\mathrm{DMFT})$ with effective-model calculations, we provide a theoretical description for Ce-based superconductors under compression. $\mathrm{DFT}+\mathrm{DMFT}$ calculations for the normal states reveal that the Kondo hybridizations are significantly enhanced under compression, while the initially localized $f$ electrons become fully itinerant via localized-itinerant crossover. We then construct an effective model and show that with the extracted Kondo coupling and RKKY exchange strengths from first-principles calculations, the ground-state phases of these materials can be properly predicted. We also show that the coexistence of magnetic correlation and Kondo hybridization can drive $\mathrm{AFM}+\mathrm{SC}$ coexisting states in a narrow compression region. Under compression, competition between Kondo and RKKY interactions can drive successive transitions, from the AFM phase to the $\mathrm{AFM}+\mathrm{SC}$ coexisting phase, then to the paramagnetic SC phase via an AFM transition which generates the QCP, and finally to the normal Kondo paramagnetic (KP) phase through an SC-KP transition induced by the localized-itinerant crossover. Our paper gives proper explanation to the pressure-induced QCP and SC-KP transition and to the phase evolution in pressured Ce-based superconductors, and can help one to understand the SC states around the ferromagnetic quantum transition points in uranium-based superconductors.

Electron dynamics driven by few-cycle laser pulses has recently attracted great interest as a means to realizing the manipulation of electron motion on the atomic timescale. Using tight-binding models and the time-dependent nonequilibrium Green's function (TD-NEGF) method, we investigated laser-pulse-induced electron dynamics in armchair graphene nanoribbons (GNRs) with and without topological states. The results show that multiphoton excitations can lead to photocurrents along the GNRs and that the corresponding transferred charges can be enhanced by a factor of several hundreds for GNRs with topological states. This enhancement effect is due to the topological states in the band gap of GNRs, which reduce the order of multiphoton absorption and increase the transition probability of excitations.

We study an XXZ spin chain at zero magnetization coupled to a collection of local harmonic baths at zero temperature. We map this system on a $(1+1)\mathrm{D}$ effective field theory using bosonization, where the effect of the bath is taken care of in an exact manner. We provide analytical and numerical evidence of the existence of two phases at zero temperature: a Luttinger liquid (LL) and an antiferromagnetic phase (AFM), separated by a phase transition akin to the Berezinsky–Kosterlitz–Thouless type. While the bath is responsible for the LL-AFM transition for subohmic baths, the LL-AFM transition for superohmic baths is due to the interactions within the spin chain.

${\mathrm{EuZn}}_2{\mathrm{P}}_2$ was reported to be an insulating antiferromagnet with $T_{\mathrm{N}}$ of 23.5 K. In this study single crystals of ${\mathrm{EuZn}}_2{\mathrm{P}}_2$ exhibiting metallic behavior and a ferromagnetic order of 72 K ($T_{\mathrm{C}}$) are successfully synthesized via a salt flux method. The presence of hole carriers induced by the Eu vacancies in the lattice is found to be crucial for the drastic changes in magnetism and electrical transport. The carriers mediate the interlayer ferromagnetic interaction, and the coupling strength is directly related to $T_{\mathrm{C}}$, as evidenced by the linear dependence of $T_{\mathrm{C}}$ and the fitted Curie-Weiss temperatures on the Eu-layer distances for ferromagnetic $\mathrm{Eu}{M}_2{X}_2$ ($M$ = Zn, Cd; $X$ = P, As). The ferromagnetic ${\mathrm{EuZn}}_2{\mathrm{P}}_2$ shows conspicuous negative magnetoresistance (MR) near $T_{\mathrm{C}}$ owing to strong magnetic scattering. The MR behavior is consistent with the Majumdar-Littlewood model, indicating that the MR can be enhanced by decreasing the carrier density. Our findings suggest that $\mathrm{Eu}{M}_2{X}_2$ has highly tunable magnetism and charge transport, making it a promising material family for potential applications in spintronics.

In this Letter we theoretically predict a distinct class of anomalous Hall effects occurring in metallic collinear antiferromagnets. The effect is quadratic and $d$-wave symmetric in an external magnetic field. In addition, the electric current, transverse to the current voltage drop and the magnetic field in the predicted effect are all in the same plane. The studied theoretical model consists of two-dimensional fermions interacting with the Néel order through momentum-dependent exchange interaction having a $d$-wave symmetry. We also find unusual linear magnetoconductivity in this model.

Using a combination of crystal structure search methods, first-principles calculations, and machine learning potential based simulations, we explored the lithium-lead system and predicted five phases: $I_4$/mcm ${\mathrm{LiPb}}_2$, Pnma LiPb, $I_4$/mmm ${\mathrm{Li}}_4\mathrm{Pb}, C2/m {\mathrm{Li}}_5\mathrm{Pb}$, and Cmcm ${\mathrm{Li}}_6\mathrm{Pb}$. Among them, $I_4$/mmm ${\mathrm{Li}}_4\mathrm{Pb}$ displayed remarkable properties, including superconductivity, plasticity, and superionic behavior at varying temperature ranges. At lower temperatures, $I_4$/mmm ${\mathrm{Li}}_4\mathrm{Pb}$ manifests superconductivity with a critical transition temperature of 4–5 K. Its superconducting behavior is attributed to the interplay between the $B_2$ _g vibration mode, which signifies the rotational motion of four-membered lithium rings within the stacking layer, and the participation of $p$-orbital electrons. As temperature rises, $I_4$/mmm ${\mathrm{Li}}_4\mathrm{Pb}$ first transitions into a plastic phase, marked by continuous collective rotation of intralayer four-membered lithium rings, and then shows superionic behavior characterized by the emergence of interlayer lithium atom diffusion. These unique behaviors stem from stronger Li-Li bonds within four-membered lithium rings and a lower energy barrier for collective motion, distinct from interstitial localized electrons in electrides found in other lithium-based systems. This work provides an intriguing platform for exploring distinct states and establishes a correlation between various physical phenomena and the system's structure and bonding.