Two-dimensional interacting electrons exposed to strong perpendicular magnetic fields generate emergent, exotic quasiparticles phenomenologically distinct from electrons. Specifically, electrons bind with an even number of flux quanta, and transform into composite fermions (CFs). Besides providing an intuitive explanation for the fractional quantum Hall states, CFs also possess Fermi-liquid-like properties, including a well-defined Fermi sea, at and near even-denominator Landau-level filling factors such as $\nu =1/2$ or $1/4$. Here, we directly probe the Fermi sea of the rarely studied four-flux CFs near $\nu =1/4$ via geometric resonance experiments. The data reveal some unique characteristics. Unlike in the case of two-flux CFs, the magnetic field positions of the geometric resonance resistance minima for $\nu <1/4$ and $\nu >1/4$ are symmetric with respect to the position of $\nu =1/4$. However, when an in-plane magnetic field is applied, the minima positions become asymmetric, implying a mysterious asymmetry in the CF Fermi sea anisotropy for $\nu <1/4$ and $\nu >1/4$. This asymmetry, which is in stark contrast to the two-flux CFs, suggests that the four-flux CFs on the two sides of $\nu =1/4$ have very different effective masses, possibly because of the proximity of the Wigner crystal formation at small $\nu$.

The InAs/GaSb heterostructure is one of the systems where the quantum spin Hall effect is predicted to arise. However, as confirmed by recent experimental studies, the most significant highlight of the effect, i.e., conductance quantization due to nontrivial edge states, is obscured by spurious conductivity arising from trivial edge states. In this Rapid Communication, we present an experimental observation of the strong localization of trivial edge modes in an InAs/GaSb heterostructure which was weakly disordered by silicon deltalike dopants within the InAs layer. The edge conduction which is characterized by a temperature-independent behavior at low temperatures and a power law at high temperatures is observed to be exponentially scaled with the length of the edge. Comprehensive analyses on measurements with a range of devices is in agreement with the localization theories in quasi-one-dimensional electronic systems.

We propose a simple solvable variant of the Sachdev-Ye-Kitaev (SYK) model which displays a quantum phase transition from a fast-scrambling non-Fermi liquid to disordered Fermi liquid. Like the canonical SYK model, our variant involves a single species of Majorana fermions connected by all-to-all random four-fermion interactions. The phase transition is driven by a random two-fermion term added to the Hamiltonian whose structure is inspired by proposed solid-state realizations of the SYK model. Analytic expressions for the saddle-point solutions at a large number $N$ of fermions are obtained and show a characteristic scale-invariant ${\sim \left|\omega \right|}^{-1/2}$ behavior of the spectral function below the transition which is replaced by a ${\sim \left|\omega \right|}^{-1/3}$ singularity exactly at the critical point. These results are confirmed by numerical solutions of the saddle-point equations and discussed in the broader context of the field.

We investigate charge ordering in the Holstein model in the presence of anisotropic hopping, $t_x,t_y=1-\delta ,1+\delta$, as a model of the effect of strain on charge-density-wave (CDW) materials. Using quantum Monte Carlo simulations, we show that the CDW transition temperature is relatively insensitive to moderate anisotropy $\delta \lesssim 0.3$, but begins to decrease more rapidly at $\delta \gtrsim 0.4$. However, the density correlations, as well as the kinetic energies parallel and perpendicular to the compressional axis, change significantly for moderate $\delta$. Accompanying mean-field theory calculations show a similar qualitative structure, with the transition temperature relatively constant at small $\delta$, and a more rapid decrease for larger strains. We also obtain the density of states $N\left(\omega \right)$, which provides clear signal of the charge ordering transition at large strain, where finite size scaling of the charge structure factor is extremely difficult because of the small value of the order parameter.

Generation of photocurrents in semiconducting materials requires dissociation of excitons into free charge carriers. While thermal agitation is sufficient to induce dissociation in most bulk materials, an additional push is required to induce efficient dissociation of the strongly bound excitons in monolayer transition metal dichalcogenides (TMDs). Recently, static in-plane electric fields have proven to be a promising candidate. In the present paper, we introduce a numerical procedure, based on exterior complex scaling, capable of computing field-induced exciton dissociation rates for a wider range of field strengths than previously reported in the literature. We present both Stark shifts and dissociation rates for excitons in various TMDs calculated within the Mott-Wannier model. Here, we find that the field-induced dissociation rate is strongly dependent on the dielectric screening environment. Furthermore, applying weak-field asymptotic theory to the Keldysh potential, we are able to derive an analytical expression for exciton dissociation rates in the weak-field region.

We study the exact solution of the Schrödinger equation for the dissipative dynamics of a qubit, achieved by means of short iterative Lanczos method (SIL), which allows us to describe the qubit and the bath dynamics from weak to strong coupling regimes. We focus on two different models of a qubit in contact with the external environment: the first is the spin boson model (SBM), which gives a description of the qubit in terms of static tunneling energy and a bias field. The second model describes an externally driven qubit, where both the bias field and the tunneling rate are controlled by a time-dependent magnetic field, following a finite time protocol. We show that in the SBM case, our solution correctly describes the crossover from coherent to incoherent behavior of the magnetization, occurring at the Toulouse point. Furthermore, we show that the bath response dramatically changes during the system dynamics, going from nonresonant at small times to resonant behavior at long times. When the external driving field is present, for fixed values of the drive duration our results show that the bath can provide beneficial effects to the success of the protocol. We find evidence for a complex interplay between nonadiabaticity of the protocol due to the external drive and dissipation effects, which strongly depends on the detailed form of the qubit-bath interaction.

A detailed structure analysis for the site-diluted $\mathrm{S}{\mathrm{n}}_x\mathrm{F}{\mathrm{e}}_{4-x}\mathrm{N}$ ($x=0.25$, 0.41, and 0.88) has been carried out through complex modeling of the neutron total scattering data. We present quantitative evidence showing the local ferromagnetic cluster size extending to ∼8 Å on average when $\mathrm{S}{\mathrm{n}}_{0.88}\mathrm{F}{\mathrm{e}}_{3.12}\mathrm{N}$ undergoes the spin-glass transition (the other two not showing such a transition). The modeling methodology used in this work involving the corefinement of the nuclear and magnetic structure in both real and reciprocal space can potentially be applied generally to explore a variety of spin-glass material problems.

Experimental evidence that the mass supertransport through solid ${}^4\mathrm{He}$ and the anomalously large matter accumulation in the bulk—the giant isochoric compressibility (also known as the syringe effect)—are both supported by a network of dislocations with a superfluid core is getting stronger since a decade ago. However, a structure of this network, as well as its relation to the basal (nonsuperfluid) dislocations which are responsible for plasticity, remain unclear. Here it is shown that superclimbing and basal edge dislocations can form bound pairs. This implies that plastic deformation should produce the syringe effect and vice versa. The experimental test is proposed. While the strength of the effect depends on the average orientation of the paired dislocations, there is a feature unique to the superfluid dislocation scenario: the supercurrents flow in the direction perpendicular to the plastic deformation.

We study the evolution of averaged transconductances in three-terminal Josephson junctions when the superconducting leads are led throughout a topological phase transition from an $s$-wave to a $p$-wave (Majorana) phase by an in-plane magnetic field $B_x$. We provide a complete description of this transition as a function of $B_x$ and a magnetic flux $\mathrm{\Phi }$ threading the junction. For that we use a spinful model within a formalism that allows us to treat on an equal footing the contribution to the transconductance from both the Andreev subgap levels and the continuum spectrum. We unveil a fractionalization in the quantization of the transconductance due to the presence of Majorana quasiparticles, reflecting the effective pumping of half a Cooper pair charge in the $p$-wave regime.

We find unusual temperature dependence of the ferromagnetic resonance (FMR) frequency $f_{\mathrm{R}}$ for the spin-reorientation (SR) transition, in which the easy axis changes depending on temperature, observed in the Nd permanent magnet, ${\mathrm{Nd}}_2{\mathrm{Fe}}_{14}\mathrm{B}$: $f_{\mathrm{R}}\sim 0$ below the SR transition temperature ($T_{\mathrm{R}}$), drastic increase of $f_{\mathrm{R}}$ around $T_{\mathrm{R}}$, and decrease from a peak at higher temperatures. It is nontrivial that the SR transition causes the unusual behavior of the FMR frequency in a wide temperature region. We show the mechanism of the temperature dependence by theoretical and computational analyses. We derive a general relation between $f_{\mathrm{R}}$ and magnetizations to help the understanding of the mechanism, and clarify that the fluctuation of the transverse magnetization is a key ingredient for the resonance in all temperature regions.

In order to enhance the performance of calculators, multilevel cell (MLC) memories have been proposed as an alternative solution to improve the communication speed between their processors and memories, and also in order to increase the effective storage density of memory devices. In this Rapid Communication, we propose a model of MLC memory based on a multiferroic (MF) composite material. We introduce a one-dimensional trilayer ferromagnetic/ferroelectric/ferromagnetic MF composite material through which we investigate theoretically the dynamics of an electromagnon excitation displaying a soliton structure with an envelope shape. It emerges from this study based on barium titanate (${\text{BaTiO}}_3$) and iron (Fe) that, for suitable values of the parameters of a single initial polarization excitation, some propagation scenarios display the encoding of the states of a system of two magnetic bits, i.e., the 11, 10, 01, and 00 states. In addition to this result, it is also realized that the system exhibits another scenario for which the signal propagating in the MF material is alternately converted from an electrical signal into a magnetic signal and reversely. Such outcomes suggest, on the one hand, the possibility to model a four-level MLC memory, and on the other hand, the modeling of an electromagnetic oscillator, based on a MF composite material.

The coupling between single-photon emitters and phonons opens many possibilities to store and transmit quantum properties. In this paper, we apply the independent boson model to describe the coupling between an optically driven two-level system and a discrete phonon mode. Tailored optical driving allows not only to generate coherent phonon states, but also to generate coherent superpositions in the form of Schrödinger cat states in the phonon system. We analyze the influence of decay and dephasing of the two-level system on these phonon preparation protocols. We find that the decay transforms the coherent phonon state into a circular distribution in phase space. Although the dephasing between two exciting laser pulses leads to a reduction of the interference ability in the phonon system, the decay conserves it during the transition into the ground state. This allows to store the phonon quantum state properties in the ground state of the single-photon emitter.

Theoretical calculations derive the effect of atomic isotopes on the phonon modes of a crystal. We derive the well-known formula for the phonon lifetime limited by isotope scattering. We also derive the equation for the influence of isotopes on the dispersion of the phonons.

The superconducting state of the filled skutterudite alloy series ${\mathrm{Pr}}_{1-x}{\mathrm{La}}_x{\mathrm{Pt}}_4{\mathrm{Ge}}_{12}$ has been systematically studied by specific heat and zero-field muon spin relaxation ($\mu \mathrm{SR}$), while the critical fields have been determined by magnetization measurements. An additional inhomogeneous local magnetic field, indicative of broken time-reversal symmetry, is observed in the superconducting states of the alloys. For $x\lesssim 0.5$, the broken-TRS phase sets in below a temperature $T_m$, distinctly lower than the superconducting transition temperature $T_c$. For $x\gtrsim 0.5,T_m\approx T_c$. The local field strength decreases as $x\to 1$, where ${\mathrm{LaPt}}_4{\mathrm{Ge}}_{12}$ is characterized by conventional pairing. The lower critical field $H_{c1}\left(T\right)$ of ${\mathrm{PrPt}}_4{\mathrm{Ge}}_{12}$ shows the onset of a second quadratic temperature region below $T_q\sim T_m$. Upper critical field $H_{c2}\left(T\right)$ measurements suggest multiband superconductivity, and point gap nodes are consistent with the specific heat data. In ${\mathrm{Pr}}_{1-x}{\mathrm{La}}_x{\mathrm{Pt}}_4{\mathrm{Ge}}_{12}$, only a single specific-heat discontinuity is observed at $T_c$, in contrast to the second jump seen in ${\mathrm{PrOs}}_4{\mathrm{Sb}}_{12}$ below $T_c$. These results suggest that superconductivity in ${\mathrm{PrPt}}_4{\mathrm{Ge}}_{12}$ is characterized by a complex order parameter.

The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase is an unconventional superconducting state found under the influence of a strong Zeeman field. This phase is identified by finite center-of-mass momenta in the Cooper pairs, causing the pairing amplitude to oscillate in real space. Repulsive correlations, on the other hand, smear out spatial inhomogeneities in $d$-wave superconductors. We investigate the FFLO state in a strongly correlated $d$-wave superconductor within a consolidated framework of Hartree-Fock-Bogoliubov theory and the Gutzwiller approximation. We find that the crucial effects of strong correlations lie in shifting the BCS-FFLO phase boundary towards a lower Zeeman field and thereby enlarging the window of the FFLO phase. In the FFLO state, our calculation features a sharp midgap peak in the density of states, indicating the formation of strongly localized Andreev bound states. We also find that the signatures of the FFLO phase survive even in the presence of an additional translational-symmetry-breaking competing order in the ground state. This is demonstrated by considering a broken-symmetry ground state with a simultaneous presence of the $d$-wave superconducting order and a spin-density wave order, often found in unconventional superconductors.

A tunneling system with a molecule between the leads was analyzed in the framework of the adiabatic approach. The adiabatic approach allowed us to consider effects of equilibrium ion positions changing and vibrational mode frequency modification due to the electrons tunneling through the molecule localized states. It was demonstrated that vibrational states become squeezed if the tunneling current flows through the molecule. The mean-square displacement of the molecule and the degree of squeezing depend on the system parameters and could be tuned by applied bias voltage. Obtained results demonstrate the possibility of molecule ions' effective “freezing” by the tunneling current.

We present a joint experiment-theory study on the role of fluorine adatoms in spin and momentum scattering of charge carriers in dilute fluorinated graphene and bilayer graphene. The experimental spin-flip and momentum scattering rates and their dependence on the density of fluorine and carrier doping are obtained through weak localization and conductivity measurements, respectively, and suggest the role of fluorine as resonant magnetic impurities. For the estimated fluorine concentration of a few hundred ppm, the observed spin lifetimes are in the range of 1–10 ps. Theoretically, we established tight-binding electronic structures of fluorinated graphene and bilayer graphene by fitting to density-functional supercell calculations and performed a comprehensive analysis of the spin-flip and momentum scattering rates within the same devices, aiming to develop a consistent description of both scattering channels. We find that resonant scattering in graphene is very sensitive to the precise position of the resonance level, as well as to the magnitude of the exchange coupling between itinerant carriers and localized spins. The experimental data point to the presence of weak spin-flip scatterers that, at the same time, relax the electron momentum strongly, nearly preserving the electron-hole symmetry. Such scatterers would exhibit resonance energies much closer to the neutrality point than what density-functional theory predicts in the dilute limit. The inclusion of a magnetic moment on fluorine adatoms allowed us to qualitatively capture the carrier-density dependence of the experimental rates but predicts a greater (weaker) spin (momentum) relaxation rate than the measurements. We discuss possible scenarios that may be responsible for the discrepancies. Our systematic study exposes the complexities involved in accurately capturing the behavior of adatoms on graphene.

The impact of agglomeration of magnetic nanoparticles on the Casimir pressure is investigated in the configuration of two material plates and a layer of ferrofluid confined between them. Both cases of similar and dissimilar plates are considered in the framework of the Lifshitz theory of dispersion forces. It is shown that for two dielectric (${\mathrm{SiO}}_2$) plates, as well as for one dielectric (${\mathrm{SiO}}_2$) and one metallic (Au) plate, an agglomeration of magnetite nanoparticles results in only quantitative differences in the values of the Casimir pressure if the optical data for Au are extrapolated to low frequencies by means of the Drude model. If, however, an extrapolation by means of the plasma model is used in computations, which is confirmed in experiments on measuring the Casimir force, one finds that the pressure changes its sign when some share of magnetic nanoparticles of sufficiently large diameter is merged into clusters of two or three items. The revealed effect of sign change is investigated in detail at different separations between the plates, diameters of magnetic nanoparticles, and shares of particles merged into clusters of different sizes. The obtained results may be useful when developing ferrofluid-based microdevices and for resolution of outstanding problems in the theory of Casimir forces.