The search for spontaneous pattern formation in equilibrium phases with genuine quantum properties is a leading direction of current research. In this paper, we investigate the effect of quantum fluctuations—zero-point motion and exchange interactions—on the phases of an ensemble of bosonic particles with isotropic hard-soft corona interactions. We perform extensive path-integral Monte Carlo simulations to determine their ground-state properties. A rich phase diagram, parametrized by the density of particles and the interaction strength of the soft-corona potential, reveals supersolid stripes, kagome, and triangular crystals in the low-density regime. In the high-density limit, we observe patterns with 12-fold rotational symmetry compatible with periodic approximants of quasicrystalline phases. We characterize these quantum phases by computing the superfluid density and the bond-orientational order parameter. Finally, we highlight the qualitative and quantitative differences of our findings with the classical equilibrium phases for the same parameter regimes.

In recent years, it became clear that the metallic regime of systems that exhibit a many-body localization (MBL) behavior shows properties that are quite different than the vanilla metallic region of the single-particle Anderson regime. Here we show that the large-scale energy spectrum of a canonical microscopical model featuring MBL displays a nonuniversal behavior at intermediate scales, which is distinct from the deviation from universality seen in the single-particle Anderson regime. The crucial step in revealing this behavior is a global unfolding of the spectrum performed using the singular value decomposition (SVD) which takes into account the sample to sample fluctuations of the spectra. The spectrum properties may be observed directly in the singular value amplitudes via the scree plot, or by using the SVD to unfold the spectra and then perform a number of states variance calculation. Both methods reveal an intermediate scale of energies that follow super-Poissonian statistics.

Electronic correlation may have an essential influence on the electronic structure in some materials with special structures and localized orbital distribution. In this work, taking a Janus monolayer FeClF as a concrete example, the correlation effects on its electronic structures are investigated by using the generalized gradient approximation plus $U$ approach. For perpendicular magnetic anisotropy (PMA), increasing electron correlation effects can induce the ferrovalley (FV) to half-valley-metal (HVM) to quantum anomalous Hall (QAH) to HVM to FV transitions. For the QAH state, there is a unit Chern number and a chiral edge state connecting the conduction and valence bands. The HVM state is at the boundary of the QAH phase, whose carriers are intrinsically 100% valley polarized. With the in-plane magnetic anisotropy, no special QAH states and prominent valley polarization are observed. However, for both out-of-plane and in-plane magnetic anisotropy, sign-reversible Berry curvature can be observed with increasing $U$. It is found that these phenomenons are related with the change of $d_{xy}/d_{x^2-y^2}$ and $d_{z^2}$ orbital distributions and different magnetocrystalline directions. It is also found that the magnetic anisotropy energy and Curie temperature strongly depend on the $U$. With PMA, taking a typical $U=2.5$ eV, the electron valley polarization can be observed with valley splitting of 109 meV, which can be switched by reversing the magnetization direction. When considering intrinsic magnetic anisotropy, the easy axis of FeClF changes from out of plane to in plane with increasing $U$, and the critical $U$ value is about 1.15 eV. With intrinsic magnetic anisotropy, a monolayer FeClF shows no special QAH and HVM states. The analysis and results can be readily extended to the other nine members of monolayer $\mathrm{Fe}XY$ ($X/Y=\text{F}$, Cl, Br, and I) due to sharing the same Fe-dominated low-energy states and electronic correlations with a FeClF monolayer. Our work emphasizes the importance of electronic correlation and magnetic anisotropy to determine the electronic state of some materials and shows that electronic correlation can induce exceptional phase transitions.

We investigate the antiferromagnetic spin Seebeck effect across the spin-flop transition in a numerical simulation based on the time-dependent Ginzburg-Landau equation for a bilayer of a uniaxial insulating antiferromagnet and an adjacent metal. By directly simulating the rate of change of the conduction-electron spin density $\mathit{s}$ in the adjacent metal layer, we demonstrate that a sign reversal of the antiferromagnetic spin Seebeck effect across the spin-flop transition occurs when the interfacial coupling of $\mathit{s}$ to the staggered magnetization $\mathit{n}$ of the antiferromagnet dominates, whereas no sign reversal appears when the interfacial coupling of $\mathit{s}$ to the magnetization $\mathit{m}$ dominates. Moreover, we show that the sign reversal is influenced by the degree of spin dephasing in the metal layer. Our result indicates that the sign reversal is not a generic property of a simple uniaxial antiferromagnet, but controlled by microscopic details of the exchange coupling at the interface and the spin dephasing in the metal layer.

We have performed magnetotransport and high-resolution angle-resolved photoelectron spectroscopy (ARPES) measurements on topological insulator ${\mathrm{Pd}}_x{\mathrm{Bi}}_2{\mathrm{Te}}_3(0\le x\le 0.20)$ single crystals. We have observed unusually high values of magnetoresistance ($\sim 1500\%$) and mobility $(\sim 93000\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{–1}{\mathrm{s}}^{–1})$ at low temperatures for pristine ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ that decrease upon Pd doping. Shubnikov–de Haas (SdH) oscillations were detected for $x=0.05$, 0.10, confirming the presence of two-dimensional topological surface states (TSSs) for these samples. Hall measurement shows the crossover from $n$-type charge carriers in pristine ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ to $p$-type charge carriers upon Pd doping. The ARPES measurements show that the conduction band crosses the Fermi level for pristine ${\mathrm{Bi}}_2{\mathrm{Te}}_3$, and the Dirac point of the TSSs and bulk-derived valence bands indicated a shift to lower binding energy upon Pd doping in a rigid-band-like way up to $x\sim 0.10$. Based on the comparison of the parameters obtained from the SdH and ARPES measurements, the reduction in the $k_{\mathrm{F}}$ value in the magnetotransport measurements is likely due to the band bending induced by the Schottky barrier.

Rashba spin-orbit coupling (SOC) described by odd powers of $\mathbf{k}$ terms in semiconductor quantum wells (QWs) plays a critical role in spintronics and quantum computing. It was believed that the Rashba SOC in two-dimensional hole gases (2DHGs) is a $\mathbf{k}$-cubic term as the lowest order, in sharp contrast to its electron counterpart in which the leading term is a $\mathbf{k}$-linear term. Our recent work [Phys. Rev. B 103, 085309 (2021)] uncovered the emergence of $\mathbf{k}$-linear Rashba SOC in 2DHGs arising from their direct dipolar coupling to the external electric field in the presence of heavy-hole-light-hole (HH-LH) mixing. Here, we explore the upper and lower bounds of this $\mathbf{k}$-linear Rashba SOC for 2DHGs in Ge/Si QWs by varying the growth orientations. By performing atomistic pseudopotential method calculations associated with symmetry analysis, we demonstrate that the upper bound of the $\mathbf{k}$-linear Rashba SOC of 2DHGs is in the [110]-oriented QWs, and the lower bound is the vanishment of the $\mathbf{k}$-linear Rashba term, giving rise to purely $\mathbf{k}$-cubic Rashba SOC, in the [111]-oriented QWs with an even number of the well monolayers (MLs). The varying of the well MLs from even to odd can also change the symmetry of QWs and thus produce different types of SOC. In the odd-ML [001]-oriented QWs, we observe a strong Dresselhaus SOC, which is, however, absent leaving behind the $\mathbf{k}$-linear Rashba SOC alone in the even-ML [001]-oriented QWs. We further illustrate that the $\mathbf{k}$-linear Rashba SOC in [001]-oriented QWs and odd-ML [111]-oriented QWs completely arises from the local interface induced HH-LH mixing, whereas in other orientations it is dominated by the QW global symmetry allowed intrinsic HH-LH mixing, which is due to the orientation-dependent breaking of the axial symmetry but is irrelevant to the local interface. We prove that the strongest intrinsic HH-LH mixing appears in the [110] orientation by doing the transformation of the Luttinger-Kohn Hamiltonian, explaining why the upper bound of the $\mathbf{k}$-linear Rashba SOC occurred in the [110]-oriented QWs. Subsequently, we illustrate clearly the strong correlation between the HH-LH mixing and the $\mathbf{k}$-linear Rashba SOC. The $\mathbf{k}$-linear Rashba SOC occurring in odd-ML [001]-oriented QWs but purely $\mathbf{k}$-cubic Rashba SOC in even-ML [111]-oriented QWs provides direct evidence for the hypothesis that the HH-LH mixing observed in [001]-oriented, e.g. GaAs/AlAs, QWs arises from the local interface symmetry $C_{2v}$ despite it is the nominal prohibition by the QW global symmetry $D_{2d}$, considering the HH-LH mixing is forbidden by the global symmetry of both QWs and is allowed by the former rather than the latter local interfaces. Our findings clarify the physical mechanism underlying the orientation dependence of the Rashba SOC and provide design rules to realize $\mathbf{k}$-linear or purely $\mathbf{k}$-cubic Rashba SOC in 2D hole systems.

General explicit analytical expressions for the charge-charge interaction energy $W(Z,Z^{\prime },R)$ between two point charges in heterostructures with three plane layers were obtained in the framework of classical electrostatics, i.e., the dielectric permittivities of the constituent media were assumed to be constant. Here, $R$ is the lateral (along the interfaces) distance between the charges, and $Z$ and $Z^{\prime }$ are their normal coordinates. The obtained results may be applied to the interaction between charges for their various arrangements in the layered system. For instance, the interaction across the interlayer was calculated as the function of the dielectric constants ${\varepsilon }_i(i=1,2,3)$ of the constituent media. It was demonstrated that the textbook Coulomb expression is far from being valid in this case. In particular, more sophisticated formulas proposed here should be used when considering interlayer excitons in heterostructures of various kinds and electron-hole superfluidity in such sandwiches.

${\mathrm{CeRh}}_3{\mathrm{Si}}_2$ has been reported to exhibit metamagnetic transitions below 5 K, a giant crystal field splitting, and anisotropic magnetic properties from single crystal magnetization and heat capacity measurements. Here we report results of neutron and x-ray scattering studies of the magnetic structure and crystal-field excitations to further understand the magnetism of this compound. Inelastic neutron scattering and resonant inelastic x-ray scattering reveal a $J_z=1/2$ ground state for Ce when considering the crystallographic $a$ direction as quantization axis, thus explaining the anisotropy of the static susceptibility. Furthermore, we find a total splitting of 78 meV for the $J=5/2$ multiplet. The neutron diffraction study in zero field reveals that, on cooling from the paramagnetic state, the system first orders at $T_{{\text{N}}_1}=4.7\mathrm{K}$ in a longitudinal spin density wave with ordered Ce moments along the $b$ axis (i.e., the [0 1 0] crystal direction) and an incommensurate propagation vector $\mathbf{k}=(0,0.43,0$). Below the lower-temperature transition $T_{{\text{N}}_2}=4.48\mathrm{K}$, the propagation vector locks to the commensurate value $\mathbf{k}=(0,0.5,0)$, with a so-called lock-in transition. Our neutron diffraction study in applied magnetic field $H\parallel b$ axis shows a change in the commensurate propagation vector and development of a ferromagnetic component at $H=3\mathrm{kOe}$, followed by a series of transitions before the fully field-induced ferromagnetic phase is reached at $H=7\mathrm{kOe}$. This explains the nature of the steps previously reported in field-dependent magnetization measurements. A very similar behavior is also observed for the $H\parallel$ [0 1 1] crystal direction.

We study phonons generated by current in a Pt nanowire by measuring the resistance of another nanowire separated from the first one by an insulating spacer. For thin spacers, the resistance varies almost linearly with current at cryogenic temperatures, while an additional quadratic contribution emerges for thicker spacers. These observations suggest a nonthermal distribution of current-generated phonons that relax via strongly nonlinear dynamical processes rather than few-phonon scattering. Our results provide insight into the nonequilibrium phonon dynamics at nanoscale, which may facilitate efficient heat management in electronic nanodevices.

We studied the magnetic properties of ${\mathrm{YCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Br}}_2\left[{\mathrm{Br}}_{1-x}{\left(\mathrm{OH}\right)}_x\right]$ ($x$ = 0.33), where ${\mathrm{Cu}}^{2+}$ ions form two-dimensional kagome layers. There is no magnetic order down to 50 mK, while the Curie-Weiss temperature is on the order of $-100$ K. At zero magnetic field, the low-temperature specific heat shows a $T^2$ dependence. Above 2 T, a linear temperature dependence term in specific heat emerges, and the value of $\gamma =C/T$ increases linearly with the field. Furthermore, the magnetic susceptibility tends to a constant value at $T=0$. Our results suggest that the magnetic ground state of ${\mathrm{YCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Br}}_2\left[{\mathrm{Br}}_{1-x}{\left(\mathrm{OH}\right)}_x\right]$ is consistent with a Dirac quantum-spin-liquid state with a linearly dispersing spinon strongly coupled to an emergent gauge field, which has long been theoretically proposed as a candidate ground state in the two-dimensional kagome Heisenberg antiferromagnetic system.

We numerically study the ground-state properties of a one-dimensional lattice model in the presence of a quasiperiodic Zeeman field, by means of the density matrix renormalization group algorithm. We map out a global phase diagram, which encloses a Bardeen-Cooper-Schrieffer (BCS) phase, a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase where the Cooper pairs obtain a finite center-of-mass momentum, and a localized phase. The FFLO phase is promoted by the quasiperiodic Zeeman field, which demonstrates a power-law pairing correlation with a critical exponent ${\eta }_{\mathrm{FFLO}}<1$ decaying much slower than the charge density and spin density correlations. By tuning the interaction and the filling factor, we find the FFLO phase is suppressed in the strong interaction and low filling regions. A large Zeeman field destroys the FFLO state and drives a superconductor-insulator transition. Furthermore, we propose this FFLO phase and the superconductor-insulator transition could be observed in the optical lattice experiment.

Bulk-boundary correspondence is a fundamental principle for topological phases where bulk topology determines gapless boundary states. On the other hand, it has been known that corner or hinge modes in higher-order topological insulators may appear due to “extrinsic” topology of the boundaries even when the bulk topological numbers are trivial. In this paper, we find that Floquet anomalous boundary states in quantum walks have similar extrinsic topological natures. In contrast to higher-order topological insulators, the extrinsic topology in quantum walks is manifest even for first-order topological phases. We present the topological table for extrinsic topology in quantum walks and illustrate extrinsic natures of Floquet anomalous boundary states in concrete examples.

Specific heat $C_B$ of a ${\mathrm{TbAl}}_3{\left({\mathrm{BO}}_3\right)}_4$ crystal was studied for 50 mK $<T<$ 300 K with emphasis on $T<1$ K where a phase transition was found at $T_c=0.68$ K. Nuclear, nonphonon ($C_m$), and lattice contributions to $C_B$ were separated. Lowering of $T_c$ with an increase in magnetic field parallel to the easy magnetization axis $\left(B_{\parallel }\right)$ was found. It was established that $C_m$ and a Grüneisen ratio depend on $B_{\parallel }$ and $T$ in a way characteristic of systems in which a classical transition is driven by quantum fluctuations (QFs) to a quantum critical point at $T=0$ by tuning a control parameter ($B_{\parallel }$). The $B_{\parallel }-T$ phase diagram was constructed, and the dynamical critical exponent $0.82\le z\le 0.96$ was assessed. Nature of the transition was not established explicitly. Magnetization studies point at the ferromagnetic ordering of ${\mathrm{Tb}}^{3+}$ magnetic moments, however, lowering of $T_c$ with increase in $B_{\parallel }$ is opposite to the classical behavior. Hence, a dominant role of QFs was supposed.

Within the celebrated Su-Schrieffer-Heeger model including electron-lattice and electron-electron interactions, the electronic ground state of polyacene ($n$-acene) is studied as a function of molecular length $n$. The results demonstrate that the ground state exhibits a phase transition from a nonmagnetic state to an antiferromagnetic state at a critical length of $n=7$. The magnetism is explained by calculating the lattice distortion and the related average hopping rate of the π electrons. It is revealed that in polyacenes, there exist two competing mechanisms that minimize the molecular energy, namely the lattice dimerization and the formation of an antiferromagnetic spin density. Since the dimerization is restricted to the regions near the ends of the molecules the former mechanism is dominant for short molecules, which therefore assume a nonmagnetic state. When the length is increased beyond the critical value, the lattice dimerization in the middle of the molecule is reduced and a rapid drop of the average hopping rate occurs. This makes the second mechanism dominant and the associated antiferromagnetic state is stabilized. The effect of different interaction strengths and values of hopping integrals on the critical length is discussed. The results are confirmed by first-principles calculations. Suggestions for the design of organic antiferromagnets with a similar ladder structure are also given.

We present an analog of the quantum-mechanical reversed fractional stimulated Raman adiabatic passage (f-STIRAP) in an acoustic system by designing three-cavity couplers with space-varying coupling strengths, which are further structured to construct acoustic multifunctional metamaterials. The agreement between analytic and simulated results verifies that the propagation of the acoustic wave mimics the evolution of reversed f-STIRAP in quantum optics. The constructed acoustic metamaterials are of optional functions, beam focusing, beam splitting, or asymmetric transmission with switchable features, depending on the wavelength of the incident acoustic wave. Our work extends the application realm of STIRAP, which may have profound impacts on exploring quantum technologies for promoting advanced acoustic devices.

We report that the magnetostriction (MS) effects occur in a paramagnetic state of a chiral magnet $\mathrm{Cr}{\mathrm{Nb}}_3{\mathrm{S}}_6$. Through a series of experimental tests at room temperature, structural changes were observed at the level of a unit cell. The structural parameters are dependent of the strength and direction of magnetic field ($H$) even at temperature excessively higher than the magnetic ordering temperature $T_{\mathrm{c}}$ of 127 K. The present paramagnetic MS prominently appeared under $H\parallel$ the $ab$ plane (easy plane) as opposed to under $H\parallel$ the $c$ axis. Features observed in the paramagnetic MS effect significantly differ from those of the spontaneous MS in the vicinity of $T_{\mathrm{c}}$ [Phys. Rev. B 102, 014446 (2020)]. In this material, the orbital angular momentum $L$ of Cr originates from the hybridization between Cr and Nb, and $L$ is strongly coupled with the crystal structure [Phys. Rev. B 99, 174439 (2019)]. The present study clarified that the symmetry of the $\mathrm{Cr}{\mathrm{S}}_6$ octahedron is sensitive to $H$ even at room temperature. The paramagnetic spin-orbit coupling should induce the distortion of $\mathrm{Cr}{\mathrm{S}}_6$ octahedron, resulting in the changes in Cr-Nb($4f$) distance via the change in the hybridization between Cr-$a_{1g}$ and Nb-$4d_{z^2}$ orbitals.