We report the existence of a charge density wave (CDW) in the ground state of the one-dimensional (1D) Kondo lattice model at the filling of $n=0.75$ in the weak-coupling region. The CDW is driven by the effective Coulomb repulsion induced by the localized spins. Based on our numerical results using the density matrix renormalization-group method, we show that the CDW phase appears in the paramagnetic region previously known as the Tomonaga-Luttinger liquid. The emergence of this phase serves as an example of a CDW phase induced without bare repulsive interactions, and it enriches the phase diagram of the 1D Kondo lattice model.

We report the discovery of a large-magnetoresistance (LMR) phenomenon in a family of ${\mathrm{BaMn}}_2{Pn}_2$ antiferromagnets ($Pn$ = P, As, Sb, and Bi) with parity-time symmetry. The resistivities of these materials are reduced by 60 times in magnetic fields $\mathbf{H}$, thus yielding a LMR of about $-98\%$. The LMR changes systematically along with the $Pn$ elements, hinting that its origin is the spin-orbit coupling and/or $d-p$ orbital hybridization. A positive MR component emerging on top of the negative LMR at low temperatures suggests an orbital-sensitive magnetotransport as $\mathbf{H}$ suppresses the conduction of the electronlike carriers in the $d$-like band but enhances that of holelike ones in the $d-p$ hybridized band. The anisotropy of the LMR reveals that the electrical conductivity is extremely sensitive to the minute changes in the direction of the antiferromagnetic moments induced by the parity-time symmetry-breaking $\mathbf{H}$, which is perpendicular to the antiferromagnetic spin-ordered direction. We attribute the observed LMR to the nontrivial low-energy bands of ${\mathrm{BaMn}}_2{Pn}_2$ antiferromagnets, which are governed by the parity-time symmetry.

Two-dimensional materials constitute an exciting platform for nonlinear optics with large nonlinearities that are tunable by gating. Hence, gate-tunable harmonic generation and intensity-dependent refraction have been observed in, e.g., graphene and transition-metal dichalcogenides, whose electronic structures are accurately modeled by the (massive) Dirac equation. We exploit on the simplicity of this model and demonstrate here that arbitrary nonlinear response functions follow from a simple iterative approach. The power of this approach is illustrated by analytical expressions for harmonic generation and intensity-dependent refraction, both computed up to ninth order in the pump field. Moreover, the results allow for arbitrary band gaps and gating potentials. As illustrative applications, we consider (i) the gate dependence of third- and fifth-harmonic generation in gapped and gapless graphene, (ii) the intensity-dependent refractive index of graphene up to ninth order, and (iii) the intensity dependence of high-harmonic generation.

We experimentally investigate the charge induction mechanism across gated, narrow, ballistic graphene devices with different degrees of edge disorder. By using magnetoconductance measurements as the probing technique, we demonstrate that devices with large edge disorder exhibit a nearly homogeneous capacitance profile across the device channel, close to the case of an infinitely large graphene sheet. In contrast, devices with lower edge disorder ($<1\mathrm{nm}$ roughness) are strongly influenced by the fringing electrostatic field at graphene boundaries, in quantitative agreement with theoretical calculations for pristine systems. Specifically, devices with low edge disorder present a large effective capacitance variation across the device channel with a nontrivial, inhomogeneous profile due not only to classical electrostatics but also to quantum mechanical effects. We show that such quantum capacitance contribution, occurring due to the low density of states across the device in the presence of an external magnetic field, is considerably altered as a result of the gate electrostatics in the ballistic graphene device. Our conclusions can be extended to any two-dimensional (2D) electronic system confined by a hard-wall potential and are important for understanding the electronic structure and device applications of conducting 2D materials.

The magnetic domain wall motion driven by a magnetic field is studied in (Ga,Mn)As and (Ga,Mn)(As,P) films of different thicknesses. In the thermally activated creep regime, a kink in the velocity curves and a jump of the roughness exponent evidence a dimensional crossover in the domain wall dynamics. The measured values of the roughness exponent ${\zeta }_{1d}=0.62\pm 0.02$ and ${\zeta }_{2d}=0.45\pm 0.04$ are compatible with theoretical predictions for the motion of elastic line ($d=1$) and surface ($d=2$) in two- and three-dimensional media, respectively.

We develop a theory for interlayer tunneling in van der Waals heterostructures driven under a strong electromagnetic field, using $\text{graphene}/h-\mathrm{BN}/\text{graphene}$ as a paradigmatic example. Our theory predicts that strong antiresonances appear at bias voltage values equal to an integer multiple of the light frequency. These features are found to originate from photon-assisted resonant tunneling transitions between Floquet sidebands of different graphene layers, and are unique to two-band systems due to the interplay of both intraband and interband tunneling transitions. Our results point to the possibility of tunneling localization in van der Waals heterostructures using strong electromagnetic fields.

Arrays of evanescently coupled waveguides in which wave behavior becomes discretized exhibit unique wave dynamics, and they offer the possibility to investigate analogous fundamental quantum phenomena at accessible time and length scales. In this Rapid Communication, we investigate the discretelike propagation of trapped modes in airborne acoustic waveguide arrays. Using numerical simulations and experiments, we analyze the emergence of acoustic discrete diffraction and spatial Bloch oscillations in the array. Furthermore, exploiting the Bloch oscillations phenomenon, we demonstrate the possibility to generate diffraction-free acoustic beams and to focus the acoustic energy within a single lattice site at distances orders of magnitude larger than the operating wavelength.

In hyperbolic two-dimensional (2D) materials, energy is channeled into their deep subwavelength polaritonic modes via four narrow beams. Here, we consider the launching of surface polaritons in hyperbolic 2D materials and demonstrate that efficient unidirectional excitation is possible with an elliptically polarized electric dipole, with the optimal choice of dipole ellipticity depending on the materials' optical constants. The selection rules afforded by the choice of dipole polarization allow turning off up to two beams, and even three if the dipole is placed close to an edge. This makes the dipole a directionally switchable beacon for the launching of subdiffractional polaritonic beams, a potential logical gate. We develop an analytical approximation of the excitation process which describes well the results of the numerical simulations and affords a simple physical interpretation.

We demonstrate the existence of a thermal analog of Coulomb drag in many-body systems which is driven by thermal photons. We show that this frictional effect can either be positive or negative depending on the separation distances within the system. Also we highlight that the persistent heat currents flowing in nonreciprocal systems at equilibrium are subject to this effect and the latter can even amplify these flows.

Surface superconductivity has recently been observed on the (001) surface of the topological crystalline insulator ${\mathrm{Pb}}_{1-x}{\mathrm{Sn}}_x\mathrm{Te}$ using point-contact spectroscopy and theoretically proposed to be of the chiral $p$-wave type. In this paper, we closely examine the conditions for realizing a robust chiral $p$-wave order in this system rather than conventional $s$-wave superconductivity. Further, within the $p$-wave superconducting phase, we identify parameter regimes where impurity bound (Shiba) states depend crucially on the existence of the chiral $p$-wave order and distinguish them from other regimes where the chiral $p$-wave order does exist but the impurity-induced subgap bound states cannot be used as evidence for it. Such a distinction can provide an easily realizable experimental test for chiral $p$-wave order in this system. As a possible application of our findings, we also show that the zero-energy Shiba states in point defects possess an internal SU(2) rotational symmetry which enables them to be useful as quantum qubits.

The recently proposed local-correlation-driven pairing mechanism, describing ferromagnetic phases (FM1 and FM2) coexisting with spin-triplet superconductivity (SC) within a single orbitally degenerate Anderson lattice model, is extended to the situation with an applied Zeeman field. The model provides and rationalizes in a semiquantitative manner the principal features of the phase diagram observed for ${\mathrm{UGe}}_2$ in the field absence [cf., Phys. Rev. B 97, 224519 (2018)]. As spin-dependent effects play a crucial role for both the ferromagnetic and SC states, the role of the Zeeman field is to single out different stable spin-triplet SC phases. This analysis should thus be helpful in testing the proposed real-space pairing mechanism, which may be regarded as complementary to spin-fluctuation theory suitable for ${}^3\mathrm{He}$. Specifically, we demonstrate that the presence of the two distinct phases, FM1 and FM2, and the associated field-driven metamagnetic transition between them, induces a respective metasuperconducting phase transformation. At the end, we discuss briefly how the spin fluctuations might be incorporated as a next step in the renormalized quasiparticle picture considered herein.

We study the nonresonantly pumped exciton-polariton system in the vicinity of the dynamical instability threshold. We find that the system exhibits unique and rich dynamics, which leads to spatiotemporal pattern formation. The patterns have a tree-like structure and are reminiscent of structures that appear in a variety of soft-matter systems. Within the approximation of slow and fast time scales, we show that the polariton model exhibits a self-replication point in analogy to reaction-diffusion systems.

Using a powerful homogenization technique, one- and two-dimensional graphene metasurfaces are homogenized both at the fundamental frequency (FF) and second harmonic (SH). In both cases, there is excellent agreement between the predictions of the homogenization method and those based on rigorous numerical solutions of Maxwell equations. The homogenization technique is then employed to demonstrate that, owing to a double-resonant plasmon excitation mechanism that leads to strong, simultaneous field enhancement at the FF and SH, the effective second-order susceptibility of graphene metasurfaces can be enhanced by more than three orders of magnitude as compared to the intrinsic second-order susceptibility of a graphene sheet placed on the same substrate. In addition, we explore the implications of our results on the development of new active nanodevices that incorporate nanopatterned graphene structures.

Using density functional theory-based first-principles calculations, we investigate the stacking order dependence of the electronic and vibrational properties of ${\mathrm{HfS}}_2-\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ heterobilayer structures. It is shown that while the different stacking types exhibit similar electronic and optical properties, they are distinguishable from each other in terms of their vibrational properties. Our findings on the vibrational properties are the following: (i) from the interlayer shear (SM) and layer breathing (LBM) modes we are able to deduce the ${\mathrm{AB}}^{\prime }$ stacking order, (ii) in addition, the ${\mathrm{AB}}^{\prime }$ stacking type can also be identified via the phonon softening of $E_g^{\text{I}}$ and $A_g^{\text{III}}$ modes which harden in the other two stacking types, and (iii) importantly, the ultrahigh frequency regime possesses distinctive properties from which we can distinguish between all stacking types. Moreover, the differences in optical and vibrational properties of various stacking types are driven by two physical effects, induced biaxial strain on the layers and the layer-layer interaction. Our results reveal that with both the phonon frequencies and corresponding activities, the Raman spectrum possesses distinctive properties for monitoring the stacking type in novel vertical heterostructures constructed by alkaline-earth-metal hydroxides.

We investigate heat current fluctuations induced by a periodic train of Lorentzian-shaped pulses, carrying an integer number of electronic charges, in a Hong-Ou-Mandel (HOM) interferometer implemented in a quantum Hall bar in the Laughlin sequence. We demonstrate that the noise in this collisional experiment cannot be reproduced in a setup with an effective single drive, in contrast to what is observed in the charge noise case. Nevertheless, the simultaneous collision of two identical levitons always leads to a total suppression even for the HOM heat noise at all filling factors, despite the presence of emergent anyonic quasiparticle excitations in the fractional regime. Interestingly, the strong correlations characterizing the fractional phase are responsible for a remarkable oscillating pattern in the HOM heat noise, which is completely absent in the integer case. These oscillations may be related to the recently predicted crystallization of levitons in the fractional quantum Hall regime.

We present quartz and molybdenum single-shock Hugoniot data to 62 Mbar and 120 Mbar, respectively. Quartz and molybdenum are attractive standard materials for Hugoniot equation-of-state impedance-matching studies. Quartz is advantageous because a reflecting shock front is supported above $\sim 1$ Mbar whose velocity can be tracked in situ to very high accuracy. Molybdenum's relatively high impedance makes it a more appropriate standard for other high-impedance material studies to avoid large departures from the standard principal Hugoniot upon release or reshock into the sample. Extensive measurements already exist for both materials up to about 10 Mbar and 10 eV, but new high-energy-density facilities and techniques have extended the experimentally accessible pressure range to >100 Mbar. The data presented here indicate which modern equation-of-state models can be reliably extended into newly-accessible experimental regimes.

Neutron diffraction experiments of ice VII at pressures up to 6.2 GPa and 10.2 kV/mm were conducted to investigate the potential ferroelectrically ordered structure of ice VII induced by a high electric field. To accomplish this, we developed a high-pressure cell assembly to allow for powder neutron diffraction to be conducted under both high-pressure and high-electric field conditions. However, the subsequent observed diffraction patterns taken in situ at these conditions do not show sufficient evidence of the proposed ferroelectrically ordered structure of ice VII. We estimate the degree of the hydrogen ordering in ice VII under the applied conditions from high-pressure $P-E$ loop measurements, and discuss the future possibilities of detecting the ferroelectrically ordered structure.

We study the transport properties and superconducting proximity effect in NSN junctions formed by a time-reversal symmetry broken Weyl semimetal (WSM) in proximity to an $s$-wave superconductor. We find that the differential conductances and induced pairing amplitudes strongly depend on the angle between the junction direction in real space and the axis separating the Weyl nodes in momentum space. We identify the influence of a chiral chemical potential, i.e., the electron population imbalance between Weyl nodes of opposite chirality, on the transport characteristics of the junction. Remarkably, we observe a net spin polarization of Cooper pairs that are generated via Andreev reflection in the two WSM regions. The spin polarization is opposite in the two WSM regions and highly sensitive to the chirality imbalance and excitation energy.

Using the numerical renormalization group method, the effect due to a Kondo impurity in an $s$-wave superconductor is examined at finite temperature $T$. The $T$ behaviors of the spectral function and the magnetic moment at the impurity site are calculated. At $T=0$, the spin due to the impurity is in a singlet state when the ratio between the Kondo temperature $T_k$ and the superconducting gap $\mathrm{\Delta }\left(0\right)$ is larger than 0.26. Otherwise, the spin of the impurity is in a doublet state. We show that the separation of the double Yu-Shiba-Rusinov peaks in the spectral function shrinks as $T$ increases if $T_k/\mathrm{\Delta }\left(0\right)<0.26$, while it expands if $T_k/\mathrm{\Delta }\left(0\right)>0.26$ and $\mathrm{\Delta }\left(0\right)$ remains constant. These features could be measured by experiments and thus provide a unique way to determine whether the spin of the single Kondo impurity is in the singlet or doublet state at zero temperature.