The geometry and morphology of magnetic domain walls (DWs) are closely related to their dynamics when driven by external forces. Under some reliable approximations DWs can be considered self-affine interfaces, so universal laws govern their behavior. On the other hand, large-scale DW structure has been less explored so far. Recently, it has been shown that bubble-like magnetic domains can be strongly deformed on a large scale by applying alternating (ac) magnetic field pulses. In the present paper, we conduct a comprehensive analysis of DW structure at both small and large length scales in bubble-like domains present in ferromagnetic thin films with perpendicular anisotropy, focusing on its initial evolution under the application of ac magnetic pulses. Results obtained from the widely used roughness correlation function $B\left(r\right)$ and its corresponding structure factor, are consistent with those obtained from the spatial autocorrelation function of DW fluctuations. Whereas the roughness exponent slightly increases during the ac evolution, a strong deformation is observed at a large scale, where a striking periodicity (statistically speaking) is observed. This period is probably determined by the boundary conditions and a characteristic intrinsic length.

The locally noncentrosymmetric ferromagnet ${\mathrm{URhGe}}_2$, which undergoes ordering at the Curie temperature $T_{\mathrm{C}}=25$ K, was subjected to a comprehensive investigation employing x-ray diffraction, magnetic susceptibility, electrical resistivity, and specific heat measurements. Our results reveal a significant heat capacity anomaly in the paramagnetic state near 30 K which is due to two simultaneous phase transitions characterized by temperatures $T_s\simeq 29.5$ K and $T_m\simeq 30$ K. In particular, with increasing applied magnetic field, $T_m$ shifts to higher temperatures, while $T_s$ remains unaffected, suggesting a different nature of these transitions and leading to a complex temperature-magnetic field phase diagram. The field-independent phase transition can be interpreted in terms of structural distortions, while the second transition defies typical behavior for ferro- or antiferromagnetic phases, suggesting a more intricate magnetic structure or multipole ordering. The electron transport shows strong anisotropy, not only in the magnitude of the resistivity but also in its temperature dependence. The three times higher residual resistivity along the crystallographic $c$ axis, compared to the $a$ axis component significantly influences its temperature dependence. While the $a$-axis resistivity behaves typically for normal ferromagnets, the $c$-axis resistivity shows a minimum in its temperature dependence well below $T_{\mathrm{C}}$. This behavior results from the competition between electron spin wave scattering and quantum corrections, dominated by the $A_{\mathrm{QC}}{T}^{1/2}$ contribution due to impurity scattering assisted electron-electron interaction. Remarkably, the $A_{\mathrm{QC}}{T}^{1/2}$ dependence with a comparable $A_{\mathrm{QC}}$ coefficient is also observed for $T\gg T_{\mathrm{C}}$, indicating the relevance of interaction quantum effects in electron transport also in the paramagnetic state.

We present the simultaneous optical and thermal analysis of a freestanding photonic semiconductor membrane made from wurtzite III-nitride material. By linking microphotoluminescence spectroscopy with Raman thermometry and other spectroscopic techniques, we demonstrate how a robust value for the thermal conductivity $\kappa$ can be obtained using only optical noninvasive means. For this, we consider the balance of different contributions to thermal transport given by, e.g., excitons, charge carriers, and heat-carrying phonons. In principle, all these contributions can be of relevance in a photonic membrane on different length scales. Further complication is given by the fact that this membrane is made from direct band gap semiconductors, designed to emit light via an ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ ($x=0.15$) quantum well embedded in GaN. Thus, III-nitride membranes similar to the one of this study have already been successfully used for laser diode structures facing thermal limitations. To meet these intricate challenges, we designed an experimental setup that enables the necessary optical and thermal characterizations in parallel. After the optical characterization by microphotoluminescence, we follow a careful step-by-step approach to quantify the thermal properties of our photonic membrane. Therefore, we perform steady-state micro-Raman thermometry, either based on a heating laser that also acts as a probe laser (one-laser Raman thermometry), or based on two lasers, providing the heating and the temperature probe separately (two-laser Raman thermometry). For the latter technique, we can obtain temperature maps over several hundreds of square micrometers with a spatial resolution less than $1\mu \text{m}$. As a result, the temperature probe volume using the two-laser Raman thermometry technique can be increased by a factor exceeding 100 compared with the conventional one-laser Raman thermometry technique, which impacts the derivation of the thermal conductivity $\kappa$. Only based on our largest temperature probe volume we derive $\kappa ={95}_{-7}^{+11}$ $\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ for the $c$ plane of our $\approx 250\text{-nm}$-thick photonic membrane near room temperature, which compares well to our ab initio calculations, applied to a simplified structure, yielding $\kappa =136 \mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$. Based on these calculations, we explain the particular importance of the temperature probe volume, as quasiballistic transport of heat-carrying phonons, which is of high relevance for determining $\kappa$, occurs on length scales beyond the penetration depths of the heating laser and even its focus spot radius. The one-laser Raman thermometry technique, therefore, fails to derive realistic $\kappa$ values, unlike the two-laser Raman thermometry that can probe temperatures over sufficiently large volumes. The present work represents a significant step towards the achievement of noninvasive, highly spatially resolved, quantitative thermometry maps on a photonic membrane made of a direct band gap semiconductor, which is of particular relevance for photonic applications.

Efficient transverse magneto-optical Kerr effect (TMOKE) at the nanoscale has attracted great interest in recent years due to the highly desirable properties it offers in nonreciprocal photonic devices. Extensive efforts have been made to achieve strong TMOKE based on the efficient absorption of magneto-optical material by using optical resonance with a high Q factor and enhanced electromagnetic field. For a magneto-optical material, however, the efficiency of TMOKE is determined not only by the absorption but also by the spatial symmetry breaking of the magneto-optical material. Here, we propose a dielectric-metal hybrid metasurface composed of a regular array of silicon nanocuboids sitting on a thin metal film. It supports various optical resonances, including Mie resonances, bound states in the continuum (BICs), surface lattice resonances (SLR), and surface plasmon polaritons (SPPs), offering us the opportunity to manipulate the Q factors of optical modes, the intensity and spatial distribution of the electromagnetic field by exploiting the coupling of different optical modes. By virtue of the highly anisotropic electromagnetic field realized by the coupling between the quasi-BIC and the SLR mode, the efficiency of TMOKE at normal incidence can be enhanced by 42%, which is six times greater than that achieved by pure quasi-BIC only. Our method provides insights for designing high-efficiency TMOKE photonic devices, thereby opening up possibilities for their use in a wide range of applications, including magnetic storage devices and nonreciprocal photonic devices.

We study exciton-mediated double resonant Raman scattering via longitudinal optical (LO) phonons in a diluted magnetic (Cd, Mn)Te/(Cd, Mg)Te quantum well. Experiments performed at 1.5 K in external magnetic field in Faraday geometry reveal strong enhancement of the LO phonon Raman line emission from the lower Zeeman sublevel of the heavy hole exciton if the upper Zeeman sublevel of either the light hole exciton or the heavy hole exciton is exactly the longitudinal optical phonon energy above the exciton ground state. In these cases a double resonance condition is satisfied, with the ingoing resonance being either the light or heavy hole exciton upper Zeeman sublevel and the outgoing resonance being the heavy hole exciton lower Zeeman sublevel. We discuss the mechanisms of the effect and demonstrate the importance of the exchange interaction in the exciton resulting in the mixing of heavy and light hole excitons active in the same circular polarization as well as the deformation-optical hole-phonon interaction. This double resonance condition can be effectively reached by varying the magnetic field applied to the quantum well. We provide theoretical arguments supporting the absence of the spin-conserving light to heavy exciton double resonant Raman scattering in experiments. We also discuss the difference between photoluminescence and resonant Raman scattering in our system with significant inhomogeneous broadening.

Heterostructures of layered transition metal dichalcogenides (TMDs) host long-lived, tunable excitons, making them intriguing candidates for material-based quantum information applications. Light absorption in these systems induces a plethora of optically excited states that hybridize both interlayer and intralayer characteristics, providing a distinctive starting point for their relaxation processes, in which the interplay between generated electron-hole pairs and their scattering with phonons play a key role. We present a first-principles theoretical approach to compute phonon-induced exciton decomposition due to rapid occupation of electron-hole pairs with finite momentum and opposite spin. Using the ${\mathrm{MoSe}}_2/{\mathrm{WSe}}_2$ heterostructure as a case study, we observe a reduction in the optical activity of bright states upon phonon scattering already in the first few femtoseconds after a photoexcitation, driving exciton interlayer delocalization and subsequent variations in the exciton spin. Our results reveal an unexpected and previously unexplored starting point for exciton relaxation dynamics, suggesting increased availability for coherent interactions and nonradiative processes through ultrafast changes in exciton momentum, spatial, and spin properties upon light excitation.

The thermal Hall effect, which arises when heat flows transversely to an applied thermal gradient, has become an important observable in the study of quantum materials. Recent experiments found a large thermal Hall conductivity ${\kappa }_{xy}$ in many high-temperature cuprate superconductors, including deep inside the Mott insulator, but the underlying mechanism remains unknown. Here, we uncover a surprising linear temperature dependence for the inverse thermal Hall resistivity, $1/{\varrho }_H=-{\kappa }_{xx}^2/{\kappa }_{xy}$, in the Mott insulating cuprates ${\mathrm{La}}_2{\mathrm{CuO}}_4$ and ${\mathrm{Sr}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2$. We also find this linear scaling in the pseudogap state of ${\mathrm{La}}_{1.6-x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ (Nd-LSCO) in the out-of-plane direction, highlighting the importance of phonons. On the electron-doped side, the linear inverse thermal Hall signal emerges in ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ (NCCO) and ${\mathrm{Pr}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ (PCCO) at various dopings, including in the strange metal. Although such dependence arises in the simple Drude model for itinerant electrons, its origin is unclear in strongly correlated Mott insulating or pseudogap states. We perform a Boltzmann analysis for phonons that incorporates skew scattering, and we are able to identify regimes where a linear $T$ inverse Hall resistivity appears. Finally, we suggest future experiments that would further our fundamental understanding of heat transport in the cuprates and other quantum materials.

The growth of sufficiently large single crystals of $\mathrm{Cu}\left(tn\right){\mathrm{Cl}}_2$ $(tn=1,3\text{−}\text{diaminopropane})$ enabled specific heat and susceptibility studies in various field orientations. The nearly invisible broad hump in zero-field specific heat at 0.6 K coincides with the change in the characteristic parameters of zero-field muon relaxation spectra. The lack of oscillations in the time spectra and their exponential character preserved down to 40 mK suggest the coexistence of static and fluctuating local fields associated with the prevalence of low-dimensional correlations. The extreme two-dimensionality is also manifested by the nonmonotonous character of the magnetic phase diagram. First-principle calculations of exchange couplings introduced a concept of a quasi-two-dimensional magnetic lattice with many couplings within the magnetic layers. The strongest ones lead to the model of a rectangular lattice with the intrachain coupling $J/k_{\mathrm{B}}=4.3$ K and the interchain coupling $J^{\prime }/J=0.46$, which provides excellent agreement with the zero-field specific heat. However, the susceptibility data suggest the importance of other weaker interactions in accord with first-principle studies. Significant broadening of field-induced specific heat anomalies may be ascribed to potential intrinsic partial magnetic disorder associated with the gradual modulation of $tn$ positions in the crystal structure.

Motivated by the recent discovery of superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under pressure, we discuss the basic ingredients of a model that captures its microscopic physics under pressure tuning. We anchor our description in terms of the spectroscopic evidence of strong correlations in this system. In a bilayer Hubbard model including the Ni $3d$ $x^2-y^2$ and $z^2$ orbitals, we show the ground state of the model crosses over from a low-spin $S=1/2$ state to a high-spin $S=3/2$ state. In the high-spin state, the two $x^2-y^2$ and the bonding $z^2$ orbitals are all close to half-filling, which promotes a strong orbital selectivity in a broad crossover regime of the phase diagram pertinent to the system. Based on these results, we construct an effective multiorbital $t\text{−}J$ model to describe the superconductivity of the system, and find the leading pairing channel to be an intraorbital spin singlet with a competition between the extended $s$-wave and $d_{x^2-y^2}$ symmetries. Our results highlight the role of strong multiorbital correlation effects in driving the superconductivity of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$.

${\mathrm{CaPd}}_2{\mathrm{Ge}}_2$ which crystallizes in ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type body-centered tetragonal structure exhibits superconductivity below the critical temperature $T_{\mathrm{c}}=1.69\mathrm{K}$. We have investigated the superconducting gap structure and time-reversal symmetry of the ground state in ${\mathrm{CaPd}}_2{\mathrm{Ge}}_2$ by means of muon spin relaxation and rotation $\left(\mu \mathrm{SR}\right)$ measurements. Our analysis of $\mu \mathrm{SR}$ data collected in a transverse magnetic field reveals BCS superconductivity with a single-band $s$-wave singlet pairing and an isotropic energy gap having the value $2\mathrm{\Delta }\left(0\right)/k_{\mathrm{B}}{T}_{\mathrm{c}}=3.50\left(1\right)$. Further, an increased relaxation rate in zero-field $\mu \mathrm{SR}$ asymmetry spectra below $T_{\mathrm{c}}$ provides evidence for the presence of a spontaneous magnetic field in the superconducting state, revealing that the time-reversal symmetry is broken in ${\mathrm{CaPd}}_2{\mathrm{Ge}}_2$.

The thermoelectric properties of nine Zintl-phase semiconductors II-I-V (II = Ca, Sr, Ba, I = Cu, Ag, Au, and V = As, Sb, Bi) are studied by using first-principles calculations. The electronic and thermal transport properties are calculated to elucidate the thermoelectric performance. The electron localization functions and crystal orbital Hamilton population show regular and anisotropic bonding in II-I-V, which makes anisotropic thermal and electronic transport properties. The phonon dispersion curve also shows element dependent distributions. We suggest that the regularity of phonon and electron distribution makes the adjusting of thermoelectric performance in $P{6}_{\text{3}}/mmc$ type Zintl-phase compounds possible. The mix of ionic and weak covalent bonding leads to the coexistence of soft phonon modes and favorable electronic properties and thus a high figure of merit (0.41–0.94). We also investigate the three phonon scattering properties. The importance of acoustic phonon softening in lowering thermal conductivity is observed. The symmetry-based three-phonon scattering pathways demonstrate the possible intense phonon-phonon scattering. These data provide a deep understanding of the thermoelectric properties in Zintl-phase compounds.

Negative magnetoresistance (NMR) is a marked feature of Dirac semimetals, and may be caused by multiple mechanisms, such as the chiral anomaly, the Zeeman energy, the quantum interference effect, and the orbital moment. Recently, an experiment on Dirac semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$ thin films revealed a new NMR feature that depends strongly on the thickness of the sample [T. Schumann et al., Phys. Rev. B 95, 241113(R) (2017)]. Here, we introduce a mechanism of inducing NMR via the presence of the Van Hove singularity (VHS) in the density of states. A theoretical fitting of the experimental data on magnetoconductivity and magnetoresistance shows good agreement, indicating that the observed NMR in thin films of ${\mathrm{Cd}}_3{\mathrm{As}}_2$ can be attributed to the VHS. This work provides insights into the underlying Dirac semimetals.

Photons are emitted or absorbed by a nanocircuit under both equilibrium and nonequilibrium situations. Here, we focus on the nonequilibrium situation arising due to a temperature difference between the leads of a quantum point contact and study the finite-frequency (colored) noise. We explore this delta-$T$ noise in the finite-frequency regime for two systems: conventional conductors described by Fermi liquid scattering theory and the fractional quantum Hall system at Laughlin filling fractions, described by the chiral Luttinger liquid formalism. We study the emission noise, its expansion in the temperature difference (focusing on the quadratic component), as well as the excess emission noise defined with respect to a properly chosen equilibrium situation. The behavior of these quantities is markedly different for the fractional quantum Hall system compared to Fermi liquids, signaling the role of strong correlations of the fractional quantum Hall effect and the importance of the nature of the charge carriers tunneling across the junction.

Realizing and manipulating valley polarization is extremely important to valleytronics. Ferrovalley materials with spontaneous valley polarization are excellent candidates for this purpose. However, for intrinsic ferrovalley materials, ferromagnetism or ferroelectric polarization is usually required, limiting the development of valleytronics, as only systems without inversion symmetry are considered. In this paper, using both group theory analysis and band structure calculations, we demonstrate that valley polarization can exist in systems with both time and space inversion symmetry, and the ferroelastic effect can control the ferrovalley states. Choosing stacking bilayer systems as an example, we achieved valley polarization switching using the shear strain, which uncovers the link between ferrovalley and ferroelasticity. Our investigations not only provide a mechanical way to manipulate valley degree of freedom but also enrich the understanding of the coupling between different ferroic properties.

The quantum anomalous Hall effect (QAHE) is a topological state of matter with a quantized Hall resistance. It has been observed in some two-dimensional insulating materials such as magnetic topological insulator films and twisted bilayer graphene. These materials are insulating in the bulk but possess chiral edge states carrying the edge current around the system. Here we discover a metallic QAHE in a topological insulator film with a magnetic sandwich heterostructure, in which the Hall conductance is quantized to $e^2/h$ but the longitudinal conductance remains finite. This effect is attributed to the existence of a pair of massless Dirac cones of surface fermions, with each contributing half of the Hall conductance due to the quantum anomaly. It is not characterized by a Chern number and is not associated with any chiral edge states. Our study offers insights into topological transport phenomena and topological metallic states of matter.