We present results from density functional theory (DFT) calculations of the lattice dynamics (phonons) and thermodynamics for $\delta$-phase plutonium. The fully relativistic electronic structure is calculated assuming a three-dimensional noncollinear magnetic structure in conjunction with DFT and the general gradient approximation for the electron exchange and correlation interactions. The electronic-structure model is further enhanced by addressing strong orbital-orbital coupling via the conventional orbital-polarization (OP) scheme as has been successfully done for plutonium. The temperature dependence of the phonons is calculated within the self-consistent ab initio lattice dynamics approach. The obtained phonons compare very well with measurements although a modest overestimation of the transverse L-point $\left[\xi \xi \xi \right]$ phonon is acknowledged. Calculated thermal vibration amplitudes and the associated Debye-Waller temperatures are close to experiments. Lattice, electronic, and magnetic contributions to the heat capacity are predicted and consistent to a few percent with that deduced from experimental data. Good agreement is only achieved when a magnetic contribution to the specific heat is recognized. The parameter-free DFT+OP electronic model is thus capable of predicting phonon properties and thermodynamic behavior of $\delta$-phase plutonium rather accurately.

Ion irradiation can significantly change material properties. Thermal conductivity degradation of reactor fuel is detrimental to safety and efficiency—driving research on how irradiation impacts heat-carrying phonons. Here, we report the measurements of phonon dispersion and lifetimes (inverse linewidths) in freestanding irradiated crystals and reveal the relationship between thermal conductivity and proton irradiation induced nanostructures in ${\mathrm{UZr}}_{2.6}$ using inelastic x-ray scattering, electron microscopy, modulated thermoreflectance, and first-principles calculations. Irradiation results in more significant increases in phonon linewidths and decreased thermal conductivity in the basal plane than that along the $c$ axis, decreasing thermal conductivity anisotropy. Microscopy reveals that this results from irradiation induced nanoprecipitates and metastable phase separation. Surprisingly, irradiation leads to smaller phonon linewidths near some zone boundaries, which we attribute to irradiation induced short-range order.

The structural and magnetic properties of the geometrically frustrated spin-$\frac{1}{2}$ capped-kagome antiferromagnet $\left(\mathrm{RbCl}\right){\mathrm{Cu}}_5{\mathrm{P}}_2{\mathrm{O}}_{10}$ are investigated via temperature-dependent x-ray diffraction, magnetization, heat capacity, and ${}^{31}\mathrm{P}$ NMR experiments on a polycrystalline sample. It undergoes a structural transition at around $T_{\mathrm{t}}\simeq 310$ K from a high-temperature trigonal $\left(P\overline{3}m1\right)$ to a low-temperature monoclinic $(C2/c)$ unit cell, where the low-temperature structure features the capped-kagome geometry of ${\mathrm{Cu}}^{2+}$ ions. Interestingly, it shows the onset of two successive magnetic transitions at $T_{\mathrm{N}1}\simeq 20$ K and $T_{\mathrm{N}2}\simeq 7$ K. The shape of the ${}^{31}\mathrm{P}$ NMR spectra unfolds the possible nature of the transitions below $T_{\mathrm{N}1}$ and $T_{\mathrm{N}2}$ to be of incommensurate and commensurate antiferromagnetic type, respectively. A large value of the Curie-Weiss temperature as compared to $T_{\mathrm{N}1}$ sets the frustration parameter $f\simeq 8$, ensuring strong magnetic frustration in the compound. From the ${}^{31}\mathrm{P}$ NMR spin-lattice relaxation rate, the leading antiferromagnetic exchange coupling is estimated to be $J/k_{\mathrm{B}}\simeq 117$ K. These unusual double magnetic transitions make this compound beguiling for further investigations.

We study the coherent dynamic interaction of a time-dependent spin-splitting field with the homogeneous superconducting order parameter $\mathrm{\Delta }\left(t\right)$ mediated by spin-orbit coupling using the time-dependent Bogoliubov–de Gennes theory. In the first part of the work we show that the linear response of the superconductor is strongly affected by the Zeeman field and spin-flip processes, giving rise to multiple resonant frequencies of the superconducting Higgs modes, which can be coupled linearly to the fluctuating part of the Zeeman field. In the second part, we analyze the nonadiabatic dynamics of quasiparticle states arising from the intersection of spectral branches from different spin subbands provoked by a monotonically changing Zeeman field. Nonadiabatic spin-flip tunneling in the spectrum leads to drastic change in the order parameter $\mathrm{\Delta }\left(t\right)$ above the Pauli limit and results in a nonequilibrium magnetization of the quasiparticle gas.

Our group has previously reported the existence of a conducting surface state (CSS) in FeSi, a candidate for a $d$-electron topological Kondo insulator (TKI), at low temperature. In this paper, we present the electrical transport properties of single crystals of FeSi studied in the phase space of temperature ($T$), magnetic field ($B$), and the angle (θ) between the electrical current and $B$. The normalized $T$-dependent electrical resistance ($R$) of a successively thinned FeSi crystal provides further confirmation of the existence of a CSS. We report that, in the CSS, the magnetoresistance (MR) exhibits a hysteresis loop bounded within $\pm 0.5\mathrm{T}$, suggesting two-dimensional magnetic ordering. The hysteretic MR is asymmetric in $B$ and anisotropic with respect to θ. Further exploration of $R\left(\theta \right)$ at a fixed field of 9 T reveals an initial progressive rotation of the axis for twofold rotational symmetry from 2 to 10 K, then a stabilized axis for twofold symmetry until, at $T>40\mathrm{K}$, the anisotropy vanishes, coincident with the disappearance of the CSS. These observations point to a possible magnetically ordered surface state that has been reported in similar systems such as FeSi nanofilms and bulk ${\mathrm{SmB}}_6$.

We propose and study a generalization of Kitaev's ${\mathbb{Z}}_2$ toric code on a square lattice with an additional global $U\left(1\right)$ symmetry. Using quantum Monte Carlo simulation, we find strong evidence for a topologically ordered ground state manifold with indications of UV-IR mixing, i.e., the topological degeneracy of the ground state depends on the microscopic details of the lattice. Specifically, the ground state degeneracy depends on the lattice tilt relative to the directions of the torus cycles. In particular, we observe that while the usual compactification along the vertical or horizontal lines of the square lattice shows a twofold ground state degeneracy, compactifying the lattice at ${45}^{\circ }$ leads to a threefold degeneracy. In addition to its unusual topological properties, this system also exhibits Hilbert space fragmentation. Finally, we propose a candidate experimental realization of the model in an array of superconducting quantum wires.

We present a theoretical study of a system consisting of a superconducting island and two quantum dots, a possible platform for building qubits and Cooper pair splitters, in the regime where each dot hosts a single electron and, hence, carries a magnetic moment. We focus on the case where the dots are coupled to overlapping superconductor states and we study whether the spins are ferromagnetically or antiferromagnetically aligned. We show that if the total number of particles is even the spins align antiferromagnetically in the flatband limit, i.e., when the bandwidth of the superconductor is negligibly small, but they align ferromagnetically if the bandwidth is finite and above some value. If the total number of particles is odd, the alignment is ferromagnetic independently from the bandwidth. This implies that the results of the flatband limit are applicable only within a restricted parameter regime for realistic superconducting qubit systems and that some care is required in applying simplified models to devices such as Cooper pair splitters.

The issue of quantum dephasing in solids subjected to strong, off-resonant excitation continues to challenge our current understanding of nonperturbative extreme nonlinear processes, such as high-order harmonic generation (HHG) and supercontinuum generation. It has been noted in a number of HHG simulations that realistic-looking spectra, with peak-to-valley contrasts that agree with experimental observations, are only obtained for very short dephasing times. In contrast, simulated spectra attain the character of a structured supercontinuum for longer dephasing times. Using realistic simulations, we establish that this behavior is a manifestation of the necessarily discrete numerical description applied to the continuum of 3D Bloch states. We observe that even when a low-resolution HHG simulation fails to produce clearly separated harmonic peaks, a properly converged, clearly defined HHG spectrum can be obtained provided the entirety of the Brillouin zone is sampled with sufficient density. We propose a solution that accelerates the convergence toward the realistic HHG spectra.

We study theoretically interaction of short optical pulses with triangular graphene quantum dots. If such quantum dots have zigzag edges then there are in-gap degenerate edge states, the number of which depends on the size of the system. We show that the nonlinear optical response, such as high harmonic generation, of triangular quantum dots is sensitive to the initial electron population of their edge states. In general, the emission spectra of quantum dots have weak dependence on the number of occupied edge states, but if half of the edge states are initially occupied, which can be realized only in the quantum dots with even number of edge states, then the even high harmonics are strongly suppressed. The suppression is the strongest when the frequency of the pulse is well below the band gap and it is weak when the pulse frequency becomes comparable to the band gap of the system.

We study theoretically the effect of electronic interactions in one-dimensional systems on electron injection using periodic Lorentzian pulses, known as levitons. We consider specifically a system composed of a metallic single-wall carbon nanotube, described with the Luttinger liquid formalism, a scanning tunneling microscope (STM) tip, and metallic leads. Using the out-of-equilibrium Keldysh Green's function formalism, we compute the current and current noise in the system. We prove that the excess noise vanishes when each leviton injects an integer number of electrons from the STM tip into the nanotube. This extends the concept of minimal injection with levitons to strongly correlated, uni-dimensional nonchiral systems. We also study the time-dependent current profile, and show how it is the result of interferences between pulses nontrivially reflected at the nanotube-lead interface.

Thin films of ice and water on soil particles play crucial roles in environmental and technological processes. Understanding the fundamental physical mechanisms underlying their formation is essential for advancing scientific knowledge and engineering practices. Herein, we focus on the role of the Casimir-Lifshitz force, also referred to as dispersion force, in the formation and behavior of thin films of ice and water on soil particles at 273.16 K, arising from quantum fluctuations of the electromagnetic field and depending on the dielectric properties of interacting materials. We employ the first-principles density functional theory (DFT) to compute the dielectric functions for two model materials, ${\mathrm{CaCO}}_3$ and $\mathrm{Al}{}_2\mathrm{O}{}_3$, essential constituents in various soils. These dielectric functions are used with the Kramers-Kronig relationship and different extrapolations to calculate the frequency-dependent quantities required for determining forces and free energies. Moreover, we assess the accuracy of the optical data based on the DFT to model dispersion forces effectively, such as those between soil particles. Our findings reveal that moisture can accumulate into almost micron-sized water layers on the surface of calcite (soil) particles, significantly impacting the average dielectric properties of soil particles. This research highlights the relevance of DFT-based data for understanding thin film formation in soil particles and offers valuable insights for environmental and engineering applications.

Monolayer transition metal dichalcogenides host tightly bound excitons, which dominate their optoelectronic response even at room temperatures. Light beams are often used to study these materials with the polarization—often termed the spin angular momentum of the light—providing the mechanism for exciting excitonic states. Light beams, however, can also carry an orbital angular momentum by creating helical structures of their phase front. In this work, we consider a Laguerre-Gaussian beam possessing an orbital angular momentum in addition to the spin angular momentum to create excitons in monolayer transition metal dichalcogenides. We derive optical selection rules that govern the allowed transitions to various exciton series using symmetry arguments. Our symmetry considerations show that we can create dark excitons using these high-order optical beams opening up new avenues for creating long-lived dark excitons with the potential of exploiting them in quantum information processing and storage.

Heat transport plays a crucial role in various applications such as waste energy harvesting, thermal barrier coatings, and heat dissipation in microelectronics. In this paper, the frequency-dependent heat transport characteristics in mass disordered ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ nanowires (NWs) are investigated based on the nonequilibrium Green's function method. The results demonstrate the coexistence of phonons with ballistic transport, diffusive transport, and Anderson localization in SiGe alloyed NWs. Ballistic phonons are observed at low frequencies, with a NW length of up to 2 $\mu \mathrm{m}$ and Ge concentrations ranging from 1 to 50%. As the Ge concentration increases, the upper frequency limit for ballistic transport shifts to lower frequencies. However, the thermal conductivity contributed by these ballistic phonons increases due to enhanced scattering and localization of mid- and high-frequency phonons. Moreover, for ultralong samples, phonon localization occurs across a wide frequency range. The localization length decreases with increasing frequency, indicating that high-frequency phonons are more prone to localization in SiGe-alloyed NWs. Additionally, the localization length decreases with increasing Ge concentration, revealing a stronger localization effect in highly mass-disordered systems. Our results contribute to the understanding of heat transport in low-dimensional disordered systems and could be beneficial to guiding the design of thermoelectric materials and thermal barrier coatings.

Noncoplanar magnetic structures, such as magnetic skyrmions, are characterized by spin chirality and usually favored by antisymmetric exchange interactions in noncentrosymmetric magnets. Here, we show that a linearly polarized electric-field pulse stabilizes a nonequilibrium spin scalar chiral state in a centrosymmetric itinerant ferromagnet. The scalar chirality has a nonmonotonic dependence on the electric-field strength, and its sign can be controlled by circular polarization. Furthermore, magnetic skyrmions are excited after the pulse decays. A photoinduced nonthermal electron distribution plays an important role for instability towards the spin scalar chiral state as well as the ${120}^{\circ }$ Néel state, depending on the next-nearest-neighbor transfer integral. These results provide an alternative route to controlling spin chirality by photoirradiation.

Recent experiments have shown that the phase diagrams of the kagome superconductors $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ are strongly impacted by changes in the $c$-axis lattice parameter. Here, we show that $c$-axis deformations impact primarily the Sb apical bonds and thus the overlap between their $p_z$ orbitals. Changes in the latter, in turn, substantially affect low-energy electronic states with significant Sb character, most notably the central electron pocket and the van Hove singularities located above the Fermi level. Based on the orbital-selective character of $c$-axis strain, we argue that these electronic states experience a non-negligible attractive electron-phonon pairing interaction mediated by fluctuations in the apical Sb bonds. We thus propose a multiband model for superconductivity in $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ that includes both the Sb pocket and the V-derived van Hove singularities. Upon comparing the theoretical phase diagram with the experimentally observed vanishing of the $T_c$ dome across a Lifshitz transition of the Sb pocket, we propose that either an $s^{+-}$ or an $s^{++}$ state is realized in $A{\mathrm{V}}_3{\mathrm{Sb}}_5$.

Among the pnictogens, the high-pressure phases of P show various structural transitions, while those of As and Sb do not. The body-centered-cubic (bcc) structure appears at 97 GPa in As and at 28.8 GPa in Sb. A transition from this strongly stable bcc structure to a new phase with further compression has not yet been reported in As or Sb in experimental or theoretical studies. The difference in the stability of the bcc structure between As (or Sb) and that of P is explained based on the investigations of the electronic structures using first-principles calculations. The occupied $d$ orbitals of As and Sb play an important role in the stability of their respective bcc structures, while the absence of such in P causes an instability in the bcc structure making it comparatively fragile.

We present charge state transition levels of 23 intrinsic defects and dopant substitutions in the compound III-V semiconductor ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$, calculated with density functional theory. We also report the Shockley-Read-Hall (SRH) recombination rate and capture coefficients for defects found to have deep trap levels. Our calculations show that seven of the considered defects exhibited deep trap levels capable of acting as electron and hole traps in devices: the ${\mathrm{As}}_{\text{In/Ga}}$ antisites, the ${\mathrm{V}}_{\text{In/Ga}}$ vacancies, the ${\left(\text{In/Ga}\right)}_{\text{As}}\text{−}{\mathrm{As}}_{\text{In/Ga}}$ double antisites, and the ${\mathrm{Sn}}_{\text{As}}$ substitution. We found that the ${\mathrm{As}}_{\text{In}}$ antisite exhibits the highest electron-capture coefficient of $C_n=2.2\times {10}^{-5}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at room temperature. The defect with the highest hole-capture coefficient was found to be the ${\mathrm{In}}_{\text{As}}\text{−}{\mathrm{As}}_{\text{In}}$ double antisite, with $C_p=3.4\times {10}^{-6}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$. Furthermore, this defect also causes the highest recombination rate in the intrinsic semiconductor, owing to its likewise relatively large electron-capture coefficient. The defects which are most likely to occur are argued to be the antisites, due to their low formation energies and matching transition levels with experiments. Additionally, it is found that the ${\mathrm{Sn}}_{\text{As}}$ substitution also causes a significant recombination in the semiconductor, but it is argued to only be of importance at very high doping levels.

We consider an open quantum system composed of a $(1+1)$-dimensional Kitaev ring coupled with the environment via $n$ particle-loss dissipators in a sunburst geometry. We describe the out-of-equilibrium dynamics of the whole apparatus in terms of Lindblad master equations and focus on the scaling behavior of the Liouvillian gap ${\mathrm{\Delta }}_{\lambda }$ with the system size $L$. We unveil different regimes, which depend on the number of dissipation sources considered in the large-size limit and the dissipation strength $w$, which can be either fixed or attenuated to zero as $w\approx 1/L$. In the second part, we develop a dynamic finite-size scaling framework close to continuous quantum transitions to monitor the time evolution of the critical correlations and the entanglement entropy, emphasizing the role of ${\mathrm{\Delta }}_{\lambda }$ in this regime.

The two-dimensional $1T\text{−}{\mathrm{CrTe}}_2$ has been an attractive room-temperature van der Waals magnet which has a potential application in spintronic devices. Although it was recognized as a ferromagnetism in the past, monolayer $1T\text{−}{\mathrm{CrTe}}_2$ was recently found to exhibit zigzag antiferromagnetism with the easy axis oriented at ${70}^{\circ }$ to the perpendicular direction of the plane. Therefore, the origin of the intricate anisotropic magnetic behavior therein is well worth thorough exploration. Here, by applying density functional theory with spin spiral method, we demonstrate that the Kitaev interaction, together with the single-ion anisotropy and other off-diagonal exchanges, is amenable to explain the magnetic orientation in the metallic $1T\text{−}{\mathrm{CrTe}}_2$. Moreover, the Ruderman-Kittle-Kasuya-Yosida interaction can also be extracted from the dispersion calculations, which explains the metallic behavior of $1T\text{−}{\mathrm{CrTe}}_2$. Our results demonstrate that $1T\text{−}{\mathrm{CrTe}}_2$ is potentially a rare metallic Kitaev material.