We present a general framework for studying strongly coupled radiative and conductive heat transfer between arbitrarily shaped bodies separated by subwavelength distances. Our formulation is based on a macroscopic approach that couples our recent fluctuating volume-current (FVC) method of near-field heat transfer to the more well-known Fourier conduction transport equation, in which case the former can induce temperature gradients throughout the bodies. Although the FVC framework can in principle be applied to arbitrary geometries, in practice it is most applicable in situations where only one of the bodies undergoes significant temperature gradients. To illustrate the capabilities of this framework, we consider an idealized, proof-of-concept geometry involving two aluminum-zinc oxide nanorods separated by a vacuum gap, with one of the rods heated by a large-temperature reservoir on one side while the other is held at room temperature. We show that the presence of bulk nanorod polaritonic resonances can result in very large radiative heat transfer rates (roughly five times larger than what is achievable in the planar configuration) and leads to nonlinear temperature profiles.

Wrinkles and blisters of graphene on Ir(111) give rise to remarkably high signals in inelastic electron tunneling spectroscopy due to graphene phonons. Spatially resolved spectra unravel the gradual increase of the graphene phonon signatures with progressive delamination of graphene from the metal surface. Spectroscopy of the Ir(111) surface resonance evidences that the graphene-metal hybridization is efficiently reduced in wrinkles and blisters. A high phonon density of states favors the observation of phonons with wave vectors near the $\overline{M}$ point of the surface Brillouin zone.

Anisotropic charge-carrier transport in black phosphorus limited by ionized impurity scattering at finite temperature is explored theoretically. The anisotropic electronic structure enters the calculation for the polarizability (screening), the momentum relaxation time, and the mobility. For finite temperature, elastic scattering is not limited to the Fermi surface and the polarizability is temperature dependent. The impact of screening is investigated in detail with its dependence on carrier density and temperature. Competing with the thermal excitation effects, the temperature dependence of the polarizability is found to dominate for $T<100$ K. As a result, the charge-carrier mobility slowly decreases with increasing temperature. The weak temperature dependence of the mobility and its anisotropy ratio of 1.9–3.2 agree with published experimental data.

Doping plays a key role in modulating electronic properties of 2D semiconductors, and thus is vitally important for next-generation nanoelectronics and optoelectronics devices. However, how to effectively tune the dopant ionization energy (IE) so as to achieve robust and controllable $n$-type or $p$-type conductivities in 2D semiconductors is still a significant challenge. Here, using first-principles calculations, we demonstrate an effective IE-tuning route for 2D semiconductors using dielectric substrates. Taking ${\mathrm{X}}_{\mathrm{S}}$ (X = Cl, Br, I) in ${\mathrm{MoS}}_2$ as examples, we show that the dielectric substrate is able to tune deep dopants to shallow ones, and the dopant IE depends on which S layer the dopant is located in. Specifically, the IE of ${\mathrm{I}}_{\mathrm{S}}$ is reduced from 0.63 eV for the freestanding ${\mathrm{MoS}}_2$, to 0.39 eV when ${\mathrm{MoS}}_2$ is on a ${\mathrm{SiO}}_2$ substrate, further to 0.17 eV when ${\mathrm{MoS}}_2$ is on an ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrate, and the IEs of ${\mathrm{I}}_{\mathrm{S}}$ in the inner and outer S layers differ by 0.22 eV with an ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrate. Correspondingly, the carrier concentrations can be tuned by selecting different substrates or doping layers. We reveal that the remarkable IE reduction is originated from the electronic and ionic screenings of the substrate. Our results not only shed light on the substrate screening effects on the dopant properties, but also suggest a practical route to achieve controllable $n$-type or $p$-type carrier concentrations for 2D semiconductors.

We present a study of the compositional and temperature-dependent magnetic properties of epitaxial CoCr thin films whose composition has a bathtublike depth profile $\mathrm{Co}/\mathrm{C}{\mathrm{o}}_{1\to 1\text{−}{x}_{\mathrm{c}}}\mathrm{C}{\mathrm{r}}_{0\to x_{\mathrm{c}}}/\mathrm{C}{\mathrm{o}}_{1\text{−}{x}_{\mathrm{c}}}\mathrm{C}{\mathrm{r}}_{x_{\mathrm{c}}}/\mathrm{C}{\mathrm{o}}_{1\text{−}{x}_{\mathrm{c}}\to 1}\mathrm{C}{\mathrm{r}}_{x_{\mathrm{c}}\to 0}/\mathrm{Co}$ with the highest Cr concentration $\left(x_{\mathrm{c}}\right)$ at the center of the sample. Polarized neutron reflectometry (PNR) shows that the effective Curie temperature varies as a function of depth and exhibits a minimum in the center of the structure. Correspondingly, we observe that the effective coupling between the two outer Co layers is strongly dependent on the magnetization of the graded CoCr spacer and can be continuously tuned via $x_{\mathrm{c}}$ and temperature $T$. In particular, for $x_{\mathrm{c}}=0.28$, magnetometry reveals a transition from one-step to two-step reversal behavior for temperatures $T$ > 260 K, indicating a transition from a fully correlated magnetic film structure to an uncoupled system containing effectively two independent magnetic sublayers. Corroborating evidence of the temperature-dependent coupling of the top and bottom regions for $x_{\mathrm{c}}=0.28$ was revealed by PNR, which demonstrated the field-dependent occurrence of antiparallel magnetization alignment on opposite interfaces at sufficiently high temperatures only.

We report on the magnetic properties of Co clusters (around 2.5 nm diameter) embedded in different matrices (C, Au, and Cu). Firstly, we accurately determine the intrinsic magnetic properties of the particles, using highly diluted samples where no interactions are detected, and a procedure relying on the theoretical description of various magnetometry measurements, and we show how both the magnetic size and anisotropy can be impacted by the nature of the matrix. Then, by considering nanoparticle assemblies of increasing concentrations, we investigate the effects of interactions between particles. In order to account for the observed evolution of the measurements, we propose a simple model where magnetic dimers are formed for distances lower than a given interaction length (of the order of one nanometer). This superferromagnetic correlation, which can be consistently inferred for each matrix, modifies the magnetic size distribution, which has a drastic effect as soon as particles are close enough to each other.

We address the theory of the coupled lattice and magnetization dynamics of freely suspended single-domain nanoparticles. Magnetic anisotropy generates low-frequency satellite peaks in the microwave absorption spectrum and a blueshift of the ferromagnetic resonance (FMR) frequency. The low-frequency resonances are very sharp with maxima exceeding that of the FMR, because their magnetic and mechanical precessions are locked, thereby suppressing the effective Gilbert damping. Magnetic nanoparticles can operate as nearly ideal motors that convert electromagnetic into mechanical energy. The Barnett damping term is essential for obtaining physically meaningful results.

We report measurements of the in-plane London penetration depth $\lambda$ in single crystals of the $\alpha -{\mathrm{PdBi}}_2$ superconductor—the $\alpha$-phase counterpart of the putative topological superconductor $\beta -{\mathrm{PdBi}}_2$, down to 0.35 K using a high-resolution tunnel-diode-based technique. Both $\lambda$ and superfluid density ${\rho }_s$ exhibit an exponential behavior for $T\le 0.35T_c$, with $\mathrm{\Delta }\left(0\right)/k_B{T}_c\sim 2.0, \mathrm{\Delta }C/\gamma T_c\sim 2.0$, and $\lambda \left(0\right)\sim 140$ nm, showing that $\alpha -{\mathrm{PdBi}}_2$ is a moderately coupling, fully gapped superconductor. The values of $\mathrm{\Delta }\left(0\right)$ and $\mathrm{\Delta }C/\gamma T_c$ are consistent with each other via strong-coupling corrections.

We study impurity scattering in the normal and $d$-wave superconducting states of line nodal semimetals and show that, due to additional scattering phase space available for impurities on the surface, the quasiparticle interference pattern acquires an extended character instead of a discrete collection of delta function peaks. Moreover, using the $T$-matrix formalism, we demonstrate that the conventional behavior of a scalar impurity in a $d$-wave superconductor breaks down on the surface of a line nodal semimetal in the quasi-flat-band limit.

We have carried out a Schrieffer-Wolff transformation on a general tight-binding Hamiltonian and obtained a $4f$-one-band effective Hubbard Hamiltonian to study the physical origin of ferromagnetism in ${\mathrm{CeO}}_{2-\delta }$ nanoparticle systems. For a low temperature regime and low concentrations of oxygen vacancies, isolated vacancies have previously been showed to form on the $\left\{100\right\}$ and $\left\{110\right\}$ surfaces and our studies indicate these will be in singlet and triplet states, respectively. This is sustained by a superexchange interaction between the $4f$ electrons of the two cerium atoms, which are the nearest neighbors of the vacancy, and ferromagnetism and antiferromagnetism can coexist. Moreover, increasing the vacancy concentration we found that pairs of vacancies, which have been previously shown to form on the $\left\{111\right\}$ surfaces, produce Nagaoka ferromagnetism and isolated vacancies in the bulk produce an antiferromagnetic sign. Furthermore, further oxygen vacancy increases are previously known to favor the formation of oxygen vacancy clusters. In this case, our results showed a weakening of the magnetic correlations with respect to temperature. Thus, at a fixed temperature, the magnetic moment is reduced when the concentration of vacancies is increased, which is in agreement with experimental results reported in the literature. Interestingly, at a room-temperature regime, the antiferromagnetic order is destroyed and only the ferromagnetic couplings, produced mainly by isolated vacancies on the $\left\{110\right\}$ surfaces, survive. Finally, as temperature is increased further, the paramagnetic behavior of $4f$ electrons dominates.

The magnetic domains in a magnetic shape-memory Ni-Mn-Ga alloy were observed by magneto-optical Kerr microscopy using monochromatic blue LED light. The domains were observed for both single- and multivariant ferroelastic states of modulated martensite. The multivariant state with very fine twins was spontaneously formed after transformation from high-temperature austenite. For both cases, bar domains separated by ${180}^{\circ }$ domain walls were found and their dynamics was studied. A quasidomain model was applied to explain the domains in the multivariant state.

We calculate the optical conductivity $\sigma (T,\mathrm{\Omega })$ of a gas of Bogoliubov quasiparticles from their Green's function and the Kubo formula. We make comparisons with corresponding normal-state and superconducting-state results. The superconducting case includes the dynamic response of the condensate through additional contributions to the Kubo formula involving the Gor'kov anomalous Green's function. The differences in the optical scattering rate are largest just above the optical gap and become progressively smaller as the photon energy is increased or the temperature is raised. Our results are compared with those obtained using a recently advocated phenomenological procedure for eliminating the effect of the condensate. In this procedure the $\delta$-function contribution at zero photon energy, proportional to the superfluid density, is dropped in the real part of the conductivity $\left[{\sigma }_1(T,\mathrm{\Omega })\right]$ and its Kramers-Kronig transform is subtracted from the imaginary part ${\sigma }_2(T,\mathrm{\Omega })$. This results in deviations from our Bogoliubov quasiparticle and superconducting-state optical scattering rates even in the region where these have merged and are, in addition, not close to the normal-state result.

The quasiskutterudite superconductors $A_3{T}_4{\mathrm{Sn}}_{13}$ ($A=\text{Sr}$, Ca; $T=\text{Ir}$, Rh, Co) are highly tunable, featuring a structural quantum critical point. We construct a temperature-lattice constant phase diagram for these isovalent compounds, establishing ${\mathrm{Ca}}_3{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$ and ${\mathrm{Ca}}_3{\mathrm{Co}}_4{\mathrm{Sn}}_{13}$ as members close to and far away from the structural quantum critical point, respectively. Deconvolution of the lattice specific heat and the electrical resistivity provide an approximate phonon density of states $F\left(\omega \right)$ and the electron-phonon transport coupling function ${\alpha }_{\text{tr}}^{2}F\left(\omega \right)$ for ${\mathrm{Ca}}_3{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$ and ${\mathrm{Ca}}_3{\mathrm{Co}}_4{\mathrm{Sn}}_{13}$, enabling us to investigate the influence of the structural quantum critical point. Our results support the scenario of phonon softening close to the structural quantum critical point, and explain the enhancement of the coupling strength on approaching structural instability.

Transport measurements under tilted magnetic fields were performed on a series of C-doped (001) GaAs/AlGaAs two-dimensional hole quantum wells. Due to a large $g$ factor, Zeeman energy is large and comparable to the cyclotron energy in these samples. On the other hand, it was found that the in-plane component $g_{\parallel }$ is small, and the effect of a tilted magnetic field is mainly to increase the effective mass of the holes. We investigate the spin transition of composite fermion states around Landau level (LL) filling factor 3/2. We found that the $\nu =4/3$ state encounters a partial- to full-spin-polarization transition, conforming to the same pattern as that of electron samples. In addition, a high-resistance phase emerges at $\nu =3/2$ under very high tilt angles. We interpret both of these phenomena as a consequence of LL crossing under a purely perpendicular magnetic field.

General expressions for the electron- and hole-acoustic-phonon deformation potential Hamiltonians $\left(H_{\text{E-DP}}\right)$ are derived for the case of Ge/Si and Si/Ge core/shell nanowire structures (NWs) with circular cross section. Based on the short-range elastic continuum approach and on derived analytical results, the spatial confinement effects on the phonon displacement vector, the phonon dispersion relation and the electron- and hole-phonon scattering amplitudes are analyzed. It is shown that the acoustic displacement vector, phonon frequencies and $H_{\text{E-DP}}$ present mixed torsional, axial, and radial components depending on the angular momentum quantum number and phonon wave vector under consideration. The treatment shows that bulk group velocities of the constituent materials are renormalized due to the spatial confinement and intrinsic strain at the interface. The role of insulating shell on the phonon dispersion and electron-phonon coupling in Ge/Si and Si/Ge NWs are discussed.

We investigate the influence of spatial dispersion on atom-surface quantum friction. We show that for atom-surface separations shorter than the carrier's mean free path within the material, the frictional force can be several orders of magnitude larger than that predicted by local optics. In addition, when taking into account spatial dispersion effects, we show that the commonly used local thermal equilibrium approximation underestimates by approximately 95% the drag force, obtained by employing the recently reported nonequilibrium fluctuation-dissipation relation for quantum friction. Unlike the treatment based on local optics, spatial dispersion in conjunction with corrections to local thermal equilibrium change not only the magnitude but also the distance scaling of quantum friction.

We discuss the emergence of zero-energy Majorana modes in a disordered finite-length $p$-wave one-dimensional superconducting ring, pierced by a magnetic flux $\mathrm{\Phi }$ tuned at an appropriate value $\mathrm{\Phi }={\mathrm{\Phi }}_{*}$. In the absence of fermion parity conservation, we evidence the emergence of the Majorana modes by looking at the discontinuities in the persistent current $I\left[\mathrm{\Phi }\right]$ at $\mathrm{\Phi }={\mathrm{\Phi }}_{*}$. By monitoring the discontinuities in $I\left[\mathrm{\Phi }\right]$, we map out the region in parameter space characterized by the emergence of Majorana modes in the disordered ring.