YPdBi is a well-studied diamagnetic topologically trivial half-Heusler alloy that is superconducting with $T_c\sim 1$ K. When strained or in thin-film form, it shows a topologically nontrivial surface state with $T_c$ $\sim 1.25\mathrm{K}$. ErPdBi is a well-studied topologically nontrivial half Heusler with $T_c$ $\sim 1.22\mathrm{K}$. In this work, we demonstrate that the $f$-electron doping in YPdBi provides a unique way to selectively tune the electronic structure and aid in increasing the superconducting transition temperature of YPdBi. This work presents systematic measurements of electrical resistivity and magnetotransport on half-Heusler thin films of ${\mathrm{Y}}_{(1-x)}\mathrm{E}{\mathrm{r}}_x\mathrm{PdBi}$ ($x=0.2$, 0.5, and 0.8), prepared using the pulsed laser deposition technique. All the films were observed to be semimetallic, with a sharp downturn in resistivity at low temperatures $T$ < 5 K; the E5 film ($T_c\sim 4.4$ K) and E8 film ($T_c\sim 3.7$ K) reach a zero-resistivity value, within the experimental limit. The doping of $f$ electron on ${\mathrm{Y}}^{+3}$ sites possibly gives rise to the improved Fermi parameters and an increase in $T_c$. Magnetoresistance measurements and first-principle calculations support that ${\mathrm{Y}}_{(1-x)}\mathrm{E}{\mathrm{r}}_x\mathrm{PdBi}$ are topologically nontrivial semimetals. The first-principle calculations also show that with an increase in the doping concentration ($x$), more $f$ bands start to appear near Fermi level ($E_F$), giving rise to an increase in the band-inversion strength due to s-f exchange interaction. The nontrivial band structure, odd-parity Cooper pair, and noncentrosymmetric crystal structure suggest the presence of unconventional superconductivity in the E5 and E8 films.

Silicon (Si) impurities are among the most widely used dopants in GaAs-based electronic and optoelectronic materials, including low-dimensional systems such as nanowires (NWs). Undesired $p$-type conduction is often observed in Si-doped GaAs NWs due to the amphoteric nature of Si, but can be mitigated by proper catalyst-free, vapor-solid growth processes. Yet, the intriguing dynamics of Si dopant incorporation and spatial distribution within the NW structure are largely unknown, which are key to understanding the resulting electrical activity on a local scale. Here, we correlate the spatial distribution of Si dopants with the electrical transport characteristics of catalyst-free, selective-area grown GaAs(Sb) NWs. Through a combination of atom probe tomography, resonant Raman scattering, and single-NW field effect transistor measurements, spatial nonuniformities in Si concentration are revealed in both the axial and the radial directions. Si dopant gradients induced by the highly nonlinear growth rate along the NW axis result in varying rectifying current-voltage ($I\text{−}V$) characteristics with decreased conductivity (lower Si concentration) towards the NW tip. Surface segregation further leads to increased Si concentrations (up to $\sim {10}^{20}\mathrm{c}{\mathrm{m}}^{-3}$) on the surface of the GaAs(Sb) sidewalls, generating a thin parasitic region of high $p$-type conductivity. Finally, removal of the Si-enriched $p$-type surface region is demonstrated by controlled wet chemical etching in citric acid, revealing the intended $n$-type conduction of the bulk region of the NW.

The spin Hall magnetoresistance (SMR) of antiferromagnetic $\mathrm{BiFe}{\mathrm{O}}_3$ thin film surfaces is investigated. SMR consistent with weak ferromagnetic order in films fabricated on (001) $\mathrm{SrTi}{\mathrm{O}}_3$ (R′ BFO) and $\mathrm{LaAl}{\mathrm{O}}_3$ (T′ BFO) substrates is found, albeit with different temperature dependencies. For T′ BFO, the SMR is enhanced at room temperature, and decays with reduced temperatures. By contrast, R′ BFO shows a monotonic decrease in SMR response with increasing temperature, mirroring the trend of a weak ferromagnet. Density functional theory shows that this intriguing difference originates due to the different octahedral rotation patterns in R′ and T′ BFO and their coupling to the applied magnetic field and spin degrees of freedom.

Grain texture evolution and coarsening after quenching can be achieved by curvature-driven growth and grain rotation. Here we examine grain rotation in coarsening, impurity-doped, two-dimensional colloidal polycrystals. We find the rate of rotation to be independent of the impurity concentration and proportional to the inverse of the grain size. The latter is rationalized by considering grain rotation driven by grain-boundary sliding and particle diffusion in the lattice. We also show that rotation driven grain growth and curvature driven growth are independent, with the latter being the dominant mechanism in our system. Next, we examine the dislocation reactions underlying grain rotation and observing its facilitation via the effective “sinking” of grain-boundary dislocations into triple junctions, as has been predicted by simulations.

The layered honeycomb magnet $\alpha \text{−}{\mathrm{RuCl}}_3$ is the most promising candidate for a Kitaev quantum spin liquid (KQSL) that can host charge-neutral Majorana fermions. Recent studies have shown significant sample dependence of thermal transport properties, which are a key probe of Majorana quasiparticles in the KQSL state, highlighting the importance of preparing high-quality single crystals of $\alpha \text{−}{\mathrm{RuCl}}_3$. Here, we present a relatively simple and reliable method to grow high-quality single crystals of $\alpha \text{−}{\mathrm{RuCl}}_3$. We use a two-step crystal growth method consisting of a purification process by chemical vapor transport (CVT) and a main crystal growth process by sublimation. The obtained crystals exhibit a distinct first-order structural phase transition from the monoclinic $(C2/m)$ to the rhombohedral $\left(R\overline{3}\right)$ structure at $\sim 150$ K, which is confirmed by the nuclear quadrupole resonance spectra with much sharper widths than previously reported. The Raman spectra show the absence of defect-induced modes, supporting the good crystallinity of our samples. The jumps in the thermal expansion coefficient and specific heat at the antiferromagnetic (AFM) transition at 7.6–7.7 K are larger and sharper than those of previous samples grown by the CVT and Bridgman methods and do not show any additional AFM transitions at 10–14 K due to stacking faults. The longitudinal thermal conductivity in the AFM phase is significantly larger than previously reported, indicating a very long mean-free path of heat carriers. All the results indicate that our single crystals are of superior quality with good crystallinity and few stacking faults, which provides a suitable platform for studying the Kitaev physics.

Kagome superconductors ${\mathrm{AV}}_3{\mathrm{Sb}}_5$ (A = K, Rb, Cs) have attracted great attention recently due to the topological electronic bands and rich many-body states. Here, we report the unusual superconducting gap of about 0.10 meV of ${\mathrm{KV}}_3{\mathrm{Sb}}_5$, which cannot be fitted by BCS theory, measured by a dilution refrigerator scanning tunneling microscope. Uniform superconducting gaps on a potassium-terminated surface have been revealed by spatially resolved scanning tunneling spectra. Temperature-dependent tunneling spectra unveil that the superconducting transition temperature is about 0.73 K on a cleaved surface. Due to the desorption of potassium, it is slightly lower than the bulk superconducting transition temperature of 0.92 K determined by transport measurement. In addition, our electronic transport measurement of thin flakes shows an enhanced superconducting transition onset temperature up to 2.15 K, which is possibly attributed to the strain effect caused by their underling cleaving tapes. Our work sheds light on understanding the unusual superconducting state of a vanadium-based kagome superconductor.

Superconductivity has been found in RuN films obtained by reactive magnetron sputtering. This novel member of the metal nitride superconductors family has a critical temperature of the superconducting transition that varies depending on the substrate, ranging from 0.77 K to 1.29 K. The parameters of the crystal lattice of the superconducting films have been determined: The lattice is cubic with rhombohedral distortion along the normal to substrate surface with parameters $a=b=c=4.559\mathrm{\AA }$ for $\mathrm{RuN}/{\mathrm{SiO}}_2$, $a=b=c=4.536\mathrm{\AA }$ for RuN/Si, and $\alpha =\beta =\gamma =87.{96}^{\circ }$ for both films. The upper critical magnetic field at zero temperature $H_{c2}\left(0\right)=2.3–4.1\mathrm{T}$ found by extrapolation our experimental data collected at $T⪆0.8$ to zero temperature using the WHH model is near the upper paramagnetic limit. An $s$-wave single-band energy gap of $\mathrm{\Delta }\left(0\right)=0.19\mathrm{meV}$ was revealed by self-field critical current experiment at temperatures down to 10 mK.

Electric field induced phototransport of regioregular poly(3-hexylthiophene) [P3HT] and squaraine (SQ) dye-sensitized samples are studied in this paper. The relative variation of photoresponse spectra shows that the trap energetics and charge transport are modified in the presence of $1\mathrm{wt}\%$ SQ dye. In the doped sample, the $S\left(V\right)/S\left(60V\right)$ ratio at 2.1 eV increases by a factor of 21 at 1800 V/cm, with a substantial increase in the photoresponse. The redistribution of the trap energy levels and enhancement in transport is associated with the variations in transit and relaxation times of carriers in the presence of the dye. The phase part of the signal consisting of photocapacitance is reduced and becomes less dependent on the optical energy in the doped sample. This is consistent with the absence of space charge contribution in dye-doped samples. The deconvoluted photoresponse signal by using Gaussian functions indicates that the trapping-detrapping processes are altered by the dye since only three Gaussian peaks are observed in the dye-doped sample. The deconvoluted photoresponse in the dye-doped sample indicates that the modified trapping-detrapping processes have enhanced the transport, which results in three Gaussian peaks.

The presence of antisite disorder in double perovskites manifests various intriguing properties like the spin-glass state, exchange bias, and memory effect. Here, we report the synthesis of a ${\mathrm{La}}_{1.5}{\mathrm{Sm}}_{0.5}{\mathrm{NiMnO}}_6$ compound that crystallizes in a monoclinic ($P2{}_1/n$) structure. The presence of multiple oxidation states of Ni(Mn) cations induces competing (ferromagnetic and antiferromagnetic) exchange interactions that originate an inhomogeneous spin state, as evident from observed magnetic anomalies in temperature-dependent magnetization measurements. A spin-glass (SG) state is evolved that manifests field cooling ($H{}_{\text{CF}}$ = 500 Oe) induced exchange bias ($H{}_{\text{EB}}\sim 153$ Oe) below spin-glass temperature $T{}_{\text{SG}}$ (65 $\pm$ 1 K). The strength of the exchange bias is reduced after successive magnetization reversal cycles performed at 5 K. The reported magnetic training effect is explained within the frameworks of metastable magnetic disorder across frozen antiphase boundaries in the frustrated SG state. Measurements of frequency-dependent ac-susceptibility $\chi \left(\omega \right)$ suggest critical slowing dynamics and memory effect in the proximity of $T{}_{\text{SG}}$, which is described using a critical slowing model resulting in relaxation exponent $\mathrm{z}\nu$ = 1.99 $\pm$ 0.04 and ${\tau }_0$ = 8.91 x ${10}^{-7}\mathrm{s}$. Employing first-principles calculations, we find the insulating ferromagnetic ground state of ${\mathrm{La}}_{1.5}{\mathrm{Sm}}_{0.5}{\mathrm{NiMnO}}_6$ in the ordered phase where Ni(Mn) appears to be in the $2+(4+$) state. Further, the presence of antisite disorder eventually results in lower magnetic moments per formula unit, which is well corroborated by experimental observations. Our findings provide a pathway for designing host materials with inhomogeneous spin-frustrated systems and variable electronic states.

By means of Brownian dynamics simulations we study the steady-state dynamic properties of a flexible active polymer in a poor solvent condition. Our results show that the effective diffusion constant of the polymer $D_{\mathrm{eff}}$ gets significantly enhanced as activity increases, much like in active particles. The simulation data are in agreement with a theoretically constructed Rouse model of active polymer, demonstrating that irrespective of the strength of activity, the long-time dynamics of the polymer chain is characterized by a universal Rouse-like scaling $D_{\mathrm{eff}}\sim N^{-1}$, where $N$ is the chain length. We argue that the presence of hydrodynamic interactions will only have an insignificant effect on the observed scaling behavior.

The large spin-orbit coupling in iridium oxides plays a significant role in driving novel physical behaviors, including emergent phenomena in the films and heterostructures of perovskite and Ruddlesden-Popper iridates. In this Letter, we study the role of epitaxial strain on the electronic behavior of thin ${\mathrm{SrIrO}}_3$ films. We find that compressive epitaxial strain leads to metallic transport behavior, but a slight tensile strain shows gapped behavior. Temperature-dependent resistivity measurements are used to examine different behaviors in films as a function of strain. We find Kondo contributions to the resistivity, with stronger effects in films that are thinner and under less compressive epitaxial strain. These results show the potential to tune ${\mathrm{SrIrO}}_3$ into Kondo insulating states and open possibilities for a quantum critical point that can be controlled with strain in epitaxial films.

Uranium-based compounds display rich and exotic physical properties, but remain less studied compared with $4f\text{−}\mathrm{electron}$ rare-earth compounds. The lack of high quality single crystal samples hinders the use of many specific techniques to study the properties of uranium-based compounds. In the present study, we successfully obtain high quality single crystalline $\mathrm{UC}{\mathrm{u}}_5$ (111) films by depositing uranium atoms on the Cu (111) substrate after annealing at 800 K. Surface structures with the increase of uranium coverage have been systematically studied, and moiré patterns are observed in the $\mathrm{UC}{\mathrm{u}}_5$ (111) films, which gradually become weaker with the increase of film thickness of $\mathrm{UC}{\mathrm{u}}_5$. $dI/dV$ spectra of $\mathrm{UC}{\mathrm{u}}_5$ films with the thickness from 1 to 5 unit cells show similar electronic properties, which exhibit a strong asymmetric dip-peak structure near the Fermi energy. Temperature-dependent $dI/dV$ measurements further confirm that this asymmetric feature is related to Kondo physics and due to the hybridization between U $5f$ electrons and surrounding conduction electrons. Different terminated surfaces can be obtained by sputtering $\mathrm{UC}{\mathrm{u}}_5$ thick films with $\mathrm{A}{\mathrm{r}}^{+}$ ions and subsequent annealing, which show drastically different electronic structure. Our results provide a path for the preparation of single crystalline uranium-based compounds and related materials.

Two-dimensional (2D) group-IV materials with tetragonal structures have attracted considerable attention recently due to their structural stability and distinctive electronic and optical characteristics. However, topological quantum states, particularly second-order topological insulators (SOTIs), are seldom reported in them. Based on first-principles and tight-binding (TB) model calculations, we find that 2D hydrogenated tetragonal stanene (T-SnH) is an exotic SOTI, identified by the second Stiefel-Whitney number $w_2=1$, along with robust corner states. Intriguingly, the SOTI in T-SnH transforms into a quantum spin Hall insulator under 2.7% tensile strain. The same topological phase transition can also occur by substituting the Sn element with the Pb element, namely, forming a T-PbH monolayer. A three-orbital TB model is constructed to understand the phase transition mechanism for the two schemes, both associated with band inversion between antibonding $s$ and bonding $p_{x,y}$ states due to the large Sn-Sn (or Pb-Pb) bond lengths. The phase transition is also rationalized well from topological quantum chemistry theory. These insights are helpful for understanding the SOTI and provide a promising material platform for topological quantum device designs and applications.

The electrode-semiconductor interface plays an important role in generating and enhancing the photogalvanic effects (PGEs) in semiconducting materials. However, knowledge of the impact of the interface on the PGE for spintronics is currently very limited. Here, we propose the two-dimensional (2D) photodetectors composed of nonmagnetic semiconductor ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ sandwiched between the half-metallic electrodes of 2D ${\mathrm{VSi}}_2{\mathrm{N}}_4$ (${\mathrm{NbSi}}_2{\mathrm{N}}_4$) and investigate the PGE induced by linear polarized light in the visible range. The ${\mathrm{VSi}}_2{\mathrm{N}}_4/{\mathrm{MoSi}}_2{\mathrm{N}}_4$ and ${\mathrm{NbSi}}_2{\mathrm{N}}_4/{\mathrm{MoSi}}_2{\mathrm{N}}_4$ interfaces cause an opposite bending of the conduction bands in ${\mathrm{MoSi}}_2{\mathrm{N}}_4$, respectively, due to the different work functions of the two electrodes. This results in a larger and fully-spin-polarized PGE photocurrent for the photodetector with the ${\mathrm{VSi}}_2{\mathrm{N}}_4$ electrodes, while a much smaller photocurrent with a lower spin polarization for the photodetector with the ${\mathrm{NbSi}}_2{\mathrm{N}}_4$ electrodes. Meanwhile, both the photodetectors possess a perfect spin-valve effect with a 100% magnetoresistance ratio in a broad visible range. These results suggest that, by using the magnetic electrodes with an appropriate work function, both the magnitude and the spin-polarization of the photocurrent can be largely enhanced, making it promising for the application of the PGE in spintronic devices.

We have investigated the electronic structure of the transition metal oxide ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ within density-functional theory using the generalized gradient approximation while considering strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band structure method. ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ can be classified as a Mott insulator since it was expected to be metallic from band structure calculations. We found that the magnetic ground state of ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ possesses an $\mathrm{AFM}\text{−}b$ magnetic structure with the Ru spin moments ordered antiferromagnetically along the $b$ axis. We have investigated the resonant inelastic x-ray scattering (RIXS) spectra at the Ru and Ca $K, L_3$, and $M_3$ edges as well as at the $\mathrm{O}K$ edge. The experimentally measured RIXS spectrum of ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ at the Ru $L_3$ edge possesses a sharp feature $\le 2\mathrm{eV}$ corresponding to transitions within the Ru $t_{2g}$ levels. The excitation located from 2 to 4 eV is due to $t_{2g}\to e_g$ transitions. The third wide structure situated at $4.5-11\mathrm{eV}$ appears due to transitions between the Ru $4d_{\mathrm{O}}$ states derived from the tails of oxygen $2p$ states and $e_g$ and $t_{2g}$ states. The RIXS spectra at the Ru $L_3$ and $M_3$ edges are quite similar. However, the corresponding RIXS spectra at the Ca site are quite different from each other due to the significant difference in the widths of core levels. The RIXS spectrum at the $\mathrm{O}K$ edge consists of three major inelastic excitations. We found that the first two low energy features $\le 2.5\mathrm{eV}$ are due to interband transitions between occupied and empty ${\mathrm{O}}_{t_{2g}}$ states which appear due to the strong hybridization between oxygen $2p$ and Ru $t_{2g}$ states in close vicinity to the Fermi level. The next major peak between 2.5 and 8 eV reflects interband transitions from occupied $\mathrm{O}2p$ to empty ${\mathrm{O}}_{t_{2g}}$ states. A wide energy interval between 4 and 11 eV is occupied by rather weak ${\mathrm{O}}_{2p}\to {\mathrm{O}}_{e_g}$ transitions.

The way metal interfaces evolve during frictional sliding and how that evolution can be externally influenced under external drivers are important questions, which are difficult to investigate experimentally because the contacts themselves are generally difficult to access. Here we focus on an elementary constituent of a general metal-metal interface, namely, an ultrathin individual nanocontact, where recent rheological studies of crystalline gold nanocontacts [Nature (London) 569, 393 (2019)] showed a dramatic and unexpected mechanical softening as a result of external oscillatory tensile stress. The question which we address through realistic nonequilibrium molecular dynamics simulations is to what extent such mechanical softening might influence the shearing habit of gold nanocontacts at room temperature. It is found that the shearing evolution, which occurs through a series of discrete slips, is indeed rheologically softened, even though not completely, by the oscillations. Differences also emerge for different types of external oscillation, tensile or rotational. The relevance of these results for future experiments will be discussed.

We report growth of high-quality single crystals of $\mathrm{CeC}{\mathrm{l}}_3$ using a modified Bridgman-Stockbarger method in an infrared image furnace. The grown crystals are characterized using single-crystal(powder) x-ray diffraction, Laue x-ray diffraction, Raman spectroscopy, magnetization, and heat-capacity probes. $\mathrm{CeC}{\mathrm{l}}_3$ crystallizes in a hexagonal structure ($P{6}_3/m$) with a weak trigonal distortion ($P\overline{3}$). The Raman spectrum at 300 K shows five clearly resolvable phonon modes at 106.8, 181.2, 189, 213, and $219.7\mathrm{c}{\mathrm{m}}^{-1}$. The magnetic susceptibility along $H\parallel c\left({\chi }^{\parallel }\right)$ and $H\perp c\left({\chi }^{\perp }\right)$ axis is measured as a function of temperature and magnetic field. ${\chi }^{\perp }$ exhibits a broad peak centered around 50 K; ${\chi }^{\parallel }$, in comparison, shows a monotonic Curie-like increase upon cooling and is about two orders of magnitude larger in size. This anisotropic behavior with qualitatively different temperature dependences shown by ${\chi }^{\parallel }$ and ${\chi }^{\perp }$ is explained using the crystal field theory. The crystal field in $\mathrm{CeC}{\mathrm{l}}_3$ splits the $J=5/2$ manifold of $\mathrm{C}{\mathrm{e}}^{3+}$ into three Kramers doublets with $|5/2,\pm 5/2\rangle$ as the ground state, and $|5/2,\pm 1/2\rangle$ at energy $E_1=61$ K, and $|5/2,\pm 3/2\rangle$ at $E_2=218$ K as the first and second excited states, respectively. Accordingly, $M$($H$) at 2 K along $H\perp c$ is small and shows a linear variation, whereas $M$(H) along $H\parallel c$ saturates readily (easy axis) to the expected value. In the specific heat, no magnetic ordering could be seen down to 2 K. However, in nonzero fields the low-temperature specific heat changes dramatically, showcasing a peak at 2.5 K under a moderate field of 30 kOe. The weak Ce-Ce exchange, large Ce moment in the crystal-field ground state, and huge anisotropy are all ingredients for realizing a high magnetocaloric effect. Indeed, measurements at low temperatures reveal a maximum entropy change of $-\mathrm{\Delta }{S}_{4f}\approx 23\pm 1\mathrm{J}\mathrm{K}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$ near 2.5 K in the field ranging from 50 to 60 kOe. These values are comparable to some of the best known Gd-based magnetocaloric materials, signifying the potential of $\mathrm{CeC}{\mathrm{l}}_3$ as a magnetic coolant.

High In content InGaAs quantum wells (In $\ge$ 75%) are potentially useful for topological quantum computing and spintronics applications. In high-mobility InGaAs quantum wells, alloy disorder scattering is a limiting factor. In this paper, we demonstrate that by growing the InGaAs quantum wells as a digital alloy, or a short period superlattice, we can reduce the alloy disorder scattering within the quantum well and increase the peak 2 K electron mobility to $545000 {\mathrm{cm}}^2$/Vs, which is the highest reported mobility for high-In content InGaAs quantum wells to the best of the authors' knowledge. Our results demonstrate that the digital alloy approach can be used to increase the mobility of quantum wells in random alloy ternary materials.