Presence Of Strong Spin-orbit Interaction Research Articles

Josephson effect of superconductors with J=32 electrons

The angular momentum of an electron is characterized well by pseudospin with $J=3/2$ in the presence of strong spin-orbit interactions. We study theoretically the Josephson effect of superconductors in which such two $J=3/2$ electrons form a Cooper pair. Within even-parity symmetry class, pseudospin-quintet pairing states with $J=2$ can exist as well as pseudospin-singlet state with $J=0$. We focus especially on the Josephson selection rule among these even-parity superconductors. We find that the selection rule between quintet states is severer than that between spin-triplet states formed by two $S=1/2$ electrons. The effects of a pseudospin-active interface on the selection rule are discussed as well as those of odd-frequency Cooper pairs generated by pseudospin dependent band structures.

Pinning of Andreev bound states to zero energy in two-dimensional superconductor- semiconductor Rashba heterostructures

We consider a two-dimensional electron gas with Rashba spin-orbit interaction (SOI) partially covered by an s-wave superconductor, where the uncovered region remains normal but is exposed to an effective Zeeman field applied perpendicular to the plane. We find analytically and numerically Andreev bound states (ABSs) formed in the normal region and show that, due to SOI and by tuning the parameters of the system deeply into the topologically trivial phase, one can reach a regime where the energy of the lowest ABS becomes pinned close to zero as a function of Zeeman field. The energy of such an ABS is shown to decay as an inverse power-law in Zeeman field. We also consider a superconductor-semiconductor heterostructure with a superconducting vortex at the center and in the presence of strong SOI, and find again ABSs that can get pinned close to zero energy in the non-topological phase.

Measurements of spin–orbit interaction in epitaxially grown InAs nanosheets

We report a low-temperature transport study of a single-gate, planar field-effect device made from a free-standing, wurtzite-crystalline InAs nanosheet. The nanosheet is grown via molecular beam epitaxy and the field-effect device is characterized by gate transfer characteristic measurements and by magnetic field orientation dependent transport measurements. The measurements show that the device exhibits excellent electrical properties and the electron transport in the nanosheet is of a two-dimensional nature. Low-field magnetoconductance measurements are performed for the device at different gate voltages and temperatures, and the characteristic transport lengths, such as phase coherent length, spin–orbit length, and mean free path, in the nanosheet are extracted. It is found that the spin–orbit length in the nanosheet is short, on the order of 150 nm, demonstrating the presence of strong spin–orbit interaction in the InAs nanosheet. Our results show that epitaxially grown, free-standing, InAs nanosheets can serve as an emerging semiconductor nanostructure platform for applications in spintronics, spin qubits, and planar topological quantum devices.

Spin-orbit interaction and snake states in a graphene p-n junction

We study a model of a $p$-$n$ junction in single-layer graphene in the presence of a perpendicular magnetic field and spin-orbit interactions. By solving the relevant quantum-mechanical problem for a potential step, we determine the exact spectrum of spin-resolved dispersive Landau levels. Close to zero energy, we find a pair of linearly dispersing zero modes, which possess a wave-vector-dependent spin polarization and can be regarded as quantum analogous of spinful snake states. We show that the Rashba spin-orbit interaction, in particular, produces a wave vector shift between the dispersions of these modes with observable interference effects. These effects can in principle provide a way to detect the presence of Rashba spin-orbit interaction and measure its strength. Our results suggest that a graphene $p$-$n$ junction in the presence of strong spin-orbit interaction could be used as a building block in a spin field-effect transistor.

Growth and electrical transport properties of La0.7Sr0.3MnO3 thin films on Sr2IrO4 single crystals

We report the physical properties of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ thin films on ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ single crystals. The manganite films are deposited using oxide molecular beam epitaxy on flux-grown (001)-oriented iridate crystals. Temperature-dependent magnetotransport and x-ray magnetic circular dichroism measurements reveal the presence of a ferromagnetic metallic ground state in the films, consistent with films grown on ${\mathrm{SrTiO}}_{3}$ and ${\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7}{\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}{\mathrm{O}}_{3}$. A parallel resistance model is used to separate conduction effects within the ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ substrate and the ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ thin films, revealing that the measured resistance maximum does not correspond to the manganite Curie temperature but results from a convolution of properties of the near-insulating substrate and metallic film. The ability to grow and characterize epitaxial perovskites on ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ crystals enables a new route for studying magnetism at oxide interfaces in the presence of strong spin-orbit interactions.

Odd-parity superconductors with two-component order parameters: Nematic and chiral, full gap, and Majorana node

Motivated by the recent experiment indicating that superconductivity in the doped topological insulator Cu$_x$Bi$_2$Se$_3$ has an odd-parity pairing symmetry with rotational symmetry breaking, we study the general class of odd-parity superconductors with two-component order parameters in trigonal and hexagonal crystal systems. In the presence of strong spin-orbit interaction, we find two possible superconducting phases below $T_c$, a time-reversal-breaking (i.e., chiral) phase and an anisotropic (i.e., nematic) phase, and determine their relative energetics from the gap function in momentum space. The nematic superconductor generally has a full quasi-particle gap, whereas the chiral superconductor with a three-dimensional (3D) Fermi surface has point nodes with lifted spin degeneracy, resulting in itinerant Majorana fermions in the bulk and topological Majorana arcs on the surface.

Zero-field spin-splitting and effective masses in p-type GaAs two-dimensional hole gases

We present magnetotransport measurements performed on two-dimensional hole gases embedded in carbon doped p-type GaAs/AlGaAs hetorostructures grown on [001] oriented substrates. A pronounced beating pattern in the Shubnikov-de Haas oscillations proves the presence of strong spin-orbit interaction in the device under study. We estimate the effective masses of spin-split subbands by measuring the temperature dependence of the Shubnikov-de Haas oscillations at different hole densities. While the lighter heavy-hole effective mass is not energy dependent, the heavier heavy-hole effective mass has a prominent energy dependence, indicating a strong spin-orbit induced non parabolicity of the valence band. The measured effective masses show qualitative agreement with self-consistent numerical calculations.

Anomalous Josephson effect induced by spin-orbit interaction and Zeeman effect in semiconductor nanowires

We investigate theoretically the Josephson junction of semiconductor nanowire with strong spin-orbit (SO) interaction in the presence of magnetic field. By using a tight-binding model, the energy levels ${E}_{n}$ of Andreev bound states are numerically calculated as a function of phase difference $\ensuremath{\varphi}$ between two superconductors in the case of short junctions. The dc Josephson current is evaluated from the Andreev levels. In the absence of SO interaction, a 0-$\ensuremath{\pi}$ transition due to the magnetic field is clearly observed. In the presence of SO interaction, the coexistence of SO interaction and Zeeman effect results in ${E}_{n}(\ensuremath{-}\ensuremath{\varphi})\ensuremath{\ne}{E}_{n}(\ensuremath{\varphi})$, where the anomalous Josephson current flows even at $\ensuremath{\varphi}=0$. In addition, the direction dependence of critical current is observed, in accordance with experimental results.

Spin-orbit splitting and effective masses inp-type GaAs two-dimensional hole gases

We present magnetotransport measurements performed on two-dimensional hole gases embedded in carbon doped p-type GaAs/AlGaAs heterostructures grown on [001] oriented substrates. A pronounced beating pattern in the Shubnikov-de Haas oscillations proves the presence of strong spin-orbit interaction in the device under study. We estimate the effective masses of spin-orbit split subbands by measuring the temperature dependence of the Shubnikov-de Haas oscillations at different hole densities. While the lighter heavy-hole effective mass is not energy dependent, the heavier heavy-hole effective mass has a prominent energy dependence, indicating a strong spin-orbit induced non parabolicity of the valence band. The measured effective masses show qualitative agreement with self-consistent numerical calculations.

Tetrahedral Magnetic Order and the Metal-Insulator Transition in the Pyrochlore Lattice ofCd2Os2O7

Cd2Os2O7 shows a peculiar metal-insulator transition at 227 K with magnetic ordering in a frustrated pyrochlore lattice, but its magnetic structure in the ordered state and the transition origin are yet uncovered. We observed a commensurate magnetic peak by resonant x-ray scattering in a high-quality single crystal. X-ray diffraction and Raman scattering experiments confirmed that the transition is not accompanied with any spatial symmetry breaking. We propose a noncollinear all-in-all-out spin arrangement on the tetrahedral network made of Os atoms. Based on this we suggest that the transition is not caused by the Slater mechanism as believed earlier but by an alternative mechanism related to the formation of the specific tetrahedral magnetic order on the pyrochlore lattice in the presence of strong spin-orbit interactions.

Two-dimensional Frustrated Antiferromagnets (MCl)LaNb2O7 (M = Mn, Co, Cr)

Magnetic susceptibility and specific heat measurements have been performed on two-dimensional spin systems (M2+Cl)LaNb2O7 (M = Mn (S = 5/2), Cr (S = 2), Co (S = 3/2)), prepared via a topotactic ion-exchange reaction. All three compounds establish antiferromagnetic order at TN = 53 K, 61 K and 52 K, respectively for M = Mn, Co, Cr. Together with TN = 78 K for M = Fe (S = 2), this result indicates that the TN is not simply scaled by the magnitude of spin. In particular, the presence of strong spin-orbit interactions is suggested for (CoCl)LaNb2O7.

Electron dephasing in wurtzite indium nitride thin films

The authors present magnetotransport measurements of electron dephasing characteristics in wurtzite indium nitride thin films grown by metal-organic vapor phase epitaxy. Pronounced weak antilocalization effects have been observed at low magnetic fields due to the presence of strong spin-orbit interactions at the top of the valence band. With the aid of the weak localization theory, they are able to demonstrate that the dephasing is connected to three separate processes of the spin-orbit, electron-phonon, and extended structural defect scatterings. The spin-orbit splitting has been determined to be 5.7meV. They have also shown that both the magnetoresistivity and resistivity can be explained using the same temperature-dependent dephasing times.

Persistent-current paramagnetism and spin-orbit interaction in mesoscopic rings.

The persistent currents in arrays of isolated mesoscopic metallic rings are shown by conventional diagrammatic analysis (within a noninteracting model) to retain their paramagnetic character even in the presence of strong spin-orbit interaction. It is shown that this result is consistent with the nonperturbative one-dimensional results of Meir et al., if these results are correctly applied to the canonical ensemble.

Numerical study of symmetry effects on localization in two dimensions.

Effects of symmetry on localization on two-dimensional square lattices are studied numerically. The inverse localization length is determined by the system-size dependence of the Thouless number in magnetic fields or in the presence of strong spin-orbit interactions. A finite-size-scaling method is also applied to the case of spin-orbit interactions. Extended states, present in each Landau level in strong magnetic fields or in the case of small randomness, are found to merge together with increasing randomness and disappear beyond a certain critical randomness. In weak magnetic fields, the field tends to reduce the localization near the band center, while the localization is enhanced in the band-tail region. Spin-orbit interactions cause effects similar to, but much stronger than, that due to a weak magnetic field. The critical randomness and exponent for a metal-insulator transition are determined in the presence of strong spin-orbit interactions.

Electronic properties and localization effects in some hydrogen-doped 4d-3d metallic glasses

Magnetoresistance and magnetic susceptibility data obtained on hydrogen-doped samples of ZrNi and ZrCu systems are reported. A mobile-stage sample container in conjunction with a 6 T superconducting coil was used to measure magnetoresistance at temperatures down to 1.7 K with a relative precision of 10 −6. The temperature profile of the magnetic susceptibility was also measured down to 2 K by Faraday's method using a Cahn electrobalance combined with a conventional magnet. A precision range of 10 −7 J T −2 mol −1 was maintained in this measurement. The samples were produced by the common melt-spinning method and were used in the as-obtained condition. Hydrogen strongly influences the quantum-mechanical interference at defects, considerably enhances the quasi-elastic electron scattering and depresses the relative contribution of the spin-orbit interaction. The Maki-Thompson interaction is likewise depressed with increasing hydrogen concentration. The results can be interpreted on the basis of current theoretical concepts based on weak localization in three-dimensional systems in the presence of strong spin-orbit interaction and superconducting fluctuations. The magnetic susceptibility data are interpreted in terms of the hydrogen influence on the electronic density of states at the Fermi level.

Magnetoresistance of hydrogen-doped Zr2Ni metallic glass.

We report the results of magnetoresistance measurements on amorphous hydrogen-doped ${\mathrm{Zr}}_{2}$Ni samples and compare them with the current theoretical concepts based on weak localisation in three-dimensional systems in the presence of strong spin-orbit interaction. We find that the hydrogen dopant strongly suppresses the spin-orbit and the Maki-Thompson contributions to magnetoresistance.

Magnetoresistance of amorphous alloys: Weak localization in three-dimensional metallic systems

We have observed an anomalous magnetoresistance at low temperature in amorphous CuZr alloys. This magnetoresistance can be accounted for in theoretical models of localization for three-dimensional metallic systems in the presence of strong spin-orbit interaction (with a significant additional contribution from the quenching of superconducting fluctuations at the lowest temperatures). We also report on similar results observed in CuTi and CuLu alloys.

Magnetoresistance of amorphous CuZr : Weak localization in a three dimensional system

We report on the observation of anomalous magnetoresistance in amorphous CuZr at low temperature. The magnetoresistance can be precisely accounted for in theoretical models of localization for 3-dimensional metallic systems in the presence of strong spin-orbit interactions (with a significant additional contribution from the quenching of superconducting fluctuations at the lowest temperatures). Magnetoresistance measurements on various other systems show that such 3-dimensional localization effects are very generally observed in amorphous alloys.

Symmetry andgvalue of the relaxed excited state of KI:TI+AXemission

We report the effect of a magnetic field applied along the $〈111〉$ and $〈100〉$ directions on the luminescent decay time of the ${A}_{X}$ emission of KI:T${\mathrm{I}}^{+}$. From the directional dependence we show that the ${A}_{X}$ emission arises from a trigonal Jahn-Teller (JT) well. The field dependence of the decay time also provides an estimate of the $g$ value of the emitting state, which we find as $g\ensuremath{\sim}1$. This is shown to be consistent with the emitting state being a JT minimum on the $^{3}T_{1u}$ adiabatic potential-energy surface in the presence of strong spin-orbit interaction.