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Register a new userAnomalous spin-momentum locked two-dimensional states in the vicinity of a topological phase transition
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We perform spin-resolved and spin-integrated angle-resolved photoemission spectroscopy measurements on a series of compositions in the BiTl(S1-xSex)2 system, focusing on x-values in the vicinity of the critical point for the topological phase transition (the band inversion composition). We observe quasi two dimensional (2D) states on the outer boundary of the bulk electronic bands in the trivial side (non-inverted regime) of the transition. Systematic spin-sensitive measurements reveal that the observed 2D states are spin-momentum locked, whose spin texture resembles the helical spin texture on the surface of a topological insulator. These anomalous states are observed to be only prominent near the critical point, thus are possibly related to strong precursor states of topological phase transition near the relaxed surface.
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Using symmetry breaking strain to tune the valley occupation of a two-dimensional (2D) electron system in an AlAs quantum well, together with an applied in-plane magnetic field to tune the spin polarization, we independently control the systems valley and spin degrees of freedom and map out a spin-valley phase diagram for the 2D metal-insulator transition. The insulating phase occurs in the quadrant where the system is both spin- and valley-polarized. This observation establishes the equivalent roles of spin and valley degrees of freedom in the 2D metal-insulator transition.
Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect, i.e. measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1-x)2Te3 to a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable spin Seebeck effect which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual spin Seebeck effect in metals and therefore opens up exciting possibilities in spintronics.
We evaluate the effective interactions in a fluid of electrons moving in a plane, on the approach to the quantum phase transition from the paramagnetic to the fully spin-polarized phase that has been reported from Quantum Monte Carlo runs. We use the approach of Kukkonen and Overhauser to treat exchange and correlations under close constraints imposed by sum rules. We show that, as the paramagnetic fluid approaches the phase transition, the effective interactions at low momenta develop an attractive region between parallel-spin electrons and a corresponding repulsive region for antiparallel-spin electron pairs. A connection with the Hubbard model is made and used to estimate the magnetic energy gap and hence the temperature at which the phase transition may become observable with varying electron density in a semiconductor quantum well.
Giant spin-splitting was recently predicted in collinear antiferromagnetic materials with a specific class of magnetic space group. In this work, we have predicted a two-dimensional (2D) antiferromagnetic Weyl semimetal (WS), CrO with large spin-split band structure, spin-momentum locked transport properties and high Neel temperature. It has two pairs of spin-polarized Weyl points at the Fermi level. By manipulating the position of the Weyl points with strain, four different antiferromagnetic spintronic states can be achieved: WSs with two spin-polarized transport channels (STCs), WSs with single STC, semiconductors with two STCs, and semiconductors with single STC. Based on these properties, a new avenue in spintronics with 2D collinear antiferromagnets is proposed.
Large fluctuations of conductivity with time are observed in a low-mobility two-dimensional electron system in silicon at low electron densities $n_s$ and temperatures. A dramatic increase of the noise power ($propto 1/f^{alpha}$) as $n_s$ is reduced below a certain density $n_g$, and a sharp jump of $alpha$ at $n_sapprox n_g$, are attributed to the freezing of the electron glass at $n_s = n_g$. The data strongly suggest that glassy dynamics persists in the metallic phase.
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