The quantum limits of contact resistance and ballistic transport in 2D transistors
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Light-matter coupling via quantum pathways for spontaneous symmetry breaking in van der Waals antiferromagnetic semiconductors
Light-matter interaction simultaneously alters both the original material and incident light. Light not only reveals material details but also activates coupling mechanisms. The coupling has been demonstrated mechanically, for instance, through the patterning of metallic antennas, resulting in the emergence of plasmonic quasiparticles and enabling wavefront engineering of light via the generalized Snell’s law. However, quantum-mechanical light-matter interaction, wherein photons coherently excite distinct quantum pathways, remains poorly understood. Here, we report on quantum interference between light-induced quantum pathways through the orbital quantum levels and spin continuum. The quantum interference immediately breaks the symmetry of the hexagonal antiferromagnetic semiconductor FePS3. Below the Néel temperature, we observe the emergence of birefringence and linear dichroism, namely, quantum anisotropy due to quantum interference, which is further enhanced by the thickness effect. We explain the direct relevance of the quantum anisotropy to a quantum phase transition by spontaneous symmetry breaking in Mexican hat potential. Our findings suggest material modulation via selective quantum pathways through quantum light-matter interaction.
Spin polarised quantised transport via one-dimensional nanowire-graphene contacts
Graphene spintronics offers a promising route to achieve low power 2D electronics for next generation classical and quantum computation. As device length scales are reduced to the limit of the electron mean free path, the transport mechanism crosses over to the ballistic regime. However, ballistic transport has yet to be shown in a graphene spintronic device, a necessary step towards realising ballistic spintronics. Here, we report ballistic injection of spin polarised carriers via one-dimensional contacts between magnetic nanowires and a high mobility graphene channel. The nanowire-graphene interface defines an effective constriction that confines charge carriers over a length scale smaller than that of their mean free path. This is evidenced by the observation of quantised conductance through the contacts with no applied magnetic field and a transition into the quantum Hall regime with increasing field strength. These effects occur in the absence of any constriction in the graphene itself and occur across several devices with transmission probability in the range T = 0.08 − 0.30.
Interracial contact shapes racial bias in the learning of person-knowledge
During impression formation, perceptual cues facilitate social categorization while person-knowledge can promote individuation and enhance person memory. Although there is extensive literature on the cross-race recognition deficit, observed when racial ingroup faces are recognized more than outgroup faces, it is unclear whether a similar deficit exists when recalling individuating information about outgroup members. To better understand how perceived race can bias person memory, the present study examined how self-identified White perceivers’ interracial contact impacts learning of perceptual cues and person-knowledge about perceived Black and White others over five sessions of training. While person-knowledge facilitated face recognition accuracy for low-contact perceivers, face recognition accuracy did not differ for high-contact perceivers based on person-knowledge availability. The results indicate a bias towards better recall of ingroup person knowledge, which decreased for high-contact perceivers across the five-day training but simultaneously increased for low-contact perceivers. Overall, the elimination of racial bias in recall of person-knowledge among high-contact perceivers amid a persistent cross-race deficit in face recognition suggests that contact may have a greater impact on the recall of person-knowledge than on face recognition.
Global self-organization of solute induced by ion irradiation in polycrystalline alloys
Most materials are brought into nonequilibrium states during processing and during their service life. Materials for nuclear and space applications, for instance, are continuously exposed to energetic particle irradiation, which is often detrimental to materials’ performance. Here we demonstrate, however, that sustained irradiation can induce self-organization of the microstructure of polycrystalline alloys into steady-state patterns and, in turn, improve their radiation resistance. Using an Al −1.5 at.% Sb alloy as a model system, we show using transmission electron microscopy and atom probe tomography that, for nanocrystalline thin films irradiated at 75 °C with 2 MeV Ti ions to large doses, the microstructure consists of finite-size, self-organized AlSb nanoprecipitates inside the grains and along the grain boundaries. Furthermore, this steady state is independent of the initial microstructure, thus self-healing. Phase field modeling is employed to construct a steady-state phase diagram and extend the experimental results to other alloy systems and microstructures.
Dynamic thermalization on noisy quantum hardware
Emulating thermal observables on a digital quantum computer is essential for quantum simulation of many-body physics. However, thermalization typically requires a large system size due to incorporating a thermal bath, whilst limited resources of near-term digital quantum processors allow for simulating relatively small systems. We show that thermal observables and fluctuations may be obtained for a small closed system without a thermal bath. Thermal observables occur upon classically averaging quantum mechanical observables over randomized variants of their time evolution that run independently on a digital quantum processor. Using an IBM quantum computer, we experimentally find thermal occupation probabilities with finite positive and negative temperatures defined by the initial state’s energy. Averaging over random evolutions facilitates error mitigation, with the noise contributing to the temperature in the simulated observables. This result fosters probing the dynamical emergence of equilibrium properties of matter at finite temperatures on noisy intermediate-scale quantum hardware.
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