We report a thermoelectric study of graphene in both zero and applied magnetic fields. As a direct consequence of the linear dispersion of massless particles, we find that the Seebeck coefficient S xx diverges with 1 / | | 2D n , where n 2D is the carrier density.We observe a very large Nernst signal S xy (~ 50 μV/K at 8 T) at the Dirac point, and an oscillatory dependence of both S xx and S xy on n 2D at low temperatures. Our results underscore the anomalous thermoelectric transport in graphene, which may be used as a highly sensitive probe for impurity bands near the Dirac point.

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The Mott relation between the electrical and thermoelectric transport coefficients normally holds for phenomena involving scattering. However, the anomalous Hall effect (AHE) in ferromagnets may arise from intrinsic spin-orbit interaction. In this work, we have simultaneously measured AHE and the anomalous Nernst effect (ANE) in Ga 1-x Mn x As ferromagnetic semiconductor films, and observed an exceptionally large ANE at zero magnetic field. We further show that AHE and ANE share a common origin and demonstrate the validity of the Mott relation for the anomalous transport phenomena.

There are two common methods in generating magnetic resonance in FMs for spin pumping, cavity FMR and microstrip waveguides [3,7,8,12,19]. FMR cavities produce modest-strength, uniform rf fields over a relatively large space (cm-scale); while microstrip waveguides produce rf fields typically in micron to sub-mm scale, and when made very close to the FMs, can generate fairly large h rf [12,19]. Since the magnitude of rf field determines the excitation strength for spin pumping and only a few reports on microstrip spin pumping presented values of h rf [12,19], in this letter, we mainly compare our results with previous reports of spin pumping using cavity FMR. respectively, which reach the resolution limit of conventional high-resolution XRD systems, demonstrating excellent crystalline quality. In this letter, we focus on two 20-nm YIG films (YIG-1 and YIG-2) for FMR and spin pumping measurements.Room-temperature FMR measurements of the YIG films are carried out in a cavity at a microwave frequency f = 9.65 GHz and power P rf = 0.2 mW. Figure 3e shows the angular dependence of V ISHE for Pt/YIG-1 and W/YIG-2 normalized by the maximum magnitude of V ISHE at θ H = 90°.The clear sinusoidal shape is characteristic of ISHE since [15]thus confirming that the observed ISHE voltage arises from FMR spin pumping. The spin pumping signals we observed in insulating YIG cannot be explained by artifacts due to thermoelectric or magnetoelectric effects, such as anisotropic magnetoresistance (AMR) or anomalous Hall effect (AHE) [13,16,32,34,35].While a spin current is generated by transfer of angular momentum from YIG to metal, simultaneously, the coupling between YIG and metal exerts an additional damping to the magnetization precession in YIG, resulting in increased linewidths [10,12], as shown in Fig. 5 4 for the three samples before (∆H 0 ) and after (∆H 1 ) the deposition of where G r , γ, and B are the real part of spin mixing conductance, the gyromagnetic ratio, factor and Bohr magnetron, respectively. Using Eq. (2), we obtain = 4.56× 10 14 and 2.30× 10 14 Ω -1 m -2 for Pt/YIG-2 and W/YIG-2, respectively, which agree with the theoretical calculations [36] and are among the highest of reported experimental values [3,5,8,9].Previously, spin pumping of Pt/YIG excited by similar cavity FMR gave ISHE voltages in the µV range [1,9,11,16]. The large spin pumping signals and high spin mixing conductance observed in our YIG films may be attributed to two possible reasons. First, the small thickness (20 nm) of our films compared to LPE films (100 nm or larger) may play an important role, as suggested by a recent report [7] that a 200-nm YIG film shows much higher spin pumping efficiency than 1-µm and 3-µm films excited by a microstrip waveguide. [7,12]. Further investigation of spin pumping in these thin YIG films using microstrip waveguides will access larger dynamic range of spin pumping. In addition, the mV-level ISHE voltages reported here using a moderate h rf will allow miniaturization of spin pumping structures while m...

We demonstrate the existence of generalized Aubry-André self-duality in a class of non-Hermitian quasiperiodic lattices with complex potentials. From the self-duality relations, the analytical expression of mobility edges is derived. Compared to Hermitian systems, mobility edges in non-Hermitian ones not only separate localized from extended states but also indicate the coexistence of complex and real eigenenergies, making possible a topological characterization of mobility edges. An experimental scheme, based on optical pulse propagation in synthetic photonic mesh lattices, is suggested to implement a non-Hermitian quasicrystal displaying mobility edges.

We present the first experimental study of the thermopower in Mn-doped GaAs ferromagnetic semiconductors. Large magnetothermopower effects in both longitudinal and transverse directions have been observed below the ferromagnetic transition temperature. Unlike magnetoresistance, neither the transverse thermopower (planar Nernst effect) nor the longitudinal thermopower explicitly depend on the strength of the in-plane magnetic field, but rather are intimately related to each other through the magnetization. These newly discovered effects can be satisfactorily explained by an extension of anisotropic magnetotransport model and place important constraints on potential microscopic descriptions of the scattering mechanisms in these materials.

Ferromagnetic resonance (FMR) driven spin pumping of pure spin currents from a ferromagnet (FM) into a nonmagnetic material (NM) promises new spin-functional devices with low energy consumption [1-6]. The mechanism of spin pumping is under intense investigation and it is widely believed that exchange interaction between the FM and NM is responsible for this phenomenon [2-5, 7]. We observe a thousand-fold exponential decay of the spin pumping from 20-nm thick Y 3 Fe 5 O 12 (YIG) films to platinum across insulating barriers, from which the exponential decay lengths of 0.16 and 0.23 nm are extracted for oxide barriers with band gaps of 4.93 eV and 2.36 eV, respectively. This prototypical signature of quantum tunneling through a barrier underscores the importance of exchange coupling for spin pumping and reveals its dependence on the characteristics of the barrier material. Generation and manipulation of spin currents is key to spintronic applications [1]. FMR driven spin pumping has been demonstrated to inject a pure spin current through angular 2 momentum transfer from an FM to an adjacent NM [2-6]. General belief assumes a dynamic coupling via exchange interaction between the precessing magnetization (M) of the FM and the conduction electrons of the NM at the NM/FM interface. This mechanism will lead to a short, atomic-scale coupling that decays exponentially with separation between the FM and NM. However, this has not been experimentally confirmed, partially due to the large dynamic range needed to measure such rapidly decaying spin pumping signal [6, 8]. Our recent demonstration of large spin pumping in Pt/YIG bilayers with mV-level inverse spin Hall effect (ISHE) voltage, V ISHE , offers a material platform with signal-to-noise ratio sufficient to quantitatively characterize the coupling range, enabling detailed insights into the spin pumping mechanism. We use three different barrier materials, including two oxide insulators and Si, to systematically investigate the barrier thickness t dependence of spin pumping in Pt/barrier(t)/YIG heterostructures. The clear exponential decays of ISHE voltage with characteristic lengths of ~0.2 nm for the oxide barriers provide decisive evidence for the predicted exchange coupling model for spin pumping. Our experiments utilize YIG thin films grown on (111)-oriented Gd 3 Ga 5 O 12 (GGG) substrates by an off-axis sputtering technique we developed for epitaxial film growth of complex materials [9-12]. Figure 1a shows a high resolution x-ray diffraction (XRD) scan of a 20-nm YIG film near the YIG (444) peak with clear Laue oscillations, indicating high uniformity throughout the film. The XRD rocking curve in the inset to Fig. 1a gives a full width at half maximum (FWHM) of 0.0185, demonstrating excellent crystalline quality. Figure 1b shows a representative FMR derivative spectrum for a 20 nm YIG film taken at radio-frequency (rf) f = 9.65 GHz and microwave power P rf = 0.2 mW with an in-plane magnetic field, from which the peak-to-peak linewidth (H) of 10 Oe is obtained [13]...

Copper indium thiophosphate, CuInP2S6, has attracted much attention in recent years due to its van der Waals layered structure and robust ferroelectricity at room temperature. In this review, we aim to give an overview of the various properties of CuInP2S6, covering structural, ferroelectric, dielectric, piezoelectric and transport properties, as well as its potential applications. We also highlight the remaining questions and possible research directions related to this fascinating material and other compounds of the same family.