| 61. |
- Khokhriakov, Dmitrii, 1991, et al.
(författare)
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Multifunctional Spin Logic Operations in Graphene Spin Circuits
- 2022
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Ingår i: Physical Review Applied. - 2331-7019. ; 18:6
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Tidskriftsartikel (refereegranskat)abstract
- Spin-based computing, combining logic and nonvolatile magnetic memory, is promising for emerg-ing information technologies. However, the realization of a universal spin logic operation, representing a reconfigurable building block with all-electrical spin-current communication, has so far remained chal-lenging. Here, we experimentally demonstrate reprogrammable all-electrical multifunctional spin logic operations in a nanoelectronic device architecture, utilizing graphene buses for spin communication and mixing and nanomagnets for writing and reading information at room temperature. This device realizes a multistate spin-majority logic operation, which is reconfigured to achieve (N)AND, (N)OR, and XNOR Boolean operations, depending on the magnetization of inputs. The results are in good agreement with the predictions from a spin-circuit model, providing an experimental demonstration of a spin-based logic unit that takes advantage of the vector nature of spin, as opposed to conventional scalar charge-based devices. These spin logic operations in large-area graphene are fully compatible with industrial fabrication pro-cesses and represent a promising platform for scalable all-electric spin-based logic-in-memory computing architecture.
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| 62. |
- Konishi, K., et al.
(författare)
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Intrinsic Mobility of Low-Density Electrons in Photoexcited Diamond
- 2022
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 17:3
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Extending the limit of charge-carrier mobility in semiconductors has been a long-standing pursuit in material science and its applications. Herein, we investigate the electron mobility via cyclotron resonance in undoped diamond under continuous-wave photoexcitation, whereby the density of charge carriers can be reduced to 108cm−3 or 1/10 of the previous detection limit [K. Konishi et al., Appl. Phys. Lett. 117, 212102 (2020)]. For low-density electrons, which obviate the effects of carrier-carrier scattering as a broadening mechanism, we observe an extraordinarily narrow cyclotron resonance spectrum. After correcting for the microwave power broadening, the highest intrinsic mobility value of 100×106 cm2V−1s−1 is obtained at 3 K, which is a 16-fold increase of the mobility compared with the previous record in diamond. Our result is beneficial for the design and application of diamond radiation detectors implemented for their practical use at cryogenic temperatures.
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| 63. |
- Korlacki, Rafal, et al.
(författare)
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Strain and Composition Dependencies of the Near-Band-Gap Optical Transitions in Monoclinic (AlxGa1-x)2O3 Alloys with Coherent Biaxial In-Plane Strain on Ga2O3(010)
- 2022
-
Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 22:6
-
Tidskriftsartikel (refereegranskat)abstract
- The bowing of the energy of the three lowest band-to-band transitions in beta-(AlXGa1-X)2O3 alloys is resolved using a combined density-functional theory (DFT) and generalized spectroscopic ellipsometry approach. The DFT calculations of the electronic band structure of both beta-Ga2O3 and theta-Al2O3 allow the linear portion of the energy shift in the alloys to be extracted, and provide a method for quantifying the role of coherent strain present in the beta-(AlXGa1-X)2O3 thin films on (010) beta-Ga2O3 substrates. The energies of band-to-band transitions are obtained using the spectroscopic ellipsometry eigenpolarization model approach [A. Mock et al., Phys. Rev. B 95, 165202 (2017)]. After subtracting the effects of strain, which also induces additional bowing and after subtraction of the linear portion of the energy shift due to alloying, the bowing parameters associated with the three lowest band-to-band transitions in monoclinic beta-(AlXGa1-X)2O3 are found.
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| 64. |
- Krasnok, A. E., et al.
(författare)
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All-Optical Switching and Unidirectional Plasmon Launching with Nonlinear Dielectric Nanoantennas
- 2018
-
Ingår i: Physical Review Applied. - 2331-7019. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- High-index dielectric nanoparticles have become a powerful platform for nonlinear nanophotonics due to special types of optical nonlinearity, e.g. caused by electron-hole plasma (EHP) photoexcitation. We propose a highly tunable dielectric nanoantenna consisting of a chain of silicon particles excited by a dipole emitter. The nanoantenna exhibits slow group-velocity guided modes, corresponding to the Van Hove singularity in an infinite structure, which enable a large Purcell factor up to several hundred and are very sensitive to the nanoparticle permittivity. This sensitivity enables the nanoantenna tuning via EHP excitation with an ultrafast laser pumping. Dramatic variations in the nanoantenna radiation patterns and Purcell factor caused by ultrafast laser pumping of several boundary nanoparticles with relatively low intensities of about 25 GW/cm2 are shown. Unidirectional surface-plasmon polaritons launching with EHP excitation in the nanoantenna on a Ag substrate is demonstrated.
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| 65. |
- Kunakova, Gunta, 1987, et al.
(författare)
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High-Mobility Ambipolar Magnetotransport in Topological Insulator Bi2Se3 Nanoribbons
- 2021
-
Ingår i: Physical Review Applied. - 2331-7019. ; 16:2
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoribbons of topological insulators (TIs) have been suggested for a variety of applications exploiting the properties of the topologically protected surface Dirac states. In these proposals it is crucial to achieve a high tunability of the Fermi energy, through the Dirac point while preserving a high mobility of the involved carriers. Tunable transport in TI nanoribbons has been achieved by chemical doping of the materials so to reduce the bulk carriers' concentration, however at the expense of the mobility of the surface Dirac electrons, which is substantially reduced. Here we study bare Bi2Se3 nanoribbons transferred on a variety of oxide substrates and demonstrate that the use of a large relative permittivity SrTiO3 substrate enables the Fermi energy to be tuned through the Dirac point and an ambipolar field effect to be obtained. Through magnetotransport and Hall conductance measurements, performed on single Bi2Se3 nanoribbons, we demonstrate that electron and hole carriers are exclusively high-mobility Dirac electrons, without any bulk contribution. The use of SrTiO3 allows therefore an easy field effect gating in TI nanostructures providing an ideal platform to take advantage of the properties of topological surface states.
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| 66. |
- Könemann, Fabian, et al.
(författare)
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Imaging the Thermalization of Hot Carriers after Thermionic Emission over a Polytype Barrier
- 2020
-
Ingår i: Physical Review Applied. - 2331-7019. ; 13:5
-
Tidskriftsartikel (refereegranskat)abstract
- The thermalization of nonequilibrium charge carriers is at the heart of thermoelectric energy conversion. In nanoscale systems, the equilibration length can be on the order of the system size, leading to a situation where thermoelectric effects need to be considered as spatially distributed, rather than localized at junctions. The energy exchange between charge carriers and phonons is of fundamental scientific and technological interest, but their assessment poses significant experimental challenges. We address these challenges by imaging the temperature change induced by Peltier effects in crystal phase engineered InAs nanowire (NW) devices. Using high-resolution scanning thermal microscopy (SThM), we study current-carrying InAs NWs, which feature a barrier segment of wurtzite (WZ) of varying length in a NW of otherwise zincblende (ZB) crystal phase. The energy barrier acts as a filter for electron transport around the Fermi energy, giving rise to a thermoelectric effect. We find that thermalization through electron-phonon heat exchange extends over the entire device. We analyze the temperature profile along a nanowire by comparing it to spatially dependent heat diffusion and electron thermalization models. We are able to extract the governing properties of the system, including the electron thermalization length of 223±9nm, Peltier coefficient and Seebeck coefficient introduced by the barrier of 39±7mV and 89±21μV/K, respectively, and a thermal conductivity along the wire axis of 8.9±0.5 W/m K. Finally, we compare two ways to extract the elusive thermal boundary conductance between the NW and underlying substrate.
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| 67. |
- Lachmann, Sagy, et al.
(författare)
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Statistical Analysis of Field-Emission Currents
- 2021
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 16:2
-
Tidskriftsartikel (refereegranskat)abstract
- The current due to cold tunneling of electrons from a metallic surface exposed to high electric fields, regularly named "dark current," is commonly described in modern literature using an analytical approximate solution provided by Murphy and Good [Phys. Rev. 102, 1464 (1956)]. This expression, which corrects earlier work by Fowler and Nordheim, is a Fowler-Nordheim-type equation: I similar to E2 exp(-a/E), where I is the dark current, E is the local electric field, and a is a system-specific constant. In this paper, a numerical approximation, rather than the analytical one given by Murphy and Good, is presented. This approximation is accurate over a wide range of fields, and is used to derive the effective field enhancement factor ,B. On the basis of this approximation, and considering local field and current fluctuations, two alternative methods for ,B estimation are presented. These methods allow instantaneous field-specific estimation of ,B, rather than the average estimate derived with current methods. The applicability of fluctuation-based methods is demonstrated by numerical simulation in a variety of conditions. The methods are applied to estimate ,B using fluctuation analysis in experimental measurements that were not dedicated for this purpose. An open-source code for the implementation of fluctuation-derived ,B estimation is provided, with an analysis of possible future experimental opportunities using dedicated experiments.
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| 68. |
- Litvinenko, A., et al.
(författare)
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Tunable Magnetoacoustic Oscillator with Low Phase Noise
- 2021
-
Ingår i: Physical Review Applied. - 2331-7019. ; 15:3
-
Tidskriftsartikel (refereegranskat)abstract
- A frequency-tunable low-phase-noise magnetoacoustic resonator is developed on the base of a parallel plate straight-edge bilayer consisting of an yttrium-iron-garnet (YIG) layer grown on a substrate of a gallium gadolinium garnet (GGG). When a YIG-GGG sample forms an ideal parallel plate, it supports a series of high-quality-factor acoustic modes standing along the plate thickness. Due to the magnetostriction of the YIG layer the ferromagnetic resonance (FMR) mode of the YIG layer can strongly interact with the acoustic thickness modes of the YIG-GGG structure, when the modes' frequencies match. A particular acoustic thickness mode used for the resonance excitations of the hybrid magnetoacoustic oscillations in a YIG-GGG bilayer is chosen by the YIG-layer FMR frequency, which can be tuned by the variation of the external bias magnetic field. A composite scheme of a magnetoacoustic oscillator, which includes a FMR-based resonance preselector, is developed to guarantee satisfaction of the Barkhausen criteria for a single-acoustic-mode oscillation regime. The developed low-phase-noise composite magnetoacoustic oscillator can be tuned from 0.84 to 1 GHz with an increment of about 4.773 MHz (frequency distance between the adjacent acoustic thickness modes in a YIG-GGG parallel plate), and demonstrates the phase noise of & minus;116 dBc/Hz at the offset frequency of 10 kHz.
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| 69. |
- Liu, Yichao, et al.
(författare)
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Acoustic Illusion Using Materials with Isotropic and Positive Parameters
- 2018
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 10:6
-
Tidskriftsartikel (refereegranskat)abstract
- Acoustic illusion devices are usually designed using transformation optics. An alternate method is proposed to achieve acoustic illusions without external devices by elaborately manipulating the acoustic scattering potential of an object. The proposed method is more of a "cosmetic operation" for an object, which modifies the scattered acoustic pressure distribution of the object to mimic another object by exchanging their scattering potentials in two symmetrical areas in the wave vector domain. The advantage of this method is the simplicity of material parameters: only positive isotropic mass density and bulk modulus are required, which is impossible with the conventional method of using transformation optics due to the complex material requirements (anisotropic and negative index parameters).
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| 70. |
- Liu, Yichao, et al.
(författare)
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Omnidirectional Conformal Cloak Without Geometrical Dispersion
- 2019
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 12:6
-
Tidskriftsartikel (refereegranskat)abstract
- The phase delay problem of invisibility cloaks designed by optical conformal mapping is referred to the optical path difference between the waves in upper and lower Riemann sheets. As the frequency changes, the phase delay varies accordingly (here, we call it geometrical dispersion), which restricts the cloaks to working only at some discrete frequencies. Here, we solve the phase-delay problem by placing an optically null medium in the lower Riemann sheet. The conformal cloaks designed by using our method have many advantages, such as a continuous working band (no geometrical dispersion), omnidirectionality, robustness under frequency shifts, and no need for any complex materials that are both anisotropic and inhomogeneous. We also design metallic microchannels to realize our cloaks.
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