We investigate the electron transport through a graphene p-n junction under a perpendicular magnetic field. By using the Landauer-Büttiker formalism combined with the nonequilibrium Green function method, the conductance is studied for clean and disordered samples. For the clean p-n junction, the conductance is quite small. In the presence of disorders, it is strongly enhanced and exhibits a plateau structure at a suitable range of disorders. Our numerical results show that the lowest plateau can survive for a very broad range of disorder strength, but the existence of high plateaus depends on system parameters and sometimes cannot be formed at all. When the disorder is slightly outside of this disorder range, some conductance plateaus can still emerge with its value lower than the ideal value. These results are in excellent agreement with a recent experiment.
Abstract. Zero-correlation linear cryptanalysis is based on the linear approximations with correlation exactly zero, which essentially generalizes the integral property, and has already been applied to several block ciphers -among others, yielding best known attacks to date on round-reduced TEA and CAST-256 as published in FSE'12 and ASI-ACRYPT'12, respectively.In this paper, we use the FFT (Fast Fourier Transform) technique to speed up the zero-correlation cryptanalysis. First, this allows us to improve upon the state-of-the-art cryptanalysis for the ISO/IEC standard and CRYPTREC-portfolio cipher Camellia. Namely, we present zero-correlation attacks on 11-round Camellia-128 and 12-round Camellia-192 with F L/F L −1 and whitening key starting from the first round, which is an improvement in the number of attacked rounds in both cases. Moreover, we provide multidimensional zero-correlation cryptanalysis of 14-round CLEFIA-192 and 15-round CLEFIA-256 that are attacks on the highest numbers of rounds in the classical single-key setting, respectively, with improvements in memory complexity.
We propose a gate-controllable spin-battery for spin current. The spin-battery consists of a lateral double quantum dot under a uniform magnetic field. A finite DC spin-current is driven out of the device by controlling a set of gate voltages. Spin-current can also be delivered in the absence of charge-current. The proposed device should be realizable using present technology at low temperature. 72.25.Pn, 73.40.Gk To be able to generate and control spin-current is of great importance for spintronics 1 . Traditionally, spin injection from a ferromagnetic material to a normal metal or semiconductor material has been used to obtain spin polarized charge-current. Spin injection into non-Fermi liquid 2 as well as by circularly polarized light 3 have also been investigated. More recently, several theoretical proposals for spin-battery were reported for the generation of pure spin-current without charge-current.4-6 The idea is that when spin-up electrons move to one direction while an equal number of spin-down electrons move to the opposite direction, the net charge-current I e = e(I ↑ + I ↓ ) vanishes and a finite spin-current I s =h 2 (I ↑ −I ↓ ) emerges. Here I ↑ (I ↓ ) is the spin-up (spin-down) electron current. Although conceptually interesting, existing spin-battery proposals all involve time dependent external fields [4][5][6] which make practical realization somewhat complicated. It is the purpose of this paper to propose and investigate a novel spin-battery design which is gate controllable involving no time varying fields.The gate controllable spin-battery is schematically shown in Fig.(1). It consists of a lateral double quantumdot fabricated in two-dimensional electron gas (2DEG) with split gate technology. The two QDs are coupled to three leads: lead-1 and 3 couple to one QD each, lead-2 couples to both. The two QDs are separated by a high potential barrier so that tunnel coupling between them can be neglected. To distinguish spin of the electrons, a magnetic field B is applied to the QDs to induce a Zeeman splitting. Two gate voltages V g,α control energy levels of the α-th QD, where α = upper, lower (u, l), indicating the upper and lower QD of Fig.(1). Finally, the terminal voltages for the three leads are set such that V 1 > V 2 > V 3 (Fig.2), they provide energy source for the spin-battery.Before presenting results, we first discuss why the system of Fig.(1) can deliver a spin-current. Due to field B, a spin degenerate level ǫ α of the α-QD is split into spin-up/down levels ǫ α↑ /ǫ α↓ . Let's assume ǫ α↑ < ǫ α↓ . By adjusting gate voltages V g,α , we shift these levels. In particular, we set V g,lower such that electron occupation number in the lower-QD is changing between 0 and 1 (even to odd), with the level ǫ lower,↑ locating between µ 1 and µ 2 , where µ i = eV i is the chemical potential of lead i. Similarly, we set V g,upper such that the upper-QD has an electron occupying state ǫ upper,↑ , while the other state ǫ upper,↓ is pushed to higher energy ǫ upper,↓ + U due to Coulomb interaction U ...
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