Microwave Dynamical Conductivity in the Quantum Hall Regime.

Dynamical conductivity contains information of dissipative and nondissipative processes induced by ac-electric fields. In the integer quantum Hall (QH) effect where the nondissipative Hall current is the most prominent feature, its robustness is assured by localized states within the Landau levels. We establish a noncontact method with a circular cavity resonator and detect the real and imaginary parts of the longitudinal and Hall conductivities at a microwave frequency in magnetic fields.

Negative resistance state in superconducting NbSe induced by surface acoustic waves.

We report a negative resistance, namely, a voltage drop along the opposite direction of a current flow, in the superconducting gap of NbSe thin films under the irradiation of surface acoustic waves (SAWs). The amplitude of the negative resistance becomes larger by increasing the SAW power and decreasing temperature. As one possible scenario, we propose that soliton-antisoliton pairs in the charge density wave of NbSe modulated by the SAW serve as a time-dependent capacitance in the superconducting state, leading to the dc negative resistance.

Etching process of narrow wire and application to tunable-barrier electron pump.

Single electron sources have been studied as a device to establish an electric current standard for 30 years and recently as an on-demand coherent source for fermion quantum optics. In order to construct the single electron source on a GaAs/AlGaAs two-dimensional electron gas (2DEG), it is often necessary to fabricate a sub-micrometer wire by etching. We have established techniques to fabricate the wire made of the fragile 2DEG by combining photolithography and electron beam lithography with one-step photoresist coating, which enables us to etch fine and coarse structures simultaneously.

Author Correction: Butterfly-shaped magnetoresistance in triangular-lattice antiferromagnet AgCrO.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Butterfly-shaped magnetoresistance in triangular-lattice antiferromagnet AgCrO.

Spintronic devices using antiferromagnets (AFMs) are promising candidates for future applications. Recently, many interesting physical properties have been reported with AFM-based devices. Here we report a butterfly-shaped magnetoresistance (MR) in a micrometer-sized triangular-lattice antiferromagnet AgCrO.

Large room temperature spin-to-charge conversion signals in a few-layer graphene/Pt lateral heterostructure.

Electrical generation and detection of pure spin currents without the need of magnetic materials are key elements for the realization of full electrically controlled spintronic devices. In this framework, achieving a large spin-to-charge conversion signal is crucial, as considerable outputs are needed for plausible applications. Unfortunately, the values obtained so far have been rather low.

Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review.

Spin Hall effect and its inverse provide essential means to convert charge to spin currents and vice versa, which serve as a primary function for spintronic phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck effect. These effects can oscillate magnetization or detect a thermally generated spin splitting in the chemical potential. Importantly this conversion process occurs via the spin-orbit interaction, and requires neither magnetic materials nor external magnetic fields.

5d iridium oxide as a material for spin-current detection.

Devices based on pure spin currents have been attracting increasing attention as key ingredients for low-dissipation electronics. To integrate such spintronics devices into charge-based technologies, electric detection of spin currents is essential. The inverse spin Hall effect converts a spin current into an electric voltage through spin-orbit coupling.

Experimental verification of comparability between spin-orbit and spin-diffusion lengths.

We experimentally confirmed that the spin-orbit lengths of noble metals obtained from weak antilocalization measurements are comparable to the spin diffusion lengths determined from lateral spin valve ones. Even for metals with strong spin-orbit interactions such as Pt, we verified that the two methods gave comparable values which were much larger than those obtained from recent spin torque ferromagnetic resonance measurements. To give a further evidence for the comparability between the two length scales, we measured the disorder dependence of the spin-orbit length of copper by changing the thickness of the wire.