Faculty Profiles - KASHIWAYA Satoshi

Yano Rikizo, Kudriashov Andrei, Hirose Hishiro T., Tsuda Taiki, Kashiwaya Hiromi, Sasagawa Takao, Golubov Alexander A., Stolyarov Vasily S., Kashiwaya Satoshi

JOURNAL OF PHYSICAL CHEMISTRY LETTERS Vol. 12 ( 17 ) page： 4180 - 4186 2021.5

Identification of spin-triplet superconductivity through a helical-chiral phase transition in Sr2RuO4 thin films International coauthorship

S. Ikegaya, S, K. Yada, K, Y. Tanaka,S. Kashiwaya, Y. Asano, Y, D. Manske

PHYSICAL REVIEW B Vol. 101 ( 22 ) page： 220501-1 - 220501-6 2020.6

System for the remote control and imaging of MW fields for spin manipulation in NV centers in diamond International coauthorship

Giacomo Mariani, Shuhei Nomoto, Satoshi Kashiwaya, Shintaro Nomura

Scientific Reports Vol. 10 ( 1 ) page： 4813 2020.3

Language：English Publishing type：Research paper (scientific journal)

Nitrogen-vacancy (NV) centers in diamond have been used as platforms for quantum information, magnetometry and imaging of microwave (MW) fields. The spatial distribution of the MW fields used to drive the electron spin of NV centers plays a key role for these applications. Here, we report a system for the control and characterization of MW magnetic fields used for the NV spin manipulation. The control of the MW field in the vicinity of a diamond surface is mediated by an exchangeable lumped resonator, coupled inductively to a MW planar ring antenna. The characterization of the MW fields in the near-field is performed by an FFT imaging of Rabi oscillations, by using an ensemble of NV centers. We have found that the Rabi frequency over a lumped resonator is enhanced 22 times compared to the Rabi frequency without the presence of the lumped resonator. Our system may find applications in quantum information and magnetometry where a precise and controlled spin manipulation is required, showing NV centers as good candidates for imaging MW fields and characterization of MW devices.

DOI： 10.1038/s41598-020-61669-w

Web of Science

PubMed

Unusual Superconducting Proximity Effect in Magnetically Doped Topological Josephson Junctions

Rikizo Yano, Masao Koyanagi, Hiromi Kashiwaya, Kohei Tsumura, Hishiro T. Hirose, Yasuhiro Asano, Takao Sasagawa, and Satoshi Kashiwaya

J. Phys. Soc. Jpn. Vol. 89 ( 3 ) page： 34072 2020.3

Language：English Publishing type：Research paper (scientific journal)

The transport properties of a topological Josephson junction fabricated from a magnetically doped topological insulator (TI) were investigated. The conductance spectra of the Nb/Fe-Bi2Te2Se/Nb junction below 1 K showed an unusual trident-shaped zero-bias conductance peak with a tiny peak width of ∼6 µV. The central peak of the trident peak presents the dc-Josephson current, and the side peaks may reflect an induced unconventional Cooper pairing. Additionally, the critical currents followed inverse to temperature, which may also reflect the presence of an unconventional proximity effect. Furthermore, microwave irradiation drived a drastic change in the conductance spectra from the peak structure into oscillatory ones, a hallmark of the ac-Josephson supercurrent. The current-phase relation of the ac-Josephson effect under high power radiofrequency-irradiation was found to be 4π-periodic. The results suggest that the junction based on magnetically doped 3D TIs may realize an unconventional Cooper pairing, thus enabling access to the basic physics of Majorana bound states and unconventional superconductivity.

DOI： 10.7566/JPSJ.89.034702

Web of Science

Time-reversal invariant superconductivity of Sr2RuO4 revealed by Josephson effects

Kashiwaya S, Saitoh, K Kashiwaya H, Koyanagi, M, Sato, M, Yada, K, Tanaka, Y, Maeno, Y

PHYSICAL REVIEW B Vol. 100 ( 9 ) page： 094530 2019.9

Language：English Publishing type：Research paper (scientific journal)

Sr2RuO4 is one of the most promising candidates of a topological superconductor with broken time-reversal symmetry because a number of experiments have revealed evidence for a spin-triplet chiral p-wavesuperconductivity. To clarify the time-reversal symmetry of
Sr2RuO4, we introduce a test that examines the invariance of the Josephson critical current under the inversion of both the current and magnetic fields, in contrast to the detection of a spontaneous magnetic field employed in past experiments. Analyses of the transport properties of the planar and corner Josephson junctions formed between
Sr2RuO4 and Nb reveal the time-reversal invariant superconductivity, most probably helical
p-wave symmetry, of Sr2RuO4. This state corresponds to a yet-to-be confirmed topological crystalline superconductivity that can host two Majorana edge modes at the surface protected by crystalline mirror symmetry.

DOI： 10.1103/PhysRevB.100.094530

Web of Science

Sensitive measurement of phase shift of an AC magnetic field by quantum sensing with multiple-pulse decoupling sequences

Ishikawa, T, Yoshizawa, A, Mawatari, Y, Kashiwaya, S, Watanabe, H

JOURNAL OF APPLIED PHYSICS Vol. 126 ( 6 ) page： 064504 2019.8

Language：English Publishing type：Research paper (scientific journal)

Magnetometry utilizing a spin qubit in a solid state possesses high sensitivity. In particular, a magnetic sensor with a high spatial resolution can be achieved with the electron-spin states of a nitrogen-vacancy (NV) center in the diamond. In this study, we demonstrated that NV quantum sensing based on multiple-pulse decoupling sequences can sensitively measure not only the amplitude but also the phase shift of an alternating-current (AC) magnetic field. In the AC magnetometry based on decoupling sequences, the maximum phase accumulation of the NV spin due to an AC-field can be generally obtained when the π-pulse period in the sequences matches the half time period of the field and the relative phase difference between the sequences and the field is zero. By contrast, the NV quantum sensor acquires no phase accumulation if the relative phase difference is π/2. Thus, this phase-accumulation condition does not have any advantage for the magnetometry. However, we revealed that the nonphase-accumulation condition is available for detecting a very small phase shift of an AC-field from its initial phase. Measurements of the real part and the imaginary part of AC impedance require the amplitude and the phase information of an AC-field, and thus, this finding is expected to provide a guide for realizing sensitive measurement of AC impedance in the micrometer and nanometer scales.
I. INTRODUCTION

DOI： 10.1063/1.5096610

Web of Science

Finite-pulse-width effect on quantum sensing for an asynchronous alternating-current magnetic field to dynamical decoupling sequences

Ishikawa, T, Yoshizawa, A, Mawatari, Y, Kashiwaya, S, Watanabe, H

AIP ADVANCES Vol. 9 ( 7 ) page： 75013 2019.7

Language：English Publishing type：Research paper (scientific journal)

Quantum sensors based on the electron spin states of nitrogen vacancy centers in diamond have found wide application in magnetometry and nuclear spin magnetic resonance measurements. Previously, we have theoretically and experimentally investigated the effect of finite pulse width on quantum sensing for synchronous alternating-current (AC) magnetic fields to dynamical decoupling sequences [T. Ishikawa et al., Phys. Rev. Appl. 10, 054059 (2018)]. However, many biological and condensed-matter systems exhibit fluctuating AC fields over time, and thus, our model needs modifications because of additional non-ideal conditions in practical measurements. Here, we investigate the effects of finite pulse width of multiple-pulse decoupling sequences on quantum sensing for asynchronous AC magnetic fields. For this purpose, we use a spin ensemble of nitrogen vacancy centers in an isotopically purified diamond film. We reveal through experiments that the finite-width pulse causes shifts in AC magnetometry signals in a free-precession-time plot. In addition, our results indicate that the finite-width pulse affects the amplitude of magnetometry signals, implying that the finite-pulse-width effect should be taken into account for realizing accurate measurement of the frequency and amplitude of asynchronous AC magnetic fields.

DOI： 10.1063/1.5097872

Web of Science

Proximity-Induced Superconducting States of Magnetically Doped 3D Topological Insulators with High Bulk Insulation

Yano, R; Hirose, HT; Tsumura, K; Yamamoto, S; Koyanagi, M; Kanou, M; Kashiwaya, H; Sasagawa, T; Kashiwaya, S

CONDENSED MATTER Vol. 4 ( 1 ) 2019.1

Influence of Dynamical Decoupling Sequences with Finite-Width Pulses on Quantum Sensing for AC Magnetometry

Ishikawa Toyofumi, Yoshizawa Akio, Mawatari Yasunori, Watanabe Hideyuki, Kashiwaya Satoshi

PHYSICAL REVIEW APPLIED Vol. 10 ( 5 ) 2018.11

Local impedance on a rough surface of a chiral p-wave superconductor

Bakurskiy S. V, Fominov Ya V, Shevchun A. F., Asano Y., Tanaka Y., Kupriyanov M. Yu, Golubov A. A., Trunin M. R., Kashiwaya H., Kashiwaya S., Maeno Y.

PHYSICAL REVIEW B Vol. 98 ( 13 ) 2018.10

Josephson effect in a multiorbital model for Sr2RuO4

Kawai Kohei, Yada Keiji, Tanaka Yukio, Asano Yasuhiro, Golubov Alexander A., Kashiwaya Satoshi

PHYSICAL REVIEW B Vol. 95 ( 17 ) 2017.5

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Papers - KASHIWAYA Satoshi