Yuita Fujisawa

Okinawa Institute of Science and Technology Graduate University

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Yoshinori Okada

Okinawa Institute of Science and Technology Graduate University

Hideaki Sakata

Kawagoe Technical High School

Satoshi Demura

Nihon University

Markel Pardo‐Almanza

Okinawa Institute of Science and Technology Graduate University

Chia-Hsiu Hsu

National Sun Yat-sen University

T. Machida

RIKEN Center for Emergent Matter Science

B. R. M. Smith

Okinawa Institute of Science and Technology Graduate University

Feng‐Chuan Chuang

National Sun Yat-sen University

Kohei Yamagami

Japan Synchrotron Radiation Research Institute

Anjana Krishnadas

Okinawa Institute of Science and Technology Graduate University

Cooperative Institutions

The University of Tokyo

Okinawa Institute of Science and Technology Graduate University

Tokyo University of Science

Osaka University

National Institute for Materials Science

Japan Science and Technology Agency

Spintronics Research Network of Japan

Tokyo Institute of Technology

Kyoto University

Tohoku University

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Observation of Supermodulation in LaO_0.5F_0.5BiSe₂ by Scanning Tunneling Microscopy and Spectroscopy

Journal of the Physical Society of Japan (2017)

Satoshi Demura N Ishida Yuita Fujisawa Hideaki Sakata

We observed surface and electronic structure of LaO0.5F0.5BiSe2 single crystal by scanning tunneling microscopy/spectroscopy (STM/STS) at 4.2 K. Square lattice composed of Bi atoms was observed at a positive sample bias voltage on the surface prepared by cleavage. At a negative sample bias voltage, a stripe structure running along Bi-Bi directions was observed as in the previous report on NdO0.7F0.3BiS2. Furthermore, we observed a supermodulation running along the diagonal directions with the period of about 5 times of the lattice constant. This seems to be indicative of structural instability of this system rather than electronic instability attributed to a nesting picture.

Cleavage (geology)

Lattice constant

Lattice (music)

10.7566/jpsj.86.113701

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Citations (3)

Uncovering hidden Fermi surface instabilities through visualizing unconventional quasiparticle interference in CeTe3

Physical Review Materials (2024)

B. R. M. Smith Yuita Fujisawa Ping Wu Tomonori Nakamura N. Tomoda

The charge density wave (CDW) state is a widespread phenomenon in low-dimensional metals/semimetals. The spectral weight of the associated folded bands (shadow bands) can be an intriguing trigger leading to additional Fermi surface instability and unexplored phase transitions. The rare earth tri-telluride CeTe3 exhibits a single CDW stabilized below ~400 K and antiferromagnetism below ~3 K. The distinct periodicities between the Te-square net, the CeTe block layer, and the CDW give rise to rich shadow band formations. In this work, we reveal the predominant scattering between the original and shadow bands at 4 K, with the scattering within the original bands being relatively suppressed at Fermi energy. This unconventional quasi-particle scattering collectively underscores the vital role of the shadow bands' spectral weight and the hidden matrix element effect, which are crucial for controlling electronic properties in this system. Furthermore, our finding points to the existence of rich and unexplored Fermi surface instabilities, which potentially play a role in controlling the nature of long-range antiferromagnetism at lower temperatures in the presence of finite charge-spin interaction.

10.1103/physrevmaterials.8.104004

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Large antiferromagnetic fluctuation enhancement of the thermopower at a critical doping in magnetic semimetal Cr1+dTe2

arXiv (Cornell University) (2022)

Mohamed Atwa Yuita Fujisawa Takatsugu Onishi Markel Pardo‐Almanza Mathieu Couillard

Cr1+dTe2 is a self-intercalated transition metal dichalcogenide that hosts tunable electronic filling and magnetism in its semimetallic band structure. Recent angle-resolved photoemission spectroscopy (ARPES) studies have unveiled a systematic shift in this semimetallic band structure relative to the chemical potential with increased Cr doping. This report presents the temperature and magnetic field dependence of the longitudinal thermopower Sxx for different Cr1+dTe2 compositions. We show that as doping increases, the sign of Sxx changes from positive to negative at the critical doping level of d ~ 0.5. This observed doping-dependent trend in the thermopower is consistent with the evolution of the semimetallic band structure from ARPES. Importantly, an anomalous enhancement of the thermoelectric response is also observed around d~0.5. Combining information from magnetometry and ARPES measurements, existence of the critical nature of the doping level dc (~0.5) is unveiled in magnetic semimetal Cr1+dTe2, where antiferromagnetic fluctuation and near-Fermi-energy pseudogap formation play a potential vital role in enhancing thermoelectric energy conversion.

Pseudogap

Magnetism

10.48550/arxiv.2206.12044

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Electronic states of domain structure in 1T-TaS_2-xSe _x observed by STM/STS

Journal of Physics Conference Series (2018)

D Fujii Takayuki Iwasaki Keiko AKIYAMA Yuita Fujisawa Satoshi Demura

We report on a systematic scanning tunneling microscopy and spectroscopy (STM/STS) study on 1T–TaS2-xSex (x = 0, 0.3, 1.0) at 4.2 K. While the compounds with x = 0 and 0.3, which undergoes the Mott transition, showed the commensurate charge density wave (CDW) with the period of (a0 is in-plane lattice constant), the compound with x=1, which shows superconductivity at 3.5 K, exhibits anomalous domain structure: The domain structure consists of regions with regular array of David-stars divided by bright contrasted walls at positive bias voltage. We found the domain wall showed the different electronic state from that of the domain.

Lattice constant

10.1088/1742-6596/969/1/012041

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Visualizing magnetic field-induced rotational electronic symmetry breaking in a spinel oxide superconductor

arXiv (Cornell University) (2023)

Yuita Fujisawa Anjana Krishnadas Chia-Hsiu Hsu B. R. M. Smith Markel Pardo‐Almanza

The spinel oxide superconductor LiTi2O4 (LTO) is an intriguing material platform where the electronic structure near the Fermi energy (EF) is derived from 3d elections on the geometrically frustrated Ti pyrochlore network. A recent angle-resolved photoemission spectroscopy (ARPES) study has revealed the existence of an exotic quasiparticle state arising from the competition between instability towards orbital ordering and geometrical frustration below 150 K. An intriguing remaining challenge is the imaging of Abrikosov vortices, which generally inherits the symmetry of the Fermi surface at k_z=0. Here, we observe surprising triangular-shaped Abrikosov vortices on an LTO(111) film, deviating from the conventional expectations of the six-fold symmetric Fermi surface at k_z=0. In combination with the experimentally observed isotropic pairing, we propose magnetic field-driven rotational electronic symmetry breaking of the underlying Fermi surface. Consequently, we observe Josephson vortices along the crystalline domain boundary, across which quasiparticle hopping is suppressed due to the symmetry-broken Fermi surface in each domain. Our discoveries point to the existence of unique physics of magnetic field-induced electronic rotational symmetry breaking in the spinel oxide superconductor LTO. This picture is in stark contrast to the other exotic superconductors with partial gap opening or long-range ordering with broken symmetry above the superconducting critical temperature at zero magnetic field.

10.48550/arxiv.2306.06711

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Superposition of $\sqrt{13}\times \sqrt{13}$ and 3 × 3 supermodulations in TaS₂probed by scanning tunneling microscopy

Journal of Physics Conference Series (2018)

Yuita Fujisawa Takayuki Iwasaki D Fujii Shun Ohta J Iwashita

We report on a scanning tunnelling microscopy study of TaS2 at 4.2 K. A surface prepared by cleavage showed a superimposed pattern of two types of charge density waves with 3a 0 × 3a 0 and periodicity, which had never been observed previously. We attribute the superposition to regular stacking of 4H b polytypes or irregular stacking of 2H and 4H b layers.

10.1088/1742-6596/969/1/012053

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Magnetotransport properties in van-der-Waals \textit{\textbf{R}}Te$_{3}$ (\textit{\textbf{R}} = La, Ce, Tb)

arXiv (Cornell University) (2024)

Tomo Higashihara Ryotaro Asama Ryoya Nakamura Mori Watanabe N. Tomoda

Rare-earth tritellurides are van-der-Waals antiferromagnets which have been attracting attention as materials not only with high mobility, but also with various states such as superconductivity under high pressure, incommensurate charge-density-wave (CDW) phase, and multiple antiferromagnetic phases. In this work, we performed longitudinal resistivity and Hall resistivity measurements simultaneously in exfoliated $R$Te$_{3}$ ($R$ =La, Ce, Tb) thin film devices, in order to investigate the influence of magnetic ordering on transport properties in van-der-Waals magnetic materials. We have obtained carrier mobility and concentration using a two-band model, and have observed an increase in carrier mobility in the antiferromagnets CeTe$_{3}$ and TbTe$_{3}$ due to the magnetic transition. Especially in CeTe$_{3}$, the carrier concentration has changed drastically below the magnetic transition temperature, suggesting the interaction between the CDW and antiferromagnetic phases. In addition, the analysis of the Shubnikov-de Haas oscillations in CeTe$_{3}$ supports the possibility of Fermi surface modulation by magnetic ordering. This research will pave the way not only for spintronic devices that take advantage of high mobility, but also for the study of the correlation between CDW and magnetism states in low-dimensional materials.

10.1103/physrevb.109.134404

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Structural Modulation in LaO0.9F0.1BiSe2 Single Crystals Revealed by Scanning Tunneling Microscopy/Spectroscopy

Journal of Physics Conference Series (2018)

N Ishida Satoshi Demura Yuita Fujisawa Shun Ohta Kikuko Miyata

We present scanning tunneling microscopy and spectroscopy measurements on a cleaved surface of the LaO0.9F0.1BiSe2 single crystals. Tunneling spectra show a finite local density of states at EF, which is consistent with metallic conductivity in bulk. In addition, the existence of the supermodulation running along the diagonal directions of Bi square lattice was revealed. The period of the supermodulation was about 3 to 5 times the length of the lattice constant. This period is close to that observed in LaO0.5F0.5BiSe2.

Lattice constant

Lattice (music)

10.1088/1742-6596/1054/1/012001

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Citations (1)

Enhancement of Tc in BiS2-based superconductors NdO0.7F0.3BiS2 by substitution of Pb for Bi

Solid State Communications (2015)

Satoshi Demura Yuita Fujisawa Satoshi Otsuki R. Ishio Yoshihiko Takano

Substitution (logic)

Lattice (music)

Shrinkage

Superconducting transition temperature

Substitution effect

10.1016/j.ssc.2015.09.002

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Citations (13)

Magnetotransport properties in van der Waals RTe3 (R=La, Ce, Tb)

Physical review. B./Physical review. B (2024)

Tomo Higashihara Ryotaro Asama Ryoya Nakamura Mori Watanabe N. Tomoda

Rare-earth tritellurides are van der Waals antiferromagnets that are a promising platform not only for spintronic devices but also for the study of the correlation between the charge density wave (CDW) and magnetic states in low-dimensional materials. Here, the authors perform longitudinal and Hall resistivity measurements in exfoliated $R$Te${}_{3}$ ($R$=La, Ce, Tb) thin film devices. The carrier mobility and concentration change at the magnetic transition temperature. The result suggests the strong coupling between the CDW and antiferromagnetic phases.

10.1103/physrevb.109.134404

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Citations (2)