arXiv subjects

Na Hyun Jo

Publications and source records attributed to Na Hyun Jo.

41 records · Page 3Linked to original sources

arXiv2017

Three-dimensionality of the bulk electronic structure in WTe2

We use temperature- and field-dependent resistivity measurements [Shubnikov--de Haas (SdH) quantum oscillations] and ultrahigh resolution, tunable, vacuum ultraviolet (VUV) laser-based angle-resolved photoemission spectroscopy (ARPES) to study the three-dimensionality (3D) of the bulk electronic structure in WTe2, a type-II Weyl semimetal. The bulk Fermi surface (FS) consists of two pairs of electron pockets and two pairs of hole pockets along the X-Gamma-X direction as detected by using an incident photon energy of 6.7 eV, which is consistent with the previously reported data. However, if using an incident photon energy of 6.36 eV, another pair of tiny electron pockets is detected on both sides of the Gamma point, which is in agreement with the small quantum oscillation frequency peak observed in the magnetoresistance. Therefore, the bulk, 3D FS consists of three pairs of electron pockets and two pairs of hole pockets in total. With the ability of fine tuning the incident photon energy, we demonstrate the strong three-dimensionality of the bulk electronic structure in WTe2. The combination of resistivity and ARPES measurements reveal the complete, and consistent, picture of the bulk electronic structure of this material.

cond-mat.mtrl-sci↗

arXiv2016

Anisotropic physical properties and pressure dependent magnetic ordering of CrAuTe$_4$

Systematic measurements of temperature dependent magnetization, resistivity and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe$_4$. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic $c$-axis below $T_\textrm{N}$ = 255 K. ARPES measurements show band reconstruction due to the magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Neel temperature decreases monotonically under pressure, decreasing to $T_\textrm{N}$ = 236 K at 5.22 GPa. The pressure dependencies of (i) $T_\textrm{N}$, (ii) the residual resistivity ratio, and (iii) the size and power-law behavior of the low temperature magnetoresistance all show anomalies near 2 GPa suggesting that there may be a phase transition (structural, magnetic, and/or electronic) induced by pressure. For pressures higher than 2 GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states.

cond-mat.str-el↗

arXiv2016

Observation of Fermi Arcs in Type-II Weyl Semimetal Candidate WTe2

We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of WTe$_2$, a material that was predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe2 were proposed to emerge at the crossing points of electron and hole pockets; and Fermi arcs connecting electron and hole pockets would be visible in the spectral function on (001) surface. Here we report the observation of such Fermi arcs in WTe2 confirming the theoretical predictions. This provides strong evidence for type-II Weyl semimetallic states in WTe2.

cond-mat.mtrl-sci↗

arXiv2015

Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples

Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibers. In this paper we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the clean separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this paper we provide examples of the growth of isotopically substituted TbCd$_{6}$ and icosahedral i-$R$Cd quasicrystals, as well as the separation of (i) the closely related Bi$_{2}$Rh$_{3}$S$_{2}$ and Bi$_{2}$Rh$_{3.5}$S$_{2}$ phases and (ii) PrZn$_{11}$ and Pr$_{2}$Zn$_{17}$.

cond-mat.mtrl-sci↗

arXiv2015

Temperature induced Lifshitz transition in WTe2

We use ultra-high resolution, tunable, VUV laser-based, angle-resolved photoemission spectroscopy (ARPES) and temperature and field dependent resistivity and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature dependent magnetoresistance. The temperature dependence of the TEP shows a change of slope at T=175 K and the Kohler rule breaks down above 70-140 K range. The Fermi surface consists of two electron pockets and two pairs of hole pockets along the X-Gamma-X direction. Upon increase of temperature from 40K, the hole pockets gradually sink below the chemical potential. Like BaFe2As2, WTe2 has clear and substantial changes in its Fermi surface driven by modest changes in temperature. In WTe2, this leads to a rare example of temperature induced Lifshitz transition, associated with the complete disappearance of the hole pockets. These dramatic changes of the electronic structure naturally explain unusual features of the transport data.

cond-mat.str-el↗