223 research outputs found
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 and icosahedral i-Cd quasicrystals, as well as the
separation of (i) the closely related BiRhS and
BiRhS phases and (ii) PrZn and PrZn.Comment: submitted to Philosophical Magazin
Tuning of layered materials: Studies of CrAuTe4, PdSn4 and WTe2
Layered materials are of great and growing interest for material scientists and condensed matter physicists, not only because of their possible applications but also because of the diverse and controllable ground states. In addition, tuning of layered materials through external fields, doping, or strain can lead to the emergence of novel phenomena. In this dissertation, the importance of the study of layered materials is emphasized in Chapter 1. Before getting into experimental results, the theoretical background and experimental methods, including growth of single crystals of selected layered materials, are introduced in Chapter 2 and Chapter 3. Chapters 4, 5 and 6 are devoted to experimental results on selected layered materials. Chapter 4 presents the physical properties of CrAuTe4 at ambient pressure and the tuning of its properties using hydrostatic pressure. The physical properties of PdSn4 are shown in Chapter 5, and then the origin of extremely large magnetoresistance in this material is discussed in comparison/contrast to the physical properties of
PtSn4. Chapter 6 focuses on the tuning of the physical properties of WTe2 using temperature, magnetic field and uniaxial strain. In appendix A, I list all the growth attempts regarding Te and Se containing materials. In appendix B, I explain the growth of single crystal, EuCd2As2, using salt (NaCl/KCl) as a solution. In appendix C, I summarize other publications during my Ph.D. years
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.Comment: 6 pages, 3 figure
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, 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.Comment: 5 pages, 4 figure
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.Comment: 5 pages, 3 figure
Fragility of Fermi arcs in Dirac semimetals
We use tunable, vacuum ultraviolet laser-based angle-resolved photoemission
spectroscopy and density functional theory calculations to study the electronic
properties of Dirac semimetal candidate cubic PtBi. In addition to bulk
electronic states we also find surface states in PtBi which is expected
as PtBi was theoretical predicated to be a candidate Dirac semimetal.
The surface states are also well reproduced from DFT band calculations.
Interestingly, the topological surface states form Fermi contours rather than
double Fermi arcs that were observed in NaBi. The surface bands forming the
Fermi contours merge with bulk bands in proximity of the Dirac points
projections, as expected. Our data confirms existence of Dirac states in
PtBi and reveals the fragility of the Fermi arcs in Dirac semimetals.
Because the Fermi arcs are not topologically protected in general, they can be
deformed into Fermi contours, as proposed by [Kargarian {\it et al.}, PNAS
\textbf{113}, 8648 (2016)]. Our results demonstrate validity of this theory in
PtBi.Comment: 6 pages, 4 figure
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