90 research outputs found
Momentum dependent ultrafast electron dynamics in antiferromagnetic EuFe2As2
Employing the momentum-sensitivity of time- and angle-resolved photoemission
spectroscopy we demonstrate the analysis of ultrafast single- and many-particle
dynamics in antiferromagnetic EuFe2As2. Their separation is based on a
temperature-dependent difference of photo-excited hole and electron relaxation
times probing the single particle band and the spin density wave gap,
respectively. Reformation of the magnetic order occurs at 800 fs, which is four
times slower compared to electron-phonon equilibration due to a smaller
spin-dependent relaxation phase space
Temperature independent band structure of WTe2 as observed from ARPES
Extremely large magnetoresistance (XMR), observed in transition metal
dichalcogendies, WTe, has attracted recently a great deal of research
interests as it shows no sign of saturation up to the magnetic field as high as
60 T, in addition to the presence of type-II Weyl fermions. Currently, there
has been a lot of discussion on the role of band structure changes on the
temperature dependent XMR in this compound. In this contribution, we study the
band structure of WTe using angle-resolved photoemission spectroscopy
(ARPES) and first-principle calculations to demonstrate that the temperature
dependent band structure has no substantial effect on the temperature dependent
XMR as our measurements do not show band structure changes on increasing the
sample temperature between 20 and 130 K. We further observe an electronlike
surface state, dispersing in such a way that it connects the top of bulk
holelike band to the bottom of bulk electronlike band. Interestingly, similar
to bulk states, the surface state is also mostly intact with the sample
temperature. Our results provide invaluable information in shaping the
mechanism of temperature dependent XMR in WTe.Comment: 7 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1705.0721
Magnetocrystalline Anisotropy and Magnetocaloric Effect Studies on the Room-temperature 2D Ferromagnetic CrTe
We present a thorough study on the magnetoanisotropic properties and
magnetocaloric effect in the layered ferromagnetic CrTe single crystals
by performing the critical behaviour analysis of magnetization isotherms. The
critical exponents =0.485(3), =1.202(5), and =3.52(3)
with a Curie temperature of K are determined by the
modified Arrott plots. We observe a large magnetocrystalline anisotropy
K=330 kJ/ at 3 K which gradually decreases with increasing
temperature. Maximum entropy change - and the relative
cooling power (RCP) are found to be 2.77 and 88.29 ,
respectively near when the magnetic field applied parallel to
-plane. Rescaled - data measured at various
temperatures and fields collapse into a single universal curve, confirming the
second order magnetic transition in this system. Following the renormalization
group theory analysis, we find that the spin-coupling is of 3D Heisenberg-type,
, with long-range exchange interactions decaying as .Comment: 10 pages, 7 figure
Electrical, Thermal and Spectroscopic Characterization of Bulk Bi2Se3 Topological Insulator
We report electrical (angular magneto-resistance, and Hall), thermal (heat
capacity) and spectroscopic (Raman, x-ray photo electron, angle resolved photo
electron) characterization of bulk Bi2Se3 topological insulator, which is being
is grown by self flux method through solid state reaction from high temperature
(950C) melt and slow cooling (2C/hour) of constituent elements. Bi2Se3
exhibited metallic behaviour down to 5K. Magneto transport measurements
revealed linear up to 400% and 30% MR at 5K under 14 Tesla field in
perpendicular and parallel field direction respectively. We noticed that the
magneto-resistance (MR) of Bi2Se3 is very sensitive to the angle of applied
field. MR is maximum when the field is normal to the sample surface, while it
is minimum when the field is parallel. Hall coefficient (RH) is seen nearly
invariant with negative carrier sign down to 5K albeit having near periodic
oscillations above 100K. Heat capacity (Cp) versus temperature plot is seen
without any phase transitions down to 5K and is well fitted (Cp = gammaT +
betaT3) at low temperature with calculated Debye temperature (ThetaD) value of
105.5K. Clear Raman peaks are seen at 72, 131 and 177 cm-1 corresponding to
A1g1, Eg2 and A1g2 respectively. Though, two distinct asymmetric characteristic
peak shapes are seen for Bi 4f7/2 and Bi 4f5/2, the Se 3d region is found to be
broad displaying the overlapping of spin - orbit components of the same.
Angle-resolved photoemission spectroscopy (ARPES) data of Bi2Se3 revealed
distinctly the bulk conduction bands (BCB), surface state (SS), Dirac point
(DP) and bulk valence bands (BVB) and 3D bulk conduction signatures are clearly
seen. Summarily, host of physical properties for as grown Bi2Se3 crystal are
reported here.Comment: 6 Pages Text + Figs; Comments Suggestions welcom
Investigation of the Anomalous and Topological Hall Effects in Layered Monoclinic Ferromagnet CrTe
We studied the electrical transport, Hall effect, and magnetic properties of
monoclinic layered ferromagnet CrTe. Our studies demonstrate
CrTe to be a soft ferromagnet with strong magnetocrystalline
anisotropy. Below 50 K, the system shows an antiferromagnetic-like transition.
Interestingly, between 50 and 150 K, we observe fluctuating magnetic moments
between in-plane and out-of-plane orientations, leading to non-coplanar spin
structure. On the other hand, the electrical resistivity data suggest it to be
metallic throughout the measured temperature range, except a at around
50 K due to AFM ordering. The Rhodes-Wohlfarth ratio
calculated from our magnetic studies
confirms that CrTe is an itinerant ferromagnet. Large anomalous
Hall effect has been observed due to the skew-scattering of impurities and the
topological Hall effect has been observed due to non-coplanar spin-structure in
the presence of strong magnetocrystalline anisotropy. We examined the mechanism
of anomalous Hall effect by employing the first principles calculations.Comment: 9 pages, 6 figures, To appear in Physical Review Material
Effect of impurity substitution on band structure and mass renormalization of the correlated FeTeSe superconductor
Using angle-resolved photoemission spectroscopy (ARPES), we studied the
effect of the impurity potential on the electronic structure of
FeTeSe superconductor by substituting 10\% of Ni for Fe which
leads to an electron doping of the system. We could resolve three hole pockets
near the zone center and an electron pocket near the zone corner in the case of
FeTeSe, whereas only two hole pockets near the zone center and
an electron pocket near the zone corner are resolved in the case of
FeNiTeSe, suggesting that the hole pocket
having predominantly the orbital character is very sensitive to the
impurity scattering. Upon electron doping, the size of the hole pockets
decrease and the size of the electron pockets increase as compared to the host
compound. However, the observed changes in the size of the electron and hole
pockets are not consistent with the rigid-band model. Moreover, the effective
mass of the hole pockets is reduced near the zone center and of the electron
pockets is increased near the zone corner in the doped
FeNiTeSe as compared to FeTeSe.
We refer these observations to the changes of the spectral function due to the
effect of the impurity potential of the dopants.Comment: 8 pages, 3 figure
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