Our meetings are usually on Fridays at 11:00 am in Sumwalt 102. You can find abstracts of the previous talks of the semester at the bottom of this
page. Looking forward to seeing you all!
Most Recent Seminar (Spring 2024):
Quantum-limit phenomena in rare-earth-based layered EuZn2As2 and CsNdSe2
Speaker:Professor Rongying Jin Date and time: March 1st, 11 am Abstract: Layered EuZn2As2 and CsNdSe2 are candidate magnetic topological materials with the magnetism from the involved
rare-earth elements. While Eu forms a square lattice with its moment orders antiferromagnetically
below 19 K in EuZn2As2, Nd in CsNdSe2 forms a triangular lattice thus never orders magnetically down to 0.04 K. By applying
pulsed magnetic fields up to 60 T, spin reorientation is observed accompanied with
giant magnetoresistance (MR) in EuZn2As2. After passing the first Landau level, the large linear MR occurs at high fields
corresponding to the quantum limit. On the other hand, the application of the magnetic
field leads to long-range magnetic ordering with the highest transition temperature
at 0.3 K in CsNdSe2, implying the quantum spin liquid ground state at the ambient condition. Our findings
help understand the intimate relationship between magnetism and electronic topology
in magnetic topological materials.
Speaker: Govinda Kharal Date and time: February 23th, 11 am Abstract: IrTe2 exhibits a trigonal structure at room temperature and experiences
a first-order structural transition, with the transition temperature determined by
whether the material is cooling or warming. We employed the second harmonic generation
(SHG) technique to investigate single crystals of IrTe2 in a temperature range spanning
from 7 K to 295 K. Using this method, we observed alterations in surface symmetries
consistent with the structural phase shifts at approximately 270 K and 165 K, as previously
reported in low energy electron diffraction (LEED), scanning tunneling microscopy
(STM), and SHG measurements conducted at near room temperature. Our SHG polarimetry
measurements revealed that the (001) plane of IrTe2 maintains a trigonal (3m) symmetry
above 270 K and then undergoes a first-order phase transition to a triclinic (1) symmetry
below 270 K. Nevertheless, the 3m symmetry persists until about 165 K. Notably, we
observed the emergence of a 3m symmetry at 7.2 K which was not documented in prior
studies at lower temperatures. This finding supports an earlier STM measurement suggesting
that the hexagonal phase with the trigonal symmetry may be related to the superconducting
phase.
Speaker: Abhinna Rajbanshi Date and time: February 23th, 11 am Abstract: Thermolelectric materials can serve for conversion between thermal and electrical
energy. In the search for new thermoelectric materials, layered SnSe and SnSe2 are
promising candidates. We have successfully synthesized SnSe and SnSe2 single crystals
by the modified Bridgman method and studied their thermoelectric properties: thermopower
(S), thermal conductivity (κ), and electrical conductivity (σ) in the temperature
range between 2 K and 400 K. Compared to SnSe2 at 300 K, we find that SnSe exhibits
higher electrical conductivity, higher thermopower, and lower thermal conductivity,
thus resulting in the higher figure of merit. Hall effect measurements reveals that
the Hall mobility in SnSe is an order higher than that in SnSe2, advancing its thermoelectric
performance.
Speaker: Volodymyr Shablenko Date and time: February 23th, 11 am Abstract: Using half-metals (e.g., Heusler alloys) as ferromagnetic elements in spintronic
devices sometimes leads to unexpected results. While using identical magnetic materials
for both fixed and free layers already generate some interesting properties [1], it
may be challenging to implement magnetization switching in such system experimentally
because the boundary between materials is not well defined in their parallel state.
Moreover, materials’ symmetry cancels the linear term in voltage dependence of the
out-of-plane torque. In this study, we calculate electric and spin currents using
a Stoner model description of half metals and find the out-of-plane torque and exchange
energy of an F/F device. Voltage dependence of the out-of-plane torque is calculated
as well. The lack of material’s symmetry generates additional anisotropy in this torque’s
angular dependence.
Speaker: Daniel Duong Date and time: February 16th, 11 am Abstract: Uranium-based compounds are an active source of interest due to the wide
variety of exotic states that they can host. UCu0.6Bi2 orders antiferromagnetically
below TN ≈ 54 K. For T < TN, there is a first-order metamagnetic transition under
the application of magnetic field. The temperature and field-orientation dependence
of the transition have been mapped using magnetization and MHz susceptibility measurements
in fields of up to 60 T and for temperatures down to 0.65 K. Unusually large hysteresis
is observed at the transition under certain conditions; the possible origin of this
and other features will be discussed.
Speaker: Govinda Kharal Date and time: February 16th, 11 am Abstract: IrTe2 exhibits a trigonal structure at room temperature and experiences
a first-order structural transition, with the transition temperature determined by
whether the material is cooling or warming. We employed the second harmonic generation
(SHG) technique to investigate single crystals of IrTe2 in a temperature range spanning
from 7 K to 295 K. Using this method, we observed alterations in surface symmetries
consistent with the structural phase shifts at approximately 270 K and 165 K, as previously
reported in low energy electron diffraction (LEED), scanning tunneling microscopy
(STM), and SHG measurements conducted at near room temperature. Our SHG polarimetry
measurements revealed that the (001) plane of IrTe2 maintains a trigonal (3m) symmetry
above 270 K and then undergoes a first-order phase transition to a triclinic (1) symmetry
below 270 K. Nevertheless, the 3m symmetry persists until about 165 K. Notably, we
observed the emergence of a 3m symmetry at 7.2 K which was not documented in prior
studies at lower temperatures. This finding supports an earlier STM measurement suggesting
that the hexagonal phase with the trigonal symmetry may be related to the superconducting
phase.
Speaker: Abhinna Rajbanshi Date and time: February 16th, 11 am Abstract: Thermolelectric materials can serve for conversion between thermal and electrical
energy. In the search for new thermoelectric materials, layered SnSe and SnSe2 are
promising candidates. We have successfully synthesized SnSe and SnSe2 single crystals
by the modified Bridgman method and studied their thermoelectric properties: thermopower
(S), thermal conductivity (κ), and electrical conductivity (σ) in the temperature
range between 2 K and 400 K. Compared to SnSe2 at 300 K, we find that SnSe exhibits
higher electrical conductivity, higher thermopower, and lower thermal conductivity,
thus resulting in the higher figure of merit. Hall effect measurements reveals that
the Hall mobility in SnSe is an order higher than that in SnSe2, advancing its thermoelectric
performance.
Speaker: Dr. Bryan Chavez Date and time: February 9th, 11 am Abstract: Second harmonic generation (SHG) has proven to be an invaluable tool for
investigating the structural, electrical, and magnetic properties of materials. The
application of SHG has become a key area of research, with recent work in the field
of quantum materials, such as with our group’s work on PtBi2, IrTe2, and BaMnSb2.
SHG comprises three components: electric dipole (ED), magnetic dipole (MD), and electric
quadrupole (EQ). In particular, magnetization-induced SHG (MSHG) has emerged as a
powerful tool for studying the symmetry and magnetization of antiferromagnetic (AFM)
and ferro/ferrimagnetic (FM) systems. While the three types of SHG have been studied
independently, materials typically do not exhibit only one type. Therefore, the analysis
of materials with combined SHG remains an active area of study, especially for newer
materials like magnetic Weyl semimetals, which can be challenging to analyze due to
interference terms arising from the combination of ED, MD, and EQ SHG. Recent studies
have attempted to bridge this knowledge gap and better classify the magnetic component.
In this talk, the impact of a sample's magnetic ordering (AFM or FM) on the SHG response
will be discussed, with a focus on the fingerprints in SHG.
Speaker: Caleb Duff Date and time: February 2nd, 11 am Abstract: Structured light is a key component of many modern applications, ranging
from super-resolution microscopy to imaging, sensing and quantum information processing.
As the utilization of these powerful tools continues to spread, the demand for technologies
that enable the spatial manipulation of fundamental properties of light, such as amplitude,
phase and polarization grows further. The rapidly advancing field of reconfigurable
integrated photonics allows entirely new routes towards beam shaping that not only
outperform existing devices in terms of speed but also have substantial potential
with respect to their footprints, robustness and conversion efficiencies. In this
study, we demonstrate how a multipurpose programmable integrated photonic processor
can generate and control a wide range of higher-order free-space structured light
beams, all starting from only a single injection waveguide. Our method controls the
distribution of light’s amplitude and phase within sub-milliseconds, and it is fully
reconfigurable and has no moving parts. These advancements broaden the spectrum of
potential methods, applications and devices that utilize spatially tailored light
by providing a pathway to combine the strengths and versatility of integrated photonics
and free-space structured light.
Speaker: Dan Hancock Date and time: January 26, 11 am Abstract: In May 2023, superconductivity was found in La3Ni2O7 at around 80K, providing
the first instance of high Tc superconductivity in nickelates. With this evidence,
a deeper search for superconductivity in the La-Ni-O system began. This paper looks
at the effects of Pr-doped polycrystalline samples of the bilayer La3Ni2O7. The goal
is to broaden the scope of nickelate superconductors and provide insight into the
mechanisms of superconductivity. Researchers found superconductivity in Pr-doped samples
that occurs in the I4/mmm space group, which differs from the initially proposed superconducting
space group of La3Ni2O7 (Fmmm). Recent research (http://arxiv.org/abs/2311.09186)
proposes that the superconducting state of La3Ni2O7 might in fact be in the I4/mmm
space group, which matches the superconducting phase of Pr-doped samples. In the Pr-doped
samples, researchers found superconductivity to begin at 10 GPa, distinctively lower
than that of La3Ni2O7 with a maximum onset of superconductivity at 78K under pressure
of 15GPa. This new information provides insight into the scope of superconducting
nickelates.
Speaker: Siavash Karbasizadeh Date and time: January 19, 11am Abstract: In condensed matter physics, materials with kagome lattice display a range of exotic
quantum states, including charge density wave (CDW), superconductivity, and magnetism.
Recently, the intermetallic kagome metal ScV6Sn6 was discovered to undergo a first-order
structural phase transition with the formation of a √3 × √3 × 3 CDW at around 92 K.
The bulk electronic band properties are crucial to understanding the origin of the
structural phase transition. Here, we conducted an optical spectroscopy study in combination
with band structure calculations across the structural transition. Our findings showed
abrupt changes in the optical reflectivity/conductivity spectra as a result of the
structural transition, without any observable gap formation behavior. The optical
measurements and band calculations actually reveal a sudden change of the band structure
after transition. It is important to note that this phase transition is of the first-order
type, which distinguishes it from conventional density-wave type condensations. Our
results provide an insight into the origin of the structural phase transition in this
new and unique kagome lattice intermetallic material.
Speaker: Paras Regmi Date and time: January 12, 11 am Abstract: In the realm of topological semimetals, the exploration of the intriguing phenomenon
of topological Hall effect (THE) emerges from the nontrivial magnetic texture in real
space, characterized by a non-zero scalar spin chirality. This paper reports a large
THE in the antiferromagnetic (AFM) state of a Dirac semimetal EuAgAs. The intrinsic
contribution of anomalous Hall effect (AHE) is considered while modelling AHE for
data analysis. EuAgAs has AFM ground state below TN. The first principal calculation
reveals that the material exhibits Dirac semimetallic ground state. Subsequently,
upon the application of external magnetic field, the transition from Dirac semimetallic
state to Weyl semimetallic state is observed. The presence of band structure anomalies
like Weyl nodes could also contribute to the Hall response observed in the material.