Bulletin of the American Physical Society
88th Annual Meeting of the Southeastern Section of the APS
Volume 66, Number 16
Thursday–Saturday, November 18–20, 2021; University Center Club, Florida State University, Tallahassee, Florida
Session M05: Thermoelectrics/Superconductivity |
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Chair: Ryan Baumbach, NHMFL Room: West Ballroom |
Friday, November 19, 2021 2:00PM - 2:30PM |
M05.00001: Quantum Materials Research for Energy Conversion Applications Invited Speaker: Kaya Wei The search for clean and renewable energy production methods is directly related to discovery of novel materials and composites with desired structural and electronic properties. Thermoelectric devices, which allow for direct energy conversion between heat and electricity, have a unique place in this effort since they enable solid state schemes for power generation and refrigeration/heating, involve no harmful gasses/liquids, avoid energy losses and wear/tear from mechanically moving parts, and take advantage of naturally occurring temperature gradients. These characteristics make them ideal for applications including electricity generation in extreme and remote environments. In order to efficiently convert energy using thermoelectricity, several optimized properties are required. These include a high electrical conductivity $\sigma $, a large Seebeck coefficient $S$, and a low thermal conductivity $\kappa $. Together, these quantities define the dimensionless thermoelectric figure of merit, \textit{ZT} $= \quad S^{2}\sigma T$/$\kappa $, where $T$ is the absolute temperature. Larger \textit{ZT} values directly correspond to more efficient thermoelectric devices and there are no known fundamental limitations on how large \textit{ZT }can be. Although all electrical conductors exhibit a thermoelectric effect, their efficacy is limited by a fundamental proportionality between electrical conductivity and the electronic component of the thermal conductivity. In this talk I will report several approaches that have been undertaken in the search for new quantum materials for potential energy conversion applications. For example, a prevailing strategy to overcome the competition between electrical and thermal conductance is to produce materials with large and cage-like unit cells where phonons are strongly scattered but electrons move easily. Following this strategy, we recently investigated the heavy-fermion compounds Yb\textit{TM}$_{2}$Zn$_{20}$ (\textit{TM} $=$ Co, Rh, Ir) and showed that they exhibit competitively high power factors in addition to large \textit{ZT} values at 35 K. Our latest results indicate that compositional modifications contribute to further enhanced thermoelectric properties. [Preview Abstract] |
Friday, November 19, 2021 2:30PM - 2:42PM |
M05.00002: Enhanced thermoelectric properties of YbCo$_2$Zn$_{20}$ through Fe and Ni Doping Jorge R. Galeano-Cabral, Benny Schundelmier, Olatunde Oladehin, Juan Ordonez, Ryan Baumbach, Kaya Wei Thermoelectricity allows direct conversion of thermal to electrical energy and vice versa. Promising thermoelectric properties have been reported for single crystals of Yb$TM_2$Zn$_{20}$ ($TM$ = Co, Rh, Ir) at low temperatures [1]. In this study, we report further enhanced thermoelectric properties of YbCo$_2$Zn$_{20}$ by introducing Fe and Ni on the Co site. Doping on the transition metal site directly affects the electrical conductivity. In addition, it allows for tuning the hybridization strength of the $f$-electron states by modifying the distance between the Yb atoms, resulting in improved Seebeck coefficient values. Having optimized electrical conductivity and Seebeck coefficient led to an enhanced thermoelectric figure of merit ($ZT$), which reflects the energy conversion efficiency of thermoelectric devices. We will also elaborate on the manufacturability of a thermoelectric device using these compounds and discuss potential thermal evaluations on the performance of such devices. [1] Wei, et. al. Sci. Adv. 5, eaaw6183 (2019). [Preview Abstract] |
Friday, November 19, 2021 2:42PM - 2:54PM |
M05.00003: Effect of tuning hybridization strength on optimizing the Seebeck coefficient of heavy fermion compounds Ce$_{x}$Sm$_{y}$Yb$_{z}$Ir$_{2}$Zn$_{20}$ (x $+$ y $+$ z $=$ 1) Benny Schundelmier, Jorge Galeano Cabral, Keke Feng, Olatunde Oladehin, Ryan Baumbach, Kaya Wei Efficient electrical production utilizing thermoelectric generators is becoming more feasible. Thermoelectricity is a two-way direct conversion between thermal energy and electrical power. Recently, 1-2-20 compounds have shown promising thermoelectric properties, especially at low temperatures. [1] In a typical 1-2-20 compound, the heavy rare earth elements are encompassed by large cage-like structures which provides an avenue for achieving reduced lattice component of the thermal conductivity. On the other hand, the strongly hybridized f-electron states contribute to large Seebeck coefficient values. Here we report the optimization of thermoelectric properties of heavy fermion compounds Ce$_{x}$Sm$_{y}$Yb$_{z}$Ir$_{2}$Zn$_{20}$ (x $+$ y $+$ z $=$ 1). By introducing different rare earth elements, we can tune the f-electron states at the Fermi level, resulting in enhanced Seebeck coefficient values. We further characterized these materials using magnetometry, EDS, and XRD. We will discuss results demonstrating the correlation between tuning the hybridization strength of the f-electron states and optimizing the thermoelectric properties of these materials. [1] Wei, et. al. Sci. Adv. 5, eaaw6183 (2019). [Preview Abstract] |
Friday, November 19, 2021 2:54PM - 3:24PM |
M05.00004: Microscopic evidence for chiral superconductivity in UTe2 Invited Speaker: Lin Jiao Spin-triplet superconductivity is a condensate of electron pairs with spin-1 and an odd parity pair wavefunction. A particularly interesting manifestation of triplet pairing is a chiral p-wave state which is topologically non-trivial and a natural platform for realizing Majorana edge modes. Triplet pairing is however rare in solid state systems and so far, no unambiguous identification has been made in any bulk compound. Since pairing is most naturally mediated by ferromagnetic spin fluctuations, uranium based heavy fermion systems containing f-electron elements that can harbor both strong correlations and magnetism are considered ideal candidate spin-triplet superconductors. In this talk I will present scanning tunneling microscopy (STM) studies of the newly discovered heavy fermion superconductor, UTe2 with a TSC of 1.6 K. We find signatures of coexisting Kondo effect and superconductivity which show competing spatial modulations within one unit-cell. Most strikingly, STM spectroscopy at step edges show signatures of asymmetric in-gap resonance, which is understood in terms of chiral tunneling. Combined with existing data indicating triplet pairing, the presence of chiral edge states suggests that UTe2 is a chiral-triplet superconductivity. [Preview Abstract] |
Friday, November 19, 2021 3:24PM - 3:36PM |
M05.00005: Charge-order dynamics in underdoped La$_{1.6-x}$Nd$_{0.4}$Sr$_{x}$CuO$_{4}$ revealed by electric pulses Bal K. Pokharel, Yuxin Wang, J. Jaroszynski, T. Sasagawa, Dragana Popovic The dynamics of the charge-order domains has been investigated in La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$, a prototypical stripe-ordered cuprate, using pulsed current injection. We first identify the regime in which nonthermal effects dominate over simple Joule heating and then demonstrate that, for small enough perturbation, pulsed current injection allows access to nonthermally induced resistive metastable states. The results are consistent with the pinning of the fluctuating charge order, with fluctuations being most pronounced at the charge-order onset temperature. The nonequilibrium effects are revealed only when the transition is approached from the charge-ordered phase. Our experiment establishes pulsed current injection as a viable and effective method for probing the charge-order dynamics in various other materials [1]. [1] Pokharel, Bal K., et al.,Appl.Phys. Lett. 118, 244104 (2021) [Preview Abstract] |
Friday, November 19, 2021 3:36PM - 3:48PM |
M05.00006: Superconducting Fluctuations and Paraconductivity in Ultrathin $a$-Pb Films near Superconductor-Insulator Transition Haoyang Liu, Ashwani Kumar, Liuqi Yu, Peng Xiong The Aslamazov-Larkin (AL) equation describes the extra conductance above $T_{c}$ of a superconductor due to superconducting fluctuations. While agreement with AL model has been found in some conventional 2D superconductors, its applicability in ultrathin limit near the superconductor-insulator transition (SIT) has not been ascertained. Here we report a study of superconducting fluctuation and paraconductivity in ultrathin 2D amorphous Pb films near SIT. The films were incrementally deposited in a dilution refrigerator. Electrical measurements were performed\textit{ in situ} at each thickness, resulting in a series of R(T) across the SIT. Paramagnetic impurities (Cr) were then incrementally deposited, driving the film back to SIT and yielding another set of R(T). The two sets of G(T) were fitted to the AL equation with $T_{c}$ and magnitude of the paraconductivity as fitting parameters. In both cases, as $T_{c}$ decreases below \textasciitilde 2 K, the paraconductivity increases precipitously, reaching more than an order of magnitude higher than the AL prediction. The significant enhancement of superconducting fluctuations near SITs suggests strong emergent electronic inhomogeneities in the uniform 2D amorphous films. [Preview Abstract] |
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