Sarah J. Watzman
Ohio State University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Sarah J. Watzman.
Physical Review B | 2016
Sarah J. Watzman; R. A. Duine; Yaroslav Tserkovnyak; Stephen R. Boona; Hyungyu Jin; Arati Prakash; Yuanhua Zheng; Joseph P. Heremans
Magnon drag is shown to dominate the thermopower of elemental Fe from 2 to 80 K and of elemental Co from 150 to 600 K; it is also shown to contribute to the thermopower of elemental Ni from 50 to 500 K. Two theoretical models are presented for magnon-drag thermopower. One is a hydrodynamic theory based purely on nonrelativistic, Galilean, spin-preserving electron-magnon scattering. The second is based on spin-motive forces, where the thermopower results from the electric current pumped by the dynamic magnetization associated with a magnon heat flux. In spite of their very different microscopic origins, the two give similar predictions for pure metals at low temperature, allowing us to semiquantitatively explain the observed thermopower of elemental Fe and Co without adjustable parameters. We also find that magnon drag may contribute to the thermopower of Ni. A spin-mixing model is presented that describes the magnon-drag contribution to the anomalous Nernst effect in Fe, again enabling a semiquantitative match to the experimental data without fitting parameters. Our paper suggests that particle nonconserving processes may play an important role in other types of drag phenomena and also gives a predicative theory for improving metals as thermoelectric materials.
APL Materials | 2016
Stephen R. Boona; Sarah J. Watzman; Joseph P. Heremans
We review the spin-Seebeck and magnon-electron drag effects in the context of solid-state energy conversion. These phenomena are driven by advective magnon-electron interactions. Heat flow through magnetic materials generates magnetization dynamics, which can strongly affect free electrons within or adjacent to the magnetic material, thereby producing magnetization-dependent (e.g., remnant) electric fields. The relative strength of spin-dependent interactions means that magnon-driven effects can generate significantly larger thermoelectric power factors as compared to classical thermoelectric phenomena. This is a surprising situation in which spin-based effects are larger than purely charge-based effects, potentially enabling new approaches to thermal energy conversion.
Journal of Physics: Condensed Matter | 2017
U Stockert; R. D. dos Reis; M. O. Ajeesh; Sarah J. Watzman; Marcus Schmidt; Chandra Shekhar; Joseph P. Heremans; Claudia Felser; M. Baenitz; M. Nicklas
The Weyl semimetal NbP exhibits an extremely large magnetoresistance and an ultra-high mobility. The large magnetoresistance originates from a combination of the nearly perfect compensation between electron- and hole-type charge carriers and the high mobility, which is relevant to the topological band structure. In this work we report on temperature- and field-dependent thermopower and thermal conductivity experiments on NbP. Additionally, we carried out complementary heat capacity, magnetization, and electrical resistivity measurements. We found a giant adiabatic magnetothermopower with a maximum of [Formula: see text] at 50 K in a field of 9 T. Such large effects have been observed rarely in bulk materials. We further observe pronounced quantum oscillations in both thermal conductivity and thermopower. The obtained frequencies compare well with our heat capacity and magnetization data.
Physical Review B | 2018
Sarah J. Watzman; Timothy M. McCormick; Chandra Shekhar; Shu-Chun Wu; Yan Sun; Arati Prakash; Claudia Felser; Nandini Trivedi; Joseph P. Heremans
Weyl semimetals expand research on topologically protected transport by adding bulk Berry monopoles with linearly dispersing electronic states and topologically robust, gapless surface Fermi arcs terminating on bulk node projections. Here, we show how the Nernst effect, combining entropy with charge transport, gives a unique signature for the presence of Dirac bands. The Nernst thermopower of NbP (maximum of 800 microV K-1 at 9 T, 109 K) exceeds its conventional thermopower by a hundredfold and is significantly larger than the thermopower of traditional thermoelectric materials. The Nernst effect has a pronounced maximum near T_M=90 +/- 20 K=mu_0/kB (mu_0 is chemical potential at T=0 K). A self-consistent theory without adjustable parameters shows that this results from electrochemical potential pinning to the Weyl point energy at T>=TM, driven by charge neutrality and Dirac band symmetry. Temperature and field dependences of the Nernst effect, an even function of the charge polarity, result from the intrinsically bipolar nature of the Weyl fermions. Through this study, we offer an understanding of the temperature dependence of the position of the electrochemical potential vis-a-vis the Weyl point, and we show a direct connection between topology and the Nernst effect, a potentially robust experimental tool for investigating topological states and the chiral anomaly.
Proceedings of SPIE | 2016
Joseph P. Heremans; Hyungyu Jin; Yuanhua Zheng; Sarah J. Watzman; Arati Prakash
This article reviews the factors limiting the figure of merit zT of conventional thermoelectrics especially at cryogenic temperatures and then highlights modern approaches used to increase zT below 200 K. Two type of materials are discussed. The first are BiSb alloys, relatively conventional thermoelectrics in which the zT is enhanced by using resonant levels. The second is the spin- Seebeck effect (SSE), a new solid-state energy conversion technology. Classical thermoelectric and SSE physics are combined to provide new concepts, like magnon-drag, in which we hope to increase the performance of solid-state coolers by exploiting the spin degree of freedom.
Physical Review B | 2018
Timothy M. McCormick; Joseph P. Heremans; Sarah J. Watzman; Nandini Trivedi
In topological Weyl semimetals, the low energy excitations are comprised of linearly dispersing Weyl fermions, which act as monopoles of Berry curvature in momentum space and result in topologically protected Fermi arcs on the surfaces. We propose that these Fermi arcs in Weyl semimetals lead to an anisotropic magnetothermal conductivity, strongly dependent on externally applied magnetic field and resulting from entropy transport driven by circulating electronic currents. The circulating currents result in no net charge transport, but they do result in a net entropy transport. This translates into a magnetothermal conductivity that should be a unique experimental signature for the existence of the arcs. We analytically calculate the Fermi arc-mediated magnetothermal conductivity in the low-field semiclassical limit as well as in the high-field ultra-quantum limit, where only the chiral Landau levels are involved. By numerically including the effects of higher Landau levels, we show how the two limits are linked at intermediate magnetic fields. This work provides the first proposed signature of Fermi arc-mediated thermal transport and sets the stage for utilizing and manipulating the topological Fermi arcs in experimental thermal applications.
Bulletin of the American Physical Society | 2018
Chandra Shekhar; Yan Sun; Nitesh Kumar; Johannes Gooth; M. Nicklas; Sarah J. Watzman; Kaustuv Manna; Vicky Suess; Lukas Muechler; Tobias Förster; Walter Schnelle; U. Zeitler; Binghai Yan; Stuart S. P. Parkin; Claudia Felser
Materials Today Physics | 2017
Koen Vandaele; Sarah J. Watzman; Benedetta Flebus; Arati Prakash; Yuanhua Zheng; Stephen R. Boona; Joseph P. Heremans
arXiv: Mesoscale and Nanoscale Physics | 2017
Sarah J. Watzman; Timothy M. McCormick; Chandra Shekhar; Arati Prakash; Claudia Felser; Nandini Trivedi; Joseph P. Heremans
arXiv: Materials Science | 2018
Satya N. Guin; Kaustuv Manna; Jonathan Noky; Sarah J. Watzman; Chenguang Fu; Nitesh Kumar; Walter Schnelle; Chandra Shekhar; Yan Sun; Johannes Gooth; Claudia Felser