Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P32: Quantum Thermoelectric SystemsFocus

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Sponsoring Units: DMP GERA FIAP Chair: Jeff Urban, Molecular Foundry, UC Berkeley Room: 332 
Wednesday, March 16, 2016 2:30PM  2:42PM 
P32.00001: Evolutionary structure search of efficient thermoelectric compounds Maribel N\'u\~nez Valdez, Artem Oganov Thermoelectric materials, which are used to harvest waste heat to generate power, are taking an important role for energy solutions. However, it is of fundamental significance the optimization of a variety of conflicting properties in order to obtain a high efficiency thermoelectric device to be costeffective for applications. This efficiency or figure of merit ($ZT$), which depends on the Seebeck coefficient, electrical resistivity and heat conductivity, is restricted by currently available materials and fabricating technologies. Therefore, the main objective of our study is the identification of thermodynamically stable compounds and their crystal structures with high $ZT$ given just a set of elements by using an evolutionary algorithm in which the figure of merit is a degree of freedom to be optimized. We test the performance of our methods within the system Bi$_2$Te$_3$Sb$_2$Te$_3$. These compounds are well known for their large $ZT$'s and their use in technological applications. Our results indicate a high feasibility for the employment of our evolutionary algorithm search using a wide variety of elements for optimizing and designing new thermoelectric materials. [Preview Abstract] 
Wednesday, March 16, 2016 2:42PM  2:54PM 
P32.00002: Highthroughput screening for thermoelectric sulphides by using crystal structure features as descriptors Ruizhi Zhang, Baoli Du, Kan Chen, Mike Reece With the increasing computational power and reliable databases, highthroughput screening is playing a more and more important role in the search of new thermoelectric materials. Rather than the well established density functional theory (DFT) calculation based methods, we propose an alternative approach to screen for new TE materials: using crystal structural features as ‘descriptors’. We show that a nondistorted transition metal sulphide polyhedral network can be a good descriptor for high power factor according to crystal filed theory. By using Cu/S containing compounds as an example, 1600+ Cu/S containing entries in the Inorganic Crystal Structure Database (ICSD) were screened, and of those 84 phases are identified as promising thermoelectric materials. The screening results are validated by both electronic structure calculations and experimental results from the literature. We also fabricated some new compounds to test our screening results. Another advantage of using crystal structure features as descriptors is that we can easily establish structural relationships between the identified phases. Based on this, two material design approaches are discussed: 1) Highpressure synthesis of metastable phase; 2) Insitu 2phase composites with coherent interface. [Preview Abstract] 
Wednesday, March 16, 2016 2:54PM  3:06PM 
P32.00003: Thermal Conductivities in Solids from First Principles: Accurate Computations and Rapid Estimates Christian Carbogno, Matthias Scheffler In spite of significant research efforts, a firstprinciples determination of the thermal conductivity $\kappa$ at high temperatures has remained elusive. Boltzmann transport techniques that account for anharmonicity perturbatively become inaccurate under such conditions. {\it Ab initio} molecular dynamics~(MD) techniques using the {\it GreenKubo}~(GK) formalism capture the full anharmonicity, but can become prohibitively costly to converge in time and size. We developed a formalism that accelerates such GK simulations by several orders of magnitude and that thus enables its application within the limited time and length scales accessible in {\it ab initio} MD. For this purpose, we determine the {\it effective} harmonic potential occurring during the MD, the associated temperaturedependent phonon properties and lifetimes. Interpolation in reciprocal and frequency space then allows to extrapolate to the macroscopic scale. For both forcefield and {\it ab initio} MD, we validate this approach by computing $\kappa$ for Si and ZrO$_2$, two materials known for their particularly harmonic and anharmonic character. Eventually, we demonstrate how these techniques facilitate reasonable estimates of $\kappa$ from existing MD calculations at virtually no additional computational cost. [Preview Abstract] 
Wednesday, March 16, 2016 3:06PM  3:42PM 
P32.00004: Local thermoelectric probes of nonequilibrium quantum systems Invited Speaker: Charles Stafford A theory of local temperature and voltage measurement in an interacting quantum system far from equilibrium is developed. We prove that a steadystate measurement by a floating thermoelectric probe is unique if it exists. Furthermore, we show that a solution exists provided there is no net local population inversion. In the case of population inversion, the system may be assigned a (unique) negative temperature. An expression for the local entropy of a nonequilibrium quantum system is introduced that, together with the local temperature and voltage, allows for a complete analysis of the local thermodynamics of the thermoelectric processes in the system. The Clausius form of the second law and the third law are shown to hold exactly locally, while the zeroth and first laws are shown to be valid to leading order in the Sommerfeld expansion. The local quantum thermodynamics underlying the enhancement of thermoelectricity by quantum interference is discussed. [Preview Abstract] 
Wednesday, March 16, 2016 3:42PM  3:54PM 
P32.00005: Nanoelectronic primary thermometry below 4 millikelvin Matthew Sarsby, Richard Haley, David Ian Bradley, Richard George, Yuri Pashkin, Jonathan Prance, David Gunnarsson, Hannele Heikkinen, Mika Prunnila, Penttilä Jari, Leif Roschier We present measurements of nanoelectronic Coulomb Blockade Thermometers that are optimised for operation below 10 mK. Their design incorporates onchip electronic filters and cooling fins with a high electronphonon coupling. By immersing the devices in the 3He/4He mixture of a dilution refrigerator, and by minimising electrical noise in the measurement circuit, the onchip electron temperature reaches a value of 3.7 mK, the lowest yet measured in any nanoelectronic device. Above 7 mK the devices are in good thermal contact with their environment and are not susceptible to selfheating. Below 7 mK the device continues to provide accurate thermometry of the onchip electron temperature, which is seen to diverge from the ambient temperature. In this regime the device provides valuable information about noise and heatleaks from the environment, which points the way towards cooling nanoelectronic structures to lower temperatures. [Preview Abstract] 
Wednesday, March 16, 2016 3:54PM  4:06PM 
P32.00006: Thermoelectric Corrections to Quantum Measurement Justin Bergfield, Mark Ratner, Charles Stafford, Massimiliano Di Ventra The voltage and temperature measured by a floating probe of a nonequilibrium quantum system is shown to exhibit nontrivial thermoelectric corrections at finite temperature. Using a realistic model of a scanning thermal microscope to calculate the voltage and temperature distributions, we predict quantum temperature variations along graphene nanoribbons subject to a thermal bias which are not simply related to the local density of states. Experimentally, the wavelength of the oscillations can be tuned over several orders of magnitude by gating/doping, bringing quantum temperature oscillations within reach of the spatial resolution of existing measurement techniques. We also find that the Peltier cooling/heating which causes the temperature oscillations can lead to significant errors in voltage measurements for a wide range of system. [Preview Abstract] 
Wednesday, March 16, 2016 4:06PM  4:18PM 
P32.00007: Deciphering the LandauerB\"uttiker Transmission Function from Single Molecule Break Junction Experiments Matthew Reuter, Stephen Tschudi When investigating the electrical response properties of molecules, experiments often measure conductance whereas computation predicts transmission probabilities. Although the LandauerB\"uttiker theory relates the two in the limit of coherent scattering through the molecule, a direct comparison between experiment and computation can still be difficult. Experimental data (specifically that from break junctions) is statistical and computational results are deterministic. Many studies compare the most probable experimental conductance with computation, but such an analysis discards almost all of the experimental statistics. In this work we develop tools to decipher the LandauerB\"uttiker transmission function directly from experimental statistics and then apply them to enable a fairer comparison between experimental and computational results. [Preview Abstract] 
Wednesday, March 16, 2016 4:18PM  4:30PM 
P32.00008: A simple Quantum heat engine operating between two negative temperatures Tolasa A DIMA, Mulugeta Bekele We study a heat engine that operates between two reservoirs at negative temperatures. A system of spinhalf particles, in the thermodynamic limit, subject to a time dependent external magnetic field, is used as a working substance because of its capability to demonstrate negative absolute temperature. We explored the finitetime quantities: period, power and efficiency. The engine is explored in its maximum power and optimum mode of operation from which its figure of merit is defined as the product of scaled power and scaled efficiency. We found that powerwise the engine provides better performance under its maximum power mode of operation than the optimized mode; however, efficiencywise, the optimized mode of operation is better than its maximum mode operation. [Preview Abstract] 
Wednesday, March 16, 2016 4:30PM  4:42PM 
P32.00009: Thermal Memristive Devices Luke Shapiro, Kamil Walczak We examine heat transfer via Coulomb Blockaded quantum systems connected to two heat reservoirs (thermal baths). Specifically, we propose simple models for negative differential thermal conductance and pinched hysteretic loops in the heat fluxes as functions of temperature. Our computational method is based on the theory of propagators, where additional mechanisms of shifting and blocking specific energy levels is incorporated. Those devices may play a major role in the future thermal management. [Preview Abstract] 
Wednesday, March 16, 2016 4:42PM  4:54PM 
P32.00010: Density of States for Warped or nonWarped Energy Bands Nicholas Mecholsky, Lorenzo Resca, Ian Pegg, Marco Fornari The goal of this talk is to investigate when band warping affects densityofstates effective mass. Further, band ``corrugation," a form of band warping referring to energy dispersions that deviate ``more severely" from being twicedifferentiable at isolated critical points, may also correlate in different ways with densityofstates effective masses and other band warping parameters. In this talk, an angular effective mass formalism is developed and used to study the electronic density of states of warped and nonwarped energy bands towards an application in thermoelectric transport design. We demonstrate effects of band warping and prove the superiority of the angular effective mass treatment for valence energy bands in cubic materials. We explore examples that can also be critical to precisely distinguish the contributions due to band warping and to band nonparabolicity in nondegenerate bands of thermoelectric materials that have a consequent practical interest. [Preview Abstract] 
Wednesday, March 16, 2016 4:54PM  5:06PM 
P32.00011: A generalized Sommerfeld expansion for thermopower calculation Jie Gu, Xiaoguang Zhang, HaiPing Cheng Kelvin formula relates the thermopower to the temperature derivative of the chemical potential. The latter can be evaluated using the Sommerfeld expansion as a standard approximation at low temperatures. We present a generalized expansion with improved accuracy at intermediate and high temperatures. We apply the formula to sodium cobaltate NaxCoO2 and other thermoelectric materials to verify its validity over a wide temperature range. [Preview Abstract] 
Wednesday, March 16, 2016 5:06PM  5:18PM 
P32.00012: Temperature Dependent Structure of Thermoelectric Ca3Co4O9 Tao Wu, Trevor Tyson, Han Zhang, Milinda Abeykoon Structural studies of thermoelectric ``Ca3Co4O9'' have been conducted for a broad range of temperatures using probes covering multiple length scales. Details on the structure and its connection to the electron transport and thermal properties will be discussed. This work is supported by DOE Grant DEFG0207ER46402. [Preview Abstract] 
Wednesday, March 16, 2016 5:18PM  5:30PM 
P32.00013: DYNAMICAL CORRECTION OF THERMOELECTRIC COEFFICIENTS FOR STRONGLY INTERACTING ELECTRONS IN THE COULOMB BLOCKADE REGIME Kaike Yang FOR MOLECULES WEAKLY COUPLED TO LEADS THE EXACT ZEROBIAS KOHNSHAM CONDUCTANCE CAN BE ORDERS OF MAGNITUDE LARGER THAN THE TRUE CONDUCTANCE DUE TO THE LACK OF DYNAMICAL EXCHANGECORRELATION (XC) EFFECTS. RECENTLY, IT HAS BEEN SHOWN [1] HOW THESE DYNAMICAL XC CORRECTIONS CAN BE CALCULATED USING ONLY QUANTITIES OBTAINED FROM STATIC DENSITY FUNCTIONAL THEORY. HERE, WE INVESTIGATE THE THERMOELECTRIC TRANSPORT AND DERIVE THE XC CORRECTION TO THE SEEBECK COEFFICIENT. WE FIND THAT THE DYNAMICAL CORRECTION TO THE SEEBECK COEFFICIENT IS DETERMINANT IN EVALUATING THE THERMOPOWER: THE ABSOLUTE VALUE OF THE DYNAMICAL CORRECTION FOR THE SEEBECK COEFFICIENT IS, FOR CERTAIN VALUES OF GATE VOLTAGE, MUCH LARGER THAN THAT OF THE KOHNSHAM TERM. FINALLY, WE COMPARE OUR DENSITY FUNCTIONAL CALCULATIONS TO THE RATE EQUATION [2] AND THE EXPERIMENTAL RESULTS [3]. [1] S. KURTH, ET AL., PRL , 030601 (2013). [2] C. W. J. BEENAKKER, ET AL., PRB , 9667 (1992). [3] J. P. SMALL, ET AL., PRL , 256801 (2003). [Preview Abstract] 
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