# Publications

2022

Jonathan B. Curtis, Nicholas R. Poniatowski, Amir Yacoby, and Prineha Narang. 1/12/2022. “Proximity-induced collective modes in an unconventional superconductor heterostructure.” arXiv. Publisher's VersionAbstract

Unconventional superconductors have been long sought for their potential applications in quantum technologies and devices. A key challenge impeding this effort is the difficulty associated with probing and characterizing candidate materials and establishing their order parameter. In this Letter, we present a platform that allows us to spectroscopically probe unconventional superconductivity in thin-layer materials via the proximity effect. We show that inducing an s-wave gap in a sample with an intrinsic d-wave instability leads to the formation of bound-states of quasiparticle pairs, which manifest as a collective mode in the d-wave channel. This finding provides a way to study the underlying pairing interactions vicariously through the collective mode spectrum of the system. Upon further cooling of the system we observe that this mode softens considerably and may even condense, signaling the onset of time-reversal symmetry breaking superconductivity. Therefore, our proposal also allows for the creation and study of these elusive unconventional states.

2021

Anthony W. Schlimgen, Kade Head-Marsden, LeeAnn M. Sager, Prineha Narang, and David A. Mazziotti. 12/29/2021. “Quantum Simulation of Open Quantum Systems Using a Unitary Decomposition of Operators.” Physical Review Letters, 127, 27, Pp. 270503. Publisher's VersionAbstract

Electron transport in realistic physical and chemical systems often involves the nontrivial exchange of energy with a large environment, requiring the definition and treatment of open quantum systems. Because the time evolution of an open quantum system employs a nonunitary operator, the simulation of open quantum systems presents a challenge for universal quantum computers constructed from only unitary operators or gates. Here, we present a general algorithm for implementing the action of any nonunitary operator on an arbitrary state on a quantum device. We show that any quantum operator can be exactly decomposed as a linear combination of at most four unitary operators. We demonstrate this method on a two-level system in both zero and finite temperature amplitude damping channels. The results are in agreement with classical calculations, showing promise in simulating nonunitary operations on intermediate-term and future quantum devices.

Dominik M. Juraschek and Prineha Narang. 12/23/2021. “Magnetic control in the terahertz.” Science, 374, 6575, Pp. 1555-1556. Publisher's VersionAbstract

Magnetic materials are central to information storage devices, with ongoing research seeking to develop faster and more energy-efficient systems. The individual bits of data, written as 1’s and 0’s, can be stored as different orientations of magnetic moments. Conventionally, an electromagnetic head is used to flip these bits between 1 and 0, and the read and write speeds using this method are currently limited to gigahertz frequencies. A substantial amount of energy is used to drive electric currents that generate the magnetic fields. Instead of manipulating magnetic moments with slow or static magnetic fields, an intriguing alternative involves coupling light from a laser to their quantum mechanical states. On page 1608 of this issue, Mashkovich

*et al.*(*1*) report the coupling of light, magnetism, and the crystal structure of a material, which opens new possibilities for controlling the magnetic state of materials on very short time scales.S. L. Moore, C. J. Ciccarino, D. Halbertal, L. J. McGilly, N. R. Finney, K. Yao, Y. Shao, G. Ni, A. Sternbach, E. J. Telford, B. S. Kim, S. E. Rossi, K. Watanabe, T. Taniguchi, A. N. Pasupathy, C. R. Dean, J. Hone, P. J. Schuck, P. Narang, and D. N. Basov. 9/30/2021. “Nanoscale lattice dynamics in hexagonal boron nitride moiré superlattices.” Nature Communications, 12, Pp. 5741. Publisher's VersionAbstract

Twisted two-dimensional van der Waals (vdW) heterostructures have unlocked a new means for manipulating the properties of quantum materials. The resulting mesoscopic moiré superlattices are accessible to a wide variety of scanning probes. To date, spatially-resolved techniques have prioritized electronic structure visualization, with lattice response experiments only in their infancy. Here, we therefore investigate lattice dynamics in twisted layers of hexagonal boron nitride (hBN), formed by a minute twist angle between two hBN monolayers assembled on a graphite substrate. Nano-infrared (nano-IR) spectroscopy reveals systematic variations of the in-plane optical phonon frequencies amongst the triangular domains and domain walls in the hBN moiré superlattices. Our first-principles calculations unveil a local and stacking-dependent interaction with the underlying graphite, prompting symmetry-breaking between the otherwise identical neighboring moiré domains of twisted hBN.

Christina A. C. Garcia, Dennis M. Nenno, Georgios Varnavides, and Prineha Narang. 9/27/2021. “Anisotropic phonon-mediated electronic transport in chiral Weyl semimetals.” Physical Review Materials, 5, 9, Pp. L091202. Publisher's VersionAbstract

Discovery and observations of exotic, quantized optical and electrical responses have sparked renewed interest in nonmagnetic chiral crystals. Within this class of materials, six group V transition metal ditetrelides, that is, XY

_{2}(X = V, Nb, Ta and Y = Si, Ge), host composite Weyl nodes on high-symmetry lines, with Kramers-Weyl fermions at time-reversal invariant momenta. In addition, at least two of these materials, NbGe_{2}and NbSi_{2}, exhibit superconducting transitions at low temperatures. The interplay of strong electron-phonon interaction and complex Fermi surface topology present an opportunity to study both superconductivity and hydrodynamic electron transport in these systems. Towards this broader question, we present an ab initio theoretical study of the electronic transport and electron-phonon scattering in this family of materials, with a particular focus on NbGe_{2}vs. NbSi_{2}, and the other group V ditetrelides. We shed light on the microscopic origin of NbGe_{2}'s large and anisotropic room temperature resistivity and contextualize its strong electron-phonon scattering with a presentation of other relevant scattering lifetimes, both momentum-relaxing and momentum-conserving. Our work explores the intriguing possibility of observing hydrodynamic electron transport in these chiral Weyl semimetals.John P. Philbin and Prineha Narang. 9/20/2021. “Computational Materials Insights Into Solid-State Multiqubit Systems.” PRX Quantum, 2, 3, Pp. 030102. Publisher's VersionAbstract

The field of materials for quantum information science is rapidly growing with a focus on scaling and integrating new solid-state qubits. However, despite the extraordinary progress, major challenges must still be overcome for scaling. Specifically, there is a critical need for efficient coupling of tens to hundreds of solid-state qubits and multiqubit error correction to mitigate environmental interactions. This Perspective looks forward to the challenges ahead in the realization of multiqubit operations and collective phenomena with a focus on solid-state quantum materials. We provide a theorists’ point of view on the modeling and rational design of these multiqubit systems. Our Perspective identifies a path for bridging the gap between the model Hamiltonians used to develop quantum algorithms and control sequences and the

*ab initio*calculations used to understand and characterize single solid-state-based qubits.Uri Vool, Assaf Hamo, Georgios Varnavides, Yaxian Wang, Tony X. Zhou, Nitesh Kumar, Yuliya Dovzhenko, Ziwei Qiu, Christina A. C. Garcia, Andrew T. Pierce, Johannes Gooth, Polina Anikeeva, Claudia Felser, Prineha Narang, and Amir Yacoby. 9/16/2021. “Imaging phonon-mediated hydrodynamic flow in WTe

_{2}.” Nature Physics. Publisher's VersionAbstractIn the presence of strong interactions, electrons in condensed matter systems can behave hydrodynamically thereby exhibiting classical fluid phenomena such as vortices and Poiseuille flow. While in most conductors large screening effects minimize electron-electron interactions, hindering the search for possible hydrodynamic candidate materials, a new class of semimetals has recently been reported to exhibit strong interactions. In this work, we study the current flow in the layered semimetal tungsten ditelluride (WTe2) by imaging the local magnetic field above it using a nitrogen-vacancy (NV) defect in diamond. Our cryogenic scanning magnetometry system allows for temperature-resolved measurement with high sensitivity enabled by the long defect spin coherence. We directly measure the spatial current profile within WTe2 and find it differs substantially from the uniform profile of a Fermi liquid, indicating hydrodynamic flow. Furthermore, our temperature-resolved current profile measurements reveal an unexpected non-monotonic temperature dependence, with hydrodynamic effects strongest at ~20 K. We further elucidate this behavior via ab initio calculations of electron scattering mechanisms, which are used to extract a current profile using the electronic Boltzmann transport equation. These calculations show quantitative agreement with our measurements, capturing the non-monotonic temperature dependence. The combination of experimental and theoretical observations allows us to quantitatively infer the strength of electron-electron interactions in WTe2. We show these strong electron interactions cannot be explained by Coulomb repulsion alone and are predominantly phonon-mediated. This provides a promising avenue in the search for hydrodynamic flow and strong interactions in high carrier density materials.

Xuezeng Tian, Xingxu Yan, Georgios Varnavides, Yakun Yuan, Dennis S. Kim, Christopher J. Ciccarino, Polina Anikeeva, Ming-Yang Li, Lain-Jong Li, Prineha Narang, Xiaoqing Pan, and Jianwei Miao. 9/15/2021. “Capturing 3D atomic defects and phonon localization at the 2D heterostructure interface.” Science Advances, 7, 38, Pp. eabi6699. Publisher's VersionAbstract

The 3D local atomic structures and crystal defects at the interfaces of heterostructures control their electronic, magnetic, optical, catalytic and topological quantum properties, but have thus far eluded any direct experimental determination. Here we determine the 3D local atomic positions at the interface of a MoS2-WSe2 heterojunction with picometer precision and correlate 3D atomic defects with localized vibrational properties at the epitaxial interface. We observe point defects, bond distortion, atomic-scale ripples and measure the full 3D strain tensor at the heterointerface. By using the experimental 3D atomic coordinates as direct input to first principles calculations, we reveal new phonon modes localized at the interface, which are corroborated by spatially resolved electron energy-loss spectroscopy. We expect that this work will open the door to correlate structure-property relationships of a wide range of heterostructure interfaces at the single-atom level.

Yaxian Wang, Georgios Varnavides, Polina Anikeeva, Johannes Gooth, Claudia Felser, and Prineha Narang. 9/1/2021. “Generalized Design Principles for Hydrodynamic Electron Transport in Anisotropic Metals.” arXiv. Publisher's VersionAbstract

Interactions of charge carriers with lattice vibrations, or phonons, play a critical role in unconventional electronic transport of metals and semimetals. Recent observations of phonon-mediated collective electron flow in bulk semimetals, termed electron hydrodynamics, present new opportunities in the search for strong electron-electron interactions in high carrier density materials. Here we present the general transport signatures of such a second-order scattering mechanism, along with analytical limits at the Eliashberg level of theory. We study electronic transport, using

*ab initio*calculations, in finite-size channels of semimetallic ZrSiS and TaAs_{2}with and without topological band crossings, respectively. The order of magnitude separation between momentum-relaxing and momentum-conserving scattering length-scales across a wide temperature range make both of them promising candidates for further experimental observation of electron hydrodynamics. More generally, our calculations show that the hydrodynamic transport regime can be realized in a much broader class of anisotropic metals and does not, to first order, rely on the topological nature of the bands. Finally, we discuss general design principles guiding future search for hydrodynamic candidates, based on the analytical formulation and our*ab initio*predictions. We find that systems with strong electron-phonon interactions, reduced electronic phase space, and suppressed phonon-phonon scattering at temperatures of interest are likely to feature hydrodynamic electron transport. We predict that layered and/or anisotropic semimetals composed of half-filled d-shells and light group V/VI elements with lower crystal symmetry are ideal candidates to observe hydrodynamic phenomena in future.Stefan Krastanov, Alexander Sanchez de la Cerda, and Prineha Narang. 8/19/2021. “Heterogeneous multipartite entanglement purification for size-constrained quantum devices.” Physical Review Research, 3, 3, Pp. 033164. Publisher's VersionAbstract

The entanglement resource required for quantum information processing comes in a variety of forms, from Bell states to multipartite GHZ states or cluster states. Purifying these resources after their imperfect generation is an indispensable step towards using them in quantum architectures. While this challenge, both in the case of Bell pairs and more general multipartite entangled states, is mostly overcome in the presence of perfect local quantum hardware with unconstrained qubit register sizes, devising optimal purification strategies for finite-size realistic noisy hardware has remained elusive. Here we depart from the typical purification paradigm for multipartite states explored in the last twenty years. We present cases where the hardware limitations are taken into account, and surprisingly find that smaller `sacrificial' states, like Bell pairs, can be more useful in the purification of multipartite states than additional copies of these same states. This drastically simplifies the requirements and presents a fundamentally new pathway to leverage near term networked quantum hardware.

Dominik M. Juraschek, Tomáš Neuman, Johannes Flick, and Prineha Narang. 8/16/2021. “Cavity control of nonlinear phononics.” Physical Review Research, 3, 3, Pp. L032046. Publisher's VersionAbstract

Nonlinear interactions between phonon modes govern the behavior of vibrationally highly excited solids and molecules. Here, we demonstrate theoretically that optical cavities can be used to control the redistribution of energy from a highly excited coherent infrared-active phonon state into the other vibrational degrees of freedom of the system. The hybridization of the infrared-active phonon mode with the fundamental mode of the cavity induces a polaritonic splitting that we use to tune the nonlinear interactions with other vibrational modes in and out of resonance. We show that not only can the efficiency of the redistribution of energy be enhanced or decreased, but also the underlying scattering mechanisms may be changed. This work introduces the concept of cavity control to the field of nonlinear phononics, enabling nonequilibrium quantum optical engineering of new states of matter.

Maarten R. van Delft, Yaxian Wang, Carsten Putzke, Jacopo Oswald, Georgios Varnavides, Christina A. C. Garcia, Chunyu Guo, Heinz Schmid, Vicky Süss, Horst Borrmann, Jonas Diaz, Yan Sun, Claudia Felser, Bernd Gotsmann, Prineha Narang, and Philip J.W. Moll. 8/10/2021. “Sondheimer oscillations as a probe of non-ohmic flow in WP

_{2}crystals.” Nature Communications, 12, 4799. Publisher's VersionAbstractAs conductors in electronic applications shrink, microscopic conduction processes lead to strong deviations from Ohm's law. Depending on the length scales of momentum conserving (l

_{MC}) and relaxing (l_{MR}) electron scattering, and the device size (d), current flows may shift from ohmic to ballistic to hydrodynamic regimes and more exotic mixtures thereof. So far, an in situ, in-operando methodology to obtain these parameters self-consistently within a micro/nanodevice, and thereby identify its conduction regime, is critically lacking. In this context, we exploit Sondheimer oscillations, semi-classical magnetoresistance oscillations due to helical electronic motion, as a method to obtain l_{MR}in micro-devices even when l_{MR}≫d. This gives information on the bulk l_{MR}complementary to quantum oscillations, which are sensitive to all scattering processes. We extract l_{MR}from the Sondheimer amplitude in the topological semi-metal WP_{2}, at elevated temperatures up to T∼50 K, in a range most relevant for hydrodynamic transport phenomena. Our data on micrometer-sized devices are in excellent agreement with experimental reports of the large bulk l_{MR}and thus confirm that WP_{2}can be microfabricated without degradation. Indeed, the measured scattering rates match well with those of theoretically predicted electron-phonon scattering, thus supporting the notion of strong momentum exchange between electrons and phonons in WP_{2}at these temperatures. These results conclusively establish Sondheimer oscillations as a quantitative probe of l_{MR}in micro-devices in studying non-ohmic electron flow.Qing-Ge Mu, Dennis Nenno, Yan-Peng Qi, Feng-Ren Fan, Cuiying Pei, Moaz ElGhazali, Johannes Gooth, Claudia Felser, Prineha Narang, and Sergey Medvedev. 8/9/2021. “Suppression of axionic charge density wave and onset of superconductivity in the chiral Weyl semimetal Ta

_{2}Se_{8}I.” Physical Review Materials, 5, 8, Pp. 084201. Publisher's VersionAbstractA Weyl semimetal with strong electron-phonon interaction can show axionic coupling in its insulator state at low temperatures, owing to the formation of a charge density wave (CDW). Such a CDW emerges in the linear chain compound Weyl semimetal Ta

_{2}Se_{8}I below 263 K, resulting in the appearance of the dynamical condensed-matter axion quasiparticle. In this study, we demonstrate that the interchain coupling in Ta_{2}Se_{8}I can be varied to suppress the CDW formation with pressure, while retaining the Weyl semimetal phase at high temperatures. Above 17 GPa, the Weyl semimetal phase does not survive and we induce superconductivity, due to the amorphization of the iodine sub-lattice. Structurally, the one-dimensional Ta-Se-chains remain intact and provide a superconducting channel in one dimension. We highlight that our results show a near-complete suppression of the gap induced by the axionic charge-density wave at pressures inaccessible to previous studies. Including this CDW phase, our experiments and theoretical predictions and analysis reveal the complete topological phase diagram of Ta_{2}Se_{8}I and its relationship to the nearby superconducting state. The results demonstrate Ta_{2}Se_{8}I to be a distinctively versatile platform for exploring correlated topological states.Tomáš Neuman, Matt Eichenfield, Matthew Trusheim, Lisa Hackett, Prineha Narang, and Dirk Englund. 7/4/2021. “A phononic interface between a superconducting quantum processor and quantum networked spin memories.” npj Quantum Information, 7, 121. Publisher's VersionAbstract

We introduce a method for high-fidelity quantum state transduction between a superconducting microwave qubit and the ground state spin system of a solid-state artificial atom, mediated via an acoustic bus connected by piezoelectric transducers. Applied to present-day experimental parameters for superconducting circuit qubits and diamond silicon-vacancy centers in an optimized phononic cavity, we estimate quantum state transduction with fidelity exceeding 99% at a MHz-scale bandwidth. By combining the complementary strengths of superconducting circuit quantum computing and artificial atoms, the hybrid architecture provides high-fidelity qubit gates with long-lived quantum memory, high-fidelity measurement, large qubit number, reconfigurable qubit connectivity, and high-fidelity state and gate teleportation through optical quantum networks.

Abraham Asfaw, Alexandre Blais, Kenneth R. Brown, Jonathan Candelaria, Christopher Cantwell, Lincoln D. Carr, Joshua Combes, Dripto M. Debroy, John M. Donohue, Sophia E. Economou, Emily Edwards, Michael F.J. Fox, Steven M. Girvin, Alan Ho, Hilary M. Hurst, Zubin Jacob, Blake R. Johnson, Ezekiel Johnston-Halperin, Robert Joynt, Eliot Kapit, Judith Klein-Seetharaman, Martin Laforest, H.J. Lewandowski, Theresa W. Lynn, Corey Rae H. McRae, Celia Merzbacher, Spyridon Michalakis, Prineha Narang, William D. Oliver, Jens Palsberg, David P. Pappas, Michael G. Raymer, David J. Reilly, Mark Saffman, Thomas A. Searles, Jeffrey H. Shapiro, and Chandralekha Singh. 7/3/2021. “Building a Quantum Engineering Undergraduate Program.” arXiv. Publisher's VersionAbstract

The rapidly growing quantum information science and engineering (QISE) industry will require both quantum-aware and quantum-proficient engineers at the bachelor's level. We provide a roadmap for building a quantum engineering education program to satisfy this need. For quantum-aware engineers, we describe how to design a first quantum engineering course accessible to all STEM students. For the education and training of quantum-proficient engineers, we detail both a quantum engineering minor accessible to all STEM majors, and a quantum track directly integrated into individual engineering majors. We propose that such programs typically require only three or four newly developed courses that complement existing engineering and science classes available on most larger campuses. We describe a conceptual quantum information science course for implementation at any post-secondary institution, including community colleges and military schools. QISE presents extraordinary opportunities to work towards rectifying issues of inclusivity and equity that continue to be pervasive within engineering. We present a plan to do so and describe how quantum engineering education presents an excellent set of education research opportunities. Finally, we outline a hands-on training plan on quantum hardware, a key component of any quantum engineering program, with a variety of technologies including optics, atoms and ions, cryogenic and solid-state technologies, nanofabrication, and control and readout electronics. Our recommendations provide a flexible framework that can be tailored for academic institutions ranging from teaching and undergraduate-focused two- and four-year colleges to research-intensive universities.

Julian Klein, Thang Pham, Joachim Dahl Thomsen, Jonathan B. Curtis, Michael Lorke, Matthias Florian, Alexander Steinhoff, Ren A. Wiscons, Jan Luxa, Zdenek Sofer, Frank Jahnke, Prineha Narang, and Frances M. Ross. 6/30/2021. “Atomistic spin textures on-demand in the van der Waals layered magnet CrSBr.” arXiv. Publisher's VersionAbstract

Controlling magnetism in low dimensional materials is essential for designing devices that have feature sizes comparable to several critical length scales that exploit functional spin textures, allowing the realization of low-power spintronic and magneto-electric hardware.[1] Unlike conventional covalently-bonded bulk materials, van der Waals (vdW)-bonded layered magnets[2-4] offer exceptional degrees of freedom for engineering spin textures. However, their structural instability has hindered microscopic studies and manipulations. Here, we demonstrate nanoscale structural control in the layered magnet CrSBr creating novel spin textures down to the atomic scale. We show that it is possible to drive a local structural phase transformation using an electron beam that locally exchanges the bondings in different directions, effectively creating regions that have vertical vdW layers embedded within the horizontally vdW bonded exfoliated flakes. We calculate that the newly formed 2D structure is ferromagnetically ordered in-plane with an energy gap in the visible spectrum, and weak antiferromagnetism between the planes. Our study lays the groundwork for designing and studying novel spin textures and related quantum magnetic phases down to single-atom sensitivity, potentially to create on-demand spin Hamiltonians probing fundamental concepts in physics,[5-9] and for realizing high-performance spintronic, magneto-electric and topological devices with nanometer feature sizes.[10,11]

Anthony W. Schlimgen, Kade Head-Marsden, LeeAnn M. Sager, Prineha Narang, and David A. Mazziotti. 6/23/2021. “Quantum Simulation of Open Quantum Systems Using a Unitary Decomposition of Operators.” arXiv. Publisher's VersionAbstract

Electron transport in realistic physical and chemical systems often involves the non-trivial exchange of energy with a large environment, requiring the definition and treatment of open quantum systems. Because the time evolution of an open quantum system employs a non-unitary operator, the simulation of open quantum systems presents a challenge for universal quantum computers constructed from only unitary operators or gates. Here we present a general algorithm for implementing the action of any non-unitary operator on an arbitrary state on a quantum device. We show that any quantum operator can be exactly decomposed as a linear combination of at most four unitary operators. We demonstrate this method on a two-level system in both zero and finite temperature amplitude damping channels. The results are in agreement with classical calculations, showing promise in simulating non-unitary operations on intermediate-term and future quantum devices.

Jonathan B. Curtis, Andrey Grankin, Nicholas R. Poniatowski, Victor M. Galitski, Prineha Narang, and Eugene Demler. 6/15/2021. “Cavity magnon-polaritons in cuprate parent compounds.” arXiv. Publisher's VersionAbstract

Cavity control of quantum matter may offer new ways to study and manipulate many-body systems. A particularly appealing idea is to use cavities to enhance superconductivity, especially in unconventional or high-T

_{c}systems. Motivated by this, we propose a scheme for coupling Terahertz resonators to the antiferromagnetic fluctuations in a cuprate parent compound, which are believed to provide the glue for Cooper pairs in the superconducting phase. First, we derive the interaction between magnon excitations of the Neél-order and polar phonons associated with the planar oxygens. This mode also couples to the cavity electric field, and in the presence of spin-orbit interactions mediates a linear coupling between the cavity and magnons, forming hybridized magnon-polaritons. This hybridization vanishes linearly with photon momentum, implying the need for near-field optical methods, which we analyze within a simple model. We then derive a higher-order coupling between the cavity and magnons which is only present in bilayer systems, but does not rely on spin-orbit coupling. This interaction is found to be large, but only couples to the bimagnon operator. As a result we find a strong, but heavily damped, bimagnon-cavity interaction which produces highly asymmetric cavity line-shapes in the strong-coupling regime. To conclude, we outline several interesting extensions of our theory, including applications to carrier-doped cuprates and other strongly-correlated systems with Terahertz-scale magnetic excitations.Dominik M. Juraschek and Prineha Narang. 6/8/2021. “Highly confined phonon polaritons in monolayers of oxide perovskites.” Nano Letters. Publisher's VersionAbstract

Two-dimensional (2D) materials are able to strongly confine light hybridized with collective excitations of atoms, enabling electric-field enhancements and novel spectroscopic applications. Recently, freestanding monolayers of perovskite oxides have been synthesized, which possess highly infrared-active phonon modes and a complex interplay of competing interactions. Here, we show that this new class of 2D materials exhibits highly confined phonon polaritons by evaluating central figures of merit for phonon polaritons in the tetragonal phases of the 2D perovskites SrTiO

_{3}, KTaO_{3}, and LiNbO_{3}, using density functional theory calculations. Specifically, we compute the 2D phonon-polariton dispersions, the propagation-quality, confinement, and deceleration factors, and we show that they are comparable to those found in the prototypical 2D dielectric hexagonal boron nitride. Our results suggest that monolayers of perovskite oxides are promising candidates for polaritonic platforms that enable new possibilities in terms of tunability and spectral ranges.Georgios Varnavides, Yaxian Wang, Philip J.W. Moll, Polina Anikeeva, and Prineha Narang. 6/1/2021. “Finite-size effects of electron transport in PdCoO

_{2}.” arXiv. Publisher's VersionAbstractA wide range of unconventional transport phenomena have recently been observed in single-crystal delafossite metals. Here, we present a theoretical framework to elucidate electron transport using a combination of first-principles calculations and numerical modeling of the anisotropic Boltzmann transport equation. Using PdCoO

_{2}as a model system, we study different microscopic electron and phonon scattering mechanisms and establish the mean free path hierarchy of quasiparticles at different temperatures. We treat the anisotropic Fermi surface explicitly to numerically obtain experimentally-accessible transport observables, which bridge between the "diffusive", "ballistic", and "hydrodynamic" transport regime limits. We illustrate that distinction between the "quasi-ballistic", and "quasi-hydrodynamic" regimes is challenging and often needs to be quantitative in nature. From first-principles calculations, we populate the resulting transport regime plots, and demonstrate how the Fermi surface orientation adds complexity to the observed transport signatures in micro-scale devices. Our work provides key insights into microscopic interaction mechanisms on open hexagonal Fermi surfaces and establishes their connection to the macroscopic electron transport in finite-size channels.